Real-time monitoring of a digestive-tract marker to reduce adverse effects of moving organs at risk (OAR) in radiotherapy for thoracic and abdominal tumors

Abstract

Purpose/ObjectiveFor the majority of thoracic and abdominal tumors, moving serial organs such as the esophagus and duodenum are the organs at risk (OAR). The aim of the present study was to evaluate the feasibility of real-time monitoring of a fiducial marker in the digestive tract and to analyze the motion of the OAR so as to determine a reasonable internal margin.Materials/MethodsA fluoroscopic real-time tumor-tracking radiotherapy (RTRT) system was used to monitor the position of a metallic fiducial marker in or near the digestive tract every 0.03 s by means of two sets of diagnostic fluoroscopy in the treatment room. We developed two methods to insert a fiducial marker into or near the digestive tract adjacent to the target volume. One method involves an intra-operative insertion technique using a thread and a bead, a 2.0-mm gold marker with a 0.5-mm pinhole. The bead can be fixed by suturing the thread into or near the organs at risk. The other technique involves endoscopic insertion of the marker into the submucosal layer of the normal digestive tract with the aid of a special long needle (Olympus, Tokyo) to avoid dropping the fiducial markers from the mucosal surface. The feasibility of inserting the submucosal marker and the stability of the marker were evaluated in this study. The motion of the esophagus and duodenum was evaluated using tracking data from the RTRT system. The position of the marker in the OAR was monitored during irradiation so as to not irradiate the tumor when the marker in the OAR was moving into the high-dose region.ResultsThirty-two patients were entered into this study. Fourteen markers (two in the mediastinum and 12 in the abdomen) in 14 patients were implanted intra-operatively without any displacement. Nineteen markers (13 in the esophagus, 2 in the stomach, and 4 in the duodenum) in 18 patients were implanted into the submucosal layer using endoscopy. The marker was successfully implanted into the submucosal layer and maintained in the same place in 12/13 cases in the esophagus, 1/2 in the stomach, and 3/4 in the duodenum. No symptomatic adverse effects related to insertion of the marker were demonstrated. The mean/standard deviation of the range of motion (median, 95% confidence interval of the marker position) of the esophagus was 3.5/1.8 (3.3, 1.5 - 6.8) mm, 8.2/3.8 (8.4, 1.3 - 15.4) mm, and 3.8/2.6 (2.6, 2.0 - 10.8) mm for lateral (R-L), cranio-caudal (C-C), and antero-posterior (A-P) directions, respectively. Respiratory and cardiac motion was detected in the frequency analysis. The magnitude of the motion varied individually and changed during the delivery of irradiation in the same patient. The range of motion was the largest in the C-C direction in 9 patients, the A-P direction in 2 patients, and in the R-L direction in none. The median range of motion (95% confidence interval of the marker position) of the duodenum was 10.4 (6.8 - 11.6) mm, 22.2 (11.2 - 25) mm, and 10.5 (10.4 - 16.2) mm for the R-L, C-C, and A-P directions, respectively. The frequency analysis showed the duodenal motion to be influenced by involuntary bowel movement as well as respiratory motion.ConclusionsIntra-operative and endoscopic insertion of a fiducial marker into the gastro-intestinal tract for the monitoring of organs at risk is safe and feasible. The motion analysis suggested that the internal margin should be determined to cover a mean range of 4, 8, and 4 mm for the esophagus and 10, 22, and 11 mm for the duodenum in R-L, C-C, and A-P directions, respectively. Using fluoroscopic individual verification of the marker every treatment day, the margin for internal motion can be individualized, and unnecessary irradiation of these digestive tracts can be significantly reduced Purpose/ObjectiveFor the majority of thoracic and abdominal tumors, moving serial organs such as the esophagus and duodenum are the organs at risk (OAR). The aim of the present study was to evaluate the feasibility of real-time monitoring of a fiducial marker in the digestive tract and to analyze the motion of the OAR so as to determine a reasonable internal margin. For the majority of thoracic and abdominal tumors, moving serial organs such as the esophagus and duodenum are the organs at risk (OAR). The aim of the present study was to evaluate the feasibility of real-time monitoring of a fiducial marker in the digestive tract and to analyze the motion of the OAR so as to determine a reasonable internal margin. Materials/MethodsA fluoroscopic real-time tumor-tracking radiotherapy (RTRT) system was used to monitor the position of a metallic fiducial marker in or near the digestive tract every 0.03 s by means of two sets of diagnostic fluoroscopy in the treatment room. We developed two methods to insert a fiducial marker into or near the digestive tract adjacent to the target volume. One method involves an intra-operative insertion technique using a thread and a bead, a 2.0-mm gold marker with a 0.5-mm pinhole. The bead can be fixed by suturing the thread into or near the organs at risk. The other technique involves endoscopic insertion of the marker into the submucosal layer of the normal digestive tract with the aid of a special long needle (Olympus, Tokyo) to avoid dropping the fiducial markers from the mucosal surface. The feasibility of inserting the submucosal marker and the stability of the marker were evaluated in this study. The motion of the esophagus and duodenum was evaluated using tracking data from the RTRT system. The position of the marker in the OAR was monitored during irradiation so as to not irradiate the tumor when the marker in the OAR was moving into the high-dose region. A fluoroscopic real-time tumor-tracking radiotherapy (RTRT) system was used to monitor the position of a metallic fiducial marker in or near the digestive tract every 0.03 s by means of two sets of diagnostic fluoroscopy in the treatment room. We developed two methods to insert a fiducial marker into or near the digestive tract adjacent to the target volume. One method involves an intra-operative insertion technique using a thread and a bead, a 2.0-mm gold marker with a 0.5-mm pinhole. The bead can be fixed by suturing the thread into or near the organs at risk. The other technique involves endoscopic insertion of the marker into the submucosal layer of the normal digestive tract with the aid of a special long needle (Olympus, Tokyo) to avoid dropping the fiducial markers from the mucosal surface. The feasibility of inserting the submucosal marker and the stability of the marker were evaluated in this study. The motion of the esophagus and duodenum was evaluated using tracking data from the RTRT system. The position of the marker in the OAR was monitored during irradiation so as to not irradiate the tumor when the marker in the OAR was moving into the high-dose region. ResultsThirty-two patients were entered into this study. Fourteen markers (two in the mediastinum and 12 in the abdomen) in 14 patients were implanted intra-operatively without any displacement. Nineteen markers (13 in the esophagus, 2 in the stomach, and 4 in the duodenum) in 18 patients were implanted into the submucosal layer using endoscopy. The marker was successfully implanted into the submucosal layer and maintained in the same place in 12/13 cases in the esophagus, 1/2 in the stomach, and 3/4 in the duodenum. No symptomatic adverse effects related to insertion of the marker were demonstrated. The mean/standard deviation of the range of motion (median, 95% confidence interval of the marker position) of the esophagus was 3.5/1.8 (3.3, 1.5 - 6.8) mm, 8.2/3.8 (8.4, 1.3 - 15.4) mm, and 3.8/2.6 (2.6, 2.0 - 10.8) mm for lateral (R-L), cranio-caudal (C-C), and antero-posterior (A-P) directions, respectively. Respiratory and cardiac motion was detected in the frequency analysis. The magnitude of the motion varied individually and changed during the delivery of irradiation in the same patient. The range of motion was the largest in the C-C direction in 9 patients, the A-P direction in 2 patients, and in the R-L direction in none. The median range of motion (95% confidence interval of the marker position) of the duodenum was 10.4 (6.8 - 11.6) mm, 22.2 (11.2 - 25) mm, and 10.5 (10.4 - 16.2) mm for the R-L, C-C, and A-P directions, respectively. The frequency analysis showed the duodenal motion to be influenced by involuntary bowel movement as well as respiratory motion. Thirty-two patients were entered into this study. Fourteen markers (two in the mediastinum and 12 in the abdomen) in 14 patients were implanted intra-operatively without any displacement. Nineteen markers (13 in the esophagus, 2 in the stomach, and 4 in the duodenum) in 18 patients were implanted into the submucosal layer using endoscopy. The marker was successfully implanted into the submucosal layer and maintained in the same place in 12/13 cases in the esophagus, 1/2 in the stomach, and 3/4 in the duodenum. No symptomatic adverse effects related to insertion of the marker were demonstrated. The mean/standard deviation of the range of motion (median, 95% confidence interval of the marker position) of the esophagus was 3.5/1.8 (3.3, 1.5 - 6.8) mm, 8.2/3.8 (8.4, 1.3 - 15.4) mm, and 3.8/2.6 (2.6, 2.0 - 10.8) mm for lateral (R-L), cranio-caudal (C-C), and antero-posterior (A-P) directions, respectively. Respiratory and cardiac motion was detected in the frequency analysis. The magnitude of the motion varied individually and changed during the delivery of irradiation in the same patient. The range of motion was the largest in the C-C direction in 9 patients, the A-P direction in 2 patients, and in the R-L direction in none. The median range of motion (95% confidence interval of the marker position) of the duodenum was 10.4 (6.8 - 11.6) mm, 22.2 (11.2 - 25) mm, and 10.5 (10.4 - 16.2) mm for the R-L, C-C, and A-P directions, respectively. The frequency analysis showed the duodenal motion to be influenced by involuntary bowel movement as well as respiratory motion. ConclusionsIntra-operative and endoscopic insertion of a fiducial marker into the gastro-intestinal tract for the monitoring of organs at risk is safe and feasible. The motion analysis suggested that the internal margin should be determined to cover a mean range of 4, 8, and 4 mm for the esophagus and 10, 22, and 11 mm for the duodenum in R-L, C-C, and A-P directions, respectively. Using fluoroscopic individual verification of the marker every treatment day, the margin for internal motion can be individualized, and unnecessary irradiation of these digestive tracts can be significantly reduced Intra-operative and endoscopic insertion of a fiducial marker into the gastro-intestinal tract for the monitoring of organs at risk is safe and feasible. The motion analysis suggested that the internal margin should be determined to cover a mean range of 4, 8, and 4 mm for the esophagus and 10, 22, and 11 mm for the duodenum in R-L, C-C, and A-P directions, respectively. Using fluoroscopic individual verification of the marker every treatment day, the margin for internal motion can be individualized, and unnecessary irradiation of these digestive tracts can be significantly reduced