Modeling Intracranial Second Tumor Risk and Estimates of Clinical Toxicity with Various Radiation Therapy Techniques for Patients with Pituitary Adenoma

Abstract

This study was designed to estimate the risk of radiation-associated tumors and clinical toxicity in the brain following fractionated radiation treatment of pituitary adenoma. A standard case of a patient with a pituitary adenoma was planned using 8 different dosimetric techniques. Total dose was 50.4 Gy (GyE) at daily fractionation of 1.8 Gy (GyE). All methods utilized the same CT simulation scan with designated target and normal tissue volumes. The excess risk of radiation-associated second tumors in the brain was calculated using the corresponding dose-volume histograms for the whole brain and based on the data published by the United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and a risk model proposed by Schneider. The excess number of second tumor cases per 10,000 patients per year following radiation is 9.8 for 2-field photons, 18.4 with 3-field photons, 20.4 with photon intensity modulated radiation therapy (IMRT), and 25 with photon stereotactic radiotherapy (SRT). Proton radiation resulted in the following excess second tumor risks: 2-field = 5.1, 3-field = 12, 4-field = 15, 5-field = 16. Temporal lobe toxicity was highest for the 2-field photon plan. Proton radiation therapy achieves the best therapeutic ratio when evaluating plans for the treatment of pituitary adenoma. Temporal lobe toxicity can be reduced through the use of multiple fields but is achieved at the expense of exposing a larger volume of normal brain to radiation. Limiting the irradiated volume of normal brain by reducing the number of treatment fields is desirable to minimize excess risk of radiation-associated second tumors.