IGRT APP.pdf

1. S895
© 2018 Journal of Cancer Research and Therapeutics | Published by Wolters Kluwer - Medknow
ABSTRACT AROICON 2018
RP: 01
A protocol for craniospinal axis localization and adaptive
dosimetric verification using cone beam CT
K. Mohamathu Rafic, J. Sujith Christopher, S. Ebenezer Suman Babu,
B. S. Timothy Peace, B. Rajesh, B. Selvamani, B. Paul Ravindran
Aim: Limitations in the longitudinal field-of-view (LFOV, ~16 cm) and
Hounsfield units (HU) inaccuracies of typical cone beam CT (CBCT)
restricts its potential use for localization and adaptive verification
of large target volumes encountered in radiotherapy. In the present
study, we aim to develop a protocol for comprehensive localization
and adaptive dosimetric verification along the craniospinal axis
(CSA) using CBCT with extended LFOV (CBCTeLFOV
). Materials
and Methods: Hybrid immobilization comprising of a thermoplastic
mask and a whole body Vac-Lok™ was used to immobilize the
anthropomorphic phantom as well as patient, from head to mid-thigh
in supine position. Planning CT (pCT) images were acquired with 3
mm slice width and 500 mm reconstruction field-of-view (RFOV). Dual
isocentre (one at C1
and the other at T1
vertebrae) VMAT treatment
plans were computed with four partial arcs. According to our protocol,
CBCT was acquired with half-fan geometry and fixed acquisition
parameters (450 mm RFOV and 2 mm slice width). Multiple
longitudinal translations of table in steps of fixed increment ‘Δ’,
resulted in 1 cm the overlap were acquired. The custom scripts coded
in MatLab capable of handling upto seven image sets simultaneously,
generates fused CBCTeLFOV
(eLFOV of 105 cm) that are assigned
with same DICOM unique identifiers as the first series. The inbuilt
misalignment management algorithm determines the optimum
registration coefficient iteratively prior to generate CBCTeLFOV
. A new
quality assurance approach was demonstrated for validation of fused
images by combining Catphan-604 and Catphan-504 phantoms.
Contour mapping accuracy/association between pCT and CBCTeLFOV
was evaluated using volumetric dice-similarity-coefficient (DSCvol
)
metric. End-to-end (E2E) treatment workflow demonstrating the actual
clinical scenario of craniospinal irradiation (CSI) was investigated
using both anthropomorphic phantom and two patients. Results and
Discussion: Slice geometry, spatial linearity and HU accuracy of
CBCTeLFOV
were in excellent agreement with pCT. Although there is
no major difference in the volumes of mapped structures, a spatial
displacement in vital structures upto 2.5 cm (±0.5 cm) was recorded
especially in the spinal PTV and kidneys. This could be due to
combined effect of a minor rotational shift, treatment setup geometry
and change in anatomy during online localization. Because there
is no anatomical deformation and treatment related uncertainties in
the anthropomorphic phantom, superior DSCvol
results with lower
standard deviation (0.97 ±0.02) was recorded. Consistent but lower
value (0.74 ±22 and 0.70 ±0.28 respectively) than the desirable
results were observed in the two patients. Although E2E dosimetric
verification of patient paradigms demonstrated the likelihood of
under-dosing the target volume, it is unknown whether these
dosimetric deviations would transform into the reduced rate of tumor-
control. Further investigations with large patient populations relating
dosimetric outcomes with common inter-fraction uncertainties within
the planned course of treatment would be required to demonstrate
the clinical significance. Conclusion: CBCTeLFOV
based localization
and dosimetric verification is necessary for determining uncertainties
beyond the actual LFOV, especially in the treatment beam boundaries
and abutting regions. Our protocol enables regular image guided
adaptive radiotherapy (not limited to CSI) with clinically desirable
accuracy without affecting the overall machine throughput.
RADIATION PHYSICS
RP: 02
Python scripting for radiobiological evaluation of robustness in
treatment plans using optimized proton pencil beam scanning
technique
M. P. Noufal, S. S. Dayananda, P. Kartikeshwar, A. Manikandan,
K. Ganapathy, T. Rajesh, C. Srinivas1, R. Jalali1
Department of Medical Physics, 1
Department of Radiation Oncology,
Apollo Proton Cancer Centre1
, Chennai, Tamil Nadu, India
Introduction: Proton therapy is susceptible to larger uncertainties,
primarily due to beam range and setup uncertainties. Traditional
treatment planning approach based on planning target volume (PTV)
margins may not be adequate to cover the Clinical Target Volume
(CTV) by the prescription dose. Therefore, robustness evaluation
should be carried out routinely in proton planning. Conventionally
robustness of the proton plans was assessed using DVHs. However,
DVHs are not a true representation of the actual treatment outcomes.
Although current version of TPS support radiobiological evolution
from nominal plans, it cannot calculate multiple perturbed scenarios
and evaluate it radio biologically. The aim of our study is to develop an
in-house script for treatment plan robustness evaluation using both
physical and radiobiological parameters. Materials and Methods:
CT datasets of four mock patients, comprising of brain, prostate,
head and neck (HN) and medulloblastoma were chosen for this
study. For each patient Intensity Modulated Proton Therapy (IMPT)
plans were generated using single filed optimized (SFO) technique
on RayStation (v7) TPS modelled for Proteus Plus proton therapy
system. Proteus Plus can deliver proton pencil beam size of minimum
3 mm sigma in air for 230 MeV proton in scanning mode. It can
modulate the energy from 4.1 to 32 g/cm2
without any range shifter.
An in-house script was written in Iron python 2.7 and implemented
through the scripting module in the Ray station TPS. Using this script,
all the possible perturbed scenarios due to set-up error of ±3 mm
in A-P, S-I and R-L, and range uncertainty of ±3.5% were simulated
and the corresponding perturbed DVHs of CTV, PTV and OARs were
obtained. For each nominal and perturbed scenarios, TCP and NTCP
were calculated based on Niemierko model in-build in the scripts.
For each plan, 24 sets of perturbed dose distributions were created,
resulting in 96 perturbed dose plans. From the resulting perturbed
dose distribution, worst case decrease in TCP for CTV and worst
case increase in NTCP for the OARs were evaluated and validated
using AAPM TG166 protocol. Results: The in-house python script
programing allows easy and quick simulation and evaluation of
perturbed dose distribution both in physical and radiobiological
parameters. The validation of our in-house python script using AAPM
TG166 protocol resulted maximum variation of ±1% in EUD, TCP and
NTCP. Although worst case scenario leads to a large difference in
physical dose distribution compare to nominal plan, radiobiological
evaluation of the same showed similar EUD, TCP and NTCP. In
comparison to the nominal plans of each clinical sites, worst case
scenario plans reduce the EUD and TCP to CTV by a maximum of
2% and 1% respectively. The worst case increase in NTCP for brain,
H&N, Prostate and medulloblastoma were 2.5% in optic chiasm,
1.1% in parotid, 0.3% in rectum and 4.2% in lens. Conclusion: We
have developed, validated and successfully implemented the in-
house python script for plan robustness evaluation. The in-house
python script allows easy and quick evaluation of perturbed dose
distribution both in physical and radiobiological parameters. All SFO
IMPT plans showed sensitivity to uncertainties in physical dose
evaluation whereas it is less appreciable in radiobiological model.
Use of radiobiological model as a supplement to robust evaluation
will help in making a proper clinical judgement of the IMPT treatment
plan.
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2. S896 Journal of Cancer Research and Therapeutics - Volume 14 - Supplement Issue 4 - 2018
AROICON 2018 Abstracts
RP: 03
Clinical application of DIBH amplitude gated technique
for stereotactic body radiotherapy (SBRT) lung and liver
oligometastases
C. P. Bhatt, Irfan Ahmad, Kundan S. Chufal, Arvind Kumar
Aim: While DIBH is an established technique for irradiation of left-
sided breast cancers, its application in SBRT for liver and lung
oligometastases remains unexplored. The main challenge in planning
is to minimize the internal organ motion to reduce the PTV size and
hence dose to surrounding normal tissue. Diaphragmatic motion is
a good internal surrogate and closely correlates with the motion of
the external surrogate marker used in the RPM gating. The purpose
of this analysis is to report the clinical implementation and our initial
experience with Deep Inspiration Breath Hold (DIBH) amplitude based
motion management for Stereotactic Body Radiotherapy Technique
(SBRT) in patients with lung and liver oligometastases. Materials and
Methods: Eight consecutive patients treated with DIBH-Amplitude-
based SBRT were included in this prospective study [Table 1]. Varian
respiratory gating system (RPM) (Varian Medical System, Palo Alto,
CA) was used for respiratory motion monitoring. All patients were
coached for 3-4 days in order to achieve a reproducible breath hold in
terms of amplitude and duration. Simulation CT scans were acquired
in free breathing and DIBH phases on Siemens Somatom Sensation
Open (Siemens Healthineers, Erlangen). A pretreatment 4D-CBCT
in free-breathing phase was acquired and orthogonal fluoroscopy
images of the treatment site were also acquired in free breathing and
DIBH phases on Varian TrueBeam 2.5. Acquired imaging data was
imported into Eclipse v13.5 and target delineation was performed
in accordance with the ongoing RTOG BR001 protocol. Treatment
planning was performed with co-planar 6MV FFF 2-3 Arc VMAT
technique and evaluated as per acceptance criteria of RTOG BR001.
The dose was escalated in consecutive patients from BED10
of 75 Gy10
up to 132 Gy10
. Patient-specific pre-treatment QA was performed for
all patients. Pre-treatment and intra-treatment positioning verification
was performed with DIBH CBCT for all patients for each treatment
fraction and corrected on a 6D treatment couch. Results: Breath-hold
for across all patients varied from 25-45 seconds. Maximum Tumor
motion measured during fluoroscopy in free-breathing varied from 8
mm to 15 mm and in DIBH it came down to 1-3 mm, which allowed
a reduction in PTV margins from 5mm to 3mm. The Dose gradient
index for all DIBH SBRT plans varied from 0.73 to 1.4 cm. Total MU’s
varied from 1794 to 4765, with total treatment time per session varying
from 11.33 minutes to 41.28 minutes and beam-on time varying from
120 seconds to 537 seconds. Conclusions: DIBH Amplitude Gated
SBRT reduced the target motion by freezing the target in the DIBH
amplitude phase, which allowed a reduction in the PTV margin. DIBH
amplitude based SBRT is a precise and reliable motion management
technique for SBRT lung and liver. The Treatment time of DIBH
gated SBRT can be reduced with treatment techniques like FFF and
Gated VMAT/IMRT for moving tumours in Liver and Lung. The main
limitation of DIBH Amplitude gated SBRT is the breath-hold time of
the patient. The DIBH process is time-consuming and dependent on
specialized training as compared to free breath SBRT.
RP: 04
Preliminary clinical experience with indigenously developed
tissue equivalent bolus in telecobalt, megavoltage photon and
electron radiation therapy
S. Senthilkumar, G. Kesavan1
Department of Radiotherapy, Madurai Medical College and
Government Rajaji Hospital, 1
Department of Radiotherapy,
Vadamalayan Hospitals Pvt. Ltd., Madurai, Tamil Nadu, India
Objectives: Frequently, in external beam therapy one must treat
superficial lesions on cancer patients; these are at or adjacent to
the skin. Telecobalt, Megavoltage photon radiotherapy penetrates
through the skin to irradiate deep seated tumors, with skin sparing
property. Hence, to treat superficial lesions, one must use a layer
of scattering material to simulate as the skin surface. Although
megavoltage electron beams are used for superficial treatments,
one occasionally needs to enhance the dose near the surface.
Such is the function of a bolus, a natural or synthetically developed
material that acts as a layer of tissue to provide a more effective
treatment to the superficial lesions. Materials used as bolus vary
from simple water to metal and include various mixtures and
compounds. Even with the modernization of the technology for
radiotherapy and the emergence of various commercial boluses,
the preparation and utilization of a bolus in clinical radiotherapy
remains an art. The main objective of this study was to present
our preliminary clinical experience with indigenously developed
tissue equivalent bolus in telecobalt, megavoltage photon and
electron radiation therapy and assess the dosimetric properties
in LINAC machine for photon and electron beams and also in
telecobat machine. Materials and Methods: The new Senflab
bolus has been fabricated successfully with the size of 30 x 30
cm2
in different thicknesses like 0.5cm, 1.0cm, 1.5cm and 2.0cm.
Ionization measurements have been made in the Varian clinac
iX machine for 6, 9,12,15, 18 MeV electron beams and for 6 and
15 MV photon beams and also in 1.25 MeV Gamma Beam. The
Senflab were place over the RW3 plastic water phantom with and
without bolus material on the surface. The same procedure were
repeated for 1.0cm, 1.5cm, 2.0cm and also for the imported bolus
for the dosimetric comparison. The stability of the bolus material
was investigated over a time duration typical of patient treatment
by weekly measurements of ionization at depth 1 cm in plastic
water phantom under a 1.0 cm thick slab of fabricated bolus in air
and in water. Results: The dosimetric properties of bolus material
were determined by comparison with imported bolus of various
thicknesses, using Gamma Photon, X-ray photon and electron
beams of various energies. Since the Senflab has both an electron
build-up characteristic and a density closer to that of water than
imported bolus, it is anticipated that this flexible tissue substitute
will find wide acceptance in radiotherapy. Conclusion: Newly
developed Senflab Bolus material does not suffer inelastic strain
from normal stresses, it does not have to be bagged or wrapped
in plastic film to maintain its shape. Senflab bolus are nontoxic,
flexible and soft. It does conform nicely to patient’s contour while
maintaining good uniformity to thickness.
Table 1
Treatment site Dose/fraction
(Gy/Fx)
Fraction (Fx) BED Maximum tumour motion in fluoroscopy
Free breath (mm) DIBH (mm)
Right lung‑central 50/10 10 75 9 2
Liver 60/10 10 96 14 2
Left lung‑peripheral 50/5 5 100 13 2
Liver 60/8 8 105 13 2
Liver 60/8 8 105 13 2
Left abdominal wall 45/3 3 112.5 8 2
Left chest wall 45/3 3 112.5 8 1
Liver 60/5 5 132 9 1
DIBH=Deep inspiration breath hold, BED=Biological Equivalent/ Effective Dose
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3. S897
Journal of Cancer Research and Therapeutics - Volume 14 - Supplement Issue 4 - 2018
AROICON 2018 Abstracts
RP: 05
The Impact of Multi Criteria Optimization (MCO) on Flattening
Filter Free (FFF) Volumetric Modulated Arc Therapy (VMAT) in
Monaco™ treatment planning system (TPS) for Craniospinal
Irradiation (CSI)
P. Mohandas, D. Khanna, T. Thiyagaraj, C. Saravanan,
Narendra Bhalla, Abhishek Puri
Aim: To study the impact of multicriteria optimization (MCO) on
flattening filter free (FFF) volumetric modulated arc therapy (VMAT)
in Monaco™ treatment planning system (TPS) for craniospinal
irradiation (CSI). Materials and Methods: Five CSI patients treated
with 23.4Gy/13 fractions followed by boost dose using 6MV-FFF
photon beam were chosen for this study. For each case, dual partial
arcs were used for cranium (50°– 180°&180°–310°), upper spine
(125°–180°& 180°–235°) and lower spine (110°–180°&180°–250°).
Conventional VMAT (c-VMAT) plans were generated with Monaco™
V5.10 TPS for Elekta Versa HD™ linear accelerator with 0.5cm leaf
width at isocenter. Keeping all other parameters constant, c-VMAT
combined MCO (VMAT-MCO) plans were generated. Evaluation of
VMAT-MCO method was done by direct comparison with c-VMAT
which was a benchmark plan. For plan comparison, conformity index
(CI), homogeneity index (HI) to planning target volume (PTV), dose
coverage to PTV (D98%) and maximum dose to PTV were compared.
For organ at risk (OAR), mean dose and dose volume received by left
lung, right lung, left eye, right eye, left parotid, right parotid, left kidney,
right kidney, heart, and liver were analyzed. In addition, max dose to
left lens, right lens, and small bowel was analyzed. The normal tissue
volume receiving dose ≥5Gy & ≥10Gy and normal tissue integral
dose (NTID) (patient volume-PTV), total monitor unit (MU) calculation
time (mins) and delivery time (mins) were compared. Results: The CI
and HI slightly improved in VMAT-MCO plan as compared to c-VMAT
plan. No significant difference was observed (P>0.05). Similarly,
no significant dose difference was observed in Dmean and D98%
to PTV, normal tissue volume receiving dose ≥5Gy & ≥10Gy and
NTID (P>0.05). The slight increase of maximum dose to PTV was
found in VMAT-MCO plan as compared to c-VMAT plan. However,
no significant dose difference was observed (P>0.05). The mean
dose, max dose and dose volume received by left lung, right lung,
left eye, right eye, left parotid, right parotid, left kidney, right kidney,
heart, liver, left lens, right lens and small bowel showed significantly
less dose in VMAT-MCO plan as compared to c-VMAT plan (P<0.05).
An increase in MU and delivery time was noticed in VMAT-MCO plan
when compared with a c-VMAT plan (P<0.05). On comparison of both
optimization plans, it was seen that there was a significant difference
in calculation time (P<0.05). Also, the VMAT-MCO plan was faster
in dose calculation as compared to c-VMAT plan. Conclusion: The
MCO-VMAT was more efficient and able to generate a better quality
plan. For craniospinal irradiation, the MCO-VMAT plan could be
used without compromising target coverage, reduced OAR dose and
calculation time as compare to c-VMAT plan.
RP: 06
Testing the IAEA code of practice TRS-483 and application for
small field dosimetry with 10MV WFF beam with truebeam linear
accelerator - Two years dosimetry experience
Rajesh Kinhikar, Vinay Saini, Suryakant Kaushik, Sudarshan Kadam,
Chandrashekhar Tambe, A. Sutar, Rituraj Upreti, Rajesh A. Kinhikar,
Deepak Deshpande, Karen Christaki1
, Saiful Huq2
Department of Medical Physics, Tata Memorial Hospital, Mumbai,
Maharashtra, India, 1
Department of Nuclear Sciences and
Applications, IAEA, Vienna, Austria, 2
Department of Radiation
Oncology, UPMC Hillman Cancer Center, University of Pittsburgh
School of Medicine, Pittsburgh, Pennsylvania, USA
Aim: To measure field output factors(OF) for range of small field
sizes(FS) in water and virtual water using three different detectors
for 10MV WFF X-ray beam and test the feasibility of fields under
study defined by FWHM for clinical use. Materials and Methods:
Five small volume ion chambers were used to measure beam quality
in water for 6x6cm2
& 4x4cm2
FS for 10MV WFF photons on Varian
TrueBeam Linac using SNC 3D Scanner RFA and in virtual water.
On basis of measured beam quality & chamber physical dimensions,
two chambers PTW Pinpoint & IBA CC01 were selected for relative
dosimetry based on lateral charge particle equilibrium condition(rLCP
)
upto 4x4cm2
FS. One diode detector passing (rLCP
) condition was also
selected for relative dosimetry. The profiles & OF were measured for
range of FS from 0.5x0.5 cm2
to 10x10cm2
. The corrections to OF
were applied from TRS 483 based on measured FHWM values for
each FS. Field size for which correction factors were not available
in TRS 483, daisy chaining method was applied to get corrected
OF. The absorbed dose to water in both SSD and SAD setup and
Cross calibration against 0.65cc chamber was also performed. All
measurements were performed at 10cm depth & normalized for the
reference FS10x10cm2
, the OF measured with three detectors was
compared. In addition, the uncertainty budget was also estimated
and reported. All these measurements were also performed, last
year with CC13, Pinpoint and EFD detector in water with SSD setup.
Results: The Maximum deviation in beam quality was found 0.67%
in water at FS 4x4cm2
.The Absorbed dose to water measurement
among detectors was found within 3%. The ND,W,10MV
differs not more
than 1.3% from ND,W, Co-60
, and maximum deviation between SSD
and SAD setup was found 0.7%. In profile measurement, FWHM of
0.5x0.5cm2
had the maximum deviation from geometrical FS. The
Corrected O.F for FS 0.5x0.5cm2
for all chambers was found higher
in virtual water phantoms than in water. Uncertainty (k=2) in Absorbed
dose to water was 2.5% for FC-65G chamber and 3.1% for all other
chambers. Uncertainty (k=2) in Corrected OF was highest for EFD
detector 4.05% in SSD setup & 3.48% and 3.48% respectively for
CC01 and Pinpoint in SAD water setup. Conclusion: IAEA code
of practice TRS483 was tested successfully and field output factor
were determined. The corrected field OF for three detectors were
found to be in close agreement (<3%) for all FS except 0.5x0.5cm2
smallest FS where maximum uncertainty was upto 4%, due to
larger contribution from correction factor uncertainty. These results
were also compared with last year measurement and found in close
agreement upto 3x3cm2.
We also found that Palmans equation can be
used to measure TPR20,10
(10) within 1% uncertainty. In absorbed dose
to water measurement, both CC01 and Pinpoint ion chamber over
responded compared to FC-65G because of steel central electrode.
In profile measurement, EFD was best detector among CC01 and
Pinpoint ion chamber except EFD had some higher positional
uncertainty compared to other chambers because of small sensitive
volume.
RP: 07
Calculation of rotational patient positional error corrected setup
margin in frameless stereotactic radiosurgery and radiotherapy
Biplab Sarkar, Anusheel Munshi, T. Ganesh, A. Manikandan,
B. K. Mohanti
Manipal Hospitals, Dwarka, New Delhi, India
Aim: To calculate the rotational positional error corrected
setup margin in frameless stereotactic radiotherapy (SRT) and
radiosurgery (SRS). Materials and Methods: A total of 79 patients
of SRS/SRT each received >1 fraction (3-6 fractions) incorporated
in this study. Two cone-beam CT scans were acquired for each
session of treatment, before any patient position correction and
after the positional correction using a robotic couch. Six dimensional
robotic couch was used to correct the patient positional setup
error obtained by first CBCT. Cone beam CT (CBCT) obtained
patient rotational (rolls, pitch, and yaw) positional errors were
reduced to equivalent translational shifts (lateral, longitudinal,
and vertical) using a mathematical formulation based on the
Wolfram MathematicaV10.0 (Champaign, IL) software platform and
described below
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4. S898 Journal of Cancer Research and Therapeutics - Volume 14 - Supplement Issue 4 - 2018
AROICON 2018 Abstracts
X =
a+c tan ² (a a +b +c )
( + + + 2 tan + 2 tan +
2 2 2
4 2 2 2 2 3 2
( )
( )
a a b a c a c ab c a
β β 2
2 2 2
2 2 2 3 2 2
2
tan +
b c tan + 2 tan + 4 tan tan + 2
tan tan +
c
a b a bc abc
β
β γ β γ
β γ a
a a c a c
4 2 3 2 2 2 2 2
tan + 2 tan tan + tan tan )
γ γ β β γ
(i)
X with sign =
( * )
( )
Modulas X Modulas a
a
(ia)
Y
(ab a + b + c )
(a + a b + a c + 2a ctan² + 2ab ctan² +
a c tan + b
2 2 2
4 2 2 2 2 3 2
2 2 2
=
β 2
2 2 2 3 2
2 2 4 2
c tan + 2a btan + 4a bc
tan tan + 2abc tan tan + a tan +
2a
β γ
β γ β γ γ
3
3 2 2 2 2 2
ctan tan + a c tan tan )
γ β β γ
(ii)
Y with sign =
( )
(Modulas Y * Modulas b)
b
(iia)
Z
(bctan² a + b + c )
(a + a b + a c + 2a ctan + 2ab ctan +
a c tan
2 2 2
4 2 2 2 2 3 2
2 2
=
β β
β
β β γ
γ β γ γ
2 2 2 2 3 2
2 2 4
+ b c tan + 2a btan + 4a bc
tantan + 2abc tan tan + a tan 2
2
3 2 2 2 2 2
+
2a ctan tan +a c tan tan )
γ β β γ
(iii)
………
Z with sign =
( )
(ModulasZ* Modulasc)
c
(iiia)
The post-positional correction setup margin was calculated using the
van Hark formula. Further, a PTV_R (PTV with rotational correction)
and PTV_NR (PTV without rotational correction) were calculated by
applying the rotation corrected and uncorrected setup margins on the
GTVs. Results: A total of 380 sessions of pre (190) and post (190)
table positional correction CBCT data was analyzed. The pre-table
position correction mean positional error for lateral, longitudinal, and
vertical translational and rotational shifts were (x) 0.08±0.09 cm, (y)
0.04±0.21 cm, (z) -0.12±0.2 cm, and (α) 0.15±1.1°, (β) 0.38±0.94 °, (γ)
-0.05±1.1° respectively. The post patient positional correction error
(in same sequence) was -0.01±0.05 cm, -0.02±0.05 cm, 0.0±0.05
cm and 0.04±0.34°, 0.13±0.44°, 0.02±0.44° respectively. The GTV
volumes show a range of 0.13 cc to 39.56 cc, with a mean volume
of 6.35±8.65 cc. Rotational correction incorporated post-positional
correction setup margin the in lateral (x), longitudinal (y), and vertical
(z) direction were 0.05 cm, 0.12 cm, and 0.1 cm, respectively. PTV_R
ranges from 0.27 cc-44.7 cc, with a mean volume of 7.7±9.8 cc. PTV_
NR ranges from 0.32 cc-46.0 cc, with a mean volume of 8.1±10.1 cc.
As a corollary we found rotational corrections become ineffective for a
tumour of radius ≥4cm. Conclusion: Historically, the setup margin for
stereotaxy was considered as 1 mm, which was empirically deduced
from the gold standard invasive, frame-based stereotaxy. Frameless
stereotaxy can achieve the same margin if a good imaging protocol
and appropriate positional corrections are incorporated. This study
is the first to incorporate the rotational patient positional error in the
setup margin calculation. Although this investigation is performed
for cranial stereotactic cases, the formulation and hence the setup
margin calculation is valid for all sites. In subsequent studies, we will
report on the rotational-error-incorporated setup margin for other sites
using cone beam imaging data.
RP: 10
In pursuit of enhancing the MAGAT polymer gel dosimeter with
nanoparticles for X-ray CT-based readout for quality assurance
in radiotherapy
S. Ebenezer Suman Babu, B. S. Timothy Peace, K. Mohamathu Rafic,
E. Winfred Michael Raj, J. Sujith Christopher, B. Paul Ravindran
Aims/Objectives: The aim of this study was to investigate the
effect of bismuth nanoparticles incorporated in the MAGAT polymer
gel dosimeter for enhanced spatial dose information for X-ray
CT. Materials and Methods: Polymer gel dosimeters work on the
principle of radiation induced polymerization that is reflected in
terms of change in the Hounsfield units (HU), also called the CT
numbers. MAGAT polymer gel belong to the category of normoxic
polymer gels that can be prepared at normal atmospheric conditions.
The MAGAT recipe taken as reference in this study consists of 5%
gelatin, 6% Methacrylic acid, 10 Mm Tetrakis Hydroxy Phosphonium
Chloride and 89% distilled water. Though the X-ray CT can be used
as a readout technique for extracting dose information from gel with a
dose sensitivity of 0.6177 HGy-1
(reported in the literature), this study
focusses on the investigation of the effect of Bismuth nanoparticles
on the dose response of MAGAT gel for X-ray CT and cone beam
computed tomography (CBCT). Various concentrations of Bismuth
nanoparticles were incorporated in the reference MAGAT gel. The
gel solutions were poured into cuvettes and acrylic cylinders of 2 cm
inner diameter and 16 cm long. All the gel dosimeters were irradiated
using a 6 MV photon beam from a linear accelerator (Truebeam,
Varian) to doses of 0, 1, 3, 5, 7, 10 and 15 Gy in a water tank of
dimensions 30 × 30 × 30 cm3
. A parallel-opposed field of 30 × 30 cm2
at the isocentre and at a source to axis distance (SAD) of 100 cm
was used for the irradiation. The dose response of the nanoparticle-
based MAGAT gel was evaluated using spectrophotometer and
compared with the reference MAGAT gel. Similarly, the HU values
of the gels in cylindrical containers were evaluated with diagnostic
X-ray CT (Biograph, Siemens) and CBCT attached to a linear
accelerator (Truebeam STX, Varian). Three cuvettes from each
(Reference, nanoparticle MAGAT) were kept unirradiated to account
for the background measurements. Results: Visible changes as well
as spectrophotometric measurements were found suggesting dose
enhancement in the MAGAT gel dosimeter. The regression analysis
of the dose response data showed linearity with R2
value of 0.993
and 0.990 for 0.5 and 0.3 mM Bismuth nanoparticles respectively.
HU values obtained from the images of the gel cylinders were found
to be 0.931 HGy-1
for the 0.5 mM Bismuth nanoparticles incorporated
MAGAT gel when compared to the value of 0.684 HGy-1
reported for
the MAGAT without nanoparticles. This is a 36% increase in the HU
values compared to the reference MAGAT gel. Conclusions: Dose
enhancement effect of the bismuth nanoparticles on the MAGAT
gel dosimeter has been investigated successfully. It is concluded
that nanoparticle incorporated MAGAT can be used to obtain an
enhanced spatial dose information from the gel dosimeter when X-ray
CT is used as a dose extraction tool.
RP: 11
Helical tomotherapy v/s step n shoot IMRT in concurrent
chemoradiation for locally advanced carcinoma cervix: An
analysis of dose distribution
Tasneem Lilamwala, Alluri K. Raju, Vinoth Kumar
Aim: Both IMRT helical tomotherapy[HT] have been adopted
for RT for whole pelvic RT in carcinoma cervix due to better dose
homogeneity,conformality and OAR sparing.The purpose of our study
is to compare dose distribution and acute toxicities for both conformal
techniques-IMRT and helical tomotherapy. Materials and Methods:
This is a retrospective analysis from October 2017 to October 2018.14
patients with pathologically provenlocally advanced carcinoma cervix
were included in this study-eight patients were in the IMRT group and
6 patients in tomotherapy. Clinical FIGO stage IIB –IVA were only
included.The treatment plan was concurrent chemoradiation which
includes 50 GY of whole pelvic RT in either 25/28 fractions along with 3
doses of intracavitary radiation [total dose 21Gy ,7 Gy per fraction ]and
weekly low dose cisplatin based chemotherapy.IMRT and HT plans
were evaluated for each patient with the same planning objective.
OAR doses were compared using Dose Volume Histograms and plan
reports. Results: The bowel parameters including Dmean,V10,V30
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5. S899
Journal of Cancer Research and Therapeutics - Volume 14 - Supplement Issue 4 - 2018
AROICON 2018 Abstracts
V40 were reduced in the tomotherapy plans when compared to
IMRT plans.Dmean for tomotherapy reduced by 5.9Gy(Dmean for
HT[21.77Gy: Dmean for IMRT [27.67Gy].V10HT[85.17%] was lower
than V10IMRT[81.67%].V30 for tomotherapy was reduced by 19.6Gy
–[V30 HT-23.73; V30IMRT-43.33%] V40HT[6.75] was also lower
than V40IMRT[21.89%]. Dmean for rectum was also reduced in HT
plans from 31.58Gy to 40.14Gy in IMRT plans.however,mean HI was
better using IMRT than tomo therapy .The monitor units[ MU] used for
mean IMRT plans were significantly lower[1020.24MUs] compared
to HT [4556.5MUs].The HT plans consistently demonstrated that the
dose received by the bowel and rectum were lower than the IMRT.
However the bladder and femur head doses on the HT and IMRT
plans were almost similar. Conclusion: This study demonstrated that
HT is definitely a better modality for bowel sparing with V30 reduced
by 19.6Gy,but at the cost of increased MUs which is 4 times more with
tomotherapy .On rectum the mean dose was reduced around 8.5 Gy.
RP: 13
Design and study of multi rotational human equivalent phantom
for VMAT dosimetry using ion chamber, EBT3 film and RPL glass
dosimeter
S. Senthilkumar, G. Kesavan1
Department of Radiotherapy, Madurai Medical College and
Government Rajaji Hospital, 1
Department of Radiotherapy,
Vadamalayan Integrated Cancer Center, Madurai, Tamil Nadu, India
E-mail: drsenthilgh@gmail.com
Objectives: The main objective of the present study was to fabricate
indigenously multi purpose multi rotational human equivalent
phantom. Secondary objective of the study was to use the developed
phantom to implement for the clinical application of pretreatment
patient specific quality assurance for Volumetric Modulated Arc
Therapy (VMAT). And also to analyze the dosimetric verification using
ion chamber, EBT3 film and RPL glass dosimeter. Materials and
Methods: Multi rotational human equivalent phantom was made up
of PMMA, which has the density of 1.18g/cm3
. The phantom consists
of 35 slices and each slice has a dimension of 1cm thickness, 35cm
length, and 20cm height.The multi rotation phantom has been design
for thoracic part with multiple provisions in both the Lungs (L1, L2,
L3, L4), Heart (H1,H2), chest wall(C1,C2), spine and target region.
The unique manual rotation system provided on both the lungs as
well in the heart region. The rotation almost covers the whole lung
and heart, which allows to measuring point dose on various positions.
The rotation was accurately moved manually with the help of labeling
on the surface of the phantom. The phantom has the provision for
Semi-flexible chamber, EBT3 film and RPL glass detector for point
dose measurement. The phantom has been used to measure the
point dose in the patient specific quality assurance of VMAT using
three different detector. In this study, measurements were performed
using rotational phantom with Semi-flexible chamber, EBT3 film
and RPL glass detector. In order to execute the patient specific QA
the phantom was scanned by a 16 slice CT scanner. VMAT patient
verification plans were generated by the Varian Eclipse treatment
planning system (TPS) for different types of thoracic region cancers.
The measurement was carried out on Varian Clinac iX for all the 3
detectors and the point dose was measured for all the three detector
and compared with each with TPS calculated dose. Results: Our
result demonstrates that a strong correlation between the calculated
dose in TPS and the dose measured in the phantom using semi-
flexible chamber, EBT3 and RPL. The percentage variation between
dose calculated in TPS and dose measured in the phantom is less
than ±2% for most of the points. The study confirmed that the observed
deviations were well within the limits of international standards and
ensured the accuracy and quality of the treatments delivered at
the authors’oncology Centre. Conclusion: The fabricated PMMA
phantom was used in the pretreatment patient-specific QA of VMAT
was validated and accepted for the dosimetric purpose, since all the
measurements carried out with it passed the deviations were well
within the acceptable limits. This study conclude that the thorax multi
rotational phantom can be used in patient specific QA measurements
for VMAT. The results revealed that all the three detector are suitable
for the patient specific QA of RapidArc treatment pretreatment patient-
specific QA.
RP: 14
Do we really need the flattening filter free beam, higher energy
and dose rate: Dosimetric comparison of FF and FFF beams for
Lung Stereotactic Body Radiation Therapy
Priyanka Agarwal, Rajesh A. Kinhikar1
, Rakhi Barman1
,
Sangeeta Hazarika1
, Naveen Mummudi2
, Anil Tibdewal2
, J. P. Agarwal2
Homi Bhabha Cancer Hospital, Varanasi, Uttar Pradesh, Departments
of 2
Radiation Oncology and 1
Medical Physics, Tata Memorial Center,
Mumbai, Maharashtra, India
Introduction: Stereotactic Body Radiation Therapy (SBRT) has
become a preferred choice to treat patients with Lung Cancer as seen
in its clinical advantages over other modalities. SBRT is conventionally
planned using 6 MV photons generated by Linac with flattening filter.
With advent of Linac capable of delivering FFF beams, SBRT is being
planned using FFF beams. In this study, we study we compared
the dosimetric differences of energy in Lung SBRT. Materials and
Methods: Eleven patients treated with SBRT using 6 MV FF photons
(5 left lung and 6 right lung) having volume planning target volume
(PTV) from 63.3cc to 240cc were retrospectively selected for this
study. The prescribed dose was 60 Gy in 8 Fractions planned
with two partial arcs on Eclipse treatment planning system (version
13.5) calculated using Acuros Algorithm. The clinical acceptance
of plan was set using RTOG guidelines 0813 0913.The plan with 6
MVFF energy were labeled as Plan A, the treatment plans for 6XFFF
and 10XFFF energies were generated keeping same optimization
constraints as that of Plan A and labeled as Plan B plan C. The
highest dose rates were used for plans with FFF energies [1400
MU/Min for 6X_FFF 2400 Mu/Min for 10X_FFF]. The three plans
were analyzed qualitatively and quantitatively for PTV and organ at
risk (OAR) doses. Results: The mean CI (coverage Index) for Plan
A, Plan B were 96% ±0.008 and for PlanC were 94%±0.012. The
mean COIN (conformity Index) for Plan A, PlanB and PlanC were
0.956±0.036, 0.957±0.037 and 0.936±0.043. The average treatment
time (TT) for Plan A, PlanB and PlanC were 3.7±0.41, 1.55±0.21 and
1.13±0.13 minutes. The high Gradient Index (GI) for PlanA, PlanB and
PlanC were 2.91±0.26, 2.88±0.27 and 2.87±0.26 respectively. For
Lung-PTV, V5 and V20, PlanB and PlanC were reduced 0.93, 1.01
and 0.86 and 0.9 times than PlanA resepectively. The mean Lung-
PTV doses were also less 0.86 and 0.9 times in PlanB and PlanC
than PlanA. The mean heart doses were comparable among three
plans, V5 for heart for PlanB were 0.946 times less, but 1.036 times
more for PlanC than PlanA. For Spine (V0.5cc), PlanB and PlanC
were 1.011 and 1.057 times more than PlanA. For Esophagus (V5cc),
PlanB and PlanC were 1.031 and 1.107 times more than PlanA. The
mean intergral dose of body for PlanB and PlanC were 0.98 and 0.99
times than PlanA respectively. Conclusion: As per study, FFF beams
were beneficial to reduce treatment time. The optimal plan can be
obtained using energy 6XFFF and mean delivered dose rate of 1000-
1200 Mu/min with no compromise with coverage index, conformity
index, integral dose of body and OAR doses. The long terms clinical
outcomes are required for studies.
RP: 15
Critical Appraisal of Robustly Optimized Intensity Modulated
Proton Therapy(IMPT) over photon based Volumetric Arc
Therapy (VMAT) and Helical Tomotherapy (HT) in AAPMTG244
C. H. Kartikeswar Patro, S. Dayananda, A. Manikandan, M. P. Noufal,
K. Ganapathy, T. Rajesh, C. Srinivas, R. Jalali
Aim and Objective: Proton treatment planning approach and
techniques differ largely from photon due to its integrated depth dose
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6. S900 Journal of Cancer Research and Therapeutics - Volume 14 - Supplement Issue 4 - 2018
AROICON 2018 Abstracts
characteristics, delivery techniques and susceptibility to uncertainties.
The aim of this study is to design site specific robust Intensity
Modulated Proton Therapy (IMPT) plan and compare the dosimetric
outcome to photon based Volumetric Modulated Arc Therapy (VMAT)
and Helical TomoTherapy (HT) plans. Materials and Methods: The
CT and contoured structure datasets of four clinical sites comprising
of anal canal, head and neck, lung and abdomen were selected from
the database of AAPM TG244. These sites represent some of the
most complicated cases in any busy radiotherapy center. All the
proton (IMPT) and photon (VMAT and HT) plans were created in
RayStation (Version7) Treatment Planning System (TPS), which is
commissioned for ProteusPlus proton therapy system, TruebeamLA
and RadiXactX9Tomotherapy. For every clinical site except lung,
four simultaneously integrated boost (SIB) treatment plans were
created. The primary goal of each treatment plan was to cover at
least 99% of CTV (D99%CTV
) 95% of PTV (D95%PTV
) by 100% of the
prescribe dose while limiting the doses to OARs within the tolerance
limit recommended in AAPM-TG244. Proton plans were created
for ProteusPlus using pencil beam scanning technique with energy
modulation ranging from 228 to 70 MeV without range shifter. For
each case, two IMPT plans were created, one optimized directly
on PTVs and second optimized to PTVs with robustness applied
to CTVs. Robustness was accounted for ±3mm setup and ±3.5%
of range uncertainty. VMAT plans were created using two full arcs
whereas HT plans were generated using 2.5 cm field width, 0.3
pitch and 2-2.5 Modulation factor. Dosimetric outcome from all the
plans were compare using standard dose volume indices considering
VMAT as reference. Moreover, normal tissue (any tissue outside
PTV) volume receiving high (≥70%), intermediate (70% and ≥40%)
and low (40% and ≥10%) dose were evaluated for each clinical sites
from each plan. Results: In all four clinical sites, competing plans
resulted comparable D99%CTV
and D95%PTV
(both for low and high risk
target) within a Standard deviation of 0.65 CoEGy. Although dose to
all OARs were within the prescribed tolerance limit of AAPM-TG244,
OAR sparing was much better with proton compare to photon. In case
of anal canal, both proton plans reduces V35Gy
to bladder and V30Gy
to
rectum by 89% and 72% respectively. The corresponding decrease
from HT plan was 67% and 58%. V45Gy
to bowel was within 3cc in
Proton and 7cc in photon plans. The mean dose to genitalia was
1Gy from both proton plans while it was 14.4Gy and 7.7Gy from
VMAT and HT. The mean of V30Gy
to femoral heads were 0%, 5%,
and 20% from both proton plans, VMAT and HT. For abdominal, V18Gy
to kidneys were 0% from proton plans which increases to 6% in HT
and 14% in VMAT. The mean dose to liver and D25%
to stomach were
3Gy and 0.6Gy from proton plans, whereas VMAT and HT plan
shows similar results with 6Gy and 12 Gy. The maximum dose to
spinal cord were slightly higher in proton plans with 34.4, 38.7 Gy
compare to 34.3, 32.2 Gy from VMAT and HT. In head and neck case,
D0.03cc
to brainstem and spinal cord were around 32Gy and 39Gy
from proton plans, 42.7Gy from VMAT and 35.5 and 32.5Gy from HT.
V30Gy
to lips were least at 1.41% in IMPT without robustness which
increases to 15.8% with robust optimization. The corresponding
values from VMAT and HT were 66.3% and 87.1%. The mean dose
to right parotid were around 17Gy from IMPT and 25Gy from photon.
The V70Gy
to mandible and mean dose to larynx were similar in all
plans. For Lung case, V10Gy
to contralateral lung were zero from
IMPT compare to 16% in VMAT and HT. In comparison to VMAT
plan, IMPT plans reduces V20Gy,
V10Gy,
and mean dose to total normal
lung to around 36%, 43% and 42% respectively. HT plan marginally
increase all these parameters with a maximum of 3%. Both IMPT
plans resulted V50Gy
to heart of 1% and mean dose to esophagus of
17Gy. The corresponding results from VMAT were 5.6%, 20.2Gy and
HT were 3.2% and 19Gy respectively. In comparison to VMAT plan,
IMPT reduces high, intermediate and low dose volumes to normal
tissue by almost 50%, 12%, 60% for anal canal, 15%, 50%, 60%
for abdomen,3%, 26%, 59% for head and neck, 17%, 52%, 68% for
lung respectively. Conclusion: IMPT plans with or without robust
optimization shows a clear dosimetric advantage over VMAT and
HT plans in terms of reduction of dose to OAR and normal tissue
doses exposed to various dose level. Although IMPT plans with or
without robust optimization shows similar dosimetric results, robustly
optimized plan must be consider for clinical implementation in cases
where the uncertainty are expected to be high.
RP: 16
IGRT android app – A daily alert tool for physician
Kanhu Charan Patro, Partha Sarathi Bhattacharyya,
Chitta Ranjan Kundu, Venkata Krishna Reddy, Madhuri Palla,
A. Priyanka Chandra, A. C. Prabu1
, Subhra Das1
, A. Srinu1
,
A. Anil Kumar1
Departments of Radiation Oncology and 1
Radiation Physics, Mahatma
Gandhi Cancer Hospital and Research Institute, Visakhapatnam,
Andhra Pradesh, India
Introduction: Image guidance in radiation oncology practices is an
essential tool to verify the treatment procedures in day to day practices.
In most of the radiotherapy facilities radiotherapy technologists do
the job of image verification as consultants hardly could make it
because of heavy patient load. In a busy schedule consultant find
it very difficult to verify the images daily online before treatment.
Hence some follow offline practices and some take the assistance
from residents or else otherwise they have to believe in radiotherapy
technicians during entire treatment period. The dependence on
radiotherapy technologists mandates thatthey should be adequately
trained for both on site and off site image verificationso that they can
handle the situation in a more efficient manner. Aim and Objective:
To make the things easy and handy, we developed an android based
app which can be downloaded free from Google play store and which
can be set to keep an watch on what is going on in treatment room as
regards to image guidance. The technologists can also communicate
difficulties in image verification through this app. Materials and
Methods: In this app any number of doctors can sign up and their
technologists can update about IGRT errors to the consultants for
further action if needed. The technologists can add patient details
at new entry and deactivate the same after completion of treatment.
During image matching, for each patient, technologist has to follow
three traffic light signs: a Green button signal that everything is OK
that technically means GTV is inside GTV; CTV is inside CTV and
can go ahead with treatment. Orange button is meant for guarded
treatment, i.e. GTV inside at least in CTV and CTV inside PTV and
to put a cautionary note for doctor and can go ahead with scheduled
treatment. Red means there is gross error can not be matched and
it needs physician intervention before treatment.If there is any OAR
discrepancy they have to click on traffic person. For security access
each doctor and technologist will have different password and there is
no chance of trespassing the directory of other doctors. At completion
of the treatment the consultant can download the IGRT matching data
in excel sheet for each patient. Conclusion: The aim of this app is
to decrease the daily errors during treatment to act as an watch dog
tool for the consultants. In second phase we are planning to have
an app for auto calculation of systematic and random errors with
individualized auto PTV calculation, individual wise, institution wise
and site wise.
RP: 17
Stereotactic radiosurgery on helical tomotherapy - An
institutional experience
Vijay Palwe, Prakash Pandit, Roshan Patil, Raj Nagarkar,
Meghraj Borade, Supriya Borade
Aims and Objectives: To determine the feasibility and safety of
Stereotactic radiosurgery on Helical Tomotherapy. Materials and
Methods: Total 8 eligible patients were identified prospectively
from August 2018 till August 2019. 5 patient were solitary brain
mets, one patient with dorsal spinal metastasis, one patient
with acoustic schwannoma and one with recurrent meningioma.
Helical TomoTherapy is designed to perform intensity-modulated
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7. S901
Journal of Cancer Research and Therapeutics - Volume 14 - Supplement Issue 4 - 2018
AROICON 2018 Abstracts
radiation therapy (IMRT) built on the ring-based gantry has tight
machine tolerances required for radiosurgery. A frameless system
of thermoplastic mask were used for patient immobilization. CT
image dataset is taken at 1.25 mm slice thickness MRI scan in the
treatment position. Both the CT and MRI image datasets fused in
Eclipse Planning System for target volume, OAR volumes, and
pseudo-structures contouring. The image dataset and the structure
set exported to TomoHD TPS. The acceptability of the treatment
plans evaluated to ensure that plan meets the target conformity index
and normal tissue dose-volume constraints. After plan is accepted,
a delivery quality assurance (DQA) plan is created. The image-
guidance system on the Helical TomoTherapy was used for patient
localization. acquisition of the MVCT image dataset at the fine level
(2 mm slice) and co-registered against the CT-simulation image
dataset. Co-registration is done primarily on the bony structures of
the skull with emphasis near the treatment region by the radiation
therapists and with the approval of the radiation oncologist. After the
approval, the treatment commences. After the first treatment session
is completed, another MVCT image dataset is immediately collected
and co-registration is performed to evaluate and confirm the patient
position. Results: All the 8 patients tolerated SRS on Tomotherapy
well without any side effects. Post SRS response assessment scans
showed significant reductions in size and enhancement in lesions.
The treatment time about 10 minutes is comparable to that for IMRT
patients. The same patient specific quality assurance for IMRT is used
for radiosurgery. As demonstrated, SRS using Helical Tomotherapy is
not a whole day event unlike SRS using other dose deliver system
or performed in the past. Patient is discharged promptly after the
CT-simulation and thin slice MRI scan and called on the treatment
day after planning is done. Standard patient specific QA for the
IMRT patients are used for the SRS patients. Overall, the workflow
for radiosurgery follows a similar procedure to that of IMRT patients.
Unlike SRS using other dose delivery systems, or performed in the
past, SRS treatment using Helical Tomotherapy is not a whole day
event but just like a typical IMRT procedure. Conclusion: Our clinical
experience indicates that the implementation of radiosurgery on the
Helical Tomotherapy unit can be streamlined. A thin-cut MRI scan is
performed, and this dataset is fused with the CT simulation dataset.
Otherwise, the clinical setup for radiosurgery is similar to that of IMRT
patients. This radiosurgery procedure is safe. The treatment time
is short about 10-15 minutes comparable to the treatment times for
IMRT patients which is more convenient for patients.
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