Longitudinal positron emission tomography (PET) evaluation of radiotherapy effect on regional cerebral blood flow and metabolism in patients with intracranial germinoma

The aim of this study was to evaluate by 15O and 18F-fluorodeoxyglucose positron emission tomography (PET) the adverse effects of radiotherapy on blood flow and metabolism in two pediatric patients with intracranial germinoma. In a 12-year-old boy with pineal germinoma, a dose of 38 Gy was given to the whole brain and an additional 22 Gy to the tumor site. Regions of interest (ROI) were placed in the gray matter and the thalamus. rCBF, rCMRO2, and rCMRGl of the gray matter, which received 38 to 50 Gy, were increased one month after radiotherapy. Although rCBF and rCMRO2 levels remained unchanged, rCMRGl was slightly decreased two years later. In contrast, rCBF and rCMRO2 of the thalamus, irradiated with 60 Gy, did not increase as much as in the gray matter. rCMRGl was decreased after one month and below the pretreatment level two years later. These changes of suppressed circulation and metabolism in the thalamus appeared to be closely related to the irradiation dose. In an 11-year-old girl with parasellar germinoma, a dose of 44 Gy was given postoperatively to the whole brain and an additional 16 Gy to the tumor site. Two weeks after surgery, rCBF, rCBV, rCMRO2, and rCMRGl of the gray matter on the operated side had decreased to 85% of the values in the contralateral gray matter, but had recovered to the contralateral values one month after radiotherapy. One year and five months later, no significant change was noted in cerebral circulation and metabolism. (author)