Photon energy spectrum emitted by a novel polymer-encapsulated {sup 103}Pd source and its effect on the dose rate constant

Journal Article · Tue Apr 15 04:00:00 EDT 2008 · Medical Physics

DOI:https://doi.org/10.1118/1.2870231· OSTI ID:21120645

Khan, Sabrina; Chen, Zhe Jay; Nath, Ravinder ^[1]

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1. Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06520 (United States)

Two independent groups have published intrinsic dosimetry parameters for the recently introduced OptiSeed{sup 103} interstitial brachytherapy source which contains {sup 103}Pd encapsulated by a novel polymer shell. The dose rate constant ({lambda}) reported by the two groups, however, differed by more than 6% and there is currently no AAPM recommended consensus value for this source in clinical dosimetry. The aim of this work was to perform an independent determination of {lambda} for the OptiSeed{sup 103} source using a recently developed photon spectrometry technique. Three OptiSeed{sup 103} sources (model 1032P) with known air-kerma strength were used in this study. The photon energy spectrum emitted along the radial direction on the source's bisector was measured in air using a high-resolution intrinsic germanium spectrometer designed and established for low-energy brachytherapy source spectrometry. The dose rate constant of each source was determined from its emitted energy spectrum and the spatial distribution of radioactivity in the source. Unlike other sources made with traditional titanium encapsulation, the photons emitted by the OptiSeed{sup 103} sources exhibited only slight spectral hardening, yielding a relative energy spectrum closer to that emitted by bare {sup 103}Pd. The dose rate constant determined by the photon spectrometry technique for water was 0.664{+-}0.025 cGy h{sup -1} U{sup -1}. This value agreed, within experimental uncertainties, with the Monte Carlo-calculated value ({sub MC}{lambda}) of 0.665{+-}0.014 cGy h{sup -1} U{sup -1} and the TLD-measured value (with a Monte Carlo-calculated solid-phantom-to-water conversion factor) of 0.675{+-}0.051 cGy h{sup -1} U{sup -1} reported by Wang and Hertel [Appl. Radiat. Isot. 63, 311-321 (2005)]. However, it differed by -6.7% from the {sub MC}{lambda} of 0.712{+-}0.043 cGy h{sup -1} U{sup -1} reported by Bernard and Vynckier [Phys. Med. Biol. 50, 1493-1504 (2005)]. The results obtained in this work provide additional information needed for establishing a consensus value for the dose rate constant for the OptiSeed{sup 103} source. It suggests that an eventual consensus value of {lambda} for the OptiSeed{sup 103} source is likely to be closer to a value of 0.668 cGy h{sup -1} U{sup -1} rather than 0.693 cGy h{sup -1}U{sup -1} as initially recommended by the source manufacturer based on the two previously published results.

• OSTI ID: 21120645
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 4 Vol. 35; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
BRACHYTHERAPY
DOSE RATES
DOSIMETRY
ENCAPSULATION
ENERGY SPECTRA
GAMMA SPECTROMETERS
KERMA
MANUFACTURERS
MONTE CARLO METHOD
PALLADIUM 103
PHANTOMS
PHOTONS
POLYMERS
RADIATION SOURCE IMPLANTS
RADIOPHARMACEUTICALS
SPATIAL DISTRIBUTION
SPECTRAL HARDENING