THE POTENTIAL FOR NORMAL TISSUE DOSE REDUCTION WITH NEOADJUVANT HORMONAL-THERAPY IN CONFORMAL TREATMENT PLANNING FOR STAGE C PROSTATE-CANCER

Purpose: Preirradiation hormonal cytoreduction of prostate cancer has been proven to reduce exposure of ven normal structures by decreasing the size of the target volume. Dose-volume histogram (DVH) analysis, h owever, does not always appear to demonstrate a strong positive benefi t with the use of neoadjuvant hormone therapy. This study analyzes var ious other factors influencing dose to normal organs, which may determ ine the success or failure of neoadjuvant hormonal therapy in achievin g its goals. Methods and Materials: Patients with bulky clinical Stage C adenocarcinoma of the prostate were given 3 months of hormone treat ment consisting of oral Flutamide and monthly Zoladex injections prior to irradiation. Computerized tomography (CT) scans of the pelvis were obtained both prior to and following hormonal treatment. Treatment pl ans were generated by three-dimensional (3D) conformal treatment plann ing. The change in the volume of the prostate was assessed along with the percentage of prescribed dose delivered to the rectum and bladder. Various factors such as prostate size, bladder/rectum size, and organ shape were studied. Both dose-volume histograms (DVH) and dose- surfa ce area histograms (DSH) were used for analysis. Results: Six of seven patients had reduction in the size of their prostates. The mean volum es of the prostate before and after hormonal manipulation were 129.1 /- 32.9 standard deviation (SD)cm(3) and 73.0+/-29.5 SD cm(3), respect ively (p = 0.0059). the volume of rectum receiving 80% of the prescrib ed dose was reduced in five of seven patients from a mean of 83.2 to 5 9.9 cm(3) (p=0.045). The volume of bladder receiving 80% of the prescr ibed dose was also reduced in five out of seven patients from a mean o f 74.5 to 40.2 cm(3) (p = 0.098). Correlation between the size of the prostate size of the prostate and volume of rectum and bladder treated was not always consistent: greater reduction in prostate size did not necessarily result in large decreases in dose to bladder or rectum. T he total size of the bladder and rectum were found to be important fac tors in normal tissue radiation exposure; the benefits of hormone ther apy may be lost if the bladder and rectum are allowed to decrease in s ize. Also, the bladder may be prone to sagging into the pelvis of some patients following hormone therapy, resulting in a less therapeutic r atio.