The need for the moving junction in craniospinal irradiation

The moving junction is used in craniospinal irradiation (CSI) to smooth out any dose inhomogeneity across the head/spine junction. The aim of this stu dy was to demonstrate the extent of the head/spine junction inhomogeneity i n treatment plans of actual patients and to compare stationary and moving j unction data. The radiotherapy plans, prescriptions and case notes of 18 pa tients (12 medulloblastomas, 3 supratentorial primitive neuroectodermal tum ours, 2 pineoblastomas and 1 pineal germinoma) treated with CSI (35 Gy in 2 1 fractions over 29 days) were examined. At 16 months median follow-up (ran ge 1.5-35.5 months), no junctional recurrences or myelopathy were observed. Using the moving junction technique the mean maximum anterior cord dose, f rom 5 cm caudal to 3 cm cephalad of the Day 1 junction, was 36.3 Gy, and th e mean minimum anterior cord dose was 32.9 Gy, with a mean within-patient v ariation of 3.4 Gy (9.7% of 35 Gy). In four patients, comparison of dose va riation across the field junction was made between the original plans and a re-plan using a stationary junction. The effect of a matched junction, a 2 mm overlap and a 3 mm gap were studied both for moving junction and statio nary junction techniques. Dose variations were similar in all cases for exa ctly-matched fields. but for a 2 mm overlap or gap the dose variation was s maller in all but one case for the moving junction technique. These data su ggest that the moving junction is important to minimize the risk of overdos e or underdose across the spine/head junction in CSI.