[Acquisition of Pulmonary Vein and Left Atrium with Trigger Angiography Non-contrast Enhanced MRI in Diastolic Phase].

OBJECTIVE: The aim of this study was to compare the image quality and the visibility of trigger angiography non-contrast enhanced (TRANCE) in diastolic phase and 3D balanced steady-state free precession (3D SSFP) sequences for the evaluation of pulmonary vein (PV) and left atrium (LA). METHODS: About 10 volunteers underwent TRANCE and 3D SSFP imaging on 1.5 T MRI. Axial images were reconstructed and regions of interest were positioned on the right superior pulmonary vein (RSPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), LA, and left atrial appendage (LAA). Contrast-to-noise ratio (CNR) between each part and muscle were calculated and compared between two sequences. The two observers independently scored the image quality of each image on the basis of PV, LA, and LAA anatomy and contour using a five-point scale, which scores were averaged and compared. RESULTS: CNRs on RSPV, RIPV, LSPV, LIPV, LA, and LAA were significantly higher in TRANCE sequence compared with 3D SSFP sequence. On visual assessment, TRANCE showed significantly higher scores in RSPV, RIPV, LSPV, LIPV compared with 3D SSFP sequence. CONCLUSIONS: TRANCE provides higher image quality in PVs and LA compared with 3D SSFP on 1.5 T MRI. On visual assessment, TRANCE provides better visibility of PVs anatomy and contour compared with 3D SSFP.

Volumetric Modulated Arc Therapy Planning for Craniospinal Irradiation With a New O-ring Linac.

This study aims to determine the feasibility of using a new O-ring linear accelerator (Halcyon, Varian Medical Systems, CA, USA) to perform treatment planning using volumetric modulated arc therapy (VMAT) for craniospinal irradiation (CSI). A 20-year-old male patient with leukemia was selected. The planning target volume (PTV) was contoured to include the entire contents of the brain and spinal canal. The PTV margin was 10 mm applied to the clinical target volume (CTV). VMAT (RapidArc, Varian Medical Systems, CA, USA) planning was performed using four isocenter with five arcs, two full rotation arcs to cover the brain and upper part of the spinal cord, and one full rotation arc for the lower part of the spinal cord. The plan was created using the auto-feathering photon optimizer calculation of the planning system. The conformity index (CI) and heterogeneity index (HI) as well as dose-volume histograms of organs at risk (OAR) were evaluated. The patient position of ±3.0 mm in the craniocaudal direction was moved in to simulate the effect of treatment inaccuracy. The total treatment time was also measured. The CI and HI were 1.09 and 8.44, respectively. The mean dose (PTV) was 105.5%, and the mean dose (OARs) was lower than the planning dose constraints. Simulations with a patient position shift of ±3.0 mm resulted in an error of less than ±10.0% of the planned dose to the spinal cord. The total treatment time was within 15 minutes. VMAT planning for CSI with Halcyon achieved high conformality, uniform dose distribution, low dose to the surrounding normal tissues, and reduced treatment time.

[Influence on measurements of pre-irradiation due to differences in ionization chamber shape or frequency in use].

Ionization chamber measurements in radiation therapy should be repeatedly performed until a stable reading is obtained. Ionization chambers exhibit a response which depends on time elapsed since the previous irradiation. In this study, we investigated the response of a set of two Farmer-style, one Plane parallel, and seven small ionization chambers, which are exposed to 4, 6, 10, and 14 MV. The results show that Farmer-style and Plane parallel ionization chambers settle quickly within 9-20 min. On the other hand, small ionization chambers exhibit settling times of 12-33 min for 6, 10, and 14 MV. It will take longer for a settling time of 4 MV. The settling time showed time dependent irradiation. The first reading was up to 0.76% lower in the Farmer-style and Plane parallel ionization chambers. The small ionization chambers had a 2.60% lower first reading and more gradual response in reaching a stable reading. In this study, individual ionization chambers can vary significantly in their settling behavior. Variation of the responses on ionization chambers were confirmed not only when radiation was not used for a week but also when it was halted for a month. Pre-irradiation of small ionization chambers is clearly warranted for eliminating inadvertent error in the calibration of radiation beams.

[A study of collimator scatter factors of rectangular irradiation fields using the virtual source plane].

Kim introduced the geometric weighting factor concept into the field mapping method, and estimated collimator scatter factors of rectangular fields by correcting collimator exchange effects. The source plane is present at a specific position in the field mapping method, and, accordingly, the geometric weighting factor is constant. In this study, we changed the position of the source plane based on the measurement results, and we estimated the collimator factors of rectangular fields using the field mapping method. A geometric weighting factor at which the measured collimator scatter factors optimally fitted a square collimator scatter factor was calculated in each field. Collimator scatter factors can be accurately calculated recursively by changing the geometric weighting factor, resulting in altering the position of the source plane, as in this method.

Polarity effect in commercial ionization chambers used in photon beams with small fields.

Ionization chambers are the instruments of choice for use in photon dosimetry. Ionization chambers together with radiographic films represent the best detectors for measurement of dose distribution for a quality assurance (QA) program in intensity-modulated radiotheraphy (IMRT). The polarity effect was investigated for seven different commercially available ionization chambers. This study concentrated on measuring the dependence of the polarity effect at various energies, and for various field size, ionization chamber, and electrometer combinations. Of the seven chambers, CC01, PTW23323, and PTW31006 had the largest polarity effect for small field sizes. The materials of the central electrode of these three chambers were steel or air-equivalent plastic C-552. The magnitude of the polarity effect was shown to be strongly dependent on the material of the collecting electrode. This polarity effect dependence was observed for the ionization chambers and small field sizes studied.