Alternative techniques as a substitute for 4D-CT Simulation in Lung cancer patients

Abstract

Background: In radiation therapy for lung cancer, the lung lesions move with respiration. Currently, there is a technique, four-dimensional computed tomography (4D-CT), that acquire images while tracking the respiratory graph during the CT scan, resulting in images with accurate size and position of the lung lesions. However, this method is complex and the cost of purchasing the equipment is quite high. 

Objectives: Conduct a study on research data regarding breath-holding techniques and slow CT as a replacement for 4D-CT. 

Materials & methods: This study used the Phillips Big Bore RT CT scanner to collect image data, utilizing a moving phantom, specifically the computerized imaging reference systems (CIRS), which is a device that simulates a tumor. The respiratory rate was set to 12 breaths per minute, which is the normal breathing rate for patients. Scans were performed using 4D-CT, inhale/exhale breath-hold CT, 4 sets of slow CT, according to difference of pitch and rotation, and standard CT. The respiratory management device used was the Sentinel 4D-CT (C-RAD AB, Sweden), which is an optical Surface Monitoring Systems (OSMS). Once the image sets for treatment planning were obtained, radiation oncologists contoured the tumor lesion on each CT image set. 

Results: The slow CT2 image set and the inhale/exhale breath-hold CT image set acquire tumor volumes of 8.16 and 9.36 cubic centimeters, respectively, which were close to the tumor volume defined using the internal target volume (ITV) obtained from the 4D-CT, 9.93 cubic centimeters. However, the inhale/exhale breath-hold method has the limitation of requiring patients to hold their breath at a normal level. 

Conclusion: The appropriate method for performing a Phillips Big Bore RT CT scan to replace 4D-CT is slow CT by setting the parameters with the lowest pitch value of 0.563 and the highest rotation time of 1 second. The results are of a quality comparable to that of 4D-CT.