Application of titanium clip marking in localization of 37 cases of rectal cancer before radiotherapy

At present, locating radiotherapy targets for rectal cancer is mostly assisted by computed tomography (CT) and/or magnetic resonance (MR) imaging. This article discusses the role of the upper and lower margins of rectal cancer lesions under colonoscopy in accurately delineating target areas of radiotherapy.

According to the Chinese colorectal cancer diagnosis and treatment specifications (2017 edition), MR and CT are recommended as GTVpositioning applications before neoadjuvant radiotherapy for rectal cancer. 9 The application of titanium clips during colonoscopy to locate the upper and lower margins of the tumor in the radiotherapy target area of rectal cancers is rarely studied in China and abroad. Therefore, applying this technique to assist in positioning and delineating the target area before radiotherapy for rectal cancer provides a new perspective.

Study design
All patients emptied their intestinal tract and bladder in advance.
Before radiotherapy localization, the same attending endoscopy physi-

Statistical analysis
Statistical analysis was carried out using SPSS 17.0 (IBM, Armonk, NY, USA). Quantitative data are described. GTV lengths and distances between the lower and anal margins obtained by each method were normally distributed (Q-Q map test), and variance analysis of the block design was carried out. The test level was α = 0.05 (bilateral), and P < 0.05 was considered statistically significant.

Comparison of GTV Titanium Clip , GTV CT , and GTV MR lengths
The average lengths of endoscopic GTV titanium clip , GTV CT , and GTV MR were 5.84 ± 2.035, 6.97 ± 1.658, and 5.45 ± 2.088 cm, respectively. The F statistic for the three different methods was F = 16.328, P = 0.000. There was no significant difference between GTV titanium clip and GTV MR by the least significant difference and Student-Newman-Keuls methods (P = 0.162), but there was between GTV titanium clip and GTV CT (P < 0.001). There were significant differences between GTV MR and GTV CT (P < 0.001)

DISCUSSION
The key and foundation of radiotherapy for rectal cancer is accurate target delineation before radiotherapy. At present, targets for rectal cancer radiotherapy are mainly located by CT and MR imaging. Titanium clips inserted by endoscopy have the benefits of being small, light, resistant to corrosion, clip tightly, and are less likely to be rejected by the body, among many other advantages. These clips have been widely applied in the digestive tract in endoscopic minimally invasive treatments of bleeding and wound suturing, surgical positioning, and other fields, and they are frequently reported in early esophageal cancer before radiotherapy positioning with good results. [11][12] As the lower section of the colorectal cancer had no obvious cavity within or near the density that could cause interference under CT localization, and MR has no radiation and high resolution of soft tissue, CT in combination with MR imaging is most commonly used to define targets for colorectal cancer radiotherapy. Domestic and foreign studies have shown that the lengths of GTVs mapped before radiotherapy for lower rectal cancer using MR localization are shorter than those under the original CT localization, and the lower margin of the tumor was further from the anal margin with higher accuracy. [13][14][15] The results of the present study are similar to the domestic study. In that study, the MR positioning method measured the average GTV length to be significantly smaller than under CT localization, and the distance between the MR-positioned margin of the GTV from the anal margin was significantly greater than that of the CT-positioned GTV margin from the anal margin. Because of its precise positioning ability, MR has been widely used in colorectal cancer in clinical radiotherapy for target delineation in China and elsewhere, and the application of endoscopic titanium clip markers in middle-to-late colorectal cancer before radiotherapy positioning is not well studied.
The present study showed that for the vast majority of patients with locally advanced rectal cancer, tumor sizes measured by endoscopic titanium clips and MR localization are significantly smaller than those measured by CT localization, and there was no significant dif- The results of the present study showed that for rectal cancer patients, the length and accuracy of a labeled tumor by endoscopyplaced titanium clips was shorter and more accurate than by CT localization, and its range was similar to that of MR, which could narrow the target area so as to reduce the radiation damage to adjacent tissues and organs. In addition, the ranges of three of our patients with endoscopic titanium clips were greater than those measured by CT and MR. This is because for some patients with rectal cancer, their advanced lesions have not invaded very deep. The appearance of these lesions is two-toned as a result of their pathological changes, and their infringement on the surrounding mucosa is shallow. By CT and MR, these are hard to image. However, with endoscopic ultrasonography and magnifying endoscopes, surgeons can directly observe the microstructure and microvascular abnormalities of these lesions and their mucosal limits, more precisely guide titanium clips to mark pathological changes, and more intuitively and accurately sketch a target for radiotherapy positioning.
A small number of patients were enrolled in the present study, which might have some influence on the results. In future studies, we should continue to expand the sample size. In addition, the length of the titanium clip itself will still bring a slight error to the marker range, which has certain disadvantages for patients with large tumors with intestinal stenosis and difficult endoscopic access. This warrants further study and discussion in the future.
Overall, titanium clips applied through colonoscopy to stage II-III colorectal tumors before radiotherapy positioning are effective for shallow advanced infiltrating lesions, and those that cannot be properly seen by CT and MR imaging. Target mapping using endoscopic titanium clips is more intuitive than CT or MR imaging, and more accurate positioning can be carried out in conjunction with CT and MR radiotherapy as auxiliary means. At the same time, the endoscopic titanium clip marking operation is simple, involves no radiation, is cost-effective, is not affected by any metal already present in the patient, and the titanium clips carry little risk of falling off. In rectal cancer, especially stage II-III colorectal cancer, marking the tumor by titanium clips to delineate target areas for radiotherapy before CT guidance enables a more accurate sketch of a target area and has important clinical value.