Effect of Magnetic Resonance Myelography on the Target Volume in Craniospinal Irradiation in Children

Aims: To examine the potential role of magnetic resonance myelography (MRM) in defining the clinical target volume for the spinal field in craniospinal irradiation in children. Materials and methods: Of the 42 patients for whom magnetic resonance imaging (MRI) of the spine was carried out, 12 patients had MRM. The width of the cerebrospinal fluid (CSF) with any lateral extension at different levels was measured from the coronal MRM. The clinical target volume was defined using MRM and the conformal field surface area was compared with the direct conventional field. The inferior border of the thecal sac was determined from MRI spine of 42 patients. Results: Coronal MRM showed variation in the width of the CSF at different levels. The maximum width was 2.9 cm (level of C2). In the same case, the width of the CSF at the level of D8 was 1.7 cm. The mean surface area of the conventional field that covered the CSF was 190.6 cm2, as compared with 150.5 cm2 using conformal field, with an 18.5% reduction in the irradiated surface area. The thecal sac ended at S2 in 40.4% of the patients, whereas it ended above and below this level in 28.6 and 31%, respectively. Conclusions: Implementation of coronal MRM during the treatment planning will improve target definition and lead to a more conformal field. Planning systems with the ability to fuse MRM with reconstructed coronal computed tomography are highly desirable. The use of MRI is highly recommended to individualise the lower border of the spinal field in craniospinal irradiation. © 2008 The Royal College of Radiologists.