Would you offer intensive CNS prophylaxis to Ph negative B-ALL patients who have possible mandibular nerve involvement on MRI face?

The patient presented with a numb chin, more to the right of his face; an MRI did report mandibular nerve opacity, which is non-specific per neuro-radiology; opacity was in the left mandibular nerve. CSF has been negative for malignant cells. His chin numbness did improve with course 1 of CALGB 10403. Does the patient need CNS prophylaxis as CNS1 or CNS3?