2092 - Helical Tomotherapy Compared to Intensity-Modulated Radiation Therapy in Hippocampal Avoidance Prophylactic Cranial Irradiation in Patients with Limited-Stage Small-Cell Lung Cancer

S. Lu¹, G. Gong², W. Li³, and H. Zhu⁴; ¹Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences,, Jinan, China, ²Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, shandong, China, ³Department of Imaging, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, ⁴Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China

Purpose/Objective(s): Hippocampal avoidance (HA) techniques have been developed to reduce the risk of neurocognitive dysfunction associated with prophylactic cranial irradiation (PCI) in patients with limited-stage small-cell lung cancer (LS-SCLC). However, applying different radiotherapy techniques to HA has not yet been further analyzed. This study discussed the dosimetric differences between intensity-modulated radiation therapy (IMRT) and helical tomotherapy (TOMO) in HA-PCI and analyzed the benefit of the dosimetric advantage in the risk of brain metastasis (BM) from a clinical perspective. Materials/

Methods: We retrospectively evaluated patients who underwent PCI from June 2020 to December 2021 at Shandong Cancer Hospital. They were divided according to hippocampal avoidance and radiotherapy techniques: IMRT without HA (non-HA-IMRT), HA-IMRT, and HA-TOMO. The cumulative incidence of BM, target coverage (TC), homogeneity index (HI), conformity index (CI), and hippocampal doses of these radiotherapy programs were evaluated.
Results: One hundred seventy-two patients were included in the analysis: 56, 78, and 38 patients in the non-HA-IMRT, HA-TOMO, and HA-IMRT groups, respectively. The 2-year cumulative incidence of BM was 31.4% in patients with HA (78 patients in the HA-TOMO group and 38 patients in the HA-IMRT group) and 23.2% in patients without HA (hazard ratio [HR]: 0.75, 95% confidence interval [95% CI]: 0.43-1.31; P=0.340). However, the 2-year cumulative incidence of BM was lower in the HA-TOMO group than in the HA-IMRT group (25.0% vs. 44.7%, HR: 0.51, 95% CI: 0.26-0.99; P=0.029). Both techniques achieved hippocampal protection, but HA-TOMO accomplished significantly better TC (96.24%±0.65% vs. 93.75%±2.45%, P<0.001), HI (0.09±0.02 vs. 0.27±0.12, P<0.001), and CI (0.88±0.02 vs. 0.85±0.04, P<0.001).
Conclusion: HA-PCI did not increase BM risk. Additionally, HA-TOMO could achieve better TC, HI, and CI with respect to the planned tumor in the brain while achieving more rapid dosing in the hippocampal region. The cumulative incidence of BM was lower with HA-TOMO than with HA-IMRT.