[Gate-users] Dose value in mGy

[Steven Marsh]

Hi Emmanual

The answer is in the definition of Gy.

Absorbed (physical) dose is in units of Gy where Gy is defined as Joules/kilogram.  

When you have a volume divided into voxels, and dose for each voxel modelled, then dose per voxel is energy deposited per voxel divided by the mass of that voxel.

Likewise, dose for the entire volume would be given by total energy deposited into that volume divide by the mass of the total volume.

Thus to get total dose to a volume from voxels of dose you need to sum the **energy deposited** into all voxels and divide by the mass of your object receiving dose (sum ((density *volume) for each voxel)).

The problem with simply summing is easily observed by considering 2 x 1kg masses side by side where each absorbs 1J of energy.  From definition each of the 1kg masses receives 1Gy of absorbed dose. Summing would indicate the 2x1kg masses receive a combined 2Gy but this is incorrect.
The total absorbed energy is 2J and the total mass is 2kg.  therefore the dose received by the combined masses is still 1Gy.

Cheers
Steve
University of Canterbury


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Today's Topics:

   1. Fixed Forced Detection algorithm: de-noising required?
      (Triltsch, Nicolas)
   2. Dose Value in mGy (Emmanuel Marfo)


----------------------------------------------------------------------

Message: 1
Date: Wed, 28 Jun 2017 11:27:03 +0200
From: "Triltsch, Nicolas" <nicolas.triltsch at tum.de>
To: Gate-users <gate-users at lists.opengatecollaboration.org>
Subject: [Gate-users] Fixed Forced Detection algorithm: de-noising
	required?
Message-ID: <588e0019-9056-18d6-8309-402494713e80 at tum.de>
Content-Type: text/plain; charset=utf-8; format=flowed

Hello Gate community, hallo Simon Rit,

I have a general question to the implementation of the fixed forced detection algorithm.

Is there a de-noising step performed at the end of one simulation run (as reported by  Colijn & Beekman 2004 or Mainegra-Hing & Kawrakow 2008) or does the implementation follow the fixed forced scheme ( Poludniowski et al. 2009) where no de-noising step is required, because scatter is registered at nodal points at the detector followed by linear interpolation.

If the latter is used, then I wonder why 10^5 to 10^6 photons are required to obtain low uncertainty images, because in the mentioned paper they use only 10^3 to 10^4 photons to gain reasonable results.

Cheers and I appreciate any help!

Nico

--
B.Sc. Nicolas Triltsch
Masterand

Technische Universität München
Physik-Department
Lehrstuhl für Biomedizinische Physik E17

James-Franck-Straße 1
85748 Garching b. München

Tel: +49 89 289 12591

nicolas.triltsch at tum.de
www.e17.ph.tum.de



------------------------------

Message: 2
Date: Wed, 28 Jun 2017 09:59:04 +0000
From: Emmanuel Marfo <emmanuel.marfo at postgrad.otago.ac.nz>
To: "gate-users at lists.opengatecollaboration.org"
	<gate-users at lists.opengatecollaboration.org>
Subject: [Gate-users] Dose Value in mGy
Message-ID:
	<SY3PR01MB156169632A074B8CC5EF4373F7DD0 at SY3PR01MB1561.ausprd01.prod.outlook.com>
	
Content-Type: text/plain; charset="iso-8859-1"

Dear Gate-Users,

Please, just a quick question about dose in mGy. Earlier on in a mail in the Gate-User mailing list. I ask about how one could get the dose voxels as one value and I had a reply that I should sum all the dose voxels matrices and multiply by 1000 to get in mGy. My supervisor did not agree with me on that. Please, is there a publication I could refer to.

Thanks.

Best regards,

Emmanuel

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