Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

Abstract

Purpose The purpose of this study was to investigate the beam quality dependence of the EBT‐XD radiochromic films for megavoltage photon and electron beam irradiations by studying their spectral response. Dose, dose rate, and interbatch dependencies were investigated as well. Methods EBT‐XD and EBT3 radiochromic films were cut into 5 cm2 × 5 cm2 pieces, placed between solid water phantoms, and irradiated with 6 and 15 MV photon beams, 6 and 10 MV flattening filter free photon beams, and 6 and 20 MeV electron beams at dose levels between 0.5 and 50 Gy. In order to measure the spectral response, the films were illuminated by a deuterium and tungsten‐halogen lamp and net absorption was measured in 400–800 nm spectral range using a fiber‐coupled optical spectrometer. Film samples were then analyzed using a flatbed scanner in the red, green, and blue channel to obtain the optical density of the films. Results The net absorption spectra of the EBT‐XD and EBT3 films showed two absorption bands centered at 635 and 585 nm, characteristic of the EBT model. However, for a given dose, the EBT‐XD films showed lower net absorbance compared to the EBT3 films. At a given dose level, the net absorption spectra and dose–response curves for EBT‐XD films showed only slight variations across various beam qualities. When a calibration curve obtained from a given beam quality is used to measure dose from films irradiated with other beam qualities, the maximum uncertainty in the calculated dose, in ranges 5–40 and 8–50 Gy for red and green channels, respectively, were ~3.1% and ~2.4%. Conclusions The response of the EBT‐XD films is dose rate independent but batch dependent. No significant beam quality dependence was observed in EBT‐XD films in the dose range up to 50 Gy.

Feasibility of proton FLASH irradiation using a synchrocyclotron for preclinical studies

“…In order to measure the dose at the entrance, the film sample was placed at the depth of 1.1 mm (WET) and 50 pulses each with 20 μs duration were delivered to the film. Films were scanned 48 h after irradiation using an Epson Expression 10000XL desktop flatbed scanner (Epson Americana Inc., Long Beach, CA, USA) 24 . The calibration curve was established at conventional dose rate using a Mevion S250 ™ clinical proton beam in Washington University in St. Louis 25 …”

“…Films were scanned 48 h after irradiation using an Epson Expression 10000XL desktop flatbed scanner (Epson Americana Inc., Long Beach, CA, USA). 24 The calibration curve was…”

Influence of 0.35 T magnetic field on the response of EBT3 and EBT‐XD radiochromic films

“…The response of EBT3 and EBT‐XD films has been shown to be independent of beam quality and dose‐rate in megavoltage photon beams, 22,23,39 therefore irradiating films to the same dose level using two entirely different machines is not a concern. Besides, any dose‐rate or beam quality dependence are further mitigated because both machines have a similar beam quality (63.15% with B = 0.35 T vs 63.5% with no magnetic field) and dose rate (650 vs 600 MU/min).…”

“…It has been shown that the response of both EBT3 and EBT-XD films is batch-dependent, but energy-independent for megavoltage photon beams, including flattening filter free (FFF) beams, and electron beams. [22][23][24] Active ingredient of both EBT3 and EBT-XD film models are "needle-like" lithium pentacosa-10,12-diynoate acid (LiPCDA) monomer crystals in which a linear polymer (poly-PCDA) can grow. The clumps of film monomers are suspended in the active layer with intermolecular distance of 0.4 nm needed for polymerization to occur.…”

“…The wide dynamic range of EBT‐XD model makes them suitable for use in advanced radiotherapy modalities, such as stereotactic body radiation therapy (SBRT). It has been shown that the response of both EBT3 and EBT‐XD films is batch‐dependent, but energy‐independent for megavoltage photon beams, including flattening filter free (FFF) beams, and electron beams 22–24 …”