Simple, routine monitoring and correction of radiation oncology treatment setup

High dose, conformal radiation therapy demands accurate patient positioning and target localization. Static diagnostic and simulation data combined with the computer generated dose plan may not represent the treatment delivered for every patient. Errors in field or patient positioning can effect target and normal tissue dose. In order to increase the probability of achieving the desired outcome, a mechanism for routine determination of setup errors and taking action if necessary is presented. Three pelvic patients were imaged during daily AP fields with an electronic portal imaging device (EPID) and a physician directed therapist intervention protocol. Therapists preported and adjusted patient setup to within physician prescribed tolerances for anatomical landmarks and field margins. The initial and final setup/positioning errors were determined through use of quantitative analysis tools available on the EPID. Fifty-five fractions and 127 images were recorded. Initial setup errors ranged from 0-100 mm and varied between patients. Standard deviations, indicative of the random error, were 2.5 and 1.9 mm for patient A, 9.3 and 5.1 mm for patient B and 9.9 and 32.9 mm for patient C for lateral and longitudinal directions. Final errors ranged from 0 mm to 11 mm and the number of ports per fraction ranged from 1 to 6. Final standard deviations were reduced to 2.3 and 1.9 mm for patient A, 2.5 and 2.1 mm for patient B and 2.4 and 3.1 mm for patient C for lateral and longitudinal directions. In this study, two of three patients had significantly improved setup from this simple interventional EPID protocol.