Abstract

INTRODUCTION

The success of radiotherapy treatment is related with accuracy of dose delivery directly. The exact dose calculation of target volume and healthy organs surround are critically important. The most important effect of calculation algorithms on dosimetric calculations is the physical properties of the material being interacted. Tumor and healthy lung tissue are affected by respiratory motion. therefore, the shape, position, density of the tumor and lung could change in tomography images. The serespiratory variations could change the size of tumor volume, the Hounsfield Unit and electron density of the treatment region.

METHODS

In our study, normalCT, BreathHoldCT and AverageCT (4DCT) scans were performed for 13 lung SBRT patients. The tumor volumes (GTV) were investigated for 13 patients patients who were scanned with each technique. The electron density and Hounsfield Unit values which are important for dose calculation were compared for three scanning techniques.

RESULTS

We determined Tumor volume (GTV) 19.3% larger at NormalCT and 31.3% larger at AverageCT than BreathHoldCT. Density of GTV decreased in NormalCT and AverageCT, while healty lung tissiues’s density were increasing. Electron density and Hounsfield Unit values at NormalCT and AverageCT were similar with healthy lung tissue. We obtained higher values For GTV, in NormalCT. In terms of electron density and Hounsfield Unit values at GTV were equivalent the water results with BreathHoldCT. The biggest difference was found in AverageCT.

DISCUSSION AND CONCLUSION

Distortion and artifacts were caused by respiratory movement which were minimized by BreathHoldCT. More solid and clear boundary images could obtain with BreathHoldCT. Electron density and Hounsfield Unit values could be calculated more accurately, independent of respiratory motion With BreathHoldCT. Lung density is increasing in NormalCT and AverageCT, which affects the dose distribution in healthy lung.