FACTORS INFLUENCING INCIDENCE OF ACUTE GRADE-2 MORBIDITY IN CONFORMALAND STANDARD RADIATION TREATMENT OF PROSTATE-CANCER

Purpose: The fundament hypothesis of conformal radiation therapy is th at tumor control can be increased by using conformal treatment techniq ues that allow a higher tumor dose while maintaining an acceptable lev el of complications. To test this hypothesis, it is necessary first to estimate the incidence of morbidity for both standard and conformal f ields. In this study, we examine factors that influence the incidence of acute grade 2 morbidity in patients treated with conformal and stan dard radiation treatment for prostate cancer. Methods and Materials: T wo hundred and forty-seven consecutive patients treated with conformal technique are combined with and compared to 162 consecutive patients treated with standard techniques. The conformal technique includes spe cial immobilization by a cast, careful identification of the target vo lume in three dimensions, localization of the inferior border of the p rostate using the retrograde urethrogram, and individually shaped port als that conform to the Planning Target Volume (PTV). Univariate analy sis compares differences in the incidence of RTOG-EORTC grade two acut e morbidity by technique, T stage, age, irradiated volume, and dose. M ultivariate logistic regression includes these same variables. Results : In nearly all categories, the conformal treatment group experienced significantly fewer acute grade 2 complications than the standard trea tment group. Only volume (prostate +/- whole pelvis) and technique (co nformal vs. standard) were significantly related to incidence of morbi dity on multivariate analysis. When dose is treated as a continuous va riable (rather than being dichotomized into two levels), a trend is ob served on multivariate analysis, but it does not reach significant lev els. The incidence of acute grade 2 morbidity in patients 65 years or older is significantly reduced by use of the conformal technique. Conc lusion: The conformal technique is associated with fewer grade 2 acute toxicities for all patients. This conclusion is valid irrespective of selection criteria except in a few cases. Older age is associated wit h increased toxicity only with the standard technique and not then at a statistically significant level. Elderly patients should not be excl uded from external beam radiation because of increased morbidity espec ially if conformal treatment is available. Volume is not significantly related to morbidity in patients with standard treatment, but it is f or conformal treatment. Furthermore, it remains significant in a multi variate analysis that also shows the advantage of conformal treatment. Grade 2 acute toxicities are more volume dependent than dose dependen t.