External dosimetry audit for quality assurance of carbon-ion radiation therapy clinical trials.

Hideyuki Mizuno,Akifumi Fukumura,Ken Yusa,Masaki Suga,Manabu Mizota,Toshiyuki Shirai,Tatsuaki Kanai,Shunsuke Yonai,Nobuyuki Kanematsu,Shinichi Minohara,Tadashi Kamada,Toshihiro Yanou

doi:10.1002/acm2.12465

Abstract

PurposeThe QA team of the Japan carbon‐ion radiation oncology study group (J‐CROS) was organized in 2015 to enhance confidence in the accuracy of clinical dosimetry and ensure that the facility QA procedures are adequate. The team conducted onsite dosimetry audits in all the carbon‐ion radiation therapy centers in Japan.Materials and MethodsA special phantom was fabricated for the onsite dosimetry audit. Target volumes such as the GTV, CTV, and PTV were contoured to the obtained CT images, and two plans with different isocenter depths were created. The dose at the isocenter was measured by an ionization chamber, in the onsite audit and compared with the calculated dose.ResultsFor all the centers, the average of the percentage ratio between the measured and calculated doses (measured/calculated) was 0.5% (−2.7% to +2.6%) and the standard deviation, 1.7%. In all the centers, the beams were within the set tolerance level of 3%.ConclusionsThe audit demonstrated that the dose at a single point in the water phantom was within tolerance, but it is a big step to say that all doses are correct. In addition, this external dosimetry audit encouraged centers to improve the quality of their dosimetry systems.

Highlights

Since 1994, in Japan, carbon‐ion radiation therapy (C‐ion RT) has been used for successfully treating tumors at various sites.[1]
This paper describes the methodology for external dosimetry audits in carbon facilities, and presents the results of the first round of audits using this methodology
As the ionization chamber for reference dose calibration, 50% of the centers used cylindrical chambers (PTW type 30013), whereas the others used plane‐parallel chambers (PTW type 23343 and type 34045)

Summary

Introduction

Since 1994, in Japan, carbon‐ion radiation therapy (C‐ion RT) has been used for successfully treating tumors at various sites.[1]. C‐ion beams exhibit increased energy deposition with the penetration depth, up to a sharp maximum at the end of their range, known as the Bragg peak. They deliver greater mean energy per unit length of their trajectory in the body The Japan carbon‐ion radiation oncology study group (J‐CROS) was established in 2014 to obtain clinical evidence through a multicenter C‐ion RT clinical trial.[3–5]. Dosimetry audit systems have been established for clinical high‐energy photon and electron beams[7–10]; there was no such audit system for C‐ion RT, in Japan. In 2014, the same year in which J‐CROS was established, medical physicists of J‐CROS institutions conducted dose intercomparison, under the same condition. The output difference was within ±0.5% for all the dosimeters

Methods

Results

Conclusion