Purpose: This study evaluates low dose‐rate brachytherapy (LDR) prostate plans to determine the biological effect of dose degradation due to prostate volume changes after the implant procedure. Methods and Materials: In this study, 39 prostate cancer patients were evaluated. Ultrasound was performed to determine the pre‐implant prostate volume. These images were used with Nucletron Spot pro 3.1 treatment planning system to create a treatment plans using Pd‐103 seeds. On the day of the procedure, after the implant, the patients were imaged using CT for post‐implant dosimetry. The prostate volumes from the pre and post implant image sets were measured. For the pre and post‐implant DVH, the biologically equivalent dose and the tumor control probability was determined using BEUD. The BEUD model used RBE= 1.75 and α/β = 4 Gy. Results: The prostate volume change between pre and post implant image sets ranged from −8% to 264%. Tumor control probability and the BEUD were reduced up to 80% and 56% respectively. As expected, the tumor control is observed to decrease as the mean dose to the prostate decreases. The post‐implant tumor dose was generally seen to decrease compared to the planned dose. This corresponded to a lower BEUD and a lower tumor control probability. However, there was no correlation between the degree of prostate enlargement and the degradation of tumor dose or tumor control. Conclusions: The biological effect of prostate growth in LDR was evaluated using BEUD. The post‐implant dose was lower than the planned dose due to an increase of prostate volume post‐implant. However, the magnitude of prostate growth was not correlated to the degree of dose degradation. Although the dose is seen to decrease post‐implant, BEUD indicates that tumor control is not significantly reduced.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging