Analysis of uncertainties in Gafchromic® EBT film dosimetry of photon beams

Abstract

Radiotherapy today employs complex techniques in order to achieve the best possible conformity of the delivered dose to the target volume. When using dynamic dose delivery techniques, it is especially important to verify the delivered dose at as many representative points as possible. As a continuous medium, Gafchromic EBT film offers an excellent spatial resolution which, together with improvements in sensitivity as compared to older types of radiochromic films, make it a promising candidate for this purpose. In this paper we investigated whether EBT films can be used for quantitative dosimetry in photon beams. There are many publications which discuss different aspects of the EBT film dosimetry. Unfortunately, they differ in the used protocols, scanning devices and variables used for the film darkening quantification which makes the sources of uncertainties difficult to compare. Therefore, the overall accuracy and reproducibility of the results which can be reached with Gafchromic EBT films in combination with a commercial flatbed scanner was investigated. Both the film properties and the influence of the readout system were analysed and compared. The total uncertainty in the net optical density determination due to the studied effects was estimated to be 1.6% at 0.3 Gy and 0.8% at 1 Gy for 60Co photons. Based on this analysis of uncertainties, the handling and scanning protocol was optimized and methods to reduce the influence of some of the uncertainties were proposed. Although Gafchromic EBT films have significant advantages, there are certain effects which have to be considered in order to achieve 5% accuracy in the dose delivered to a patient.

Dosimetric characterization and use of GAFCHROMIC EBT3 film for IMRT dose verification

“…In 2009, the GAFCHROMIC EBT film was replaced by the GAFCHROMIC EBT2 film that incorporates a yellow marker dye in the active layer and a synthetic polymer as the binder component. Several works have been published studying some EBT and EBT2 properties, such as film homogeneity, ( 1 , 2 ) scanning orientation dependence, ( 3 – 7 ) energy dependence, ( 4 , 8 – 10 ) absorption spectra, ( 11 ) postcoloration behavior, ( 2 , 4 – 5 , 7 – 8 , 12 – 13 ) high‐dose dependence, ( 7 ) temperature dependence, ( 7 , 14 – 15 ) and ambient light sensitivity. ( 7 ) …”

Adaptation and security validation of an irradiator suitable for use of cesium-137 sources

“…Figure 1 shows the layout of the radiator side section. Radiochromic films have been widely used in dosimetric procedures, where it is necessary to know the planar behavior of doses [3] [4]. Accordingly, to determine the distribution of doses on the surface of the sample holder, radiochromic films of the EBT-3 generation from ISP were used.…”

PIXEL-BASED CORRECTION METHOD FOR GAFCHROMIC®EBT FILM DOSIMETRY

“…Ahead of scanning, the scanner window was wiped clean with alcohol and the outer frame of the scanner plate was marked for identification of the center point of the plate to enhance film positioning reproducibility. Since the response of the scanner is stabilized after the third scan [18][19], data from the first three scans were discarded in image acquisition in order to avoid the warm-up effect of the scanner lamp. Background subtraction was conducted by scanning of an unexposed film from the same batchnumber packet.…”