Accumulation of sublethal radiation damage and its effect on cell survival.

Determine the extent of sublethal radiation damage (SRD) in a cell population that received a given dose of radiation and the impact of this damage on cell survival.We developed a novel formalism to account for accumulation of SRD with increasing dose. It is based on a very general formula for cell survival that correctly predicts the basic properties of cell survival curves, such as the transition from the linear-quadratic to a linear dependence at high doses.

Monte Carlo evaluation of target dose coverage in lung stereotactic body radiation therapy with flattening filter-free beams.

Aim: Previous studies showed that replacing conventional flattened beams (FF) with flattening filter-free (FFF) beams improves the therapeutic ratio in lung stereotactic body radiation therapy (SBRT), but these findings could have been impacted by dose calculation uncertainties caused by the heterogeneity of the thoracic anatomy and by respiratory motion, which were particularly high for target coverage. In this study, we minimized such uncertainties by calculating doses using high-spatial-resolution Monte Carlo and four-dimensional computed tomography (4DCT) images. We aimed to evaluate more reliably the benefits of using FFF beams for lung SBRT.

Using FFF Beams to Improve the Therapeutic Ratio of Lung SBRT.

Aim: To investigate the extent to which lung stereotactic body radiotherapy (SBRT) treatment plans can be improved by replacing conventional flattening filter (FF) beams with flattening filter-free (FFF) beams.

Material And Methods: We selected 15 patients who had received SBRT with conventional 6-MV photon beams for early-stage lung cancer. We imported the patients' treatment plans into the Eclipse 13.

Impact of Intra-Fractional Motion on Dose Distributions in Lung IMRT.

Aim: To investigate the impact of intra-fractional motion on dose distribution in patients treated with intensity-modulated radiation therapy (IMRT) for lung cancer.

Materials And Methods: Twenty patients who had undergone IMRT for non-small cell lung cancer were selected for this retrospective study. For each patient, a four-dimensional computed tomography (CT) image set was acquired and clinical treatment plans were developed using the average CT.

On calculation of the average linear energy transfer for radiobiological modelling.

Applying the concept of linear energy transfer (LET) to modeling of biological effects of charged particles usually involves calculation of the average LET. To calculate this, the energy distribution of particles is characterized by either the source spectrum or fluence spectrum. Also, the average can be frequency-or dose-weighted.

A simple model for calculating relative biological effectiveness of X-rays and gamma radiation in cell survival.

Objectives: The relative biological effectiveness (RBE) of X-rays and γ radiation increases substantially with decreasing beam energy. This trend affects the efficacy of medical applications of this type of radiation. This study was designed to develop a model based on a survey of experimental data that can reliably predict this trend.

AAPM Task Group 329: Reference dose specification for dose calculations: Dose-to-water or dose-to-muscle?

Linac calibration is done in water, but patients are comprised primarily of soft tissue. Conceptually, and specified in NRG/RTOG trials, dose should be reported as dose-to-muscle to describe the dose to the patient. Historically, the dose-to-water of the linac calibration was often converted to dose-to-muscle for patient calculations through manual application of a 0.

Systematic microdosimetric data for protons of therapeutic energies calculated with Geant4-DNA.

The purpose of this study was to generate physical data needed for microdosimetry-based models of proton RBE. Our focus was on the frequency and dose average lineal energies, y  and y  . We report data for proton energies from 0.

Radiotherapy of lung cancers: FFF beams improve dose coverage at tumor periphery compromised by electronic disequilibrium.

The purpose of this work was to investigate radiotherapy underdosing at the periphery of lung tumors, and differences in dose for treatments delivered with flattening filter-free (FFF) beams and with conventional flattened (FF) beams. The true differences between these delivery approaches, as assessed with Monte Carlo simulations, were compared to the apparent differences seen with clinical treatment planning algorithms AAA and Acuros XB. Dose was calculated in a phantom comprised of a chest wall, lung parenchyma, and a spherical tumor (tested diameters: 1, 3, and 5 cm).

Average stopping powers for electron and photon sources for radiobiological modeling and microdosimetric applications.

This study concerns calculation of the average electronic stopping power for photon and electron sources. It addresses two problems that have not yet been fully resolved. The first is defining the electron spectrum used for averaging in a way that is most suitable for radiobiological modeling.

A new formalism for modelling parameters α and β of the linear-quadratic model of cell survival for hadron therapy.

We propose a new formalism for calculating parameters α and β of the linear-quadratic model of cell survival. This formalism, primarily intended for calculating relative biological effectiveness (RBE) for treatment planning in hadron therapy, is based on a recently proposed microdosimetric revision of the single-target multi-hit model. The main advantage of our formalism is that it reliably produces α and β that have correct general properties with respect to their dependence on physical properties of the beam, including the asymptotic behavior for very low and high linear energy transfer (LET) beams.

Radial dose distributions from carbon ions of therapeutic energies calculated with Geant4-DNA.

We report on radial dose distributions [Formula: see text] for carbon ions calculated with Geant4-DNA code. These distributions characterize ion tracks on a nanoscale and are important for understanding the biological effects of ion beams. We present data for carbon ion beams in the energy range from 20 to 400 MeV u.

Radial dose distributions from protons of therapeutic energies calculated with Geant4-DNA.

Models based on the amorphous track structure approximation have been successful in predicting the biological effects of heavy charged particles. Development of such models remains an active area of research that includes applications to hadrontherapy. In such models, the radial distribution of the dose deposited by delta electrons and directly by the particle is the main characteristic of track structure.

Electron slowing-down spectra in water for electron and photon sources calculated with the Geant4-DNA code.

Recently, a very low energy extension was added to the Monte Carlo simulation toolkit Geant4. It is intended for radiobiological modeling and is referred to as Geant4-DNA. Its performance, however, has not been systematically benchmarked in terms of transport characteristics.

Formulation of the multi-hit model with a non-Poisson distribution of hits.

Purpose: We proposed a formulation of the multi-hit single-target model in which the Poisson distribution of hits was replaced by a combination of two distributions: one for the number of particles entering the target and one for the number of hits a particle entering the target produces. Such an approach reflects the fact that radiation damage is a result of two different random processes: particle emission by a radiation source and interaction of particles with matter inside the target.

Methods And Materials: Poisson distribution is well justified for the first of the two processes.

Dosimetric impact of fiducial markers in patients undergoing photon beam radiation therapy.

Fiducial markers are widely used in image-guided radiation therapy to correct for setup error and organ motion. These markers, however, can cause dose perturbations in the target volume for patients undergoing external-beam radiation therapy. The goal of this study was to determine the dosimetric impact of various types of fiducial markers commonly used in patients receiving photon radiation therapy.

Displacement of periurethral stranded seeds and its dosimetric consequences in prostate brachytherapy.

Purpose: The use of stranded seeds for prostate brachytherapy has raised concern that displacement of strands, particularly in the periurethral region, may result in inadequate coverage of the prostate. We sought here to evaluate the displacement of periurethral stranded seeds after a prostate brachytherapy implant (Day 0) and its dosimetric consequences 1 month later (Day 30).

Methods And Materials: Subjects were 10 consecutive patients who underwent implantation with (125)I stranded seeds via a peripheral-loading technique.

Out-of-field photon dose following removal of the flattening filter from a medical accelerator.

The aim of this paper is to determine the effect of removing the flattening filter from a linear accelerator on the out-of-field photon dose. A Monte Carlo model was used to simulate 6 MV and 18 MV photon beams from a Varian 2100 accelerator with the flattening filter in place and with it removed. The out-of-field photon doses and composition (head leakage, patient scatter and collimator scatter) were calculated from square open fields in a water tank as a function of distance from central axis, field size and depth.

Validation of a new grid-based Boltzmann equation solver for dose calculation in radiotherapy with photon beams.

A new grid-based Boltzmann equation solver, Acuros, was developed specifically for performing accurate and rapid radiotherapy dose calculations. In this study we benchmarked its performance against Monte Carlo for 6 and 18 MV photon beams in heterogeneous media. Acuros solves the coupled Boltzmann transport equations for neutral and charged particles on a locally adaptive Cartesian grid.

Stereotactic radiotherapy for lung cancer using a flattening filter free Clinac.

The objective of this study was to assess the feasibility of stereotactic radiotherapy for early stage lung cancer using photon beams from a Varian Clinac accelerator operated without a flattening filter. Treatment plans were generated for 10 lung cancer patients with isolated lesions less than 3 cm in diameter. For each patient, two plans were generated, one with and one without the flattening filter.

Treatment vault shielding for a flattening filter-free medical linear accelerator.

The requirements for shielding a treatment vault with a Varian Clinac 2100 medical linear accelerator operated both with and without the flattening filter were assessed. Basic shielding parameters, such as primary beam tenth-value layers (TVLs), patient scatter fractions, and wall scatter fractions, were calculated using Monte Carlo simulations of 6, 10 and 18 MV beams. Relative integral target current requirements were determined from treatment planning studies of several disease sites with, and without, the flattening filter.

Feasibility of a multigroup deterministic solution method for three-dimensional radiotherapy dose calculations.

Purpose: To investigate the potential of a novel deterministic solver, Attila, for external photon beam radiotherapy dose calculations.

Methods And Materials: Two hypothetical cases for prostate and head-and-neck cancer photon beam treatment plans were calculated using Attila and EGSnrc Monte Carlo simulations. Open beams were modeled as isotropic photon point sources collimated to specified field sizes.

Energy spectra, sources, and shielding considerations for neutrons generated by a flattening filter-free Clinac.

Neutron production is an unwanted result of high-energy radiation therapy and results in secondary exposure of patients and radiation therapists to radiation. Recent studies have shown that delivering therapy using a standard medical accelerator with the flattening filter removed may reduce neutron fluence by nearly 70% over the course of prostate intensity-modulated radiation therapy (IMRT). In the current study, the 197Au Bonner sphere technique was used to compare the neutron spectrum produced when the filter is present and when it is absent.

Monte Carlo investigation of collimator scatter of proton-therapy beams produced using the passive scattering method.

As a proton-therapy beam passes through the field-limiting aperture, some of the protons are scattered off the edges of the collimator. The edge-scattered protons can degrade the dose distribution in a patient or phantom, and these effects are difficult to model with analytical methods such as those available in treatment planning systems. The objective of this work was to quantify the dosimetric impact of edge-scattered protons for a representative variety of clinical treatment beams.

A Monte Carlo model for out-of-field dose calculation from high-energy photon therapy.

As cancer therapy becomes more efficacious and patients survive longer, the potential for late effects increases, including effects induced by radiation dose delivered away from the treatment site. This out-of-field radiation is of particular concern with high-energy radiotherapy, as neutrons are produced in the accelerator head. We recently developed an accurate Monte Carlo model of a Varian 2100 accelerator using MCNPX for calculating the dose away from the treatment field resulting from low-energy therapy.