Cavity theory applications for kilovoltage cellular dosimetry

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Computational Biology

Background:

• Establishing relationships between bulk tissue and cellular radiation dose is crucial for accurate radiobiology and radiotherapy.
• Current model-based dose calculation algorithms (MBDCAs) require robust methods to link macroscopic dose descriptors to microscopic energy deposition.
• Cavity theory offers a framework to bridge the gap between macroscopic and microscopic dose calculations.

Purpose of the Study:

• To investigate the relationship between macroscopic (bulk tissue) and microscopic (cellular) dose descriptors using cavity theory and Monte Carlo (MC) simulations.
• To evaluate different cavity theory approaches (SCT, LCT, ICT) for calculating dose-to-water in μm-sized cavities within tissue phantoms.
• To compare cell nucleus doses calculated by the most accurate cavity theory approach with MC simulations in multicellular models.

Main Methods:

• Utilized small, large, and intermediate cavity theory (SCT, LCT, ICT) for incident photons (20–370 keV).
• Compared cavity theory predictions of dose-to-water-in-medium (D_w,m) to dose-to-medium-in-medium (D_m,m) with MC simulation results in water cavities within tissue phantoms.
• Calculated cell nucleus doses (D_nuc) using the best-performing ICT approach and compared them with MC simulations in multicellular soft tissue models.

Main Results:

• An intermediate cavity theory (ICT) approach, specifically [Formula: see text], demonstrated the best agreement with MC simulations for dose-to-water in μm-sized cavities.
• ICT predictions for cell nucleus doses (D_nuc) showed strong agreement with MC simulations, with agreement within [Formula: see text] in [Formula: see text] of cases (maximum disagreement 8.8%).
• Estimates of dose-to-water using SCT on MC results for D_m,m or D_nuc differed significantly, highlighting sensitivity to geometry and composition.

Conclusions:

• Cavity theory, particularly the developed ICT approach, is a viable tool for linking MBDCAs dose calculations to energy deposition in cellular targets.
• The study does not support the conversion of dose-to-medium to dose-to-water using SCT for MBDCAs, given the sensitivity of energy deposition to surrounding factors.
• Accurate dosimetry at the cellular level requires careful consideration of the geometry and elemental composition of the microscopic environment.