Purpose: To design and build an anthropomorphic prostate phantom for dosimetric quality assurance testing in HDR brachytherapy.
Methods: The prostate model was developed from 3D ultrasound images of a fully implanted prostate previously treated with HDR brachytherapy at our institution. Images and clinical contours were imported into Slicer3D to create the design elements of the phantom. Space was included in the model to allow for insertion of clinical brachytherapy needles and a variety of dosimeters. The model was printed on a Lulzbot 3D printer at 100% infill using 2.85 mm PLA filament. A CT of the printed phantom was acquired, and a test brachytherapy plan created in BrachyVision and then delivered using a GammaMedIX afterloader. Dosimetry measurements were taken in triplicate using an A1SL ion chamber and corrected for temperature and pressure.
Results: The phantom consists of a 7.2 cm (L/R) x 6 cm (A/P) x 7.5 cm (S/I) block which encompasses four removable prostate quadrants and 12 needle tracks. It is bisected to include a central coronal plane film; the prostate is further split at midline for a sagittal plane film. There are 4 locations to insert optically stimulated luminescence dosimeters (OSLDs). There are 2 locations to insert an A1SL ion chamber, roughly corresponding to the positions of the urethra and rectum. The nominal total treatment time for the test plan was 315.5 seconds for a 10 Ci source. At the urethral and rectal positions, the average total charge over triplicate measurements was 28.0±0.2 nC and 18.3±0.1 nC, respectively; the percent difference with repeat measurements was <2% and <2.5%, respectively.
Conclusion: 3D printing an anthropomorphic prostate phantom for HDR brachytherapy quality assurance was feasible using an inexpensive desktop printer. Initial ion chamber constancy measurements have reasonable agreement. Future work will include self-calibration as well as OSLD and film dosimetry.