Stereotactic conformal radiotherapy for pituitary adenomas: technique and preliminary experience

OBJECTIVE Stereotactic conformal radiotherapy (SCRT) is a high precision te chnique of fractionated radiotherapy which ensures accurate delivery of rad iation with reduction in the volume of normal tissue irradiated as compared to conventional external beam radiotherapy. We describe the technique and preliminary experience of SCRT in patients with residual and recurrent pitu itary adenomas. PATIENTS AND METHODS Between February 1995 and March 1999, 22 patients (mea n age: 45.3, range: 20-67 years) with residual or recurrent pituitary adeno mas (13 nonfunctioning, nine secretory) were treated with SCRT. All were im mobilized in a relocatable Gill-Thomas-Cosman (GTC) frame and tumour was lo calized on a postcontrast planning computerized tomography (CT) and MRI sca n. The gross tumour volume (GTV) and the critical structures were outlined on contiguous 2-3 mm separated slices. A margin of 5 mm (12 patients) to 10 mm (10 patients) was grown around GTV in three-dimensions (3-D) to generat e the planning target volume (PTV). The treatment was delivered by three (f ive patients) and four (17 patients) maximally separated conformal fixed fi elds with each field conformed to the shape of the tumour using customized lead alloy blocks (19 patients) or multileaf collimator (three patients). T he patients were treated on a 6-MV linear accelerator to a dose of 45 Gy in 25 fractions (18 patients) and 50 Gy in 30 fractions (four patients). RESULTS The technique of SCRT has become a part of the routine work of the radiotherapy department. The treatment was well tolerated with minimal acut e toxicity. One patient developed transient quadrantanopia 2 weeks after tr eatment with full recovery after a short course of corticosteroids. One pat ient had a transient visual deterioration 7 months after treatment due to c ystic degeneration of the tumour which fully recovered following surgical d ecompression. Nine of the 15 patients presenting with visual impairment had improvement after treatment and the visual status remained stable in all o thers. One patient with acromegaly and one with a prolactinoma achieved nor malization of elevated hormonal abnormality four and 10 months after SCRT, respectively. The remaining seven patients with a secretory adenoma had dec lining hormone levels at last follow-up. Newly initiated hormone replacemen t therapy was required in five patients. At a median follow-up of 9 months (range 1-44 months), the 1 and 2 year actuarial progression free and overal l survival were 100%. CONCLUSION Stereotactic conformal radiotherapy is a high precision techniqu e suitable for the treatment of pituitary adenomas requiring radiotherapy. Preliminary results suggest effective tumour control and low toxicity withi n the range expected for conventional external beam radiotherapy. While the technique is of potential benefit in reducing the volume of normal brain i rradiated, the advantages in terms of sustained tumour control and reduced toxicity over conventional radiotherapy need to be demonstrated in long-ter m prospective studies.