Dose and energy dependence of response of Gafchromic® XR-QA film for kilovoltage x-ray beams

• Published in: Physics in medicine & biology Vol. 51; no. 11; pp. 2871 - 2881
• Main Authors: Rampado, O, Garelli, E, Deagostini, S, Ropolo, R
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 07.06.2006
• Subjects: Calibration; Dose-Response Relationship, Radiation; Film Dosimetry - instrumentation; Film Dosimetry - methods; Humans; Radiation Dosage; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - instrumentation; Radiotherapy Planning, Computer-Assisted - methods; Reproducibility of Results; Sensitivity and Specificity; Time Factors; X-Ray Film; X-Rays
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/51/11/013

There is a growing interest in Gafchromic films for patient dosimetry in radiotherapy and in radiology. A new model (XR-QA) with high sensitivity to low dose was tested in this study. The response of the film to different x-ray beam energies (range 28-145 kVp with various filtrations, dose range 0-100 mGy) and to visible light was investigated, together with the after exposure darkening properties. Exposed films were digitized with a commercially available, optical flatbed scanner. A single functional form for dose versus net pixel value variation has been determined for all the obtained calibration curves, with a unique fit parameter different for each of the used x-ray beams. The film response was dependent on beam energy, with higher colour variations for the beams in the range 80-140 kVp. Different sources of uncertainties in dose measurements, governed by the digitalization process, the film response uniformity and the calibration curve fit procedure, have been considered. The overall one-sigma dose measurement uncertainty depended on the beam energy and decreased with increasing absorbed dose. For doses above 10 mGy and beam energies in the range 80-140 kVp the total uncertainty was less than 5%, whereas for the 28 kVp beam the total uncertainty at 10 mGy was about 10%. The post-exposure colour variation was not negligible in the first 24 h after the exposure, with a consequent increase in the calculated dose of about 10%. Results of the analysis of the sensitivity to visible light indicated that a short exposure of this film to ambient and scanner light during the measurements will not have a significant impact on the radiation dosimetry.