Patterns of relapse following hippocampal avoidance prophylactic cranial irradiation for small cell lung carcinoma

Hippocampal avoidance techniques are an evolving standard of care for patients undergoing cranial irradiation. Our aim was to assess the oncological outcomes and patterns of failure following hippocampal avoidance prophylactic cranial irradiation (HA-PCI) as a standard of care in unselected patients with both limited and extensive stage small cell lung carcinoma.

Consecutive patients with small cell lung carcinoma with a complete (limited stage) or good partial (extensive stage) response following chemotherapy were eligible to receive HA-PCI, with a total dose of 25 Gray in 10 fractions. All patients had a negative baseline MRI brain scan with gadolinium prior to HA-PCI. Patients had baseline and follow up Common Toxicity Criteria Adverse Event assessments. Following completion of HA-PCI, all patients had three-monthly MRI brain scans with gadolinium until confirmation of intracranial relapse, as well as three-monthly CT of the chest, abdomen and pelvis. Overall and progression-free survival were calculated using the Kaplan-Meier method.

A total of 17 consecutive patients, 9 men and 8 women, with a mean age of 70 years received HA-PCI between May 2016 and June 2020 after completion of their initial chemotherapy. There were no Grade 4 or greater adverse events. No patient had an isolated hippocampal avoidance zone relapse alone; three of 17 patients had multifocal relapses that included the hippocampal avoidance zone.

In our series, there were no hippocampal only relapses and we conclude that HA-PCI is a safe alternative to standard PCI in the setting of small cell lung cancer.