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.

Keywords: Craniospinal irradiation; Field junction; Proton therapy.