Attempt for a Complete Protocol of TBI

Abstract

As the dose inside tissue is strongly dependent on the density of the desired object, every patient is scanned in 8 planes on the CT. In the following the calculation of lung dose is done by a treatment planning system using an inhomogeneity correction. The dose inside the lung is calculated pixel by pixel for every patient undergoing TBI. It can be shown that the resulting dose distribution will always lead to differences inside the lung of the order of 0.5–1 Gy. However these differences exist only in small areas, the edges of the lung. The mean lung dose, defined as the average over the lung area, is the most representative number and is calculated individually. It can be seen that the dose values and the dose differences inside the lung vary strongly. The reason for this is, that the relation between lung area and lung body area within the CT-slice is varying strongly from patient to patient. Therefore the shielding of the lung is calculated individually for every patient and the resulting dose is reduced below 8 Gy. Similarly the dose distribution and shielding is calculated for neck and head. After the 8th patient the doserate was lowered from 12–20 down to 4cGy/min on the body surface during radiation on. Additionally with the reduction of doserate the total absorbed dose in the abdomen midplane was not considered a criterion of radiation anymore. We believe, the abdomen dose should result from the average of the dose on 4 points on the surface in the lung plane with 10.5 Gy. A planning technique measuring these 4 points with TLD’s without calculating the correct lung size is missing the enormous differences in lung dose.