Premium
Dosimetry on transverse axes of 125 I and 192 Ir interstitial brachytherapy sources
Author(s) -
Nath Ravinder,
Meigooni Ali S.,
Meli Jerome A.
Publication year - 1990
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 - 10.1118/1.596584
Subject(s) - dosimeter , brachytherapy , dosimetry , nuclear medicine , physics , kerma , monte carlo method , dose rate , ionization chamber , imaging phantom , materials science , ionization , optics , ion , radiation therapy , mathematics , medicine , statistics , medical physics , quantum mechanics
Dose rates along the transverse axes of 125 I model 6702, 125 I model 6711 and 192 Ir 0.2‐mm steel sources for interstitial brachytherapy have been measured in a solid‐water phantom for distances up to 10 cm using LiF thermoluminescent dosimeters (TLDs). Specific dose rate constants, the dose rates in water per unit source strength 1 cm along the perpendicular bisector of the source, are determined to be 0.90±0.03, 0.85±0.03, and 1.09±0.03 cGy h − 1 U − 1 for 125 I model 6702, 125 I model 6711 and 192 Ir 0.2‐mm steel sources, respectively (1 U=unit of air kerma strength =1 μGy m 2 h − 1 =1 cGy cm 2 h − 1 ). In older and obsolete units of source strength (i.e., mCi apparent), these are 1.14±0.03, 1.08±0.03, and 4.59±0.15 cGy h − 1 mCi − 1 (apparent). Currently accepted values of specific dose rate constant for 125 I sources are up to 20% higher than our measured values which are in good agreement with the results of our Monte Carlo simulations. But for 192 Ir there is good agreement between our measured value of the specific dose rate constant and currently accepted values. The radial dose function for 125 I model 6702 is found to be consistently larger than that for 125 I model 6711, with an increasing difference as the distance from the source increases. Our measured values for the radial dose function for 125 I sources are in good agreement with the results of our Monte Carlo simulation as well as the measured values of Schell e t a l . [Int. J. Radiat. Oncol. Biol. Phys. 13 , 795–799 (1987)] for model 6702 and Ling e t a l . [Int. J. Radiat. Oncol. Biol. Phys. 9 , 1747–1752 (1983)] for model 6711. However, some of the recently reported Monte Carlo values of the radial dose function for 125 I sources are significantly larger than measured values; up to 18% at a distance of 5 cm. Our measured radial dose function for the 192 Ir seed is in good agreement with our Monte Carlo calculated values, and with both our earlier data for the high activity 192 Ir source of a remote afterloader and recommended values by Meisberger e t a l . [Radiol. 90 , 953–957 (1968)].