HIGH-PRECISION CONFORMAL RADIOTHERAPY (HPCRT) OF PROSTATE-CANCER - A NEW TECHNIQUE FOR EXACT POSITIONING OF THE PROSTATE AT THE TIME OF TREATMENT

Purpose: Biopsies taken 2 years after radiotherapy of localized prosta te cancer indicate residual tumor cells in 20-60% of cases, and the pr ognosis for these patients is unfavorable. More precise methods of loc alization of the prostate are desirable to increase the dose to the pr ostate tumor and minimize the volume of adjacent sensitive tissues tha t are currently included in the planning target volume. We have sought a method to more accurately locate the prostate at the time of treatm ent, allowing a reduction of the volume of rectum and bladder included in the high dose region during dose escalation. Methods and Results: We have developed a new technique using a special urethral catheter(pa tent pending), containing markers that can be visualized by the radiot herapy machine for accurate positioning of the prostate. The catheter is used throughout the treatment planning procedure and the isocenter is placed on one of the markers. On the treatment couch the markers ar e visualized on port-films and with portal imaging immediately before dose delivery. A beam-center-marker on the accelerator makes it possib le to adjust the isocenter position to within 1 mm, giving very high p recision, independent of external fixation. The technique involves a s imple patient setup. The method has been tested in five patients with conventional dose level (70 Gy) and in 24 patients in the first Scandi navian dose escalation study with external beam radiotherapy. No incre ase in acute side-effects was observed. Conclusion: With the new high precision conformal radiotherapy (HPCRT) technique we have developed a technique that allows us to increase the dose to the prostate without excessive side effects. The method reduces the uncertainties in prost ate localization, is easy to handle, and feasible in routine treatment . (C) 1998 Elsevier Science Inc.