Optimization of stereotactically-guided conformal treatment planning of sellar and parasellar tumors, based on normal brain dose volume histograms

Purpose: To investigate the optimal treatment plan for stereotactically-gui ded conformal radiotherapy (SCRT) of sellar and parasellar lesions, with re spect to sparing normal brain tissue, in the context of routine treatment d elivery, based on dose volume histogram analysis. Methods and Materials: Computed tomography (CT) data sets for 8 patients wi th sellar- and parasellar-based tumors (6 pituitary adenomas and 2 meningio mas) have been used in this study. Treatment plans were prepared for 3-copl anar and 3-, 4-, 6-, and 30-noncoplanar-field arrangements to obtain 95% is odose coverage of the planning target volume (PTV) for each plan. Conformal shaping was achieved by customized blocks generated with the beams eye vie w (BEV) facility. Dose volume histograms (DVH) were calculated for the norm al brain (excluding the PTV), and comparisons made for normal tissue sparin g for all treatment plans at greater than or equal to 80%, greater than or equal to 60%, and greater than or equal to 40% of the prescribed dose. Results: The mean volume of normal brain receiving greater than or equal to 80% and greater than or equal to 60% of the prescribed dose decreased by 2 2.3% (range 14.8-35.1%, standard deviation sigma = 7.5%) and 47.6% (range 2 5.8-69.1%, sigma = 13.2%), respectively, with a 4-field noncoplanar techniq ue when compared with a conventional 3-field coplanar technique. Adding 2 f urther fields, from 4-noncoplanar to 6-noncoplanar fields reduced the mean normal brain volume receiving greater than or equal to 80% of the prescribe d dose by a further 4.1% (range -6.5-11.8%, sigma = 6.4%), and the volume r eceiving greater than or equal to 60% by 3.3% (range -5.5-12.2%, sigma = 5. 4%), neither of which were statistically significant. Each case must be con sidered individually however, as a wide range is seen in the volume spared when increasing the number of fields from 4 to 6. Comparing the 4- and 6-fi eld noncoplanar techniques to a 30-field conformal field approach (simulati ng a dynamic are plan) revealed near-equivalent normal tissue sparing. Conclusion: Four to six widely spaced, fixed-conformal fields provide the o ptimum class solution for the treatment of sellar and parasellar lesions, b oth in terms of normal brain tissue sparing and providing a relatively stra ightforward patient setup. Increasing the number of fields did not result i n further significant sparing, with no clear benefit from techniques approa ching dynamic conformal radiotherapy in the cases examined. (C) 1999 Elsevi er Science Inc.