ESTRO 2024 - Abstract Book

S3264

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

1519

Digital Poster

Dosimetry and conformity of 3D printed bolus in common skin head and neck radiotherapy scenarios

David Odgers 1 , Chamitha Weerasinghe 1 , Patrick Estoesta 1 , Will Lewin 2,3 , Eva Tomaskovic-Crook 2,3,4 , Robin Hill 1,2,5 , Jeremy Micah Crook 2,3,4 1 Chris O'Brien Lifehouse, Department of Radiation Oncology, Sydney, Australia. 2 Chris O'Brien Lifehouse, Arto Hardy Family Biomedical Innovation Hub, Sydney, Australia. 3 The University of Sydney, School of Medical Sciences, Faculty of Medicine and Health, Sydney, Australia. 4 University of Wollongong, Intelligent Polymer Research Institute, AIIM Facility, Innovation Campus, Wollongong, Australia. 5 The University of Sydney, Institute of Medical Physics, School of Physics, Sydney, Australia

Purpose/Objective:

Three-dimensional (3D) printed boluses are an emerging tool for personalised radiation therapy. Traditional bolus is prepared manually and limited by factors such as material inhomogeneity and insufficient anatomic conformity. 3D printed boluses may enable easier application, greater durability, and more precise anatomical conformity, which is important in regions of the body with irregular geometries. Furthermore, contemporary polymer materials provide dosimetric advantages compared to earlier iterations of 3D printed bolus, and allow simpler workflows for clinical implementation. This study compared two conventional boluses made from dental wax and vinyl gel sheets with two 3D printed boluses produced with thermoplastic polyurethane (TPU) and polylactic acid (PLA) designed for fitting on an anthropomorphic head phantom. Boluses were compared in terms of conformity with the phantom and surface dosimetry on the phantom under bolus using radiochromic film.

Material/Methods:

Four bolus materials were used to create boluses for two treatment sites on the head phantom: the posterior auricle and nasal alar. The 3D printed boluses were designed using virtual boluses generated by the Eclipse treatment planning software (TPS). One VMAT plan was prepared for each site and TPS dose was calculated for two scenarios: (1) the head phantom with virtual bolus applied in Eclipse, and (2) the head phantom with physical bolus applied and using the original VMAT plan. The anatomic conformity of each physical bolus with the phantom was assessed by measurement of air gaps visible on the CT scans, using the Malone Bolus Fit Classification System [1]. Comparison of bolus shape and dimensions was performed using Dice similarity coefficients (DSCs) and Hausdorff distance measurements. Surface doses were measured using Gafchromic EBT3 film placed on phantom surface under each bolus, and compared to TPS-calculated doses.

Results:

All bolus types, except for the vinyl gel sheet, demonstrated a good fit (some minor air gaps <5mm) as determined with the Malone Bolus Fit Classification System [1]. The vinyl gel exhibited a poor fit, with bolus-to-phantom distances