ESTRO 36 Abstract Book

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S793 ESTRO 36 2017
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calculation.
Conclusion
It has been shown that the attenuation varies with gantry
angle. The inclusion of Fraxion in Monaco improves the
calculation from 7% difference to 1% in the worst case
(150º, 5x5 open field), furthermore, the skin dose
increment and the dose in the build-up region are
correctly calculated.
EP-1498 IMRT and VMAT commissioning for Versa HD
linear accelerator using AAPM TG-119
S. Sharma1, V. Subramani1, P. Kumar1, S. Bhaskar1, S.
Pathy1, S. Thulkar1, M. Sairem 1, A. Binjola1, P. Agarwal1,
N. Dhayanethi1, P. Kumar1, S. Chander 1
1 All India Institute of Medical Sciences, Radiation
Oncology, New Delhi, India
Purpose or Objective
The purpose of the study is to evaluate the end to end
commissioning accuracy of intensity modulated radiation
therapy (IMRT) and volumetric modulated arc therapy
(VMAT) for Versa HD linear accelerator using AAPM TG-119
protocol.
Material and Methods
Phantom with contoured structure set was downloaded
from AAPM website provided with the TG119 report and
above structure sets were used as the patient for all plans
created in the study. IMRT [step and shoot (SMLC) and
dynamic (DMLC)] and VMAT plans were created for TG119
test cases. All the plans were generated using Monaco 5.1
treatment planning system (TPS) for Elekta Versa HD
(Crawley UK) linear accelerator. All plans were created
using 7-9 beams for IMRT (as per TG119) and single arc for
VMAT for energy 6MV, 6MV-FFF & 10MV-FFF (FFF-
Flattening filter free). Prescription and planning goals
were as kept as per TG119. For point dose measurement
CC01 (0.01cc) ion chamber was used and measurements
were carried out as per TG119 specified points in high and
low dose gradient regions. Point dose difference was
calculated as ratio of difference between measured and
planned dose with prescription dose. Similarly for planar
dose measurement I'matriXX (IBA, Scanditronix Wellhofer,
Germany) along with multicube-lite phantom was used
and measurement plane was kept at 11cm depth. Planned
and measured dose planes were compared using gamma
index criteria (dose difference/distance to agreement) of
3%/3mm and 2%/2mm. All measurements were performed
by keeping phantom on couch at gantry angle zero.
Confidence limit calculation was done as specified in
TG119.
Results
All planning goals have been achieved as per TG119 report
shown in figure-1. At high dose point measurement mean
dose differences averaged over different techniques
(IMRT/VMAT) planned with different energies for all test
cases was 0.002±0.020, and corresponding confidence
limit (mean + 1.96σ i.e. σ stand for standard deviation)
was 0.041. At low dose point measurement mean dose
averaged over different techniques planned with different
energies for all test cases was -0.004±0.021, and
corresponding confidence limit was 0.045. For planar dose
measurement gamma passing rate averaged over all test
cases was 99.40%±0.40 for 3%/3mm criteria and
97.82%±0.13 for 2%/2mm criteria respectively. Present
work overall confidence limit (100-mean + 1.96σ i.e. σ
stand for standard deviation) for composite planar dose
measurement was 1.38(i.e., 98.62% passing) for 3%/3mm
and 2.45(i.e., 97.55% passing) for 2%/2mm criteria.
Gamma analysis results for a representative measurement
are shown in figure-2.