Rectal Toxicity and Rectal Dosimtry in LDR 125I Permanent Prostate Implants – A Long-Term Study of 1006 Patients

Purpose: To describe the acute and late rectal toxicity in 1006 uniformly treated prostate brachytherapy patients and determine whether rectal DVH, patient or treatment factors are associated with rectal toxicity. Materials and Methods: 1006 consecutive patients implanted between August 1989 and October 2003 (median followup: 60 mo, range: 11-124 mo) were included. Rectal dosimetry was calculated as rectal DVH using 30 day post implant CT. Logistic regression model examined the significance of patient, implant and dosimetry factors (prostate V100, V150 and D90 and rectal VR150, VR100 and VR50 (volume of the rectum receiving 150%, 100% and 50% of the prescribed dose in cc) on development of acute rectal toxicity (<6 months), subacute (6 months) and late (>12 months after the implant) using modified RTOG scale. Results: Acute, subacute and late grade 1 rectal toxicity developed in 19%, 12% and 23% and grade 2 in 6%, 3% and 7.4%,respectively, late grade 3 toxicity in 1% and late grade 4 in 0.2% of patients. Factors associated with acute ≥ grade 2 toxicity were need for any or prolonged catheterization (p = 0.02 and 0.03, respectively). Factors associated with late ≥ grade 2 toxicity were no hormone therapy (p = 0.03, HR = 0.61) and presence of acute toxicity (p < 0.0001 with acute grade 1 toxicity, HR = 2.77, with acute grade 2 toxicity, HR = 4). Dosimetry factors associate with late grade ≥ 1 toxicity were: prostate V150 (p = 0.04, HR=1.01), rectal VR150 (p = 0.01, HR = 1.3), VR100 (p = 0.0007, HR = 1.1), VR 50 (p = 0.003, HR = 1.05). Late grade ≥ 2 toxicity was associated with VR 150 (p = 0.07, HR = 1.4), VR 100 (p = 0.02 HR = 1.2). Multivariate analysis will be presented at the meeting. Conclusions: Late rectal ≥2 toxicity in this cohort is 8%. Catheterization is associated with higher rate of any acute rectal toxicity. Higher rectal dose and acute rectal toxicity are associated with late ≥2 rectal toxicity. Severe late rectal toxicity after prostate brachytherapy is very rare.