Medical Physics

Medical Physics

  • Tomasz W Wysokinski added an answer:
    7
    Are there any issues around medical gas lines in the primary beam in a linac bunker?

    We are currently building a new high-energy linac bunker. The medical gas lines (oxygen, nitrous oxide, medical air, medical vacuum) are planned in one of the lateral primary beams. Is there any literature on this or does anybody have any useful info on possible issues around this? This question is not around the shielding, but about possible problems with the interaction of radiation with the gas in the lines.

    Tomasz W Wysokinski

    For oxygen we normally use SS lines and valves. Mixing  metals will increase probability of corrosion, especially if the gas is not dry. The other concern is potential for self ignition that can occur at the valve if the flow become unstable.

  • Andreas Bockisch added an answer:
    5
    Why does the spiral of a positron have a larger radius than that of an electron in a bubble chamber?

    The pair of electron-positron have been produced in the pair production process.

    Andreas Bockisch

    They are identical, the direction is mirrored.

  • Abhinav Jha added an answer:
    11
    What software can calculate apparent diffusion coefficient in brain images?

    Apparent diffusion coefficient can show water's molecules diffusion.

    Abhinav Jha

     A quite late answer, if you want to just compute a mean ADC value, you could use the method in this paper: http://www.ncbi.nlm.nih.gov/pubmed/25242901

    The method uses the statistics of the mean magnitude MR data to compute the ADC so it is more accurate than a simple regression-based technique.  

  • Pedro Almendral added an answer:
    6
    Are compton-scattered gamma or X-rays linearly polarized?

    Since unpolarized light becomes polarized by Rayleigh scattering (specially if the scattering angle is 90º), one may think that the same happens with X or gamma rays in the Compton scattering. And if this scattered radiation undergoes a second scattering, the angular distribution (differential cross section) will not have azimuthal symetry any more as ussually assumed, due to the polarization. Am I right?

    If that is true, it is not mentioned at all in the context of radiation transport in medical physics or other practical applications of X- or gamma radiations. I suppose in the worst scenario it would lead to very small changes in the absorbed dose distribution, but may there be any situation in which the effect is not negligible? Do Monte Carlo simulations ( with EGSnrc, MCNP, PENELOPE, GEANT, etc) take this into account?

    Pedro Almendral

    Thanks everyone, specially Jorge E. Fernandez for the references. It seems that the papers on this topic deal mainly with X-ray spectroscopy or with polarimeters for astrophysics or particle physics studies, but apparently there is little literature on the impact of polarization effects on absorbed dose distributions calculated by monte carlo methods. ¿Perhaps because the impact is small and the assumption of no-polarization works well enough in most practical problems when the primary beam is unpolarized?

  • Mokhtar Elzamzamy added an answer:
    1
    Are the other vendors like Hitachi, Toshiba, Bruker, United Imaging providing Arterial Spin Labeling sequences too?
    I only know about SIEMENS, Phillips and GE
    Mokhtar Elzamzamy

    You have to ask the wendors directly on their web sites.

  • Joseph L Alvarez added an answer:
    8
    Has any one experience with thermo-luminescent dosimeters calibrated in electron beam to measure electron dose?

    I measured electron dose with TLDs which was calibrated in photon beam. I want to check my results with the results measured by TLDs calibrated in electron beam. I am not convinced myself with the result. Does anyone has data ?

    Joseph L Alvarez

    I agree with Hanno, more information is needed. I have calibrated TLDs in electron beams at different depths of material. Dose is highly depth dependent. If you have a full 6 Mev beam incident on an unshielded TLD, a thin TLD will be nearly uniformly irradiated. The thicker the TLD the less uniformly irradiated. A Cs137 calibration will be essentially uniformly irradiated. The Cs137 calibration is the average over the TLD volume. The lower the energy of the electron, the less valid is the Cs137 volume calibration.  

    You say, "The doses were measured outside the treatment area. I got really small doses for all points of interest for 6 Mev electron beam than photon beam with same energy."

    Please provide a sketch, depth of TLD in material, thickness of TLD, and type of material.

  • Parvaiz Ahmad Shiekh added an answer:
    7
    Do cells experience mechanical force if they are place in magnetic or electromagnetic field ?

    Physical stimulation of cells damage them. Is it possible to use magnetic force which can create a mechanical force on cells to stimulate them. If possible, what will be its prerequisites?

    Parvaiz Ahmad Shiekh

    @Aziz

    thanks for answer. u can drop me the article ASAP

  • Ghanshyam Dass Jindal added an answer:
    3
    How ICG signal is different from ECG signal while denoising of artefacts?

    However there are many papers on denoising of ECG signal, and same thing can be applied for ICG signal.

    Ghanshyam Dass Jindal

    Ensemble Averaging Method suggested by Dr DeMarzo is the best for getting rid of respiratory artifacts in ICG signal, which permits accurate analysis. Now a days, ICG is employed for Cardiac Output Monitoring in ICU/ICCU, there again one can employ the same method  (ensemble averaging) in running mode. Meaning at any time one averages recent 8 cardiac cycles. When 9th comes in 1st cycle gets out of averaging. Similarly when 10th cycle comes in 2nd cycle gets out and so on.  

  • Reina Jimenez added an answer:
    3
    Has anyone experienced better dosimetric outcomes with symmetric planning in LDR prostate brachy?

    Is there any literature evidence on symmetric planning and its advantages over asymmetric planning in ldr brachy. Thanks

    Reina Jimenez

    After more than 600 patients implanted one thing is certain to me: Each prostate is unique, and despiting more of them are symetric in their external aspect, internal composition,  drive by biopsy results,  made us to plan almost symetric distributions of needles but asymetric distribution of dose. One of the wonders of brachytherapy is the power of intensity modulated therapy design for each prostate form and content.. We also use 0.496 U and D90 is ever greater than planned. More dose in Ca nodules, better local control. All of this happened inside the gland. D90 must ever respect  margins 2-3 mm for rectal wall,  up to 4 mm  outside the capsule in the rest of the gland  

  • Michele Di Foggia added an answer:
    3
    Which laser should be used for composition analysis of bone in Raman Spectroscopy?

    Using raman spectroscopy I want  to find compositional constituents of bone sample.

    Michele Di Foggia

    FT-Raman spectroscopy using the 1064 nm Nd:YAG laser has been successfully used for the characterization of bone: in some cases fluorescence was almost absent.

  • Mark Collins added an answer:
    4
    Are there any studies about the late effects of simultaneously integrated boost techniques?

    I am working on SIB technique planning. I have done dosimetry on Phantom but I am curious about acute and late effects.

    Mark Collins

    Hi,

    Take a look here http://www.icr.ac.uk/our-research/our-research-centres/clinical-trials-and-statistics-unit/clinical-trials/import_high this is a trial a lot of UK departments are recruiting for. Also, a number of UK department use SIB in prostate treatments, delivering a different dose to the seminal vesicle and the prostate.

  • Prashant Shukla added an answer:
    1
    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

    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.

  • Yuan jl added an answer:
    4
    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?

    • [Show abstract] [Hide abstract]
      ABSTRACT: Purpose: To fully characterize the spread-out Bragg peak from the Mevion S250 Proton Therapy System using Monte Carlo simulations, evaluate the slope of the spread-out Bragg peak in the treatment field, and correct this slope by virtually applying beam current modulation. Methods: MCNPX simulations were performed on the Mevion S250 for each of the 24 beamline configurations, with the modulator wheel rotated in 1 degree increments. Energy deposition was tallied in a water phantom, resulting in 8,640 central axis depth-dose calculations. These data were imported into MATLAB and the slope of the spread-out Bragg peak (SOBP) was evaluated for a constant beam current. An iterative algorithm was developed to determine the optimal beam current modulation (BCM) profile as a function of modulator wheel position for each configuration. These BCM profiles were then applied virtually to the MCNPX SOBP data and slope values were recalculated for the optimized SOBP profiles. Results: Ideally SOBP slope would measure 0.0 %/cm in the treatment field, corresponding to a uniform dose delivery. Prior to BCM correction, slopes between -1.0 and +2.0 %/cm were observed across all beamline configurations. These were reduced to ±0.2 %/cm by applying optimized BCM profiles. The algorithm converged quickly, validating its underlying assumption that the optimal SOBP profile can be determined by considering only a single dose values at the depths of maximum individual Bragg peak dose. Conclusions: Optimized BCM profiles adequately reduce SOBP slope in the treatment field, and may be further studied using time-resolved MCNPX simulations. The algorithm presented efficiently calculates BCM profiles, fully accounting for beamline scatter and partial-shining effects across adjacent steps on the range modulator wheels, and without requiring direct measurements. Future work includes applying this same algorithm to optimize the SOBP distal dose profile. Partially supported by MEVION Medical Systems, Inc.
      No preview · Article · Jun 2012 · Medical Physics
    Yuan jl

    @B.M. Schneider

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

  • Abbas Haghparast added an answer:
    1
    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

    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:
    5
    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

    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:
    5
    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

    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:
    3
    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

    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:
    7
    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

    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:
    1
    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

    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

  • Matteo Levantino added an answer:
    5
    Can somebody suggest a source of tabulated spectral data of absorption coefficients for myoglobin and oxy-myoglobin?
    -
  • Hakan Akyildirim added an answer:
    11
    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

    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:
    18
    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

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

  • Lambert Zijp added an answer:
    1
    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

    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:
    5
    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

    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:
    4
    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

    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:
    4
    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.

    + 2 more attachments

    Dushyant Kumar

    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:
    6
    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

    Thanks for your good explanation and the references.

  • Andrey Borodach added an answer:
    4
    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.

    + 2 more attachments

    Andrey Borodach

    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

  • Sergio Faermann added an answer:
    3
    LINACS?
    T lead.
    Sergio Faermann

    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.

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