Computer simulation dose studies in heterogeneous media for electron and proton beam radiotherapy of static and moving targets
The energy-dependent electron loss model (ELM) and proton loss model (PLM) have been developed to predict dose deposition in heterogeneous slab media. Predictions of dose deposition in heterogeneous slab media are compared to the Monte Carlo calculations and experimental measurements. Slab media studied comprised water/bone/water and water/lung/water and incident beam energies between 10MeV and 18MeV for electron beams and 100MeV and 160MeV for proton beams. Dose discrepancies at large depths beyond the interface were within 5% of maximum dose. This error may be attributed to the assumption of a Gaussian energy distribution for the charge particles at depth. The computational cost is low compared to Monte Carlo simulations making the ELM and PLM attractive as a fast dose engine for dose optimization algorithms. To simulate a more realistic and challenging clinical treatment, a mathematical 3-D phantom was defined to simulate inferior-superior motion of a lung tumor target. Lung size and density change during the breathing cycle was modeled from full inspiration to full expiration. Sensitivity to dose error due to the respiratory motion of the target and the right lung, defined as the organ at risk (OAR), was studied for intensity modulated proton therapy (IMPT) and intensity modulated x-ray therapy (IMXT). Effects of rotational or lateral setup error on the dose distribution were studied independently and simultaneously with breathing.
Sandison, Purdue University.
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