Multichannel dosimetry with radiochromic film like Gafchromic EBT2 is shown to have significant advantages over single channel dosimetry. It is recommended that the dosimetry protocols described be implemented when using this radiochromic film to ensure the best data integrity and dosimetric accuracy.

The authors have developed a simplified and efficient protocol to measure doses delivered by an IMRT or VMAT plan using only the patient film, one calibration film, one unexposed film, and applying a single scan to acquire a digital image for calculation and analysis. The simplification and timesaving offer a potential practical solution for using radiochromic film for routine treatment plan quality assurance without sacrificing spatial resolution for convenience.

Purpose: A new method to evaluate radiochromic film dosimetry data scanned in multiple color channels is presented. The multi‐channel method allows for the separation and removal of the non‐dose‐dependent portions of a film image and performs superior to the traditional single channel method. Methods: Exposed radiochromic films were scanned in RGB format on a flatbed color scanner and measured to build calibration. Images were converted to dose maps using both single color channel and multi‐channel method. The multi‐channel method allows for the separation of the scanned signal into one dose‐dependent part and another dose‐independent part and enables the correction of a variety of disturbances including non‐ uniformities of the film as well as scanner related artifacts. The fundamental mathematics of the two methods is described and the dose maps calculated with both methods are compared and analyzed. Results: The multi‐channel dosimetry method was shown to remove effectively non‐dose dependent abnormalities from radiochromic dosimetry film images and improve the integrity of the dose information and also reduces random noise in the dose images and mitigates scannerrelated artifacts such as lateral position dependence. In providing an ability to calculate dose maps from data in all the color channels the multi‐channel method provides the ability to examine the agreement between the color channels. The method permit compensation for nonuniformities in the film, increases the signal to noise level, mitigates scanners effect of the calculated dose map and extends the evaluable dose range to 10 cGy – 100. Conclusions: Multi‐channel dosimetry is shown to have significant advantages over single channel method in ensuring the best data integrity and dosimetric accuracy. All authors are employees of International Specialty Products, Manufacturer of Gafchromic Films

We have demonstrated a simplified protocol to measure doses delivered by an IMRT treatment plan using only the patient film, one calibration film, one unexposed film, and applying a single scan to acquire a digital image for calculation and analysis. The simplification and time-savings provide a practical solution for using radiochromic film for routine IMRT QA without sacrificing spatial resolution for convenience. David Lewis, Andre Micke and Xiang Yu are all employed by Ashland Specialty Ingredients the manufacturer of GAFCHROMIC EBT3 radiochromic film that is the subject of the work presented in the Abstract.

Purpose: Triple channel correction acquisition (TCCA) is a model‐based method for obtaining the characteristic curve of Gafchromic EBT2 film (EBT2). In this study the TCCA method was applied to EBT2 film dosimetry of intensity modulated radiation therapy (IMRT) and intensity modulated arc therapy (IMAT). Method and Materials:EBT2 films were calibrated by a field‐by‐field method in 13 steps. All films were scanned by using flat‐bed scanners at one day after the irradiation. Seven characteristic curves obtained by the TCCA method were compared with those of a single channel acquisition (SCA) method. For clinical applications, the planar dose distributions of IMRT and IMAT plans were compared with dose distributions measured with EBT2 films. The film analyses were performed by applying both TCCA and SCA. We chose two IMRT plans and two Varian IMAT (RapidArc) plans, which were created by the BrainLAB i‐plan and Eclipse Varian treatment planning systems for IMRT and RapidArc, respectively. Results: The constancy of the characteristic curves obtained by TCCA was better than that of SCA. The most significant difference between the characteristic curves of TCCA and SCA was observed in a low dose range between 25 cGy and 100 cGy. The results of clinical cases demonstrated that the dose difference between the measured and planned doses in high dose gradient regions was smaller with TCCA than that with SCA. Conclusions: We showed that characteristic curves obtained by the TCCA method have a good constancy compared with those of SCA. The potential advantage of TCCA was seen in high dose gradient regions in clinically relevant IMRT and IMAT cases. Hence, EBT2 film dosimetry with the TCCA method can be used for high precision patient specific QA.

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