A primary study on setting the limit ring in intensity-modulated radiation therapy treatmentplanning in lung cancer

Background：the influence of the limit ring on the final dose distribution inthe design of the lung cancer intensity-modulated radiation therapy (imrt)plan was studied. materials and methods: a total of 20 patients with lungcancer in 2017 were selected. seven radiation beams were designed for eachpatient, and the limit ring width (rw) was set at 0.6, 0.8, 1.0, and 1.2 cm,respectively. the distance between the inner diameter of the limit ring andthe target area (rd) was set 0.6, 0.8, 1.0, and 1.2 cm, respectively. the otherparameters used in the plan were set at the same position. in addition, theconformity index (ci) and homogeneity index (hi) were calculated, andnormal tissues were assessed. results: under the condition of the same number of radiation beams and the same distance between the limit ring and the target area, the smaller the limit ring, the better the ci of the target area and the less the hi of the target area. when the size of the limit ring was set the same, the closer the limit ring was to the target area, the better the ci ofthe dose in the target area, and the less the hi of the target area. conclusions: in central lung cancer, when the target volume is approximately 800 cc, the optimal dose distribution is obtained when the rw is set at 0.8 com and the rd is set at 0.6 cm.