Weekly localization films and detection of field placement errors.

Abstract

Abstract Quality control of radiation therapy delivery becomes increasingly important as more complex field arrangements are devised and higher precision is required. It is difficult for designers of cooperative protocols to know how often to recommend that portal check films be obtained in order to assure conformity to protocol requirements. In order to help establish a baseline rate of field placement errors (FPE) that may be expected in the delivery of radiation therapy and correlate these errors to anatomic regions and specific treatment sites, the portal films were reviewed for 337 males who were seen in consultation over a 1 year period at Wood Veterans Administration Hospital Radiation Therapy Department. Deviations of greater than 0.5 cm from the planning films were recorded as FPE's according to four categories: field malposition, field malrotation, patient malposition and block malposition. The overall FPE rate was 15% (10% if error limit set at 1.0 cm or greater); the pelvic and upper aero-digestive tract regions had the highest rates, 27% and 17% respectively, while the cranial region was least error prone (7%). Field malposition, namely, cephalo-caudad and/or transverse field shift, was the most common FPE and it comprised 74% of all errors. A simple in-house field placement control program is described.