Dosimetric study of bevel factors in IOERT with mobile linacs: Towards a unified code of practice

Dosimetry in intraoperative electron radiotherapy (IOERT) poses distinct challenges, especially with inclined applicators deviating from international protocols. Ion recombination in ionization chambers, electron beam degradation due to scattering in cylindrical applicators, coupled with a lack of a well-defined beam quality surrogate, complicate output factor determination with ionization chambers. Synthetic diamond-based detectors, offer potential solutions; however, their suitability requires further exploration.

This study addresses output factor determination for beveled applicators. Objectives include assessing the suitability of PTW microDiamond detectors and determining correction factors for ionization chamber measurements based on energy variations at the depth of maximum dose (z_max) for beveled applicators. Experimental data are compared against results obtained from Monte Carlo simulations.

We conducted measurements using both PTW microDiamond and IBA CC01 detectors. In addition to benchmarking bevel factors with penEasy, we employed Monte Carlo simulations to determine angular response correction factors for microDiamond detectors and to evaluate energy variations at z_max for beveled applicators.

The findings indicate that angular response correction factors are unnecessary for microDiamond detectors with beveled applicators. However, variations in mean energy at z_max potentially impact absorbed dose calculations with ionization chambers, particularly with the most inclined applicators.

Based on our results, the study recommends using microDiamond detectors over cylindrical ionization chambers for output factor determination in IOERT with inclined applicators. Addressing energy variations at z_max is crucial to improve accuracy in ionization chamber measurements. These findings have implications for dosimetry protocols in IOERT, contributing to enhanced delivery in clinical practice.