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

Abstract

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.

On the cutting edge of intensity modulated radiotherapy and simultaneous integrated boost (IMRT-SIB): The case of a patient with 8 brain metastases

“…IMRT has been also proposed for brain metastases treatment. In particular, IMRT has been evaluated in several planning studies, with the aim to spare neural stem cells during WB irradiation, [10][11][12] to treat by stereotactic technique multiple metastases 13 , to simultaneously boost the dose to 2-3 brain metastases during WB 14 and for radiosurgery of multiple brain metastases or large irregular lesions. 15 Furthermore, IMRT has been used in some clinical studies on brain metastases.…”

Benefits and difficulties during brain radiotherapy planning with hippocampus sparing

“…The most frequently recommended PCI regimen is whole brain irradiation to a total dose of 25 Gy in 10 fractions of 2.5 Gy [48]. It has also been demonstrated that PCI may contribute to the impairment of cognitive functions as a result of post-radiation depopulation of NSCs within the hippocampus [49,50].…”

Hippocampal sparing in brain radiotherapy

“…Intensity Modulated Arc Therapy), 77.1% of the IMRT and 42.3% for IMPT (Intensity Modulated Proton Therapy). Tarnawski et al [79] reported that it was possible to achieve a 45% dose reduction when using helical tomotherapy as well as IMRT when planning PCI for 10 patients suffering from small cell lung cancer, whilst still preserving the therapeutic radiation dose to the rest of brain. Similar findings were demonstrated by Gondi et al [80] on five patients when WBRT (30Gy / 10fr) was prescribed using helical IMRT or tomotherapy, where dose levels were respectively reduced by 87% and 81% for the hippocampus.…”