- Measurable tumor on magnetic resonance imaging (MRI), computed tomography (CT) scan, or x-ray defined as minimum of 20 mm in at least one dimension; measurable is defined as minimum of 20 mm in at least one dimension; for patients who are in first response (i.e., those patients with persistent sites of tumor after frontline therapy, but who have never relapsed), a biopsy of a lesion or bone marrow must demonstrate viable neuroblastoma following completion of therapy; if the lesion was irradiated, the biopsy must be done at least 4 weeks after radiation is completed