Initial clinical experience with computer-controlled conformal radiotherapy of the prostate using a 50-MeV medical microtron

Purpose : We have described previously a model for delivering computer-controlled radiation treatments. We report here on the implementation and first year's clinical experience with such treatments using a 50 MeV medical microtron. Methods and Materials : The microtron is equipped with a multileaf collimator and is capable of setting up and treating a sequence of fixed fields called segments, under computer control. An external computer derives machine parameters for the segments from a three-dimensional treatment planning system, transfers them to the microtron control computer, checks the machine settings before allowing dose delivery to begin, and records the treatment. We describe the patient treatment methodology, portal film acquisition, electronic portal imaging, and quality assurance. Results : Patient treatments began in July 1992, comprising six-segment conformal treatments of the prostate. Using the recorded treatment data, the system performance has been examined and compared to other treatment machines. The average treatment time is 10 min, of which 4 min is for computer-controlled setup and irradiation; the remaining time is for patient positioning and checking of clearances. Long-term reproducibility of computer-controlled setup of the gantry and multileaf position is better than 0.5° and 1 mm, respectively. Termination due to a machine fault has occurred in 5.5% of treatments, improving to 2.5% in recent months. Conclusion : Our initial experience indicates that computer-controlled segmental therapy can be performed reliably on a routine basis. Treatment times with the microtron are significantly shorter than with conventional linacs, and setup accuracy is consistent with that needed for conformal therapy. We believe that treatment times can be further improved through software upgrades and integration of electronic portal imaging.