physical and equivalent biologic dose received by the spinal cord during thoracic irradiation

ABSTRACT

The anteroposterior separation at the level of the thoracic vertebrae 4 and 5 and the depth of the spinal cord from the posterior chest wall were measured for a random sample of 50 Egyptian patients referred to Kasr El-Eini Center of Radiation Oncology and Nuclear Medicine [NEMROCK]. Assuming that the spinal cord is at the central axis beam, the dose received by the spinal cord was calculated using the percentage depth dose tables for Cobalt-60 [SSD-80] and 10 MV linear accelerator [FSD=100]. For two parallel opposed fields techniques of irradiation, it was found that the spinal cord received a higher dose [up to 10%] than that prescribed at the reference point [midline]. The larger the separation, the higher the dose received by the thoracic spinal cord. For internal mammary field, [in breast cancer cases] it was found that the spinal cord received about 50% or more of the prescribed dose. Moreover, the biological equivalence of the physical dose absorbed at the spinal cord was calculated using the linear Quadratic Model