OBJECTIVES:~Primary~To assess the effectiveness of samarium Sm 153 lexidronam pentasodium (as determined by a 30% decline in the PSA level within 12 weeks) followed by either three-dimensional conformal radiation therapy or intensity-modulated radiation therapy in patients with rising prostate-specific antigen levels (PSA) after radical prostatectomy prostate cancer.~Secondary~To assess the proportion of patients completing protocol treatment.~To evaluate hematological toxicity at 12 weeks.~To evaluate samarium Sm 153 lexidronam pentasodium-related adverse events at 12 weeks.~To evaluate the acute and late radiation therapy-related events having occurred up to 24 weeks from the end of radiation therapy.~To compare the freedom from progression rate at 2 years to that predicted by the Kattan Nomograms.~OUTLINE: Patients receive samarium Sm 153 lexidronam pentasodium (SM) IV on day 1. Patients are closely monitored for prostate-specific antigen (PSA) level and SM-associated toxicity for 12 weeks. After the 12 weeks, patients undergo either intensity-modulated radiation therapy or 3-dimensional conformal radiation therapy 5 days a week for 7-8 weeks. Patients may receive hormonal therapy (after radiation therapy) at the discretion of their physician.~Treatment continues in the absence of disease progression (defined as a PSA doubling time less than 3 months), severe thrombocytopenia (defined as a platelet count of 25,000 cells/mm³ or less), or unacceptable toxicity.~After completion of study treatment, patients are followed up at 3 months, 6 months, and 12 months, every 6 months for 2 years, and then annually thereafter.
RATIONALE: Giving samarium Sm 153 lexidronam pentasodium and 3-dimensional (3-D) conformal radiation therapy or intensity-modulated radiation therapy may keep prostate cancer from growing in patients with rising prostate-specific antigen (PSA) levels after radical prostatectomy for prostate cancer.~PURPOSE: This phase II trial is studying how well samarium Sm 153 lexidronam pentasodium and 3-D conformal radiation therapy or intensity-modulated radiation therapy work in treating patients with rising PSA levels after radical prostatectomy for prostate cancer.