Students regularly struggle with visualization and modeling of physical phenomena. Incorporating smartphones into teaching strategies has the potential to improve learning outcomes while simultaneously augmenting students' digital literacy skills in an applied context. This chapter discusses two smartphone applications developed by the authors and the accompanying research efforts in understanding how students might learn with this technology. The first app pairs augmented reality (AR) with smartphone magnetometers to visualize three-dimensional magnetic fields in space. The second uses light detection and ranging (LiDAR) technology available on modern iPhone models to plot position-time and velocity-time graphs based on users' motions. Each was developed with the support of students, teachers, software developers, and educational psychologists. In this chapter, the authors share their perspectives and other recommendations for the use and development of similar technologies to improve learning.

Data modeling and graphing skill sets are foundational to science learning and careers, yet students regularly struggle to master these basic competencies. Further, although educational researchers have uncovered numerous approaches to support sense-making with mathematical models of motion, teachers sometimes struggle to enact them due to a variety of reasons, including limited time and materials for lab-based teaching opportunities and a lack of awareness of student learning difficulties. In this paper, we introduce a free smartphone application that uses LiDAR data to support motion-based physics learning with an emphasis on graphing and mathematical modeling. We tested the embodied technology, called LiDAR Motion, with 106 students in a non-major, undergraduate physics classroom at a mid-sized, private university on the U.S. East Coast. In identical learning assessments issued both before and after the study, students working with LiDAR Motion improved their scores by a more significant margin than those using standard issue sonic rangers. Further, per a voluntary survey, students who used both technologies expressed a preference for LiDAR Motion. This mobile application holds potential for improving student learning in the classroom, at home, and in alternative learning environments.

PURPOSE:The aim of this study was to investigate thermoluminescent dosimeters (TLD) and radiochromic EBT3 film inside MR/CT visible geometric head and thorax phantoms in the presence of: 0, 0.35, and 1.5 T magnetic fields. METHODS:Thermoluminescent Dosimeters reproducibility studies were examined by irradiating IROC-Houston's TLD acrylic block five times under 0 and 1.5 T configurations of Elekta's Unity system and three times under 0 and 0.35 T configurations of ViewRay's MRIdian Cobalt-60 (60 Co) system. Both systems were irradiated with an equivalent 10 × 10 cm2 field size, and a prescribed dose of 3 Gy to the maximum depth deposition (dmax). EBT3 film and TLDs were investigated using two geometrical Magnetic Resonance (MR)-guided Radiation Therapy (MRgRT) head and thorax phantoms. Each geometrical phantom had eight quadrants that combined to create a centrally located rectangular tumor (3 × 3 × 5 cm3 ) surrounded by tissue to form a 15 × 15 × 15 cm3 cubic phantom. Liquid polyvinyl chloride plastic and Superflab were used to simulate the tumor and surrounding tissue in the head phantom, respectively. Synthetic ballistic gel and a heterogeneous in-house mixture were used to construct the tumor and surrounding tissue in the thorax phantom, respectively. EBT3 and double-loaded TLDs were used in the phantoms to compare beam profiles and point dose measurements with and without magnetic fields. GEANT4 Monte Carlo simulations were performed to validate the detectors for both Unity 0 T/1.5 T and MRIdian 0 T/0.35 T configurations. RESULTS:Average TLD block measurements which, compared the magnetic field effects (magnetic field vs 0 T) on the Unity and MRIdian systems, were 0.5% and 0.6%, respectively. The average ratios between magnetic field effects for the geometric thorax and head phantoms under the Unity system were -0.2% and 1.6% and for the MRIdian system were 0.2% and -0.3%, respectively. Beam profiles generated with both systems agreed with Monte Carlo measurements and previous literature findings. CONCLUSIONS:TLDs and EBT3 film dosimeters could potentially be used in MR/CT visible tissue equivalent phantoms that will experience a magnetic field environment.

Purpose High energetic carbon (C-) ion beams undergo nuclear interactions with tissue, producing secondary nuclear fragments. Thus, at depth, C-ion beams are composed of a mixture of different particles with different linear energy transfer (LET) values. We developed a technique to enable isolation of DNA damage response (DDR) in mixed radiation fields using beam line microscopy coupled with fluorescence nuclear track detectors (FNTDs). Methods We imaged live cells on a coverslip made of FNTDs right after C-ion, proton or photon irradiation using an in-house built confocal microscope placed in the beam path. We used the FNTD to link track traversals with DNA damage and separated DNA damage induced by primary particles from fragments. Results We were able to spatially link physical parameters of radiation tracks to DDR in live cells to investigate spatiotemporal DDR in multi-ion radiation fields in real time, which was previously not possible. We demonstrated that the response of lesions produced by the high-LET primary particles associates most strongly with cell death in a multi-LET radiation field, and that this association is not seen when analyzing radiation induced foci in aggregate without primary/fragment classification. Conclusions We report a new method that uses confocal microscopy in combination with FNTDs to provide submicrometer spatial-resolution measurements of radiation tracks in live cells. Our method facilitates expansion of the radiation-induced DDR research because it can be used in any particle beam line including particle therapy beam lines. Category Biological Physics and Response Prediction.

To investigate beam profiles for small square fields from a 1.5 T MRI – 7 MV linear accelerator system (MR-Linac) measured with Gafchromic film, Fricke gel films, and a microDiamond detector. EBT-3 radiochromic films were irradiated to 4 Gy at isocenter distance at 5 cm depth inside a water phantom. 2x2, 3x3, 5x5, and 10x10 cm2 fields were delivered by an MR-Linac while the magnetic field (B-field) was turned off. Fricke-type gels were manufactured in-house, poured into 5-mm thick sheets and stored at 4⁰C for 24 hours prior to irradiation. The gel sheets were placed at isocenter at 5 cm depth in a solid water phantom and irradiated to 4Gy for each field size. All gels and films were scanned with an Epson 10000XL flatbed scanner pre- and post-irradiation. In-plane and cross-plane beam profiles were measured for all four field sizes with a PTW60019 microDiamond detector at 5 cm depth inside a water phantom under the same conditions. In-plane and cross-plane profiles measured with the planar detectors were analyzed and compared to profiles obtained with the microDiamond detector. All measurements were repeated with the B-field turned on. With the B-field off, in-plane and cross-plane profiles measured with film agreed to approximately 1% with microDiamond measurements. Compared to the microdiamond data, the 10x10 cm2 cross-plane profile from film measurements indicated slightly more than 1% higher signal more than 3 cm away from the central axis. The 80/20 penumbra regions overlapped for both detectors. The shape of the cross-plane profiles measured with gel dosimetry conformed with both film and microDiamond. The gel measurements exhibited more signal variations inside the radiation field and reported lower doses in the penumbra. With the B-field on, the effect of the magnetic field was clearly seen. In-plane profiles appeared symmetric while cross-plane profiles were noticably asymmetric. Film and microDiamond measurements agreed within 1-2% for all four fields. The shape of the profiles measured with gels agreed with both film and microDiamond. In regions of non-uniform thickness the gels demonstrated variations in signal. Both microDiamond and EBT-3 film offer a valuable means to measure small fields with steep dose gradients from the MR-Linac. Maintaining good quality control during the fabrication process of gel sheets is crucial to obtain uniform sheet thickness. Further investigation of gel sheets will be pursued as an alternative to film measurements.

PURPOSE:The aim of this study was to examine the effect of submillimeter air gaps that may exist between an ionization chamber and solid phantoms when measurements are performed in a magnetic field. METHODS:Geant4 Monte Carlo simulations were performed using a model of a PTW 30013 Farmer chamber in a water phantom. Symmetrical and asymmetrical air gaps of various thicknesses were modeled surrounding the chamber, and the dose to the air cavity of the chamber was scored in each case. Magnetic fields were modeled parallel to the long axis of the chamber with strengths of 0, 0.35 T, 1.0 T, and 1.5 T. To examine the phenomenon in more detail, the gyroradii of the electrons responsible for the energy deposited in the chamber were scored as they entered the chamber and the total energy deposited was split into three components: energy originating from inside the chamber, in the immediate vacinity of the chamber, or outside the chamber. RESULTS:Differences in the chamber dose of 1.6% were observed for asymmetric air gaps just 0.2 mm thick. No effect greater than 0.5% was observed for the symmetrical air gaps investigated in this work (1.4 mm thick or less) for this chamber/magnetic field configuration. The mean gyroradius of contributing electrons as they first enter the chamber was 4 mm. The presence of the air gap reduced the energy contributions from electrons released in the immediate vicinity of the chamber, and this loss was not completely compensated for when a magnetic field was present. CONCLUSIONS:The gyroradius of most electrons was too large to be responsible for the air gap effect via the electron return effect; instead, the effect is attributed to the loss of energy contributions from electrons originating inside the air gap volume, which is not completely compensated for by more distant electrons owing to their reduced range in the magnetic field. When the chamber is parallel with the magnetic field, symmetric air gaps have a smaller effect (< 0.5%) compared to asymmetric air-gaps (up to 1.6%) on the chamber response.

PURPOSE The purpose of this study was to acquire beam data for an MR-linac, with and without a 1.5 T magnetic field, by using a variety of commercially available detectors to assess their relative response in the magnetic field. The impact of the magnetic field on the measured dose distribution was also assessed. METHODS An MR-safe 3D scanning water phantom was used to measure output factors, depth dose curves, and off-axis profiles for various depths and for field sizes between 2 × 2 cm2 and 22 × 22 cm2 for an Elekta MR-linac beam with the orthogonal 1.5 T magnetic field on or off. An on-board MV portal imaging system was used to ensure that the reproducibility of the detector position, both with and without the magnetic field, was within 0.1 mm. The detectors used included ionization chambers with large, medium, and small sensitive volumes; a diamond detector; a shielded diode; and an unshielded diode. RESULTS The offset of the effective point of measurement of the ionization chambers was found to be reduced by at least half for each chamber in the direction parallel with the beam. A lateral shift of similar magnitude was also introduced to the chambers' effective point of measurement toward the average direction of the Lorentz force. A similar lateral shift (but in the opposite direction) was also observed for the diamond and diode detectors. The measured lateral shift in the dose distribution was independent of depth and field size for each detector for fields between 2 × 2 cm2 and 10 × 10 cm2 . The shielded diode significantly misrepresented the dose distribution in the lateral direction perpendicular to the magnetic field, making it seem more symmetric. The percentage depth dose was generally found to be lower with the magnetic field than without, but this difference was reduced as field size increased. The depth of maximum dose showed little dependence on field size in the presence of the magnetic field, with values from 1.2 cm to 1.3 cm between the 2 × 2 cm2 and 22 × 22 cm2 fields. Output factors measured in the magnetic field at the center of the beam profile produced a larger spread of values between detectors for fields smaller than 10 × 10 cm2 (with a spread of 2% at 3 × 3 cm2 ). The spread of values was more consistent when the output factors were measured at the point of peak intensity of the lateral dose distribution instead (except for the shielded diode which differed by up to 2% depending on field size). CONCLUSIONS The magnetic field of the MR-linac alters the effective point of measurement of ionization chambers, shifting it both downstream and laterally. Shielded diodes produce incorrect and misleading dose profiles. The output factor measured at the point of peak intensity in the lateral dose distribution is more robust than the conventional output factor (measured at central axis). Diodes are not recommended for output factor measurements in the magnetic field.

Magnetic resonance imaging-guided radiotherapy (MRIgRT) is an emerging technology that requires the use of radiation fields in the presence of magnetic (B) fields. In the presence of B-fields the Lorentz force influences the trajectories of the secondary electrons, which in turn affects both the dose distribution in water and the dose-response of ionization chambers and several other detectors. Thus, dosimetry in the presence of a B-field requires understanding both the B-field effects on the dose distribution and the response of detectors. In this paper we present measured data to show effects of the B-field on the dose distributions, response of ionization chambers, and presence of air-gaps surrounding the sensitive volume of the detector.

Patients undergoing prostate intensity modulated arc therapy were retrospectively investigated using the CBCT images acquired for setup purposes to determine the volumetric variability of the target and organs at risk. This was achieved using a novel CT deformable registration algorithm based on analysis of phase correlation in the Fourier domain. For between 10 and 21 of their 37 fractions, the patients were scanned using an on-board imager. A transformation vector field, calculated by the registration algorithm for each CBCT image, was used to deform the CT so the plan could be recalculated using the original MU. This allowed the determination of the dosimetric implications of any changes from the time of acquisition of the planning CT to immediately prior to a given treatment fraction. The variation in mean dose to the target did not result in any significant under-dosing for any patient, with the minimum mean dose never decreasing by greater than 2% of the planned amount. The rectum saw volumetric variations between −21% and 2% of the planning volume. This never resulted in a decrease in the mean dose, but caused increases of up to 34%. The bladder saw volumetric variations in the range of −10% to 19% of the planning volume. Mean dose values changed between −11% and 17% of the planned mean dose. Despite these variations, neither OAR exceeded our institutional dose–volume constraints at any fraction. Future work will be completed to investigate any trends in organ displacements, volume deformations, and the dosimetric impact of these changes.

Purpose: The use of radiotherapy fields smaller than 3 cm in diameter has resulted in the need for accurate detector correction factors for small field dosimetry. However, published factors do not always agree and errors introduced by biased reference detectors, inaccurate Monte Carlo models, or experimental errors can be difficult to distinguish. The aim of this study was to provide a robust set of detector-correction factors for a range of detectors using numerical, empirical, and semiempirical techniques under the same conditions and to examine the consistency of these factors between techniques. Methods: Empirical detector correction factors were derived based on small field output factor measurements for circular field sizes from 3.1 to 0.3 cm in diameter performed with a 6 MV beam. A PTW 60019 microDiamond detector was used as the reference dosimeter. Numerical detector correction factors for the same fields were derived based on calculations from a geant4 Monte Carlo model of the detectors and the Linac treatment head. Semiempirical detector correction factors were derived from the empirical output factors and the numerical dose-to-water calculations. Results: The PTW 60019 microDiamond was found to over-respond at small field sizes resulting in a bias in the empirical detector correction factors. The over-response was similar in magnitude to that of the unshielded diode. Good agreement was generally found between semiempirical and numerical detector correction factors except for the PTW 60016 Diode P, where the numerical values showed a greater over-response than the semiempirical values by a factor of 3.7% for a 1.1 cm diameter field and higher for smaller fields. Conclusions: Detector correction factors based solely on empirical measurement or numerical calculation are subject to potential bias. A semiempirical approach, combining both empirical and numerical data, provided the most reliable results.

Purpose: In MRI-linac integrated systems, the presence of the magnetic (B-)field has a large impact of the dose-distribution and the dose-responses of detectors; yet established protocols and previous experience may lead to assumptions about the commissioning process that are no longer valid. This study quantifies parameters that change when performing dosimetry with an MRI-linac including beam quality specifiers and the effective-point-of-measurement (EPOM) of ionization chambers. Methods: We used the Geant4 Monte Carlo code for this work with physics parameters that pass the Fano cavity test to within 0.1% for the simulated conditions with and without a 1.5 T B-field. A point source model with the energy distribution of an MRI-linac beam was used with and without the B-field to calculate the beam quality specifiers %dd(10)× and TPR2010, the variation of chamber response with orientation and the how the B-field affects the EPOM of ionization chambers by comparing depth-dose curves calculated in water to those generated by a model PTW30013 Farmer chamber. Results: The %dd(10)× changes by over 2% in the presence of the B-field while the TPR2010 is unaffected. Ionization chamber dose-response is known to depend on the orientation w.r.t. the B-field, but two alternative perpendicular orientations (anti-parallel to each other) also differ in dose-response by over 1%. The B-field shifts the EPOM downstream (closer to the chamber center) but it is also shifted laterally by 0.27 times the chamber's cavity radius. Conclusion: The EPOM is affected by the B-field and it even shifts laterally. The relationship between %dd(10)× and the Spencer-Attix stopping powers is also changed. Care must be taken when using chambers perpendicular to the field as the dose-response changes depending on which perpendicular orientation is used. All of these effects must be considered when performing dosimetry in B-fields and should be accounted for in future dosimetry protocols. This project was partially funded by Elekta Ltd.

Monte Carlo models of radiotherapy linacs require the accurate calibration of source parameters including the spot-size of the primary electron beam incident on the target. This parameter is especially important for small field calculations. The calibration of this parameter usually relies on performing small field measurements, which have high uncertainties, and numerous Monte Carlo dose calculations over a range of spot-sizes which is a time consuming process. Here we show that measurements of the collimated photon energy-fluence distribution of a linac beam using a simple movable slit-collimator/detector system can be used as a surrogate to determine the spot-size of the primary electron beam based on a Monte Carlo derived calibration curve. The results of this method were found to be accurate to within (0.1–0.3) mm when compared to an independent method. The calibration curve was derived for an Elekta Precise 6 MV beam but was also found to be robust across a range of beam energies and linac models. Monte Carlo models of radiotherapy linacs require the accurate calibration of source parameters including the spot-size of the primary electron beam incident on the target. This parameter is especially important for small field calculations. The calibration of this parameter usually relies on performing small field measurements, which have high uncertainties, and numerous Monte Carlo dose calculations over a range of spot-sizes which is a time consuming process. Here we show that measurements of the collimated photon energy-fluence distribution of a linac beam using a simple movable slit-collimator/detector system can be used as a surrogate to determine the spot-size of the primary electron beam based on a Monte Carlo derived calibration curve. The results of this method were found to be accurate to within (0.1–0.3) mm when compared to an independent method. The calibration curve was derived for an Elekta Precise 6 MV beam but was also found to be robust across a range of beam energies and linac models.

Purpose:In MRI-linac integrated systems, the presence of the magnetic (B-)field has a large impact of the dose-distribution and the dose-responses of detectors; yet established protocols and previous experience may lead to assumptions about the commissioning process that are no longer valid. This study quantifies parameters that change when performing dosimetry with an MRI-linac including beam quality specifiers and the effective-point-of-measurement (EPOM) of ionization chambers.Methods:We used the Geant4 Monte Carlo code for this work with physics parameters that pass the Fano cavity test to within 0.1% for the simulated conditions with and without a 1.5 T B-field. A point source model with the energy distribution of an MRI-linac beam was used with and without the B-field to calculate the beam quality specifiers %dd(10)× and TPR2010, the variation of chamber response with orientation and the how the B-field affects the EPOM of ionization chambers by comparing depth-dose curves calculated in water to those generated by a model PTW30013 Farmer chamber.Results:The %dd(10)× changes by over 2% in the presence of the B-field while the TPR2010 is unaffected. Ionization chamber dose-response is known to depend on the orientation w.r.t. the B-field, but two alternative perpendicular orientations (anti-parallel to each other) also differ in dose-response by over 1%. The B-field shifts the EPOM downstream (closer to the chamber center) but it is also shifted laterally by 0.27 times the chamberu0027s cavity radius.Conclusion:The EPOM is affected by the B-field and it even shifts laterally. The relationship between %dd(10)× and the Spencer-Attix stopping powers is also changed. Care must be taken when using chambers perpendicular to the field as the dose-response changes depending on which perpendicular orientation is used. All of these effects must be considered when performing dosimetry in B-fields and should be accounted for in future dosimetry protocols.This project was partially funded by Elekta Ltd.