Tumour volume comparison between 16-row multi-detector computed tomography and 320-row area-detector computed tomography in patients with small lung tumours treated with stereotactic body radiotherapy: Effect of respiratory motion

Margins to compensate for respiratory-induced mismatches between lung tumor and fiducial marker positions using four-dimensional computed tomography

Background and purpose

Tumors and fiducial markers do not always exhibit synchronous motion across different respiratory phases, in a phenomenon called the target localization error (TLE). We determined the margin to compensate for the TLE using four-dimensional computed tomography (4D-CT).

Materials and methods

We analyzed data from 21 lung tumor patients with fiducial markers; 11 for TLE determination and 10 for validation. Shifted CT images were generated by aligning the centroids of the fiducial markers in the reference phase of 4D-CT with those in each respiratory phase, and the union of gross tumor volumes (GTVs) was determined (G T V u n i o n s h i f t ). Conversely, variations in GTV centroids across the respiratory phases were calculated, and the 95th percentile of the root mean square error was defined as the TLE. Using this TLE, a GTV with an added TLE (G T V T L E r e f ) was generated in the reference phase. Subsequently, a treatment plan assuming dynamic tumor tracking (DTT) was created for the planning target volume, derived by adding an isotropic 5 mm margin toG T V T L E r e f , and the dose coverage forG T V u n i o n s h i f t was evaluated.

Results

The TLEs (standard deviations of the root mean square error) were 2.0 (0.8) mm, 2.1(0.7) mm, and 3.2 (1.1) mm in the left - right, anterior - posterior, and superior - inferior directions, respectively. A dosimetric evaluation revealed thatG T V u n i o n s h i f t did not receive 100 % of the prescribed dose in four of 10 cases owing to artifacts.

Conclusion

The TLE can be compensated by adding an anisotropic margin to the GTV in the reference phase, a critical consideration in DTT.

Preoperative Staging Diagnosis of Colorectal Cancer Based on Multi-Row Spiral CT

Colorectal cancer is a common malignant tumor of digestive tract, and its incidence has increased significantly in recent years. The 5-year survival rate of patients with early local colorectal cancer is more than 90%, with local invasion of about 68%, and distant metastasis of less than 10%. Therefore, early diagnosis and early treatment is an effective means for the prevention and treatment of colorectal cancer. At present, X-ray air-barium double contrast radiography and fiberoptic endoscope are most commonly used in the examination of colorectal tumors in the world. These two methods have the advantages of simple operation, intuition and low cost. However, it is limited to judge the depth of tumor invasion, whether to break through the serosa, lymphatic metastasis, and distant metastasis. In this work, it can be confirmed that the measurement of preoperative tumor vascular volume reconstruction density is feasible in the preoperative evaluation of colorectal cancer, it will provide clinicians with more valuable information about preoperative tumor staging. Besides, multi-slice spiral CT has the advantages of less trauma, high speed, and clear image. It can not only judge the location of the tumor, the depth, and extent of tumor invasion, and show distant organ metastasis, but also has good application value in tumor staging. In this paper, the clinical data and MSCT imaging data of patients with colorectal cancer were analyzed retrospectively, and the value of MSCT in the diagnosis of colorectal cancer was discussed.