Medical Radiation Physics - Science topic

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Dear Prof. Nancy Ann Watanabe

I guess that in the long rule, solar radiation in some cities like Barranquilla Co (200 days a year and 600 kV / h daily) will be more beneficial for industrial purposes, but the associated heat waves will be more detrimental to people's health.

Yes, minimum dose rate 50 cGy/min at SSD=80 cm for Field size= 10 X 10 cm x cm is acceptable for external beam radiotherapy. Because below this dose rate the treatment reproducibility will decreased and treatment outcomes will be affected.

Linear

No of course because of the radiation hazards

Thank you, Pablo.

How did Dr Sasidharan S Lucky determine the survival of cancer organoids? LQ is a model for cellular clonogenic inactivation. Target theory was proposed in the 1940s based on experiments in bacteria, but the LQ model has broadly been used for clonogenic survival curve since mid-1970s ( )

It is old but great question with useful answer.

Hi

EGSnrc has two main derived codes for specific purpose:BEAMnrc and dosxyznrc

BEAMnrc code used to simulate linear accelerator and dosxyznrc used for 3-D dose calculation in the cartesian volume. for running beamnrc you must get the full specification of your point source and then define it in  a text file named egs input file.after the simulation of beamnrc complete,code generate phase space file which contain information about charge,energy,direction and etc of particle.

finally the phase space file use as a input file for dosimetry with dosxyznrc code.

with best regards

milad

Dear Nada,

I've found a free PDF file of the book you wanted at the link below (I don't know if it is a legal site):

Regards,

Tatsuo

Every software for calculating organ dose has laid down etiquette and procedures. Carefully go through the procedures or request directly from the manufacturers.

Thank you.

You can also read the attached useful paper.

Check the SNM dose calculator:

It derives the dose from 131I-MIBG from ICRP 106.

I'm not sure, if someone can provide measured data as gamma (photon) spectroscopy for such X-ray tubes is hard to perform. Scintillator-based detectors mostly have a too rough energy resolution for this purpose. Semiconductor-based detectors are mostly too sensitive resulting in dead time problems. One can increase the distance to the X-ray tube or use collimation to decrease the photon flux photon, but then you will loose low energy photons which would otherwise contribute to your spectrum. In addition, low energy photons are also absorbed inside the cover of the detector (stainless steel cap for cooling).

But maybe you are lucky and someone solved these problems :-)

As mentioned above, the equivalent dose limits are currently recommended only for the lens of the eye, the skin, the hands and feet. Historically, however, ICRP (or its predecessor IXRPC) had recommended specific “dose limits” for “blood forming organs”, “gonads”, “thyroid”, “bone”, “hands and forearms”, “feet and ankles”, and “head and neck”.

Precisely speaking, the term “dose limits” has been used for workers since the 1977 recommendations (in Publication 26), and for the public since the 1966 recommendations (in Publication 9), until which time the terms “tolerance dose” assuming thresholds for all radiation effects and “maximum permissible dose” assuming no thresholds for all radiation effects had been used. It was the 1977 recommendations that recommended dividing all radiation effects into tissue reactions (called nonstochastic effects at that time though) with a threshold, and stochastic effects with no thresholds, for which equivalent dose limits and effective dose limits are recommended.

For more details of such historical changes, please see the following paper (especially, Supplementary Tables 7 and 8).

It sounds like you have 0.11 R/hr, then you add 2 cm Pb shielding.  So you will calculate a new dose rate after the shielding.  Using 2 cm Pb, and Cs-137 gamma (0.66 MeV), I get a reduction of about 0.14: That is, the 0.11 rem/hr dose rate would be reduced to 0.14 of this, or about 0.016 mrem/hr.  In order to get a stay time, you need an allowable dose. If you assume 0.1 Rem (100 mrem or 1 mSv), then your stay time would be 0.1 rem / 0.016 rem/hr, or about 6 hours.

A short tip to tld in randso. Drill small cylindrical holes, enough to put a small cylindrical pmma tube with a central hole for cylindrical tlds. You will get commercial hints by PTW in germany Freiburg.

Different lifestyles in different populations would indeed be important.

ERR in each study is obtained after consideration of various lifestyle factors and other confounders, but the background incidence of disease varies among countries and also within the country.

thank you so much for your answer.

The MIRD system is a good practical system for dosimetry of radionuclides in the human body.  It is well suited to radiation protection applications where organ doses are of interest, and it may not be possible to determine the exact shape and biological performance of the organs of interest.  Idealised organ shapes may be used, and microscopic variations in does are not reckoned.  The weaknesses of the system are in the way real biology may depart from the assumptions.  This is particularly evident in the mass and shape of organs, the uptake and distribution of radionuclides in the organs, the kinetics of uptake and elimination, microdosimetry and so on.  However, it is a good methodology, provided you are alert to its limitations.

Dear Mohammed,

an upper estimate of the dose is the so-called KERMA (kinetic energy released in material).

 This Kerma K is calculated according to equation 2,4 of the attached file for the case of a mono-energetic x-ray photon energy flux.

The x-ray spectrum flux  Io(E)  is entered via the integral in equation 2,5 of the  attached file via PSI'(E)  = E*Io(E).

The mA setting as well as the kVp setting and other characteristics of the tube (anode material,  target angle and filtration) are included in Io(E).

Remark 1: the attached file is a copy of page 22 of ' Introduction to Radiological Physics and Radiation Dosimetry' by Frank. H. Attix.

Remark 2: Sorry, but there is no open source known to me in the internet for reliably calculating the x-ray spectrum.

hi

the applicators plays an important role during the electron beam therapy because they flattening the electron beam  around of treatment field size and without applicator the beam profile get a cone shape.

Ruediger

The majority of the dose comes from the higher energy gammas from the Ra progeny. Calculation is difficult. Dose rate depends upon shape, size, the matrix containing the Ra and distribution of Ra in material. The HVL of 4 mm is for a point source. Many medical sources have a listed HVL of 12 - 14 mm. See attached.

What type instrument are you using for measuring dose rate? Some instruments over respond to low energy gammas making the measurement too high. Check with simple shielding. If the dose rate is easily reduced by shielding you have over response.

Consider repackaging. Is the Ra uniformly distributed? If not, place higher dose rate material in the center. Can you add filler, for example, wet soil? If uniformly distributed place material in smaller containers and then filler in the 200 L drums to hold them in the center.

How you shield will come down to cost.

The EGSnrc is a friendly Monte Carlo code where you can find the phase space for several linear accelerators. So you need to use  BEAMnrc to generate the beam and Flurznrc to calculate the electron fluence.

The internal safety checks on the MRI scanner for SR (slew rate) is built into the control software of the scanner.  As a user you are not able to prescribe a protocol or scan that will exceed these limits.  If you are a developer the gradient waveforms will not exceed these limits as the software will not allow you to compile and run the waveforms.

This is true for all major clinical vendors.  That is because it is a requirement for safety laws in the US, EU, and all countries that follow those conventions.

As for exceeding SR limitations, it would be necessary to reach very high SR rates to induce significant currents for cardiac stimulation.  Lower excessive SR will induce tingling or shocks only at extrema in the gradient fields with current flows over long distances of the body say the sagittal plane.  The sensations (tingling or shocks) will be localized to the extreme lower back or the bridge of the nose.  

For a clinical scanner in convention configuration you would not be able to exceed the SR limits in any accepted clinical operational mode.

If you want to calculate the proton dose you will find an established protocol in IAEA 398. I attend this report for you.

I don´t directly know the attenuation coefficient for these energies, but there is a rule of thumb, just use the half nominal energy. Example: X6 you use 3 MeV photon energy, x18 9 MeV etc.

Because the main interaction is compton effect in this energy range your error will be small if not meeting the exact energy. Most of flattening filters were constructed experimentally. If you want to know some experimental date for attenuation coefficient, please let me know, I will send you experimental results and some more remarks about influence of field size, scattered radiation etc.

.

hi read this article i think will be useful for you

Dear Bob,

Actually, some of them appear to be not quite safe. For example, there are risks of a Gallbladder Radionuclide Scan.

The Risks of a Gallbladder Radionuclide Scan

There is a risk of exposure to radiation with this test. The gallbladder radionuclide scan uses small amounts of radioactive tracers. However, this test has been used for over 50 years and there are no known long-term side effects from such low doses of radiation. The benefits of the tests outweigh the risk of radiation exposure (Radiology, 2012).

There is, however, a rare chance of an allergic reaction, which is typically mild.

On the other hand, others were proved to be safe. For example, in the bone scan:

The amount of the radionuclide injected into your vein for the procedure is small enough that there is no need for precautions against radioactive exposure. The injection of the tracer may cause some slight discomfort. Allergic reactions to the tracer are rare, but may occur.

Hoping this will be helpful,

Rafik

Dear Dr. Gawad,

Although I have heard of the Ellis NSD-concept, I have more experience with the LQ-model (by Fowler and Barendsen). The literature on missed radiation fractions is extensive; for practical purposes I recommend the papers by Nuran Bese et al. (2007) and by Roger Dale et al (2002) [1,2]. 

If you do not have access to these two papers, do not hesitate to send me an e-mail, so I can forward them as pdf-attachments.

There are several (more or less freeware) LQ-model software packages, that also have a a module for compensation of missed fractions.

See amongst others: http://www.eyephysics.com/tdf/

Sincerely yours,

Lukas Stalpers, radiation oncologist

AMC - University of Amsterdam, The Netherlands

1. Bese NS, Hendry J, Jeremic B. Effects of prolongation of overall treatment time due to unplanned interruptions during radiotherapy of different tumor sites and practical methods for compensation. Int J Radiat Oncol Biol Phys. 2007;68(3):654-61

2. Dale RG, Hendry JH, Jones B, Robertson AG, Deehan C, Sinclair JA. Practical methods for compensating for missed treatment days in radiotherapy, with particular reference to head and neck schedules. Clin Oncol (R Coll Radiol). 2002; 14: 382–393

You might want to look at the method developed by Walter Huda and me.  Using the free-in-air isocenter kerma, we measured the ratio to organ doses in multiple anthropomorphic phantoms.  Very easy approach to organ dose:

Darrion, you can find here an example of pelvic cavity phantom: http://www.cirsinc.com/file/Products/002PRA/002PRA_DS_070113.pdf

Once the dose is expressed as effective dose it is an estimate of detriment, mainly cancer risk. ICRP states that this is for doses lower than deterministic effects, about 0.05 Sv. Consequently, this is in the range of radiation protection. Nevertheless, the risk was calculated from even higher doses and extrapolated to lower doses.

The range of doses in your case should apply as the risk is considered linear. 

Do you plan to give the risk information to patients?

The stone-free rate for stones of <970 HU is significantly higher (96%) vs 38% for stones of ≥ 970 HU (P < 0.001). In addition,  a linear relationship between the calculus density and the success rate of ESWL has been identified. Even in children, SFR was significantly higher with stones of <600 HU.

I used glass beads and measured a DDD accumulative dose of both components and there are interesting findings so wanted to cross-check with any published data but couldn’t find any.

I am sending the results to you via message.

So, if I understood that right, you really want to know (an estimate of) the whole spectrum, not specifically the ratio of characteristic radiation to bremsstrahlung. Analytical models, as probably found in the books mentioned above, can likely give you a good general idea, but will not be very accurate for a particular tube. A semi-analytical model (most likely what Javier Miranda was referring to) should be suitable for standard x-ray tubes. SpekCalc (see attached link and related publications) is one from the medical field you might want to look at. I have not used that software, but would expect it to perform well for this purpose from reading two of their background papers. I could probably also provide you with a copy of my own model (developed for use in non-destructive testing). If you want a more general accurate model, a Monte Carlo code is an option. Among those BEAMnrc is fairly fast and not too complicated to use. In particular for Megavolt beams, which you mentioned in your answer, this is the way to go.

Measurement is indeed unlikely to be successful in the described situation. As you mention, filtration would strongly influence the result. The alternative is collimation and sufficiently increasing the distance between source and detector. For the sources you describe the latter is probably not feasible.

Dear Richard,

thats exactly the point. We should differentiate between screening techniques like mammography screening, TB etc and the indicated examination in a special case. In Germany screening must be approved. And the concerned circle is the population. Effective dose could be right even with all limitation of risk models.  Abusus of X-ray examination because of laziness of the examiners must be avoided and restricted.

Hello

XRF is applied in anti-cancer research to study the two dimensional distribution and concentration of metals and other biologically important elements, like phosphorus or sulfur, in cell or tissue samples. Thus, the direct assignment of the metal distribution to specific biological functions and targets is possible, e.g. DNA binding or accumulation in membrane regions. To quantify the elements in the tissue or cells the collected spectra and peak intensities must be calibrated against a standard of known composition and concentrations of the elements in question

pleas , see the attachments

Good Luck

To physically measure the dose (rather than modelling), you can use a RANDO or ATOM phantom and use either TLDs or MOSFETs, this is measuring the organ doses directly, from which you can calculate E. This is more accurate than any modelling method, however it is significantly more time consuming, so it would depend on the reason that you are calculating E.

As well as the method of using the E/DLP factor, there is also the IMPACT Excel spreadsheet, which uses the SR250 montecarlo dataset to calculate E from the selected parameters and the CTDI values, the SR250 MC dataset is £50, but the spreadsheet is free.

If you are interested, I have attached an article from one of my PhD students on the variety of ways to calculate and measure E.

Dear Christoph,

take care for Co-59 contaminations of your structures. Using high energy photon beams you will produce neutrons by nuclear photo reactions. These neutrons could be captured by metalls containing natural Cobalt. The result would be 60- Co with the known problems.

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.

Kinga's explanation correctly accounts for the differences in peak shapes.

An x-ray or gamma photoelectron peak is nearly Gaussian. A full photon energy photoelectron is produced by a photon that has had no prior scattering losses. The photoelectric effect occurs in the detector so all the energy of the photoelectron is deposited in the detector. The Gaussian shape results from stochastic effects of the collection process in the detector and the conversion process to an electronic pulse.

Full energy peaks of alpha and beta particles have the same stochastic collection and conversion processes, so a full energy alpha or beta particle will produce a nearly Gaussian shape. Alpha and beta particles originate outside the detector, unlike the photoelectron produced in the detector. Alpha and beta particles lose energy in the process of reaching the detector and the detector active volume. Alpha and mono-energetic beta particles will show a low energy tailing because of the losses. The larger the angle of incidence on the detector, the larger the losses.

A good, introductory spectrometry text should include the explanation of peak shapes.

Leon's answer above is correct in that it will give you a numerical value that you can use as a starting point. However, it will not directly give you optical density. There are a few other things you need to do (including scanning each film prior to irradiation, calibrating your scanner etc.).

You might find some useful information in this MSc thesis from the University of Wollongong:

You may also find this article on ResearchGate useful:

(it is for EBT3 but shouldn't be radically different I think).

Fluorine binds to most metals, forming a very strong bond with Al3+, which can form complexes with metal-binding chelates. The aluminum fluoride bond is stronger than 60 other metal-fluoride bonds, e.g., bond energy of 670 kJ/mol. The aluminum-fluoride bond is highly stable in vivo, and small amounts of AlF complexes are compatible with biological systems.

The pH is critically important for the formation of (AlF)2+-chelate complexes. If the pH is too high, metals would form hydroxide complexes and precipitate, and if it is too low, then the preferred fluoride species in the equilibrium would be HF. Studies of AlF complexes suggested that pH 4 would favor a 1:1 aluminum-fluoride complex, and pH 4 was compatible with the metal complex formation.

An example of complex; please see attached file.

I am not sure what you mean by "commissioning TBI". As far as I know the commissioning refers to the characteristics of the LINAC you will be using and not to the TBI method in itself

If you are thinking about in vivo dosimetry, you can find several papers on the use of EBT Gafchromic films Look for instance at the following:

or at

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

Be cautious, first you have to determine the relation between count rate and activity. It´s not trivial because of geometric effects, efficiency and kind of radionuclide. You have to take care with dead times because of saturation count losses by the special counter you use. If you want to check this behaviour of your counter use a strong source and go closer and closer with your counter. You will certainly experience constant count rates in contradicction to inverse square law.

If you have found a reliable and quantiative relation between count rate and activity you can use gamma constants for gamma emitting radionuclides or beta conversion factors for beta emission.

yes "acquire image during" the epid does have to be setup as such but it isn't a big deal. Obviously you would still calculate the fluence pattern at the epid however it would be after passing through the patient data set. This is a form of in-vivo dosemtry. Peter Greer is an acknowledged expert with epid http://au.linkedin.com/pub/peter-greer/57/61b/934 or https://www.researchgate.net/profile/Peter_Greer and has published in this area check out his RG profile

Measuring absorption spectrum of blood is much easier said then done. Blood is not a true solution, rather a colloid, so it will have very strong scattering. On top of that whole blood is very unstable thing when taken out of an organism, it tends to clot very quickly.

Bottom line, it's unlikely there is a reliable way to measure absorption spectrum of whole blood. It is though obvious that it is dominated by hemoglobin, and spectrum of that protein you can easily google.

EMI material reflects the radiations, conducting materials like metals can also be used but they are bulky , so any material which shows some conductivity and is flexible can be used as a material for EMI shielding like flexible graphite etc. For more details the following paper may be referred:

The absorbed dose is due to electromagnetic interactions between radiation and target.

Other interaction kinds play a minor role. Therefore, uncharged particles (photons and neutrons) contribute to the absorbed dose through the charged particles they set in motion (electrons and ions). The charged particle fluence in a tiny volume in the target, is a balance between particles entering into the volume and outgoing particles. The absorbed dose is proportional to charged particle fluence (more exactly, it is the limit value when the volume tends to 0). At depths smaller than the mean charged particle range, the entering charged-particle swarm is smaller than the outgoing swarm. On the contrary, at deeper depths , the outgoing swarm is smaller (because of the primary neutral beam attenuation).

That gives rise to a charged-particle fluence maximum, hence to a maximum dose, at about to the mean charged-particle range. Higher is photon or neutron energy, bigger is the mean charged-particle range, deeper is the depth the maximum absorbed dose is reached.

Absorbed dose to an organ is defined as the energy absorbed (from radiation) divided by the mass of the organ.

In order to calculate the energy absorbed in an organ, you need to know the total activity of the pharmaceutical in that organ and such quantity is time dependent.

You need some information such as the bio-kinetic model (biologic distribution) for the animal that you have used in your experiment. You also need organ dose calculation software that will sum up all the radiation energies from all the source organs to the target organs in the animal under study.

The most common software is known as OLINDA (organ level internal dose assessment) written by Dr. Michael Stabin, of Vanderbilt University; but this software is applied to human data and not to animal data as far as I know! But you can check out the software applications available online. I guess you may be able to benefit from the software phantom results by using the following relation

A (phantom) = A(animal) [( m/Mphantom) /(m/Manimal)] where m is the organ mass and M the total body mass.

using the animal organs mass to obtain an approximation of the doses to the organs; anyway what is done is usually an estimate of the organ dose; do not forget that an estimate has always an associated uncertainty.

To convert the measured counts in each organ to an activity in (Bq) deposed into the organ; you need to calculate a factor relating the counts registered by the gamma counter used and the corresponding standard radiation source (radiopharmaceutical) activity in (Bq). Then once you have the determined the activity you need another factor that will relate the integrated Activity in time measured in (Bq.hr) to the absorbed dose in (rads) and this is what is missing the so called (S) factor. You need the software for that because (the software uses Monte Carlo simulations results and mathematical phantoms).

Good luck

A little more on the topic might help as well. Many radionuclides can undergo multiple decays or can emit multiple energies of radiation. The fraction of the time that a nuclide undergoes a specific decay mode is the branching ratio. For example, potassium-40 (K-40) will decay via beta emission 89% of the time and emits a gamma the other 11% of the time. So the branching ratio of K-40 beta decay is 89%.

Is Mobile Phone Radiofrequency Radiation All Bad?

SMJ Mortazavi.

Journal of Medical Hypotheses and Ideas, In Press, Accepted Manuscript, Available online 2 September 2013

Dear Editor

In 1992, Dr. Sheldon Wolff published his widely cited paper ‘Is Radiation All Bad? The Search for Adaptation’ [1]. Dr. Wolff was widely honoured for his findings on the stimulatory effects of low doses of ionising radiation. Now, due to exponential increase in mobile phone use (4.6 billion users globally), we should ask a new question, “Is mobile phone radiofrequency (RF) radiation all bad?” It should be noted that, currently in some parts of the globe, mobile phones are the most reliable or even the only phones attainable. A large body of evidence indicates that when cells are pre-exposed to low doses of ionising radiation and DNA-damaging agents, such as ultraviolet (UV) radiation, alkylating agents, oxidants and heat, they become more resistant to high doses of those agents and in some cases to similar agents, a phenomenon that is usually referred to as the adaptive response. The induction of adaptive response after pre-exposure to low doses of ionising radiation was first described by Olivieri et al. for radiation-induced chromosomal aberrations in human lymphocytes [2]. Other investigators and I have recently indicated that RF radiation can induce an adaptive response phenomenon [3], [4] and [5]. We have also recently revealed that pre-exposure of laboratory animals to RF radiation emitted from a GSM (Global System for Mobile Communications) mobile phone increases their resistance to a subsequent bacterial infection [6] and [7]. As discussed in our work, this phenomenon may have implications in humans’ long-term stay in space [8]. However, the potential beneficial effects of (RF) radiation are not limited only to the induction of adaptive phenomena. Previously, we have indicated that the visual reaction time (VRT) of university students was significantly affected by a 10-min exposure to electromagnetic fields (EMFs) emitted by a mobile phone [9]. Furthermore, we have previously shown that occupational exposures to radar radiations decreased reaction time in radar workers [10]. Altogether, our results revealed that these exposures caused decreased reaction time, which might lead to a better response to different hazards and decrease the probability of human errors and fatal accidents. Meanwhile, cognitive beneficial effects of long-term exposure to high-frequency EMFs have been indicated by some studies. Using a word interference test, in 2007, Arns et al. showed that long-term heavy cellphone use resulted in better performance in normal subjects [11]. Moreover, Schuz et al. in 2009 reported that long-term cellphone users (subscribers of 10 years or more) had a 30–40% decreased risk of hospitalisation due to Alzheimer’s disease (AD) and vascular dementia [12]. In this light, it will be challenging to investigate if there are other RF-induced stimulating effects and to explore their potential applications. Further research may shed light on the dark areas of the health effects of short- and long-term human exposure to RF radiation.

Dear Tim,

I'm a radiochemist developing target-specific radiopharmaceuticals at MGH.

While there are undoubtedly technical challenges, integrating a cell sorting device with a radioactive detector is feasible. Sensitivity need not be an issue but flow rate might need to be controlled. If you use a positron-emitting radionuclide coupled with coincident detection you can achieve sensitivities generally exceeding that achievable of photon counting with fluorescence (in theory both are zero background methods). Also, you should look up the work people (including myself) have done on imaging radioactivity with Cerenkov emissions (Cerenkov luminescence imaging). I don't think standard FACS detectors would be sensitive enough to see this low level optical emissions from small amounts of activity but certainly you could build one.

Safety is not a major problem - we handle radioactivity all the time, and for this experiment labeling cells, you would only use nano-Ci amounts. You simply need to manage the waste stream (and have a license to work with the specified nuclides.

Are you interested in small molecules or macromolecular constructs? My advice would be different in each case. Happy to talk offline if you .

Determination of the conversion factor for the estimation of effective dose in lungs, urography and cardiac procedures

(Thesis for Master of Science in Medical Radiation Physics) may be helpful

Hi, what energy are the x-rays? And is it a diagnostic or therapeutic beam?