A collapsed-cone based transit EPID dosimetry method.

PURPOSE: To develop a transit-dose portal dosimetry method based on a commercial collapsed-cone algorithm. METHODS: A Varian Clinac21EX (Varian Medical Systems, USA), equipped with an amorphous-silicon EPID aS1000, was used. Dose calculations were performed with the collapsed-cone algorithm of Pinnacle3 v8.0 m (Philips Medical Systems, USA). A model for the energy of 6 MV was made in Pinnacle3 and afterwards validated for clinical use. A virtual phantom with different densities was contoured and superimposed on the patient images, simulating the presence of the EPID during the treatment. Corrections for photon spectral variations were introduced using Matlab (Mathworks, USA). Transit dosimetry was verified with an anthropomorphic phantom, on which different treatment fields were simulated in locations of skull, thorax and pelvis. In addition, a prostate treatment with IMRT was administered thereon. Dose distributions were compared with gamma index. RESULTS: The dose differences at the central point did not exceed 2%, except for the 20 x 20 cm2 field size centered in the skull. The model presented in this work, assumes that the dimensions of the solid water phantom, are infinite, except for the thickness. The mean values for the gamma index pass rates were 85.62% for (3%, 3 mm), 91.73% (4%, 3 mm) and 95.68% (5%, 3 mm). CONCLUSIONS: The value of 95% for γ (5%, 3 mm) can be established as the value below which the origin of the discrepancies should be investigated. It should be considered that the proposed method is complementary and not a substitute for pre-treatment dosimetry.

Right lateral versus left lateral view for forearm coronary angiography. An operator radiation exposure and image quality study.

OBJECTIVES: The aim of this study was to analyze the operator radiation exposure (ORE) and the image quality in a coronary angiography (CA) of the standard left lateral view (LLV) and compare it with an alternative right lateral view (RLV). BACKGROUND: Interventional cardiologists are exposed to high doses of scatter radiation, especially in angulated projections. METHODS: We prospectively included consecutive patients who underwent diagnostic CA. A standard +90° LLV and an alternative RLV (-90°) were done in each patient with the same protocol. The operator effective dose rate (mSv/h) was determined for each projection with digital dosimeters located in the collar, waist and knee. The image quality of both the LLV and RLV was analyzed and compared to a standard projection. RESULTS: 116 patients were enrolled; left coronary artery (LCA) was assessed in 52 patients and right coronary artery (RCA) in 64 patients. The ORE was significantly lower with the RLV compared to the conventional LLV with a maximum ORE reduction of 91.5% in the operator waist (LLV: 6.84 mSv h-1 versus RLV: 0.58 mSv h-1, p < 0.001). No significant differences in image quality were observed for the RCA in both projections. For the LCA, a slight loss of quality was observed with the RLV. CONCLUSIONS: -90° RLV is associated with a significant decrease in ORE compared to the conventional +90° LLV without losing image resolution for the RCA and resulting in a slight quality loss for the LCA evaluation. The RLV should be the first choice for RCA evaluation. For the LCA, the RLV loss of resolution should be balanced with the benefit of minimizing ORE, mainly in cases with long fluoroscopy times, such as complex percutaneous coronary interventional procedures.