Hypofractionated Stereotactic Radiotherapy Using CyberKnife as a Boost Treatment for Head and Neck Cancer, a Multi-institutional Survey: Impact of Planning Target Volume

Aim: To evaluate the role of hypofractionated stereotactic radiotherapy (hSRT) as a boost treatment for head and neck cancer. Patients and Methods: We conducted a multi-institutional retrospective review for the outcome of boost irradiation using CyberKnife for head and neck cancer patients from the charts of four Institutes. Twenty-five patients were treated with hSRT boost for primary site with a median follow-up of 28 months. Treatment sites were 11 nasopharynx, 7 oropharynx, one hypopharynx, 3 nasal cavity or paranasal sinus and three oral cancers. All patients underwent preceding conventional radiotherapy of 35 to 72 Gy (median, 50 Gy) in 1.2- to 2Gy-fractions. The dose and fractionation scheme of the Cyberknife SRT boost was individualized and the prescribed dose ranged from 12 Gy to 35 Gy in 1 to 5 fractions (median, 15 Gy in 3 fractions). Results: There were 18 complete responses, 6 partial responses and one progressive disease, resulting in 96% (24/25) response rate. Local control (LC) rates at 2- and 5-years were 89% and 71%, respectively. Progression-free survival (PI'S) and overall survival (OS) at 2- and 5-years were 70%/ 83% and 70%/ 70%, respectively. Planning target volume (PTV) at boost treatment planning and initial response were predisposing factors for PFS and OS. Patients with PTV <= 20 cm(3) showed better PFS (92%) and OS (100%) than those with a PTV > 20 cm(3) (PFS 61% and OS, 47%). Good initial response predicts better outcome in LC, PFS and OS. Conclusion: The results of the present study showed potential benefits of the CyberKnife hSRT boost. Smaller PTV and good initial response predict good outcome.