TY - JOUR
T1 - A secondary air kerma strength standard for Yb-169 interstitial brachytherapy sources
AU - Das, R. K.
AU - Mishra, V.
AU - Perera, H.
AU - Meigooni, A. S.
AU - Williamson, J. F.
PY - 1995
Y1 - 1995
N2 - Ytterbium-169 (169Yb) is promising new intermediate low-energy isotope for interstitial implantation. To date, no air kerma strength (S K) standard for this source exists that can serve as a sound foundation for comparing various dose measurements and theoretical calculations. The authors have solved this problem by adapting the free air measurement technique of Goetsch et al., originally developed for 192Ir (see Med. Phys., vol. 18, p.462-7, 1991). Using a 100 cm3 spherical ion chamber with NIST traceable external beam calibrations in a free air geometry, the authors have measured the air kerma strength of 6 different source batches (2 type 6 batches, 3 type 8 batches, and 1 experimental high-intensity source). Room scatter corrections, derived from an empirical fit to the data (following Goetsch et al.) and/or directly by Monte Carlo simulation, yielded identical results with a reproducibility of 1%. The ratio (SK/A vendor) of measured SK to the vendor's contained activity assay averaged 1.554 cGy cm2 mCi-1 h-1 (0.0420 mu Gy m2 MBq-1 h-1), in conflict with the expected value of 1.34 (0.0362), derived from Monte Carlo calculations. The measured (SK/Avendor) for the type 8 seeds varies by as much as 10% whereas the SK/dose calibrator reading ratio varies by no more than 0.3%, suggesting that the reproducibility of Avendor is relatively poor. These discrepancies may help explain the variation (as large as 28%) in published dose rate constants for 169Yb.
AB - Ytterbium-169 (169Yb) is promising new intermediate low-energy isotope for interstitial implantation. To date, no air kerma strength (S K) standard for this source exists that can serve as a sound foundation for comparing various dose measurements and theoretical calculations. The authors have solved this problem by adapting the free air measurement technique of Goetsch et al., originally developed for 192Ir (see Med. Phys., vol. 18, p.462-7, 1991). Using a 100 cm3 spherical ion chamber with NIST traceable external beam calibrations in a free air geometry, the authors have measured the air kerma strength of 6 different source batches (2 type 6 batches, 3 type 8 batches, and 1 experimental high-intensity source). Room scatter corrections, derived from an empirical fit to the data (following Goetsch et al.) and/or directly by Monte Carlo simulation, yielded identical results with a reproducibility of 1%. The ratio (SK/A vendor) of measured SK to the vendor's contained activity assay averaged 1.554 cGy cm2 mCi-1 h-1 (0.0420 mu Gy m2 MBq-1 h-1), in conflict with the expected value of 1.34 (0.0362), derived from Monte Carlo calculations. The measured (SK/Avendor) for the type 8 seeds varies by as much as 10% whereas the SK/dose calibrator reading ratio varies by no more than 0.3%, suggesting that the reproducibility of Avendor is relatively poor. These discrepancies may help explain the variation (as large as 28%) in published dose rate constants for 169Yb.
UR - http://www.scopus.com/inward/record.url?scp=0029021433&partnerID=8YFLogxK
U2 - 10.1088/0031-9155/40/5/003
DO - 10.1088/0031-9155/40/5/003
M3 - Article
C2 - 7652005
AN - SCOPUS:0029021433
SN - 0031-9155
VL - 40
SP - 741
EP - 756
JO - Physics in medicine and biology
JF - Physics in medicine and biology
IS - 5
M1 - 003
ER -