In-vivo dosimetry with Gafchromic films for patients with sarcoma.

Background: The aim of the study was to evaluate Gafchromic films as in-vivo detectors for intensity modulated radiation therapy for patients with sarcomas and to assess the quality of irradiation in these patients. Materials and methods: Phantom measurements were used to validate the measurements performed with the Gafchromic. The uncertainty of the measurement method and that in determining the reference dose value obtained from the treatment planning system (TPS) were independently estimated. In-vivo measurements were performed in 21 patients with sarcomas who were irradiated with dynamic techniques using a 5 × 5 Gy. For each patient, measurements were taken at four points using films placed on the skin under a 1 cm bolus. The results of the measurements obtained in the 96 treatment sessions were analysed. The treatment quality was assessed based on the differences between the doses calculated using the TPS and those measured. Results: The uncertainty of measurements was less than 0.8% (one standard deviation). Owing to differences in the dose gradient, the uncertainty of the reference dose reading from the TPS had an individual value at each measurement point. The uncertainties were less than 3% for more than 95% of the points; 93% of the in vivo measurements showed a difference of less than 7% between the measurements and calculations. Conclusions: Gafchromic films can be used for in vivo dosimetry using dynamic techniques. This method made it possible to detect errors of 7% with a probability of approximately 95%. The results obtained for 21 patients with sarcoma demonstrated high-quality preparation and delivery of irradiation.