Margin-free Fractionated Stereotactic Radiotherapy for Pediatric Brain Tumors.

BACKGROUND: Conventional radiotherapy (RT) to pediatric brain tumors exposes a large volume of normal brain to unwarranted radiation causing late toxicity. We hypothesized that in well demarcated pediatric tumors lacking microscopic extensions, fractionated stereotactic RT (SRT), without target volume expansions, can reduce high dose normal tissue irradiation without affecting local control. METHODS: Between 2008 and 2017, fifty-two pediatric patients with brain tumors were treated using the CyberKnife (CK) with SRT in 180-200 cGy/fraction. Thirty representative cases were retrospectively planned for intensity modulated RT (IMRT) with 4-mm PTV expansion. We calculated the volume of normal tissue within the high or intermediate dose region adjacent to the target. Plan quality and radiation dose-volume dosimetry parameters were compared between CK and IMRT plans. We also reported overall survival (OS), progression-free survival (PFS) and local control (LC). RESULTS: Tumors included low-grade gliomas (n=28), craniopharyngiomas (n=16) and ependymomas (n=8). The volumes of normal tissue receiving high (≥80% of prescription dose or ≥40 Gy) or intermediate (80%>dose≥50% of the prescription dose or 40Gy>dose≥25Gy) dose were significantly smaller with CK vs. IMRT plans (p<0.0001 for all comparisons). With a median follow-up of 3.7 (range 0.1-9.0) years, 3-year LC was 92% for all patients. Eight failures occurred: one craniopharyngioma (marginal), two ependymomas (both in-field), and five low-grade gliomas (2 in-field, 1 marginal, and 2 distant). CONCLUSIONS: Fractionated SRT using CK without target volume expansion appears to reduce the volume of irradiated tissue without majorly compromising local control in pediatric demarcated brain tumors. These results are hypothesis-generating and should be tested and validated in prospective studies.