Comparison Of Dose Distribution In Cyberknife Radiotherapy Plan, Conformal Radiotherapy Plan And Intensity Modulated Radiotherapy Plan For Patients With Small Lung Tumors

Background and objective：The purpose of this study is to investigate thedosimetric characteristics of CyberKnife radiotherapy plan, conformal radiotherapy planand intensity modulated radiotherapy plan in the treatment of small lung tumors, discusstheir differences on the protection of organs with high risks, and evaluate theiradvantages.Methods：Having selected16patients with small lung tumors in our center, we gottheir localization images of CT. Each case was given the CyberKnife radiotherapy plan,3D conformal radiotherapy plan with five fields and intensity modulated radiotherapyplan. We unified the target volumes, normal organs and prescripted dose of three plansfor each case, and made the dose of planning target volume (PTV) agree with that of95%PTV. Then evaluated the CI (conformal index) and HI (uniform index) of PTV ineach plan, the proportion of5-30Gy irradiated pulmonary volume taken in the wholelung volume (V5, V10, V20, V30), and the maximum dose to esophageal and spinalcord. We used the paired t test to compare every two of the three plans.Results：①The CI of CK,3D-CRT and IMRT plans were0.72,0.46,0.70,respectively. Group CK> Group3D-CRT (t=28.625, P=28.625), Group CK=GroupIMRT (t=2.064, P=0.057), Group3D-CRT <Group IMRT (t=14.853, P=0.000).②The HI value were1.33,1.10,1.08, respectively. Group CK> Group3D-CRT(t=15.763, P=15.763),Group CK>Group IMRT (t=22.06, P=22.06),Group3D-CRT=Group IMRT (t=2.386, P=2.386).③The V5, V10, V20, V30of two lung lobeswere minimum in Group CK (21.77%,12.85%,8.98%,12.85%),Group IMRT takesecond place (31.98%,22.9%,14.04%,22.9%), and Group3D-CRT had the maximumvalues (40.05%,28.61%,18.91%,28.61%);Group CK <Group3D-CRT (t=10.97,8.69,4.64,5.19, P=0.000,<0.001,<0.001,<0.001),Group CK <Group IMRT (t=4.51, 9.64,3.11,3.08, P=0.000<0.001,0.007,0.008),Group3D-CRT>Group IMRT (t=2.56,6.10,7.57,6.77, P=0.022<0.001,<0.001,<0.001).④The maximum dose toesophagus in Group CK,Group3D-CRT and Group IMRT plans were22.43±11.49Gy,36.24±8.06Gy,8.06±11.34Gy, respectively. Group CK <Group3D-CRT (t=7.206,P=7.206),Group CK=Group IMRT (t=2.341, P=0.053), Group3D-CRT>GroupIMRT (t=4.227, P=4.227); The maximum dose to Spinal cord were:13.45±4.69Gy,16.00±5.39Gy,5.39±5.40Gy, respectively.Group CK <Group IMRT <Group3D-CRT (t=2.676,10.985,6.389, P=0.017,0.000,0.000); All three plans of met therequirement that the maximum does to esophagus≤60Gy and the one of spinal cord≤40Gy.Conclusion：The CyberKnife radiotherapy plan (CK), conformal radiotherapyplan(3D-CRT) and intensity modulated radiotherapy plan(IMRT) of treating small lungtumors suggested: The CyberKnife radiotherapy plan gave the minimal damage to thelung in comparison with conformal radiotherapy plan and intensity modulatedradiotherapy plan. However, the homogeneity of the targets was poorer.