Author: Xiaoda Cong, Xuanfeng Ding, Gang Liu, Peilin Liu, Lewei Zhao 👨🔬
Affiliation: Department of Radiation Oncology, Stanford University, Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Corewellhealth William Beaumont University Hospital 🌍
Purpose: This study quantitatively evaluates the interplay effect in intensity-modulated proton therapy (IMPT) for lung cancer stereotactic body radiotherapy (SBRT) using two different machine delivery sequence models: IBA ProteusONE (synchrocyclotron based, pulsed beam) and IBA ProteusPlus (cyclotron based, continuous beam). The goal is to compare plan quality and delivery efficiency between the two system
Methods:
An interplay evaluation tool was developed to integrate 4D-CT data and generate 4D dynamic dose distribution base on the validated delivery sequence models for both systems. Simulations were based on a 5-second patient breathing cycle. Five lung cancer SBRT cases planned with IMPT were retrospectively analyzed. Dosimetric metrics, including CTV D99%, D1%, Homogeneity Index (HI), and Conformity Index (CI), were used to quantify interplay effects. Effective beam-on time (including spot irradiation, spot switching, and burst switching) and static delivery time were also compared.
Results:
The IBA ProteusONE model showed a mean CTV D99% degradation of 1.83%, compared to 3.61% for the IBA ProteusPlus. For CTV D1%, the IBA ProteusONE increased by 3.01%, while the IBA ProteusPlus increased by 5.11%. The IBA ProteusONE demonstrated smaller reductions in HI (-0.05 vs. -0.116) and CI (-0.02 vs. -0.014) compared to the IBA ProteusPlus. However, the IBA ProteusONE had significantly longer effective beam-on time (45.55 s vs. 11.66 s) and static delivery time (70.23 s vs. 41.91 s)(Table 1, Figure 1 in the supporting document).
Conclusion:
The interplay effect differs significantly between the two proton systems. The IBA ProteusONE provides better target dose “robustness” but requires longer beam-on and delivery times compared to the IBA ProteusPlus. These findings highlight the trade-offs between dosimetric robustness and delivery efficiency in lung cancer SBRT with IMPT.