Photon energy dependence of the sensitivity of radiochromic film and comparison with silver halide film and LiF TLDs used for brachytherapy dosimetry

Abstract

There is a new radiochromic film, a highly uniform, thin (100-microns) detector whose sensitive layer (6 microns thick) changes from colorless to blue by dye polymerization without processing, upon exposure to ionizing radiation. Because the dose gradients around brachytherapy sources are steep, the high spatial resolution offered by film dosimetry is an advantage over other detectors such as thermoluminescent dosimeters (TLDs). This compares the photon energy dependence of the sensitivities of GafChromic film, silver halide verification film (Kodak X-Omat V Film), and lithium fluoride TLDs (Harshaw), over the photon energy range 28 keV to 1.7 MeV, which is of interest in brachytherapy. Sensitivity of the radiochromic film is observed to decrease by about 30% as effective photon energy decreases from 1710 keV (4-MV x rays) to 28 keV (60-kV x rays, 2-mm A1 filter). In contrast, the sensitivity of verification film increases by 980% and that of LiF TLDs increases by 41%. The variation of the sensitivity of radiochromic film with photon energy is considerably less than that for silver halide film and similar to that for LiF TLDs, but in the opposite direction. Radiochromic film, like LIF TLDs, does not exhibit the drastic sensitivity changes below 127 keV that silver halide film exhibits. Dose distribution in the immediate vicinity of a high activity (370 GBq) brachytherapy 192Ir source has been mapped using radiochromic film and is presented to illustrate the applicability of this new technology to brachytherapy dosimetry.

Gafchromic film dosimetry of a new HDR brachytherapy source

“…Radiochromic film is a powerful 2D dosimeter, which exhibits useful characteristics including high spatial resolution, near tissue/water equivalence $false({\mathrm{normalZ}}_{\text{eff},\text{EBT}}=6.98,{\mathrm{normalZ}}_{\text{eff},\text{water}}=7.3false)$, 1 , 2 the possibility of using in water, and lower sensitivity to visible light. In addition, it has been shown to have an energy independence response for HDR brachytherapy applications 3 , 4 …”

Monte Carlo calculations and experimental measurements of the TG‐43U1‐recommended dosimetric parameters of 125I (Model IR‐Seed2) brachytherapy source

“…To obtain the calibration factor, 18 TLD chips were placed in a custom‐designed Plexiglas slab phantom in a kilovoltage X‐ray (120 kVp) field that was calibrated using the TRS 398 protocol of the International Atomic Energy Agency (IAEA) (9) . E(r) was the correction factor for the energy dependence of the TLDs between the calibration beam and the ${}^{125}\mathrm{I}$ photons, which is equal to unity in this study (10) . The parameter d(T) is a correction factor which was used to account for source decay during the exposure (7) …”

Dosimetric comparison of extended dose range film with ionization measurements in water and lung equivalent heterogeneous media exposed to megavoltage photons

“…Despite some limitations, film offers a convenient medium for easily generating profiles and two‐dimensional distributions. In addition to the popular Kodak XV film and the variety of other existing verification films, 36 – 39 Kodak has recently released a new type of film that allows exposures at an extended dose range (EDR). The objective of this research is to provide a dosimetric evaluation of the new Kodak EDR film in homogeneous and lung density heterogeneous media.…”