Online

ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
Patient-specific QA using DVH analysis provides better clinical relevance of complex VMAT plans
Ahamed YOOSUF, British Virgin Islands
PO-1344

Abstract

Patient-specific QA using DVH analysis provides better clinical relevance of complex VMAT plans
Authors: Abdulrahman AlHadab.(King Abdulaziz Medical City, Department of Oncology, Riyadh, Saudi Arabia), Mamdooh Alqathami.(King Abdulaziz Medical City, Department of Oncology, Riyadh, Saudi Arabia), Salem AlShehri.(King Abdulaziz Medical City, Department of Oncology, Riyadh, Saudi Arabia), Ahamed YOOSUF.(King Abdulaziz Medical City, Department of Oncology, Riyadh, Saudi Arabia)
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Purpose or Objective

In this work, we report our clinical experience using Dose-volume-histogram (DVH), with ionization based transmission detector and model-based verification system, as a pre-treatment patient-specific quality assurance (QA) tool to determine the clinical relevance of complex volumetric modulated arc therapy (VMAT) plans which is difficult in traditional conventional gamma based analysis.

Material and Methods

73 subsequent treatment plans grouped into four clinical sites (Head and Neck, Thorax, Abdomen, and Pelvis) were evaluated. The average dose (Davg) and dose received by 1% (D1) of the planning target volumes (PTVs) and organs at risks (OARs) calculated (Monte Carlo algorithm) using the treatment planning system (TPS) were compared to a model-based computation (collapsed cone algorithm , COMPASS) and reconstructed dose (utilizing measured fluence, DOLPHIN detector) using DVH analysis. The correlation between traditional gamma analysis (3% 3mm) and DVH based analysis for targets was evaluated.

Results

Linear regression affirmed good correlation between TPS plans and computed dose using a model-based verification system (r2=1). The average percentage difference between TPS calculated and reconstructed dose for PTVs achieved using DVH analysis are as follows: Head and Neck – 0.57%±2.8 (Davg) & 2.6%±2.7 (D1), Abdomen – 0.19%±2.8 & 1.64%±2.2, Thorax – 0.24%±2.1 & 3.12%±2.8, Pelvis 0.37%±2.4 & 1.16%±2.3 respectively. Figure 1 illustrates the comparison of computed / reconstructed and calculated dose to PTVs for all cases. Likewise, the reconstructed dose for individual OARs correlated well with TPS planned dose except for small structures in head and neck cases. The average percentage of passed gamma values achieved was above 95% for all cases. However, no correlation was observed between gamma passing rates and DVH difference (%) for PTVs (r2=0.11).
Figure 1: Comparison of TPS calculated dose for PTV (mean) to: (a) Computed dose (CC algorithm) and (b) Compass reconstructed (measured using Dolphin Detector).

Figure 1: Comparison of TPS calculated dose for PTV (mean) to: (a) Computed dose (CC algorithm) and (b) Compass reconstructed (measured using Dolphin Detector).

Conclusion

DVH analysis of treatment plan using a model-based verification system and transmission detector provided better clinical relevance for all cases for complex VMAT plans as compared to traditional gamma based analysis.