Is a quasi-3D dosimeter better than a 2D dosimeter for Tomotherapy delivery quality assurance?

Aitang Xing,Sankar Arumugam,Gary Goozee,Shrikant Deshpande,Armia George,Philip Vial,Lois Holloway

doi:10.1088/1742-6596/573/1/012077

Abstract

Delivery quality assurance (DQA) has been performed for each Tomotherapy patient either using ArcCHECK or MatriXX Evolution in our clinic since 2012. ArcCHECK is a quasi-3D dosimeter whereas MatriXX is a 2D detector. A review of DQA results was performed for all patients in the last three years, a total of 221 DQA plans. These DQA plans came from 215 patients with a variety of treatment sites including head-neck, pelvis, and chest wall. The acceptable Gamma pass rate in our clinic is over 95% using 3mm and 3% of maximum planned dose with 10% dose threshold. The mean value and standard deviation of Gamma pass rates were 98.2% ± 1.98(1SD) for MatriXX and 98.5%±1.88 (1SD) for ArcCHECK. A paired t-test was also performed for the groups of patients whose DQA was performed with both the ArcCHECK and MatriXX. No statistical dependence was found in terms of the Gamma pass rate for ArcCHECK and MatriXX. The considered 3D and 2D dosimeters have achieved similar results in performing routine patient-specific DQA for patients treated on a TomoTherapy unit.

Highlights

It is recommended standard practice that the Tomotherapy plan for each patient be checked in the form of delivery quality assurance (DQA) prior to treatment [1]
If MatriXX was used for 2D dose measurements, another plan was created using the Tomotherapy cheese phantom for point dose measurement
The Gamma pass rates were scattered in the same range between 92% and 100 % for both patients measured with MatriXX and ArcCHECK

Summary

Introduction

It is recommended standard practice that the Tomotherapy plan for each patient be checked in the form of delivery quality assurance (DQA) prior to treatment [1]. DQA is a procedure in which the patient plan is copied and delivered to a phantom. The deliverability and accuracy of the patient plan is verified by comparing the dose calculated by the treatment planning system (TPS) and measured by one detector or detector array inserted or embedded in the phantom. A single ionization chamber with small air cavity can be used to verify the dose at single points in a phantom [2]. To measure a dose distribution across different locations in the phantom, an array of detectors is required. Detector arrays along with the phantom can be classified as a 2D or 3D dosimeter according to how the detectors are distributed geometrically in space [3, 4].

Objectives

Methods

Results