The cranial-spinal junction in medulloblastoma: Does it matter?

Purpose: Late effects of treatment in children and young adults with medull oblastoma can be influenced by the technique employed in radiating the cran iospinal axis. The purpose of this study is to determine whether the placem ent of the cranial-spinal junction has an impact on dose to the cervical sp inal cord and surrounding organs. Methods and Materials: Five patients underwent computed tomography (CT) sim ulation in the prone position for craniospinal irradiation. A dose of 36 Gy was prescribed to the entire neuraxis. The doses to the cervical spinal co rd and surrounding organs were calculated using a cranial-spinal junction a t the C1-C2 vertebral interspace (high junction) or at the lowest point in the neck, with exclusion of the shoulders in the lateral cranial fields (lo w junction). The volume of critical organs at risk, as well as dose to thes e structures using the cranial and spinal field(s) were outlined and calcul ated using the CMS FOCUS 3-dimensional treatment planning system. Results: The average dose to the cervical spinal cord was 11.9% higher than the prescribed dose with the low junction, and 6.7% higher with the high j unction. However, doses to the thyroid gland, mandible, pharynx, and larynx were increased by an average of 29.6%, 75.8%, 70.6%, and 227.7%, respectiv ely, by the use of the high junction compared to the low junction. Conclusion: A higher dose to the cervical spinal cord can be minimized by u sing a high junction. However, this would be at the cost of substantially i ncreased doses to surrounding organs such as the thyroid gland, mandible, p harynx, and larynx. This can be critical in children and young adults, wher e hypothyroidism, mandibular hypoplasia, and development of second malignan cies may be a late sequela of radiation therapy. (C) 1999 Elsevier Science Inc.