Development of a Novel Readout System for Radiochromic Film Dosimetry

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Alexander, Kevin
Radiochromic film dosimetry , Medical Physics
As radiation therapy treatment modalities continue to develop, patient dose delivery has become increasingly complex. The verification of dose delivery and the quality assurance (QA) to ensure that a prescribed dose is accurately and precisely delivered to a patient is critical. Radiochromic film dosimetry has been adopted in the clinic as a convenient option for QA because it provides verification in a two dimensional plane, is essentially energy independent, is near tissue equivalent, and has high spatial resolution. Unfortunately, it is not always easy to use. Radiochromic films are typically read out using an advanced flatbed scanner, such as the commercially available Epson 10000XL scanner (commonly used in the clinic). However, difficulties overcoming imaging artifacts on these scanners, related to such factors as directional dependence of the film orientation and non-uniform scanner sensitivity, have necessitated the development of strict protocols for film readout and sophisticated image correction techniques. Based on experience with optical tomography using the Vista Optical CT Scanner, a simpler readout technique based on components of the Vista scanner was investigated. In this work, a setup consisting of a camera and light box, interfaced with computer image acquisition software was developed and characterized for the purpose of imaging radiochromic film. Two cameras (a colour and a greyscale camera) were tested and benchmarked using a commonly used Epson 10000XL scanner. The optical properties of the system were optimized and various film calibration models were tested. Single channel and triple channel dosimetry methods were implemented and applied to film imaging data. Validation tests examined simple irradiations as well as more complex intensity modulated radiation therapy plans. Studies using the prototype film imaging system showed that film imaging is orientation independent, and that good agreement is found using single channel dosimetry methods with the greyscale camera and red light illumination. While further improvements to the light box are needed to effectively implement triple channel dosimetry methods and to make the system more practical for clinical use, this simple imaging technique shows good promise to simplify and improve on existing film dosimetry readout.
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