To accurately verify the dose of intensity-modulated radiation therapy (IMRT), we have used a global optimization method to investigate a new dose-verification algorithm. In practical application of this quality assurance (QA) procedure, verification of the dose using calculated and measured dose distributions involves a subtle problem in the region of high dose gradient. Consideration of systematic errors shows that the large dose differences in high-dose-gradient regions are due to the unexpected shift of measuring devices. We have proposed an optimization algorithm to correct this error, and an optimization method to minimize the average dose difference has been used in this study. The relationship between the dose-verification procedure and the applied optimization algorithm is explained precisely. Optimization dramatically reduced the difference between measured and calculated dose distributions in all cases investigated. The obtained results support the relevance of our explanations for the problem in the high-dose-gradient region. We have described this dose-verification procedure for IMRT and intensity-modulated radiosurgery. Through this study we have also developed an intuitive reporting method that is statistically reasonable.
The dosimetry for radiocolloid therapy of cystic craniopharyngiomas is investigated. Analytical calculations based on the Loevinger and the Berger formulae for electrons and photons, respectively, are compared with Monte Carlo simulations. The role of the material of which the colloid introduced inside the craniopharyngioma is made of as well as that forming the cyst wall is analyzed. It is found that the analytical approaches provide a very good description of the simulated data in the conditions where they can be applied (i.e., in the case of a uniform and infinite homogeneous medium). Howev…
The radiation effects induced by Co60 serve as a reference system for the consideration of LET and RBE in normal and tumor tissue dose-effect relations are usually handled by the linear-quadratic model (LQ). This approximation excellently works up to the shoulder domain. In particle therapy we have strictly differ between RBE in the initial plateau and environment of the Bragg peak. Thus for protons LET and RBE of the initial plateau agree with Co60, whereas in the Bragg peak domain both properties are increased,, but RBE of SOBP only varies between 1.1 and 1.17. The RBE of carbon ions is incr…
A new strategy for radiation therapy dosimetry planning (RTDP) used to reduce dose estimation errors due to respiratory motion in breast treatment was illustrated and evaluated in this study. On CT data set acquired for breast treatment, six different RTDP tangential techniques were performed: (i) three-dimensional conformal radiotherapy (3DCRT) with physical wedge, (ii) 3DCRT with virtual wedge, (iii) motion management technique (MMT) with physical wedge, (iv) MMT with virtual wedge, (v) 3DCRT with field-in-field, and (vi) intensity-modulated radiation therapy (IMRT) with direct aperture opti…
Charged particle therapy (CPT) is an advanced modality of radiation therapy which has grown rapidly worldwide, driven by recent developments in technology and methods of delivery. To ensure safe and high quality treatments, various instruments are used for a range of different measurements such as for quality assurance, monitoring and dosimetry purposes. With the emergence of new and enhanced delivery techniques, systems with improved capabilities are needed to exceed existing performance limitations of conventional tools. The Medipix3 is a hybrid pixel detector able to count individual proton…
Artificial intelligence for simplified patient-centered dosimetry in radiopharmaceutical therapies
Bern University Hospital, University of Bern（伯尔尼大学医院，伯尔尼大学）；BC Cancer Research（不列颠哥伦比亚省癌症研究中心）；Geneva University Hospital（日内瓦大学医院）；University of British Columbia（不列颠哥伦比亚大学）
The advanced imaging and delivery techniques in proton therapy allow conformal high-dose irradiation of the target volume with high accuracy using pencil beam scanning or beam shaping apertures. These irradiation methods increasingly include small radiation fields with large dose gradients, which require detector systems with high spatial resolution for quality assurance. In addition the measurement of all success parameters for daily quality assurance with only one proton field and one simple detector system would save a lot of time in clinical usage. Based on their good spatial resolution an…
In particle therapy, knowledge of the stopping-power ratios (STPRs) of the ion beam for air and water is necessary for accurate ionization chamber dosimetry. Earlier work has investigated the STPRs for pristine carbon ion beams, but here we expand the calculations to a range of ions (1 <= z <= 18) as well as spread out Bragg peaks (SOBPs) and provide a theoretical in-depth study with a special focus on the parameter regime relevant for particle therapy. The Monte Carlo transport code SHIELD-HIT is used to calculate complete particle-fluence spectra which are required for determining STPRs acco…
An innovative dose rate independent 2D Ce-doped YAG scintillating dosimetry system for time resolved beam monitoring in ultra-high dose rate electron FLASH radiation therapy
This paper focuses on some dosimetry aspects of proton therapy and pencil beam scanning based on the experience accumulated at Paul Scherrer Institute(PSI). The basic formalism for absolute dosimetry in proton therapy is outlined and the two main techniques and equipment to perform the primary beam monitor chamber calibration are presented. Depth-dose curve and lateral beam width measurements are exposed and discussed in detail, with particular attention to the size of the ionization chamber and the characteristic of scintillating-CCD dosimetry systems, respectively. It is also explained how t…
Organized by Working Group 6 "Computational Dosimetry" of the European Radiation Dosimetry Group (EURADOS), a group of intercomparison exercises was conducted in which participants were asked to solve predefined problems in computational dosimetry. The results of these comparisons were published in a series of articles in this virtual special issue of Radiation Measurements. This paper reviews the experience gained from the various exercises and highlights the resulting conclusions for future exercises, as well as regarding the state of the art and the need for development in terms of quality …
Background and Objective: Recent experimental studies using ultra-high dose rate radiation therapy (FLASH-RT) have shown improved normal tissue sparing and comparable tumor control compared to conventional dose rate RT. Pencil beam scanning (PBS) proton therapy with superior dosimetry characteristics has begun to draw attention to the delivery of conformal FLASH-RT for preclinical studies. This review aims to provide recent updates on the development of PBS FLASH-RT. Methods: The information summarized in this review article is based on search results in databases such as PubMed and search eng…
While spatial dose conformity delivered to a target volume has been pushed to its practical limits with advanced treatment planning and delivery, investigations in novel temporal dose delivery are unfolding new mechanisms. Recent advances in ultra-high dose radiotherapy, abbreviated as FLASH, indicate the potential for reduction in healthy tissue damage while preserving tumor control. FLASH therapy relies on very high dose rate of > 40Gy/sec with sub-second temporal beam modulation, taking a seemingly opposite direction from the conventional paradigm of fractionated therapy. FLASH brings uniqu…
Adapting a 3D scanning water phantom for use in brachytherapy dosimetry
Royal Brisbane & Women’s Hospital（皇家布里斯班妇女医院）；Herston Biofabrication Institute（赫斯顿生物制造研究所）；University of Queensland（昆士兰大学）；Queensland University of Technology（昆士兰科技大学）
Adaptive radiation therapy (ART) could protect organs at risk (OARs) while maintain high dose coverage to targets. However, there still lack efficient online patient QA methods. We aim to develop a clinically relevant online patient quality assurance (QA) solution for ART using daily CT scans and electronic portal imaging device (EPID)-based in vivo dosimetry. Ten patients with rectal cancer at our center were included. Patients' daily CT scans and portal images were collected to generate reconstructed 3D dose distributions. Contours of targets and OARs were recontoured on these daily CT scans…
Sensitivity of silicon-to-water dose conversion and Bragg-peak metrics to stopping-power datasets in proton dosimetry
Instituto de Pesquisas Energéticas e Nucleares（能源与核研究研究所）；Departamento de Física, Centro de Investigación en Óptica y Nanofísica, Universidad de Murcia（穆尔西亚大学光学与纳米物理研究中心物理系）；Departament de Física, Universitat d’Alacant（阿利坎特大学物理系）；Instituto de Física da Universidade de São Paulo（圣保罗大学物理研究所）；National Physical Laboratory（英国国家物理实验室）
Collimator angle is usually rotated when planning volumetric modulated arc therapy (VMAT) due to the leakage of radiation between multi-leaf collimator (MLC) leaves. We studied the effect of the collimator angles on the results of dosimetric verification of the VMAT plans for head and neck patients. We studied VMAT plans for 10 head and neck patients. We made 2 sets of VMAT plans for each patient. Each set was composed of 10 plans with collimator angles of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45 degrees. Plans in the first set were optimized individually and plans in the second set shared the 30 …
BACKGROUND: Targeted Radionuclide Therapy (TRT) is a fast-growing field garnering much interest, however, dosimetry calculation techniques remain relatively simple. PURPOSE: To introduce egs_mird, a new Monte Carlo application built in EGSnrc which allows users to model full patient tissue and density (using clinical CT images) and radionuclide distribution (using clinical PET images) for fast and detailed TRT dose calculation. METHODS: The novel application egs_mird is introduced, including its structure and variation reduction approaches. A new egs++ source class egs_internal_source and a mo…
A dosimetric and robustness analysis of Proton Arc Therapy (PAT) with Early Energy Layer and Spot Assignment (ELSA) for lung cancer versus conventional Intensity modulated therapy (IMPT)
With the increasing complexity of external beam therapy, so-called "end-to-end" tests are intended to cover all steps from therapy planning to follow-up to fulfill the high demands on quality assurance. As magnetic resonance imaging (MRI) gains growing importance in the treatment process and established phantoms (such as the Alderson head) cannot be used for those tests, novel multimodality phantoms have to be developed. Here, we present a feasibility study for such a customizable multimodality head phantom. We used a set of patient CT images as the basis for the anthropomorphic head shape. Th…
A liquid isooctane (C$_{8}$H$_{18}$) filled ionization linear array for radiotherapy quality assurance has been designed, built and tested. The detector consists of 128 pixels, each of them with an area of 1.7 mm $\times$ 1.7 mm and a gap of 0.5 mm. The small pixel size makes the detector ideal for high gradient beam profiles like those present in Intensity Modulated Radiation Therapy (IMRT) and radiosurgery. As read-out electronics we use the X-Ray Data Acquisition System (XDAS) with the Xchip developed by the CCLRC. Studies concerning the collection efficiency dependence on the polarization …
Ion chamber dosimetry is being used to calibrate dose for cell irradiations designed to investigate photoactivated Auger electron therapy at the Louisiana State University CAMD synchrotron facility. This study performed a dosimetry intercomparison for synchrotron-produced monochromatic x-ray beams at 25 and 35 keV. Ion chamber depth-dose measurements in a PMMA phantom were compared with the product of MCNP5 Monte Carlo calculations of dose per fluence and measured incident fluence. Monochromatic beams of 25 and 35 keV were generated on the tomography beamline at CAMD. A cylindrical, air-equiva…
Purpose: To verify dose delivery and quality assurance of volumetric modulated arc therapy (VMAT) for head and neck cancer. Method: The Imaging and Radiation Oncology Core Houston (IROC-H) head and neck phantom with thermo- luminescent dosimeters (TLDs) and films, were imaged with computed tomography scan and the reconstructed image was transferred to pinnacle treatment planning system (TPS). On TPS the planning target volume (PTV), secondary target volume (STV) and organ at risk (OAR) were delineated manually and a treatment plan was made. The dose constraints were determined for the concerne…
Quality assurance (QA) for medical linear accelerators is indispensable for appropriate cancer treatment. Some international organizations and western advanced countries provide QA guidelines for linear accelerators. Currently, QA regulations for linear accelerators in Korean hospitals specify a system in which each hospital stipulates its independent hospital-based protocols for QA procedures (HP_QAPs) and conducts QA based on these HP_QAPs while regulatory authorities verify whether items under these HP_QAPs have been performed. However, because this regulatory method cannot guarantee the qu…
Given the sensitivity of proton therapy to anatomical variations, this cancer treatment modality is expected to benefit greatly from integration with magnetic resonance (MR) imaging. One of the obstacles hindering such an integration are strong magnetic field induced dose distortions. These have been predicted in simulation studies, but no experimental validation has been performed so far. Here we show the first measurement of planar distributions of dose deposited by therapeutic proton pencil beams traversing a one-Tesla transversal magnetic field while depositing energy in a tissue-like phan…
Treatment planning system calculations in inhomogeneous regions may present significant inaccuracies due to loss of electronic equilibrium. In this study, three different dose calculation algorithms, pencil beam, collapsed cone, and Monte-Carlo, provided by our planning system were compared to assess their impact on the three-dimensional planning of lung and breast cases. A total of five breast and five lung cases were calculated using the PB, CC, and MC algorithms. Planning treatment volume and organs at risk delineation was performed according to our institutions protocols on the Oncentra Ma…
Paul Scherrer Institute（保罗谢勒研究所）；The Skandion Clinic（斯坎迪翁诊所）；St. Jude Children’s Research Hospital（圣裘德儿童研究医院）；Johns Hopkins Medicine（约翰霍普金斯医学）；Harvard Medical School（哈佛医学院）；Mayo Clinic（梅奥诊所）
Background and purpose: To propose a novel machine learning-based method for reliable and accurate modeling of linac beam data applicable to the processes of linac commissioning and QA. Materials and methods: We hypothesize that the beam data is a function of inherent linac features and percentage depth doses (PDDs) and profiles of different field sizes are correlated with each other. The correlation is formulated as a multivariable regression problem using a machine learning framework. Varian TrueBeam beam data sets (n=43) acquired from multiple institutions were used to evaluate the framewor…
Liquid scintillating phantoms have been proposed as a means to perform real-time 3D dosimetry for proton therapy treatment plan verification. We have studied what effect radiation damage to the scintillator will have upon this application. We have performed measurements of the degradation of the light yield and optical attenuation length of liquid scintillator and water-based liquid scintillator after irradiation by 201 MeV proton beams that deposited doses of approximately 52 Gy, 300 Gy, and 800 Gy in the scintillator. Liquid scintillator and water-based liquid scintillator (composed of $5\%$…
Wuhan University（武汉大学）；University of Texas MD Anderson Cancer Center（德克萨斯大学MD安德森癌症中心）；University of Texas Southwestern Medical Center（德克萨斯大学西南医学中心）；Shenzhen Bay Laboratory（深圳湾实验室）
Dose verification based on proton-induced positron emitters is a promising quality assurance tool and may leverage the strength of artificial intelligence. To move a step closer towards practical application, the sensitivity analysis of two factors needs to be performed: biological washout and depth selection. selection. A bi-directional recurrent neural network (RNN) model was developed. The training dataset was generated based upon a CT image-based phantom (abdomen region) and multiple beam energies/pathways, using Monte-Carlo simulation (1 mm spatial resolution, no biological washout). For …
