Clinical correlates of high intraprostatic brachytherapy dose volumes

Abstract

Purpose: To determine if high intraprostatic dose regions correlate with postimplant urinary or rectal morbidity, potentially providing some objective basis for recommendations regarding dose homogeneity.Methods: Eighty-two patients with 1997 AJC clinical stage T1c–T2a prostatic carcinoma (Gleason Grade 2–6, PSA 4–10 ng/ml) were randomized to implantation with 125I (144 Gy) vs. 103Pd (125 Gy, NIST-1999). Isotope implantation was performed by standard techniques, using a modified peripheral loading pattern. The 125I source strength ranged from 0.4 to 0.89 mCi (median: 0.55 mCi), and the 103Pd source strength ranged from 1.3 to 1.6 mCi (median: 1.5 mCi). The total number of 125I sources implanted ranged from 30 to 186 (median: 69). The total number of 103Pd sources ranged from 60 to 182 (median: 106). A postimplant computed tomography scan was obtained within 2 to 4 hours postimplant. The V100, V200, and V300s were calculated as the percent of the total prostate receiving greater than two, three, or four times the prescription dose, respectively. Treatment-related morbidity was monitored by mailed questionnaires using standard American Urologic Association and Radiation Therapy Oncology Group criteria at 1, 3, 6, 12, and 24 months. The ΔAUA score was taken as the AUA (American Urologic Association) score at the time of interest minus the preimplant score.Results: The mean V100, V200, and V300 were 90% (±8%), 35% (±13%), and 14% (±7%), respectively. Higher-dose parameters (V300) correlated more closely with each other than lower-dose parameters. The ΔAUA at 1 month had increasing association with higher-dose volumes, the closest association being with V300. However, there was substantial scatter in the data, as evidenced by the low r values. There was no correlation between high-dose volumes and ΔAUA at 12 months. Urinary morbidity scores were greatest at the 1-month time point, with no correlation between urinary morbidity and high-dose volumes. There was no correlation between rectal morbidity and high-dose volumes.Conclusion: Expending substantial effort to monitor and modify higher-dose volumes, at least in the setting of modified peripheral loading patterns, is unlikely to substantially decrease implant-related morbidity.