[Gate-users] Dose Actor Voxels?

[Ben Kopchick]

Hi Josh,

In your original test, if you average the dose of the 1000 voxels do you
get the same dose as the single voxel? I believe this should be the test as
Dose (Gy) is dependent on the mass of the material.

Best,

Benjamin Kopchick

On Tue, Jan 15, 2019 at 11:25 AM Josh Knowland <
jknowland at lucernodynamics.com> wrote:

> To continue what I have found –
>
>
>
> The correct dose is not simply dividing by the total number of voxels in
> the doseActor. In fact, I have to divide by the total number of voxels in
> the union of the doseActor and the geometry volume its attached to.
>
>
>
> For instance, if I make my cube of water 100mm on a side, but make the
> doseActor 125mm on a side, I will only register dose within the volume of
> the cube. This makes sense – I should register zero dose for those voxels
> outside of the water cube.
>
>
>
> However, during dose calculation, the doseActor multiplies by the number
> of voxels that fell within the water cube. When using complex geometry from
> STL files, I can’t know this number.
>
>
>
> It seems the calculation would be fine if the doseActor is contained
> completely within your geometry, but how can you encompass an entire
> geometry (say, a liver organ modeled in STL) using the rectangular solid
> doseActor? I can’t know exactly how many doseActor voxels actually fall
> within the liver.
>
>
>
>
>
>
>
>
>
> *From:* Josh Knowland
> *Sent:* Tuesday, January 15, 2019 11:06 AM
> *To:* 'gate-users at lists.opengatecollaboration.org' <
> gate-users at lists.opengatecollaboration.org>
> *Subject:* RE: Dose Actor Voxels?
>
>
>
> Sorry, I had a typo. I meant:
>
>
>
>    - Dose from doseActor seems to always *multiply* by the number of
>    doseActor voxels. If I sum the dose output and then *divide* by the
>    number of voxels, I get the same as if I calculate dose from Edep.
>
>
>
>
>
> *From:* Gate-users <gate-users-bounces at lists.opengatecollaboration.org> *On
> Behalf Of *Josh Knowland
> *Sent:* Tuesday, January 15, 2019 11:03 AM
> *To:* gate-users at lists.opengatecollaboration.org
> *Subject:* Re: [Gate-users] Dose Actor Voxels?
>
>
>
> Hi Matthew, thank you for the reply.
>
>
>
> Here is what I have done to try to verify the calculations:
>
>
>
>    - Simulation of 1 liter of water hit with F18 positrons.
>    - Calculated dose three ways:
>       - Summing Edep from Singles output and converting to Gray.
>       - Summing Edep from doseActor and converting to Gray.
>       - Summing dose from doseActor (already Gray).
>    - Edep from Singles and summed Edep from doseActor always agree.
>    - Dose from doseActor seems to always divided by the number of
>    doseActor voxels. If I sum the dose output and then multiply by the number
>    of voxels, I get the same as if I calculate dose from Edep.
>
>
>
> Can anyone explain this? When the dose map is already divided by voxel,
> why can’t I just sum all the voxels? I get the same results using
> VolumeWeighting or MassWeighting (of course, I’m using 1 liter of water, so
> that’s the same.)
>
>
>
> Thank you all,
>
> Josh
>
>
>
>
>
>
>
>
>
>
>
> *From:* Matthew Strugari <matthew.strugari at dal.ca>
> *Sent:* Tuesday, January 15, 2019 10:22 AM
> *To:* Josh Knowland <jknowland at lucernodynamics.com>;
> gate-users at lists.opengatecollaboration.org
> *Subject:* Re: Dose Actor Voxels?
>
>
>
> Hi Josh,
>
>
>
> I am not entirely familiar on the behaviour of the doseActor, but it
> appears that the output dose is given as the dose per voxel. Hence, the
> same dose is deposited after integration in each case.
>
>
> Matthew
> ------------------------------
>
> *From:* Gate-users <gate-users-bounces at lists.opengatecollaboration.org>
> on behalf of Josh Knowland <jknowland at lucernodynamics.com>
> *Sent:* January 14, 2019 2:53:48 PM
> *To:* gate-users at lists.opengatecollaboration.org
> *Subject:* [Gate-users] Dose Actor Voxels?
>
>
>
> All,
>
>
>
> Can you explain how the voxel size and number impacts the calculated dose
> by the doseActor?
>
> I have simulated a 1 liter cube of water containing 0.01 mCi of 18F
> positrons. When I enable the doseActor using 1000 voxels each 1cm^3, I get
> a total of *2.43E-05 Gy.* However, if I enable the doseActor using only 1
> voxel of size 10cm^3, I get a dose of *2.43E-02 Gy.*
>
>
>
> I get the same total energy deposited no matter the voxel size and number,
> why not dose?
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