The influence of prostate volume on outcome after high-dose-rate brachytherapy alone for localized prostate cancer

To determine whether late genitourinary toxicity, biochemical control of prostate cancer, and dosimetric parameters in patients with large prostate glands is different from those variables in men with smaller glands after treatment with high-dose-rate brachytherapy alone (HDR-BT).

From November 2003 to July 2009, 164 patients with locally advanced prostate carcinoma were sequentially enrolled and treated with 34 or 36 Gy in 4 fractions and 31.5 Gy in 3 fractions of (192)Ir HDR-BT alone. The median follow-up time was 71 months. Gland size was not considered in the selection criteria for this study. Estimates of freedom from biochemical relapse (FFbR) and late morbidity, stratified by median clinical target volume (CTV), were obtained, and differences were compared.

The median CTV volume was 60 cc (range, 15-208 cc). Dose-volume parameters D90 and V100 (ie, minimum dose to 90% of the prostate volume and volume receiving 100% of the prescribed isodose) achieved in patients with glands ≥60 cc were not significantly different from those with glands <60 cc (P≥.2). Nonetheless, biochemical control in patients with larger CTV was significantly higher (91% vs 78% at 6 years; P=.004). In univariate and multivariate analysis, CTV was a significant predictor for risk of biochemical relapse. This was not at the expense of an increase in either moderate (P=.6) or severe (P=.3) late genitourinary toxicity. The use of hormonal therapy was 17% lower in the large gland group (P=.01).

Prostate gland size does not affect dosimetric parameters in HDR-BT assessed by D90 and V100. In patients with larger glands, a significantly higher biochemical control of disease was observed, with no difference in late toxicity. This improvement cannot be attributed to differences in dosimetry. Gland size should not be considered in the selection of patients for HDR-BT.