Orbital mold brachytherapy for recurrent orbital mesenchymal chondrosarcoma: a case report

Introduction
The aim of this case report is to present a case of orbital mesenchymal chondrosarcoma sarcoma with multiple recurrences, and to report technical details of a contemporary approach for orbital brachytherapy that can be used in low-resource settings.

Material and methods
A 46-year-old female diagnosed with recurrent orbital mesenchymal chondrosarcoma of the left orbit presented with her third local recurrence. The patient proceeded with conservative surgery with planned adjuvant high-dose-rate brachytherapy 2 weeks post-surgery. Brachytherapy mold applicator was fabricated using thermoplastic mask, ProGuide catheter needles, catheter fixation buttons, and a strip of gauze. Ideal catheter placement was done with CT simulation planning.

Results
High-risk clinical target volume (HR-CTV) corresponded to gross tumor residual, and intermediate-risk clinical target volume (IR-CTV) corresponded to the whole orbit. Flexitron iridium-192 high-dose-rate (HDR) brachytherapy plan was generated using Oncentra brachytherapy planning system. The treatment plan had HR-CTV total dose of 55.6 Gy and equivalent dose in 2 Gray fractions (EQD2) of 96 Gy. IR-CTV total dose was 45.5 Gy and EQD2 of 70 Gy. The plan was evaluated using dose-volume histogram and dosimetric parameters, which showed adequate irradiation of tumor volume and at-risk areas. The patient underwent orbital brachytherapy without any adverse events, except for mild skin erythema. One-year post-treatment showed no local recurrence and no soft tissue necrosis or swelling.

Conclusions
In the previously irradiated orbital sarcoma patient, adjuvant brachytherapy is an effective and safe modality for the delivery of sufficient radiation dose to the target, as presented in the current case report. The materials used in the brachytherapy applicator are easily available in majority of radiation therapy centers and can be manufactured even in low-resource settings.