Room: Exhibit Hall | Forum 7
Purpose: To quantitatively evaluate the effectiveness of motion interplay mitigation using spot-scanning proton arc (SPArc) therapy for lung stereotactic body radiotherapy (SBRT).
Methods: To simulate the mobile lung SBRT target treatment, a set of digital lung tumor phantoms 4DCT with different breathing induced motion in superior inferior (SI) direction (with amplitudes: 5, 10, 15 and 20mm) were created. Target was simulated using a sphere with 4cm in diameter. Intensity Modulated Proton Therapy (IMPT) plans were generated using a single field optimization (SFO) technique with lateral and posterior beams and SPArc plans were generated using a partial arc from 180 to 30 degree clockwise with sampling frequency of 2.5 degree. The robust optimization was performed considering Â±3.5% range and 5mm setup uncertainties. 6000cGy relative biological effectiveness [RBE] was prescribed to internal target volume (ITV) in 5 fractions. To assess the breathing induced interplay effect, the dynamic dose was calculated by synchronizing the breathing pattern with the simulated proton machine delivery sequence. Interplay effect from different numbers volumetric repainting using IMPT were analyzed in comparison with SPArc treatment.
Results: Target dose degraded as the tumor motion amplitude increased. The mitigation of interplay effect of using SPArc is significant better than IMPT through all the different motion amplitudes. More specially, the relative target D99 degradation vis single fraction on average for IMPT vs SPArc are 2.51%vs0.0%(p=0.001),4.01%vs0.10%(p<0.001),6.61%vs1.29%(p<0.001),8.40%vs1.70%(p<0.001). Target coverage can be compensated by increasing the total number of repainting using IMPT. The study found that the effectiveness of such motion mitigation using SPArc was about 5 to 7 times repainting using IMPT for 20mm motion amplitude and the deliver time increased to 628s compared to 490s in SPArc.
Conclusion: SPArc is capable to mitigate the interplay effect in lung SBRT and as effective as several times repainting using IMPT delivery depending motion amplitude.
Funding Support, Disclosures, and Conflict of Interest: Grant/Research Support: Beaumont Herb and Betty Fisher research seed grant award; Ion Beaumont Application Inc. (IBA) research funding; A patent related to the proton arc therapy is licensed to Ion Beaumont Application Inc.