Decent amount of information, decent amount of misinformation in this thread. fiji and medgator are most correct Having used both TBs and Ethos:
Truthfully, I don’t know much about it besides that it’s the new big thing. I know it can do planning and treatment at one go and ART but that’s it. I don’t actually know any other therapist that has used it.
Now that everyone’s getting rid of their Trilogy machines, most centers I’ve seen at least have opted to get another Varian Truebeam instead, from fancy proton centers to rural areas. They always state their reason for it is the amount of patients each can take and not the price difference.
What are your opinions on using it? Is it going to be one of those machines that only work for some patients like a cyberknife/gammaknife or can it be applied to all like our current Truebeams?
First off, Halcyon has been around for multiple years. Ethos is a Halcyon that has adaptive software loaded onto it. The hardware is otherwise the same, IIRC.
Trilogy is an old machine. If you are happy with Trilogy does, a TrueBeam is the upgrade that is in-line with what Halcyon does.
Halcyon/Ethos (H/E) is an excellent machine for doing most routine VMAT patients quicker in multiple ways than TB. H/E CBCT is faster than TB. Delivery is faster than TB due to 6MV-FFF beams.
The disadvantages of H/E (compared to TB) are in the following:
Most 3D treatments are worse b/c you are locked into 6MV-FFF beams.
No 6 DoF couch
Base CBCT isn't as good quality (maybe? depends on opinions) as TB, ESPECIALLY around gas - hypersight is reportedly supposed to correct this (I do not have access to it yet)
Can't do half beam blocks cleanly
No collimator rotation - just two rows of MLCs that 'act' like it
No couch kicks
Software 'requires' you do a CBCT prior to beam on every fraction, even if not reimbursable, thus can affect throughput
Max field size for a single iso about 14x14, but IMO plan quality degrades at higher ends. A longer field can be treated by doing a second iso-blended to the initial but are overall capable of giving much lower quality VMAT plans than doing a 20x20 field on a TB even with VMAT.
Forgive me if I’m wrong, but doesn’t using the 6FFF energy mean that it’s limited to patients with a thinner body habitus and SRS/SBRTs?
From what I recall from dosimetry many prostate patients end up being an 18MV due to their weight and the 6FFF is something really utilized for SRS/SBRTs and sometimes breast radiation.
Definitive prostate patients exclusively get IMRT. IMRT/VMAT with an 18MV beam I would consider borderline malpractice due to the neutron generation. Some consider IMRT/VMAT with a 10MV beam as acceptable, but many stick with 6MV (whether it is FFF or not).
6MV-FFF is primarily used for SRS/SBRT, but it can also be used with IMRT/VMAT without very significant differences in plan quality. 3D plans with 6MV-FFF look worse as the dMax is lower and thus penetrating deeper targets requires more complex beam arrangements or significantly more heterogeneity than a 10MV or 15-18MV beam.
This may be an issue indeed, if you have obese patients. We generally treat those with higher energies on C-arm linacs too.
In my experience, the Ethos in IGRT mode (which is basically a Halcyon) is excellent for pallative cases, mainly bone mets.
- The treatment couch can be lowered extensively, meaning patients with pain / mobility impairment can get on/off it very easily
- Positioning, image acquisition and treatment are very fast, meaning patients in pain only need to be on the treatment couch for a short period of time.
We use our Ethos extensively as a Halcyon exactly for these patients when we are not doing adaptive treatments.
A clinic with 3-4 linacs can easily fill up a Halcyon with palliative cases.
I am not sure if there would be a reimbursement problem in the US (since you have to treat with IMRT/VMAT on the Halcyon), for us it's not a problem.
This may be true in the non-US, but -
H/E is routinely horrible for palliative patients in the US due to frequent issues of getting IMRT/VMAT insurance approval and the fact that 6MV-FFF is trash for 3D plans for most things that require palliation, including all non-cervical spine, anything in the pelvis or abdomen. It's fine for like extremities and maybe standard whole brain.
If routinely doing IMRT for palliation, then yes, it is faster on CBCT and delivery than TB.
