Conformal radiotherapy of challenging paraspinal tumors using a multiple arc segment technique

Purpose: Target volumes that wrap around the spinal cord are difficult to t reat. We present and evaluate a refined multiple are segment (MAS) techniqu e that is applicable with standard three-dimensional (3D) radiotherapy equi pment and may be a solution for facilities that do not get have full access to intensity-modulated radiotherapy (IMRT). Methods and Materials: The presented technique consisted of 13 isocentric c oplanar beam's eye view shaped fields,delivered as 20 degrees or 10 degrees are segments with an integrated multileaf collimator (MLC) using automatic sequential field delivery. Dose-volume histograms (DVH) for this technique were compared to a modified bar-are technique (MBA) modeled as 30 static f ields and to an inverse planned IMRT technique using 7 coplanar, equispaced beams delivered with the same MLC. Results: Compared to the MBA technique, maximum dose and target coverage we re similar when using 80% of the maximum dose as the reference dose. Howeve r, the MAS technique reduced the maximum doses (to greater than or equal to 1% of the organs at risk [OAR]) by 9% for the spinal cord, 17% for the esop hagus, and 25% for the trachea, as well as the mean doses. Although inverse planned IMRT could further reduce exposure of OAR except for the spinal co rd and improve target coverage, our forward planned MAS technique seems to achieve clinically comparable results. Conclusion: Substituting a series of small split-field are segments for lar ge static fields and using additional narrow paraspinal segments significan tly improves the sparing of organs at risk for paraspinal targets, Although these results are not quite as good as those achieved with IMRT, for facil ities not yet equipped with inverse treatment planning capability, the pres ented technique enables dose escalation for primary paraspinal tumors and r etreatment of recurrent lesions, (C) 2000 Elsevier Science Inc.