Analysis of Early Outcomes of Pencil Beam Proton Therapy Compared with Passive Scattering Proton Therapy for Clival Chordoma

Objective: To assess the early outcomes of the following 2 types of proton therapy: passive scattering proton therapy (PSPT) and pencil beam proton therapy (PBPT). Methods: The consecutive patients who had surgery in our facility were retrospectively reviewed. Results: Thirty-two patients were identified (PBPT 22 patients [69%]). The mean (±standard deviation [SD]) tumor size was 3.8 ± 1.8 cm, and the most common location was the upper clivus (41%). Four cases (13%) were revision surgeries referred from elsewhere, and 2 cases underwent additional surgery elsewhere to achieve near-total resection before radiation. The cerebrospinal fluid leak occurred in 3 patients (9%). The mean (±SD) prescribed dose of PSPT and PBPT was 74 ± 3 Gy and 72 ± 3 Gy, respectively (P = 0.07). The mean (±SD) fractionation of PSPT and PBPT was 39 ± 2 and 36 ± 2, respectively (P = 0.001). Radiation toxicities were recorded in endocrine (11 patients [34%]), ophthalmic (3 patients [9%]), otologic (7 patients [22%]), and radiation necrosis (4 patients [13%]). PSPT was associated with endocrinopathy (odds ratio [OR], 10.5; 95% confidence interval, 1.86–59.4, P = 0.008), and radiation dose was associated with otologic toxicity (OR 1.57; 95% confidence interval, 1.02–2.44; P = 0.04). The gross-near total resection group had better progression-free survival than the subtotal resection group regardless of radiation therapy (P = 0.01). Overall, 3-year progression-free survival was 73%, and 5-year overall survival was 93%. Conclusions: The PBPT group showed comparable outcome to the PSPT group. The degree of resection was more important than the modality of proton therapy. Further follow-up and cases are necessary to evaluate the benefit of PBPT.