title: Dosimetry of the 198Au source used in interstitial brachytherapy.
abstract: The American Association of Physicists in Medicine Task Group 43 reports, AAPM TG-43 and its update TG-43U1, provide an analytical model and a dosimetry protocol for brachytherapy dose calculations, as well as documentation and results for some sealed sources. The radionuclide 198Au (T(1/2)=2.70 days, Egamma=412 keV) has been used in the form of seeds for brachytherapy treatments including brain, eye, and prostate tumors. However, TG-43 reports have no data for 198Au seeds, and none have previously been obtained. For that reason, and because of the conversion of most treatment planning systems to TG-43 based methods, both Monte Carlo calculations (MCNP 4C2) and thermoluminescent dosimeters (TLDs) are used in this work to determine these data. The geometric variation in dose is measured using an array of TLDs in a solid water phantom, and the seed activity is determined using a high purity germanium detector (HPGe) and a well ionization chamber. The results for air kerma strength, Sk, per unit apparent activity, are 2.063 (MCNP) and 2.089 (measured) U mCi(-1), values close to those published in 1991 in the AAPM Task Group 32 report. The dose rate constant, lambda, is found equal to 1.115 (MCNP) and 1.095 (measured) cGy h(-1) U(-1). The radial dose function, g(r), anisotropy function, F(r, theta), and anisotropy factor, phi(an)(r), are also given.
authors: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, California 94550, USA.
authors: Lucile S
authors: LS
authors: Dauffy
authors: Leslie A
authors: LA
authors: Braby
authors: Barry M
authors: BM
authors: Berner
mesh_terms: D016880:Anisotropy; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D002138:Calibration; D006050:Gold Radioisotopes; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000628:therapy; D011829:Radiation Dosage; D011868:Radioisotopes; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013819:Thermoluminescent Dosimetry
chemical_list: D006050:Gold Radioisotopes; D011868:Radioisotopes