• Mack Roach, Michelle DeSilvio, Richard Valicenti, David Grignon, Sucha O Asbell, Colleen Lawton, Charles R Thomas, and William U Shipley.
• University of California San Francisco, San Francisco, CA 94143-1708, USA. roach@radonc17.ucsf.edu
• Int. J. Radiat. Oncol. Biol. Phys. 2006 Nov 1; 66 (3): 647-53.

PurposeThe 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 > or = 10 x 11 cm but < 11 x 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 MaterialsEligible 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 x 11 cm), with the larger field considered an "MP" field and the smaller a PO field.ResultsThe 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.ConclusionsThis 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%.

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