Challenging case of a re-irradiation in a dorsal spine primitive neuroectodermal tumor: Role of modern image-guided pencil beam proton therapy

Extradural primary primitive neuroectodermal tumor (PNET) is a rare aggressive disease mostly occurring in young adults. We present a locally recurrent case of dorsal PNET in the fifth decade of life after a prolonged disease-free interval of 10 years. The patient received radiation therapy in fairly large fields twice in his lifetime and was planned for third-time radiation to a few overlapping paraspinal areas over a period of three decades. Keeping in mind previous irradiations, possible target volume in proximity to organs at risk (OARs) patient was planned for consolidtive radiation using the most conformal technique available, which is proton beam therapy with image guided pencil beam scanning technique. Special dose constraints for the spinal cord and other OARs were set, and proton therapy plan was generated at our institute. When compared with parallelly generated intensity-modulated radiation therapy plan with the same dose prescription and dose constraints using helical tomotherapy, intensity-modulated proton therapy plan showed superior dosimetric benefit in terms of coverage and significant sparing of OARs.