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SU‐E‐T‐155: Calibration of Variable Longitudinal Strength 103Pd Brachytherapy Sources
Author(s) -
Reed J,
Radtke J,
Micka J,
Culberson W,
DeWerd L
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 - 10.1118/1.4924517
Subject(s) - kerma , anisotropy , physics , monte carlo method , azimuth , calibration , optics , brachytherapy , detector , dosimetry , transverse plane , point source , computational physics , materials science , nuclear medicine , medicine , statistics , mathematics , structural engineering , engineering , quantum mechanics , radiation therapy
Purpose: Brachytherapy sources with variable longitudinal strength (VLS) allow for a customized intensity along the length of the source. These have applications in focal brachytherapy treatments of prostate cancer where dose boosting can be achieved through modulation of intra‐source strengths. This work focused on development of a calibration methodology for VLS sources based on measurements and Monte Carlo (MC) simulations of five 1 cm 1 ⁰ 3 Pd sources each containing four regions of variable 1 ⁰ 3 Pd strength. Methods: The air‐kerma strengths of the sources were measured with a variable‐aperture free‐air chamber (VAFAC). Source strengths were also measured using a well chamber. The in‐air azimuthal and polar anisotropy of the sources were measured by rotating them in front of a NaI scintillation detector and were calculated with MC simulations. Azimuthal anisotropy results were normalized to their mean intensity values. Polar anisotropy results were normalized to their average transverse axis intensity values. The relative longitudinal strengths of the sources were measured via on‐contact irradiations with radiochromic film, and were calculated with MC simulations. Results: The variable 1 ⁰ 3 Pd loading of the sources was validated by VAFAC and well chamber measurements. Ratios of VAFAC air‐kerma strengths and well chamber responses were within ±1.3% for all sources. Azimuthal anisotropy results indicated that ≥95% of the normalized values for all sources were within ±1.7% of the mean values. Polar anisotropy results indicated variations within ±0.3% for a ±7.6° angular region with respect to the source transverse axis. Locations and intensities of the 1 ⁰ 3 Pd regions were validated by radiochromic film measurements and MC simulations. Conclusion: The calibration methodology developed in this work confirms that the VLS sources investigated have a high level of polar uniformity, and that the strength and longitudinal intensity can be verified experimentally and through MC simulations. 103 Pd sources were provided by CivaTech Oncology, Inc.