An investigation of high-Z material for bolus in electron beam therapy.

. Electron beam treatment often requires bolus to augment surface dose to nearly 100%. There are no optimum bolus materials and hence a high-Z based clothlike material is investigated to reduce air column in treatment that provides optimum surface dose.

The role of volume averaging effects, beam hardening, and phantom scatter in dosimetry of grid therapy.

. Current reference dosimetry methods for spatially fractionated radiation therapy (SFRT) assume a negligible beam quality change, perturbation, or volume-averaging correction factor. Therefore, the aim of this work was to investigate the impact of the grid collimators on the dosimetric characteristics of a 6 MV photon beam.

Development of novel ionization chambers for reference dosimetry in electron flash radiotherapy.

Background: Reference dosimetry in ultra-high dose rate (UHDR) beamlines is significantly hindered by limitations in conventional ionization chamber design. In particular, conventional chambers suffer from severe charge collection efficiency (CCE) degradation in high dose per pulse (DPP) beams.

Purpose: The aim of this study was to optimize the design and performance of parallel plate ion chambers for use in UHDR dosimetry applications, and evaluate their potential as reference class chambers for calibration purposes.

Computational and experimental small field dosimetry using a commercial plastic scintillator detector for the 0.35 T MR-linac.

Purpose: Although plastic scintillator detectors (PSDs) are considered ideal dosimeters for small field dosimetry in conventional linear accelerators (linacs), the impact of the magnetic field strength on the response of the PSD must be investigated.

Methods: A linac Monte Carlo (MC) head model for a low-field MR-linac was validated for small field dosimetry and utilized to calculate field output factors (OFs). The MC-calculated OFs were compared with the treatment planning system (TPS)-calculated OFs and measured OFs using a Blue Physics (BP) Model 10 commercial PSD and a synthetic diamond detector.

Thermoluminescent dosimeters (TLD-100) for absorbed dose measurements in alpha-emitting radionuclides.

Early works that used thermoluminescent dosimeters (TLDs) to measure absorbed dose from alpha particles reported relatively high variation (10%) between TLDs, which is undesirable for modern dosimetry applications. This work outlines a method to increase precision for absorbed dose measured using TLDs with alpha-emitting radionuclides by applying an alpha-specific chip factor (CF) that individually characterizes the TLD sensitivity to alpha particles. Variation between TLDs was reduced from 21.

Grid/lattice therapy: consideration of small field dosimetry.

Small-field dosimetry used in special procedures such as gamma knife, Cyberknife, Tomotherapy, IMRT, and VMAT has been in evolution after several radiation incidences with very significant (70%) errors due to poor understanding of the dosimetry. IAEA-TRS-483 and AAPM-TG-155 have provided comprehensive information on small-fields dosimetry in terms of code of practice and relative dosimetry. Data for various detectors and conditions have been elaborated.

Dependence of surface dose on atomic number in megavoltage photon beams.

Background: Surface dose in megavoltage photon radiotherapy has a significant clinical impact on the skin-sparing effect. In previously published works, it was established that the presence of medium atomic number (Z) absorbers, such as tin, decreases the surface dose. It was concluded that high-Z absorbers, such as lead, increase the surface dose, relative to medium-Z absorbers, due to the increased contributions from photoelectrons and electron-positron pairs.

A diffusion-leakage model coupled with dose point kernels (DPK) for dosimetry of diffusing alpha-emitters radiation therapy (DaRT).

Background: Diffusing alpha-emitters radiation therapy (DaRT) is a novel brachytherapy technique that leverages the diffusive flow of Ra progeny within the tumor volume over the course of the treatment. Cell killing is achieved by the emitted alpha particles that have a short range in tissue and high linear energy transfer. The current proposed absorbed dose calculation method for DaRT is based on a diffusion-leakage (DL) model that neglects absorbed dose from beta particles.

Characterization of a segmented printed circuit board (PCB) as a standard for absorbed dose to water from alpha-emitting radionuclides.

Background: Our previous work introduced and evaluated a standard for surface absorbed dose rate per unit radioactivity to water from unsealed alpha-emitting radionuclides used in targeted radionuclide therapy (TRT). An overall uncertainty over 4.0% at k = 1 was reported for the absorbed dose to air measurements, which was partially attributed to the rotational alignment uncertainty in the geometrical setup.

Dose-rate dependence and IMRT QA suitability of EBT3 radiochromic films for pulse reduced dose-rate radiotherapy (PRDR) dosimetry.

Background: Pulsed reduced dose rate (PRDR) is an emerging radiotherapy technique for recurrent diseases. It is pertinent that the linac beam characteristics are evaluated for PRDR dose rates and a suitable dosimeter is employed for IMRT QA.

Purpose: This study sought to investigate the pulse characteristics of a 6 MV photon beam during PRDR irradiations on a commercial linac.

Biological Characterization of the Effects of Filtration on the Xoft Axxent® Electronic Brachytherapy Source for Cervical Cancer Applications.

Low-energy X-ray sources that operate in the kilovoltage energy range have been shown to induce more cellular damage when compared to their megavoltage counterparts. However, low-energy X-ray sources are more susceptible to the effects of filtration on the beam spectrum. This work sought to characterize the biological effects of the Xoft Axxent® source, a low-energy therapeutic X-ray source, both with and without the titanium vaginal applicator in place.

Measurement of the modified TG43 parameters for the bare S7600 Xoft Axxent source model.

Purpose: The purpose of this work is to provide measured data for the modified TG43 parameters [DeWerd et al.] for the newest, Galden-cooled S7600 Xoft Axxent source model.

Methods: The measurement of radial dose distributions at distances of 1 cm to 4 cm from the source was performed using TLD100 microcubes, EBT3 film, and an Exradin A26 microionization chamber.

A multi-institutional comparison of acceptance testing data for a 0.35 T MRI scanner.

To present and quantify the variability in the acceptance testing data for the imaging component of the 0.35 T magnetic resonance-linear accelerator (MR-linac).The current acceptance testing protocol by the MR-linac vendor was described along with the equipment and scanner parameters utilized throughout the process.

On the perturbation effect and LET dependence of beam quality correction factors in carbon ion beams.

Background: In a recent study, we reported beam quality correction factors, f , in carbon ion beams using Monte Carlo (MC) methods for a cylindrical and a parallel-plate ionization chamber (IC). A non-negligible perturbation effect was observed; however, the magnitude of the perturbation correction due to the specific IC subcomponents was not included. Furthermore, the stopping power data presented in the International Commission on Radiation Units and Measurements (ICRU) report 73 were used, whereas the latest stopping power data have been reported in the ICRU report 90.

An independent Monte Carlo-based IMRT QA tool for a 0.35 T MRI-guided linear accelerator.

Purpose: To develop an independent log file-based intensity-modulated radiation therapy (IMRT) quality assurance (QA) tool for the 0.35 T magnetic resonance-linac (MR-linac) and investigate the ability of various IMRT plan complexity metrics to predict the QA results. Complexity metrics related to tissue heterogeneity were also introduced.

On the length used for CT ionization chambers to determine CTDI.

Computed tomography dose index (CTDI) calculations based on measurements made with CT ionization chambers require characterization of two chamber properties: radiation sensitivity and effective length. The sensitivity of a CT ionization chamber is currently determined in some countries by calibration in an x-ray field that irradiates the entire chamber. Determination of the effective length is left to the user, and this value is frequently assumed to be equivalent to the nominal length-typically 100 mm-stated by the manufacturer.

A multi-institutional comparison of dosimetric data for a 0.35 T MR-linac.

A comparison of percent depth dose (PDD) curves, lateral beam profiles, output factors (OFs), multileaf collimator (MLC) leakage, and couch transmission factors was performed between ten institutes for a commercial 0.35 T MR-linac.The measured data was collected during acceptance testing of the MR-linac.

Monte Carlo-derived ionization chamber correction factors in therapeutic carbon ion beams.

The accuracy of electromagnetic transport in the GEANT4 Monte Carlo (MC) code was investigated for carbon ion beams and ionization chamber (IC)-specific beam quality correction factors were calculated. This work implemented a Fano cavity test for carbon ion beams in the 100-450 MeV/u energy range to assess the accuracy of the default electromagnetic physics parameters. Theand themultiple Coulomb scattering models were evaluated and the impact of,andparameters on the accuracy of the transport algorithm was investigated.

Evaluation of the GEANT4 transport algorithm and radioactive decay data for alpha particle dosimetry.

A Fano cavity test was implemented in GEANT4 Monte Carlo code to evaluate the alpha particle transport algorithm. GEANT4 alpha emission data for Pb, Ra, Th, and Ac was compared with the MIRD and RADAR decay databases. Optimal electromagnetic transport parameters (dRover of 0.

Development and evaluation of a GEANT4-based Monte Carlo Model of a 0.35 T MR-guided radiation therapy (MRgRT) linear accelerator.

Purpose: The aim of this work was to develop and benchmark a magnetic resonance (MR)-guided linear accelerator head model using the GEANT4 Monte Carlo (MC) code. The validated model was compared to the treatment planning system (TPS) and was also used to quantify the electron return effect (ERE) at a lung-water interface.

Methods: The average energy, including the spread in the energy distribution, and the radial intensity distribution of the incident electron beam were iteratively optimized in order to match the simulated beam profiles and percent depth dose (PDD) data to measured data.

A Monte Carlo Investigation of Dose Point Kernel Scaling for α-Emitting Radionuclides.

Density-based dose point kernel (DPK) scaling accuracy was investigated in various homogeneous tissue media. Using GEometry ANd Tracking 4 Monte Carlo code, DPKs were generated for 5, 8 MeV monoenergetic α particles and Ra, Ac, and Th. Dose was scored in 1 μm thick concentric shells and DPKs were scaled based on the tissue's mass density and compared with the water DPK.

Characterizing a PTW microDiamond detector in kilovoltage radiation beams.

Purpose: The aim of this work was to characterize the dosimetric properties of the PTW microDiamond (60019) single crystal synthetic diamond detector (DD) in kilovoltage x-ray beams. The following characteristics were addressed in this study: required preirradiation dose, dose-rate linearity, energy dependence, and percent depth dose response of the DD.

Methods: UWADCL x-ray beams, characterized by NIST-traceable ionization chambers, were used in this study.