- Plan to begin partial brain radiotherapy within 24-72 hours after beginning AQ4N, and within 35 days (5 weeks) of the surgery, or if surgery cannot be performed, the biopsy that confirms GBM diagnosis. Radiation therapy must be given by external beam to a partial brian field in daily fractions of 2.0 Gy, to a planned total dose to the tumor of 60.0 Gy over 6 weeks.