The use of new GAFCHROMIC® EBT film for I125 seed dosimetry in Solid Water® phantom

Abstract

Radiochromic film dosimetry has been extensively used for intravascular brachytherapy applications for near field within 1 cm from the sources. With the recent introduction of new model of radiochromic films, GAFCHROMIC EBT, with higher sensitivity than earlier models, it is promising to extend the distances out to 5 cm for low dose rate (LDR) source dosimetry. In this study, the use of new model GAFCHROMIC EBT film for 125I seed dosimetry in Solid Water was evaluated for radial distances from 0.06 cm out to 5 cm. A multiple film technique was employed for four 125I seeds (Implant Sciences model 3500) with NIST traceable air kerma strengths. Each experimental film was positioned in contact with a 125I seed in a Solid Water phantom. The products of the air kerma strength and exposure time ranged from 8 to 3158 U-h, with the initial air kerma strength of 6 U in a series of 25 experiments. A set of 25 calibration films each was sequentially exposed to one 125I seed at about 0.58 cm distance for doses from 0.1 to 33 Gy. A CCD camera based microdensitometer, with interchangeable green (520 nm) and red (665 nm) light boxes, was used to scan all the films with 0.2 mm pixel resolution. The dose to each 125I calibration film center was calculated using the air kerma strength of the seed (incorporating decay), exposure time, distance from seed center to film center, and TG43U1S1 recommended dosimetric parameters. Based on the established calibration curve, dose conversion from net optical density was achieved for each light source. The dose rate constant was determined as 0.991 cGy U(-1)h(-1) (+/-6.9%) and 1.014 cGy U(-1)h(-1) (+/-6.8%) from films scanned using green and red light sources, respectively. The difference between these two values was within the uncertainty of the measurement. Radial dose function and 2D anisotropy function were also determined. The results obtained using the two light sources corroborated each other. We found good agreement with the TG43U1S1 recommended values of radial dose function and 2D anisotropy function, to within the uncertainty of the measurement. We also verified the dosimetric parameters in the near field calculated by Rivard using Monte Carlo method. The radial dose function values in Solid Water were lower than those in water recommended by TG43U1S1, by about 2%, 3%, 7%, and 14% at 2, 3, 4, and 5 cm, respectively, partially due to the difference in the phantom material composition. Radiochromic film dosimetry using GAFCHROMIC EBT model is feasible in determining 2D dose distributions around low dose rate 125I seed. It is a viable alternative to TLD dosimetry for 125I seed dose characterization.

Gafchromic film dosimetry of a new HDR brachytherapy source

“…An estimate of the combined uncertainties has been calculated using a simple quadrature sum of individual components to provide an overall uncertainty. The detailed step‐by‐step analysis of the uncertainties of the measured doses is described by Chiu‐Tsao et al (1) According to MC simulations, the values obtained for type A uncertainty were less than 0.1% for all points except for the longitudinal axis (z‐axis) points where the statistical uncertainty was below 0.5%. The statistical uncertainty in the simulation of air‐kerma strength is less than 0.4%.…”

“…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 …”

Dosimetric evaluation of a novel high dose rate (HDR) intraluminal / interstitial brachytherapy applicator for gastrointestinal and bladder cancers

“…Another method to fit a curve to the delivered dose (D) versus measured netOD is using an analytical expression: ( 27 , 28 , 20 ) $D_{\mathit{fit}}=b.\mathit{netOD}+c\cdot {\mathrm{italicnetOD}}^n$ where b , c and n are the fitting parameters. Since Devic et al ( 20 ) found that the fit procedure returns the best results for a fitting parameter of $\mathrm{normaln}=2.5$, other two parameters were calculated.…”

Dose distribution verification for GYN brachytherapy using EBT Gafchromic film and TG-43 calculation

“…Air kerma strength (S K ) for GZP6 HDR brachytherapy system from Monte Carlo code was obtained 4414 × 10 −6 and 4077 × 10 −6 Gy m 2 h −1 for source of CH 3 and CH 4 , respectively. The value of measured air kerma strength was obtained by taking into account the date of measurement 4207 × 10 −6 ± 1% Gym 2 h −1 for CH 3 and 3864.5 × 10 −6 ± 1% Gym 2 h −1 for CH 4 .…”

“…3 Different investigators had demonstrated the usefulness of the EBT Gafchromic films for brachytherapy source dosimetry. 4 These films require no chemical processing and they are insensitive to ambient light. Therefore, they can be cut to the shape of the experimental geometry for the best representation of a dosimetric setup.…”