Simulation study of comparative dosimetric analysis of coplanar horizontal-port scanned carbon-ion beam therapy in the head and neck.

Abstract

Carbon-ion radiotherapy (CIRT) has demonstrated success in treating radioresistant disease within the head and neck, owing to its unique physical and radiobiological properties. Construction cost remains prohibitive; a center offering only a horizontal port may bridge this difficulty, but removal of the vertical port may prohibit treatment of disease near critical organs-at-risk. Building a center only containing a horizontal treatment port has been proposed as one method for cost savings. 20 complex cases of head and neck cancer previously treated with conventional CIRT were retrospectively planned using horizontal-port-only treatment incorporating non-coplanar treatment angles to achieve greater degrees of freedom. These were dosimetrically compared with the previous plans. Comparable D95 coverage of both planning target volume and gross tumor volume with ability to meet organ-at-risk constraints were feasible with horizontal-port-only treatment. Collectively differences were noted in PTV D95, brain stem Dmax, contralateral eye Dmax and V10 Gy (RBE); further qualitative differences were noted on a plan-by-plan basis dependent on disease location. Horizontal-port-only treatment employing non-coplanar angles was feasible for complicated head and neck disease typically treated with CIRT, though careful consideration is necessary on a plan-by-plan basis. It is worth noting that non-coplanar approaches are not typically used with the current treatment gantry and may extend further the difference between horizontal port planning and a gantry-based gold-standard.