Fig 1.
Process diagram for proton patient-specific QA.
Independent checks of the dose calculation and treatment delivery system are both vital components of the process.
Fig 2.
MU difference histograms for prostate (a) and liver (b) fields. The difference between the planned and delivered MU are analyzed spot-by-spot to verify that predefined action thresholds have not been exceeded.
Fig 3.
Spot position deviation analysis in the time domain.
The random and systematic components of spot position deviations in both x (a) and y (b) are computed and compared to predefined action thresholds. The green circles represent the raw position deviation, while the black dots show the running average deviation in an energy spill. The tolerance for the systematic component of the error is given by the solid blue lines, which the running average deviation (black dots) should not cross. Analogously, the tolerance for the random component of the error is given by the dotted red lines (fixed expansion of the running systematic average), which the positional deviations (green circles) should not exceed.
Fig 4.
Projected spot position deviation histograms.
The systematic and random components of the error (Eqs 1 and 2) are shown on log-linear histograms. Spots subject to regular tolerances (a) are separated from those governed by expanded tolerances (b).
Fig 5.
Projected spot position deviation histograms for a sub-optimal plan delivery.
The systematic and random components of the error (Eqs 1 and 2) are shown on log-linear histograms. Spots subject to regular tolerances (a) are separated from those governed by expanded tolerances (b). The close approach of the y systematic data points to their corresponding tolerance (black line) suggests the potential for triggering a machine interlock during subsequent deliveries of this plan.
Fig 6.
Analytic vs. Monte Carlo dose calculation comparison.
Dose distributions calculated using the analytic TPS algorithm (a) are compared to those calculated with our GPU-accelerated, Monte Carlo dose second check system (b). Part (c) shows the absolute dose difference between (a) and (b) in a zoomed-in region for this 1440-cGy prescription dose. The scale bar of 100 cGy to 250 cGy corresponds to the percent range of 6.9% to 17.4%. A dose profile (d) through this region clearly shows an area of greater than 10% lower radiation dose in the target when comparing the Monte Carlo curve (pink) to the analytic TPS (blue).