Reirradiation of Utracentrally Located Thoracic Tumors Using a 10-Fraction Hypofractionated Stereotactic Body Radiation Therapy Course: A Detailed Dosimetric Analysis.

Purpose: There is very little information detailing outcomes and toxicity following reirradiation for ultracentrally located thoracic tumors, and detailed dosimetric data are nonexistent. These data are critical for the safe management of these extremely difficult cases. Methods and Materials: The records of 15 individuals undergoing 10-fraction hypofractionated stereotactic body radiation therapy for the management of ultracentrally located thoracic tumors between 2009 and 2020 at a single institution were retrospectively reviewed. Treatment outcomes and toxicity were analyzed. A detailed dosimetric analysis of treatment plans and centrally located organs at risk (OARs) from the initial reirradiation and cumulative radiation therapy courses were presented. Results: At a median follow up of 10 months, the 1- and 3-year overall survival, progression-free survival, and local control were 52% and 28%, 33% and 28%, and 76% and 61%, respectively. Treatment-related adverse events were low, with 5 individuals (33%) developing ≥grade 2 pneumonitis (grade 2 = 4, grade 3 = 1). Dosimetric parameters were not associated with the development of clinically relevant pneumonitis. No adverse events involving central OARs (esophagus, great vessels, and primary bronchial tree) were identified. The median cumulative mean lung dose was 24 Gy equivalent total doses in 2 Gy fractions (EQD2) (range, 10-33 Gy), with a volume receiving 20 G (V20) of 33% (range, 11%-51%). The median esophageal, primary bronchial tree, and great vessel maximum doses (Dmax) were 93.2 Gy (EQD2) (range, 50-148 Gy), 163 Gy (range, 77-204 Gy), and 191 Gy (range, 129-262 Gy), respectively. Conclusions: The current investigation is the first to provide detailed cumulative dosimetric data from a cohort of patients comprised entirely of ultracentrally located thoracic tumors. Despite unfavorable anatomic tumor location, given an intimate association with critical OARs, delivering an ablative dose with a 10-fraction hypofractionated stereotactic body radiation therapy course can serve as a feasible option for these challenging cases.