TLD, diode and Monte Carlo dosimetry of an¹⁹²Ir source for high dose-rate brachytherapy

Abstract

Very few dosimetry data are available for the current generation of high-dose-rate (HDR) 192Ir sources, which have broad application in remotely afterloaded brachytherapy. We have measured the two-dimensional dose rate distribution around a microSelectron-HDR source and used the results to validate Monte Carlo simulations. Thermoluminescent dosimeters (TLDs) in solid-water phantoms were used to measure the transverse-axis dose rates in the distance range 0.5-10 cm and the polar dose-rate profiles at 1.5, 3 and 5 cm distance from the source. At close distances, 2-40 mm from the HDR source, we performed transverse axis dose-rate measurements with a Si diode in water. We performed diode measurements at the same distances also for a pulsed dose-rate (PDR) source to compare the results for 192Ir sources with different encapsulation. Both the HDR and the PDR sources were decayed, separated from their cables and calibrated prior to the measurements. The measured dose rates were compared with Monte Carlo photon transport calculations, which realistically modelled the experimental and source geometry at each measurement point. Agreement between Monte Carlo photon transport absolute dose-rate calculations and measurements was, on average, within 5%. From the transverse-axis experimental data, we deduced a value for the dose-rate constant lambda 0 of 192Ir HDR sources of 1.14 cGy h-1 U-1 +/- 5%. This value agrees within the experimental error with the Monte Carlo estimate of 1.115 cGy h-1 U-1 +/- 0.5%. Excellent agreement with previously measured anisotropy functions was observed. Higher anisotropy is observed for the point at 0 degree along the source cable for which no previous data have been reported.

Monte Carlo calculations and experimental measurements of dosimetry parameters of a new source

“…This code package has been used extensively in dosimetric characterization of brachytherapy sources, and compares favorably with experimental measurement data. 8,10,22,23,25 One of the major advantages of this code package is the availability of combinatorial geometric modeling routines that allow creation of complex structures, using basic geometric objects. 29 A realistic geometric model of the MED3633 103 Pd source was developed based on manufacturer's drawings, as shown in Fig.…”

“…Various detectors have been used for such purposes, including diode detectors, 2-10 thermoluminescent dosimetry ͑TLD͒ chips and rods, [10][11][12][13][14][15][16][17][18][19] and diamond detectors. 20 With appropriate corrections for geometry and energy response, both the diode detectors and the ͑TLD͒ detectors have been shown to be adequate for the characterization of brachytherapy source dosimetry.…”

“…20 With appropriate corrections for geometry and energy response, both the diode detectors and the ͑TLD͒ detectors have been shown to be adequate for the characterization of brachytherapy source dosimetry. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][21][22][23] Monte Carlo calculations have been used extensively for dosimetric characterization of brachytherapy sources, 8,10,[22][23][24][25][26][27] especially for low-energy sources such as 125 I seeds.…”

Monte Carlo study of dosimetric parameters and dose distribution effect of inhomogeneities and source position of GammaMed Plus source

“…Monte Carlo (MC) simulation is now becoming an accepted dose calculation methodology in brachytherapy. [1][2][3] It is recommended in American Association of Medical Physicists (AAPM) Task Group TG-43U [4] and TG-43U1 [5] state that dose distribution data of the brachytherapy sources in use should be obtained either by experimental measurement or by MC simulation using appropriate code respectively, which then to be used as input data in TPS for planning of exact dose delivery in brachytherapy treatment.…”

Computation of relative dose distribution and effective transmission around a shielded vaginal cylinder with Ir192 HDR source using MCNP4B

“…Theoretical and experimental methods have been used to characterize dose distributions of high dose rate ͑HDR͒ 192 Ir sources in a water medium. [3][4][5][6][7][8] Ir source is most commonly used for intracavitary treatment of vaginal and cervical malignancies. Vaginal cylinders are often used to deliver dose to the vaginal apex, upper vagina, and/or to the entire vaginal surface for the management of post-operative endometrial cancer or cervical cancer.…”