Clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy technique for craniospinal irradiation.

PURPOSE: To demonstrate the clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy (IMRT) technique for photon craniospinal irradiation (CSI). METHODS: Patients who received supine, hybrid IMRT CSI from 2009 to 2014 were included in this retrospective review. Clinical target volume (CTV) was defined as intracranial contents and thecal sac, including nerve roots. Dose was prescribed such that >99% of CTV received >99% of prescription and >95% of the planning target volume received >95% of prescription, with no attempt to include vertebral bodies. Lateral fields were utilized at the cranium and upper cervical spine. Spine fields were either single posterior or 2-3 obliques. Plans were generated with a hybrid of forward and inverse planned IMRT. Inferior borders of the cranium fields and superior border of the lower spine field were designed with 6-15 cm long, gradual dose gradients by sequential closing of multileaf collimator leaves using forward planned multiple static segment IMRT delivery. The sliding window upper spine IMRT field was created by the inverse planning system to match gradients of the brain and lower spine fields. The lower spine field gradient was similarly completed. RESULTS: The cohort consisted of 34 patients. Median CSI dose was 36 Gy (range: 18-39.6 Gy). With a median follow up of 59.4 months, there were no isolated recurrences or spinal myelopathies at CTV margins or field gradients. Eleven patients had recurrence, all of which were intracranial. CONCLUSIONS: Our hybrid forward and inverse planned IMRT supine CSI technique did not result in any isolated recurrences or myelopathies at CTV margins or field gradients. This suggests our target volumes and blended gradients are appropriate for highly conformal three-dimensional planning.