# Radiochromic Films for the Two-Dimensional Dose Distribution Assessment
## 3 Instruments for Dose Reading
### Flatbed Scanners  
Flatbed scanners for the analysis of RCFs are widely used, in particular in medical applications, for their several advantages over other techniques. Flatbed scanners feature either a fluorescent lamp or an LED (the latter can be found in the latest models) light source and a system of light detectors, which, in most cases, is based on Charge Coupled Device (CCD) technology. The digitization of the RCF allows high spatial resolution dosimetry measurements, as well as accurate studies of the beam profile and homogeneity. It should be noticed that flatbed scanners have not been developed for RCF measurements and therefore their use for this specific purpose is not trivial. Referred works about RCF dosimetry with flatbed scanner discuss these aspects, as well as the techniques to mitigate them. The main concepts are reported here. The stability of the light source in flatbed scanners for measurements with RCFs is a source of uncertainty to be considered. [PERSON] et al. studied the performance of the Epson Expression 10000 XL scanner, featuring a xenon fluorescent lamp, for IMRT dosimetry measurements [70]. They concluded that this scanner has excellent reproducibility, if at least seven scans are done before its use. [PERSON] et al. studied the performance of LED-based scanners, in particular of the Epson V800 scanner featuring a white LED light source [71]. They found that the reproducibility and long-term stability of LED-based scanners are slightly better than those of scanners using a fluorescent light source. They also found a non-uniform response (up to 9%) in LED-based scanners greater than that in fluorescent-based scanners. Flatbed scanners used for RCF measurements have proved to have a non-uniform response in the direction perpendicular to the scan direction [72; 73]. The scanner response decreases as the distance of the scan's position from the scanner center increases. This effect, also referred to as lateral scan effect (or lateral response artifact) has been deeply studied in the literature and it can be mainly ascribed to the polarization of the light transmitted through the RCF, as it polarizes upon irradiation [63]. As a consequence of this, the lateral response artifact increases with the increase of the RCF level of darkening and, thus, with the dose. Contributions to the lateral response artifact come also from the scattering of the light with the RCF, variations in optical path, and cross talk, which is relevant only for small fields and high dose gradients [74]. For relatively small pieces of RCF, a cardboard centering mask can be used to further guarantee the reproducibility of the measurements, while corrections are needed for large RCF scanning. [PERSON] and [PERSON] proposed a methodology to solve lateral scanning artifacts based on correlating the response of the RCF calibration curves at different lateral positions in the flatbed scanner by means of a two-point rescaling [75]. Multichannel techniques, which evaluate the dose according to the information from the three color channels RGB, have been proved to reduce these effects, as well as to improve the precision of the measurement [76; 77]. Software for image analysis, such as ImageJ and MATLAB, are commonly used in combination with flatbed scanners to provide quantitative dose, as well as dose profile information. FilmQA Pro software from Ashland Inc. is specifically designed for Gafchromic(tm) film measurements in quality assurance (QA) medical applications and it uses a proprietary multichannel algorithm to remove non-dose contributions [78; 79]. [PERSON] et al. described the analysis procedures with both FilmQA Pro and ImageJ software, by achieving \(\pm\)2% accuracy with both software [80]. RiseScan is a software package based on LabView that can be used for analysis of Rise B3 and FWT RCFs, as well as for Gafchromic(tm) films [81; 82].