Abstract
Volumetric Modulated Arc Therapy (VMAT) is an important modality for radical radiotherapy
of all major treatment sites. This study aims to compare Analytical Anisotropic Algorithm
(AAA) and the two dose-reporting modes of Acuros XB (AXB) algorithm -the dose to medium
option (Dm) and the dose to water option (Dw) in Volumetric Modulated Arc Therapy (VMAT) of carcinoma lung and carcinoma prostate.
We also compared the measured dose with Treatment Planning System calculated dose
for AAA and the two dose reporting options of Acuros XB using Electronic Portal Imaging
Device (EPID) and ArcCHECK phantom. Treatment plans of twenty patients each who have
already undergone radiotherapy for cancer of lung and cancer of prostate were selected
for the study. Three sets of VMAT plans were generated in Eclipse Treatment Planning
System (TPS), one with AAA and two plans with Acuros-Dm and Acuros-Dw options. The Dose Volume Histograms (DVHs) were compared and analyzed for Planning
Target Volume (PTV) and critical structures for all the plans. Verification plans
were created for each plan and measured doses were compared with TPS calculated doses
using EPID and ArcCHECK phantom for all the three algorithms. For lung plans, the
mean dose to PTV in the AXB-Dw plans was higher by 1.7% and in the AXB-Dm plans by 0.66% when compared to AAA plans. For prostate plans, the mean dose to PTV
in the AXB-Dw plans was higher by 3.0% and in the AXB-Dm plans by 1.6% when compared to AAA plans. There was no difference in the Conformity
Index (CI) between AAA and AXB-Dm and between AAA and AXB-Dw plans for both sites. But the homogeneity worsened in AXB-Dw and AXB-Dm plans when compared to AAA plans for both sites. AXB-Dw calculated higher dose values for PTV and all the critical structures with significant
differences with one or two exceptions. Point dose measurements in ArcCHECK phantom
showed that AXB-Dm and AXB-Dw options showed very small deviations with measured dose distributions than AAA for
both sites. Results of EPID QA also showed better pass rates for AXB-Dw and AXB-Dm than AAA for both sites when gamma analysis was done for 3%/3 mm and 2%/2 mm criteria.
With reference to the results, it is always better to choose Acuros algorithm for
dose calculations if it is available in the TPS. AXB-Dw plans showed very high dose values in the PTV when compared to AAA and AXB-Dm in both sites studied. Also, the volume of PTV receiving 107% dose was significantly
high in AXB-Dw plans compared to AXB-Dm plans in sites involving high density bones. Considering the results of dosimetric
comparison and QA measurements, it is always better to choose AXB-Dm algorithm for dose calculations for all treatment sites especially when high density
bony structures and complex treatment techniques are involved. For patient specific
QA purposes, choosing AXB-Dm or AXB-Dw does not make any significant difference between calculated and measured dose distributions.
Keywords
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Article info
Publication history
Published online: June 08, 2022
Accepted:
April 21,
2022
Received in revised form:
March 18,
2022
Received:
December 10,
2021
Identification
Copyright
© 2022 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
