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Patient-assessed late toxicity rates and principal component analysis after image-guided radiation therapy for prostate cancer.

Skala M, Rosewall T, Dawson L, Divanbeigi L, Lockwood G, Thomas C, Crook J, Chung P, Warde P, Catton C

Department of Radiation Oncology, Princess Margaret Hospital, University of Toronto, Toronto, ON, Canada.

PURPOSE: The aims of this study were to determine the incidence of patient-assessed late toxicity after high-dose, image-guided radiation therapy in a cohort of men with prostate cancer; and to correlate toxicity with conventional dosimetric parameters and rectal and bladder dose-volume histograms (DVH) reduced using principal component analysis. METHODS AND MATERIALS: Toxicity questionnaires were sent to 690 men treated for localized prostate cancer to 75.6 Gy or 79.8 Gy using three-dimensional conformal radiation therapy (3DCRT) or intensity-modulated radiation therapy (IMRT) between 1997 and 2003 at the Princess Margaret Hospital. Toxicity was graded according to the modified Radiation Therapy Oncology Group (RTOG)-late effects normal tissue (LENT) scoring system. Late rectal and bladder toxicity scores were dichotomized as < Grade 2 and > or = Grade 2, and correlated with dosimetric parameters and with the first three principal components of rectal and bladder DVHs. RESULTS: In all, 63% of the patients completed the questionnaire. At a median follow-up of 37 months, the incidence of late rectal toxicity RTOG Grades 1, 2, and 3 was 25.2%, 2.5%, and 0.7% respectively. The incidence of late urinary toxicity RTOG Grade 1, 2, and 3 was 16.5%, 8.8%, and 0.9% respectively. Maintenance of erectile function sufficient for intercourse was reported in 68%. No dosimetric parameter analyzed, including principal component analysis reduction of DVHs, correlated with late toxicity. CONCLUSIONS: Postal questionnaire was effective for collection of patient-assessed late toxicity data. The incidence of late toxicity was low, with a lack of correlation to dosimetric parameters. We attribute this to the use of conformal techniques and daily image guidance.

Published 4 June 2007 in Int J Radiat Oncol Biol Phys, 68(3): 690-8.
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