Evaluation of the truebeam machine performance check (MPC): OBI X-ray tube alignment procedure.

Alignment of the On-Board Imager (OBI) X-ray tube is important for ensuring imaging to treatment isocenter coincidence, which in turn is important for accurate Image Guided Radiotherapy (IGRT). Varian introduced a new X-ray tube alignment procedure for the TrueBeam linac in software version 2.5 MR2 as part of the machine performance check (MPC) application.

A proposed method for linear accelerator photon beam steering using EPID.

Beam steering is the process of calibrating the angle and translational position with which a linear accelerator's (linac's) electron beam strikes the x-ray target with respect to the collimator rotation axis. The shape of the dose profile is highly dependent on accurate beam steering and is essential for ensuring correct delivery of the radiotherapy treatment plan. Traditional methods of beam steering utilize a scanning water tank phantom that makes the process user-dependent.

Automatic Substitute Computed Tomography Generation and Contouring for Magnetic Resonance Imaging (MRI)-Alone External Beam Radiation Therapy From Standard MRI Sequences.

Purpose: To validate automatic substitute computed tomography CT (sCT) scans generated from standard T2-weighted (T2w) magnetic resonance (MR) pelvic scans for MR-Sim prostate treatment planning.

Patients And Methods: A Siemens Skyra 3T MR imaging (MRI) scanner with laser bridge, flat couch, and pelvic coil mounts was used to scan 39 patients scheduled for external beam radiation therapy for localized prostate cancer. For sCT generation a whole-pelvis MRI scan (1.

Transit dosimetry in IMRT with an a-Si EPID in direct detection configuration.

In this study an amorphous silicon electronic portal imaging device (a-Si EPID) converted to direct detection configuration was investigated as a transit dosimeter for intensity modulated radiation therapy (IMRT). After calibration to dose and correction for a background offset signal, the EPID-measured absolute IMRT transit doses for 29 fields were compared to a MatriXX two-dimensional array of ionization chambers (as reference) using Gamma evaluation (3%, 3 mm). The MatriXX was first evaluated as reference for transit dosimetry.

Evaluation of an a-Si EPID in direct detection configuration as a water-equivalent dosimeter for transit dosimetry.

Purpose: A major problem associated with amorphous silicon (a-Si) electronic portal imaging devices (EPIDs) for transit dosimetry is the presence of a phosphor layer, which can introduce large deviations from water-equivalent behavior due to energy-dependent response and visible light scattering. In this study, an amorphous silicon EPID was modified to a direct detection configuration by removing the phosphor layer, and the accuracy of using it for transit dosimetry measurements was investigated for 6 and 18 MV treatment beams by comparison to ion-chamber in water measurements.

Methods: Solid water and copper were both evaluated as buildup materials.