Two Novel Irradiation Methods for Angiosarcoma of Total Scalp Irradiation

Abstract

<h3>Purpose/Objective(s)</h3> Due to large, irregular and superficial spread of the complex target, conventional radiotherapy via photon and electron beams matching technique for angiosarcoma of total scalp irradiation (TSI) presents major technical and dosimetric challenges. To increase superficial target coverage, reduce normal brain dose, and eliminate the difficulty of patient set up and fields matching, we propose two novel irradiation methods: fully-automated non-coplanar HyperArc VMAT and co-planar Halcyon delivery platform utilizing a 3D-printed 1 cm scalp bolus. <h3>Materials/Methods</h3> The technical and dosimetric performance of the proposed two novel methods was simulated using nine previously treated TSI patients in our institution. HyperArc plans utilized 6MV-FFF beam (800 MU/min) on SBRT-dedicated Linac with fully-automated HyperArc module and 1 cm 3D-printed scalp bolus for dose build up to the superficial target to deliver a prescription dose of 70 Gy in 35 fractions. For comparison, these plans were re-planned via 4 full-arcs on recently installed fast rotating co-planar Halcyon Linac equipped with 6MV-FFF (800 MU/min) with lower mean energy of 1.3 MeV and nominal depth of maximum dose at 1.3 cm. Identical isocenter location and similar planning parameters and objectives, were used on both Linac platforms. Plan quality, including BED10 and treatment delivery accuracy and efficacy, was compared. <h3>Results</h3> Both platforms generated highly conformal, homogenous TSI plans and showed statistically insignificant differences on target coverage, mean target dose, conformity, and dose homogeneity. The average BED10 of the mean target dose was 92.0 ± 1.4 Gy (HyperArc) vs 93.4 ± 0.9 Gy (Halcyon) (p = 0.06). HyperArc provided mean brain dose and V60Gy of 8.1 ± 1.5 Gy and 0.8 ± 0.9 cc respectively, compared to 8.5 ± 1.4 Gy (p > 0.05) and 1.4 ± 0.7 cc (p = 0.04), on Halcyon. For both platforms, significantly lower maximal dose of < 5 Gy was observed in organs at risk (OARs), including spinal cord, brainstem, optic pathway, hippocampi, eyes and lenses, and cochlea (p > 0.05 for all OARs). Halcyon plan complexity slightly decreased as seen in the average decreases of total monitor units, modulation factor and beam-on time by 119, 0.6, and 0.6 min respectively, and the estimated overall treatment time was reduced by an average of 2.4 min. Treatment time for both platforms was less than 15 minutes. Portal dosimetry quality assurance results of HyperArc and the corresponding Halcyon plans were 99.8% and 100%, demonstrating comparable treatment delivery accuracy. <h3>Conclusion</h3> We demonstrated that both Halcyon and HyperArc platforms can deliver an accurate and efficient treatment of greater than 90 Gy BED10 to large, complex and superficial angiosarcoma of the scalp and face with significantly lower mean brain dose of less than 10 Gy. Clinical use of these platforms is underway in our center and highly recommended to other centers, including community centers, expanding the use of Halcyon Linac to underserved patient cohort.