Correction Method on Mismatched Posterior Edge of Medial and Lateral Tangential Fields for Three Fields Techniques in Breast Cancer / 대한방사선종양학회지

PURPOSE: The target volume for the three field technique in breast cancer include the breast tangential and supraclavicular areas. The techniques rotating the gantry and couch angles, to match these two areas, will geometrically produce mismatching of the posterior edge between the medial and lateral tangential beams. This mismatch was confirmed by film dosimetry and three-dimensional computer planning. The correction methods of this mismatching were studied in this article. MATERIALS AND METHODS: After the supraclavicular field was simulated using a half beam block and the medial and lateral tangential fields, by the rotation of the couch and gantry, we compared the following two methods to correct the mismatch. The first method was the rotation of collimator until a line drawn on the posterior edge of tangential beams before the rotation of couch aligned the line drawn on the posterior edge after the rotation. The second method was the rotation of collimator according to the formula developed by the author as follows; Co=2sin(-1){sin angle x sin (C/2)} (Co: collimator angle, angle: angle between tangential beam and table, C: couch angle) RESULTS: The film dosimetry showed the mismatching of posterior edges of the medial and lateral tangential fields prior to the rotation of collimator, while the posterior edges matched well after the rotation of collimator according to the formula. The three-dimensional computer plan also showed that the posterior edges matched well after the rotation of collimator accordingly. The DVH of the ipsilateral lung with the proper rotation of collimator angle was better than that without the rotation of collimator angle. CONCLUSION: The mismatching of the posterior edges of the medial and lateral tangential fields can be recognized on the three field technique in breast irradiation when the gantry and couch are simultaneously rotated and can be corrected with the proper rotation of the collimator angle. The radiation dose to the ipsilateral lung could be lowered with this technique.

Lumbar disk herniation associated with posterior bony edge separation of the vertebral body / 中华骨科杂志

Objective To study the mechanism and the nomenclature of the lumbar disk herniation associated with posterior bony edge separation of the vertebral body, based on its CT findings in transverse and sagittal planes. Methods 18 patients with lumbar disk herniation were evaluated with the CT scan and sagittal reconstruction. Results There were 19 lumbar herniated disks associated with separated posterior bony edge of the vertebral body which protruded into the spinal canal. There was bony defect filled with disk material. In the sagittal plane, the bony separation and the posterior edge of the vertebral body formed the “V” type defect at 15 levels, and 4 were irregular or triangular. 15 cases of the disc herniation had bony separations and 4 had bone connection with the vertebral body. There were bony defect and sclerosis on the vertebral body edge. Conclusion The main mechanism was the separation compression of the herniated disk on the posterior vertebral body. The bony separation was the secondary change. So the authors suggest that such anatomical pathologic changes be named as intervertebral disk herniation associated with posterior bony separation of the lumbar vertebrae.