Prophylactic cranial irradiation (PCI), hippocampal avoidance (HA) whole brain radiotherapy (WBRT) and stereotactic radiosurgery (SRS) in small cell lung cancer (SCLC): Where do we stand?

Small cell lung cancer (SCLC) is an aggressive form of lung cancer associated with an increased risk of develping brain metastases (BM), which are a significant cause of morbidity and mortality. Prophylactic cranial irradiation (PCI) was first introduced in the 1970s with the aim of reducing BM incidence and improving survival and quality of life (QoL). Prospective clinical trials and meta-analyses have demonstrated its effectiveness in reducing BM incidence and improving survival, across all stages of the disease following response to induction chemotherapy. Despite its long history, "unknowns" surrounding PCI use still exist and there are particular subgroups of patients for which its use remains controversial. PCI is known to cause neurocognitive toxicity which can have a significant impact on a patient's QoL. Strategies to minimise this, including the use of hippocampal avoidance radiotherapy techniques, neuroprotective drugs and stereotactic radiosurgery in place of whole brain radiotherapy for the treatment of BM, are under evaluation. This review offers a summary of the key PCI trials published to date and the current treatment recommendations based on available evidence. It also discusses the key questions being addressed in ongoing clinical trials and highlights others where there is currently a knowledge gap and therefore where further data are urgently required.