Hippocampal avoidance during whole-brain radiotherapy is performed to prevent neural stem cell injury causing neurocognitive dysfunction. Nevertheless, the estimated risk of metastases in hippocampal avoidance area in small-cell lung cancer is unknown. The current study aimed to characterize the metastatic distribution within the brain relative to the hippocampus, estimate the incidence of hippocampal metastasis in patients with small-cell lung cancer, and identify clinical and radiographic variables that may be associated with the risk of hippocampal avoidance area metastasis. Patients with small-cell lung cancer treated with therapeutic whole-brain radiotherapy between January 2010 and December 2015 were reviewed. T1-weighted, postcontrast axial magnetic resonance images obtained just before therapeutic cranial irradiation were retrieved and reviewed for each patient. The hippocampal avoidance area was defined as hippocampus and 5-mm ring area adjacent to the hippocampus to account for necessary dose falloff between the hippocampus and the whole-brain planning target volume. Metastatic lesions within hippocampal avoidance area were defined as hippocampal metastasis. Hippocampal metastasis rate and characteristics of patients with hippocampal metastasis were analyzed and compared to patients without hippocampal metastasis. Fifty-four patients evaluated with cranial magnetic resonance imaging were enrolled. Hippocampal metastasis rate was 32% (17 patients). A total of 4.4% of all metastases involved the hippocampal avoidance area. The most common location was frontal lobe. Being younger than 65 years of age was found to be an independent risk factor for HM (odds ratio: 4.8, 95% confidence interval: 1-23.2, P = .049). The number of brain metastases was significantly higher in patients with hippocampal metastasis (P = .027), and hippocampal metastasis rate was also higher in patients having larger hippocampus (P = .026) and larger brain volumes (P = .02). Hippocampal metastasis might be more common in small-cell lung cancer. Reducing the dose to the hippocampus by hippocampal avoiding whole-brain radiotherapy plan in small-cell lung cancer may be risky for the development of HM compared with other malignant solid tumors.

Objective: Mean lung dose (MLD) and percent of total lung (TL) volume that receive a dose greater than 20 Gy (V₂₀) have been the most validated parameters in the prediction of radiation pneumonitis (RP). However, these parameters present mean values of TL parenchyma and predict the right and the left lung as a unique functional organ unit, not take into account the difference in function and dose density between the lungs. Furthermore, there have been very limited data evaluating ipsilateral lung dosimetric constraints in addition to TL parameters to predict RP in non-small cell lung cancer (NSCLC) patients treated with radiochemotherapy (RCT). Methods: Between 2010 and 2017, clinical–radiological findings of NSCLC patients treated with RCT were evaluated in terms of RP, retrospectively. MLD, V₂₀, and V₃₀ values of ipsilateral lung were assessed from dose–volume histogram and registered. The primary endpoint was to assess the relation between ipsilateral lung dose constraints and RP risk. Results: There were 75 patients. There was ≥Grade 2 RP in 33 cases (%44). In univariate analysis, ipsilateral MLD, ipsilateral V₂₀, ipsilateral V_30, and TL V₃₀ were found to be significant. Ipsilateral MLD and PTV were found to be the independent risk factors for RP. Cutoff values for RP risk were determined as 18Gy, 35%, and 28% for ipsilateral MLD, ipsilateral V₂₀, and ipsilateral V₃₀, respectively. Predictive values for ipsilateral MLD and ipsilateral V₂₀ were higher than TL. Conclusions: In NSCLC patients treated with RCT, MLD, V₂₀, and V₃₀ values of ipsilateral lung parameters might increase the predictability of RP risk in addition to TL parameters. Advances in Knowledge: Cutoff values for RP risk were determined as 18Gy, 35%, and 28% for ipsilateral MLD, ipsilateral V₂₀, and ipsilateral V₃₀, respectively. Predictive values for ipsilateral MLD and ipsilateral V₂₀ were higher than TL.

Journal of Cancer Metastasis and Treatment is an open access journal, focusing on basic and clinical studies related to cancer cell, cell biology, oncology, radiation therapy and radiology, obstetrics and gynecology, pediatrics, surgery, hematology, neuro-oncology, etc.