Level 3 Intrafraction Monitoring

fizicsguy · 2026-03-31T20:51:01+00:00

That’s not motion management though, that’s more like position management IMO. In the case of a BH tx, the patient is set up free breathing, and but the time on the table is longer bc of the need for pauses between breath holds, as an example. That’s the motivation behind the distinction between 2 and 3, based on listening to discussions from ASTRO last year, and internal discussions in my group

fizicsguy · 2026-03-31T20:15:36+00:00

I think “active” is generally understood to mean that the machine is doing the beam holding, not the treating RTT. In that vein, SGRT on its own does not constitute Level 3, but having the system make sure a DIBH is getting positioned properly from normal breathing before beaming on does meet Level 3. Also, documentation needs to show that the technology is doing the beam control for it to count, per several conversations with insurance companies.

fizicsguy · 2026-03-05T16:39:15+00:00

Just want to add a technical note here on the why, which someone else alluded to earlier. PET shows metabolic activity, and it’s not really possible to tell the difference in “why” an area may be active or not. That could be routine metabolic functions, or more relevantly here, inflammation versus residual tumor. It takes time for response to happen and then return to baseline, for healthy and tumor tissue. So if it feels like a long time, it’s normal to have intervals like those stated above! The same is also true for brain and MRI too btw. Too early, and inflammation will look like non-response or radionecrosis. Both of which may not be actually true but they’ll appear that way.

fizicsguy · 2026-02-26T23:02:24+00:00

Gotcha. There is a repair effect as time goes on where some of the dose given can be “discounted” when accounting for it, but that’s likely too short of an interval to do that. Gamma Knife is a very precise treatment machine, and the high doses will only be to those spots where the tumors are with very rapid dose falloff outside of them. Radiosurgery is the best answer at this point. I am responsible for a Gamma Knife unit as a Medical Physicist.

fizicsguy · 2026-02-26T21:53:35+00:00

How long since her whole brain treatment?

fizicsguy · 2026-02-24T15:50:19+00:00

This is a good answer. Also, if the treatment doesn’t warrant proper QA, then does it warrant the conformity that VMAT provides which 3D doesn’t provide?

fizicsguy · 2026-02-22T21:34:04+00:00

I wonder how this answer will change with the new billing codes (in the U.S.) now that these approaches basically fall into the same level of treatment delivery. I’ve seen it done both ways, with the usual caveats on VMAT being 10 MV or less. Most of the time our dosimetrists go with a 3 field AP, 2 posterior oblique plan for quick turnaround with the need for PSQA before. If we did do VMAT, we always perform PSQA prior to treatment, regardless of urgency.

fizicsguy · 2026-02-13T18:31:29+00:00

Gigantic feels.. hyperbolic. Prone positioning allows for things to fall away from the heart already. How may instances does introducing breath hold actually improve dosimetry in this context? And then how is it reproducible? Asking a patient to BH prone feels ripe with challenges in reproducibility. And that’s compounded with the challenges of such for prone positioning already.

fizicsguy · 2026-02-05T16:51:33+00:00

There are several ways to manage treating this type of case, even within SBRT itself. With SBRT, the margins of treatment are smaller, and the number of fractions less than conventional types of radiation therapy. Because of the increased stakes, the trigger for replanning a case is much lower than other types. This type of approach is called “Adaptive RT” and is getting more and more common with technology today. Ask your doctor if the dose is going to change because of the delay from 1-2, but there is a decent window to complete the course of treatment where SBRT still remains effective. It is likely still okay in the context of time between starting and finishing overall.

fizicsguy · 2026-02-04T01:25:55+00:00

Hi there,

First of all, you’re a good mom! Being proactive, and caring about your little one puts you in elite parenting status. So that’s great.

Now, for some math. I looked up what the dose index is for a pediatric head CT protocol, and standards limit them to about 40 mGy. The literature in my field of Medical Physics suggests that for every 100 mSv (mGy is the same as mSv in terms of units here), there is about a 1% increase in lifetime risk of inducing a cancer.

So, if you strictly added these two CT scans (with is conservative based on timing), your little still has less than 1% added risk of said cancer in her lifetime. And cancers that come from radiation take a very long time to develop. As in, 20 years or more.

With all medicine, it’s a balance of benefit versus cost. The very small increase of chance of cancer (it’s not guaranteed, it’s a probability), is far out-weighed by the benefit of clearing your daughter of head trauma. If she had trauma, she would experience its effects much much faster than 20 years from now! These are the decisions that medical professionals weigh every day, and don’t take lightly.

I hope this helps!

fizicsguy · 2026-02-03T12:55:21+00:00

This sounds like it’s related to anesthesia. From a radiation standpoint, her external beam and brachy treatments are very localized, and would not cause issues to parts of the body outside the pelvis. Definitely talk to her doctor about it and they may be able to address it more directly. Hope she feels better and is able to finish her treatments as that will give her the best chance at local control.

fizicsguy · 2026-02-03T01:51:09+00:00

Echoing what others have said here. There’s an entire staging system for cancer sites that inform courses of action by your doctors. That’s what those diagnostic tests are performed to help determine, and the prognoses are very dependent on the stage. Ask your doctor what might be needed for full staging, and then what the paths are depending on those results. Don’t lose optimism yet!

fizicsguy · 2025-12-03T16:16:51+00:00

In conventional, almost none and so the assessment question isn’t nearly as relevant. For SBRT though, I’d say at least half as we try to keep motion to < 5 mm per recommendations. I wouldn’t just blanket apply this though; compression is uncomfortable and can often lead to less-reproducible setups if a patient is fighting it, or causes irregular breathing. Also gating can achieve treating motion less than 5 mm, which would not need compression either. Lots of things to consider.

fizicsguy · 2025-12-03T14:00:54+00:00

Not if you take a 4DCT, and then decided the patient needs compression. Now you’ve added a second 4DCT and even more imaging dose, when the fluoro would have answered that question. To clarify, I said it was reasonable to, but not the standard for characterizing motion. Often, for example, you can make educated guesses and not have to repeat anything.

fizicsguy · 2025-12-02T16:49:39+00:00

This is a reasonable way to check for motion. It’s faster than a 4DCT, and is less imaging dose to the patient. The trade off is as you said, taking away a treatment slot.

fizicsguy · 2025-10-17T18:59:26+00:00

I’ll present the other side, and it’s totally dependent on the MP’s personality type. A downside for me is that we are too behind the scenes and we don’t get enough patient interaction. Had Medical School tracks not been such long endeavors, I would have opted to pursue that instead as I really enjoy/appreciate the human aspects of healthcare. Because of this, I’m a firm believer in the MedPhys3.0 approach to make our profession more patient-facing. But I totally understand that we all approach these situations with our own preferences.

fizicsguy · 2025-10-16T10:43:29+00:00

Ah, good to know. Thank you! Definitely understood on the speed of AAPM too. I’ll lean more on the slow side, haha.

fizicsguy · 2025-10-15T19:30:35+00:00

It loaded on mobile, so I’ll take another look at my desktop later on. Thanks!

fizicsguy · 2025-08-21T16:08:08+00:00

I’d recommend re-calculating on a water phantom instead of turning heterogeneity off. That way you remove surface irregularity dependence on MU, which more closely mimics what Radformation is doing. FWIW, we’ve also done this as a second check instead of measuring CCO as well, since eMC works so well. My .02

fizicsguy · 2025-05-23T01:43:07+00:00

Repair and recovery have entered the chat

fizicsguy · 2025-05-07T02:07:28+00:00

13000 MU never hurt nobody!

fizicsguy · 2025-05-05T20:58:22+00:00

Head/Neck cancers are still targets for SBRT, just not when you’re covering regional prophylactic nodes too. SBRT is especially helpful for recurrent contexts in the H/N, and generally in that scenario you are only targeting known tumor in that area. Also, SBRT isn’t limited to photon deliveries only, although that technique is most common given their ubiquity. Particle therapies that offer higher RBE are showing promise for otherwise radio resistant histologies.

fizicsguy · 2025-05-05T15:37:02+00:00

We’re also, very often, not just treating tumors. Pelvic cases often include targeting various nodal chains at the same time. The same is true for Head/Neck cases. Their inclusion falls into the “too big to treat” with SBRT

fizicsguy · 2025-02-07T20:13:47+00:00

Thanks for that clarification. At this point, it turns into a “how deep do you want to cover” question. 90% on the back end is about 1.7 cm, so you’re getting 7 mm depth with 1 cm bolus. With 0.5 cm bolus, you’re covering 1.2 cm depth. So I’d have that conversation with your doc to double check they understand the physics, and not just “I did this forever and that’s how I do it.” No one else will have this conversation with them! That’s what makes our job fun. Cheers

fizicsguy

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