Toxicity and Efficacy of Multitarget Thoracic Stereotactic Body Radiation Therapy.

Purpose: With the increasing use of stereotactic body radiation therapy (SBRT) for primary and metastatic cancer, use of multitarget thoracic (MTT) SBRT is rising. Given the limited safety and efficacy data, we report the experience of this strategy from a large academic center.
Methods and Materials: Between 2012 and 2021, patients who received SBRT for ≥2 thoracic targets separated by ≤1 year were retrospectively reviewed. The primary endpoint was clinically significant radiation pneumonitis (CSRP) requiring steroids, oxygen, or intubation. Secondary endpoints included local failure (LF), initiation or change of systemic therapy (ICST), progression-free survival, and overall survival. Competing risk analysis was used to evaluate the cumulative incidence of CSRP, LF, and ICST. Univariate and multivariable analyses were performed to look for clinical and dosimetric predictive factors of CSRP and LF.
Results: One hundred ninety patients (481 lesions) were treated with MTT SBRT with a median follow-up of 19.7 months. Indications for SBRT were oligometastases (n = 70; 36.8%), oligoprogression (n = 62; 32.6%), curative intent in patients with primary lung cancer (n = 37; 19.5%), and control of dominant areas of metastatic progression (n = 21; 11.0%). The number of irradiated tumors ranged from 2 to 7 and the majority of SBRT courses were delivered simultaneously (88.2%). Overall, 14 patients (7.4%) had CSRP, with 5 cases requiring oxygen. The cumulative incidence of CSRP at 6 and 12 months was 5.3% and 7.6%, respectively. The cumulative incidence of LF at 2 years was 10.5%. The cumulative incidence of ICST at 2 years was 41.1%. Median progression-free survival was 11.8 months and median overall survival was 51.3 months. On multivariable analysis, a higher lung V35 _Gy (hazard ratio, 2.59; P = .02) was a statistically significant predictor of CSRP and colorectal histology predicted for higher LF (hazard ratio, 2.12; P = .02).
Conclusions: In one of the largest institutional series of MTT SBRT, rates of CSRP and LF were low. Optimizing plans to lower the lung V35 _Gy may decrease the risk of CSRP.
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