Room: Track 3
Purpose: It is challenging to create highly conformal treatment plans using commercially available vaginal cylinders for high dose rate brachytherapy. These applicators, whether single or multi-channel, are limited in both the depth to which they can treat and the location of lesions for which they are suitable. In particular, it is challenging to treat lesions above the vaginal vault. We have developed a partially automated workflow for the in-house design and 3D-printed manufacture of patient specific cylindrical templates (PSCTs) which allow the use of both interstitial and intracavitary catheters. As part of the validation of these applicators, we compare treatment plans based on PSCTs to clinical plans for patients previously treated using transperineal interstitial brachytherapy at our centre.
Methods: Images and treatment plans for 5 patients previously treated using a combination of vaginal cylinder and interstitial catheters were anonymized. PSCT treatment plans were created, and the doses to the HRCTV (D90%, V100%) and OAR (bladder, rectum, sigmoid, small bowel; D2cm2) were determined. To ensure treatment plans resulted in printable templates, each plan was then modelled using custom written software, which interfaces with the Eclipse Scripting API and the Solidworks API. Optimized PSCT treatment plans were compared to the original treated plan.
Results: PSCT treatment plans resulted in similar tumour coverage, with HRCTV V100 values increasing by 2%±6% and D90 by 0.1%±3%). OAR doses remained below clinical dose limits in all cases. The bladder, rectum, sigmoid, and small bowel D2cm3 changing by -5%±4%, 2%±2%, -2%±10% and 2%±4%, respectively. All changes are mean percent difference between the PSCT plan and clinical plan.
Conclusion: The PSCT stands to be a preferable alternative to current HDRBT templates/applicators for many patients with vaginal and post-operative locally recurrent endometrial cancers. Clinically equivalent or improved treatment plans can be created compared to standard-of-care techniques.