[A study of dose distribution of high energy X-ray in lung measured by film method]

Measurement was carried out for 6 MV X-rays using an inhomogeneity phantom with films. The films were set parallel or perpendicular to the beam axis. Measurement data were compared with values obtained by a JARP dosimeter, to assess the accuracy of evaluation. 1) The data measured by perpendicular films showed underestimation but were more accurate than those measured by parallel films when compared with the JARP method. 2) The difference in measurement between the perpendicular films with multi-layers and a single layer was 0.4%. 3) The difference in measurement between packed and unpacked films was 1.5%. The former overestimated values, but they were closer to the JARP values than those of unpacked film. 4) In comparison with the JARP method, accuracy decreased in the following order: perpendicular packed film with multiple layers, perpendicular packed film with a single layer, perpendicular unpacked film with multiple layers, perpendicular unpacked film with a single layer, parallel film. 5) The values measured by films in the inhomogeneity phantom were closer to those measured by the JARP method than values measured in a water-equivalent phantom. The reason was that there was less scatter in the lung of the inhomogeneity phantom than in the water-equivalent phantom.