ESTRO 2024 - Abstract Book

S183

Brachytherapy - GI, paediatric, miscellaneous

ESTRO 2024

neck rhabdomyosarcoma (HNRMS) as well as pediatric brachytherapy for gynecological RMS. The 3D-printed moulds were based on the pre-operative CT-images and the pre-plan. The workflow of preparing a 3D-printed mould consisted of seven steps: 1) pre-treatment imaging (CT/MRI); 2) delineation of the target volume and organs at risk; 3) pre-planning in Oncentra Brachy (Elekta, Veenendaal) including catheter construction and optimalization; 4) design of the 3D-mould (Autodesk Fusion 360, United States); 5) 3D-printing and post-processing of the mould; 6) validation of the mould by means of permeability and irradiability testing; 7) sterilization of the 3D-mould (Figure 1). Whenever feasible, an additional fitting session was performed, with the goal to optimize the 3D-mould.

Results:

Twelve consecutive pediatric patients with a median age of 3.6 years (range 0.3-21.8) were treated with PDR in combination with a 3D-printed mould. Ten patients were treated with 3D-printed moulds made out of Biomed Clear and two patients with a combination of two moulds from Biomed Clear and PEEK. Two examples can be found in Figure 2. The histological tumor types were: six embryonal RMS, four alveolar RMS, one rhabdoid and one germ cell tumor. Six patients were treated as part of their first-line treatment and six underwent salvage AMORE. The following brachytherapy schedules were used: 32-36 pulses of 125 cGy every 2.1h, and 100-105 pulses of 50 cGy every hour. After a median follow-up of 11 months (range 1-31), no unexpected acute toxicity was reported and all patients have persistent local control.