Author: Huisi Ai, Scott Glaser, Yi Lao, Percy Lee, Sara N. Lim, An Liu, Bo Liu, Borna Maraghechi, Kun Qing, Chengyu Shi, William T. Watkins, Terence Williams, Qiuyun Xu, Jiahua Zhu 👨🔬
Affiliation: WashU Medicine, Graduate Program in Bioengineering, University of California San Francisco-UC Berkeley, City of Hope Orange County, Department of Radiation Oncology, City of Hope National Medical Center, Department of Radiation Oncology, City of Hope Orange County, Department of Radiation Oncology, City of Hope Medical Center 🌍
Purpose: To employ a novel surface dose mapping approach for localized assessment of the dosimetric impact of Ethos adaptive radiotherapy (ART) for prostate cancer (PC).
Methods: This study included 11 PC patients treated with 40 Gy in 5 fractions using Ethos ART. Dosimetric comparisons were conducted across three scenarios: planned (P), non-adaptive accumulated (NA), and adapted (A). For each scenario and fraction, 3D bladder surface models (SMs) were generated through surface mesh triangulation and constrained-harmonic registration. Rectum SMs were constructed using surface parameterization, equalizing the skeletonized rectum wall in planes orthogonal to its centerline. These methods enabled localized dose accumulations across fractions and facilitates inter-subject comparisons. For each patient, 3 surface dose models (SDMs) were generated: SDM_P (planning SM sampled on plan dose), SDM_NA (delivered SM sampled on plan dose), and SDM_A (delivered SM sampled on adapted doses). Localized dosimetric comparisons among scenarios were performed on SDMs using paired group t-tests.
Results: Localized analyses revealed reduced dose around the bladder trigone in the SDM_NA compared to the SDM_P, though most regions did not reach statistical significance. ART resulted in statistically significant dose reductions in the same region (4.78 ± 1.47 Gy, p < 0.05), with the net adaptive effect (SDM_NA vs. SDM_A) also reaching significance. Similarly, on the rectum surface, significant dose reductions were observed in the anterior rectum near the RT target in adapted scenarios compared to planned (2.29 ± 0.89 Gy, p < 0.05), with net adaptive effects also reaching statistical significance. Collectively, these findings highlight enhanced organs-at-risk (OARs) sparing achieved through ART, independent of inter-fraction deviations.
Conclusion: A novel surface dose mapping framework addressing anatomical inaccuracies of DVH metrics for distensible hollow OARs was developed to assess the dosimetric impact of Ethos ART. The results demonstrated OAR sparing with ART beyond the effects of inter-fraction motion.