Comprehensive evaluation and new recommendations in the use of Gafchromic EBT3 film

Abstract

BackgroundGafchromic film's unique properties of tissue‐equivalence, dose‐rate independence, and high spatial resolution make it an attractive choice for many dosimetric applications. However, complicated calibration processes and film handling limits its routine use.PurposeWe evaluated the performance of Gafchromic EBT3 film after irradiation under a variety of measurement conditions to identify aspects of film handling and analysis for simplified but robust film dosimetry.MethodsThe short‐ (from 5 min to 100 h) and long‐term (months) film response was evaluated for clinically relevant doses of up to 50 Gy for accuracy in dose determination and relative dose distributions. The dependence of film response on film‐read delay, film batch, scanner type, and beam energy was determined.ResultsScanning the film within a 4‐h window and using a standard 24‐h calibration curve introduced a maximum error of 2% over a dose range of 1–40 Gy, with lower doses showing higher uncertainty in dose determination. Relative dose measurements demonstrated <1 mm difference in electron beam parameters such as depth of 50% of the maximum dose value (R50), independent of when the film was scanned after irradiation or the type of calibration curve used (batch‐specific or time‐specific calibration curve) if the same default scanner was used. Analysis of films exposed over a 5‐year period showed that using the red channel led to the lowest variation in the measured net optical density values for different film batches, with doses >10 Gy having the lowest coefficient of variation (<1.7%). Using scanners of similar design produced netOD values within 3% after exposure to doses of 1–40 Gy.ConclusionsThis is the first comprehensive evaluation of the temporal and batch dependence of Gafchromic EBT3 film evaluated on consolidated data over 8 years. The relative dosimetric measurements were insensitive to the type of calibration applied (batch‐ or time‐specific) and in‐depth time‐dependent dosimetric signal behaviors can be established for film scanned outside of the recommended 16–24 h post‐irradiation window. We generated guidelines based on our findings to simplify film handling and analysis and provide tabulated dose‐ and time‐dependent correction factors to achieve this without reducing the accuracy of dose determination.

Technical note: High‐dose and ultra‐high dose rate (UHDR) evaluation of Al2O3:C optically stimulated luminescent dosimeter nanoDots and powdered LiF:Mg,Ti thermoluminescent dosimeters for radiation therapy applications

“…44 Although some have suggested that the dynamic range of Gafchromic EBT3 film is limited to doses less than 10 Gy, particularly for the red channel, 14,25 several others have either used or reported the feasible use of Gafchromic EBT3 film at higher dose ranges using multi-channel dosimetric analysis of film by incorporating the green and blue channels. 9,[25][26][27][31][32][33] In this study and in a prior study, 31 we have demonstrated the feasible and accurate use of Gafchromic EBT3 film at doses ≥ 40 Gy using a single polynomial equation for netOD values measured in the red channel allowing for ease of use in single-channel film dosimetry for high-dose settings. Similar to previous recommendations for Gafchromic EBT3 film, AAPM's TG-191 report states the recommendation that the use of OSLDs and TLDs be limited to a cumulative dose of 10 Gy because of reported changes in sensitivity and supralinear behavior caused by the population of charge carriers in the deep traps.…”

“…1,2,6,7,[9][10][11]32,33 The films were scanned at 24 h post-irradiation using an Epson 10000XL flatbed scanner (Seiko Epson Corporation, Nagano, Japan) and analyzed using ImageJ and MATLAB using the red channel only as previously described. 31 2.1.2 Thermoluminescent dosimeters (TLDs) LiF:Mg,Ti TLD powder (∼25 mg) was packaged in single-use plastic envelopes (1 cm × 1 cm) before their irradiation. At 24 h after irradiation, the weight of the powdered TLD was measured by using a precision lab scale by subtracting the weight of the plastic envelope from the total weight of the TLD packet.…”

“…Nevertheless, these dosimeters have the potential for use beyond this recommended 10-Gy limit. [24][25][26][27][28][29][30][31] A recent publication from Liu et al demonstrated the feasible use of Gafchromic EBT3 film at extended doses up to at least 50 Gy when utilizing only the red channel for dose measurements, without increasing the uncertainty in dose determination. 31 The aim of this study is to determine the usability of Al 2 O 3 :C OSLDs and single-use powder-based LiF:Mg,Ti TLDs with Gafchromic EBT3 film under high-dose, ultra-high DPP, and ultra-high dose rate conditions that extend beyond their recommended use in their respective Task Group reports 14,20 for applications in calibration and dose verification for FLASH RT.…”