Cognitive performance after postoperative pituitary radiotherapy: a dosimetric study of the hippocampus and the prefrontal cortex

Objective: The hippocampus and prefrontal cortex (PFC) are important for memory and executive functioning and are known to be sensitive to radiotherapy (RT). Radiation dosimetry relates radiation exposure to specific brain areas. The effects of various pituitary RT techniques were studied by relating detailed dosimetry of the hippocampus and PFC to cognitive performance. Methods: In this cross-sectional design, 75 non-functioning pituitary macroadenoma (NFA) patients (61+/-10 years) participated and were divided into irradiated (RT+, n=30) and non-irradiated (RT-, n=45) groups. The RT+ group (who all received 25 fractions of 1.8 Gy; total dose: 45 Gy) consisted of three RT technique groups: three-field technique, n=10; four-field technique, n=15; and five-field technique, n=5. Memory and executive functioning were assessed by standardized neuropsychological tests. A reconstruction of the dose distributions for the three RT techniques was made. The RT doses on 30, 50, and 70% of the volume of the left and right hippocampus and PFC were calculated. Results: Cognitive test performance was not different between the four groups, despite differences in radiation doses applied to the hippocampi and PFC. Age at RT, time since RT, and the use of thyroid hormone varied significantly between the groups; however, they were not related to cognitive performance. Conclusion: This study showed that there were no significant differences on cognitive performance between the three-, four-, and five-field RT groups and the non-irradiated patient group. A doseresponse relationship could not be established, even with a radiation dose that was higher on most of the volume of the hippocampus and PFC in case of a four-field RT technique compared with the three-and five-field RT techniques.