[Exclusive irradiation of clinically localized prostatic carcinoma: comparison with various techniques]

The frequency of prostate cancer is on the increase and many intracapsular tumors are diagnosed in asymptomatic and relatively young patients. Radiotherapy is an effective alternative to surgery when the technique which reduces the rate of acute reactions and late side-effects is chosen. On the other hand, dose distribution on the target volume and dose delivered to surrounding tissues (rectum and femoral heads) depend on several variables, namely irradiation technique, treatment planning simulation procedures and study and patient positioning. 5 by 5 mm CT studies of the prostate and/or seminal vesicles and the execution of retrograde urethrography to define the prostatic apex plan are essential steps of the simulation procedure. To compare the adequacy of various techniques, we analyzed several isodose distribution maps of nonconformational treatments, calculated by our radiotherapy planning system on the central slice. Arc and multiportal (3 or 4 fields) techniques were considered. The statistical analysis of our results demonstrated that the 4-field perpendicular technique permits better dose distribution to the target volume than the 3-field perpendicular technique; it also reduces the dose to the femoral heads. However, a combination of anterior irradiation with two oblique posterior fields is preferred in hip prosthesis patients. The comparison between arc and static multiportal techniques shows that the former gives a markedly lower dose (up to 50%) to posterior rectal wall. The bilateral arc appears to be the best technique, especially when the patient restraining device is good, because it permits homogeneous irradiation of the target volume, even at high doses, and marked reduction of the dose to the posterior rectal wall and femoral heads; consequently, treatment morbidity is lower.