Dose and energy dependence of response of Gafchromic XR-QA film for kilovoltage x-ray beams.
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.
Rampado
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O
Struttura Complessa Fisica Sanitaria, Azienda Ospedaliera San Giovanni Battista, Corso Bramante 88, 10126 Torino, Italy. orampado@molinette.piemonte.it
Garelli
E
E
Deagostini
S
S
Ropolo
R
R
D002138:Calibration; D004307:Dose-Response Relationship, Radiation; D005373:Film Dosimetry / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D014962:X-Ray Film; D014965:X-Rays