Application of alanine and ionization chamber dosimetry with a 3D-printed prostate phantom for quality assurance in high dose rate brachytherapy.

PURPOSE: This work aims to determine the feasibility of performing accurate dosimetry measurements with an ionization chamber and alanine dosimeters for clinically acceptable high dose rate brachytherapy (HDR-BT) plans using a custom three-dimensional (3D)-printed anthropomorphic prostate phantom with realistic anatomy and needle positions.

METHODS

A prostate model was developed in 3DSlicer and included space for 12 HDR-BT needles and an A1SL ionization chamber and alanine dosimeter at positions corresponding to the urethra and rectum. CT images of the 3D-printed phantom were acquired and a brachytherapy plan was created in BrachyVision for a whole-gland prostate 15-Gy prescription. The planned dose at the urethral and rectal positions were 15.95 Gy and 9.93 Gy respectively for the A1SL ionization chamber, and 15.98 Gy and 9.63 Gy for the alanine, respectively. Two separate rounds of irradiation, each with five dose deliveries, were measured at both organ positions using both dosimeters.

RESULTS

The percent difference between absolute measured and planned A1SL ionization chamber doses at the urethral and rectal positions were respectively (2.3 ± 0.2)% and (5.0 ± 1.1)% for round one, and (2.0 ± 0.9)% and (2.0 ± 0.9)% for round two. Similarly, the percent difference between absolute measured and planned alanine doses at the urethral and rectal positions were respectively (1.3 ± 3.3)% and (2.3 ± 0.9)% for round one, and respectively (4.2 ± 0.4)% and (1.5 ± 0.4)% for round two.

CONCLUSIONS

A crucial need was addressed by demonstrating clinically acceptable plans can be delivered and measured on a 3D-printed prostate phantom. All absolute dose measurements were in good agreement, demonstratingclinical utility of the end-to-end testing methodology established in this work.