| Objective: To evaluate the respiration-induced target volume motion and study the variance of dosimetry in 3DCRT for mid-thoracic esophageal carcinoma in order to guide the radiation oncologist to choose the expansion margin for ITV.Methods: From September 2007 to October 2008, 10 patients with mid-thoracic esophageal carcinoma from the Fourth Hospital of Hebei Medical University were included in this study. All patients were instablized with body thermoplastic membrane in free breathing (FB). They were first scanned by multi-spiral CT simulator in FB with the same position as before. And then they were re-scanned in breath-hold after normal inspiration and expiration (IBH and EBH) respectively with the same scanning range. Then the CT images of three series were transferred through local network to the treatment planning system (ADAC Pinnacle 8.0c) and reconstructed separately. The target volume and organs at risk (OARs) were outlined following the same standard. As the objective of this study was to evaluate the movement of GTV, the lymph nodes and their regional lymphatics were not included in the target. The motion of the center point of GTV, the center point of each slice of GTV and the edge of the GTV in selected slice was measured respectively to obtain the comprehensive value of GTV motion in three directions. The motion of the spinal cord, the diaphragm, the apexes of bilateral lungs and kidneys was measured at the same time. Plan1 was designed in the images of FB and transported completely to the images of IBH and EBH as Plan2 and Plan3 respectively to observe the dosimetric variance in target volume.Results: (1) The GTV motion between IBH and EBH: It was 0.23±0.17cm (mean±a standard variation), 0.54±0.17 cm, 0.21±0.17 cm in the left-right (X), the cranial and caudal (Y), and anterior-posterior (Z) directions. And the 95% confidence interval of the motion was 0.21~0.25cm, 0.53~0.56 cm, 0.19~0.22cm in three directions. (2) The direction of GTV motion: No motion was noticed in 8.2%, while 73.3% to the right side (0.27±0.17cm) and 18.5% to the left side (0.19±0.15cm) in the X-axis when IBH were compared with EBH. 100% were noticed to caudal in the Y-axis. In the Z-axis, No motion was noticed in 8.2%, while 16.6% to the posterior (0.13±0.13cm) and 75.2% to the anterior (0.25±0.17cm) when IBH were compared with EBH. (3) The comparison of different measuring methods of GTV motion: There was a statistical difference in different measuring methods of different respiratory phases besides no difference in Y axis of three different respiratory phases and X axis of between FB and EBH. (4) The comparison of GTV motion between FB-IBH and FB-EBH: A statistical difference was found in the X and Y axis for the comprehensive value, but no statistical difference was found in three directions when only measuring the motion of GTV center. There was also a statistical difference in the X and Y axis when measuring the motion of GTV center slice by slice. A statistical difference was only found in Y axis when measuring the edge motion of the GTV. (5) The GTV motion in different directions: Significant difference was found in all three directions when for all measuring methods (P=0.000). The motion in Y axis was the largest in numerical value. (6) The motion at OARs: The motion of the diaphragm and right kidney was larger in IBH-EBH than that in FB-EBH. No statistical difference was found in the motion of the spinal cord in three levels, the left and right apex of lungs, diaphragm, and kidneys. (7) The correlation analysis of GTV 3D motion: The 3D motion is correlated with the variance of lung volumes in IBH-EBH (r= 0.683,P=0.032) and without GTV volume and length. (8) Dosimetric evaluation of target volume in different plans: For GTV, there was a statistical difference in V100 of the three plans (P= 0.040). The V100 of the Plan1 and the Plan2 was both 100%, which was more than the 98.7% of the Plan3. No significant difference was found in other indexes of the three respiration phases. For CTV, the V100 and V95 were better in Plan1 and no significant difference was found in other indexes. While for PTV, the Dmin, V100 and V95 was better in Plan1 and no significant difference was found in other indexes. (9) Dosimetric evaluation of OARs in different plans: There were no significant difference in all the indexes for the spinal cord, lung and heart in the three plans.Conclusions: 1. The respiration-induced GTV motion in 3D-conformal radiotherapy for mid-thoracic esophageal carcinoma was 0.23±0.17cm, 0.54±0.17cm, 0.21±0.17cm in the X, Y and Z axis respectively. 2. Compared to EBH, the GTV tend to move to the right, the caudal and the anterior side in IBH. 3. The GTV motion for mid-thoracic esophageal carcinoma is correlated with the variance of lung volumes in IBH-EBH and without GTV volume and length. 4. The internal margin of mid-thoracic esophageal carcinoma from CTV to ITV is a radial margin of 0.3 cm and the cranial and caudal margin of 0.6 cm as reference. 5. The change in dose distribution was not so much with the standard expansion. It can meet the needs of clinical treatment. |
PDF Full Text Request