Author: Kenneth W. Gregg, Beatriz Guevara, Lauren E Henke, Rojano Kashani, Kyle O'Carroll, Gisele Castro Pereira, Christian Erik Petersen, Alex T. Price, Meiying Xing, Reine abou Zeidane 👨🔬
Affiliation: university hospital, University Hospitals Seidman Cancer Center 🌍
Purpose:
Experimental data have shown the inconsistent monitor unit and target coverage in Ethos 1.1. This can lead to inaccurate dose delivery, compromising patient safety and treatment outcomes. We conducted an early evaluation study for stereotactic adaptive radiotherapy (STAR) for pancreatic cancer with Ethos 2.0 to investigate the dosimetry and MLC complexity difference between the scheduled plan and adapted plan.
Methods: Six patients received pancreas or post-op pancreas STAR on the ETHOS 2.0 system. Initial pans were created based on their simulation and clinical adaptive plans were based on anatomy-of-the-day. The prescription was 50 Gy in 5 fractions. The initial plan was applied to the patient’s anatomy-of-the day and was recalculated to obtain the scheduled plans (PS). PS was compared with the reoptimized adaptive plans (PA) using dose-volume histogram metrics, with selection of the superior plan.
Results: Adaptive plans were more feasible and beneficial for patients, with successful workflow completion in all of 30 fractions. PS application to daily anatomy created OAR constraint violations in all fractions. There were 20 stomach, 13 duodenum, 19 small bowel, and 12 large bowel PI OAR constraint violations. In contrast, OAR violations occurred 0 in adaptive plans. STAR also improved planning tumor volume Dmin ≥ 500cGy/fx and D95 coverage in 21 out of 30(70%) and 23 out of 30(77%) fractions, respectively. In addition, no difference in MLC complexity was observed except that small aperture score increased from 0.159 to 0.185. MU is very stable, average 5.15% variation.
Conclusion:
PA not only resolved OAR hard constraint violations but also improved target coverage compared with scheduled STAR for the ablation of pancreatic cancer which may lead to reduced toxicity, improved precision and enhanced stability of Ethos 2.0. We will summarize more data to further evaluate the advantages and disadvantages of Ethos 2.0 system in the clinic.