An advanced junction concept in pediatric craniospinal irradiation by proton pencil beam scanning

Abstract Purpose To present an advanced junction concept in craniospinal irradiation (CSI) by proton pencil beam scanning (PBS). Materials and methods In PBS CSI, whole brain irradiation (WBI) is commonly delivered by opposed lateral-beams, whereas spine irradiation is delivered by posterior entrances. Since lateral-beams would cross a large portion of the patient at the shoulder level, the junction between WBI and spine irradiation cannot extend below that level, thus the size of the lateral-beams needs to be limited and the number of required isocenters can increase. To overcome such limitation, a pseudo-junction was introduced below the posterior fossa, to turn in this region the WBI beam arrangement to a single posterior beam pointed at the same isocenter, that was matched to the posterior spinal beam more caudally, below shoulder level, in the true-junction. After assessing robustness of the technique to range and setup uncertainties, twenty-three treated patients were reviewed to estimate the percentage that might benefit of being treated by two instead of three isocenters. Results Target coverage at the junction levels resulted robust, with D95% > 95% on pseudo-junction and D95% > 90% on the true-junction . By the advanced junction concept, 91% of patients might by treated with only two isocenters, whereas, by the conventional method, 83% of patients required three isocenters. Conclusion With the presented junction concept the number of isocenters can be reduced, with a consequent relevant reduction of treatment time, which is particularly valuable in the management of pediatric patients under anesthesia.