Physicists In Medicine Research Articles

Accuracy of Acuros^{text {TM}} BV as determined from GATE monte-carlo simulation

The American Association of Physicists in Medicine’s Task Group No.43 has provided a standardised dose calculation methodology that is now the international benchmark for all brachytherapy dosimetry publications and treatment planning systems. However, limitations in this methodology has seen the development of Model-Based Dose Calculation Algorithms (MBDCA). In 2009, Varian (Varian Medical Systems, Palo Alto, CA, USA) released Acuros^{text {TM}} BrachyVision (ABV) which calculates dose by explicitly solving the Linear Boltzmann Transport Equation. In this study we have assessed the accuracy of ABV dose calculations within a range of materials relevant to high dose rate brachytherapy with an iridium-192 (^{text {192}}Ir) source. Accuracy assessment has been achieved by implementing a modelled GamaMed Plus ^{text {192}}Ir source within a series of phantoms using the GEANT4 Application for Emission Tomography (GATE) to calculate dose for comparison with dose as determined by ABV. Comparisons between GATE and ABV were made using point-to-point profile comparisons and 1D gamma analysis. Source validation results yielded good agreement with published data. Spectrum and TG43U1 comparisons showed no major differences, with TG43U1 comparisons agreeing within ± 1%. Point-to-point comparisons showed large differences between GATE and ABV near the source and in low density materials. 1D gamma analysis pass criteria of 2%/1 mm and 2%/2 mm yielded passing rates ranging between 51.72–100% and 62.07–100% respectively. A critical analysis of this study’s results suggest that ABV is unable to accurately calculate doses in low density materials. Furthermore, spatial accuracy of dose near the source is within 2 mm.

Evaluating Risk of FLASH Experiments on a Clinical LINAC with Failure Mode and Effects Analysis

<h3>Purpose/Objective(s)</h3> Use of clinical linear accelerators in ultra-high dose rate (UHDR) mode can provide a conduit for wider access to UHDR FLASH effects, sparing normal tissue, but care needs to be taken in the use of such systems to ensure errors are avoided. A Failure Modes and Effects Analysis (FMEA) was conducted with a team involved in converting a LINAC between clinical use and UHDR experimental mode for more than one year, following the proposed methods of AAPM (The American Association of Physicists in Medicine) Task Group 100 report. <h3>Materials/Methods</h3> A team of 9 professionals with extensive experience outlined the process map and workflow for analysis, and developed fault trees for potential errors, as well as failure modes that would results. The team scored the categories of severity magnitude (S), occurrence likelihood (O), and detectability potential (D) on a scale of 1 to 10, so that a risk priority number (RPN=S*O*D) could be assessed for each potential failure. <h3>Results</h3> A total of 46 potential failure modes were identified, including 5 with RPN>100, all during converting and experimental use in UHDR mode and none during conversion to clinical mode. These failure modes involved 1) patient set up, 2) gating mechanisms in delivery, and 3) detector in the beam stop mechanism. Identified methods to mitigate errors included 1) use of a checklist post conversion, 2) use of robust radiation detectors, 3) automation of QA and beam consistency checks, and 4) implementation of surface guidance during beam delivery. <h3>Conclusion</h3> The FMEA process was considered critically important in this setting of a new use of a LINAC, and the expert team developed a higher level of confidence in the ability to safely move UHDR LINAC use towards expanded research access.

Small-field dosimetry with detector-specific output correction factor for single-isocenter stereotactic radiotherapy of single and multiple brain metastases.

Recently, the International Atomic Energy Agency and the American Association of Physicists in Medicine reported correction factors (CFs) for detector-response variation considering the uncertainty in detector readings in small-field dosimetry. In this study, the effect of CFs on small-field dosimetry measurements was evaluated for single-isocenter stereotactic radiotherapy for brain metastases. The output factors (OPFs) were measured with and without CFs in a water-equivalent sphere phantom using TrueBeam with a flattening-filter-free energy of 10 MV. Five detectors were used in a perpendicular orientation: CC01, 3D pinpoint ionization chambers, unshielded SFD detector, shielded EDGE detector, and microDiamond detector. First, the square-field sizes were set to 5-100mm using a multi-leaf collimator (MLC) field. The OPFs were evaluated in the presence and absence of CFs. Second, single-isocenter stereotactic irradiation was performed on 22 brain metastases in 15 patients following dynamic conformal arc (DCA) treatment. The equivalent field size was calculated using the MLC aperture for each planning target volume. For the OPFs, the mean deviations from the median of the doses measured with detectors other than the CC01 for square-field sizes larger than 10mm were within ± 4.3% of the median without CFs, and ± 3.3% with CFs. For DCA plans, the deviations without and with CFs were -2.3 ± 1.9% and -4.8 ± 2.4% for CC01, -1.1 ± 3.0% and 1.0 ± 1.6% for 3D pinpoint, 8.8 ± 3.0% and 2.9 ± 2.8% for SFD, -3.1 ± 3.0% and -13.5 ± 4.0% for EDGE, and 8.9 ± 2.1% and 0.8 ± 1.9% for microDiamond. This feasibility study confirmed that the deviation of the detectors can be reduced using an appropriate detector with CFs.

Diffusion and kinetic energy of electrons accelerated by focused few-cycle azimuthally polarized pulses

Using the model of the focused few-cycle azimuthally polarized ultrashort pulses based on the complex sink-source method, the electron acceleration by the pulses is studied. Under the same peak intensity and beam waist width, the maximum exit kinetic energy of electrons will be increased with the increase of the time domain widths of the pulses. Then, with the further increase of the pulse time domain widths, the maximum exit kinetic energy of the electron will be slowly decreased. The diffusion angle of the electron beam can be as small as 2° and changes little with the carrier envelope phase of the pulse. When the carrier envelope phase is changed, the diffusion angle of the electron beam is reduced by more than 1 order of magnitude with the increase of the time domain widths of the pulses. For the first time, to the best of our knowledge, we found that, by choosing the pulse with the appropriate time domain width, an electron beam with a small diffusion angle and high kinetic energy can be obtained at the same time. When the pulse duration is increased, the radiation spectrum of the acceleration radiation is found to undergo a significant redshift for the first time. These studies can be applied in the fields of high-energy physics experiments, medicine, material detection, and others.

In vivo Dosimetry for Dose Verification of Total Skin Electron Beam Therapy Using Gafchromic® EBT3 Film Dosimetry.

Total skin electron beam therapy (TSEBT) is an important skin-directed radiotherapeutic procedure done in the treatment of cutaneous T-cell lymphomas, namely, mycosis fungoides (MF). This procedure is usually done at larger source-to-surface distances with the patient standing on a rotatory platform. As the patient has to stand in different positions without any rigid immobilization devices, there are chances that the total skin may not get uniformly irradiated which could lead to nonuniform dose distributions. Therefore, all the necessary arrangements should be made to evaluate the dose for different regions of the skin using suitable in vivo dosimeters at the radiotherapy centers offering these treatments. This study aimed to evaluate the consistency between the delivered and planned doses in vivo during TSEBT using Gafchromic EBT3 film dosimetry. The surface dose for the six MF patients treated for TSEBT at our hospital from 2018 to 2022 was measured and evaluated. 2 cm × 2 cm Gafchromic® EBT3 films were used to measure skin dose at reference body positions of clinical interest. All the patients were treated with the modified Stanford technique. The irradiated film strips were analyzed for the dose using the IMRT OmniPro software. The doses at respective positions were expressed as mean dose ± standard deviation and the deviation was calculated as the percentage of the prescribed dose. One hundred and fifty-four Gafchromic® EBT3 film strips irradiated on six TSEBT patients showed a maximum dose variation of 2.00 ± 0.14 Gy, in the central body regions. The dose variation in the peripheral areas such as hands and ears was larger. A variation of 2 ± 0.32 Gy was observed on the hands and ears. The uniformity of the dose delivered to maximum body parts was within -7% and +16% for the peripheral areas like hands. The American Association of Physicists in Medicine recommends a dose uniformity of 8% and 4% in the vertical and horizontal patient plane for direct incident beam; however, for oblique incidences like in the modified Stanford technique, the dose variation is about 15%. In vivo dosimetry using Gafchromic EBT3 film dosimetry for TSEBT yields objective data to find the under or overdose regions. That can be useful to provide quality treatment, especially when treatments tend to be as complex as TSEBT.

Academic program recommendations for graduate degrees in medical physics: AAPM Report No. 365 (Revision of Report No. 197).

Academic program recommendations for graduate degrees in medical physics: AAPM Report No. 365 (Revision of Report No. 197).

AAPM WGPDMP Report 373: The content, structure, and value of the Professional Doctorate in Medical Physics (DMP)

The Professional Doctorate in Medical Physics (DMP) was originally conceived as a solution to the shortage of medical physics residency training positions. While this shortage has now been largely satisfied through conventional residency training positions, the DMP has expanded to multiple institutions and grown into an educational pathway that provides specialized clinical training and extends well beyond the creation of additional training spots. As such, it is important to reevaluate the purpose and the value of the DMP. Additionally, it is important to outline the defining characteristics of the DMP to assure that all existing and future programs provide this anticipated value. Since the formation and subsequent accreditation of the first DMP program in 2009–2010, four additional programs have been created and accredited. However, no guidelines have yet been recommended by the American Association of Physicists in Medicine. CAMPEP accreditation of these programs has thus far been based only on the respective graduate and residency program standards. This allows the development and operation of DMP programs which contain only the requisite Master of Science (MS) coursework and a 2‐year clinical training program. Since the MS plus 2‐year residency pathway already exists, this form of DMP does not provide added value, and one may question why this existing pathway should be considered a doctorate. Not only do we, as a profession, need to outline the defining characteristics of the DMP, we need to carefully evaluate the potential advantages and disadvantages of this pathway within our education and training infrastructure. The aims of this report from the Working Group on the Professional Doctorate Degree for Medical Physicists (WGPDMP) are to (1) describe the current state of the DMP within the profession, (2) make recommendations on the structure and content of the DMP for existing and new DMP programs, and (3) evaluate the value of the DMP to the profession of medical physics.

Dosimetric analysis of intracavitary brachytherapy applicators: a practical study.

PurposeIntracavitary brachytherapy is one of the important methods of gynecological cancer treatment. The effect of attenuation is not considered in the dose calculation method released by the American Association of Physicists in Medicine Task Group No. 43 Report. In this study, the effect of high-dose rate brachytherapy applicators on dose distribution was measured using Gafchromic films and well-type ionization chamber.Materials and MethodsA plan created by the treatment planning system was first executed using a well-type ionization chamber with a water equivalent elasto-gel in place for charge collection. Again, same plan was executed using central tandems of various angulations with different diameters of vaginal cylinders and charge collection was measured. For in vitro dose measurements this plan was also executed on tandem and vaginal cylinder assembly with Gafchromic films fixed on the surface of vaginal cylinder.ResultsThe results show that the central tandem when used with different vaginal cylinders resulted in increase in effective attenuation of the beam. The central tandem of 300 angulations when used with a 35-mm diameter vaginal cylinder results in maximum attenuation whereas the 0º tandem when used with 20-mm diameter vaginal cylinder results in least attenuation of the beam.ConclusionDue to the attenuation by various applicators used in brachytherapy for the treatment of gynecological cancers, it can be concluded that the difference between practical dose and the treatment planning system calculated dose should be considered for the correct estimation of the dose to the target and the organs-at-risk.

Dosimetric comparison of AcurosBV with AAPM TG43 dose calculation formalism in cervical intraductal high‐dose‐rate brachytherapy using three different applicators

AbstractPurposeTo compare the dosimetric effects of American Association of Physicists in Medicine (AAPM) TG43 dose formalism and AcurosBV (grid‐based Boltzmann solver, GBBS) formalism on high‐dose‐rate (HDR) brachytherapy planning for cervical cancer patients irradiated using three different applicators.MethodsA TG43 plan and a AcurosBV plan were generated for each of the 30 patients. Twenty patients who had undergone whole pelvic radiotherapy followed by cervical HDR brachytherapy and the remaining 10 patients who underwent total hysterectomy only gave HDR brachytherapy also were enrolled in this study. The patients were divided into three groups according to the types of applicators used: tandem and ovoid (T&amp;O), tandem and ring (T&amp;R), and cylinder. To compare the dosimetric parameters, the cumulative dose‐volume histograms (DVHs) were measured. We also compared the doses at 90% of the volume (D90%), the volume receiving 100% and 150% of the prescribed dose (V100% and V150%) for the clinical target volume (CTV‐HR), and the doses of point A, the dose receiving 0.1 and 2 cc of the volume (D0.1cc and D2cc) for the organs‐at‐risk (OARs).ResultsCompared with the AcurosBV plans, TG43 plans predicted higher D90%, V100%, and V150% of CTV‐HR, dose of point A, and D0.1cc and D2cc of OARs in three types of applicators. Except D2cc of sigmoid in T&amp;R and cylinder applicators, the D90%, V100%, and V150% of CTV‐HR; the dose of point A and the D0.1cc and D2cc of bladder, rectum, and small bowel exhibited significant discrepancies (all p &lt; 0.05). The effects of the three types of applicators on the dose distribution were quite different due to the differences in the materials: The dose difference of CTV‐HR and OARs was greatest (around 10%) for T&amp;O applicators but only 1–5% for T&amp;R and cylinder applicators.ConclusionsAcurosBV was more accurate in calculating the doses in the air cavity and high‐density substance than TG43. In the clinical setting, AcurosBV exhibited different dosimetric distributions in the cervix plans for HDR brachytherapy, especially in treatment planning when using T&amp;O applicators. The AcurosBV algorithm should be considered when using T&amp;O applicators or other materials with a much higher or lower density (metal or air) than soft tissue. However, If the density is close to that of soft tissue, considering AcurosBV algorithm requires more calculation time, TG43 could still be selected when using applicators in clinical.

A Research Study on use and Importance of the Diagnostic Radiology Reference Values

Aim: References values (RVs) remain being utilized for the radiation quantities from specific bits of radiography apparatus to doses from comparable equipment evaluated in nationwide reviews. RVs optional through American Connection of Physicists in Medicine were established from General Assessment of X-ray trends review, which was conducted by government radiation defense services through understanding and also encouragement of United States Food and Drug Government, Symposium of Radioactivity Control Program Executives, and also American College of Radiology. The RVs used by the American Association of Physicists in Medicine approximate 90th percentile of questionnaire results. As a result, hardware that exceeds the RVs uses higher radiation doses than 90% of apparatus in studies. Radioactive quantities for precise projects should be monitored yearly using standardized ghosts, as suggested through USA College of Radiology. Whenever RVs remain reached, medical physicist must examine source too, in collaboration through radiologist in charge, evaluate if such dosages are warranted or even if the imaging equipment must be adjusted to decrease individual radiation quantities. RVs remain important instruments for likening individual radiation exposures across the UK and giving details concerning radiography performance and reliability. Keywords: Diagnostic radiology, Reference Values, Importance, impacts.

Diversity and Professional Advancement in Medical Physics

PurposeWhile disparities in the inclusion and advancement of women and minorities in science, technology, engineering, mathematics, and medical fields have been well documented, less work has focused on medical physics specifically. In this study, we evaluate historical and current diversity within the medical physics workforce, in cohorts representative of professional advancement (PA) in the field, and within National Institutes of Health (NIH)–funded medical physics research activities. Methods and MaterialsThe 2020 American Association of Physicists in Medicine (AAPM) membership was queried as surrogate for the medical physics workforce. Select subsets of the AAPM membership were queried as surrogate for PA and early career professional advancement (ECPA) in medical physics. Self-reported AAPM-member demographics data representative of study analysis groups were identified and analyzed. Demographic characteristics of the 2020 AAPM membership were compared with those of the PA and ECPA cohorts and United States (US) population. The AAPM-NIH Research Database was appended with principal investigator (PI) demographics data and analyzed to evaluate trends in grant allocation by PI demographic characteristics. ResultsWomen, Hispanic/Latinx/Spanish individuals, and individuals reporting a race other than White or Asian alone comprised 50.8%, 18.7%, and 32.4% of the US population, respectively, but only 23.9%, 9.1%, and 7.9% of the 2020 AAPM membership, respectively. In general, representation of women and minorities was further decreased in the PA cohort; however, significantly higher proportions of women (P < .001) and Hispanic/Latinx/Spanish members (P < .05) were observed in the ECPA cohort than the 2020 AAPM membership. Analysis of historical data revealed modest increases in diversity within the AAPM membership since 2002. Across NIH grants awarded to AAPM members between 1985 and 2020, only 9.4%, 5.3%, and 1.7% were awarded to women, Hispanic/Latinx/Spanish, and non-White, non-Asian PIs, respectively. ConclusionsDiversity within medical physics is limited. Proactive policy should be implemented to ensure diverse, equitable, and inclusive representation within research activities, roles representative of PA, and the profession at large.

Assessment of using a gamma index analysis for patient-specific quality assurance in Japan.

PurposeThe Task Group 218 (TG‐218) report was published by the American Association of Physicists in Medicine in 2018, recommending the appropriate use of gamma index analysis for patient‐specific quality assurance (PSQA). The paper demonstrates that PSQA for radiotherapy in Japan appropriately applies the gamma index analysis considering TG‐218.Materials/methodsThis survey estimated the acceptance state of radiotherapeutic institutes or facilities in Japan for the guideline using a web‐based questionnaire. To investigate an appropriate PSQA of the facility‐specific conditions, we researched an optimal tolerance or action level for various clinical situations, including different treatment machines, clinical policies, measurement devices, staff or their skills, and patient conditions. The responded data were analyzed using principal component analysis (PCA) and multidimensional scaling (MDS). The PCA focused on factor loading values of the first contribution over 0.5, whereas the MDS focused on mapped distances among data.ResultsResponses were obtained from 148 facilities that use intensity‐modulated radiation therapy (IMRT), which accounted for 42.8% of the probable IMRT use in Japan. This survey revealed the appropriate application of the following universal criteria for gamma index analysis from the guideline recommendation despite the facility‐specific variations (treatment machines/the number of IMRT cases/facility attributes/responded [representative] expertise or staff): (a) 95% pass rate, (b) 3% dose difference and 2‐mm distance‐to‐agreement, and (c) 10% threshold dose. Conditions (a)–(c) were the principal components of the data by the PCA method and were mapped in a similar distance range, which was easily clustered from other gamma index analytic factors by the MDS method. Conditions (a)–(c) were the universally essential factors for the PSQA in Japan.ConclusionWe found that the majority of facilities using IMRT in each region of Japan complied with the guideline and conducted PSQA with deliberation under the individual facility‐specific conditions.

AAPM MEDICAL PHYSICS PRACTICE GUIDELINE 5.b: Commissioning and QA of treatment planning dose calculations-Megavoltage photon and electron beams.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. While must is the term to be used in the guidelines, if an entity that adopts the guideline has shall as the preferred term, the AAPM considers that must and shall have the same meaning.Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

An evaluation of quality assurance guidelines comparing the American College of Radiology and American Association of Physicists in Medicine task group 284 for magnetic resonance simulation.

PurposeThe purpose of this study was to evaluate similarities and differences in quality assurance (QA) guidelines for a conventional diagnostic magnetic resonance (MR) system and a MR simulator (MR‐SIM) system used for radiotherapy.MethodsIn this study, we compared QA testing guidelines from the American College of Radiology (ACR) MR Quality Control (MR QC) Manual to the QA section of the American Association of Physicists in Medicine (AAPM) Task Group 284 report (TG‐284). Differences and similarities were identified in testing scope, frequency, and tolerances. QA testing results from an ACR accredited clinical diagnostic MR system following ACR MR QC instructions were then evaluated using TG‐284 tolerances.ResultsFive tests from the ACR MR QC Manual were not included in TG‐284. Five new tests were identified for MR‐SIM systems in TG‐284 and pertained exclusively to the external laser positioning system of MR‐SIM systems. “Low‐contrast object detectability” (LCD), “table motion smoothness and accuracy,” “transmitter gain,” and “geometric accuracy” tests differed between the two QA guides. Tighter tolerances were required in TG‐284 for “table motion smoothness and accuracy” and “low contrast object detectability.” “Transmitter gain” tolerance was dependent on initial baseline measurements, and TG‐284 required that geometric accuracy be tested over a larger field of view than the ACR testing method. All tests from the ACR MR QC Manual for a conventional MR system passed ACR tolerances. The T2‐weighted image acquired with ACR sequences failed the 40‐spoke requirement from TG‐284, transmitter gain was at the 5% tolerance of TG‐284, and geometric accuracy could not be evaluated because of required equipment differences. Table motion passed both TG‐284 and ACR required tolerances.ConclusionOur study evaluated QA guidelines for an MR‐SIM and demonstrated the additional QA requirements of a clinical diagnostic MR system to be used as an MR‐SIM in radiotherapy as recommended by TG‐284.

"The Medical Physicist and Cancer Care: Transcending Your Comfort Zone"

"Professor M. Saiful Huq is an esteemed Medical Physi-cist, Past-President of the American Association of Physicists in Medicine (AAPM), Professor of Radiation Oncology at the University of Pittsburgh School of Medicine, Pittsburgh, Pen-nsylvania, USA and the Director of Medical Physics Division for the UPMC CancerCenter. Dr. Huq is responsible for the development of scientific activities of a large group of physicists and management of clinical medical physics operations of 21 cancer centers in western Pennsylvania, USA. He has served as an expert on many International Atomic Energy Agency (IAEA) initiatives, developing various documents (example, author of IAEA TRS398 CoP, author of IAEA/AAPM CoP on small field do-simetry, Member of the IAEA research project ""Testing the recommendations of the IAEA AAPM Code of Practice for the Dosimetry of Static Small Photon Fields"" ) which provide guidance to the worldwide radiotherapy community regarding various aspects of cancer therapy using external beam radiation. "

Comparison of SNR Assessment Techniques for Routine Multi-Element RF Coil QC Testing

In the UK, the Institute of Physics and Engineering in Medicine (IPEM) provides guidance to Medical Physics departments on appropriate Quality Control (QC) tests to evaluate MRI scanners used in routine clinical practice. The method recommended for the rigorous annual assessment of the SNR produced by RF coils uses a sequence and regions of interest (ROIs) recommended by IPEM, and calculates SNR through a subtraction calculation (IPEM recommended Method). This method was compared to alternative methods proposed by NessAiver at the 2019 American Association of Physicists in Medicine meeting in their talk on RF coil testing. Comparisons were completed for sequences and regions of interest (ROIs) recommended by IPEM and NessAiver. Testing was performed at 1.5 T using the scanner’s integrated body coil and at 3.0 T using a peripheral Head/Neck coil. Calculation of SNR using the mean of the background noise, assessed using the NessAiver recommended sequence and ROIs (NessAiver Noise-Average Method), typically offered the lowest variability in SNR results. Additionally, the SNR results produced by the IPEM Recommended Method were less repeatable than those from the NessAiver Noise-Average Method (p<0.001). Furthermore, the significance level to which a simulated reduction in SNR could be detected using the IPEM Recommended Method (p<0.001) was less than with the NessAiver Noise-Average Method (p≥0.0031). Finally, when comparing the test duration of each method, use of the NessAiver Noise-Average Method results in a 90% reduction in acquisition time per SNR result, when compared to the IPEM Recommended Method.

AAPM task group report 303 endorsed by the ABS: MRI implementation in HDR brachytherapy-Considerations from simulation to treatment.

The task group (TG) on magnetic resonance imaging (MRI) implementation in high-dose-rate (HDR) brachytherapy (BT)-Considerations from simulation to treatment, TG 303, was constituted by the American Association of Physicists in Medicine's (AAPM's) Science Council under the direction of the Therapy Physics Committee, the Brachytherapy Subcommittee, and the Working Group on Brachytherapy Clinical Applications. The TG was charged with developing recommendations for commissioning, clinical implementation, and on-going quality assurance (QA). Additionally, the TG was charged with describing HDR BT workflows and evaluating practical consideration that arise when implementing MR imaging. For brevity, the report is focused on the treatment of gynecologic and prostate cancer. The TG report provides an introduction and rationale for MRI implementation in BT, a review of previous publications on topics including available applicators, clinical trials, previously published BT-related TG reports, and new image-guided recommendations beyond CT-based practices. The report describes MRI protocols and methodologies, including recommendations for the clinical implementation and logical considerations for MR imaging for HDR BT. Given the evolution from prescriptive to risk-based QA, an example of a risk-based analysis using MRI-based, prostate HDR BT is presented. In summary, the TG report is intended to provide clear and comprehensive guidelines and recommendations for commissioning, clinical implementation, and QA for MRI-based HDR BT that may be utilized by the medical physics community to streamline this process. This report is endorsed by the American Brachytherapy Society.

Performance evaluation of image reconstruction algorithms for a megavoltage computed tomography system on a helical tomotherapy unit

Objective. To evaluate the impact of image reconstruction algorithm selection, as well as imaging mode and the reconstruction interval, on image quality metrics for megavoltage computed tomography (MVCT) image acquisition for use in image-guided (IGRT) and adaptive radiotherapy (ART) on a next-generation helical tomotherapy system. Approach. A CT image quality phantom was scanned across all available acquisition modes for filtered back projection (FBP) and both iterative reconstruction (IR) algorithms available on the system. Image quality metrics including noise, uniformity, contrast, spatial resolution, and mean CT number were compared. Analysis of DICOM data was performed using ImageJ software and Python code. ANOVA single factor and Tukey’s honestly significant difference post-hoc tests were utilized for statistical analysis. Main Results. Application of both IR algorithms noticeably improved noise and image contrast when compared to the FBP algorithm available on all previous-generation helical tomotherapy systems. Use of the FBP algorithm improved image uniformity and spatial resolution in the axial plane, though values for the IR algorithms were well within tolerances recommended for IGRT and/or MVCT-based ART implementation by the American Association of Physicists in Medicine (AAPM). Additionally, longitudinal resolution showed little dependence on the reconstruction algorithm, while a negligible variation in mean CT number was observed regardless of the reconstruction algorithm or acquisition parameters. Statistical analysis confirmed the significance of these results. Significance. An overall improvement in image quality for metrics most important to IGRT and ART—mainly image noise and contrast—was evident in the application of IR when compared to FBP. Furthermore, since other imaging parameters remain identical regardless of the reconstruction algorithm, this improved image quality does not come at the expense of additional patient dose or an increased scan acquisition time for otherwise identical parameters. These improvements are expected to enhance fidelity in IGRT and ART implementation.

Machine learning for contour classification in TG-263 noncompliant databases.

A large volume of medical data are labeled using nonstandardized nomenclature. Although efforts have been made by the American Association of Physicists in Medicine (AAPM) to standardize nomenclature through Task Group 263 (TG‐263), there remain noncompliant databases. This work aims to create an algorithm that can analyze anatomical contours in patients with head and neck cancer and classify them into TG‐263 compliant nomenclature. To create an accurate algorithm capable of such classification, a combined approaching using both binary images of individual slices of anatomical contours themselves, as well as center of mass coordinates of the structures are input into a neural network. The center of mass coordinates were scaled using two normalization schemes, a simple linear normalization scheme agnostic of the patient anatomy, and an anatomical normalization scheme dependent on patient anatomy. The results of all of the individual slice classifications are then aggregated into a single classification by means of a voting algorithm. The total classification accuracy of the final algorithms was 97.6% mean accuracy per class for nonanatomically normalization scheme, and 97.9% mean accuracy per class for anatomically normalization scheme. The total accuracy was 99.0% (13 errors in 1302 structures) for the nonanatomically normalization scheme, and 98.3% (22 errors in 1302 structures) for the anatomically normalization scheme.

Investigation of the dosimetric parameters of 125I BEBIG IsoSeed® I25.S06 source: GATE 8.2 Monte Carlo code

Permanent implantation of the iodine-125 brachytherapy sources is an irradiation technique for the treatment of the localized cancer. As described by the American Association of Physicists in Medicine (AAPM) Task group 43 (TG-43U1), it is crucial to determine the dose distribution around the brachytherapy seed before its effective clinical practice or even before releasing the sources for the treatment. In the present work, according to TG-43U1 report, the dosimetric parameters of BEBIG iodine-125 Low Dose Rate brachytherapy IsoSeed® I25.S06 source model was investigated. To perform the dose calculations, we have used GEANT4 Application for Emission Tomography (GATE) Monte Carlo simulations. Interesting results have been found. In particular, the dosimetric quantities like the radial dose function gL(r), the anisotropy function F(r,θ) and the dose rate constant Λ have been obtained. In addition, our data are in good agreement with the previous published works. It is also remarked that, GATE Monte Carlo code reproduces accurate dosimetric parameters results.