Radiation therapy port films: a quality assurance study

The purpose of this study was to assess the port film acceptance rate in a large community practice setting and to catalog the reasons for rejection.

Between December 1993 and July 1996, a quality assurance monitor log was maintained on 4,150 patients who underwent a total of 4,450 treatment courses. Port films were taken at the beginning and at the half way point in the treatment course. A total of 20,735 port films were compared with the matching simulation films. We recorded the site being treated, the radiation oncologist who reviewed the films and the reason for rejection.

The monthly acceptance rate varied from a low of 67% to a high of 83%, with a gradual upward trend. The single most common reason for rejecting films was a centering problem-12% of all films taken were rejected for this reason. The next most common problems were block placement or body setup errors that caused 3.4% and 2.7% of the films to be rejected, respectively. Average acceptance rates between 10 different sites (abdomen, brain, breast, chest, extremities, head and neck, pelvis, prostate, rectum and spine) varied from 68% to 80%. Individual differences between 12 radiation oncologists reviewing the films varied from 67% to 87%.

A detailed analysis of field localization errors allowed us to identify areas where improvement was needed and suggested that specific guidelines for acceptance would help reduce the variability noted in the acceptance rate between sites and physicians.