An Iterating Method to Calculate the Geometry of Range Modulation Wheel in Passive Proton Therapy

In the passive method of proton therapy, range modulation wheel is used to scatter the single energy proton beam. It rounds and scatters the single energy proton beam to the spectrum of particles that covers cancerous tissue by a change in penetration depth. Geant4 is a Monte Carlo simulation platform for studying particles behaviour in a matter. We simulated proton therapy nozzle with Geant4. Geometric properties of this nozzle have some effects on this beam absorption plot. Concerning the relation between penetration depth and proton particle energy, we have designed a range modulation wheel to have an approximately flat plot of absorption energy. An iterative algorithm programming helped us to calculate the weight and thickness of each sector of range modulation wheel. Flatness and practical range are calculated for resulting spread-out Bragg peak.