Study Of Radiation Target Margin Definition By4DCT For Non Small Cell Lung Cancer

This study mainly focuses on calculating tumor margin in the treatment planningfor non-small cell lung cancer (NSCLC) radiotherapy. In the study, four-dimensionalcomputed tomography (4DCT) and Cone-beam Computer Tomography (CBCT) wasused for assessing movement of clinical target volume (CTV) and set-up deviation.Then, using the data of movement and set-up deviation, we can calculate theradiotherapy treatment target margin.To measure the CTV movement due to respiration and other organ motions,3DCTand4DCT simulation scan was performed for14patients. All patients were divided intotwo groups, patients with tumor in lower lobe of the lung named group A, the upperlobe ones called group B. The gross tumor volume (GTV) on each of the ten respiratoryphase of the4DCT image set was delineated and fused to produce GTV-IGTV. In orderto study the accuracy and reproducibility of patient and beam set-up, CBCT imagesfrom14patients were evaluated. Discrepancies between planned and actual fieldpositions were measured and the systematic and random errors were calculated. Then,the combined effect of these variations was evaluated.Average differences between the position of the target center on direction of x, y,and z coordinates were less than1mm, with no significant difference (P <0.05).Thestandard deviations of the centra and edge movement with tumor in group A were0.09cm and0.35cm in the medio-lateral directions,0.12cm and0.55cm in thedorso-ventral directions,0.66cm and0.42cm in the cranio-caudal directions. And thesame tumor data as group A, with tumor in group B were0.14cm and0.20cm in themedio-lateral directions,0.05cm and0.21cm in the dorso-ventral directions,0.09cmand0.16cm in the cranio-caudal directions The standard deviations of the systematicset-up errors and the random erros were0.23cm and0.09cm in the medio-lateraldirections,0.25cm and0.08cm in the dorso-ventral directions,0.42cm and0.18cm inthe cranio-caudal directions.With the combined effect of tumor motion and set-up movement, we conclude thatthe magin of group A for two confidence levels of90%and95%were0.61cm and0.73cm in the medio-lateral directions,0.93cm and1.12cm in the dorso-ventral directions,1.31cm and1.57cm in the cranio-caudal directions. And the values of group B for two confidence levels of90and95%were0.43cm and0.51cm in the medio-lateraldirections,0.38cm and0.45cm in the dorso-ventral directions,0.61cm and0.73cm inthe cranio-caudal directions.It is recommended that the target margin were0.50cm in the transversal plane and1.00cm in the cranially and caudally in Radiation Therapy Oncology Group. But themargin used in this paper is more accurate, giving the reference data for individualizedradiotherapy treatment.