Magnetic field induced dose effects in radiation therapy using MR-linacs.

MR-guided radiotherapy (MRgRT) is one of the most significant advances in radiotherapy in recent years. The hybrid systems were designed to visualize patient anatomical and physiological changes during the course of radiotherapy, enabling more precise treatment. However, before MR-linacs reach their full potential in delivering safe and accurate treatments to patients, the radiotherapy team must understand how a magnetic field alters the dosimetric properties of the radiation beam and its potential impact on treatment quality and clinical outcomes.

Clinical implementation of kVCT-guided tomotherapy with ClearRT.

A helical fan-beam kilovoltage computed tomography (kVCT) was recently introduced into Tomotherapy units. This study aims to share the initial experience of kVCT in clinical workflow, compare its performance with that of the existing megavoltage computed tomography (MVCT), and explore its potential in adaptive planning. We retrospectively enrolled 23 patients who underwent both MVCT and kVCT scans.

Effects on skin dose from unwanted air gaps under bolus in an MR-guided linear accelerator (MR-linac) system.

Bolus is commonly used in MV photon radiotherapy to increase superficial dose and improve dose uniformity for treating shallow lesions. However, irregular patient body contours can cause unwanted air gaps between a bolus and patient skin. The resulting dosimetric errors could be exacerbated in MR-Linac treatments, as secondary electrons generated by photons are affected by the magnetic field.

A novel method for monitoring the constancy of beam path accuracy in CyberKnife.

The aim of current work was to present a novel evaluation procedure implemented for checking the constancy of beam path accuracy of a CyberKnife system based on ArcCHECK. A tailor-made Styrofoam with four implanted fiducial markers was adopted to enable the fiducial tracking during beam deliveries. A simple two-field plan and an isocentric plan were created for determining the density override of ArcCHECK in MultiPlan and the constancy of beam path accuracy respectively.

Performance evaluation of the CyberKnife system in real-time target tracking during beam delivery using a moving phantom coupled with two-dimensional detector array.

The aim of the current study was to evaluate the tracking error of the Synchrony Respiratory Tracking system by conducting beam-by-beam analyses to determine the variation in the tracking beams measured during target motion. A moving phantom of in-house design coupled with a two-dimensional (2D) detector array was used to simulate respiratory motion in the superoinferior (SI) and anteroposterior (AP) direction. A styrofoam block with four implanted fiducial markers was placed on top of the detector to enable the fiducial-based respiratory tracking.

Development of a novel methodology for QA of respiratory-gated and VMAT beam delivery using Octavius 4D phantom.

The objective of this study was to develop and evaluate a series of quality assurance (QA) techniques based on Octavius 4D phantom for testing of respiratory-gated treatment delivery, integrity of dose rate vs gantry speed in volumetric-modulated arc therapy (VMAT) commissioning, and multileaf collimator (MLC) positioning accuracy of a linear accelerator. An Octavius 4D phantom capable of rotating with the gantry and recording the detector signal with a sampling rate of 10 Hz was isocentrally set up and an inclinometer was also installed to measure the gantry angle simultaneously. A simple arc test was created and delivered with gating function activated to measure the timing accuracy of the gating window.

Accuracy in contouring of small and low contrast lesions: comparison between diagnostic quality computed tomography scanner and computed tomography simulation scanner-A phantom study.

To evaluate the accuracy in detection of small and low-contrast regions using a high-definition diagnostic computed tomography (CT) scanner compared with a radiotherapy CT simulation scanner. A custom-made phantom with cylindrical holes of diameters ranging from 2-9 mm was filled with 9 different concentrations of contrast solution. The phantom was scanned using a 16-slice multidetector CT simulation scanner (LightSpeed RT16, General Electric Healthcare, Milwaukee, WI) and a 64-slice high-definition diagnostic CT scanner (Discovery CT750 HD, General Electric Healthcare).

The dosimetric effect of zipper artifacts on tomotherapy adaptive dose calculation--a phantom study.

Tomotherapy adaptive dose calculation offers the ability to verify and adjust the therapeutic plan during the treatment. Using tomotherapy adaptive dose calculation, the planned fluence pattern can be used to recalculate the dose distribution on pretreatment megavoltage computed tomography (MVCT) images. Zipper artifacts, which appear as increased density in the central region of MVCT images, may affect the accuracy of adaptive dose recalculation.