Modelling treatment couch (Elekta)

Aurélien Vasseur

unread,

Apr 13, 2012, 6:15:38 AM4/13/12

to pinnacl...@googlegroups.com

Dear all,

We're trying to model our treatment couch (BeamEvo, Elekta) to incorporate it in Pinnacle planning. We have no info from Elekta about constituents, accurate geometry, and so on.
Did some of you this work? Are you using average value of density or did you create shell and inner part? And how do you manage the junction between head part and the "body" of the couch?

Thanks.
Aurélien Vasseur
Medical Physicist, PhD
Auxerre (France)

Kaurin, Darryl G

unread,

Apr 17, 2012, 3:22:55 PM4/17/12

to pinnacl...@googlegroups.com

See attached, which was a poster at ASTRO last yr.

After we did this, we found out that the region of interest accuracy was limited with a grid -we wanted a 3mm shell for one couch and a 4mm thick shell for another couch. We found later that the shells were were 4-5mm thick after the couches were transferred from the model organ library to the patient QA plan - with some variability. We found that if we dropped the density from 0.65 to 0.60 g/cc with the couch that came over from the organ model library, we achieved approximately the original results.

If attachments come through, I am attaching the pdf for ROI precision, which describes limitations for thin contours, and the poster. Abstract is below if the attachments don't come through.

Darryl

Author Block:
D. G. Kaurin1,2, E. Marshall1,2, M. M. Zaini1,3, M. A. Lavilla2, L. E. Sweeney1,2, S. Mahendra1,2,
1
Northwest Medical Physics Center, Lynnwood, WA, 2Seattle Cancer Care Alliance, Seattle, WA, 3Skagit Valley
Hospital Regional Cancer Center, Mount Vernon, WA

Abstract:

Purpose/Objective(s):
Our institution has two accelerators that are beam matched, one having a kevlar couch

and the other carbon-fiber. We were concerned about couch attenuation for volume modulated arc therapy

(VMAT), as well as being able to switch patients to either unit without replanning. The couches were

characterized dosimetrically to determine if the couches needed to be included in the treatment plan, and if

patients could be treated on either couch without additional planning.

Materials/Methods:

Attenuation measurements of both couches were made by positioning an ion chamber with buildup cap on top of

the couch and measuring transmission of a 5cmx5cm beam at ten different posterior gantry angles (PA and then

every 10 degees up to 10 degrees below the horizontal) for 6MV and 10MV energies, relative to an unattenuated

beam.

Both couches were CT’d and imported into the treatment planning system (TPS). Attenuation measurements

were simulated in the TPS. The couches were contoured as shells of varying thickness and density, with air in the

middle of the couch, as the recommended TPS air threshold density for the entire couch attenuated the beam too

much. We had good measurement agreement for a kevlar couch model shell of 3-mm-thickness, and the carbonfiber

model shell of 4-mm-thickness, both with 0.65g/cc density. Both couches were stored in the TPS organ

model library.

To validate the couch models, five prostate patients (two 6MV, three 10MV cases) with test VMAT plans were

copied onto a cylindrical phantom with a central 0.13cc ion chamber and also a rectangular phantom with a 2-

demonsional diode array in a sagittal orientation. Doses and fluences were calculated for both phantoms, both

couches and no couch (30 plans); and measured (20 measurements).

Results:

Ion chamber results comparing the phantom plan with and without the couch gave a 1% improvement in

measured-to-calculated values. Planar fluences were evaluated using absolute dose with 3% in 3mm gamma

criteria, with comparisons between the phantom plan with and without the couch showing no improvement in

measured-to-calculated values (agreement range/average: 93.7-100/98.51% with couch, 97.2-100/99.1% no

couch). To further investigate the planar doses, calculated planar doses between the kevlar and carbon-fiber

couches were compared to each other; with differences only noticeable using a criteria of 1% in 1mm gamma

(agreement range/average: 92.1-100/97.1%).

Conclusions: Prostate patient treatment plans may benefit about

1% with inclusion of the treatment couch. It will be fine clinically for patients to be treated using the couch they

were not planned with for several fractions. These results may not be applicable for other disease-sites that have

Aurélien Vasseur

unread,

Apr 19, 2012, 3:50:03 PM4/19/12

to pinnacl...@googlegroups.com

Thank you very much for all your tips/advices.

-A.

Ileana

unread,

Jun 12, 2013, 10:41:05 AM6/12/13

to pinnacl...@googlegroups.com

I am going through the process of modelling the iBeam Evo carbon fiber couch in Pinnacle. In the very near future I won’t be able to get a CT scan study of the couch. I am asking to myself if it would make sense to ask for a “.roi” file for this type of couch that I could just import, being aware of the fact that densities should be measured or at least verify on site.

We are no treating patients, just going through the process of understanding Pinnacle modelling and the impact that the variation of different parameters have in clinical IMRT plans, by means of delivering the plans to a Phantom-2D Array system and performing Gamma Analysis against the RTDoses.

Any advice will be much appreciated

Ileana

Feygelman, Vladimir

unread,

Jun 12, 2013, 10:52:14 AM6/12/13

to pinnacl...@googlegroups.com

There are plenty of ways (and opinions) on how to best do this. In the absence of a CT scan, I am old enough to remember how to use solder wire and a digitizer, so that is how I contoured my first (Novalis) couch. Maybe someone in this group would be kind enough to share with you a CT scan of their couch in question. Both a single contour and a shell would do the trick for attenuation, however we found that the shell typically works better because you don’t need to drop the air density threshold too low to cause problems.

-VF

Vladimir Feygelman, PhD

Associate Member, Radiation Oncology

tel: (813) 745-2757 | fax: (813) 745-7231 | email: vladimir....@moffitt.org

From: pinnacl...@googlegroups.com [mailto:pinnacl...@googlegroups.com] On Behalf Of Ileana

Sent: Wednesday, June 12, 2013 10:41 AM
To: pinnacl...@googlegroups.com

--

--
You received this message because you are subscribed to the Google
Groups "pinnacle3-users" group.
To post to this group, send email to pinnacl...@googlegroups.com
To subscribe to this group, send email to
pinnacle3-us...@googlegroups.com
To unsubscribe from this group, send email to
pinnacle3-use...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/pinnacle3-users?hl=en

---

You received this message because you are subscribed to the Google Groups "pinnacle3-users" group.

To unsubscribe from this group and stop receiving emails from it, send an email to pinnacle3-use...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.

Please consider the environment before printing this email.

This transmission may be confidential or protected from disclosure and is only for review and use by the intended recipient. Access by anyone else is unauthorized. Any unauthorized reader is hereby notified that any review, use, dissemination, disclosure or copying of this information, or any act or omission taken in reliance on it, is prohibited and may be unlawful. If you received this transmission in error, please notify the sender immediately. Thank you.

Ileana

unread,

Jun 13, 2013, 5:16:39 AM6/13/13

to pinnacl...@googlegroups.com, vladimir....@moffitt.org

Thanks for your comment, Vladimir, I had tried already my best creating the couch as two ROIs of foam and carbon fiber and using the density override option, it served the purpose to compare plans delivered to an array in a phantom against the calculated ones with and without the couch, I just wanted to have as precise as possible shape of the couch.

Thanks for your time

Ileana

Aurélien Vasseur

unread,

Jun 18, 2013, 3:07:33 AM6/18/13

to pinnacl...@googlegroups.com

Dear Ileana,

Some replies from this thread were private but useful. I allow myself to give the names of some (very very) helpful and (very very) pleasant people you maybe could contact:
1) Single contour: Pierre-Alain Tercier @ Hôpital cantonal, Fribourg (Swiss)
2) Shell: Gilles Dy @ Centre d'Oncologie Saint Vincent, Saint Grégoire (France)
3) CT scan: Michael Weber @ Park Nicollet Methodist Hospital (Minnesota, US)

M. Weber gave me the whole CT scan of the iBeam Evo. The file exchange must obviously be done via FTP.
P.A. Tercier and G. Dy provided me working scripts (and installation instructions!).

As all this work is not mine, I'd rather not give you this files myself without permission...
Feel free to contact me if you need mail adresses.

-A.

Ileana

unread,

Jun 18, 2013, 10:42:50 AM6/18/13

to pinnacl...@googlegroups.com

Dear Aurélien

Thank you very much indeed for your your helpful message, I had contacted Pinnacle help desk about the CT Scan for the couch but they have not come back to me yet. Knowing that other commercial softwares like BrainLab offer a CT scan of some couches, I thought it would make sense if the provided one as well.

I will contact the physicist as per your advice but I would also like to have your e-mail address, it is may be the way I have the settings to visualize the group posts but I don't see it, could you please sent me an e-mail to: pata...@gmail.com? I will really appreciate it.

Thanks again for your time

Kind Regards

Ileana

Hobie Shackford

unread,

Jun 20, 2013, 10:46:34 PM6/20/13

to pinnacl...@googlegroups.com, Ileana

Ileana:

I am just getting through my emails after vacation.

If you have the model based segmentation module in your system I posted an couch "organ" model on MedPhys Files:

http://www.medphysfiles.com/index.php?name=Downloads&file=details&id=61

Hobie Shackford

Providence, RI

From: Ileana <pata...@gmail.com>
To: pinnacl...@googlegroups.com

Sent: Wednesday, June 12, 2013 10:41 AM

Subject: [p3rtp] Re: Modelling treatment couch (Elekta)

--

Ileana

unread,

Jun 24, 2013, 9:41:56 AM6/24/13

to pinnacl...@googlegroups.com, Ileana, Hobie Shackford

Hello Hobie

I just downloaded it.

Thanks a lot

Ileana

Reply all

Reply to author

Forward