GAIN IN TARGET DOSE FROM USING COMPUTER-CONTROLLED RADIATION-THERAPY (CCRT) IN THE TREATMENT OF NONSMALL CELL LUNG-CANCER

Purpose: A study was undertaken to evaluate the gain from Computer Controlled Radiation Therapy in the treatment of non-small cell lung cancer. The purpose of this study is two-fold: (a) to measure the gain in the minimum target dose provided by Computer Controlled Radiation Therapy and (b) to determine the change in the minimum target dose as a function of the lung tolerance limits. Methods and Materials: Six cases of non-small cell lung cancer were studied by simulating treatments with conventional and Computer Controlled Radiation Therapy techniques. For conventional treatments, a boost dose was delivered to the gross tumor volume via a pair of opposed oblique fields with a fixed gantry angle. For Computer Controlled Radiation Therapy, the gantry angle was allowed to change along the longitudinal axis of the patient. Prescriptions had to satisfy a bound on the maximum dose in the spinal cord and a limit on the amount of contralateral lung which could exceed 20 Gy. The boost dose was increased until either a tolerance limit was reached or minimum target dose of 80 Gy was delivered. Results: A minimum target dose of 80 Gy could be given to three of four patients who could not receive 80 Gy with conventional therapy. A minimum target dose of 80 Gy could be given to the remaining two patients with either technique. Conclusion: The gain from computer controlled radiation therapy strongly depended on the chosen lung tolerance limit. A 10 to 20 Gy gain in minimum target dose could be found for some patients, but the gain was significantly reduced for a relatively small decrease in the amount of lung permitted a dose above 20 Gy.