Verification of Ir-192 near source dosimetry using GAFCHROMIC^®film

Abstract

Intravascular brachytherapy treatments of in-stent restenosis have been performed extensively using Ir-192 ribbon. Task Group 60 of the American Association of Physicists in Medicine (AAPM) recommends a dose reference point at 2 mm from the source center for these treatments. However, it is known that the source can be as close as 0.5 mm to the arterial wall if not centered in the lumen. Therefore, the source dosimetry needs to be characterized at these close distances to accurately determine the amount of dose delivered for noncentered cases. In this paper, we report the verification of the dose distributions around Ir-192 seed sources at radial distances from 0.5 mm to 6 mm using GAFCHROMIC film. We evaluated an Ir-192 single seed source and a train of 6 seeds spaced 1 mm apart enclosed in a nylon ribbon. Each source was placed in a homogeneous solid water phantom directly below a stack of GAFCHROMIC films (MD-55-2). The calibration curve of the lot of films used in the experiment was established for Ir-192 by exposing a set of calibration films, one at a time, to an Ir-192 high dose rate (HDR) source. All films were scanned 5 or more days after exposure with a Lumisys Model 150 microdensitometer. The data were acquired and evaluated using RIT113 (Radiological Imaging Technology) software and analyzed using Excel and IDL (Interactive Data Language) software. Isodose curve plots in the plane containing the source's longitudinal axis and dose rate plots in the radial direction were obtained. For both configurations, the dose rates along the transverse axes agree to within the margin of error with previous Monte Carlo results. The isodose curve plots display hot spots near the seed ends, which is consistent with the leakage of beta particles and electrons from the unsealed seed ends as predicted with Monte Carlo calculations.

Temperature and hydration effects on absorbance spectra and radiation sensitivity of a radiochromic medium

“…[1][2][3][4][5][6][7] While many of the current polymer systems are utilized for two-or three-dimensional dose representation, high spatial resolution offers potential for successful implementation in point-based measurements. Radiochromic materials commercially available in GAFCHROMIC ® films ͑International Specialty Products, Wayne, NJ͒ have the desired high spatial resolution [8][9][10] and are able to provide sufficient signal from a subcubic millimeter volume.…”

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

“…( 24 ) There are several studies which fit a third order polynomial to the calibration data to convert NOD to dose. ( 21 , 25 , 26 ) Using this method, an increasing incline was obtained in our experiment in higher doses, which is in contrast with the saturation effect in the films.…”

A Study on the Dose Distributions in Various Materials from an Ir-192 HDR Brachytherapy Source

“…Gafchromic film (MD-55, Nuclear Associates, USA) was used due to its excellent spatial resolution (0.2 mm), tissue equivalent 6.5 atomic number, and low sensitivity to room luminosity [19], [20], [21]. The MD-55 has a thickness of approximately 0.3 mm and dose ranges from 3 to 100 Gy.…”