title: Cavity theory applications for kilovoltage cellular dosimetry.
abstract: Relationships between macroscopic (bulk tissue) and microscopic (cellular) dose descriptors are investigated using cavity theory and Monte Carlo (MC) simulations. Small, large, and multiple intermediate cavity theory (SCT, LCT, and ICT, respectively) approaches are considered for 20 to 370 keV incident photons; ICT is a sum of SCT and LCT contributions weighted by parameter d. Considering μm-sized cavities of water in bulk tissue phantoms, different cavity theory approaches are evaluated via comparison of [Formula: see text] (where Dw,mis dose-to-water-in-medium and Dm,mis dose-to-medium-in-medium) with MC results. The best overall agreement is achieved with an ICT approach in which [Formula: see text], where L is the mean chord length of the cavity and β is given by [Formula: see text] (RCSDAis the continuous slowing down approximation range of an electron of energy equal to that of incident photons). Cell nucleus doses, Dnuc, computed with this ICT approach are compared with those from MC simulations involving multicellular soft tissue models considering a representative range of cell/nucleus sizes and elemental compositions. In [Formula: see text] of cases, ICT and MC predictions agree within [Formula: see text]; disagreement is at most 8.8%. These results suggest that cavity theory may be useful for linking doses from model-based dose calculation algorithms (MBDCAs) with energy deposition in cellular targets. Finally, based on the suggestion that clusters of water molecules associated with DNA are important radiobiological targets, two approaches for estimating dose-to-water by application of SCT to MC results for Dm,mor Dnucare compared. Results for these two estimates differ by up to [Formula: see text], demonstrating the sensitivity of energy deposition within a small volume of water in nucleus to the geometry and composition of its surroundings. In terms of the debate over the dose specification medium for MBDCAs, these results do not support conversion of Dm,mto Dw,musing SCT.
authors.affiliation: Carleton Laboratory for Radiotherapy Physics, Physics Dept, Carleton University, Ottawa, K1S 5B6, Canada.
authors.forename: P A K
authors.initials: PAK
authors.lastname: Oliver
authors.forename: Rowan M
authors.initials: RM
authors.lastname: Thomson
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000379:methods*; D001943:Breast Neoplasms / Q000532:radiotherapy; D003528:Carcinoma, Adenoid Cystic / Q000532:radiotherapy; D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy; D002467:Cell Nucleus / Q000528:radiation effects*; D004583:Electrons; D005260:Female; D006801:Humans; D008545:Melanoma / Q000532:radiotherapy; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019042:Muscle Neoplasms / Q000532:radiotherapy; D019047:Phantoms, Imaging; D017785:Photons; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D014407:Tumor Cells, Cultured; D014867:Water
chemical_list: D014867:Water