SU-FF-T-147: Determination of TG43 Parameters for Cs-131 Model CS-1R2 Seed Using Radiochromic EBT Film Dosimetry

Abstract

Purpose: To measure the 2D dose distributions for Cs‐131 seed model CS‐1R2 for distances from 0.06cm to 4cm using radiochromic EBT film dosimetry. TG43 dosimetric parameters were generated. Method and Materials: Each radiochromic film (GAFCHROMIC® EBT lot ♯35076) was in contact with a model CS‐1R2 seed (IsoRay Medical) at the center of a solid water phantom, 30×30×20cm. A multiple film technique was employed. More than 50 films were separately exposed to 10 seeds, with the product of air kerma strength and exposure time between 14 and 800 Uhr. The seed strength ranged from 10 to 4U (NIST traceable) during the experimental runs. For calibration, 15 films (of the same lot) were exposed to 50kV x‐ray (M50) in air at 100cm SSD with doses ranging from 0.2 to 20Gy. Since the EBT film response is almost identical for M50 and M40 x‐rays, the energy response can be considered to be flat in this region and thus also the same for the Cs‐131 energy. All experimental, calibration and background films were scanned (pixel resolution 0.2mm) using a CCD camera‐based densitometer, with red and green light sources. Conversion from net optical density readings to doses were achieved based on the calibration curve established for each light source used in scanning. The 2D dose values in cylindrical coordinates were converted to polar coordinates, and the TG43 parameters were generated. Results: The dose rate constant, radial dose function and 2D anisotropy function were determined, and compared with those reported by other authors. General agreement was found. Conclusion: It is feasible to determine TG43 parameters for Cs‐131 model CS‐1R2 seed in solid water phantom using radiochromic EBT film. This method is superior to TLD dosimetry (1) in providing data with high spatial resolution for distances down to 0.06 cm and (2) within reasonably achievable time frame.

Radiochromic film dosimetry: Past, present, and future

“…Chiu-Tsao et al [56] employed EBT film model to determine the TG-43 (AAPM protocol for brachytherapy dose calculations) parameters for the Cs-131 and Cs-132 seed sources. Le et al [57] used EBT film to assess dose heterogeneity in intra-operative HDR brachytherapy, and Evans et al [58] have demonstrated the use of the radiochromic films in a brachytherapy auto-radiograph QA Figure 6 Justification of the uncertainty estimation analysis: relative percent error in dose delivered (above) and relative one sigma uncertainty (below) for EBT GAFCHROMICä film model (From [22]).…”

Optimizing the dynamic range extension of a radiochromic film dosimetry system

“…17 The high spatial resolution, energy independence of response, 18,19 and near tissue-equivalence of EBT film make it suitable for dose distribution measurements in radiation fields with high dose gradients. Apart from the IMRT QA measurements, EBT film model has found use in a number of additional dosimetry applications: brachytherapy, [20][21][22][23] total skin electron therapy ͑TSET͒, 24,25 electron therapy, 26,27 skin dose measurements, 28,29 total body irradiation ͑TBI͒, 30 lung 31,32 and breast 33 phantom measurements, stereotactic radiotherapy, [34][35][36] dosimetry characterization of proton therapy beams, 37 as well as dose verification during cell irradiation in radiobiological experiments. 38 The dynamic range of the EBT model GAFCHROMIC™ film in the red channel of its absorption spectrum is very well suited for dose measurements of up to approximately 8 Gy.…”