Multiple fractionated stereotactic radiotherapy of residual pituitary macroadenomas: initial experience

We describe our initial experience with fractionated stereotactic radiotherapy (SRT) for the treatment of 19 patients with secretory and nonsecretory pituitary macroadenomas. The primary endpoints of local control and the documentation of any MRI T2-weighted changes in contiguous brain tissues are discussed.

Between 1/95 and 1/97, 19 patients were planned with the X-Knife 3-D planning system (Radionics, Burlington, Mass., USA) and received a median dose of 46 Gy in daily 2.0-Gy fractions. Treatments were delivered stereotactically with a dedicated 600SR linear accelerator (Varian Corporation, Palo Alto, Calif., USA). Immobilization was achieved with the Gill-Thomas-Cosman relocatable frame. The mean tumor size was 2.24 cm. The mean prescription isodose was 87%. The mean age was 53 years (10 male, 9 female). The mean follow-up time was 10 months (range 1-24 months). The mean optic chiasm and brain stem doses were calculated at 38 and 13 Gy, respectively. All patients were evaluated with pre- and postgadolinum-enhanced MRI scans and Humphrey visual field tests.

In the posttreatment period, local control (absence of tumor progression) has been achieved in all of the patients. The treatment was well tolerated in all patients. No acute complications, no visual changes and no T2-weighted MRI or proton density changes were documented in any of the 19 patients.

These preliminary results suggest that SRT compares favorably with conventional radiotherapy in achieving local control. The doses to the brainstem and the temporal lobes are significantly decreased and at early follow-up no white matter changes are seen on MRI after SRT. The true frequency of grade 1-4 changes are likely underestimated as similar changes often occur in association with tumor edema or after surgery. Given the uncertain neurocognitive significance of the white matter changes associated with treating these benign tumors by conventional radiotherapy, we are currently treating all pituitary adenomas with fractionated SRT to reduce the potential sequelae.