The Impact Of Secondary Positioning By Scanning CT On The Tumor Volume And Normal Tissue Dosimetry In The Three Dimensional Conformal Radiation Therapy For Non-small Cell Lung Cancer

Objective: This study aims to analyze the impact of secondary positioning by scanning CT on the tumor volume and normal tissue dosimetry in the three dimensional conformal radiation therapy for central type non-small cell lung cancer, and to calculate the dosimetry changes in the tumor and the surrounding normal tissues, therefore provide the rationale for the clinical treatment of lung cancer to improve target dose and reduce side effect of radiotherapy for normal tissue.Methods: 53 patients with non small cell lung cancer(NSCLC) validated by pathology or cytology subjected with radiation therapy between January 2010 and April 2014 in the Department of Oncology, Affiliated Hospital of Binzhou Medical College. All patients signed the informed consent, and were fixed by thermoplastic body membrane on the position fixed frame. After positioned by GE double helix CT machine for the first time,the images were defined as CT1 and transmitted to the treatment planning system Pinnacle7.6 c through PACS network, define the primary focal target tumor location(GTV1) and the surrounding normal tissues and organs according to the situation of lesions located in CT image, and design the entire conformal radiotherapy plan as total dose of 58-66Gy(Plan0). The plan is defined as Plan1 when radiation dose reaches 38-42 Gy, then scan the patients again and defined the images as CT2; sketch the primary tumor GTV2 and the normal tissues and organs again, and record the primary tumor volume and lung volume from the CT1 and CT2 images, and analyze their volume changes. Redesign the radiotherapy plan as Plan2 according to the CT2 image with dose of 24-28 Gy. Overlap the plan1 and plan2 to get the actual radiotherapy(Plan1+2) and the dose volume parameters, compare with the volume parameters of the radiotherapy Plan0, anal size parameters changes such as V5,V20,V30 and MLD of lung, V30 of heart, and Dmax of the spinal cord.Results: Totally all patients were subjected with(20.0±4.2) irradiation fractions before treatment plan changing. The GTV1 volume in the first CT1 images were(153.2±104.1)cm3, the GTV2 volume in CT2 images were(79.98±56.8)cm3. The GTV volume of the later decreased(71.98 ± 34.6) cm3, and there was statistically significant between the differences(t=4.29, P=0.001). The volume of the lung suffered from disease of the first CT1 images was(1324 ± 62.3) cm3, and the whole lung volume were(2876 ± 82.1)cm3.The lung volume of the secondary positioning CT2 images were(1543.2±84.6) cm3, and the whole lung volume were(3124.2 ± 124.3) cm3; compared with the two CT images,the volume of the lung suffered from disease increased(183.1 ± 56.2) cm3, all lung increased(164.2 ±34.6) cm3, and there was statistically significant between the differences(suffered side t = 2.98, P = 0.047 and all lung t = 3.21, P = 0.048).The mean lung dose of ipsilateral and all lung descended(4.6± 10.1) % and(4.1±8.7) % respectively, compared with the first plan. The heart of V30 irradiated dose dropped(2.68 ±1.3) % and the Dmax of spinal cord descended(12.4 ±2.8) %. The mean lung dose(MLD) of the entire plan Plan0 was(25.2 ± 8.6) Gy, all lung MLD was(13.8±5.8) Gy, the lung suffered from disease MLD of Plan1+2 was(22.1±6.4)Gy, all lung MLD was(12.3±4.6) Gy, which fell(4.6 ± 10.1) % and(4.1 ± 8.7) %, respectively,and the differences were statistically significant(P=0.03 and 0.02, respectively). The heart V30 of Plan0 irradiated dose was(21.7±4.6) Gy, the Dmax dose of spinal cord was(56.9±12.6) Gy; the heart V30 of Plan1+2 was(24.4 ± 5.3) Gy, the dose decreased(2.68 ±1.3) %, and the Dmax of spinal cord was(45.5 ± 8.9) Gy, decreased(12.4±2.8) %.Conclusion:1. According to the changes of tumor volume in radiotherapy of CT scan,redesign radiotherapy plan could reduce the irradiated dose of suffered disease lung,healthy lung and all lung, and reduce the side effect of radiotherapy. The irradiated dosage to the surrounding normal tissues(heart and spinal cord) have also been changed,which also effectively protect the normal organs.2. Through the analysis of the dose volume parameters in the first and secondary scan plans, the real treatment parameters could be obtained, therefore we can provide the rationale for treatment plan improvement and to improve the curative effect and reduce radiotherapy side effects.