The treatment of esophageal cancer is made difficult by the close proximity of the esophagus to the spinal cord and the requirement to treat the esophageal target volume to doses greater than or equal to 60 Gy while limiting the cored dose to
less
than
or equal to 46 Gy. By placing the patient in the prone position, the esophagus can be displaced away from the spinal cord. We explored the results of this commonly used technique on 10 patients who have undergone simulation in both supine and
prone
positions both AP and lateral orthogonal radiographs were obtained in both positions. The distance between contrast material in the esophagus and spinal cord was noted in at least four transverse planes through the thoracic esophagus on each of
the 10
patients. the four transverse planes were located t 3 cm above the carina, at the carina, 3cm below the carina ad 6cm below the carina. The mean displacement (±1 SD) of the esophagus away from the spinal cord when the patient was in the prone
position
ocmpared to supine at each of these levels was 1.3(±0.8)cm, 1.6(±0.9)cm, 1.7(±1.0)cm, and 1.9(±1.1) cm. The range of displacement for all 40 displacement determinations was 0 to 4.3cm with a mean of 1.6cm. to evaluate further the consequences
of
prone positioning on treatment planing and doses received to target volumes and critical structures, we performed 3-dimesional treatment planning with a patient in both prone and supine position. The requirements were to achieve a tumor volume
dose
of
60 Gy while keeping the spinal cord dose below 46Gy. Two types of conventional treatment plans were examined in prone and supine positions. A 6-field plan consisted of delivery of 40 Gy through a large 3-field beam arrangement followed by
delivery
of 20
Gy through large 3-field beam arrangement followed by delivery of 20 Gy through a similar 3-field cone down. An 8-field plan involved the delivery of 30 Gy through AP/PA beams followed by a 3-field beam arrangement to 40 Gy and a subsequent
3-field
cone-down for the final 20 Gy. Regarding the primary consideration of coverage of target volume with avoidance of spinal cord, prone positioning was superior to supine positioning whether 6-or 8-field arrangements were used.
|