DVH analysis using a transmission detector and model-based dose verification system as a comprehensive pretreatment QA tool for VMAT plans: Clinical experience and results.

Ahamed B Mohamed Yoosuf,Salem Alshehri,Mamdooh Alqathami,Abdulrahman Alhadab

doi:10.1002/acm2.12743

Abstract

PurposeDose volume histogram (DVH)‐based analysis is utilized as a pretreatment quality assurance tool to determine clinical relevance from measured dose which is difficult in conventional gamma‐based analysis. In this study, we report our clinical experience with an ionization‐based transmission detector and model‐based verification system, using DVH analysis, as a comprehensive pretreatment QA tool for complex volumetric modulated arc therapy plans.Methods and MaterialsSeventy‐three subsequent treatment plans categorized into four clinical sites (Head and Neck, Thorax, Abdomen, and Pelvis) were evaluated. The average dose (Dmean) and dose received by 1% (D1) of the planning target volumes (PTVs) and organs at risks (OARs) calculated using the treatment planning system (TPS) were compared to a computed (model‐based) and reconstructed dose, from the measured fluence, using DVH analysis. The correlation between gamma (3% 3 mm) and DVH‐based analysis for targets was evaluated. Furthermore, confidence and action limits for detector and verification systems were established.ResultsLinear regression confirmed an excellent correlation between TPS planned and computed dose using a model‐based verification system (r 2 = 1). The average percentage difference between TPS calculated and reconstructed dose for PTVs achieved using DVH analysis for each site is as follows: Head and Neck — 0.57 ± 2.8% (Dmean) and 2.6 ± 2.7% (D1), Abdomen — 0.19 ± 2.8% and 1.64 ± 2.2%, Thorax — 0.24 ± 2.1% and 3.12 ± 2.8%, Pelvis 0.37 ± 2.4% and 1.16 ± 2.3%, respectively. 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 (r 2 = 0.11). The results demonstrate a confidence limit of 5% (Dmean and D1) for PTVs using DVH analysis for both computed and reconstructed dose distribution.ConclusionDVH analysis of treatment plan using a model‐based verification system and transmission detector provided useful information on clinical relevance for all cases and could be used as a comprehensive pretreatment patient‐specific QA tool.

Highlights

A radical development in radiotherapy treatment planning techniques combined with advanced imaging and delivery systems with various degrees of freedom allows the delivery of high doses with steep dose gradients aimed at the target while sparing surrounding normal tissues.[1,2] Volumetric modulated arc therapy (VMAT) and stereotactic body radiotherapy (SBRT) techniques are routinely used in clinical practice to treat complex targets in various treatment sites.[2,3]Due to reduced safety margin and high doses delivered in short fraction, any potential errors in planning and delivery would lead to serious consequences for patients.[1]
This study aimed to present the clinical experience on utilizing a model‐based quality assurance (QA) tool and Dolphin transmission detector, using Dose volume histogram (DVH)‐ based analysis, as a comprehensive patient‐specific pretreatment QA for complex techniques planned for different clinical sites
The DVH parameters (Dmean and dose received by 1% (D1)), averaged on 73 cases, with corresponding Pearson's correlation coefficient value for target volumes and organs at risk (OAR) between treatment planning system (TPS) calculated and Compass computed/reconstructed doses are presented in Tables 1 and 2

Summary

Introduction

Due to reduced safety margin and high doses delivered in short fraction, any potential errors in planning and delivery would lead to serious consequences for patients.[1] The dose delivery to the target is influenced by uncertainties in the planning (complexity of plans) and delivery (design of the multileaf collimators) systems.[4] each treatment plan created using complex techniques requires a comprehensive patient‐specific pretreatment quality assurance (QA) procedure to verify the dose calculation generated in the treatment planning system (TPS) and delivery system such as linear accelerator. To verify the beam delivery, 2D detector arrays equipped with ionization chambers or semiconductor detectors are commonly used and play a major role to ensure that an IMRT treatment plan is accurately delivered.[5,6,7]

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