Single high-dose radiotherapy for experimental rat prolactinoma

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Background : Single high-dose radiotherapy, i.e. gamma knife, is remarkable for the treatment for human prolactinoma. Objective and hypothesis : To clarify the hormonal and pathological effects of single high-dose radiotherapy for human prolactinoma, we used rat prolactinoma model. Method : A 5-week-old male Fischer 344 rat was subcutaneously implanted with 5 mg of diethylstilbestrol (DES) Seven weeks later, prolactinoma was induced and the tumor was treated with single high-dose radiotherapy with 10 mm collimator. Four weeks later, the rats were sacrificed, and weight of pituitary gland, serum prolactin(PRL) and Ki-67(MIB-5) labeling index were measured. Results : Of the control group (n=4), weight of pituitary gland was 7.2 mg, serum PRL was 35.8 ng/ml and MIB-5 labeling was 0.59 %. Of the rats with DES implant and without radiotherapy (n=5) weight of pituitary gland was 11.6 mg, serum PRL was 559 ng/ml and MIB-5 labeling was 0.88 %. Of the rats with DES implant and with 16 Gy radiotherapy (n=4), weight of pituitary gland was 11.1 mg, serum PRL was 121 ng/ml and MIB-5 labeling was 0.46 %. Of the rats with DES implant and with 32 Gy radiotherapy (n=5), weight of pituitary gland was 7.7 mg, serum PRL was 16.8 ng/ml and MIB-5 labeling was 0.38 %. Conclusions : Single high-dose radiotherapy is effective in the treatment for prolactinoma, dose-dependently. A dose of 32 Gy is recommended to practical use.