Estimating normal tissue toxicity in radiosurgery of the CNS: application and limitations of QUANTEC

Minimizing radiation-induced normal tissue damage in the central nervous system (CNS) is a key objective and primary impetus for stereotactic radiosurgery and radiotherapy. The recently published Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) study provides updated dose/volume/ outcome data on normal tissue tolerance for sixteen anatomic sites, including the CNS. Most of the data used to develop the relationship between dose, volume and normal tissue toxicity derived from large field, conventionally fractionated regimens, and quantitative dose/volume/outcome data at high doses per fraction to limited volumes is much sparser. Nonetheless, QUANTEC provides some limited recommendations for dose constraints in stereotactic radiosurgery/ radiotherapy of the CNS. This paper critically reviews the findings, recommendations and limitations of QUANTEC as they apply to radiosurgery of the CNS, as well as presenting suggestions to establish and validate clinically meaningful dose/volume/toxicity relationships in this setting.