Abstract：Objective To improve the beam directions for the intensity-modulated radiotherapy, to minimize the irradiation dose for the affected side of crystal and cornea as well as other normal tissues while improving the target dose, so as to improve the quality of patient's long-term survival. Methods Five patients with orbital adenoid cystic carcinoma ( left) were recruited. All the target areas of irradiation included the left lower wall and top wall of the affected side of orbit. The beam directions were taken as the following three types: a) conventional coplanar uniform division of 9 beams; b) unconventional coplanar non-uniform division of 5 beams; c) unconventional non-coplanar non-uniform division of 6 beams ( hereinafter referred to respectively as 9 beams, 5 beams and 6 beams). The proposed dose volume histogram ( DVH), the dose distributions as well as the physical and biological parameters ( maximum, minimum and mean doses, conformity indexes ( CI) and equivalent uniform dose ( EUD)) of the above three plans were comparod. Results The D98% and V95% of 6 beams PTV were 1.3% and 0.6% as well as 11.4% and 0.6% larger than those of 9 beams and 5 beams respectively, D2% was 1% smaller than 5 beams, but CI and EUD had no obvious differences. For OARs, 6 fields were superior to 9 and 5 beams except that Dmin of brainstem was slightly worse than 5 beams. Conclusions In view of the comparisons of the irradiated doses for the target and the organs at risk, the third method, i.e., unconventional non-uniform division of 6 beams has the obvious advantage of dosimetry, which is superior to the other two Methods.
2013, Vol. 24 
