Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_2_3128 - Improved dose distribution with 3D printed vaginal cylinder applicator for VariSource HDR afterloader

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Improved dose distribution with 3D printed vaginal cylinder applicator for VariSource HDR afterloader
Y. Xu1, S. C. Lin1, R. J. Hamilton2, C. J. Watchman2, and S. T. Dougherty2; 1Banner University Medical Center, Tucson, AZ, 2University of Arizona, Tucson, AZ

Purpose/Objective(s): Most commercially available single channel HDR vaginal cylinder applicators for the VariSource afterloader do not provide adequate dose coverage near the apex (close to the patient cervix) of the device due to the self-shielding effect and the location of the most distal dwell position of the HDR source. To improve the dose coverage, this study utilizes 3D printed vaginal cylinder applicators having distal dwell positions much closer to the apexes.

Materials/Methods: 24mm and 30mm diameter vaginal cylinders were created in FreeCAD and printed with 3D system CubePro 3D printer (0.2mm resolution). The design of the cylinders facilitates use of a standard HDR catheter (1.9 mm diameter) which includes a half moon nylon button at the distal end. This allows the most distal dwell position in a 3D printed cylinder to be only 3mm from the apex (regardless the cylinder diameter), as compared to the 7mm and 9mm distances from the apex for 23mm and 30mm commercial cylinders with, respectively. In-house template plans from our planning software (with uniform dose to a depth of 5mm from surface of each cylinder) were delivered using commercial vaginal cylinders, then the same plans were delivered using 3D printed counterparts. Gafchromic films that were cut to fit the mid-line shape of the cylinders were exposed during each delivery.

Results: The film dosimetry clearly reveals inadequate dose coverage at the apex of commercial vaginal cylinders where the dose at the 5mm prescription depth is 40% and 30% less than the prescription dose for the 23mm and 30mm cylinders, respectively. The 3D printed cylinders demonstrate an overdose at the apex of 3D printed cylinders, which was expected due to the proximity of the most distal dwell position. To avoid overdosing using 3D printed cylinders, new optimized plans were created and delivered for 24mm and 30mm diameter cylinders. Film dosimetry of the new plans show uniform dose coverage around the entire 3D printed cylinders.

Conclusion: 3D printed vaginal cylinders with distal dwell positions closer to the apex, combined with optimized treatment plans, alleviate under dosing at the apex and provide a much more uniform dose distribution compared to commercial cylinders.

Author Disclosure: Y. Xu: None. S. Lin: None. R.J. Hamilton: None. C.J. Watchman: President; Arizona Chapter of AAPM. S.T. Dougherty: None.

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