Purpose: This study aimed to evaluate the effects of having a detailed electron density (ED) curve in dose calculation and compare it with the standard electron density curve using CATphan.
Methods: A Philips Bigbore PET/CT scanner was used in this study with the same parameters for image acquisition, energy (120 kVp), current (700 mAs), slice thickness (1 mm). Images ware exported to Eclipse TPS, utilising AcurosXB algorithm. Two Hounsfield unit-electron density (HU-ED) curves were plotted in TPS; different planning techniques were used from a single field, multiple fields and VMAT technique all with an equal number of Monitor units for each plan (200 MU). Three phantoms were used in this study. Namely, a CATphan model 504 include 7 inserts with electron density ranging from (Air 0.004 up to Teflon 6.243), CIRS model 062 include 26 inserts with ED ranging from (Lung inhale 0.205 up to StainlessSteel 23.101), and universal body phantom with metal inserts used for absolute dose verification with variety of beam energies (6 MV up to 10 MV FFF). Measurements were carried out in Varian TrueBeam 2.7, using CC13 IBA ion-chamber.
Results: A significant improvement in dose calculation was noticed based on the measurement that was performed. The maximum difference between the two curves ware obtained in a single field in stainless steel +8.9%, and the minimum difference was in soft tissue +0.3%. A consistent result also measured in verification plans an enhancement in multiple fields by +2.9% and +1.4% in VMAT.
Conclusion: The effect of using the HU-ED conversion curve with more calibration points and extended to include metals that could be present in the patient's body is shown to be important in overall dose calculation. The inclusion of the proposed HU-ED conversion provides enhanced dose calculation and hence, better clinical assessment.