The feasibility and efficacy of new SBRT technique HyperArc for recurrent nasopharyngeal carcinoma: noncoplanar cone-based robotic system vs. noncoplanar high-definition MLC based Linac system.

ABSTRACT

The purpose of this study was to evaluate the feasibility and efficacy of HyperArc (HA) for recurrent nasopharyngeal cancer (NPC) by comparing it with the CyberKnife system (CK). Fifteen patients with recurrent nasopharyngeal cancer who were treated using the noncoplanar cone-based robotic CK system were enrolled. CK was delivered with a median dose of 37.5 Gy in 5 fractions. The delivered CK treatment plans were the sources for the corresponding homogeneous HA (HA-H) and inhomogeneous HA (HA-IH) plans. The HA-H plans were generated to meet the corresponding treatment plan criteria for the CK plans. The HA-IH plans were designed to emulate the corresponding inhomogeneous CK isodose distributions. These three SBRT treatment plans were compared with target coverage, sparing of organs at risk (OARs), and dose distribution metrics. The HA-H and HA-IH plans consistently exhibited CTV and PTV coverage levels similar or better to those of the CK plans but significantly reduced the dose to OARs. Using the HA techniques (both HA-H and HA-IH plans), the mean maximal doses to the spinal cord, brainstem, optic nerves, and optic chiasm were reduced by approximately 60%, compared to the CK plans. The high dose spillage, conformity, and homogeneity indices of the HA-H plans were significantly better than those of the CK plans. The HA-IH plans showed faster dose falloff and similar conformity of the HA-H plans and dose heterogeneity of the CK plans. Here we demonstrated the HA treatment plan system for recurrent NPC is feasible, either homogeneous or inhomogeneous delivery. Excellent sparing of OARs and dosimetric distribution and very efficient delivery make HA an attractive SBRT technique for recurrent NPC treatment.