INDICATIONS FOR EXCLUDING THE SEMINAL-VESICLES WHEN TREATING CLINICALLY LOCALIZED PROSTATIC ADENOCARCINOMA WITH RADIOTHERAPY ALONE

Purpose: The indications for treating the seminal vesicles (SV) in pat ients with clinically localized carcinoma of the prostate are controve rsial. We sought to define subgroups of patients in whom coverage coul d be avoided, using pretreatment prostate specific antigen (PSA) value s and the Gleason score. Because the rectum is the major dose-limiting structure, we also measured the extent of rectal sparing achieved by excluding the SV from external beam treatment fields. Methods and Mate rials: We retrospectively studied lateral x-ray simulation films of 43 patients treated with standard four-field radiotherapy and dose-volum e histograms of eight patients treated with conformal radiotherapy. Th e rectal surface areas were measured and the volumes were calculated i ncluding and excluding the SV. The pathology reports of patients treat ed with radical prostatectomy alone between 1987 and 1993 were reviewe d. Patients without preoperative PSA levels or biopsy Gleason scores, or who received neoadjuvant hormonal therapy were excluded. Of the 368 remaining patients, 66 (18%) had preoperative PSA levels less than or equal to 4, 172 (47%) had PSA levels 4-10, and 130 (35%) had PSA leve ls > 10. The Gleason score was less than or equal to 6 in 269 (73%), a nd 99 (27%) had a score greater than or equal to 7. Results: The reduc tion in the total irradiated rectal areas to full doses when the SV we re excluded ranged from 5 to 67% in individual patients (median, 44%). The median reduction in the irradiated rectal volumes to 50% of the p rescribed dose, as determined by dose-volume histograms, was 51% (rang e: 37-76%). The median reduction in bladder volumes was 9% (range: 6%- 15%). The incidence of SV involvement was 19% (70 out of 368). Patient s with normal PSA levels (less than or equal to 4 ng/mL) had a 3% (2 o ut of 66) rate of SV involvement. Patients with PSA levels between 4-1 0 ng/mL had a 8% (10 out of 126) rate of SV involvement. All other cas es had at least 20% rate of SV involvement, with a combined rate of 33 %. Using a cutoff of 15%, two low risk groups were identified: all pat ients with PSA levels less than or equal to 4, and patients with PSA 4 -10 and Gleason score less than or equal to 6. These constituted 52% ( 192 out of 368) of all patients. Overall, the low-risk patients had a 6% (12 out of 192) incidence of SV involvement vs. 33% (58 out of 176) for the high risk patients (p less than or equal to .001). Conclusion s: Excluding the SV from the treatment field can significantly reduce (40% -50%) the volume of irradiated rectum. Our data confirm that pret reatment PSA levels and Gleason scores can be effectively used to defi ne subgroups of patients in whom SV irradiation can be avoided. We pro pose excluding the SV in all patients with PSA levels less than or equ al to 4, and patients with PSA levels 4-10 and a Gleason score less th an or equal to 6. (C) 1997 Elsevier Science Inc.