RADIOTHERAPY OF THE ESOPHAGEAL CANCER USING PARALLEL OPPOSED 4 FIELDS WITH THEIR MEDIAL HALVES BEING BLOCKED

This method was investigated to decrease the lung and spinal cord radiation dose and volume dose.The beam was angled 20 degrees to the left and right from mid-line. Four fields with their medial halves being blocked, 2 from anterior and 2 from posterior, were used in opposed fashion.The dose distribution around the tumor were ideally obtained setting the ratio of anterior and posterior dose to 1:2.The radiation dose to the spinal cord was below 65% of total tumor dose. Although volume dose and radiated area of the lung by this method were greater than paralleled opposed 2 field method which was the worst one for the spinal cord injury, they were less than inverted Y method, rotatory method, and other conventional methods.Thus, the radiation dose to the normal tissue may be minimal in the majority of patients with the esophageal cancer.This method is easy to perform and easy to apply clinically. In particular, the method may be superior if the cancer involved long area of the esophagus.