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

Abstract

To assess the early outcomes of the following 2 types of proton therapy: passive scattering proton therapy (PSPT) and pencil beam proton therapy (PBPT). The consecutive patients who had surgery in our facility were retrospectively reviewed. Thirty-two patients were identified (PBPT 22 patients [69%]). The mean (±standard deviation [SD]) tumor size was 3.8±1.8cm, 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±3Gy and 72±3Gy, 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%. 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.