Implementing the optimized hippo-avoidance prophylactic cranial irradiation for limited-stage small cell lung cancer by tomotherapy and volumetric modulated arc therapy

Background: Hippo-avoidance prophylactic cranial irradiation (HA-PCI) requires a hippocampal avoidance zone expanded from hippocampus to ensure dose fall-off and compensate for setup errors. Most studies recommend a 5-mm margin, while it could be optimized to a 2-mm expansion. Here, we showed the details of optimized HA-PCI for limited-stage small cell lung cancer (LS-SCLC).

Methods: This cohort study reviewed patients with LS-SCLC receiving optimized HA-PCI from August 2014 to June 2020 in the National Cancer Center of China. The hippo-related dose parameters were summarized. The comparison of the Hopkins Verbal Learning Test-Revised (HVLT-R) scores in different time points was conducted. The Kaplan-Meier method was used to calculate the survival rates.

Results: A total of 112 patients were included. The average doses of hippocampus and hippocampal avoidance zone were 6.80 Gy (IQR: 6.40-7.44) and 7.63 Gy (IQR: 7.14-8.39). No differences were observed in the two radiation techniques (tomotherapy [TOMO] vs. volumetric-modulated arc therapy [VMAT]). The decline of HVLT-R score remained in a low level and not significant in assessable patients (p = 0.095). With a median follow-up of 52 months (95% CI: 47.2-56.7), the 2-year overall survival and progression-free survival were 74.1% and 50.0%, respectively. Two intracranial recurrence lesions (2.3%) located <2 mm from the hippocampus.

Conclusions: Optimized HA-PCI could achieve similar dose limitation by TOMO and VMAT techniques with favorable efficacy and minor toxicity.