Preliminary epi-diode characterization for HDR brachytherapy quality assurance

A A Romanyukha,V Perevertaylo,A B Rosenfeld,I Fuduli,A Cerrotta,D Mazzeo,T Al-Salmani,M Petasecca,E Pignoli,M Carrara,C Fallai,M Lerch,D Cutajar

doi:10.1088/1742-6596/1154/1/012026

Abstract

High Dose Rate vaginal brachytherapy for endometrial cancer has evolved from simple single-channel (i.e. cylindrical applicator) deliveries to treatments involving several channels (i.e. multichannel applicator) for the radiotherapy source to dwell, increasing the complexity of the dose distribution, and allowing more space for potential errors. For this reason real-time treatment verification has gained a greater importance than ever before, and more methods need to be developed in order to provide assurance that the dose delivery has been carried out as intended by the hospital staff. P-type silicon epi diodes have been designed at the Centre for Medical Radiation Physics (CMRP) in Australia to suit the specific needs of HDR BT, and characterized in the clinical BT facility of the Fondazione IRCCS (INT) in Italy. They have shown great potential for BT treatment verification in real time due to their radiation hardness, dose rate independence, flexibility in physical design, and ability to monitor the treatment at a 1-kHz readout frequency. Their dynamic range has been determined as ±17 to ±20 mm and dwell time calculation accuracy of > 0.1 s has been shown. If placed on the same longitudinal plane of a treatment accessory, these detectors would enable coverage of about 40 mm for source position and dwell time tracking. Respective detector positioning at (0, +3, −3 mm) would extend this range to 45-50 mm, depending on the catheter location, proving to be sufficient for the majority of treatment cases. Further studies are encouraged to develop diodes with a wider dynamic range.

Highlights

High dose rate (HDR) brachytherapy (BT) is a radiotherapy (RT) technique that is characterized by its ability to deliver a highly conformal dose to the target volume, and often delivers high doses per fraction that have a steep dose gradient [1]
P-type silicon epi diodes have been designed at the Centre for Medical Radiation Physics (CMRP) in Australia to suit the specific needs of HDR BT, and characterized in the clinical BT facility of the Fondazione IRCCS (INT) in Italy
The objective of this study is to evaluate the suitability of epi diodes that have been developed at the Centre for Medical Radiation Physics (CMRP), and evaluate their sensitivity with respect to measurement settings, source air-kerma strength (SK), and source-to-detector distance, as well as to establish a method for source dwell time verification

Summary

Introduction

High dose rate (HDR) brachytherapy (BT) is a radiotherapy (RT) technique that is characterized by its ability to deliver a highly conformal dose to the target volume, and often delivers high doses per fraction that have a steep dose gradient [1]. In the simplest gynaecological treatments the HDR source is administered using a cylindrical applicator with a single central channel for the source to dwell in a range of positions and dwell times, and can be customized based on. Flexibility in the treatment leads to higher complexity and presents more room for error, for example transfer tube connections may be accidentally switched during treatment setup in the case of multiple applicator channels. For this reason treatment verification is desirable, especially one that is available in real-time and allows the treatment to be interrupted in case an error is detected

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