Whole-pelvis, "mini-pelvis," or prostate-only external beam radiotherapy after neoadjuvant and concurrent hormonal therapy in patients treated in the Radiation Therapy Oncology Group 9413 trial

Purpose: The Radiation Therapy Oncology Group (RTOG) 9413 trial demonstrated a better progression-free survival (PFS) with whole-pelvis (WP) radiotherapy (RT) compared with prostate-only (PO) RT. This secondary analysis was undertaken to determine whether "mini-pelvis" (MP; defined as ≥10 × 11 cm but <11 × 11 cm) RT resulted in progression-free survival (PFS) comparable to that of WP RT. To avoid a timing bias, this analysis was limited to patients receiving neoadjuvant and concurrent hormonal therapy (N&CHT) in Arms 1 and 2 of the study. Methods and Materials: Eligible patients had a risk of lymph node (LN) involvement >15%. Neoadjuvant and concurrent hormonal therapy (N&CHT) was administered 2 months before and during RT for 4 months. From April 1, 1995, to June 1, 1999, a group of 325 patients were randomized to WP RT + N&CHT and another group of 324 patients were randomized to receive PO RT + N&CHT. Patients randomized to PO RT were dichotomized by median field size (10 × 11 cm), with the larger field considered an "MP" field and the smaller a PO field. Results: The median PFS was 5.2, 3.7, and 2.9 years for WP, MP, and PO fields, respectively (p = 0.02). The 7-year PFS was 40%, 35%, and 27% for patients treated to WP, MP, and PO fields, respectively. There was no association between field size and late Grade 3+ genitourinary toxicity but late Grade 3+ gastrointestinal RT complications correlated with increasing field size. Conclusions: This subset analysis demonstrates that RT field size has a major impact on PFS, and the findings support comprehensive nodal treatment in patients with a risk of LN involvement of >15%.