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Session: Monte Carlo Applications in RT - I [Return to Session]

Modeling of Highly Spatially Fractionated Radiation Therapy (grid-RT) Through the Implementation of the Monte Carlo Software TOPAS for Optimization of Mini-GRID Design

M Sprenger*, S Brundage, M Oldham, Duke University Medical Center, Durham, NC


WE-C930-IePD-F4-6 (Wednesday, 7/13/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 4

Purpose: Grid-RT is of substantial interest as a new investigational approach for exploring novel mechanisms of radiation biology. The optimal grid design is not well understood and monte-carlo (MC) modeling can be implemented to study and explore the dosimetry characteristics of a range of grid designs compatible with a small animal irradiator. Here the primary design goals are to maximize the peak-to-valley (P2V) ratio to promote an anti-cancer immune response in combination with checkpoint blockades.

Methods: TOPAS MC simulations were designed to simulate a range of lead mini grids (both bar and pencil beam), with varying bar/pencil thickness and spacings. Each grid is 20x20x3 mm and placed 3 cm above a 5x5x5 cm water phantom. Grid setups are irradiated with 10^9 photons in simulations and three different parameters are individually incremented: lead thickness, beam energy, and beam divergence. Dose profiles through the central beamlets to a 1 mm depth was made for P2V ratio calculations. Grid thickness of between 2 and 4 mm was explored, together with bar/pencil spacing ranging from 1.0 mm to 1.5 mm.

Results: Simulations of the lead mini grids demonstrate grid P2V ratio can be improved by a factor of 7 when decreasing the photon energy from 225 keV to 75 keV. Increasing Lead thickness from 3 to 4 mm was observed to increase P2V ratio by a factor of two at 225 keV. Photon divergence can decrease peak to valley ratio, in the case of a 1.25 mm pencil beam grid, from 74 to 53. Previous work of similar grid design reported a P2V ratio of 26.3.

Conclusion: Primary factors affecting peak-to-valley ratios include the thickness of lead, beam energy and grid pencil/bar size. These simulations suggest that substantial increase in P2V ratios (factor of 7) are possible with judicious choice of these design parameters.


Monte Carlo, Grids


TH- Small Animal RT: Development (new technology and techniques)

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