On multichannel film dosimetry with channel-independent perturbations

Abstract

Purpose: Different multichannel methods for film dosimetry have been proposed in the literature. Two of them are the weighted mean method and the method put forth by Micke et al and Mayer et al. The purpose of this work was to compare their results and to develop a generalized channel-independent perturbations framework in which both methods enter as special cases. Methods: Four models of channel-independent perturbations were compared: weighted mean, Micke-Mayer method, uniform distribution and truncated normal distribution. A closed-form formula to calculate film doses and the associated Type B uncertainty for all four models was deduced.To evaluate the models, film dose distributions were compared with planned and measured dose distributions. At the same time, several elements of the dosimetry process were compared: film type EBT2 versus EBT3, different waiting-time windows, reflection mode versus transmission mode scanning, and planned versus measured dose distribution for film calibration and for γ-index analysis.The methods and the models described in this study are publicly accessible through IRISEU. Alpha 1.1 (http://www.iriseu.com). IRISEU. is a cloud computing web application for calibration and dosimetry of radiochromic films. Results: The truncated normal distribution model provided the best agreement between film and reference doses, both for calibration and γ-index verification, and proved itself superior to both the weighted mean model, which neglects correlations between the channels, and the Micke-Mayer model, whose accuracy depends on the properties of the sensitometric curves.With respect to the selection of dosimetry protocol, no significant differences were found between transmission and reflection mode scanning, between 75 ± 5 min and 20 ± 1 h waiting-time windows or between employing EBT2 or EBT3 films. Significantly better results were obtained when a measured dose distribution was used instead of a planned one as reference for the calibration, and when a planned dose distribution was used instead of a measured one as evaluation for the γ-analysis. Conclusions:The truncated normal distribution model of channel-independent perturbations was found superior to the other three models under comparison and we propose its use for multichannel dosimetry.

Treating lung cancer with dynamic conformal arc therapy: a dosimetric study

“…Images were acquired in 48-bit RGB mode using 72 dpi resolution with the image-processing options turned off. The doses were obtained using the Radiochromic.com (http://radiochromic.com/) web application [10], v1.1 through v2.5.…”

Correcting scan‐to‐scan response variability for a radiochromic film‐based reference dosimetry system

“…This latter advance has made it possible to correct response values for the effects of nonuniformity in the thickness of the active layer in the films. [20][21][22][23][24] Nevertheless, it is well recognized that several of the properties of radiochromic film require special attention in measuring the film response on a CCD-based document scanners. These include film orientation on the scanner, 25 postexposure changes, [26][27][28] as well as the lateral response artifact.…”

Evaluation and mitigation of potential errors in radiochromic film dosimetry due to film curvature at scanning

“…However, care must be taken to reduce uncertainties associated with film dosimetry including film batch and scan orientation consistency, postexposure time, scanner warm‐up characteristics, and lateral film position on the scanner (7) . There are published recommendations for accurate film dosimetry, notably AAPM Task Group 55 (8) and much work published in the literature to reduce uncertainties in specific aspects of film dosimetry techniques 9 , 10 , 11 , 12 , 13 . However, no prior publication has considered the uncertainty introduced in film dosimetry by film curling at the point of scanning, which is often undetected or deemed insignificant by the operator, but may introduce a substantial dose error.…”

“…(7) There are published recommendations for accurate film dosimetry, notably AAPM Task Group 55 (8) and much work published in the literature to reduce uncertainties in specific aspects of film dosimetry techniques. (9)(10)(11)(12)(13) However, no prior publication has considered the uncertainty introduced in film dosimetry by film curling at the point of scanning, which is often undetected or deemed insignificant by the operator, but may introduce a substantial dose error. Two commonly used flatbed scanners for film dosimetry, the Epson 10000XL and the Epson V750, both have a gap of several millimeters between the scanner glass plate and scanner lid which permits natural curling of film at scanning.…”