Publications by authors named "Amir Hossein Karimi"

8 Publications

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Feasibility of 18-MV grid therapy from radiation protection aspects: unwanted dose and fatal cancer risk caused by photoneutrons and scattered photons.

Comput Methods Programs Biomed 2022 Jan 12;213:106524. Epub 2021 Nov 12.

Department of Radiation Oncology, Advocate Lutheran General Hospital, 1700 Lutheran, Park Ridge, Illinois, USA. Electronic address:

Purpose: Photoneutron production is a common concern when using 18-MV photon beams in radiation therapy. In Spatially Fractionated Grid Radiation Therapy (SFGRT), the grid block in the collimation system modifies the neutron production, photon scattering, and electron contamination in and out of the radiation field. Such an effect was studied with grids made of different high-Z materials by Monte Carlo simulations. The results were also used to evaluate the lifetime risk of fatal cancers.

Methods: MCNPX® code (2.7.0 extensions) was employed to simulate an 18-MV LINAC (Varian 2100 C/D). Three types of grid made of brass, cerrobend, and lead were used to study the neutron and electron fluence. Output factors for each grid with different field sizes were calculated. A revised female MIRD phantom with an 8-cm spherical tumor inside the liver was used to estimate the dose to the tumor and the critical organs. A 20-Gy SFGRT plan with Anterior Posterior (AP) - Posterior Anterior (PA) grid beams was compared with a Conventional Fractionated Radiation Therapy (CFRT) plan which delivered 40-Gy to the tumor by AP-PA open beams. Neutron equivalent dose, photon equivalent dose, as well as lifetime risks of fatal cancer were calculated in the organs at risk.

Results: The grid blocks reduced the fluence of contaminant electrons inside the treatment field by more than 50%. The neutron fluences per electron-history in SFGRT plans with brass, cerrobend and lead were on average 55%, 31% and 31% less than that of the CFRT plan, respectively. However, when converting to fluences per delivered dose (Gy), the cerrobend and lead grid may incur higher neutron dose for 20 × 20 cm field size and above. The changes in neutron mean energy, as well as the correlated radiation weighting factors, were insignificant. The total risk due to the photoneutrons in the SFGRT plans was 87% or lower than that in the CFRT plans. In both SFGRT and CFRT plans, the contribution of the primary and scattered photons to the fatal cancer risk was 2 times or more than the photoneutrons. The total risks from photons in SFGRT with brass, cerrobend, and lead blocks were 1.733, 1.374, and 1.260%, respectively, which were less than 30% of the total photon-risk in CFRT (5.827%).

Conclusion: In the brass, cerrobend, and lead grids, the attenuation of photoneutrons outweighs its photoneutron production in 18-MV SFGRT. The total cancer risks from photons and photoneutrons in the SFGRT plans were 30% or less of the risks in the CFRT plans (5.911%). Using 18 MV photon beams with brass, cerrobend, and lead grid blocks is still a feasible option for SFGRT.
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http://dx.doi.org/10.1016/j.cmpb.2021.106524DOI Listing
January 2022

Monte Carlo evaluation of out-of-field dose in 18 MV pelvic radiotherapy using a simplified female MIRD phantom.

Biomed Phys Eng Express 2021 Nov 11;8(1). Epub 2021 Nov 11.

Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.

This study was devoted to determining the unwanted dose due to scattered photons to the out-of-field organs and subsequently estimate the risk of secondary cancers in the patients undergoing pelvic radiotherapy. A typical 18 MV Medical Linear Accelerator (Varian Clinac 2100 C/D) was modeled using MCNPXcode to simulate pelvic radiotherapy with four treatment fields: anterior-posterior, posterior-anterior, right lateral, left lateral. Dose evaluation was performed inside Medical Internal Radiation Dose (MIRD) revised female phantom. The average photon equivalent dose in out-of-field organs is 8.53 mSv Gy, ranging from 0.17 to 72.11 mSv Gy, respectively, for the organs far from the Planning Treatment Volume (Brain) and those close to the treatment field (Colon). Evidence showed that colon with 4.3049% and thyroid with 0.0020% have the highest and lowest risk of secondary cancer, respectively. Accordingly, this study introduced the colon as an organ with a high risk of secondary cancer which should be paid more attention in the follow-up of patients undergoing pelvic radiotherapy. The authors believe that this simple Monte Carlo (MC) model can be also used in other radiotherapy plans and mathematical phantoms with different ages (from childhood to adults) to estimate the out-of-field dose. The extractable information by this simple MC model can be also employed for providing libraries for user-friendly applications (e.g. '.apk') which in turn increase the public knowledge about fatal cancer risk after radiotherapy and subsequently decrease the concerns in this regard among the public.
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http://dx.doi.org/10.1088/2057-1976/ac35a1DOI Listing
November 2021

Prospects and challenges of cancer systems medicine: from genes to disease networks.

Brief Bioinform 2021 Sep 1. Epub 2021 Sep 1.

Department of Molecular & Cell Biology, James Cook University, Townsville, QLD 4811, Australia.

It is becoming evident that holistic perspectives toward cancer are crucial in deciphering the overwhelming complexity of tumors. Single-layer analysis of genome-wide data has greatly contributed to our understanding of cellular systems and their perturbations. However, fundamental gaps in our knowledge persist and hamper the design of effective interventions. It is becoming more apparent than ever, that cancer should not only be viewed as a disease of the genome but as a disease of the cellular system. Integrative multilayer approaches are emerging as vigorous assets in our endeavors to achieve systemic views on cancer biology. Herein, we provide a comprehensive review of the approaches, methods and technologies that can serve to achieve systemic perspectives of cancer. We start with genome-wide single-layer approaches of omics analyses of cellular systems and move on to multilayer integrative approaches in which in-depth descriptions of proteogenomics and network-based data analysis are provided. Proteogenomics is a remarkable example of how the integration of multiple levels of information can reduce our blind spots and increase the accuracy and reliability of our interpretations and network-based data analysis is a major approach for data interpretation and a robust scaffold for data integration and modeling. Overall, this review aims to increase cross-field awareness of the approaches and challenges regarding the omics-based study of cancer and to facilitate the necessary shift toward holistic approaches.
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http://dx.doi.org/10.1093/bib/bbab343DOI Listing
September 2021

A Homozygous Truncating Mutation in Causing IHPRF1: Detailed Clinical Manifestations and a Review of Literature.

Appl Clin Genet 2020 27;13:151-157. Epub 2020 Aug 27.

Department of Internal Medicine, Semnan University of Medical Sciences, Semnan, Iran.

Infantile hypotonia, with psychomotor retardation and characteristic facies 1 (IHPRF1), is a rare disorder characterized by global developmental delay and dysmorphic features. This syndrome is caused by genetic anomalies within the gene. The current report examines a 9-year-old female IHPRF1 patient. Our objective was to contribute to the delineation of the underlying factors influencing this rare condition. Whole exome sequencing (WES) was utilized to identify the disease-causing mutation in the affected individual. Subsequently, Sanger sequencing was performed for the patient, her parents, and two close relatives in order to confirm the detected mutation. Moreover, detailed clinical examinations including EEG, echocardiography, and biochemical/physical tests were carried out to elucidate the effects of the mutation. WES identified a homozygous nonsense mutation in the gene (c.2563C>T p.R855X). This mutation was confirmed by Sanger sequencing in the patient and her family members and segregated with the autosomal recessive inheritance pattern of IHPRF1. Moreover, genotype-phenotype correlation analysis confirmed the disease-causing nature of this mutation. The current report provides the first detailed description of a patient with this homozygous nonsense mutation (c.2563C>T p.R855X) and expands the clinical spectrum of IHPRF1 disease. Possible influences of sex and other factors on this disease are discussed and a review of the literature is also provided.
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http://dx.doi.org/10.2147/TACG.S261781DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7459142PMC
August 2020

Grid therapy vs. conventional radiotherapy - 18 MV treatments: Photoneutron contamination along the maze of a linac bunker.

Appl Radiat Isot 2020 Apr 29;158:109064. Epub 2020 Jan 29.

Unidad Academica de Estudios Nucleares de la Universidad Autonoma de Zacatecas C. Cipres 10, Fracc, La Peñuela, 98068, Zacatecas, Zac, Mexico. Electronic address:

The present Monte Carlo study was devoted to the comparison of photoneutron contamination (per 1 Gy photon dose), along the maze of a radiotherapy bunker, between two 18-MV modalities: grid therapy (with grids made of brass, cerrobend, and lead) and conventional radiotherapy. It was turned out that both in grid therapy and in conventional radiotherapy, with increasing distance from the entrance of treatment hall (toward the maze entrance), fluence and ambient dose equivalent of neutrons decrease. Evidence also shows that in grid therapy, independent of materials used in the grid construction, photoneutron contamination along the maze is 45±6 % larger than conventional radiotherapy.
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http://dx.doi.org/10.1016/j.apradiso.2020.109064DOI Listing
April 2020

Essential considerations for accurate evaluation of photoneutron contamination in Radiotherapy.

Appl Radiat Isot 2019 Mar 5;145:24-31. Epub 2018 Dec 5.

Department of Nuclear Engineering, Faculty of Advanced Sciences and Technologies, University of Isfahan, Isfahan, Iran.

Nowadays, high-energy X-rays produced by medical linear accelerators (LINACs) are widely used in many Radiation Therapy (RT) centers. High-energy photons (> 8 MeV) produce undesired neutrons in the LINAC head which raise concerns about unwanted neutron dose to the patients and RT personnel. Regarding the significance of radiation protection in RT, it is important to evaluate photoneutron contamination inside the RT room. Unfortunately, neutron dosimeters used for this purpose have limitations that can under the best conditions cause to > 10% uncertainty. In addition to this uncertainty, the present Monte Carlo (MC) study introduces another uncertainty in measurements (nearly up to 20%) when neutron ambient dose equivalent (H(10)) is measured at the patient table or inside the maze and the change in neutron energy is ignored. This type of uncertainty can even reach 35% if H(10) is measured by dosimeters covered by a layer of B as converter. So, in these cases, neglecting the change in neutron energy can threaten the credibility of measured data and one should attend to this energy change in order to reduce measurement uncertainty to the possible minimum. This study also discusses the change in neutron spectra and H(10) at the patient table caused by removing a typical RT room from MC simulations. Under such conditions, neutron mean energy (Ē) overestimated by 0.2-0.4 MeV at the patient table. Neutron fluence (φ) at the isocenter (IC) was underestimated by 23-54% for different field sizes that caused H(10) to be miscalculated up to 24%. This finding informs researchers that for accurate evaluation of H(10) at the patient table, simulating the RT room is an effective parameter in MC studies.
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http://dx.doi.org/10.1016/j.apradiso.2018.12.007DOI Listing
March 2019

Photoneutron Dose Estimation in GRID Therapy Using an Anthropomorphic Phantom: A Monte Carlo Study.

J Med Signals Sens 2018 Jul-Sep;8(3):175-183

Department of Radiotherapy and Oncology, Jundishapur University of Medical Sciences, Ahvaz, Iran.

Background: In the past, GRID therapy was used as a treatment modality for the treatment of bulky and deeply seated tumors with orthovoltage beams. Now and with the introduction of megavoltage beams to radiotherapy, some of the radiotherapy institutes use GRID therapy with megavoltage photons for the palliative treatment of bulky tumors. Since GRID can be a barrier for weakening the photoneutrons produced in the head of medical linear accelerators (LINAC), as well as a secondary source for producing photoneutrons, therefore, in terms of radiation protection, it is important to evaluate the GRID effect on photoneutron dose to the patients.

Methods: In this study, using the Monte Carlo code MCNPX, a full model of a LINAC was simulated and verified. The neutron source strength of the LINAC (Q), the distributions of flux (φ), and ambient dose equivalent (H*[10]) of neutrons were calculated on the treatment table in both cases of with/without the GRID. Finally, absorbed dose and dose equivalent of neutrons in some of the tissues/organs of MIRD phantom were computed with/without the GRID.

Results: Our results indicate that the GRID increases the production of the photoneutrons in the LINAC head only by 0.3%. The calculations in the MIRD phantom show that neutron dose in the organs/tissues covered by the GRID is on average by 48% lower than conventional radiotherapy. In addition, in the uncovered organs (by the GRID), this amount is reduced to 25%.

Conclusion: Based on the findings of this study, in GRID therapy technique compared to conventional radiotherapy, the neutron dose in the tissues/organs of the body is dramatically reduced. Therefore, there will be no concern about the GRID effect on the increase of unwanted neutron dose, and consequently the risk of secondary cancer.
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http://dx.doi.org/10.4103/jmss.JMSS_13_18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6116319PMC
September 2018

Automated detection and cell density assessment of keratocytes in the human corneal stroma from ultrahigh resolution optical coherence tomograms.

Biomed Opt Express 2011 Oct 29;2(10):2905-16. Epub 2011 Sep 29.

Keratocytes are fibroblast-like cells that maintain the optical clarity and the overall health of the cornea. The ability to measure precisely their density and spatial distribution in the cornea is important for the understanding of corneal healing processes and the diagnostics of some corneal disorders. A novel computerized approach to detection and counting of keratocyte cells from ultra high resolution optical coherence tomography (UHR-OCT) images of the human corneal stroma is presented. The corneal OCT data is first processed using a state-of-the-art despeckling algorithm to reduce the effect of speckle on detection accuracy. A thresholding strategy is then employed to allow for improved delineation of keratocyte cells by suppressing similarly shaped features in the data, followed by a second-order moment analysis to identify potential cell nuclei candidates. Finally, a local extrema strategy is used to refine the candidates to determine the locations and the number of keratocyte cells. Cell density distribution analysis was carried in 3D UHR-OCT images of the human corneal stroma, acquired in-vivo. The cell density results obtained using the proposed novel approach correlate well with previous work on computerized keratocyte cell counting from confocal microscopy images of human cornea.
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http://dx.doi.org/10.1364/BOE.2.002905DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3191454PMC
October 2011
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