E. C. Amoah1, D. Pokhrel2,3, M. C. Kenamond1, M. E. Bernard1, and R. C. McGarry1; 1University of Kentucky, Lexington, KY, 2University of Kentucky, Department of Radiation Medicine, Lexington, KY, 3University of Kentucky, Radiation Medicine, Lexington, KY
Purpose/Objective(s): Oligometastatic (=5 lesions) lung cancers or synchronous primary lung tumors with associated co-morbidities may not retain their treatment position during SBRT treatments when using multiple isocenters due to longer treatment times, back pain, or shortness of breath. Lung SBRT using SIMT VMAT plans with flattening filter free (FFF) beam can reduce treatment time, improve patient comfort, and improve clinic efficiency. Herein we present our clinical results for treating multiple primary or oligometastatic lung cancers using SIMT lung SBRT. Materials/
Methods: Sixty-two patients with synchronous primary lung cancers or oligometastatic lung lesions (two, n= 51; three, n= 6; four, n= 3; five n=2; total tumors = 142) were simulated with 4D-CT based MIP images and/or abdominal compression and treated with highly conformal SIMT SBRT plans using co/non-coplanar VMAT geometry. Common prescriptions were 50-55 Gy in 5 fractions (50 pts), and 54 Gy in 3 fractions (12 pts), prescribed to each PTV margin with the 70-80% isodose line. Advanced Acuros-XB dose engine for 6FFF beam was used for tissue heterogeneity corrections. NRG RTOG-0618/0813 protocols criteria were used for plan quality evaluation and dose constraints to organs-at-risk (OAR). CBCT-guided SIMT treatment was delivered every other day with 6DOF PerfectPitch couch corrections, and overall treatment time was within 15 minutes. Reported outcomes includes tumor local control (LC) rates and toxicities profiles using CTCAE v5 guidelines. Results: All SIMT lung SBRT plans met RTOG-0618/0813 requirements for target coverage and dose to OAR. Average PTV volume was 16.2 cc (range, 2.17–167.8 cc). Mean follow up after last fraction dose was 20 months (range 0–67.2 months). Of the 62 patients treated, 54 had an adequate post-treatment chest CT scan to assess LC. Among patients with treated and followed up tumors, LC was achieved in 51/54 (94.4%), and for toxicities, 33/54 (61%) of patients developed CTCAE grade 1 asymptomatic pneumonitis on chest CT in on average, 6.2 months after SIMT lung SBRT. No symptomatic pneumonitis, esophagitis, or rib fracture occurred. CTCAE grade 2 chest wall pain occurred in 1 patient with pre-existing neuropathic rib pain which was managed with gabapentin. Thirty-six patients had distant metastasis and 22 patients died from distant failure or a competing comorbidity. Conclusion: Highly conformal SIMT lung SBRT for synchronous primary or oligometastatic lung cancers was safe, fast, and an effective treatment option demonstrating excellent tumor LC rates (>94%) with low treatment related toxicity. SIMT improved patients’ compliance and comfort for those who may not tolerate traditional extended treatment course/time and reduces isocenter shifts with repeated CBCT imaging for patient set up and verification. SIMT improves clinic workflow and potentially reduced intra-fractional set up errors. Kaplan-Meier estimate with longer clinical follow up in a larger patient cohort of SIMT lung SBRT is warranted.
