Feasibility of reducing the irradiation dose in regions of active neurogenesis for prophylactic cranial irradiation in patients with small-cell lung cancer.

Prophylactic cranial irradiation (PCI) is performed on patients with limited or extensive small-cell lung cancer to reduce incidence of brain metastases and prolong survival. PCI may induce neurocognitive impairment. Decreasing irradiation of neural stem cells (NSC) might reduce PCI-induced toxicity. We tested the feasibility of reducing irradiation doses to neural stem cell (NSC) regions while maintaining prescribed doses to the planned target volume (PTV). Irradiation plans utilizing intensity-modulated radiotherapy (IMRT), helical TomoTherapy, and RapidArc for 10 consecutive lung cancer patients were evaluated. The dose distribution, dose-volume histograms, and dose homogeneity indexes were analyzed. Planned and actual dose distributions were compared by dosimetric analysis. Both helical tomotherapy and LINAC-based IMRT reduced the radiation dose to the NSC regions by approximately 45% while maintaining the full dose to the rest of brain. Measured dose distributions matched the planned dose distributions.Protecting the regions of active neurogenesis is technically feasible. Whether reducing the dose by 35% to 45% is sufficient to reduce treatment toxicity, however, can only be addressed in a randomized study. Further reducing the dose within the NSC region might also significantly decrease the dosage to the PTV.