The value of treatment portal films in radiotherapy for bronchial carcinoma.
In 1985, thoracic irradiation was performed in 74 patients with lung cancer in our centre. For a total of 182 field set-ups, 142 portal films were taken and compared to the simulator radiograph. In 46 cases (33%), the portal films were at variance with the simulator film. Minimal differences, demanding no further correction were seen in four cases (2.9%). There were no errors due to misplacement of a transparent plastic plate on which the field (with central axis and blocks) is outlined. A slight patient malposition was found on eight portal films (5.6%). In 5.6%, the centre of the plastic plate did not match the field centre. Wrong block position was the most common type of error: 26 cases (18.3%). In 18 of these, the marking of treatment field edges and blocks on the plastic plate was incorrect. The tumour was even partially shielded in 16 of these. In the other eight cases, block placement was erroneous at treatment set-up. Even in the presence of careful simulation and field set-up, portal film remains an indispensable step in the quality control of radiotherapy for lung cancer.
D002283:Carcinoma, Bronchogenic / Q000532:radiotherapy*; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D011785:Quality Assurance, Health Care; D013679:Technology, Radiologic / Q000295:instrumentation