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SU‐F‐T‐49: Dosimetry Parameters and TPS Commissioning for the CivaSheet Directional Pd‐103 Brachytherapy Source
Author(s) -
Rivard MJ
Publication year - 2016
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 - 10.1118/1.4956184
Subject(s) - brachytherapy , dosimetry , nuclear medicine , superposition principle , radiation treatment planning , kerma , physics , radiation , materials science , radiation therapy , optics , medicine , quantum mechanics
Purpose: The CivaSheet is a new LDR Pd‐103 brachytherapy device offering directional‐radiation for preferentially irradiating malignancies with healthy‐tissue sparing. Observations are presented on dosimetric characterization, TPS commissioning, and evaluation of the dosesuperposition‐ principle for summing individual elements comprising a planar CivaSheet Methods: The CivaSheet comprises individual sources (CivaDots, 0.05cm thick and 0.25cm diam.) inside a flexible bioabsorbable substrate with a 0.8cm center‐to‐center rectangular array. All non‐radioactive components were measured to ensure accuracy of manufacturer‐provided dimensional information. The Pd spatial distribution was gleaned from radioactive and inert samples, then modeled with the MCNP6 radiation‐transport‐code. A 6×6 array CivaSheet was modeled to evaluate the dose superposition principle for treatment planning. Air‐kerma‐strength was estimated using the NIST WAFAC geometry. Absorbed dose was estimated in water with polar sampling covering 0.05≤r≤15cm in 0.05cm increments and 0°≤θ≤180° in 1° increments. These data were entered into VariSeed9.0 and tested for the dose‐superposition‐principle. Results: The dose‐rate‐constant was 0.579 cGy/h/U with g(r) determined along the rotational‐axis of symmetry (0°) instead of 90°. gP(r) values at 0.1, 0.5, 2, 5, and 10cm were 1.884, 1.344, 0.558, 0.088, and 0.0046. F(r,θ) decreased between 0° and 180° by factors of 270, 23, and 5.1 at 0.1, 1, and 10cm. The highest dose‐gradient was at 92°, changing by a factor of 3 within 1° due to Au‐foil shielding. TPS commissioning from 0.1≤r≤11cm and 0°≤θ≤180° demonstrated 2% reproducibility of input data except at the high‐dose‐gradient where interpolations caused 3% differences. Dose superposition of CivaDots replicated a multi‐source CivaSheet array within 2% except where another CivaDot was present. Following implantation, the device is not perfectly planar. TPS accuracy utilizing the dose‐superposition‐principle through geometric repositioning of CivaDots supersedes TPS limitations of intersource shielding effects Conclusion: Dosimetric characterization, source commissioning, and evaluation of the dose‐superposition‐principle with VariSeed9.0 permits treatment planning for the CivaSheet brachytherapy device. Research supported in part by CivaTech Oncology, Inc.