Quantifying the spatial distribution of the accumulated dose uncertainty using the novel delta index.

Inter- and intra-fractional anatomical changes during a radiotherapy treatment can cause differences between the initially planned dose and the delivered dose. The total delivered dose can be accumulated over all fractions by using deformable image registration (DIR). However, there is uncertainty in this process which should be accounted for.

An improved calibration procedure for accurate plastic scintillation dosimetry on an MR-linac.

Plastic scintillation dosimeters (PSDs) are highly suitable for real-time dosimetry on the MR-linac. For optimal performance, the primary signal (scintillation) needs to be separated from secondary optical effects (Cerenkov, fluorescence and optical fiber attenuation). This requires a spectral separation approach and careful calibration.

Treatment planning evaluation and experimental validation of the magnetic resonance-based intrafraction drift correction.

Background And Purpose: MRI-guided online adaptive treatments can account for interfractional variations, however intrafraction motion reduces treatment accuracy. Intrafraction plan adaptation methods, such as the Intrafraction Drift Correction (IDC) or sub-fractionation, are needed. IDC uses real-time automatic monitoring of the tumor position to initiate plan adaptations by repositioning segments.

Experimental validation of multi-fraction online adaptations in magnetic resonance guided radiotherapy.

Background And Purpose: Radiotherapy plan verification is generally performed on the reference plan based on the pre-treatment anatomy. However, the introduction of online adaptive treatments demands a new approach, as plans are created daily on different anatomies. The aim of this study was to experimentally validate the accuracy of total doses of multi-fraction plan adaptations in magnetic resonance imaging guided radiotherapy in a phantom study, isolated from the uncertainty of deformable image registration.

Gating and intrafraction drift correction on a 1.5 T MR-Linac: Clinical dosimetric benefits for upper abdominal tumors.

This work reports on the first seven patients treated with gating and baseline drift correction on the high-field MR-Linac system. Dosimetric analysis showed that the active motion management system improved congruence to the planned dose, efficiently mitigating detrimental effects of intrafraction motion in the upper abdomen.

Dementia Caregivers' Perspectives on Disaster Preparedness: Barriers, Resources, and Recommendations.

Background And Objectives: Disaster preparedness is an urgent concern, particularly for caregivers of persons with dementia. Developing and executing plans for oneself and another person who needs care can be difficult when the care recipient is cognitively impaired. We sought to better understand caregivers' disaster preparedness for the purpose of generating guidance for future interventions to increase caregiver resilience.

"We Did More Damage": How COVID-19 Collapsed the Care Convoys of Residents Living With Dementia.

COVID-19 regulations have posed challenges for long-term care (LTC). However, few studies have examined how such regulations influenced the care of residents living with dementia. Our objective was to gain an understanding of LTC administrative leaders' perceptions regarding the impact of the COVID-19 response on this population.

On the feasibility of cardiac substructure sparing in magnetic resonance imaging guided stereotactic lung radiotherapy.

Background: Lung stereotactic body radiotherapy (SBRT) has proven an effective treatment for medically inoperable lung tumors, even for (ultra-)central tumors. Recently, there has been growing interest in radiation-induced cardiac toxicity in lung radiotherapy. More specifically, dose to cardiac (sub-)structures (CS) was found to correlate with survival after radiotherapy.

Till Death Do Us Part?: Exploring the Social Convoys of Conjugally Bereaved Women.

Objectives: The hierarchical mapping technique (HMT) is used to study social convoys, peoples' support systems. Recent research integrating the HMT and the continuing bonds framework suggests that deceased persons may be influential convoy members. Extending this idea, the current study aimed to gain insight regarding how older conjugally bereaved women view the role of a deceased romantic partner in their convoy.

Towards mid-position based Stereotactic Body Radiation Therapy using online magnetic resonance imaging guidance for central lung tumours.

Central lung tumours can be treated by magnetic resonance (MR)-guided radiotherapy. Complications might be reduced by decreasing the Planning Target Volume (PTV) using mid-position (midP)-based planning instead of Internal Target Volume (ITV)-based planning. In this study, we aimed to verify a method to automatically derive patient-specific PTV margins for midP-based planning, and show dosimetric robustness of midP-based planning for a 1.

First experimental demonstration of VMAT combined with MLC tracking for single and multi fraction lung SBRT on an MR-linac.

Background And Purpose: VMAT is not currently available on MR-linacs but could maximize plan conformality. To mitigate respiration without compromising delivery efficiency, MRI-guided MLC tumour tracking was recently developed for the 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden) in combination with IMRT.

Acceptance procedure for the linear accelerator component of the 1.5 T MRI-linac.

Purpose: To develop and implement an acceptance procedure for the new Elekta Unity 1.5 T MRI-linac.

Methods: Tests were adopted and, where necessary adapted, from AAPM TG106 and TG142, IEC 60976 and NCS 9 and NCS 22 guidelines.

Initial Clinical Experience of MR-Guided Radiotherapy for Non-Small Cell Lung Cancer.

Curative-intent radiotherapy plays an integral role in the treatment of lung cancer and therefore improving its therapeutic index is vital. MR guided radiotherapy (MRgRT) systems are the latest technological advance which may help with achieving this aim. The majority of MRgRT treatments delivered to date have been stereotactic body radiation therapy (SBRT) based and include the treatment of (ultra-) central tumors.

Dosimetric evaluation of MRI-guided multi-leaf collimator tracking and trailing for lung stereotactic body radiation therapy.

Purpose: The treatment margins for lung stereotactic body radiotherapy (SBRT) are often large to cover the tumor excursions resulting from respiration, such that underdosage of the tumor can be avoided. Magnetic resonance imaging (MRI)-guided multi-leaf collimator (MLC) tracking can potentially reduce the influence of respiration to allow for smaller treatment margins. However, tracking is accompanied by system latency that may induce residual tracking errors.

Improving the imaging performance of the 1.5 T MR-linac using a flexible, 32-channel, on-body receive array.

High impedance coils (HICs) are suitable as a building block of receive arrays for MRI-guided radiotherapy (MRIgRT) as HICs do not require radiation-attenuating capacitors and dense support materials. Recently, we proved the feasibility of using HICs to create a radiation transparent (i.e.

Design and feasibility of a flexible, on-body, high impedance coil receive array for a 1.5 T MR-linac.

The lack of radiation-attenuating tuning capacitors in high impedance coils (HICs) make HICs an interesting building block of receive arrays for MRI-guided radiotherapy (MRIgRT). Additionally, their flexibility and limited channel coupling allow for low-density support materials, which are likely to be more radiation transparent (radiolucent). In this work, we introduce the use of HICs in receive arrays for MRIgRT treatments.

Adaptive radiotherapy: The Elekta Unity MR-linac concept.

Background And Purpose: The promise of the MR-linac is that one can visualize all anatomical changes during the course of radiotherapy and hence adapt the treatment plan in order to always have the optimal treatment. Yet, there is a trade-off to be made between the time spent for adapting the treatment plan against the dosimetric gain. In this work, the various daily plan adaptation methods will be presented and applied on a variety of tumour sites.

Feasibility of stereotactic radiotherapy using a 1.5 T MR-linac: Multi-fraction treatment of pelvic lymph node oligometastases.

Online adaptive radiotherapy using the 1.5 Tesla MR-linac is feasible for SBRT (5 × 7 Gy) of pelvic lymph node oligometastases. The workflow allows full online planning based on daily anatomy.

Monte Carlo simulations of out-of-field surface doses due to the electron streaming effect in orthogonal magnetic fields.

The out-of-field surface dose contribution due to backscattered or ejected electrons, focused by the magnetic field, is evaluated in this work. This electron streaming effect (ESE) can contribute to out-of-field skin doses in orthogonal magnetic resonance guided radiation therapy machines. Using the EGSnrc Monte Carlo package, a phantom is set-up along the central axis of an incident 10 [Formula: see text] 10 cm 7 MV FFF photon beam.

Cardiac Structure Doses in Women Irradiated for Breast Cancer in the Past and Their Use in Epidemiological Studies.

Purpose: Incidental cardiac exposure during radiation therapy may cause heart disease. Dose-response relationships for cardiac structures (segments) may show which ones are most sensitive to radiation. Radiation-related cardiac injury can take years to develop; thus, studies need to involve women treated using 2-dimensional planning, with segment doses estimated using a typical computed tomography (CT) scan.

Monte Carlo simulations of out-of-field skin dose due to spiralling contaminant electrons in a perpendicular magnetic field.

Purpose: The purpose of this study was to evaluate the potential skin dose toxicity contribution of spiralling contaminant electrons (SCE) generated in the air in an MR-linac with a 0.35 or 1.5 T magnetic field using the EGSnrc Monte Carlo (MC) code.

Dosimetric feasibility of the hybrid Magnetic Resonance Imaging (MRI)-linac System (MRL) for brain metastases: The impact of the magnetic field.

Background And Purpose: We aimed to investigate the suitability of treating patients with single brain metastases using stereotactic radiosurgery (SRS) with the MRL and to characterize the dosimetric impact at tissue-air interfaces resulting primarily from the electron return effect (ERE).

Material And Methods: 24 patients treated for intact single brain metastases were analyzed. Three radiotherapy plans with the same prescribed dose were generated for each case: (1) noncoplanar volumetric modulated arc therapy (VMAT), (2) coplanar step-and-shoot intensity modulated radiotherapy (IMRT) on the MRL in the absence (MRLB=0), and (3) in the presence of the transverse magnetic field (MRLB=1.

F-fluoromisonidazole uptake in advanced stage non-small cell lung cancer: A voxel-by-voxel PET kinetics study.

Purpose: The aim of this study was to determine the relative abilities of compartment models to describe time-courses of F-fluoromisonidazole (FMISO) uptake in tumor voxels of patients with non-small cell lung cancer (NSCLC) imaged using dynamic positron emission tomography. Also to use fits of the best-performing model to investigate changes in fitted rate-constants with distance from the tumor edge.

Methods: Reversible and irreversible two- and three-tissue compartment models were fitted to 24 662 individual voxel time activity curves (TACs) obtained from tumors in nine patients, each imaged twice.

Constancy checks of well-type ionization chambers with external-beam radiation units.

Constancy checks of a well-type ionization chamber should be performed regularly as part of a quality assurance regime. The goal of this work was to test the feasibility of using a linear accelerator and an orthovoltage unit to check the constancy of a well-type chamber's response to an external radiation source. The reproducibility, linearity with dose, variation with dose-rate, and variation between energy-matched units of the well-type chamber response when exposed to 6 MV beams was examined.

Estimation of input functions from dynamic [18F]FLT PET studies of the head and neck with correction for partial volume effects.

Background: We present a method for extracting arterial input functions from dynamic [18F]FLT PET images of the head and neck, directly accounting for the partial volume effect. The method uses two blood samples, for which the optimum collection times are assessed.

Methods: Six datasets comprising dynamic PET images, co-registered computed tomography (CT) scans and blood-sampled input functions were collected from four patients with head and neck tumours.