A dose calculation algorithm for radiosurgery treatment room shielding optimization.

Area of Science:

• Medical Physics
• Radiotherapy Engineering
• Radiation Shielding

Background:

• Conventional radiotherapy shielding design methods often overestimate required wall thicknesses due to simplifying assumptions.
• The Leksell Gamma Knife (LGK) produces complex, anisotropic leakage radiation fields, challenging traditional shielding calculations.
• Monte Carlo (MC) simulations offer accuracy but are computationally intensive for routine design.

Purpose of the Study:

• Develop a rapid dose calculation algorithm for estimating radiation dose rates outside treatment room barriers.
• Enable iterative optimization of treatment room parameters, including wall thickness and LGK unit positioning.
• Provide a computationally efficient alternative to MC simulations for LGK facility design.

Main Methods:

• Algorithm utilizes pre-calculated MC phase space data of photons emitted by the LGK.
• Photons are raytraced to the exterior, and their dose contribution is calculated using pre-defined depth-dose profiles based on energy, angle, and barrier thickness.
• Iterative process optimizes barrier thicknesses to meet specified maximum external dose rate limits.

Main Results:

• The algorithm demonstrated good agreement with full MC simulations for dose distributions in typical rooms.
• Maximum external dose rates were estimated within a 2 cm concrete thickness error margin.
• Optimization using the algorithm showed potential for reducing barrier thicknesses compared to conventional methods.

Conclusions:

• The developed algorithm is a viable, faster alternative to traditional shielding design methods for LGK rooms.
• It overcomes limitations of conventional methods and is significantly quicker than full MC simulations.
• The algorithm's flexibility allows for optimization of LGK placement and barrier materials, potentially reducing costs and material usage.