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Comparison of dose calculation algorithms for colorectal cancer brachytherapy treatment with a shielded applicator
Author(s) -
Yan Xiangsheng,
Poon Emily,
Reniers Brigitte,
Vuong Te,
Verhaegen Frank
Publication year - 2008
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 - 10.1118/1.2982149
Subject(s) - electromagnetic shielding , brachytherapy , dosimetry , radiation treatment planning , shielded cable , monte carlo method , nuclear medicine , superposition principle , thermoluminescent dosimeter , biomedical engineering , algorithm , medicine , materials science , radiation therapy , computer science , physics , mathematics , radiology , dosimeter , telecommunications , statistics , quantum mechanics , composite material
Colorectal cancer patients are treated at our hospital with Ir192 high dose rate (HDR) brachytherapy using an applicator that allows the introduction of a lead or tungsten shielding rod to reduce the dose to healthy tissue. The clinical dose planning calculations are, however, currently performed without taking the shielding into account. To study the dose distributions in shielded cases, three techniques were employed. The first technique was to adapt a shielding algorithm which is part of the Nucletron PLATO HDR treatment planning system. The isodose pattern exhibited unexpected features but was found to be a reasonable approximation. The second technique employed a ray tracing algorithm that assigns a constant dose ratio with/without shielding behind the shielding along a radial line originating from the source. The dose calculation results were similar to the results from the first technique but with improved accuracy. The third and most accurate technique used a dose‐matrix‐superposition algorithm, based on Monte Carlo calculations. The results from the latter technique showed quantitatively that the dose to healthy tissue is reduced significantly in the presence of shielding. However, it was also found that the dose to the tumor may be affected by the presence of shielding; for about a quarter of the patients treated the volume covered by the 100% isodose lines was reduced by more than 5%, leading to potential tumor cold spots. Use of any of the three shielding algorithms results in improved dose estimates to healthy tissue and the tumor.