Intensity-modulated radiation therapy (IMRT) for prostate cancer with the use of a rectal balloon for prostate immobilization: Acute toxicity and dose-volume analysis

Purpose: To report acute toxicity and to evaluate the relationship between dose-volume effects and acute toxicity in patients with localized prostate cancer, treated with intensity-modulated radiation therapy (IMRT). Methods and Materials: Acute toxicity (both lower gastrointestinal [GI] and genito-urinary [GU]) in 100 patients treated with IMRT definitively to a p rescribed dose of 70 Gy were assessed using RTOG scoring criteria. A rectal balloon was used for prostate immobilization, Mean doses to seminal vesicl es, prostate, bladder, and rectum were recorded. Average irradiated bladder and rectal volumes above 65, 70, and 75 Gy were assessed. A relationship b etween dose volume and clinical toxicity was evaluated. All patients comple ted the full duration of acute toxicity assessment. Results: Mean doses to the prostate and seminal vesicles were 75.8 and 73.9 Gy. This represents a moderate dose escalation. Acute GI toxicity profile was very favorable. Eleven percent and 6% of the patients had grade 1 and 2 GI toxicity, respectively, while 83% had no GI complaint, For GU complaint s, 38% and 35% had grade 1 and 2 toxicity, respectively, while 27% had no c omplaints. There was no grade 3 or higher acute GI or GU toxicity. Mean dos es to the bladder were 22.8, 23.4, and 26.1 Gy for grade 0, 1, and 2 GU tox icity, respectively (p = 0.132, There is no statistically significant relat ionship between acute GU toxicity and the bladder volume receiving > 65 Gy, > 70 Gy, or > 75 Gy. In evaluating acute GI toxicity, there are very few g rade 1 and 2 events, No relationship was found between acute rectal toxicit y and mean rectal dose or irradiated rectal volumes receiving more than 65, 70, and 75 Gy, Conclusion: The findings are important with regard to the safety of IR IRT, especially in reducing acute GI toxicity. Dose escalation with IMRT using a prostate immobilization technique is feasible. The findings are also impo rtant because they contribute to the clinical and dosimetric correlation as pect in the use of IMRT to treat prostate cancer. A larger cohort may be ne eded to determine if there is a relationship between acute GU toxicity and (a) mean bladder dose and (b) irradiated bladder volume receiving > 65 Gy, > 70 Gy or > 75 Gy. A larger cohort of patients treated to a higher dose ma y be needed to show a relationship between dose volume and acute GI toxicit y. (C) 2001 Elsevier Science Inc.