We investigated tolerable doses to organs at risk (OARs) in the mediastinum and pulmonary hilum following stereotactic body radiotherapy for centrally located lung tumors. Between 2005 and 2012, 381 patients with lung tumors were treated with stereotactic body radiotherapy of 40 to 60 Gy in five fractions. From among these patients, we extracted those who received greater than 25 Gy irradiation to OARs and analyzed dosimetric factors in relation to grade 3 to 5 toxicities. In total, 398 OARs in 133 patients were analyzed, with a median follow-up of 33 (range, 3-87) months. The numbers receiving greater than 25 Gy irradiation to the aorta, vena cava, pulmonary artery, pulmonary vein, bronchus, trachea, heart, and esophagus were 72, 33, 73, 60, 55, 13, 69, and 23, respectively. The corresponding median Dmax 0.5 ml were 43.8, 32.0, 32.2, 29.1, 28.4, 28.7, 41.1, and 21.7 Gy. Of these patients, two developed grade 5 and one grade 3 hemoptysis, and two had grade 3 obstructive pneumonia. Two patients with grade 5 hemoptysis received high doses at the pulmonary artery and bronchus (59.2 and 54.4 Gy, and 61.3 and 59.6 Gy, respectively). No other grade 3 to 5 toxicities occurred. Therapeutic indications and dose-intensity should be carefully determined for patients with central tumors, especially when doses to the pulmonary artery and bronchus in the pulmonary hilum exceed 50 Gy. Tolerable doses for other OARs might, however, be higher than in this study, though longer follow-up is necessary to assess this possibility.

Systemic chemotherapy has enabled prolongation of survival in patients with stage IV colorectal cancer. This has subsequently increased the relative significance of local therapy for patients with oligometastases because they can be cured by removal of oligometastatic lesions. One of the most frequently reported tumor histologies for oligometastases is colorectal cancer. Resection is the standard therapy in most settings of oligometastases. Recently, studies have shown that stereotactic body radiotherapy (SBRT) may become a treatment option that provides high local control with minimal morbidity. Two-year local control rates following SBRT for hepatic and pulmonary oligometastases are almost over 80% and are even higher for patients treated with high-dose regimens. The indications of SBRT for other metastatic sites or conditions include isolated lymph nodes, spinal and adrenal metastasis, and post-surgical pelvic recurrence. Many retrospective studies have indicated that SBRT for various lesions results in good outcomes with low morbidity, both in the curative and palliative setting. However, few reports with a high level of evidence have indicated the efficacy of SBRT compared to standard therapy. Hereafter, the optimal indication of SBRT needs to be prospectively investigated to obtain convincing evidence.