2394 - Reporting Inter-Fraction Patient Positioning Accuracy Using Hyperarc Stereotactic Radiotherapy for Recurrent Head and Neck Cancers with Initial Clinical Outcomes

D. Pokhrel¹, S. McCarthy², J. A. Knight II^2,3, M. R. Kudrimoti², and E. S. Yang¹; ¹University of Kentucky, Department of Radiation Medicine, Lexington, KY, ²University of Kentucky, Lexington, KY, ³University of Kentucky, Radiation Medicine, Lexington, KY

Purpose/Objective(s): To assess inter-fraction patient positioning accuracy using the fully automated HyperArc module for large recurrent head and neck (R-HN) cancers with Encompass support system and provide early clinical outcomes. Materials/

Methods: Thirty-two R-HN patients treated with 30–40 Gy in 5 fractions to the planning target volume (PTV), a 2-3 mm expansion of the gross tumor volume (GTV), delineated on co-registered MRI or diagnostic CT images. Mean GTV and PTV volumes were 23.9 cc (5.5–53.1 cc) and 50.3 cc (16.9–91.6 cc), respectively. Plans used a 6FFF beam, Encompass support device with Q-Fix mask and mouthpiece bite. Dose was prescribed to the 70-80% isodose line with a PTVD_95%= the prescription dose and calculated with AcurosXB dose engine. Treatments were delivered every other day with CBCT-guided PerfectPitch couch corrections. Values of inter-fractional translational and rotational positioning errors were recorded for a total of 160 fractions. Patients underwent CT imaging follow-up at 3-month intervals from SRT treatment. Clinical outcomes reported include tumor local control (LC), distant failure, and treatment related head and neck toxicities following CTCAE criteria (v5.0).
Results: HyperArc SRT plans provided highly conformal target coverage, steep dose gradient, and low doses to adjacent critical organs. Average inter-fractional couch corrections were 1.7 ± 3.4 mm (-8.3–8.8 mm); -0.8 ± 2.4 mm (-5.7–7.4 mm); and -0.7 ± 2.4 mm (-7.0–7.6 mm) in the vertical, longitudinal, and lateral translations, respectively. Additionally, 0.9 ± 1.2^o (-2.4–3.0^o); 0.2 ± 1.4^o (-2.9–3.0^o); and 0.2 ± 1.4^o (-2.9–3.0^o) in the pitch, roll, and yaw rotations, respectively. Average beam-on-time was 3.6 min. Mean door-to-door time was within the 15 min treatment slot. Median follow-up interval was 6.3 months (0–24 months). Six (19 %) patients passed away prior to the 3-month follow-up. Tumor LC was observed in 22/26 (85%) evaluable patients with follow-up CT imaging and physical exam. Four (15%) patients experienced local tumor progression. No acute toxicities were reported in this cohort. Eight (31%) patients had distant progression, including metastases to neck and lung region (n=1), occipital scalp (n=1), carotid encasement (n=1), pulmonary metastases to left upper lobe (n=1), dermal metastasis (n=1), and leptomeninges spread (n=1). No patients developed grade 2+ toxicities to the head and neck region.
Conclusion: HyperArc SRT treatment for relatively large R-HN cancers using Encompass support system with Q-Fix mask and mouthpiece bite achieves highly reproducible patient setup with an average inter-fractional patient positioning errors < 2 mm/1.2^o. The treatment shows to be effective with high tumor local control rate and low radiation-induced toxicity. Longer follow-up results for a larger patient cohort will be reported. Clinical implementation of the HyperArc module for recurrent head and neck SRT programs at other institutions, especially in the community hospitals, is encouraged.