Skin dose investigations on a 0.5 T parallel rotating biplanar linac-MR using Monte Carlo simulations and measurements.

Background: The Alberta rotating biplanar linac-MR has a 0.5 T magnetic field parallel to the beamline. When developing a new linac-MR system, interactions of charged particles with the magnetic field necessitate careful consideration of skin dose and tissue interface effects.

Seminal Vesicle Treatment for Localized Prostate Cancer Treated with External Beam Radiotherapy.

This study retrospectively reviewed data from men with localized prostate cancer treated with external beam radiotherapy (EBRT). We identified 359 men with localized prostate cancer treated with curative EBRT at the Cross Cancer Institute between 2010-2011. The volume of seminal vesicles (SVs) treated as well as dose values were extracted.

Tumor Volume Predicts for Pathologic Complete Response in Rectal Cancer Patients Treated With Neoadjuvant Chemoradiation.

Objectives: Nonoperative management (NOM) of locally advanced rectal cancer is an emerging approach allowing patients to preserve their anal sphincter. Identifying clinical factors associated with pathologic complete response (pCR) is essential for physicians and patients considering NOM.

Materials And Methods: In total, 412 locally advanced rectal cancer patients were included in this retrospective analysis.

Uncertainties Associated with Clonogenic Assays using a Cs-137 Irradiator and Ir-192 Afterloader: A Comprehensive Compilation for Radiation Researchers.

Clonogenic assays are the gold standard for measuring cell clonogenic survival and enable quantification of a cell line's radiosensitivity through the calculation of the surviving fraction, the ratio of cell clusters (colonies) formed after radiation exposure compared to the number formed without exposure. Such studies regularly utilize Cs-137 irradiators. While uncertainties for specific procedural aspects have been described previously, a comprehensive review has not been completed.

BAIRDA: a novelsetup to quantify radiobiological parameters for cervical cancer brachytherapy dose estimations.

. Brachytherapy (BT) dose prescriptions for locally advanced cervical cancer are made with account for the radiobiological parameters,ratio and halftime of repair (). However, a wide range of parameter values has been reported which can challenge commonly held equivalencies between dose prescriptions.

Disassembly of microtubules by intense terahertz pulses.

The biological effects of terahertz (THz) radiation have been observed across multiple levels of biological organization, however the sub-cellular mechanisms underlying the phenotypic changes remain to be elucidated. Filamentous protein complexes such as microtubules are essential cytoskeletal structures that regulate diverse biological functions, and these may be an important target for THz interactions underlying THz-induced effects observed at the cellular or tissue level. Here, we show disassembly of microtubules within minutes of exposure to extended trains of intense, picosecond-duration THz pulses.

More Is Not Better When It Comes to Treating Rectal Cancer With Multimodal Chemoradiation Beyond the Standard Radiation Dose of 5040 cGy.

Background: Radiation dose schedules for neoadjuvant chemoradiation for rectal cancers differ, with the most common dose schedule using 5040 cGy in 28 fractions.

Objectives: The aim of this retrospective study was to assess the benefit of higher radiation doses beyond 5040 cGy in the context of pathological response and follow-up events.

Setting: The database from a provincial tertiary cancer center in Canada was the source of information for this study.

Dosimetric Parameters Predicting Late Small Bowel Toxicity in Patients With Rectal Cancer Receiving Neoadjuvant Chemoradiation.

Purpose: The aim of this study was to identify dosimetric parameters that predict late small bowel (SB) toxicity after neoadjuvant long course chemoradiation (CRT) for rectal cancer.

Methods And Materials: Four hundred eighty-six consecutive patients with locally advanced rectal cancers (clinical T3/T4 or N1/N2) who received CRT followed by surgery and had dosimetric data available for analysis were included in this study. The dose-volume relationship between small bowel irradiation and late small bowel toxicity was evaluated and a mathematical model to predict for late SB toxicity was derived.

Radiobiological dose calculation parameters for cervix cancer brachytherapy: A systematic review.

The GEC-ESTRO recommendation in cervical cancer treatment planning, including external beam radiotherapy and brachytherapy boosts, is to use radiobiological dose calculations. Such calculations utilize the linear-quadratic model to estimate the effect of multiple cellular response factors and dose delivery parameters. The radiobiological parameters utilized in these calculations are literature values estimated based on clinical and experimental results.

Cardiac-sparing radiation therapy using positioning breast shell for patients with left-sided breast cancer who are ineligible for breath-hold techniques.

Purpose: Patients with left-sided breast cancer (LSBC) are at increased risk of cardiac morbidity from adjuvant breast radiation therapy (ABRT). Breath-hold (BH) techniques substantially reduce the radiation received by heart during radiation therapy for LSBC. However, a subset of patients with LSBC are ineligible for BH techniques due to an inability to breath-hold or because of other comorbidities.

Minimal skin dose increase in longitudinal rotating biplanar linac-MR systems: examination of radiation energy and flattening filter design.

The magnetic fields of linac-MR systems modify the path of contaminant electrons in photon beams, which alters patient entrance skin dose. Also, the increased SSD of linac-MR systems reduces the maximum achievable dose rate. To accurately quantify the changes in entrance skin dose, the authors use EGSnrc Monte Carlo calculations that incorporate 3D magnetic field of the Alberta 0.

Intensity-Modulated Radiotherapy (IMRT) vs Helical Tomotherapy (HT) in Concurrent Chemoradiotherapy (CRT) for Patients with Anal Canal Carcinoma (ACC): an analysis of dose distribution and toxicities.

Purpose: Intensity-modulated radiotherapy (IMRT) and helical tomotherapy (HT) have been adopted for radiotherapy treatment of anal canal carcinoma (ACC) due to better conformality, dose homogeneity and normal-tissue sparing compared to 3D-CRT. To date, only one published study compares dosimetric parameters of IMRT vs HT in ACC, but there are no published data comparing toxicities. Our objectives were to compare dosimetry and toxicities between these modalities.

Spatial and temporal distribution of γH2AX fluorescence in human cell cultures following synchrotron-generated X-ray microbeams: lack of correlation between persistent γH2AX foci and apoptosis.

Formation of γH2AX foci (a marker of DNA double-strand breaks), rates of foci clearance and apoptosis were investigated in cultured normal human fibroblasts and p53 wild-type malignant glioma cells after exposure to high-dose synchrotron-generated microbeams. Doses up to 283 Gy were delivered using beam geometries that included a microbeam array (50 µm wide, 400 µm spacing), single microbeams (60-570 µm wide) and a broad beam (32 mm wide). The two cell types exhibited similar trends with respect to the initial formation and time-dependent clearance of γH2AX foci after irradiation.

Modulation factors calculated with an EPID-derived MLC fluence model to streamline IMRT/VMAT second checks.

This work outlines the development of a robust method of calculating modulation factors used for the independent verification of MUs for IMRT and VMAT treatments, to replace onerous ion chamber measurements. Two-dimensional fluence maps were calculated for dynamic MLC fields that include MLC interleaf leakage, transmission, and tongue-and-groove effects, as characterized from EPID-acquired images. Monte Carlo-generated dose kernels were then used to calculate doses for a modulated field and that field with the modulation removed at a depth specific to the calculation point in the patient using in-house written software, Mod_Calc.

2D lag and signal nonlinearity correction in an amorphous silicon EPID and their impact on pretreatment dosimetric verification.

Purpose: This investigation provides measurements of signal lag and nonlinearity separately for the Varian aS500 electronic portal imaging device (EPID), and an algorithm to correct for these effects in 2D; their potential impact on intensity modulated radiation therapy (IMRT) verification is also investigated. The authors quantify lag, as a function of both delivered monitor units (MU) and time, by using a range of MUs delivered at a clinically used rate of 400 MU∕min. Explicit cumulative lag curves are thus determined for a range of MUs and times between the end of irradiation and the end of image acquisition.

Skin dose in longitudinal and transverse linac-MRIs using Monte Carlo and realistic 3D MRI field models.

Purpose: The magnetic fields of linac-MR systems modify the path of contaminant electrons in photon beams, which alters patient skin dose. To accurately quantify the magnitude of changes in skin dose, the authors use Monte Carlo calculations that incorporate realistic 3D magnetic field models of longitudinal and transverse linac-MR systems.

Methods: Finite element method (FEM) is used to generate complete 3D magnetic field maps for 0.

Sci-Sat AM: Brachy - 01: Evaluation of dose-volume metrics for microbeam radiation therapy.

Microbeam radiation therapy (MRT) is an experimental technique delivering an array of high dose synchrotron X-ray microbeams. Development of metrics to predict the biological efficacy of MRT dose distributions is needed to guide further MRT research and for potential translation to human trials. The most commonly used metric is the peak-to-valley-dose ratio (PVDR) relating the dose at the microbeam center to that between two microbeams.

WE-E-BRB-06: Monte Carlo Calculations of the Skin Dose for Longitudinal Linac-MR System Using Realistic Three-Dimensional Magnetic Field Modeling.

Purpose: This study quantifies the effects of the magnetic field of a longitudinal linac-MR system (B-field parallel to beam direction) on skin dose due to the confinement of contaminant electrons, using Monte Carlo calculations and realistic 3-D models of the magnetic field.

Methods: The complete realistic 3-D magnetic fields generated by the bi-planar Linac-MR magnet assembly are calculated with the finite element method using Opera- 3D. EGSnrc simulations are performed in the presence of ∼0.

SU-E-T-469: The Effects of Patient Anatomy and Parallel Magnetic Fields on Beamlet Dose Distributions.

Purpose: Beamlets are generated in a patient geometry in the presence of a magnetic field to investigate the effects of tissue density and magnetic field on beamlet dose distributions, which is important for the optimization of photon fluence to be delivered by a linac-MR system.

Methods: 50×50 mm fields were placed with isocenter in the middle of a patient's right lung. Each treatment field was decomposed into 100 beamlets (each 5×5 mm ).

Evaluation of dose-volume metrics for microbeam radiation therapy dose distributions in head phantoms of various sizes using Monte Carlo simulations.

This work evaluates four dose-volume metrics applied to microbeam radiation therapy (MRT) using simulated dosimetric data as input. We seek to improve upon the most frequently used MRT metric, the peak-to-valley dose ratio (PVDR), by analyzing MRT dose distributions from a more volumetric perspective. Monte Carlo simulations were used to calculate dose distributions in three cubic head phantoms: a 2 cm mouse head, an 8 cm cat head and a 16 cm dog head.

Population TCP estimators in case of heterogeneous irradiation: a new discussion of an old problem.

Purpose: To investigate the capacity of two phenomenological expressions to describe the population tumor response in case of a heterogeneous irradiation of the tumor. The generalization of the individual tumor control probability (TCP) models to include the case of a heterogeneous irradiation is a trivial problem. However, an analytical solution that results in a closed form population TCP formula for the heterogeneous case is, unfortunately, a very complex mathematical problem.

Sci-Thurs PM: Delivery-06: 2-D lag and response nonlinearity corrections for dynamic IMRT verification using an EPID.

In recent years, EPIDs have been used for pre-treatment IMRT verification. Although EPID lag and signal nonlinearities have been investigated, they have not been implemented in the verification process. In dynamic sliding-window IMRT delivery, the dose delivered, and the time between the end of dose delivery and the end of image acquisition differ between pixels.

Analytic investigation into effect of population heterogeneity on parameter ratio estimates.

Purpose: A homogeneous tumor control probability (TCP) model has previously been used to estimate the alpha/beta ratio for prostate cancer from clinical dose-response data. For the ratio to be meaningful, it must be assumed that parameter ratios are not sensitive to the type of tumor control model used. We investigated the validity of this assumption by deriving analytic relationships between the alpha/beta estimates from a homogeneous TCP model, ignoring interpatient heterogeneity, and those of the corresponding heterogeneous (population-averaged) model that incorporated heterogeneity.

Fundamental form of a population TCP model in the limit of large heterogeneity.

A population tumor control probability (TCP) model for fractionated external beam radiotherapy, based on Poisson statistics and in the limit of large parameter heterogeneity, is studied. A reduction of a general eight-parameter TCP equation, which incorporates heterogeneity in parameters characterizing linear-quadratic radiosensitivity, repopulation, and clonogen number, to an equation with four parameters is obtained. The four parameters represent the mean and standard deviation for both clonogen number and a generalized radiosensitivity that includes linear-quadratic and repopulation descriptors.

Limitations of a TCP model incorporating population heterogeneity.

The variation between individuals in their dose-response characteristics complicates attempts to extract estimates of radiobiological parameters (e.g. alpha, beta, etc) from fits to clinical dose-response data.