Dosimetric effect of Varian high-definition multi-leaf collimator leaf position error on stereotactic body radiation therapy for lung tumors / 中华放射肿瘤学杂志

ABSTRACT

Objective:To evaluate the effect of leaf position error of Varian high-definition multi-leaf collimator (HD120) on the dosimetry of stereotactic body radiation therapy (SBRT) for lung tumors.Methods:Nine SBRT plans based on HD120 for lung tumors were selected as the reference plans. The parameters of the plans were modified by the in-house program based on the Varian Eclipse 15.6 scripting application program interface to generate the simulation plans with three types of leaf position errors including the isotropic systematic error, the anisotropic systematic error and the random error, respectively. Then, the dosimetric metric deviation between each simulation plan and the corresponding reference plan was calculated and regression analysis was performed to evaluate the dosimetric effect of three types of leaf position errors of HD120 on SBRT.Results:The planning target volume (PTV) D 99%, D 2cm and V 5Gy of double lungs were decreased quadraticly with the increase of the absolute value of the isotropic systematic error. The first-order sensitivity was -0.06%/mm to -0.26%/mm, and the second-order sensitivity was -0.55%/mm 2 to -1.17%/mm 2 ( R2=0.96-0.99, P<0.01). The maximum change of PTV D 99% was -3.13%. The linear regression analysis of the effects of the anisotropic systematic error and random error showed that the sensitivity of CI was 25.16%/mm ( R2=0.98, P<0.01) and -4.84%/mm( R2=0.99, P<0.01), and the sensitivity of other dosimetric deviations with the anisotropic systematic error was 4.80%/mm to 5.12%/mm ( R2=0.96-0.98, P<0.01), whereas the sensitivity with the random error was -0.47%/mm to -1.01%/mm ( R2=0.96-0.99, P=0-0.02). Conclusions:The dosimetric deviation of SBRT plan based on HD120 for lung cancer is highly sensitive to the anisotropic systematic error of leaf position, but less sensitive to the random error. In addition, the isotropic systematic error of leaf position will lead to the decrease of target coverage to a certain extent. Consequently, it is necessary to strictly control the systematic error of HD120 leaf position in the implementation of SBRT plan in clinical work.