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Measurement and calculation of heterogeneity correction factors for an Ir‐192 high dose‐rate brachytherapy source behind tungsten alloy and steel shields
Author(s) -
Kirov A. S.,
Williamson J. F.,
Meigooni A. S.,
Zhu Y.
Publication year - 1996
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597733
Subject(s) - materials science , brachytherapy , tungsten , imaging phantom , shields , dosimeter , dosimetry , monte carlo method , thermoluminescent dosimeter , thermoluminescence , detector , ovoid , shield , optics , nuclear medicine , electromagnetic shielding , physics , composite material , geometry , metallurgy , mathematics , radiation therapy , optoelectronics , medicine , statistics , petrology , luminescence , geology
Shields made of high atomic number material are commonly used in vaginal applicators with high dose‐rate (HDR) 192 Ir remotely afterloaded brachytherapy sources. However little data is available for the dose distribution around such shields. Heterogeneity correction factors (HCFs) are defined as the ratio of the dose to a point with the heterogeneity (shield) in place, divided by the dose to the same point with no heterogeneity. Using thermoluminescent dosimeters (TLDs) in solid water phantom we have measured the HCFs behind 6 and 20 mm diam tungsten alloy disks, 4 and 2 mm thick and a 4 mm thick steel disk, positioned 15 mm from the source. For each measurement point, the heterogeneity correction factors were also inferred from Monte Carlo simulations, which accurately modeled the experimental geometry. The agreement between measured and calculated HCFs on the average was within 6%. Tungsten alloy disks resulted in about two times greater dose reduction in water (HCF≊0.4, for 20×4 mm disk) than for a steel disk with the same dimensions (HCF≊0.85). Reducing the disk diameter to 6 mm increased the dose transmission up to about 25%. Increasing the source‐to‐detector distance from 4 to 7 cm caused a change in HCF from 2% to more than 20%, depending on disk material and diameter. The detector artifact effects arising from the finite size and different composition of the TLD chips were determined.