Integrated Feathering Method For Craniospinal Irradiation

Traditional Craniospinal Irradiation (CSI) plans require the development and delivery of multiple feathered plans to distribute dose heterogeneities throughout the spine. This increases the planning workload since multiple plans must be created for a single patient and complicates the delivery as a new plan must be administered every few days with high precision at the match lines, necessitating the measurement of skin gap. To eliminate the need for feathered CSI treatment plans, a novel planning method was implemented using multiple control points to create a dose gradient at the match lines to produce a homogeneous dose to the spinal cord while reducing the planning workload and simplifying delivery. One CSI patient was simulated in the prone position, and a plan developed using the feather-free method. Bilateral cranial fields were designed using conventional methods with couch and collimator rotation to eliminate divergence with the upper spinal field while minimizing divergence into the lenses. Spinal posterior-to-anterior fields were designed with the couch rotated to 90 degrees to allow gantry rotation about the length of patient’s spine and collimator rotation of 90 degrees to allow appropriate field blocking with the MLCs. A match line was placed for the two spinal fields to allow roughly 2cm overlap between the superior and inferior edges of the posterior-to-anterior fields. Control points were created to shift the jaws a few millimeters and create a dose gradient to reduce hot spots in the overlap region, integrating the feathers into a single treatment plan. The integrated feathering treatment plan was able to deliver a highly uniform dose to the spinal cord using a single plan for the entire course without the need to measure skin gap. Hot spots for the integrated feathering method were calculated to be 106% with no cold spots in the spinal cord. This is much more homogenous than conventional methods which produced plans with hot spots of 114% and cold spots of 90% at the cord level. Exact shifts were calculated and relayed to the technicians for delivery to simplify set-up and reduce the possibility of errors since skin gap measurements were not necessary. Integrating the feathering by use of multiple control points helped mitigate set-up errors by reducing the dosimetric impact of slight shifts. Simulated shift errors between 2 and 5mm in the inferior-to-superior direction increased hot spots by only 8-12% for the integrated plan, compared to 4-47% for the conventional plan. A method for planning CSI has successfully been developed to eliminate the need for feathering treatment delivery. This novel method uses multiple control points to achieve a dose gradient at the match lines, producing a homogeneous dose distribution and eliminating the need for feathering. This helps to reduce the planning workload and simplify clinical delivery while administering a highly homogeneous dose to the spinal cord.