Temperature dependence and temporal stability of stacked radiochromic sheets for three‐dimensional dose verification

Abstract

Purpose Recently a novel radiochromic sheet dosimeter, termed as PRESAGE sheets, consisting of leuco crystal violet dye and radical initiator had been developed and characterized. This study examines the dosimeter’s temporal stability and storage temperature dependence postirradiation, and its applicability for dose verification in three dimensions (3D) as a stack dosimeter. Methods PRESAGE sheets were irradiated using 6 MV photons at a dose range of 0–20 Gy with the change in optical density measured using a flatbed scanner. Following their irradiation, PRESAGE sheets were stored in different temperature environments (–18 °C, 4 °C, and 22 °C) and scanned at different time points, ranging from 1 to 168 h postirradiation, to track changes in measured signal and linearity of dose response. Multiple PRESAGE sheets were bound together to create a 12 × 13 × 8.7 cm3 film stack, with EBT3 film inserted between the sheets in the central region of the stack, that was treated using a clinical VMAT plan. Based on the results from the time and storage temperature study, two‐dimensional (2D) relative dose distribution measurements in PRESAGE were acquired promptly following irradiation at selected planes in the coronal, sagittal, and axial orientation of the film stack and compared to the treatment planning system calculations in their respective axes. Dose distribution measurements on the coronal axis of the stack dosimeter were also independently verified using EBT3 film. Results The dose response was observed to be linear (R2> 0.995) with sheets stored in colder temperatures retaining their signal and dose response sensitivity for extended periods postirradiation. Sheets stored in 22 °C environment should be measured within an hour postirradiation. Sheets stored in a 4 °C and −18 °C environment can be scanned up to 20‐ and 72 h postirradiation, respectively, while preserving the integrity of their dose response sensitivity and linearity of dose response within a mean absolute percent error of 2.0%. For instance, at 20 h postirradiation the dose response sensitivity for sheets stored in a −18 °C, 4 °C, and 22 °C temperature environment was measured to be 97%, 91%, and 77% of their original values measured within an hour postirradiation, respectively. The 2D gamma pass rate for central slices exceed 95% for PRESAGE film stack compared with treatment planning system on selected planes in the axial, coronal, and sagittal orientation and EBT3 film in the coronal orientation using a 2D gamma index of 2%/2mm. The gamma pass rate in comparing the calculated dose distribution with the measured dose distribution from PRESAGE‐LCV was observed to decrease in sheets scanned at later elapsed times postirradiation. In one example, the gamma pass rate for 2%/2mm criteria in the coronal plane was observed to decrease from 97.7% pass rate when scanned within an hour postirradiation to 92.1% pass rate when scanned at 20 h postirradiation under room temperature conditions. Conclusions This is the first study to demonstrate that the temporal s...

Feasibility of a Reusable Radiochromic Dosimeter

“…Both Formulations 1 and 3 show a decrease in clearing time upon reirradiation, with cuvettes in the present work stored at room temperature. PRESAGE samples stored in colder environments, such as refrigerated (4 • C) or freezing (−18 • C), exhibit greater stability in their temporal response and thus can be measured at later elapsed times postirradiation while preserving their signal and maintaining a high degree of linearity [12]. Another factor influencing decay time is the dosimeter size, where scaling up from a small dosimeter cuvette to a larger 1 kg dosimeter has seen decay rates decrease by 3× [9].…”

A comprehensive investigation of the performance of a commercial scintillator system for applications in electron FLASH radiotherapy

“…[7][8][9][10][11] Despite their dose-rate independence, these passive detectors require a post-irradiation wait time to achieve the signal stabilization required for accurate measurements. 7,[12][13][14][15][16] For the clinical translation and implementation of FLASH-RT, detector systems that can accurately monitor dose delivery in real time to validate machine output and verify the dose rate and the DPP delivered in UHDR beamlines will be critical. Ion chambers are recommended by national and international protocols for reference dosimetry in conventional RT, 17,18 but their ability to provide accurate dosimetry in UHDR beamlines is limited because ion chambers are subject to changes in sensitivity caused by significant ion recombination, which depends on specific beam parameters such as DPP.…”

“…Detectors that have been established to be dose‐rate independent include passive detectors such as radiochromic film, thermoluminescent dosimeters, optically stimulated luminescence dosimeters, and alanine‐based dosimeters 7–11 . Despite their dose‐rate independence, these passive detectors require a post‐irradiation wait time to achieve the signal stabilization required for accurate measurements 7,12–16 . For the clinical translation and implementation of FLASH‐RT, detector systems that can accurately monitor dose delivery in real time to validate machine output and verify the dose rate and the DPP delivered in UHDR beamlines will be critical.…”

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

“…The extent of color changes produced in film also does not correlate linearly with dose, except when PRESAGE sheets are used. 4,5 Rather, film requires a time-dependent calibration to convert the measured OD reading to a dose value, because the polymerization reaction never fully stabilizes 6 . For this reason, it is important to ensure the delay (irradiation to scanning) to be the same as used for film-calibration, which further limits film usability.…”

“…However, radiochromic film is a passive dosimeter, limited by the need for a complicated and time‐consuming calibration and delayed time to readout (recommended 16–24 h) to allow the polymerization reaction to stabilize upon irradiation 1,3 . The extent of color changes produced in film also does not correlate linearly with dose, except when PRESAGE sheets are used 4,5 . Rather, film requires a time‐dependent calibration to convert the measured OD reading to a dose value, because the polymerization reaction never fully stabilizes 6 .…”