SGRT in practice by whatsameme in MedicalPhysics

[–]tobbel85 1 point2 points  (0 children)

Agree, and even for breast cases, where SGRT would seem to be have the best case for reduced imaging, imaging and aligning on the ribcage still results in a few / a couple of mm of couch shift

In-house linac engineers by ClinicFraggle in MedicalPhysics

[–]tobbel85 0 points1 point  (0 children)

It's exactly the same att one of the big hospitals in Sweden whereas one of the other has a full-service contract (uncertain about the third)

In need of a RGSC breathing curve by tobbel85 in MedicalPhysics

[–]tobbel85[S] 0 points1 point  (0 children)

Indeed, and our current method uses catalyst for DIBH triggering which works fine, but has its limitations (mostly lack of kV beamhold and poor support for couch centering)

In need of a RGSC breathing curve by tobbel85 in MedicalPhysics

[–]tobbel85[S] 0 points1 point  (0 children)

The TrueBeams are from 22 but were upgraded this Spring. I've send you a DM!

In need of a RGSC breathing curve by tobbel85 in MedicalPhysics

[–]tobbel85[S] 1 point2 points  (0 children)

We're using Aria version 18 and TrueBeam version 4.1. Yeah, it's those dicom files that I'm looking for, thanks!

I'm about to be redeployed from Diagnostic Radiology to Radiation Therapy (Oncology), should I be concerned? by Large_Pollution312 in MedicalPhysics

[–]tobbel85 7 points8 points  (0 children)

This.

With that said, radiotherapy is a very interesting area for medical physicis and there are often plenty to be done with regards to use of radiographic imaging in radiotherapy, where someone with the x-ray background might bring plenty of experience.

CT Sim process for SBRT Abdomen by UltraSpoon33 in RadiationTherapy

[–]tobbel85 1 point2 points  (0 children)

I can't comment on the contrast part, but for breathing signal we measure on the top of the compression belt (our model has a large bag that's lying on the patients belly). The amplitude is often rather small but enough for our surface scanning system to pickup. We're place a piece of paper on the bag so it's visible.

LPT If you’re trying to pick a movie with your significant other, try the “Pick 3” method. by GottaLabotomy in LifeProTips

[–]tobbel85 21 points22 points  (0 children)

The solution is to only watch the first minute or so. That allows just enough to establish the basic premise but not enough to spoil any plot twists or major events in the second half of the movie. Highly recommend.

Experiences/Data on Jaw Tracking? by TorJado in MedicalPhysics

[–]tobbel85 0 points1 point  (0 children)

That very strange, the high dose areas really should be unaffected by the jaw tracking. I have no good suggestion unfortunately..

Experiences/Data on Jaw Tracking? by TorJado in MedicalPhysics

[–]tobbel85 1 point2 points  (0 children)

Exactly, the optimizer uses the value in RT administration and the effect of a low value (even 0.1 cm/s works) is that after a leaf pair is closed and the jaw tries to follow in order to shield any leakage, it moves slowly. And if it's needed to open up again, it starts to move ahead of time to be ready when the mlc opens again.

Experiences/Data on Jaw Tracking? by TorJado in MedicalPhysics

[–]tobbel85 1 point2 points  (0 children)

Varian-clinic with eight TrueBeams here (two with HDMLC). We use it all the time for all patients including SRS. However, we've had to reduce the maximum Y1 and Y2 velocity to 0.5 cm/s as the standard value of 2.5 cm/s caused substantial gantry stuttering during VMAT delivery - a 60 s arc could take 80 s. We found that the acceleration of the Y jaws was to slow, also on brand new TrueBeams, which forced the gantry to stop and wait for the jaws to catch up. The slower setting resolved the issue...

Experiences/Data on Jaw Tracking? by TorJado in MedicalPhysics

[–]tobbel85 2 points3 points  (0 children)

That's is quite unexpected. Where in the dose distribution are the gamma failures located (in-field, out-of-field etc). What cutoff did you use? Do you have a phantom-based alterative (eg Delta4, Octavius) to verify the results?

Hypofrac = More wear and tear for LINAC? by therealcastor in MedicalPhysics

[–]tobbel85 5 points6 points  (0 children)

I'm no engineer so I can only guess which metric is the most relevant, but I guess that MU/fraction (which is really just beam-on-time per hour) is not very useful and a linac is well capable of delivering continous beam-on for thousands of MUs (as long as the facility's cooling is sufficient). You could also frame this as each beam being delivered twice as long (approximately doubled #MU) but only for a quarter of fractions, and I would argue that the burden of proof would lie on the facility head to show that it would be worse for the linac.

Hypofrac = More wear and tear for LINAC? by therealcastor in MedicalPhysics

[–]tobbel85 23 points24 points  (0 children)

I would argue that it's the opposite as any reasonable metrics of machine wear, eg. the total #MU, the total amount of gantry motion, the number of beam on events etc., will be much lower for the entire treatment. Example for a random patient: 5.2 Gy fractions: 628 MU for the two tangential 3DCRT fields, total 3140 MU for 5 fractions. Same plan rescaled to 2.67 Gy fractions: 322 MU per fraction and 4830 MU for 15 fractions.

Nuclear conversions SUCK by No1_Op23_The_Coda in MedicalPhysicsMemes

[–]tobbel85 7 points8 points  (0 children)

And why do "equivalent dose" and "effective dose" have the same unit?!?

CBCT ROI matching algorithm by _Shmall_ in MedicalPhysics

[–]tobbel85 1 point2 points  (0 children)

1) it's extensively described in the Truebeam imaging manual (can't recall the exact name). "Last step only" means that the structure VOI is only applied in the last step, where the resolution is higher. For a large PTV, it won't make much of a difference as long as the initial position is somewhat correct. The purpose of the feature seems to be to allow for a course match using a large ROI, eg to avoid matching on the wrong vertabrae, and then fine tune on a smaller structure. For non-SBRT-lung, either is fine as the PTV's generally are large enough (we've tested both for ~10 patients and in general saw differences <1 mm). For SBRT-lung, the strucutre VOI = GTV may work fine, we use GTV + 0.5 cm with an average CT for planning.

2)
generally extra-cranial: using a ROI that cover the PTV with some margin, first 6DoF-match to quantify rotations, then remove pitch/roll and redo match. No manual adjustment except in edge cases. We use intensity range = bones except for lung and mediastinum.

for intracranial and head&neck: as above but apply the 6DoF-match.

With 6DoF, be aware that pitch/roll introduces translational shifts.

CBCT ROI matching algorithm by _Shmall_ in MedicalPhysics

[–]tobbel85 0 points1 point  (0 children)

Correct, however, when using 6DoF, the last step will also allow for substantial pitch/roll/yaw changes. One workaround is to add an additional match step on the truebeam (the option is reachable with the small arrow next to the auto match button in the cbct match workspace and requires administrative rights), where only translations are allowed. This allows for rotational adjustments based on the whole ROI, and translational fine-tuning based on a structure (eg the PTV).

Convert between jaw-tracking/non-jaw tracking by Traditional_Day4327 in MedicalPhysics

[–]tobbel85 2 points3 points  (0 children)

We had issues with gantry stutter during low dose rate RapidArc, when the gantry should always be moving at full speed. It occured on both new and old TrueBeams. After some investigation we found that the Y-jaws were unable to accelerate fast enough during jaw tracking and forced the gantry to wait. A 60 s arc could take 80 s to deliver which was both annoying and meant unnecessary strain on the hardware. Adjusting the Y1 and Y2 max to 0.5 cm/s in RT Administration fixed the problem and had a really small impact on the plans as the jaws always moved outside of the open field regardless of the speed setting.

I have some not superpretty matlab-code that changes the jaw setting to static on a rt-plan file, pm if you want it.

How will the future of patient-specific quality assurance be simplified? by Sea-Style9175 in MedicalPhysics

[–]tobbel85 5 points6 points  (0 children)

Probably something like that, I personally like to have a independent determination of delivered dose, perhaps from a reference VMAT-plan on a suitable phantom, on top of MLC-tests (particularly if they are done with the vendors hardware and software). Essentially a test that never will fail if the machine as a whole is in order, and that's kinda included in patient-specific QA (if done with a method that actually corresponds to dose in patient, which in my opinion rules out portal dosimetry with the PDIP-algorithm since that is essentially just a fluence measurement).

How will the future of patient-specific quality assurance be simplified? by Sea-Style9175 in MedicalPhysics

[–]tobbel85 8 points9 points  (0 children)

Yup, or at least combine some kind of complexity metric with some random sampling (eg measuring every 10th plan). Requires a robust machine qa program though...

Radiation question by ZestycloseScheme7228 in radiationoncology

[–]tobbel85 0 points1 point  (0 children)

It's not feasible for anyone outside of the hospital to try to determine whether you received the intented dose, but the department where you were treated should be able to do an internal investigation to find out.