DOSIMETRIC EVALUATION OF TWO DIFFERENT TOTAL BODY IRRADIATON TECHNIQUES USING ECLIPS TREATMENT PLANNIG SYSTEM

Purpose : This study compares the organ doses at risk by using the Eclipse treatment planning system for two common total body irradiation techniques (TBI) at extended source skin distance.

Material and Methods: 3D treatment plans with AP-PA (anteroposterior) technique were created retrospectively for 20 patients treated bilateral TBI. For each patient, the whole body, kidneys, lungs, thyroid and liver were contoured to create (DVH) dose volume histograms and examine 3D dose volume distributions. The mean doses of thyroid, lung, kidney, liver, whole body and treatment volumes and the maximum doses of 2% volumes (D2) were calculated from the dose volume histogram and transferred to the SPSS file. The non-parametric Wilcoxon test was used to compare the dose values for two techniques.

Results: Thyroid gland mean doses were significantly lower in lateral technique (11.98 and 12.64 Gy, p = 0.21). It was observed no statistically dose difference between the two techniques in terms of lung doses. Since, the lungs were protected by lead blocks in both of two techniques. The mean doses of liver and kidney were lower in the lateral TBI technique (p = 0.002 and p = 0.004, respectively). D₂ doses of liver were lower in AP-PA planning technique (p = 0.032). In comparison of the hot points between the two techniques, the lateral position was significantly superior (p <0.0001).

Conclusions: In present study, it was observed that the bilateral position was superior to the AP-PA position in order to prevent the hot spots. In the AP-PA position, it is more difficult to tolerate the body irregularities. Additionally, when comparing the dose distributions of the organs (liver, kidney, thyroid), it was seen that the results were statistically better in the lateral position. The lateral position provides an advantage in terms of more homogenous dose distribution and better quality planning.