Dosimetric advantages of O-ring design radiotherapy system for skull-base tumors

作者：Ogura Kengo; Mizowaki Takashi^*; Ishida Yuichi; Hiraoka Masahiro

来源：Journal of Applied Clinical Medical Physics, 2014, 15(2): 226-234.

DOI：10.1120/jacmp.v15i2.4608

• dynamic conformal arc radiotherapy
• dosimetric comparison
• O-ring design radiotherapy system
• skull-base tumors
• fractionated stereotactic radiotherapy

The purpose of this study was to investigate whether a new O-ring design radiotherapy delivery system has advantages in radiotherapy planning for skull-base tumors. Twenty-five patients with skull-base tumors were included in this study. Two plans were made using conventional (Plan A) or new (Plan B) techniques. Plan A consisted of four dynamic conformal arcs (DCAs): two were horizontal, and the other two were from cranial directions. Plan B was created by converting horizontal arcs to those from caudal directions making use of the O-ring design radiotherapy system. The micromultileaf collimators were fitted to cover at least 99% of the planning target volume with prescribed doses, 90% of the dose at the isocenter. The two plans were compared in terms of target homogeneity, conformity, and irradiated volume of normal tissues, using a two-sided paired t-test. For evaluation regarding target coverage, the homogeneity indices defined by the International Commission on Radiation Units and Measurements 83 were 0.099 +/- 0.010 (mean +/- standard deviation) and 0.092 +/- 0.010, the conformity indices defined by the Radiation Therapy Oncology Group were 1.720 +/- 0.249 and 1.675 +/- 0.239, and the Paddick's conformity indices were 0.585 +/- 0.078 and 0.602 +/- 0.080, in Plans A and B, respectively. For evaluation of irradiated normal tissue, the Paddick's gradient indices were 3.118 +/- 0.283 and 2.938 +/- 0.263 in Plans A and B, respectively. All of these differences were statistically significant (p-values < 0.05). The mean doses of optic nerves, eyes, brainstem, and hippocampi were also significantly lower in Plan B. The DCA technique from caudal directions using the new O-ring design radiotherapy system can improve target homogeneity and conformity compared with conventional DCA techniques, and can also decrease the volume of surrounding normal tissues that receives moderate doses.

• 出版日期2014