Application of a Digital Spirit Water Level to Measure and Determine The Slope of The Chest Surface in Radiotherapy Positioning of Breast Cancer Patients.

Abstract

         This research is to study the efficiency and accuracy of the application of using the laser system with the digital spirit water level (DSL) compared to using a laser system, which is a standard method. The study examined and assessed the errors, which could be caused by many factors, such as the use of fixation devices, the expertise of the radiotechnologist, and the patient. In the positioning of breast cancer patients before radiation therapy, using the Three Dimension Conformal Radiotherapy (3DCRT) techniques, Intensity Modulated Radiotherapy (IMRT) techniques, Volumetric Arc radiotherapy (VMAT) techniques. In ELEKTA Infinity^TH and Accuray TomoH radiation machines of totaling 34 cases by selecting according to the inclusion and exclusion criteria, which assessed the error in 3 dimensions: left-right (X-axis), head-foot (Y-axis), and front-back (Z-axis) from X-rays in kV-kV-imaging mode and Cone Beam Computed Tomography (CBCT) mode. Compared with computed tomography simulation image. The results were the group of breast cancer patients who received pre-irradiation positioning using only the laser system had mean error in the X-axis, Y-axis, and Z-axis of -0.23±2.67 mm, -0.09±2.02 mm, and 3.09±2.84 mm, respectively. The groups using the laser and DSL systems had mean error in the X-axis, Y-axis, and Z-axis of -1.01±1.54 mm, -0.38±2.05 mm, and -0.26±1.68 mm, respectively. When analyzed by the independent t-tests to compare the mean error between the 2 systems, it was found that the mean in the X-axis and Y-axis was not significantly different (P=0.305 and P=0.689 respectively), while the mean in the Z-axis was significantly different (P=0.003). The study of the average time for patient positioning found that the positioning using the Laser system average of 40±21.87 minutes, while using the Laser system and DSL average of 7.94±6.13 minutes, which was statistically significantly different (P<0.001). In addition, the average number of repeated imaging sessions between the laser system and the laser system and DSL were compared and found to be 8.00±4.37 times and 1.58±1.23 times, respectively, which were statistically significantly different (P<0.001). The Total Vector Error (TVE) of the device using the laser system and the device using the Laser and DSL system were 3.12 and 1.11 mm, respectively. The average error of the planning target volume margin (PTV margin) in the X-axis, Y-axis, and Z-axis of the device using the laser system and the device using the Laser and DSL system were 11.34, 12.49, 17.48 and 8.85, 8.92, 7.56 mm, respectively. In summary, the comparison of the use of two systems, the standard laser system and the laser system combined with DSL, found that the positioning error values ​​in breast cancer patients were not significantly different in the X-axis and Y-axis, except in the Z-axis. Therefore, the use of the laser system and DSL helped increase the accuracy of patient positioning, especially in the Z-axis, reduce the overall mean error (TVE), reduce the PTV margin error, and reduce the time for patient positioning, as well as reduce the number of re-imaging. There are resulting in patients not receiving unnecessary additional radiation doses according to the principles of safety and radiation hazard prevention.