International Journal of Particle Therapy
Purpose: We proposed an experimental approach to build a precise machine-specific model for standard, volumetric, and layer repainting delivery based on a cyclotron accelerator system. Then, we assessed the interplay effect using a 4D mobile lung target phantom compared to a generic delivery sequence model from West German Proton Therapy Essen (WPE). Methods: The machine delivery log files, from an IBA ProteusPLUSt system, were retrospectively analyzed to quantitatively model energy layer switching time, spot switching time, and spot drill time for standard and volumetric repainting delivery. To quantitatively evaluate the interplay effect, a series of digital thoracic 4DCT image sets were used. The interplay effect was assessed based on the 4D dynamic dose accumulation method. Different delivery technique such as standard delivery (n¼1), volumetric repainting delivery (n¼2,3,4) and layer repainting delivery (n¼2,3,5,25) were simulated based on the machine-specific delivery sequence model and WPE model. Results: The results showed that the WPE model’s spot delivery sequence deviated from the log file significantly compared to the machine-specific model. Based on the treatment delivery calculation of a lung treatment plan with target size (65 mm3 ) and layer repainting 25 times (n¼25), the difference is about 21.01%. Such a difference also resulted in different interplay effects estimation between the two models even though both institutions used the same proton system from IBA and calculated using the same 4DCT imaging set. Conclusion: A precise machine-specific delivery sequence is highly recommended to ensure an accurate estimation of mobile target treatment’s interplay effect.
Zhao L, Liu G, Shen J, Lee A, Yan D, Deraniyagala R, et al. Assessing the interplay effect based on a precise machine-specific delivery sequence and time for cyclotron accelerator proton therapy system. Int J Part Ther. 2022 Spring;8(4):96.