ESTRO 2024 - Abstract Book

S259

Brachytherapy - Gynaecology

ESTRO 2024

Ryan Brown, Judith Martland, Florence Ko, Mark Stevens, Marita Morgia, Jeremy Booth

Northern Sydney Cancer Centre, Radiation Oncology, St Leonards, Australia

Purpose/Objective:

Treatment management for endometrial, vaginal, vulva and recurrent cervical cancer patients utilises HDR brachytherapy (HDR-BT) as a standard of care. Traditional vaginal cylinder applicators offer standard solutions for patient treatments, however, are limited in their ability to conform to complex anatomy or targets, and optimisation of the dose distribution is limited to a single channel. More advanced techniques employ interstitial free-hand implants, or manually constructed wax moulds, however these methods are resource-intensive, invasive, and require higher skill in the implant process. Custom 3D printed applicators offer a patient-specific solution whereby the applicator-patient geometry is optimised to improve target coverage and OAR doses, leading to more favourable clinical outcomes. This study investigates the commissioning, workflow considerations and benefits for implementing custom 3D-printed applicators in HDR-BT gynaecological treatments.

Material/Methods:

Test 3D-printed slabs, phantoms and patient applicators were generated using the Oncentra Brachytherapy (OCB) treatment planning system (TPS), in conjunction with the Adaptiiv 3DBrachy software. All devices were 3D printed by Adaptiiv Medical Technologies using BioMed Clear resin material. Commissioning tests characterised geometric accuracy, reproducibility, mean HU/electron density, uniformity, optimal catheter channel size, dosimetric characterisation, material characterisation and end-to-end testing. A clinical workflow was developed and implementation conducted, such that, eligible patients would undergo simulation and planning as per the standard of care pathway (vaginal cylinder or wax mould depending on the extent of disease), as well as the 3D printed custom applicator pathway. A final CT scan was performed with the 3D-printed applicator in situ to confirm accuracy of positioning and a final treatment plan generated. The best applicator and treatment plan would then be chosen for patient treatment, as decided by the primary Radiation Oncologist. Commissioning testing established that the 3D-printed applicators were geometrically accurate, reproducible, uniform, biocompatible, rigid and sterilisable via gas sterilisation techniques. The mean HU (100 HU) and electron density (1.06 g/cm3) were not significantly different from standard HDR-BT applicators. Dosimetric characterisation in slab phantom geometry revealed a difference of less than 3% between measurement and TPS prediction over the first 3 cm depth. End-to-end in vivo phantom testing results with clinical patient plans were within 10% of TPS prediction. Clinical workflow considerations established for the custom 3D-printed applicator design process included: use of MRI for target volume delineation when appropriate, use of contrast material (dental alginate mixture) in CT simulation for vault delineation, 3 mm catheter hole diameter in custom 3D-printed applicator design, pre-plan generation for optimal catheter placement and post-plan with 3D-printed custom applicator in situ to verify integrity of manufacture. For all clinical patients simulated with both techniques, the custom 3D-printed applicator plan was superior and selected for patient treatment. There were significant differences in plan dosimetry where vaginal cylinder applicators were the comparator, however even for more advanced techniques, such as custom wax moulds (Figure 1), there were dosimetric advantages in selecting the custom 3D-printed applicator plan. DVH comparisons of 3D-printed custom applicator plans vs standard of care applicator plans were noted to exhibit equivalent or better plan dosimetry, superior target coverage, lower OAR doses and improved dose homogeneity (Table 1). Results: