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SU‐E‐T‐123: Anomalous Altitude Effect in Permanent Implant Brachytherapy Seeds
Author(s) -
Watt E,
Spencer DP,
Meyer T
Publication year - 2015
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 - 10.1118/1.4924484
Subject(s) - kerma , brachytherapy , ionization chamber , nuclear medicine , materials science , dosimetry , implant , physics , medicine , ionization , radiation therapy , surgery , ion , quantum mechanics
Purpose: Permanent seed implant brachytherapy procedures require the measurement of the air kerma strength of seeds prior to implant. This is typically accomplished using a well‐type ionization chamber. Previous measurements (Griffin et al., 2005; Bohm et al., 2005) of several low‐energy seeds using the air‐communicating HDR 1000 Plus chamber have demonstrated that the standard temperature‐pressure correction factor, P TP , may overcompensate for air density changes induced by altitude variations by up to 18%. The purpose of this work is to present empirical correction factors for two clinically‐used seeds (IsoAid ADVANTAGE™ 103 Pd and Nucletron selectSeed 125 I) for which empirical altitude correction factors do not yet exist in the literature when measured with the HDR 1000 Plus chamber. Methods: An in‐house constructed pressure vessel containing the HDR 1000 Plus well chamber and a digital barometer/thermometer was pumped or evacuated, as appropriate, to a variety of pressures from 725 to 1075 mbar. Current measurements, corrected with P TP , were acquired for each seed at these pressures and normalized to the reading at ‘standard’ pressure (1013.25 mbar). Results: Measurements in this study have shown that utilization of P TP can overcompensate in the corrected current reading by up to 20% and 17% for the IsoAid Pd‐103 and the Nucletron I‐125 seed respectively. Compared to literature correction factors for other seed models, the correction factors in this study diverge by up to 2.6% and 3.0% for iodine (with silver) and palladium respectively, indicating the need for seed‐specific factors. Conclusion: The use of seed specific altitude correction factors can reduce uncertainty in the determination of air kerma strength. The empirical correction factors determined in this work can be applied in clinical quality assurance measurements of air kerma strength for two previously unpublished seed designs (IsoAid ADVANTAGE™ 103 Pd and Nucletron selectSeed 125 I) with the HDR 1000 Plus well chamber.

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