Abstract
For scanning beam particle therapy, the plan delivery accuracy is affected by spot size deviation, position deviation and particle number deviation. Until now, all plan verification systems available for particle therapy have been designed for pretreatment verification. The purpose of this study is to introduce a method for online plan delivery accuracy checks and to evaluate the sensitivity of plan delivery accuracy to different beam parameter errors. A program was developed using MATLAB to reconstruct doses from beam parameters recorded in log files and to compare them with the doses calculated by treatment planning system (TPS). Both carbon ion plans and proton plans were evaluated in this study. The dose reconstruction algorithm is verified by comparing the dose from the TPS with the reconstructed dose under the same beam parameters. The sensitivity of plan delivery accuracy to different beam parameter errors was analyzed by comparing the dose reconstructed from the pseudo plans that manually added errors with the original plan dose. For the validation of dose reconstruction algorithm, mean dose difference between the reconstructed dose and the plan dose were 0.70% ± 0.24% and 0.51% ± 0.25% for carbon ion beam and proton beam, respectively. According to our simulation, the delivery accuracy of the carbon ion plan is more sensitive to spot position deviation and particle number deviation, and the delivery accuracy of the proton plan is more sensitive to spot size deviation. To achieve a 90% gamma pass rate with 3 mm/3% criteria, the average spot size deviation, position deviation, particle number deviation should be within 23%, 1.9 mm, and 1.5% and 20%, 2.1 mm, and 1.6% for carbon ion beam and proton beam, respectively. In conclusion, the method that we introduced for online plan delivery verification is feasible and reliable. The sensitivity of plan delivery accuracy to different errors was clarified for our system. The methods used in this study can be easily repeated in other particle therapy centers.
Highlights
Proton and carbon ion radiotherapy has gained great attention in recent years and has been used for different tumor sites [1,2,3,4]
The reconstructed dose distribution can be exported in DICOM format
We introduced a method and developed verification software based on log files for scanning beam proton and carbon ion radiotherapy, which considered the impacts of spot size deviation, spot position deviation and particle number deviation
Summary
Proton and carbon ion radiotherapy has gained great attention in recent years and has been used for different tumor sites [1,2,3,4]. The physical characteristics of sharp dose peak at a particular range in tissue make the delivered dose distribution sensitive to delivery uncertainties that could make the Bragg-peak located at an incorrect position [8, 9]. This may result in an insufficient dose in the target region or severe side effects. The log files of our radiotherapy system recorded for each treatment fraction include the information for actual delivered spot position, spot size and particle number in each spot for each iso-energy slice (IES). For scanning beam proton and carbon ion radiotherapy, the sensitivity of plan delivery accuracy to the spot size deviation, position deviation and particle number deviation is very important for quality assurance and beam delivery system setting
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