Consideration of the target area of radiotherapy for lung cancer with 4DPET

Abstract Objective Through the study of 4‐dimensional (4D) positron emission tomography (PET)/computed tomography (CT) for lung tumor, the delineation of the lung tumor target area was analyzed, the accurate target area was received, and the radiation dose of normal tissue was compared . Methods The average 4DPET volume, 3DPET volume, average 4DCT volume, and 3DCT volume of 10 tumors were compared. Taking the relative difference between the average 4D volume and the 3D volume as the difference of the volumes, the influence of the tumor size and the range of motion for 4D volume and 3D volume were studied respectively, then the target areas were delineated respectively, and the radiation doses of the normal tissues associated with the respective target areas were compared after the intensity‐modulated radiation therapy plan was formulated. Results The PET volumes of all tumors were smaller than those of CT, no matter 4D or 3D, from small to large, the volume sizes were 3DPET volume, average 4DPET volume, 3DCT volume and average 4DCT volume. The relative volume difference was related to the respiratory movement and the size of the tumors. The average 4DPET volume was 22.8% larger than the average 3DPET volume, and the volume ratio was 1.23. The volume of the average 4DCT was 15.4% larger than that of the average 3DCT, and the volume ratio was 1.16. The average volume of 4DCT was 59.5% larger than that of 4DPET. When the movement amplitude of the tumor was greater than 3 mm and less than 5 mm, the larger the tumor volume, the larger the volume ratio of the average 4DCT volume to the average 4DPET volume, with the maximum value being 1.54. When the tumor movement amplitude was greater than 5 mm, the ratio was about 1.4. When the volume of conventional 3DCT was larger than 5 cm3, the ratio of the average 4DCT volume to the average 4DPET volume was 1.9. The planning target area internal target volume (ITV)3DCT was much larger than that of ITV3DPET, intersected ITV4DCTave and ITV4DPETave, the dose V20 and V5 of normal lung tissue, and the dose V30 of heart were increased accordingly. Of these, the dose of lung and heart of ITV4DPETave was the lowest. The V20 and V5 of lung of ITV4DPETave was about 2% lower than ITV4DCTave. Conclusion To delineate lung tumor targets at various positions, particular attention should be paid to the effect of breathing exercises on large movements and large volumes. The target volume seemed to be overestimated by 4DCT, and the average multiphased 4DPET volume was more accurate for delineating the target area while reducing the radiation dose of the lung.