ABSTRACT
Objective:To investigate the effects of CT images reconstructed using different field of view (FOV) sizes on the automatic segmentation of organs at risk and dose calculation accuracy in radiotherapy after radical mastectomy.Methods:Under the same scanning conditions, CT values-electron density conversion curves were established by reconstructing the original CT images of a phantom placed at the isocenter and extended FOV (eFOV) positions using FOV sizes of 50, 60, 70 and 80 cm. Then, these curves were compared. A standard phantom with a known volume was scanned, and the automatic segmentation result of the phantom on CT images reconstructed using different FOV sizes was compared. A total of 30 patients in Guangdong Second Provincial General Hospital from January 2020 to June 2022 with breast cancer were randomly selected. Through simulated positioning, their CT images were reconstructed using different FOV sizes for the purpose of automatic segmentation of organs at risk, followed by comparison between the outcomes of automatic segmentation and physicians′segmentation. The treatment plan established based on CT images reconstructed using a FOV size of 50 cm (FOV 50 images for short) was applied to CT images reconstructed using FOV sizes of 60, 70 and 80 cm (FOV 60, FOV 70 and FOV 80 images for short) for dose calculation, and the dose calculation result were compared. Results:The CT values - electron density conversion curves derived from CT images reconstructed using different FOV sizes were roughly consistent. At the isocenter, the difference between the segmented volume and actual volume of the standard phantom increased up to a maximum of 6 cm 3 (4.8%) with an increase in the FOV size. As indicated by the automatic segmentation result, the segmentation accuracy of the spinal cord, trachea, esophagus, thyroid, healthy mammary gland, and skin decreased with an increase in the FOV size ( t = -28.43-8.23, P < 0.05). The comparison of dose calculated based on CT images reconstructed using different FOV sizes showed that there was no statistically significant differences( P>0.05) in the dose to target volume ( V95) and the maximum and average doses in the supraclavicular lymph node region, as well as the dose to organs at risk. The coverage for planned target volume decreased with an increase in the FOV size, with a maximum difference of 4.06%. Conclusions:It is recommended that, for radiotherapy after radical mastectomy, FOV 50 images should be selected for the automatic segmentation of organs at risk, CT-values-electron density conversion curves should be established based on the electron density phantom images of the eFOV region, and the eFOV 80 images should be preferred for dose calculation.
ABSTRACT
Objective To evaluate the feasibility of using medical image analysis for adaptive radiotherapy of lung cancer by drawing the individual contours automatically or interactively and adjusting the planning target volume weekly for reducing the volume of the excessive irradiated normal lung tissue.Methods Many CT images of the GTV and dynamic X-ray fluoroscope data of 23 patients were acquired and all the data were used for working out the tumor radiotherapy plan(TPS) and positioning the patient and to measure reduction in GTV volume.A planning study was conducted to determine the amount of lung-sparing that could have been achieved if adaptive therapy had been used.Treatment plans were created in which the target volumes were reduced after tumor reduction was measured.Results A total of 6313 CT imaging sessions and 78 groups of X-ray dynamic fluoroscope data were performed on 23 lung patients.The GTV was reduced by 70%～80% during the course of treatment.Based on these treatment planning studies,the dose of ipsilateral lung can be reduced significantly by adapting the treatment delivery.Conclusion Medical image analysis can be used to position the GTV and CTV of the tumors.This technology can help to work out the individual TPS and adjust the radiotherapy treatment plan adaptively during the course of treatment and reduce the dose of normal tissues as well as insure the effect of tumor treatment.