A 2D detector array for relative dosimetry and beam steering for FLASH radiotherapy with electrons.

Background: FLASH radiotherapy is an emerging treatment modality using ultra-high dose rate beams. Much effort has been made to develop suitable dosimeters for reference dosimetry, yet the spatial beam characteristics must also be characterized to enable computerized treatment planning, as well as quality control and service of a treatment delivery device. In conventional radiation therapy, this is commonly achieved by beam profile scans in a water phantom using a point detector.

Quantitative, real-time scintillation imaging for experimental comparison of different dose and dose rate estimations in UHDR proton pencil beams.

Background: Ultra-high dose rate radiotherapy (UHDR-RT) has demonstrated normal tissue sparing capabilities, termed the FLASH effect; however, available dosimetry tools make it challenging to characterize the UHDR beams with sufficiently high concurrent spatial and temporal resolution. Novel dosimeters are needed for safe clinical implementation and improved understanding of the effect of UHDR-RT.

Purpose: Ultra-fast scintillation imaging has been shown to provide a unique tool for spatio-temporal dosimetry of conventional cyclotron pencil beam scanning (PBS) deliveries, indicating the potential use for characterization of UHDR PBS proton beams.

Electron beam response corrections for an ultra-high-dose-rate capable diode dosimeter.

Background: Ultra-high-dose-rate (UHDR) electron beams have been commonly utilized in FLASH studies and the translation of FLASH Radiotherapy (RT) to the clinic. The EDGE diode detector has potential use for UHDR dosimetry albeit with a beam energy dependency observed.

Purpose: The purpose is to present the electron beam response for an EDGE detector in dependence on beam energy, to characterize the EDGE detector's response under UHDR conditions, and to validate correction factors derived from the first detailed Monte Carlo model of the EDGE diode against measurements, particularly under UHDR conditions.

Characterization of a diode dosimeter for UHDR FLASH radiotherapy.

Background: Ultra-high dose rate (UHDR) FLASH beams typically deliver dose at rates of  >40 Gy/sec. Characterization of these beams with respect to dose, mean dose rate, and dose per pulse requires dosimeters which exhibit high temporal resolution and fast readout capabilities.

Purpose: A diode EDGE Detector with a newly designed electrometer has been characterized for use in an UHDR electron beam and demonstrated appropriateness for UHDR FLASH radiotherapy dosimetry.

The probe-format graphite calorimeter, Aerrow, for absolute dosimetry in ultrahigh pulse dose rate electron beams.

Purpose: The purpose of this investigation is to evaluate the use of a probe-format graphite calorimeter, Aerrow, as an absolute and relative dosimeter of high-energy pulse dose rate (UHPDR) electron beams for in-water reference and depth-dose-type measurements, respectively.

Methods: In this paper, the calorimeter system is used to investigate the potential influence of dose per pulses delivered up to 5.6 Gy, the number of pulses delivered per measurement, and its potential for relative measurement (depth-dose curve measurement).

Validation of an improved helical diode array and dose reconstruction software using TG-244 datasets and stringent dose comparison criteria.

The original helical ArcCHECK (AC) diode array and associated software for 3D measurement-guided dose reconstruction were characterized and validated; however, recent design changes to the AC required that the subject be revisited. The most important AC change starting in 2014 was a significant reduction in the overresponse of diodes to scattered radiation outside of the direct beam, accom-plished by reducing the amount of high-Z materials adjacent to the diodes. This change improved the diode measurement accuracy, but in the process invalidated the dose reconstruction models that were assembled based on measured data acquired with the older version of the AC.

Evaluating dosimetric accuracy of flattening filter free compensator-based IMRT: measurements with diode arrays.

Purpose: Compensator-based IMRT coupled with the high dose rate flattening filter free (FFF) beams offers an intriguing possibility of delivering an intensity modulated radiation field in just a few seconds. As a first step, the authors evaluate the dosimetric accuracy of the treatment planning system (TPS) FFF beam model with compensators.

Methods: A 6 MV FFF beam from a TrueBeam accelerator (Varian Medical Systems, Palo Alto CA) was modeled in PINNACLE TPS (v.

Optimizing the accuracy of a helical diode array dosimeter: a comprehensive calibration methodology coupled with a novel virtual inclinometer.

Purpose: The goal of any dosimeter is to be as accurate as possible when measuring absolute dose to compare with calculated dose. This limits the uncertainties associated with the dosimeter itself and allows the task of dose QA to focus on detecting errors in the treatment planning (TPS) and/or delivery systems. This work introduces enhancements to the measurement accuracy of a 3D dosimeter comprised of a helical plane of diodes in a volumetric phantom.

Characterization of a multi-axis ion chamber array.

Purpose: The aim of this work was to characterize a multi-axis ion chamber array (IC PROFILER; Sun Nuclear Corporation, Melbourne, FL, USA) that has the potential to simplify the acquisition of LINAC beam data.

Methods: The IC PROFILER (or panel) measurement response was characterized with respect to radiation beam properties, including dose, dose per pulse, pulse rate frequency (PRF), and energy. Panel properties were also studied, including detector-calibration stability, power-on time, backscatter dependence, and the panel's agreement with water tank measurements [profiles, fractional depth dose (FDD), and output factors].

Calibration of a novel four-dimensional diode array.

Purpose: The aim of this work is to develop effective calibration methods for a novel fourdimensional (4D) diode array for pretreatment verification of intensity-modulated radiation therapy (IMRT) and rotational therapy.

Methods: A novel 4D diode array (ArcCHECK, Sun Nuclear, Melbourne, FL) was developed to meet the needs of appropriate and efficient quality assurance for IMRT and especially rotational radiotherapy. The diode array presents a consistent detector image in beam's eye view at arbitrary gantry angles due to isotropic arrangement of diodes in a three-dimensional (3D) cylindrical phantom.

Novel dosimetric phantom for quality assurance of volumetric modulated arc therapy.

The objective of this work is to assess the suitability and performance of a new dosimeter system with a novel geometry for the quality assurance (QA) of volumetric modulated arc therapy (VMAT). The new dosimeter system consists of a hollow cylinder (15 and 25 cm inner and outer diameters) with 124 diodes embedded in the phantom's cylindrical wall forming four rings of detectors. For coplanar beams, the cylindrical geometry and the ring diode pattern offer the advantage of invariant perpendicular incidence on the beam central axis for any gantry angle and also have the benefit of increasing the detector density as both walls of the cylinder sample the beam.

A prototype quantitative film scanner for radiochromic film dosimetry.

We have developed a high resolution, quantitative, two-dimensional optical film scanner for use with a commercial high sensitivity radiochromic film (RCF) for measuring single fraction external-beam radiotherapy dose distributions. The film scanner was designed to eliminate artifacts commonly observed in RCF dosimetry. The scanner employed a stationary light source and detector with a moving antireflective glass film platen attached to a high precision computerized X-Y translation stage.

Important considerations for radiochromic film dosimetry with flatbed CCD scanners and EBT GAFCHROMIC film.

In this study, we present three significant artifacts that have the potential to negatively impact the accuracy and precision of film dosimetry measurements made using GAFCHROMIC EBT radiochromic film when read out with CCD flatbed scanners. Films were scanned using three commonly employed instruments: a Macbeth TD932 spot densitometer, an Epson Expression 1680 CCD array scanner, and a Microtek ScanMaker i900 CCD array scanner. For the two scanners we assessed the variation in optical density (OD) of GAFCHROMIC EBT film with scanning bed position, angular rotation of the film with respect to the scan line direction, and temperature inside the scanner due to repeated scanning.