Dosimetric Considerations for Ytterbium-169, Selenium-75, and Iridium-192 Radioisotopes in High-Dose-Rate Endorectal Brachytherapy
Autor: | Harry Glickman, Shoemaker Tristan, Samar Kaifi, Te Vuong, Shirin A. Enger, Gabriel Famulari |
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Rok vydání: | 2019 |
Předmět: |
Organs at Risk
Cancer Research medicine.medical_treatment Brachytherapy Selenium Radioisotopes Urinary Bladder computer.software_genre 030218 nuclear medicine & medical imaging 03 medical and health sciences Isotopes of selenium 0302 clinical medicine Voxel Hounsfield scale medicine Humans Dosimetry Radiology Nuclear Medicine and imaging Femur Ytterbium Pelvic Bones Radiation treatment planning Radioisotopes Radiation medicine.diagnostic_test Rectal Neoplasms business.industry Rectum Radiotherapy Dosage Magnetic resonance imaging Iridium Radioisotopes Oncology 030220 oncology & carcinogenesis Tomography Tomography X-Ray Computed Nuclear medicine business Monte Carlo Method computer |
Zdroj: | International Journal of Radiation Oncology*Biology*Physics. 105:875-883 |
ISSN: | 0360-3016 |
Popis: | Purpose To investigate differences between prescribed and postimplant calculated dose in 192Ir high-dose-rate endorectal brachytherapy (HDR-EBT) by evaluating dose to clinical target volume (CTV) and organs at risk (OARs) calculated with a Monte Carlo–based dose calculation software, RapidBrachyMC. In addition, dose coverage, conformity, and homogeneity were compared among the radionuclides 192Ir, 75Se, and 169Yb for use in HDR-EBT. Methods and Materials Postimplant dosimetry was evaluated using 23 computed tomography (CT) images from patients treated with HDR-EBT using the 192Ir microSelectron v2 (Elekta AB, Stockholm, Sweden) source and the Intracavitary Mold Applicator Set (Elekta AB, Stockholm, Sweden), which is a flexible applicator capable of fitting a tungsten rod for OAR shielding. Four tissue segmentation schemes were evaluated: (1) TG-43 formalism, (2) materials and nominal densities assigned to contours of foreign objects, (3) materials and nominal densities assigned to contoured organs in addition to foreign objects, and (4) materials specified as in (3) but with voxel mass densities derived from CT Hounsfield units. Clinical plans optimized for 192Ir were used, with the results for 75Se and 169Yb normalized to the D90 of the 192Ir clinical plan. Results In comparison to segmentation scheme 4, TG-43–based dosimetry overestimates CTV D90 by 6% (P = .00003), rectum D50 by 24% (P = .00003), and pelvic bone D50 by 5% (P = .00003) for 192Ir. For 169Yb, CTV D90 is overestimated by 17% (P = .00003) and rectum D50 by 39% (P = .00003), and pelvic bone D50 is significantly underestimated by 27% (P = .007). Postimplant dosimetry calculations also showed that a 169Yb source would give 20% (P = .00003) lower rectum V60 and 17% (P = .00008) lower rectum D50. Conclusions Ignoring high-Z materials in dose calculation contributes to inaccuracies that may lead to suboptimal dose optimization and disagreement between prescribed and calculated dose. This is especially important for low-energy radionuclides. Our results also show that with future magnetic resonance imaging–based treatment planning, loss of CT density data will only affect calculated dose in nonbone OARs by 2% or less and bone OARs by 13% or less across all sources if material composition and nominal mass densities are correctly assigned. |
Databáze: | OpenAIRE |
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