<qa>  How many weeks must elapse since the last dose of radiation therapy to a lesion- Radiation: At least 4 weeks since last dose of radiation therapy to at least one lesion being used as criteria for study eligibility; only 2 weeks must elapse since the last dose of radiation small port to a lesion not used for study eligibility; at least 6 months must have elapsed since the last dose of prior craniospinal XRT and radiation to 50 of the pelvis or TBI 