Determination of the beam quality correction factor for the PTW Semiflex 3D ionization chamber for the reference dosimetry at ZAP-X.

Purpose: The self-shielding radiosurgery system ZAP-X consists of a 3 MV linear accelerator and eight round collimators. For this system, it is a common practice to perform the reference dosimetry using the largest 25 mm diameter collimator at a source-to-axis distance (SAD) of 45 cm with the PTW Semiflex3D chamber placed at a measurement depth of 7 mm in water. Existing dosimetry protocols do not provide correction for these measurement conditions.

A unified deep-learning framework for enhanced patient-specific quality assurance of intensity-modulated radiation therapy plans.

Background: Modern radiation therapy techniques, such as intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT), use complex fluence modulation strategies to achieve optimal patient dose distribution. Ensuring their accuracy necessitates rigorous patient-specific quality assurance (PSQA), traditionally done through pretreatment measurements with detector arrays. While effective, these methods are labor-intensive and time-consuming.

Impact of nuclear fragmentation on the stopping power ratio ofC ion beams.

: Nuclear fragmentation generates a diverse dosimetric environment in the path ofC ion beams. Concise parametrization of the beam's composition is paramount for determining key correction factors in clinical dosimetry. This study sets out to provide such a parametrization based on detailed Monte Carlo simulations of clinically relevantC beams.

Fano cavity test and investigation of the response of the Roos chamber irradiated by proton beams in perpendicular magnetic fields up to 1 T.

. The aim of this work is to investigate the response of the Roos chamber (type 34001) irradiated by clinical proton beams in magnetic fields..

Proton dosimetry in a magnetic field: Measurement and calculation of magnetic field correction factors for a plane-parallel ionization chamber.

Background: The combination of magnetic resonance imaging and proton therapy offers the potential to improve cancer treatment. The magnetic field (MF)-dependent change in the dosage of ionization chambers in magnetic resonance imaging-integrated proton therapy (MRiPT) is considered by the correction factor , which needs to be determined experimentally or computed via Monte Carlo (MC) simulations.

Purpose: In this study, was both measured and simulated with high accuracy for a plane-parallel ionization chamber at different clinical relevant proton energies and MF strengths.

Comprehensive investigation of lateral dose profile and output factor measurements in small proton fields from different delivery techniques.

Background And Purpose: As a part of the commissioning and quality assurance in proton beam therapy, lateral dose profiles and output factors have to be acquired. Such measurements can be performed with point detectors and are especially challenging in small fields or steep lateral penumbra regions as the detector's volume effect may lead to perturbations. To address this issue, this work aims to quantify and correct for such perturbations of six point detectors in small proton fields created via three different delivery techniques.

Validating a double Gaussian source model for small proton fields in a commercial Monte-Carlo dose calculation engine.

Purpose: The primary fluence of a proton pencil beam exiting the accelerator is enveloped by a region of secondaries, commonly called "spray". Although small in magnitude, this spray may affect dose distributions in pencil beam scanning mode e.g.

Charge collection efficiency, underlying recombination mechanisms, and the role of electrode distance of vented ionization chambers under ultra-high dose-per-pulse conditions.

Purpose: Investigating and understanding of the underlying mechanisms affecting the charge collection efficiency (CCE) of vented ionization chambers under ultra-high dose rate pulsed electron radiation. This is an important step towards real-time dosimetry with ionization chambers in FLASH radiotherapy.

Methods: Parallel-plate ionization chambers (PPIC) with three different electrode distances were build and investigated with electron beams with ultra-high dose-per-pulse (DPP) up to 5.

Investigating the lateral dose response functions of point detectors in proton beams.

. Point detector measurements in proton fields are perturbed by the volume effect originating from geometrical volume-averaging within the extended detector's sensitive volume and density perturbations by non-water equivalent detector components. Detector specific lateral dose response functions() can be used to characterize the volume effect within the framework of a mathematical convolution model, where() is the convolution kernel transforming the true dose profile() into the measured signal profile of a detector().

Model-based machine learning for the recovery of lateral dose profiles of small photon fields in magnetic field.

. To investigate the feasibility to train artificial neural networks (NN) to recover lateral dose profiles from detector measurements in a magnetic field..

The magnetic field dependent displacement effect and its correction in reference and relative dosimetry.

This study investigates the perturbation correction factors of air-filled ionization chambers regarding their depth and magnetic field dependence. Focus has been placed on the displacement or gradient correction factorPgr.Additionally, the shift of the effective point of measurementPeffthat can be applied to account for the gradient effect has been compared between the cases with and without magnetic field.

Systematic end-to-end testing of multiple target treatments using the modular RUBY phantom.

The RUBY head phantom in combination with the System QA insert MultiMet can be used for simultaneous point dose measurements at an isocentric and two off-axis positions. This study investigates the suitability of the system for systematic integral end-to-end testing of single-isocenter multiple target stereotactic treatments. Several volumetric modulated arc therapy plans were optimized on a planning CT of the phantom positioned in a stereotactic mask on the stereotactic treatment board.

Corrections of photon beam profiles of small fields measured with ionization chambers using a three-layer neural network.

The purpose of this work is to study the feasibility of photon beam profile deconvolution using a feedforward neural network (NN) in very small fields (down to 0.56 × 0.56 cm ).

The dose response of PTW microDiamond and microSilicon in transverse magnetic field under small field conditions.

The aim of the present work is to investigate the behavior of two diode-type detectors (PTW microDiamond 60019 and PTW microSilicon 60023) in transverse magnetic field under small field conditions. A formalism based on TRS 483 has been proposed serving as the framework for the application of these high-resolution detectors under these conditions. Measurements were performed at the National Metrology Institute of Germany (PTB, Braunschweig) using a research clinical linear accelerator facility.

VHEE beam dosimetry at CERN Linear Electron Accelerator for Research under ultra-high dose rate conditions.

The aim of this work is the dosimetric characterization of a plane parallel ionization chamber under defined beam setups at the CERN Linear Electron Accelerator for Research (CLEAR). A laser driven electron beam with energy of 200 MeV at two different field sizes of approximately 3.5 mm FWHM and approximately 7 mm FWHM were used at different pulse structures.

The role of the construction and sensitive volume of compact ionization chambers on the magnetic field-dependent dose response.

Purpose: The magnetic-field correction factors of compact air-filled ionization chambers have been investigated experimentally and using Monte Carlo simulations up to 1.5 T. The role of the nonsensitive region within the air cavity and influence of the chamber construction on its dose response have been elucidated.

Ion collection efficiency of ionization chambers in ultra-high dose-per-pulse electron beams.

Purpose: The ion collection efficiency of vented ionization chambers has been investigated in an ultra-high dose-per-pulse (DPP) electron beam. The role of the chamber design and the electric field strength in the sensitive air volume have been evaluated.

Methods: An advanced Markus chamber and three specially designed parallel plate air-filled ionization chambers (EWC: End Window Chamber) with varying electrode distance of 0.

The dose response of high-resolution diode-type detectors and the role of their structural components in strong magnetic field.

Purpose: This study aims to investigate the dose response of diode-type detectors in the presence of strong magnetic field and to understand the underlying mechanisms leading to the observed magnetic field dependence by close examinations on the role of the detector's design.

Materials And Methods: Three clinical diode-type detectors (PTW microSilicon type 60023, PTW microDiamond type 60019, and IBA Razor diode) have been studied. Measurements were performed at the linear accelerator experimental facility of the German National Metrology Institute (PTB, Braunschweig) with electromagnets up to 1.

Monte Carlo simulated beam quality and perturbation correction factors for ionization chambers in monoenergetic proton beams.

Purpose: Beam quality correction factors provided in current codes of practice for proton beams are approximated using the water-to-air mass stopping power ratio and by assuming the proton beam quality related perturbation correction factors to be unity. The aim of this work is to use Monte Carlo simulations to calculate energy dependent beam quality and perturbation correction factors for a set of nine ionization chambers in proton beams.

Methods: The Monte Carlo code EGSnrc was used to determine the ratio of the absorbed dose to water and the absorbed dose to the sensitive air volume of ionization chambers related to the reference photon beam quality ( Co).

Evaluation of the RUBY modular QA phantom for planar and non-coplanar VMAT and stereotactic radiations.

Purpose: This study evaluates the clinical use of the RUBY modular QA phantom for linac QA to validate the integrity of IGRT workflows including the congruence of machine isocenter, imaging isocenter, and room lasers. The results have been benchmarked against those obtained with widely used systems. Additionally, the RUBY phantom has been implemented to perform system QA (End-to-End testing) from imaging to radiation for IGRT-based VMAT and stereotactic radiations at an Elekta Synergy linac.

Analysis of the applicability of two-dimensional detector arrays in terms of sampling rate and detector size to verify scanned intensity-modulated proton therapy plans.

Purpose: The introduction of advanced treatment techniques in proton therapy, such as intensity-modulated proton therapy, leads to an increased need for patient-specific quality assurance, especially an accurate treatment plan verification becomes inevitable. In this study, signal theoretical analysis of dose distributions in scanned proton therapy is performed to investigate the feasibility and limits of two-dimensional (2D) detector arrays for treatment plan verification.

Methods: 2D detector arrays are characterized by two main aspects: the distance between the single detectors on the array or the sampling frequency; and the lateral response functions of a single detector.

Experimental determination of the recombination correction factor k for SNC 125c, SNC 350p and SNC 600c ionization chambers in pulsed photon beams.

Accurate ionization chamber measurements of the absorbed dose to water require the correction of incomplete collection of charges created within the chamber volume. According to current dosimetry protocols such as the TRS-398 or the DIN 6800-2, incomplete charge collection is accounted for by the correction factor k, which can be determined numerically or experimentally. The method proposed by Burns & McEwen (Phys.

Small field output correction factors of the microSilicon detector and a deeper understanding of their origin by quantifying perturbation factors.

Purpose: The aim of this study is the experimental and Monte Carlo-based determination of small field correction factors for the unshielded silicon detector microSilicon for a standard linear accelerator as well as the Cyberknife System. In addition, a detailed Monte Carlo analysis has been performed by modifying the detector models stepwise to study the influences of the detector's components.

Methods: Small field output correction factors have been determined for the new unshielded silicon diode detector, microSilicon (type 60023, PTW Freiburg, Germany) as well as for the predecessors Diode E (type 60017, PTW Freiburg, Germany) and Diode SRS (type 60018, PTW Freiburg, Germany) for a Varian TrueBeam linear accelerator at 6 MV and a Cyberknife system.