Medical Physics

Medical Physics

  • Prashant Shukla added an answer:
    What differences can be seen in the degree of polarization (DOP) for forward and backscattered mode from a thin epithelial tissue section?

    I want to understand, how differently polarized light influence on forward and back scattered mode. Some articles mentioned results are different from thin and thick tissue. What is the boundary decided for thick and thin tissue?

    Prashant Shukla · Indian Institute of Technology Kanpur

    Pl. see this reference "A. D. Kim, M. Moscoso, Phys. Rev. E 64, 026612 (2001)."

    if light is circularly polarized then in backscatteing mode because of helicity flip depolarization will be more.

  • Hanno Krieger added an answer:
    Reasons behind the different peak shapes in radiation spectrometry?

    In case of alpha spectroscopy the peak shape is different from that observed in photo peak of photon spectroscopy. I have not observed one for mono-energetic electrons.

    What are the reasons of different shape of these peaks?

    Hanno Krieger · retired from Justus-Liebig-Universität Gießen

    A literature tip is ICRU report  49.

  • Yuan jl added an answer:
    How can I optimize this SOBP curve in MATLAB?

    Could you give more detail about how to optimize the needed SOBP from many known different energies' bragg peaks?

    Yuan jl · Chinese Center For Disease Control And Prevention

    @B.M. Schneider

    happy new year,i"m looking forward to your reply about the optimized problem

  • Abbas Haghparast added an answer:
    What dimensionals and which materials does one use for miniphantom for SC using film dosimetry?

    I want to built a miniphantom for SC measuring using EBT2 film for small field 6MV photon beam,  2 plexiglass cubes (density 1.19g/cm3) dimensions 3x3 with height of 5 cm for top and 10cm for bottom as a holder.

    1- Which materials do you recomment for top for electron contamination in small field film dosimetry? Brass top or plexiglass

    2- Is it necessary to calculate the equivalent thickness for top (plexi or brass)? 

    3- What dimensional did you consider for your phantom? lateral dimensions and top thickness?

    Abbas Haghparast · Kermanshah University of Medical Sciences

    It dependent to your protocol.  For estro is 5 cm lateral and 10 cm depth of phantom. Brass used for 10 mv and higher. In iaea protocol use of build up phantom. You can use of fc65 instead of ebt2.

  • Y.P.Y.P. Ariyasinghe added an answer:
    How does to calculate treatment time of Cobalt-60 Teletherapy unit ?

    How does to calculate treatment time of Cobalt-60 Teletherapy unit ?

    Y.P.Y.P. Ariyasinghe · Teaching Hospital, Kandy

    There are two technique.

    1.       SSD

    2.       SAD

    1 SSD,   

    treatment time for Co60 = Prescribe daily dose/(PDD(x,y)%  X  BSF(x,y)  X  Machine Output rate(x,y) X (802/80.52))

    2 SAD,

    treatment time for Co60 = Prescribe daily dose /(TAR(x,y) X machine Output rate(x,y) )

    x- Field width

    y- Field high

  • Sajjad Ahmed Memon added an answer:
    What is the differences of the monitor unit (MU) calculation method between the Report of the AAPM TG 71 and the old method?

    "Monitor Unit Calculation for External photon and electron beams : Report of the AAPM Therapy Physics Committee Task Group No.71"  --> published 26 february 2014.

    Is it the newest method?

    and then is it applicable for cobalt-60 (treatment time calculation) ?

    For each formalism of MUs calc which uses isocentric or PDD formalism, what is the difference in monitor unit (MU) calculation method between Report of the AAPM TG 71 and the old method?

    In last method,field size determinations for Sc,Sp&PDD in SSD technique are same value. But in aapm 71,there are different. How about it?

    Please discuss it here! :))

    Thank you.

    Sajjad Ahmed Memon · Nuclear Institute of Medicine & Radiotherapy (NIMRA)

    AAPM TG 71 can be applicable for cobalt-60 for treatment time calculation but it wholly used for LINAC for MU calculations. in report MU can be replaced by Treatment Time in formalism.

  • Yagoubi Wassima added an answer:
    How can I deconvolute a reverse peak in origin 8.5 ?

     I want to deconvolute a reverse peak using origin 8.5 , plz give the steps.

    Yagoubi Wassima · Université Amar Telidji Laghouat

    I think, the version origin8.5  does not allow for the deconvolution but version 8.6 can do it with the peak analyzer. (see  OriginLab tutorial)

  • Nahid Chegeni added an answer:
    Does any written program exist, for optical density measuring for EBT2 film by MATLAB?

    I apply EBT2 Film for dosimetry. to measure collimator scatter factor (Sc), I want to use Matlab for reading the optical density of the films . How can I write a program for MATLAB to average the optical density for some points in a circle with radius of 0.5 cm?

    Nahid Chegeni · Ahvaz Jondishapour University of Medical Sciences

    Dear friends

    Thanks for all your suggestions. I will consider all key points. I also want to thank to Mr.  Leon Dunn for his program.

  • Philip Von Voigts-Rhetz added an answer:
    Can anyone share with me the egsinp (input file) of Beamnrc code for calculating the phase space file of a True BEAM LINAC (FFF)?

    Monte Carlo simulation for FFF LINAC (TURE BEAM)

    Philip Von Voigts-Rhetz · Technische Hochschule Mittelhessen

    I am sorry, but no one can share you beaminputifles. For constructing a real model, a "non-disclosure agreement" is signed with the company's.
    But you can find phsp files at the IAEA database.
    https://www-nds.iaea.org/phsp/phsp.htmlx

    kind regards

  • Signe Helbo added an answer:
    Can somebody suggest a source of tabulated spectral data of absorption coefficients for myoglobin and oxy-myoglobin?
    -
    Signe Helbo · Aarhus University

    Hi Serge,

    There is a sort of a "bible" of myoglobin and hemoglobin in where you will find extinction coefficients and all sorts of other data on both proteins.

    Best Signe

  • Hakan Akyildirim added an answer:
    Easy to use program for dosimetry simulation?

    Hi. Currently, I'm working with the simulation of a device to measure density. The goal is to determine if the design will be compliant with the regulations of my country over devices using radioactive materials. So, I have to do a simulation of the device.

    I'm already familiar with the GEANT 4 framework, but my supervisor told me to look at FLUKA/Flair. So, I was wondering if someone knows a better program to do this. I know there is a framework called GAMOS that works with GEANT 4 to do dosimetry, but I'm not sure if the purpose (more specifically the produced output) is what I need. So if anyone knows which of these software, or, even better, other software better for this, I'd be very happy to know. Thank you in advance.

    Hakan Akyildirim · T.C. Süleyman Demirel Üniversitesi

    I can suggest you to use FLUKA, if you have some time to learn the code. Using it with FLAIR interface, you can save time and calculate requested quantities easily.

  • DEEPAK KUMAR AKAR added an answer:
    Can any one explain the ICRP dose limits, radiation weighting factors and tissue weighting factors?

    ICRP has revised its dose limits, radiation and tissue weighting factors a number of times in its reports.

    Can any one explain the basis on which they were derived/ judged and what basis was they were revised?

    Any discussions, references including review articles or presentations will be appreciated.

    DEEPAK KUMAR AKAR · Bhabha Atomic Research Center

    For some of the judgements e.g radiation weighting factor for proton it seems so but not sure?

  • Lambert Zijp added an answer:
    How to create a fluence map from dynalog files?

    I extracted successfully actual leaf positions, control points and dose rate by using matlab. Now need help to build fluence map with dynalog file.

    Lambert Zijp · Netherlands Cancer Institute

    I have no experience with those Varian files, but you might try "Dynalog Analysis Package":

    http://www.mike-hughes.org/medphys/dynalog.html

  • Marios Bazis added an answer:
    Does anyone know how to find the dose in multiple volumes on example B1 in GEANT4?

    I am working with the easiest example B1 and I want to find the dose in multiple shapes (G4_Bone_compact_ICRU) and not only the general dose.

    I have already made 3 ideal shapes with distance 2mm and I want to find the dose in each shape.

    Thanks in advance. 

    Marios Bazis · Carl von Ossietzky Universität Oldenburg

    At first step it cannot link and compile the whole file HandsOn_5 in order to use the G4SensitiveDetector . I am using Virtual studio express. 

  • Roberto Capote added an answer:
    How can I read the file IAEA.phsp ​​in the MCNPX code?
    Despite the IAEA document to recommend the disclosure of IAEA.phsp ​​files and it is not clear how this is done in different codes for existing Monte Carlo, I am especially interested in the MCNPX code.
    Roberto Capote · International Atomic Energy Agency (IAEA)

    There is no official tool as we estimulate developers to implement the IAEA interfase into their codes. It is done for Penelope, EGSnrc and Geant-4. Not for the others.

    To convert those files into ASCII will be very unefficient.

    But there are available examples from the website that you can use to read the files and write them into whatever format is available.

  • Dushyant Kumar added an answer:
    How do I generate a slice profile of refocusing pulses in MRI?

    ​Hi,

    I am wondering if someone can help me out with some slice profile simulation.

    I am trying to simulate the slice profile of 180 degree refocusing pulse surrounded by “crusher pair”. I can simulate without crusher pair, but I am unable to incorporate the effect of crusher pair along X and Z direction.

    Any help would be appreciated.

    I am also attaching generating code, along with RF profile and the corresponding plot. Please see the attachment.

    I simulated the slice profile of refocusing pulse using Fourier transform and Bloch equation. X-axis on plots 3rd and 4th rows are HZ; while, it's bin# for Fourier transform. I would convert Hz to corresponding slice thickness later.

    Dushyant Kumar · University Medical Center Hamburg - Eppendorf

    Dear Dr. Schilling,

    Thanks for responding.

    I would double check my code. 

    Also I would go through the paper that you referred.

    Regards,

    Dushyant

  • Bagher Aslibeiki added an answer:
    Which materials are the best candidates for magnetic hyperthermia cancer therapy?

    For magnetic hypermedia therapy different materials have been studied in literature. The question is that, which nanoparticles are the most appropriate candidates for hypothermia therapy. May be the first answer is iron oxide(Fe3o4&gammaFe2O3) nanoparticles. but why? If the only reason for this answer is the nontoxic nature of these nanoparticles? Or there are other reasons?

    Bagher Aslibeiki · University of Tabriz

    Thanks for your good explanation and the references.

  • Andrey Borodach added an answer:
    Physicists, help calculate the nozzle effects in the biliary tree. Do they any matter for the bile hydrodynamics?

    There are a system of the physiologic (normal) narrowings and distentions in the human biliary tree (see the pictures below):

    1) a cone-shaped zone narrows the distal common bile duct when it opens into the intestine resembling a convergent nozzle;

    2) a cone-shaped zone ('neck') narrows the gall bladder in place where it and the cystic duct join together resembling a convergent nozzle too (when bile flows into the gall bladder lumen from the common bile duct);

    3) the same cone-shaped zone of the gall bladder may act as a divergent nozzle when the dense, viscous bile flows out from it into the bile duct.

    Under pathological conditions, each of the cones' apertures (or all of them) may become increased markedly. I'd like to learn more about possible hydrodynamic effects of these conditions even in some first approximation.

    Andrey Borodach · Novosibirsk State Medical University

    Thank you again! Shall be reading at once!

    Studies on the biliary ducts and the gallbladder biomechanics (or, at least, related to) are scarce indeed. What I know of is as follows:

    1) Walsh T.H., Akoglu T. The muscle content and contractile capability of the common bile duct .  Ann R Coll Surg Engl. 1979; 61(3):206-209;

    2) Die Biokonstruktion der extrahepatische Gallenwege des Menschen / R.Henning, D.Steiner, W.Lierse, G.Weinland, P.Matthaes // Aktuel. Chir. – 1988. - Bd.23. – S.74-8

    3) Gallensaure-unabhangige Wirkung von Hymecromon auf die Gallesekretion und die Motilität der Gallenwege / R.M.Hoffmann, G.Schwarz, C.Pohl, D.J.Ziegenhagen, W.Kruis // Dtsch. Med. Wochenschr. – 2005. – Bd.130, H.34-35. – S.1938-43

  • Amin Asadi added an answer:
    Can anybody tell me how to import CT-Numbers in dosxyz-nrc software?

    Please show me the guideline of importing CT numbers in dosxyznrc software 

    Amin Asadi · Shahid Sadoughi University of Medical Sciences and Health Services

    Thanks Dear Sandro. I appreciate you

  • Sergio Faermann added an answer:
    LINACS?
    T lead.
    Sergio Faermann · Soroka University Medical Center,Ben Gurion University of the Negev, Meir Medical Center,Israel

    I would like to warn about the use of Antimony

    My concern about the use of Antimony have started when I took notice of the report of materials that appear on the restricted substances list, published by the European Union ( REACH)-"Regulation Concerning the Registration, Evaluation, Authorization and Restriction of Chemicals"-
    (http://www.echa.europa.eu ) and (http://esis.jrc.ec.europa.eu/ index.php?PGM=pbt)- substances of very high concern.(Antimony is considered a carcinogenic material)
    Antimony is an important material employed by many manufacturers and also electronic component manufacturers ,and I don't know if they are aware of these publication and may be other countries will adopt similar restrictions.

  • Timo Eppig added an answer:
    I want to connect anterior surface corneal Zernike (the Z[4,0], or Z8) with the asphericity Q value. Is there a formula that provides this connection?

    Corneal Asphericity and Zernike coefficients

    Timo Eppig · Universität des Saarlandes

    To my knowledge it 1st order spherical aberration (Z(4,0) / Z8) is not enough for representing aspherics which can be described by an aspheric coefficient (Q) or a conic constant. You need at least Z(2,0) or Z3 (defocus). Using Z(4,0) and Z(2,0) only you will get a rough approximation. You would need at least 2nd and 3rd order spherical aberration to calculate Q or accurately.

    See also a publication from Tim Schwiegerling et al.:

    "The effects of Radial Keratotomy on the Asphericity of the Cornea"

    Please note that the conic constant k is equivalent to Q (refer also to publication from Antonio Calossi). There are several definitions of the conic constant which may be confusing. You wil havbe to check which one applies.

  • Kevin Flintham added an answer:
    What is the relationship between applied kVp of conventional x-ray and backscatter?
    I am carring out practical work to find a mathematical equation between kVP and the backscatter factor.
    Kevin Flintham · Mid Yorkshire Hospitals NHS Trust

    In order to carry out your work, as long as the other factors mentioned here remain constant then obtaining a mathematical relationship should be relatively straightforward. Remember to control for field size, mAs, incident material, secondary incident material (eg is there a wall just behind your target), filtering and HVL.

    Once all other factors are controlled for then simply varying kVp will allow measurements of backscatter to be undertaken.

    Bear in mind also that the location of the detector will affect how much backscatter is detected (angle from the incident beam).

    Depending on your resources you could do multiple experiments to assess these relationships individually, but also be aware that for some of these factors there is an interlinking effect, eg increasing kVp will increase backscatter but it will also affect the scattering angles as well so there will be two factors changing from the one exposure change.

    Good luck.

  • Daniel Van Gent added an answer:
    What are the biological effects of low energy X-ray radiation?
    Gamma radiation has more penetrating power than X -rays of few keV (~10keV) and can lead to radiation sickness at dose levels of 100mRem acute exposure. However being low energy photons, X-rays will deposit maximum energy in skin. So what are the biological implications of this effect?
    Daniel Van Gent · Washington State Department of Health

    Dear Prasanta Kumar Sahani,

    Low energy X-ray is often referred to as "soft x-ray," but that is a potentially misleading designation that tends to diminish the potentially dangerous biological effects of low energy x-ray.

    "Hard" ultraviolet radiation is taken to be non-ionizing radiation and x-ray radiation is by definition ionizing radiation. However, there is no clear cut boundary between "hard ultraviolet" radiation and "soft x-ray" radiation. The definition of "ionizing" and "non-ionizing" depends largely upon the medium a given energy of electromagnetic energy is propagating in, for example, whether propagating through air or water.

    I do not have much time this evening to expound, but "soft x-ray" can be extremely dangerous to the the live skin and eyes. Medical and dental x-ray machines in the U.S. are required by the FDA to have aluminum filters built in to them to largely eliminate the lower energy x-rays that tend to damage skin and eyes in patients subjected to x-ray for this very reason.

    In prior postings in this thread, some of the contributors mentioned that for x-ray photons at 10 keV maximum energy, the predominant mode of ionization is by the Photoelectric Effect where the incoming x-ray transfers all of its kinetic energy into orbital electrons of the medium in which the x-ray is interacting, thus producing photoelectrons of about the same kinetic energy as the incoming x-ray photons. Keeping in mind that a sufficient intensity and quantity of hard  U.V. radiation can produce severe skin and eye burns if it is intense enough, one would expect that "soft" x-ray at even higher energy than the hard U.V. would be at least as penetrating and biologically damaging as "hard" U.V. photon for photon.  The primary mode of biological damage in both cases is similar, biological damage results primarily from "indirect" ionization products (reactive free radicals produced in water) in both cases. Peroxyl moieties and peroxides chemically react with and damage cellular components which can result in deterministic tissue injury at sufficient exposure intensities of soft x-ray.  Probabilistic injury (DNA damage) occurs at both low and high doses of x-ray radiation to biological tissues.

    10 keV x-ray photons are essentially at the same energy as those generated by the cathode ray tubes (CRT) in old style TVs and computer monitors. Prolonged unprotected exposure of the eyes and skin to CRT generated x-rays can cause severe burns and damage to these organs, including cataracts (but cataracts show up later).

    I will be glad to add more information about biological effects of low energy x-rays later if you wish.

    Regards,

    Daniel Van Gent

  • Ali Chaparian added an answer:
    How can you get the more accurate molecular interference form factors included in the cross-section data in EGSnrcMP?
    I am using EGSnrcMP to simulate scattered radiation at diagnostic x-ray energies. EGS apparently still uses the independent atom approximation for coherent scatter. Does anyone know how to get the more accurate molecular interference form factors included in the cross-section data, for materials such as water, Lucite, aluminium, calcium, ICRU tissue, etc.? Thanks in advance.
    Ali Chaparian · Shahid Sadoughi University of Medical Sciences and Health Services

    You can use EGS5 Code.

  • ait chikh Sounya added an answer:
    Can anyone tell me the most common problems in Varian Clinac iX linear accelerator operation?
    Our department has a Clinac iX accelerator, which often has various problems, such as damage to the cooling system, power supply damage, and now klystron damage. It seems to me that this type of damage is not normal for three-year-old accelerator, so I want to find out whether similar problems happen to someone else who uses Clinac iX series accelerators.
    ait chikh Sounya · Service de Radiotherapie, Centre Pierre et Marie Curie, Algeria

    we have the same problems

  • Giovanni Borasi added an answer:
    How can I carry out mouse tumor Xenograft positioning to spare vital organs during an irradiation with collimated mega-voltage X radiation?
    Would be possible to implant a prostate PC-3 tumor cell in a gluteus of a mice (or rat) so that it will grow somewhat laterally respect to the animal normal contour?
    If that would be possible, a Radiotherapy 6 MV highly collimated single beam could hit the tumor (of about 1 cm3 size) but not vital organs of the animal. If that would be a wrong way, is there a better localization of the tumor Xenograft to obtain the desired result ? Thanks in advance for the help!
    Giovanni Borasi · Italian National Research Council

    Dear Daniel,

    thanks a lot for your very useful information. May be you have some paper or some picture showing the setting you used. Details are very important! I'm planning an experiment mixing HIFU and RT. I would like to destroy the (more internal?) hypoxic region of the tumor with HIFU, induce hyperthermia in the outer parts of the tumor and complete the treatment with radiations. To have the best synergy I think that we need to be very fast and the delay between HIFU and RT should not exceed 10-15 min. To do things better we could give half  HIFU-Hyperthermia treatment before and half after RT. That's more complex and I've not yet taken a decision. I'm thinking to a a double RT dose levels of 15 and 30 Gy in a single session, to simulate in some way the Radio-surgery treatments. I'm oriented to use Prostate LNCaP xenograf, but other choices (for example PC3) are possible. At the treatment time the tumor size we hypothesize to be about 0.5 cm3. Is that too big for the animal? Have you some suggestion for me? In the project I've created a "Consulting group" of experts supporting in some way the experiment. There is, of course also an "operative" group.I would be honored if you would accept to enter into our "Consulting Group" . The experiment will be done in collaboration with my friend, Prof. Andreas Melzer in Dundee (UK) and other researcher.

    All my best,

    Gianni

  • Frank Gräbner added an answer:
    What would be the most efficient material for EMI shielding?
    We know that different composite materials have been developed foe EMI shielding so far ,but i would like to know what kind of material can be a potential candidate for efficient shielding of susceptible electronic devices such as some medical equipment?
    Frank Gräbner · Hörmann IMG

    Hallo,

    I think the best shielding material is a Zn thick layer.

    All the best

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