The Study Of Respiratory Gating On Lung Cancer Radiotherapy

Respiratory movement significantly affected the location and size of lung tumor. To ensure the target tumor does not "leak", the effectof respiratory movement need to be considered.Clinically,PTV is on thebasis of CTV groups outside enlarging security boundary(IM + SM). Social security boundary extended greatly increase the PTV including more normal tissue around the tumor,which lead to a more normal tissue around the tumor "exposed" in the high dose area and increase the risk of the NTCP, limits the increase of the tumor target radiation dose.The technique of DIBH-Gating can effectively reduce the tumor mobility in the direction of superior and inferior,and reduces the security boundary value of CTV need caused by respiratory movement,and reduce the PTV.At the same time,the technique of Gating reduce organ to accept the average dose and volume by irradiation. To ensure the premise of the same NTCP, radiation dose of the tumor target is expected to further improve. This study was designed to location and 4D-CT scanning, FB-Gating scanning and DIBH-Gating scanning 、designing plan and to analysis and comparison of three sets of different radiotherapy plan, discusses the dosimetry advantage of Gating technology applied in lung cancer and the clinical feasibility.It providing clinical reference for other parts tumor research using the Gating.Twelve patients with lung cancer in Zhe Jiang Cancer Hospital were selected to obtain a set of 4D-CT,FB-Gatingg-CT and DIBH-CT scan, and 10 patients were irradiated using the FB-Gatingg technique,2patients retreating the group.The diaphragm repeatability and GTV movement of the 10 patients were measured breathe freely in radiotherpty. Three sets of each patient radiotherapy plan: 4D plan, FB-Gating plan and DIBH-Gating plan,and assess the tumor geometric size: ITV and PTV,and dosimetric benefits of organs.The average mobile degrees of tumor target is respectively(1.46 ± 0.56),(2.47±1.85) mm,(7.45±5.53) mm in the X, Y, Z axis.The movement of diaphragm was 12.65± 5.6 mm(7.0 ~ 16.2 mm)with free breathe.Though the little difference between tumor targets, the ITVs difference is obviously, which is(111±45)cm3、(94±44)cm3 in ITVFB and ITV4 Drespectively.so the PTVs differed significantly,which is( 190±57) cm3( 163±60) cm3( 116±42) cm3 in PTV4 D 、PTVFB-Gatingg 、 PTVDIBH.The lung’s V20 was(20.17±4.50)% 、(18.45±4.55)%、(15.90±3.66)% in 4D, FB-Gatingg and DIBH-Gating plan respectively. And DIBH-Gating plan in lung V20 was reduced by 21.1%,among the 4D plan.It is feasible to use Gating to radiotherapy for patients with lung cancer.The reproducibility in DIBH-Gating plan is inferior to the reproducibility in FB-Gating plan. Compared with the 4D plan, DIBH-Gating plan could obviously reduce the target volumes and increase the lung tissue,and reduce the dose of lung received.but more complex inplemenation process.Therefore,dosimetry and target volume comparison: DIBH-Gating plan is superior to the FB-Gating plan,which is better than that of 4D-CT.