Updated Results of the Montpellier IMRT Prostate Cancer Cohort: Focus on Elderly Patients

Abstract

In our institution intensity modulated radiation therapy (IMRT) is routinely used to treat prostate cancer since 2001. We present the updated results of our series with a median follow-up of 47 months (range, 6-101). Elderly patients (EP), aged ≥75 years, are particularly analyzed. Up to July 2008, 373 patients were treated with IMRT using a 6-field technique by dynamic multileaf collimation with 18 MV photons. All patients received the entire treatment course to a prescribed total dose of 80 Gy (minimum PTV dose of 76 Gy, excluding rectum). No pelvic irradiation was applied. Androgen ablation therapy (AAT) was delivered for 6 months and 2-3 years in intermediate and high-risk patients (d'Amico classification), respectively (n = 139). If possible, bilateral ilioobturator lymphadenectomy (n = 37) was performed in high-risk patients. PSA failure was defined as nadir + 2. Toxicity was assessed according to the NCI/CTCAE v.3.0. Multivariate analysis using the Cox model was performed to assess factors that may impact on PSA relapse. Logistic regression was used to correlate clinical and physical parameters with grade ≥ 2 gastro-intestinal (GI) and genitourinary (GU) toxicities. Median follow-up were 47 months (range, 6-101), 49 months and 39 months, for all patients, <75 y and EP, respectively. Median age was 69 years (range, 40-81). Sixty two patients were ≥ 75 years (17%). One hundred thirty-eight, 167, and 68 patients were classified as low (group 1), intermediate (group 2), and high-risk (group 3), respectively. The respective 5-year biochemical-free survival was 94%, 79% and 88%, respectively. Five-year biochemical relapse-free survival was 93% for EP (95% CI, 0.79-0.97) and 82% (95% CI, 0.75-0.87) for the others (p = 0.6). In group 2 (n = 23 recurrences), multivariate analysis showed that the absence of AAT and the number of positive biopsies impact on PSA relapse (p = 0.02, HR 2.4 and p = 0.002, HR 3.25, respectively). For patients without AAT, multivariate analysis showed that the PSA nadir >0.6 (HR: 7.4), the time to PSA nadir ≤ 28.3 months (HR: 13.1) and Gleason score ≥ 8 (HR 8.2) were predictive for biochemical recurrence. The incidence of late grade ≥ 2 rectal and urinary toxicities were 8.8% and 11%, respectively. Five-year ≥ G2 late toxicity free survival was 79% (95% CI, 73%-84%) for <75 y and 80% (95% CI, 64%-89%) for EP (p = 0.79).The dose received by 50% of the rectum was the only factor significantly correlated with late grade ≥ 2 rectal bleeding (p = 0.02). For bladder toxicity, no parameters reach significance. IMRT to 80 Gy can provide good carcinologic results and low late toxicity rates in all prostate cancer subgroups. For EP, biochemical control and tolerance are comparable to younger patients. Intermediate-risk patients seem to benefit from a 6-month AAT combined to high dose IMRT.