The impact of rectal spacers in MR-guided adaptive radiotherapy.

Background And Purpose: The use of stereotactic ablative radiotherapy (SABR) for prostate cancer has increased significantly. However, SABR can elevate the risk of moderate gastrointestinal (GI) side effects. Rectal spacers mitigate this risk by reducing the rectal dose.

Adapting outside the box: Simulation-free MR-guided stereotactic ablative radiotherapy for prostate cancer.

Background And Purpose: Magnetic resonance (MR)-guided radiotherapy (MRgRT) enhances treatment precision and adaptive capabilities, potentially supporting a simulation-free (sim-free) workflow. This work reports the first clinical implementation of a sim-free workflow using the MR-Linac for prostate cancer patients treated with stereotactic ablative radiotherapy (SABR).

Materials And Methods: Fifteen patients who had undergone a prostate-specific membrane antigen positron emission tomography/CT (PSMA-PET/CT) scan as part of diagnostic workup were included in this work.

Technical note: Cryostat transmission characterization for MR linac - temporal stability, clinical impact and change implementation.

Background: In the Unity MR linac (Elekta AB, Stockholm, Sweden), the radiation beam traverses the cryostat and the coil support structure. The resulting beam attenuation must be considered for output calibration and its variation with gantry angle must be characterized in the treatment planning system (TPS).

Purpose: The aim of this work was to investigate the impact of a change of the cryostat transmission characterization (CTC) curve, due to the helium level modification, on clinical treatment plan dosimetry and to report on the experience with the CTC curve update.

Towards simulation-free MR-linac treatment: utilizing male pelvis PSMA-PET/CT and population-based electron density assignments.

. This study aimed to investigate the dosimetric impact of using population-based relative electron density (RED) overrides in lieu of simulation computerized tomography (CT) in a magnetic resonance linear accelerator (MRL) workflow for male pelvis patients. Additionally, the feasibility of using prostate specific membrane antigen positron emission tomography/CT (PSMA-PET/CT) scans to assess patients' eligibility for this proposed workflow was examined.

MR-Linac guided adaptive stereotactic ablative body radiotherapy for recurrent cardiac sarcoma with mitral valve bioprosthesis - a case report.

We present the first case in the literature of a 78-year-old woman with recurrent cardiac sarcoma adjacent to a bioprosthetic mitral valve treated with magnetic resonance linear accelerator (MR-Linac) guided adaptive stereotactic ablative body radiotherapy (SABR). The patient was treated using a 1.5 T Unity MR-Linac system (Elekta AB, Stockholm, Sweden).

ACPSEM position paper: dosimetry for magnetic resonance imaging linear accelerators.

Consistency and clear guidelines on dosimetry are essential for accurate and precise dosimetry, to ensure the best patient outcomes and to allow direct dose comparison across different centres. Magnetic Resonance Imaging Linac (MRI-linac) systems have recently been introduced to Australasian clinics. This report provides recommendations on reference dosimetry measurements for MRI-linacs on behalf of the Australiasian College of Physical Scientists and Engineers in Medicine (ACPSEM) MRI-linac working group.

Introduction of radiation therapist-led adaptive treatments on a 1.5 T MR-Linac.

The introduction of magnetic resonance (MR) linear accelerators (MR-Linac) marks the beginning of a new era in radiotherapy. MR-Linac systems are currently being operated by teams of radiation therapists (RTs), radiation oncology medical physicists (ROMPs) and radiation oncologists (ROs) due to the diverse and complex tasks required to deliver treatment. This is resource-intensive and logistically challenging.

Old dogs, new tricks: MR-Linac training and credentialing of radiation oncologists, radiation therapists and medical physicists.

The introduction of magnetic resonance (MR) linear accelerators (MR-Linacs) into radiotherapy departments has increased in recent years owing to its unique advantages including the ability to deliver online adaptive radiotherapy. However, most radiation oncology professionals are not accustomed to working with MR technology. The integration of an MR-Linac into routine practice requires many considerations including MR safety, MR image acquisition and optimisation, image interpretation and adaptive radiotherapy strategies.

Experimental characterisation of the magnetic field correction factor,kB⃗,for Roos chambers in a parallel MRI-linac.

Reference dosimetry on an MRI-linac requires a chamber specific magnetic field correction factor,kB⃗.This work aims to measure the correction factor for a parallel plate chamber on a parallel MRI-linac.kB⃗is defined as the ratio of the absorbed dose to water calibration coefficient in the presence of the magnetic field,ND,wB⃗relative to that under 0 T conditions,ND,w0T.

Characterizing magnetically focused contamination electrons by off-axis irradiation on an inline MRI-Linac.

Purpose: The aim of this study is to investigate off-axis irradiation on the Australian MRI-Linac using experiments and Monte Carlo simulations. Simulations are used to verify experimental measurements and to determine the minimum offset distance required to separate electron contamination from the photon field.

Methods: Dosimetric measurements were performed using a microDiamond detector, Gafchromic EBT3 film, and MOSkin .

Early experience with MR-guided adaptive radiotherapy using a 1.5 T MR-Linac: First 6 months of operation using adapt to shape workflow.

Introduction: The magnetic resonance linear accelerator (MRL) offers improved soft tissue visualization to guide daily adaptive radiotherapy treatment. This manuscript aims to report initial experience using a 1.5 T MRL in the first 6 months of operation, including training, workflows, timings and dosimetric accuracy.

In-line MRI-LINAC depth dose measurements using an in-house plastic scintillation dosimeter.

Plastic scintillation dosimeters (PSDs) have many properties that make them desirable for relative dosimetry with MRI-LINACs. An in-house PSD, Farmer ionisation chamber and Gafchromic EBT3 film were used to measure central axis percentage depth dose distributions (PDDs) at the Australian MRI-LINAC Mean errors were calculated between each detector's responses, where the in-house PSD was on average within 0.7% of the Farmer chamber and 1.

Towards real-time 4D radiation dosimetry on an MRI-Linac.

4D radiation dosimetry using a highly radiation-sensitive polymer gel dosimeter with real-time quantitative magnetic resonance imaging (MRI) readout is presented as a technique to acquire the accumulated radiation dose distribution during image-guided radiotherapy on an MRI-Linac. Optimized T -weighted Turbo-Spin-Echo (TSE) scans are converted into quantitative ΔR maps and subsequently to radiation dose maps. The concept of temporal uncertainty is introduced as a metric of effective temporal resolution.

MRI-LINAC beam profile measurements using a plastic scintillation dosimeter.

Plastic scintillation dosimeters (PSDs) possess many desirable qualities for dosimetry with LINACs. These qualities are expected to make PSDs effective for MRI-LINAC dosimetry, however little research has been conducted investigating their dosimetric performance with MRI-LINACs. In this work, an in-house PSD was used to measure 8 beam profiles with an in-line MRI-LINAC, compared with film measurements.

Dosimetric Optimization and Commissioning of a High Field Inline MRI-Linac.

Unique characteristics of MRI-linac systems and mutual interactions between their components pose specific challenges for their commissioning and quality assurance. The Australian MRI-linac is a prototype system which explores the inline orientation, with radiation beam parallel to the main magnetic field. The aim of this work was to commission the radiation-related aspects of this system for its application in clinical treatments.

High resolution silicon array detector implementation in an inline MRI-linac.

Purpose: Dynamic dosimaging is a concept whereby a detector in motion is tracked with magnetic resonance imaging (MRI) to validate the amount and position of dose in a radiation therapy treatment on an MRI-linac. This work takes steps toward the realization of dynamic dosimaging with the novel high resolution silicon array detector: MagicPlate-512 (M512). The performance of the M512 was assessed in a 1.

Technical Note: Experimental characterization of the dose deposition in parallel MRI-linacs at various magnetic field strengths.

Purpose: Dose deposition measurements for parallel MRI-linacs have previously only shown comparisons between 0 T and a single available magnetic field. The Australian MRI-Linac consists of a magnet coupled with a dual energy linear accelerator and a 120 leaf Multi-Leaf Collimator with the radiation beam parallel to the magnetic field. Two different magnets, with field strengths of 1 and 1.

First measurements with a plastic scintillation dosimeter at the Australian MRI-LINAC.

MRI-LINACs combine MRI and LINAC technologies with the potential for image guided radiation therapy with optimal soft-tissue contrast. In this work, we present the advantages and limitations of plastic scintillation dosimeters (PSDs) for relative dosimetry with MRI-LINACs. PSDs possess many desirable qualities, including magnetic field insensitivity and irradiation angle independence, which are expected to make them suitable for dosimetry with MRI-LINACs.

Technical Note: The first live treatment on a 1.0 Tesla inline MRI-linac.

Purpose: This work describes the first live imaging and radiation delivery performed on a prototype 1.0 T inline MRI-Linac system in a rat brain tumor model, which was conducted on 29 January 2019.

Methods: A human scale 1.

Imaging performance of a dedicated radiation transparent RF coil on a 1.0 Tesla inline MRI-linac.

This work describes the first imaging studies on a 1.0 Tesla inline MRI-Linac using a dedicated transmit/receive RF body coil that has been designed to be completely radio transparent and provide optimum imaging performance over a large patient opening. A series of experiments was performed on the MRI-Linac to investigate the performance and imaging characteristics of a new dedicated volumetric RF coil: (1) numerical electromagnetic simulations were used to measure transmit efficiency in two patient positions; (2) image quality metrics of signal-to-noise ratio (SNR), ghosting and uniformity were assessed in a large diameter phantom with no radiation beam; (3) radiation induced effects were investigated in both the raw data (k-space) and image sequences acquired with simultaneous irradiation; (4) radiation dose was measured with and without image acquisition; (5) RF heating was studied using an MR-compatible fluoroptic thermometer and; (6) the in vivo image quality and versatility of the coil was demonstrated in normal healthy subjects for both supine and standing positions.

Photons, protons or carbon ions for stage I non-small cell lung cancer - Results of the multicentric ROCOCO in silico study.

Purpose: To compare dose to organs at risk (OARs) and dose-escalation possibility for 24 stage I non-small cell lung cancer (NSCLC) patients in a ROCOCO (Radiation Oncology Collaborative Comparison) trial.

Methods: For each patient, 3 photon plans [Intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT) and CyberKnife], a double scattered proton (DSP) and an intensity-modulated carbon-ion (IMIT) therapy plan were created. Dose prescription was 60 Gy (equivalent) in 8 fractions.

Benefit of particle therapy in re-irradiation of head and neck patients. Results of a multicentric in silico ROCOCO trial.

Background And Purpose: In this multicentric in silico trial we compared photon, proton, and carbon-ion radiotherapy plans for re-irradiation of patients with squamous cell carcinoma of the head and neck (HNSCC) regarding dose to tumour and doses to surrounding organs at risk (OARs).

Material And Methods: Twenty-five HNSCC patients with a second new or recurrent cancer after previous irradiation (70Gy) were included. Intensity-modulated proton therapy (IMPT) and ion therapy (IMIT) re-irradiation plans to a second subsequent dose of 70Gy were compared to photon therapy delivered with volumetric modulated arc therapy (VMAT).

Challenges in radiobiological modeling: can we decide between LQ and LQ-L models based on reviewed clinical NSCLC treatment outcome data?

Aim: To study the dose-response of stage I non-small-cell lung cancer (NSCLC) in terms of long-term local tumor control (LC) after conventional and hypofractionated photon radiotherapy, modeled with the linear-quadratic (LQ) and linear-quadratic-linear (LQ-L) approaches and to estimate the clinical α/β ratio within the LQ frame.

Material And Methods: We identified studies of curative radiotherapy as single treatment through MedLine search reporting 3-year LC as primary outcome of interest. Logistic models coupled with the biologically effective dose (BED) at isocenter and PTV edge according to both the LQ and LQ-L models with α/β = 10 Gy were fitted.

Dosimetric robustness against setup errors in charged particle radiotherapy of skull base tumors.

Background: It is expected that physical dose deposition properties render charged particle dose distributions sensitive to targeting uncertainties. Purpose of this work was to investigate the robustness of scanned-beam particle therapy plans against setup errors for different optimization modalities, beam setups and ion species.

Material And Methods: For 15 patients with skull base tumors, localized in regions of severe tissue density heterogeneity, scanned lateral-opposed-beam treatment plans were prepared with the treatment planning system TRiP98, employing different optimization settings (single- and multiple-field modulation) and ion species (carbon ions and protons).