P186] A superior alternative to the conventional Varian two-marker RPM(TM) box for respiration monitoring

Abstract

Purpose To test a novel two-marker respiratory motion surrogate (NRS) against the Varian two-marker RPM™ box (TMB) with respect to surface dose enhancement and detected motion amplitude with and without tilt. Methods NRS was made from 0.25 mm thick polyester and consisted of a 9 mm tall circular base with either a 60 mm or a 72 mm tall vertical stalk (XL version). Reflective markers were placed on the stalk with 30 mm spacing to emulate the TMB. The reflectors on the NRS were placed 21 mm (33 mm for the XL version) above the base, making them visible to the monitoring system on all patients. The narrow base (38 mm diameter) enabled flexible positioning of the surrogate on the sternum, regardless of adiposity or chest curvature. Surface dose enhancement was measured with Gafchromic EBT3™ film with and without respiratory motion surrogates. The vertical amplitude of a pre-programmed motion platform (15 mm amplitude, 4s period) was measured with the surrogates in two motion management systems, one wall-mounted and one couch-mounted. The influence of surrogate angle was measured by tilting it in the axial and sagittal planes. Non-parametric statistics was applied to all comparisons. Results Surface dose was enhanced by up to 45% and 235% and the area of at least 25% surface dose enhancement was 9.7cm2 and 71.7cm2 under the NRS and TMB, respectively. The inter- and intrasystem differences in detected motion were 0.06). Conclusions The novel respiratory motion surrogate has replaced the commercial motion management surrogate in clinical use in our clinic due to its superior versatility in positioning, improved skin sparing and identical performance.