First radiotherapy of human metastatic brain tumors delivered by a computerized tomography scanner (CTRx)

Purpose: This Phase I study was designed to evaluate the computed tomograph y (CT) scanner as a device for radiation therapy of human brain tumors (CTR x). This first use in humans of a modified CT for treatment was founded on extensive research experience with canine tumors. An additional objective w as to increase the therapeutic radiation dose to tumors compared to normal tissue by concentration of infused contrast material in tumors, an effect a vailable at diagnostic x-ray energies but not at megavoltage energies. Methods and Materials: A small metastatic brain tumor in each of eight pati ents received 3-5-weekly fractions of 5 Gy equivalent per fraction from a C T scanner modified to deliver radiation therapy. In each patient, one addit ional tumor, lying completely outside the volume treated by CTRx, served as a control. The tumor receiving CTRx was treated after infusion of iodinate d x-ray contrast media (CM) for dose enhancement. Many of these patients al so received conventional 40 Gy whole brain radiation, before, during, or af ter CTRx treatment. Results: None of the patients showed adverse reactions to the CM or necrosi s of the normal brain from the CTRx boost radiation. Monte Carlo calculatio ns of the radiation dose distributions in a model tumor showed that the CTR x irradiation of tumors carrying 10 mg or more of iodine per gram of tumor was as good or better than the dose distribution from conventional 10-MV X- rays. The treated tumor in two of the patients vanished after four treatmen ts, whereas a control tumor in one patient remained constant and grew ii-fo ld in another patient. Conclusion: The CTRx concept effectively combines a modified CT scanner as a diagnostic device, as a simulator dedicated to radiotherapy, and as a tre atment machine. Thus, CTRx could be very useful for radiation oncologists i n controlling CM-enhanced and other small brain tumors. (C) 1999 Elsevier S cience Inc.