Program Information
Experimental Validation of a 4D Dose Calculation for Scanned Proton Beam Therapy
M Krieger1,2 , G Klimpki1,2 , G Fattori1 , J Hrbacek1 , D Oxley1 , S Safai1 , D Weber1,3 , A Lomax1,2 , Y Zhang1*, (1) Paul Scherrer Institute, Villigen PSI, Switzerland, (2) ETH Zurich, Zurich, Switzerland, (3) University Hospital of Zurich, Zurich, Switzerland
Presentations
TU-H-CAMPUS-TT-2 (Tuesday, August 1, 2017) 4:30 PM - 5:30 PM Room: Therapy ePoster Theater
Purpose: To verify the accuracy of the estimated dose distribution by a 4D dose calculation in comparison to measurements.
Methods: A single-field plan (0.6Gy), optimised for a liver patient case (CTV volume: 403cc), was delivered to a homogeneous PMMA phantom and measured by a scintillating-CCD system in 4 water equivalent depths ranging from entrance to mid-SOBP. Various motion scenarios (no motion and motions with varying periods: 3.7s and 4.4s) were simulated using a 4D Quasar phantom and logged by an optical tracking system in real-time. Three motion mitigation approaches (single delivery, 6x layered and 6x volumetric rescanning) were applied, resulting in 14 individual measurements. 4D dose distributions were then calculated (using a deforming dose grid) in water by directly taking into account the delivery log files which contain information on the actually delivered spot positions, fluences and time stamps. The resulting CCD intensity values were scaled to match the amplitude of the central axis profile with the corresponding calculated distribution (without quenching correction). 2D gamma analysis was used to quantify the agreement of the measurement with the calculation for all pixels with >5% of the maximum calculated dose.
Results: For stationary conditions, a mean 3%/3mm gamma score of 98.84% was achieved with a range of 95.6%-100.0% for all measured depths. In the presence of motion without mitigation, gamma agreements of 97.6–99.9% were achieved, whilst the agreement for rescanning delivery was 99.0%-100.0% for layered and 94.7%-100.0% for volumetric rescanning. The mean gamma score overall scenarios was 98.6% standard deviation: 1.8%).
Conclusion: This study demonstrates that the deforming grid 4D dose calculation is able to predict the complex patterns of 4D dose distributions for PBS proton therapy with high dosimetric accuracy, and can be used as a valid clinical tool for 4D treatment planning, motion mitigation selection and eventually 4D optimisation applications.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by the Swiss National Science Foundation grant No. 320030_163330/1.
Contact Email: