Conformal proton radiation treatment for retroperitoneal neuroblastoma: introduction of a novel technique

Postoperative irradiation for locoregionally advanced neuroblastoma requires coverage of the paraspinal retroperitoneum. The proximity of both kidneys and the liver, and a more complex target configuration, can pose a dosimetric challenge for conventional X-ray treatment and intraoperative irradiation. We utilized proton radiation therapy (PRT) to reduce dose to uninvolved kidneys, liver, intestine, and spinal cord.

A 4-year-old male underwent PRT for neuroblastoma of the right adrenal gland, following chemotherapy and delayed surgical resection. Clinical target volume (CTV), boost volume, and normal structures were outlined on the 3D treatment planning CT scan. The patient received 25.2 CGE (cobalt Gray equivalent) to the CTV and 34.2 CGE to the boost region, using 1.8 CGE per fraction, five treatments per week. Dose-volume histograms (DVHs) were obtained for target and nontarget structures.

The 95% isodose volume enclosed CTV and boost volumes. The dose to 50% of the ipsilateral kidney, with tumor involvement of the medial renal surface, was < or = 16 CGE (47% of prescribed total dose). Doses to 50% and 20% of the contralateral kidney in close proximity to deep left-side, paraspinal soft tissue involvement were restricted to 1 CGE and 10 CGE, respectively. Eighty percent of the liver received 27 CGE (80% of prescribed dose). Using a patch technique, unique to charged particle therapy, the spinal cord was almost completely spared during boost volume irradiation.

PRT can achieve excellent dose conformity for advanced retroperitoneal, paraspinal lesions, while respecting normal tissue tolerance levels.