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

Abstract

Abstract 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.

Keywords

• hippocampal avoidance zone
• prophylactic cranial irradiation
• small cell lung cancer