Craniospinal irradiation with spinal IMRT to improve target homogeneity

Purpose: To report a new technique for the spinal component of craniospinal irradiation (CSI) in the supine position, to describe a verification procedure for this method, and to compare this technique with conventional plans. Methods and Materials: Twelve patients were treated between 1998 and 2006 with CSI using a novel technique. Sixteen-children were treated with a conventional field arrangement. All patients were followed for outcomes and toxicity. CSI was delivered using a posteroanterior (PA) intensity-modulated radiation therapy (IMRT) spinal field matched to conventional, opposed lateral cranial fields. Treatment plans were generated for each patient using the IMRT technique and a standard PA field technique. The resulting dosimetry was compared to determine target homogeneity, maximum dose to normal tissues, and total monitor units delivered. Results: Evaluation of the spinal IMRT technique compared with a standard PA technique reveals a 7% reduction in the target volume receiving >= 110% of the prescribed dose and an 8% increase in the target volume receiving > 95% of the prescribed dose. Although target homogeneity was improved, the maximum dose delivered in the paraspinal muscles was increased by approximately 8.5% with spinal IMRT compared to the PA technique. Follow-up evaluations revealed no unexpected toxicity associated with the IMRT technique. Conclusions: A new technique of spine IMRT is presented in combination with a quality assurance method. This method improves target dose uniformity compared to the conventional CSI technique. Longer follow-up will be required to determine any benefit with regard to toxicity and disease control.