Technology requirements for prostate SBRT

[radoncle]

Hi,

I was wondering what type of
equipment people feel comfortable with performing prostate SBRT (8 Gy x 5 for example) as definitive treatment for prostate ca.

For example, is CBCT on a standard linac adequate? What about truebeam vs elekta with clarity etc? There’s obviously a backstory here.. just wanted to a sense of people’s opinions. Thanks

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[elementaryschooleconomics]

I'm curious about your backstory with this question, haha.

Currently, for prostate SBRT, I prefer SpaceOAR VUE with either Calypso or gold fiducials, depending on body habitus. CBCT prior to every treatment using a TrueBeam.

I wouldn't feel comfortable not using a CBCT for any SBRT/SRS treatment. I can't comment on TrueBeam vs Elekta, but I use a TrueBeam for any SBRT/SRS I'm doing and love it.

*Edit: forgot to mention, I contour and plan in Eclipse, and would consider getting an MRI with rigid fusion to aid in target delineation (the MRI was a necessity in the pre-VUE days, but it can be annoying to coordinate, and I haven't decided if it's something I'm going to continue on with in the current VUE era - curious to hear from others!)

 

[radoncle]

I'm curious about your backstory with this question, haha.

Currently, for prostate SBRT, I prefer SpaceOAR VUE with either Calypso or gold fiducials, depending on body habitus. CBCT prior to every treatment using a TrueBeam.

I wouldn't feel comfortable not using a CBCT for any SBRT/SRS treatment. I can't comment on TrueBeam vs Elekta, but I use a TrueBeam for any SBRT/SRS I'm doing and love it.

*Edit: forgot to mention, I contour and plan in Eclipse, and would consider getting an MRI with rigid fusion to aid in target delineation (the MRI was a necessity in the pre-VUE days, but it can be annoying to coordinate, and I haven't decided if it's something I'm going to continue on with in the current VUE era - curious to hear from others!)

thanks for your response..
let’s just say some serious complications were developed at another center when prostate SBRT was done also using spaceoar and CBCT (no fiducial) with the 5 fraction regimen. Lifelong serious complications for the patient. It appears dosimetric constraints were met with a VMAT plan. Trying to figure out if this is a cautionary tale vs a case of bad luck vs some other preventable error etc. And also trying to learn any lessons about who should or shouldn’t be doing these procedures depending upon the technology available etc. Any feedback is appreciated.

 

[elementaryschooleconomics]

thanks for your response..
let’s just say some serious complications were developed at another center when prostate SBRT was done also using spaceoar and CBCT (no fiducial) with the 5 fraction regimen. Lifelong serious complications for the patient. It appears dosimetric constraints were met with a VMAT plan. Trying to figure out if this is a cautionary tale vs a case of bad luck vs some other preventable error etc. And also trying to learn any lessons about who should or shouldn’t be doing these procedures depending upon the technology available etc. Any feedback is appreciated.

Ah I'm sorry to hear that.

Honestly, if you went back and reviewed the plan and everything checked out, and there was nothing else weird about the case, my money would be on bad luck. It feels like every week either a patient or a colleague (or both) tells me they're having a "one in a million" complication or issue.

 

[seper]

To be conservative, drop the dose to 7.25 X 5. Use it only for low risk disease. With that, SBRT is mostly harmless

 

[Reaganite]

Ah I'm sorry to hear that.

Honestly, if you went back and reviewed the plan and everything checked out, and there was nothing else weird about the case, my money would be on bad luck. It feels like every week either a patient or a colleague (or both) tells me they're having a "one in a million" complication or issue.

Yup, exactly. Any Varian machine probably 21Ex and up (i.e. any machine from last 20 years) with CBCT, VMAT, and appropriate QA is capable of delivering safe SBRT. Sh** happens. Practice long enough, and you'll see it all. I had a patient develop a rectal fistula after 45 Gy whole pelvis. (Patient otherwise NED). You don't mention the toxicity, but there are reports of patients with SPACEOAR developing fistulae after XRT if the spacer infiltrated the rectal wall.

 

[cancer_doc]

If it passed dosimetric constraints, and this complication is rectal related or periprostatic fistula, then it's likely SpaceOAR-related toxicity or very bad luck. Of course, this is all assumption on my part since this complication is not disclosed.

For me, I also recommend SpaceOAR for all prostate SBRT and will be transitioning to an MR-linac platform to deliver it.

 

[radoncle]

If it passed dosimetric constraints, and this complication is rectal related or periprostatic fistula, then it's likely SpaceOAR-related toxicity or very bad luck. Of course, this is all assumption on my part since this complication is not disclosed.

For me, I also recommend SpaceOAR for all prostate SBRT and will be transitioning to an MR-linac platform to deliver it.

Patient developed a rectourethral fistula requiring permanent urostomy and colostomy. I received enough info to know that constraints were met, CBCT and spaceoar were used.
Sounded like bad luck but I don’t do prostate SBRT so I figured I’d ask those with more experience for feedback. Sounds like several people have had issues with SpaceOar even with standard fractionated RT. Not sure if that may have contributed here. Sad case.

 

[DoctwoB]

To be conservative, drop the dose to 7.25 X 5. Use it only for low risk disease. With that, SBRT is mostly harmless

For low risk disease, drop the dose to 0 x 5 and tell him he won’t die of prostate cancer. You’ll be right.

 

[JS1987]

TrueBeam, fiducials, CBCT. It’s all you need.

SpaceOAR if you feel you need it. Most don’t use it outside of the US.

 

[radoncle]

TrueBeam, fiducials, CBCT. It’s all you need.

SpaceOAR if you feel you need it. Most don’t use it outside of the US.

Are fiducials generally necessary?

 

[JS1987]

Are fiducials generally necessary?

Generally.

Matching to the prostate with CBCT can easily be done, but fiducials make the IGRT process much smoother and gives me more confidence with tight margins.

If treating the primary in low volume M1 and using 35/5 or 36/6, I may treat without fiducials. I don’t use fiducials for hypofrac or conventional at all. Practice varies on all of the above and depends on the machines you have available. On a TrueBeam the above is tolerated very well and patients do great.

 

[Palex80]

To be conservative, drop the dose to 7.25 X 5. Use it only for low risk disease. With that, SBRT is mostly harmless

You guys still treat low-risk disease?

 

[medgator]

You guys still treat low-risk disease?

Treating the physician

 

[elementaryschooleconomics]

Generally.

Matching to the prostate with CBCT can easily be done, but fiducials make the IGRT process much smoother and gives me more confidence with tight margins.

If treating the primary in low volume M1 and using 35/5 or 36/6, I may treat without fiducials. I don’t use fiducials for hypofrac or conventional at all. Practice varies on all of the above and depends on the machines you have available. On a TrueBeam the above is tolerated very well and patients do great.

I also prefer to use CBCT without fiducials for hypofrac or conventional.

However, I sometimes try to factor in the potential human error in planning, even if I perceive it to be sub-optimal from an efficiency standpoint. In this case, the therapists I usually work with are used to having fiducials in every prostate case, regardless of treatment scheme. So their workflow is to immediately look for fiducials when setting the patient up on the machine and adjusting from there. They are certainly capable of setting a prostate patient up with just CBCT, but I have noticed there's a higher likelihood I get called to the machine for shifts etc if it's CBCT alone. I think that anything which branches you off from the standard workflow is a branch where error can occur, which I'd prefer to minimize, if possible.

I'm probably overthinking it here, but I have observed a lot of people treating the plan they approve in Eclipse as absolute gospel instead of considering it a mathematical probability with any number of downstream events capable of causing problems.

 

[medgator]

I also prefer to use CBCT without fiducials for hypofrac or conventional.

However, I sometimes try to factor in the potential human error in planning, even if I perceive it to be sub-optimal from an efficiency standpoint. In this case, the therapists I usually work with are used to having fiducials in every prostate case, regardless of treatment scheme. So their workflow is to immediately look for fiducials when setting the patient up on the machine and adjusting from there. They are certainly capable of setting a prostate patient up with just CBCT, but I have noticed there's a higher likelihood I get called to the machine for shifts etc if it's CBCT alone. I think that anything which branches you off from the standard workflow is a branch where error can occur, which I'd prefer to minimize, if possible.

I'm probably overthinking it here, but I have observed a lot of people treating the plan they approve in Eclipse as absolute gospel instead of considering it a mathematical probability with any number of downstream events capable of causing problems.

Fiducials whenever possible. It optimizes workflow and improves throughout imo. Plus some therapists simply don't feel comfortable with CBCT and you invariably end up getting called to the machine for every fx

 

[BobbyHeenan]

I use fiducials on prostate SBRT and prefer them on spaceOAR (non Vue) patients.

I don't always get fiducials on my 60/20 or 70/28 cases (most don't). If they have spaceOAR placed I do like to have fiducials though, as prostate/rectum interface can be tricky to see I think.

For prostate SBRT I use a truebeam, fiducials, spaceOAR. I use the real time image guidance tracking the fiducials as well during the treatment and turn the beam off if they drift outside of fids + 2mm margin. With the FFF beam that pretty much never happens.

The complication mentioned above I would bet is from the spaceOAR and SBRT combo. I've been getting increasingly nervous about that happening. Was a recent case report regarding it.

 

[TheWallnerus]

thanks for your response..
let’s just say some serious complications were developed at another center when prostate SBRT was done also using spaceoar and CBCT (no fiducial) with the 5 fraction regimen. Lifelong serious complications for the patient. It appears dosimetric constraints were met with a VMAT plan. Trying to figure out if this is a cautionary tale vs a case of bad luck vs some other preventable error etc. And also trying to learn any lessons about who should or shouldn’t be doing these procedures depending upon the technology available etc. Any feedback is appreciated.

I have a data series treating ~1000 prostate patients of varying risk profiles to 81 Gy in 45 fx. 5y bDFS was 94% and the rate of grade zero rectal toxicity was 98%, 1% gr1, 1% gr2. Used fiducials, kV and CBCT hybrid, no SpaceOAR. Not a single "lifelong" serious complication.

I am so excited for the dawning of the Age of Prostate SABR. Yay.

"And also trying to learn any lessons about who should or shouldn’t be doing these procedures depending upon the technology available etc"

The most important technology in radiation oncology is a wetware 30Hz/10 exabyte/3 petaflop massively parallel processor we all carry between our ears. It is this technology which is far, far more responsible for bad outcomes in rad onc versus other simplistic technologies such as CBCT, SpaceOAR, etc.

 

[Mandelin Rain]

I use fiducials on prostate SBRT and prefer them on spaceOAR (non Vue) patients.

I don't always get fiducials on my 60/20 or 70/28 cases (most don't). If they have spaceOAR placed I do like to have fiducials though, as prostate/rectum interface can be tricky to see I think.

For prostate SBRT I use a truebeam, fiducials, spaceOAR. I use the real time image guidance tracking the fiducials as well during the treatment and turn the beam off if they drift outside of fids + 2mm margin. With the FFF beam that pretty much never happens.

The complication mentioned above I would bet is from the spaceOAR and SBRT combo. I've been getting increasingly nervous about that happening. Was a recent case report regarding it.

Agreed. Assuming a bit here, but it sounds like it happened fairly early too. Probably a SpaceOAR issue.

 

[OTN]

I never use the SpaceOAR and have not had any significant GI toxicity to speak of with prostate SBRT.

 

[communitydoc13]

I've been getting increasingly nervous about that happening. Was a recent case report regarding it.

I'll be damned if I can tell on planning MRI whether there is meaningful infiltration of Spaceoar into rectal wall. It's clearly there sometimes (uro places our spacers), and I have had rads call it on their MRI read. But, I have no idea when this will be clinically significant. In general not a big enthusiast.

As these "anecdotal" grade IV toxicities become more apparent the question will be: How many excess grade II toxicity do you accept to avoid a single grade IV.

I would prefer to never SBRT prostate but alas I'm now losing patients when I don't offer.

 

[BobbyHeenan]

I'll be damned if I can tell on planning MRI whether there is meaningful infiltration of Spaceoar into rectal wall. It's clearly there sometimes (uro places our spacers), and I have had rads call it on their MRI read. But, I have no idea when this will be clinically significant. In general not a big enthusiast.

As these "anecdotal" grade IV toxicities become more apparent the question will be: How many excess grade II toxicity do you accept to avoid a single grade IV.

I would prefer to never SBRT prostate but alas I'm now losing patients when I don't offer.

I have very similar thoughts and experiences in this regard.

I quit advocating as heavily for spaceOAR recently. Only in highly motivated patients.

With that said I have had a couple of proctitis cases last couple of years (non spaceOAR) that are bothersome . But NOTHING near fistula requiring ostomy.

 

[Mandelin Rain]

"Too make this treatment shorter and more convenient for you, we're going to add this invasive procedure where we stick a long needle through your perineum and shoot goo somewhere (hopefully) betwixt your prostate and rectum. Then, we're going to add an extra diagnostic scan where you spend 45 minutes in a coffin sized tube that sounds like someone is throwing wrenches at it. Convenience!"

 

[RickyScott]

"Too make this treatment shorter and more convenient for you, we're going to add this invasive procedure where we stick a long needle through your perineum and shoot goo somewhere (hopefully) betwixt your prostate and rectum. Then, we're going to add an extra diagnostic scan where you spend 45 minutes in a coffin sized tube that sounds like someone is throwing wrenches at it. Convenience!"

Better to put it this way: So that you can travel to manhattan, so that your insurance can pay 10 x cms prices, we are going to .....
(and as bonus we can virtue signal about hypofract, draw pts away from the community to further screw the job market, while we graduate 6 residents a year, 3 of which went on to fellowships in 2021..)

 

[Palex80]

Better to put it this way: So that you can travel to manhattan, so that your insurance can pay 10 x cms prices, we are going to .....

But parking is free!

 

[BobbyHeenan]

"Too make this treatment shorter and more convenient for you, we're going to add this invasive procedure where we stick a long needle through your perineum and shoot goo somewhere (hopefully) betwixt your prostate and rectum. Then, we're going to add an extra diagnostic scan where you spend 45 minutes in a coffin sized tube that sounds like someone is throwing wrenches at it. Convenience!"

This is not untrue.

But to their credit, they did run a randomized trial with spaceOAR....albeit standard fractionation...showing benefit.

HOWEVER, I think margins on that trial were bigger than I typically use. I *think* eventually PACE and NRG GU 005 will help clarify some of these questions.

Internal anecdotal experience with SBRT in training about a decade ago was that we were seeing slightly more proctitis/rectal bleeding than we were with standard or hypofrac. So I personally felt like spaceOAR may be the solution to help...

I'm still feeling out how our cancer center is going to be offering SBRT. We do it both on and off trial. My enthusiasm is good for it, but it's been tempered as these scary case reports come up. I still feel most comfortable at 70 in 28 or 60/20 without spaceOAR for the majority of my patients it seems.

 

[elementaryschooleconomics]

But parking is free!

I'm enjoying Palex's bomb throwing from across the ocean. Don't rub it in, we struggle enough as it is!!

 

[RickyScott]

But parking is free!

No it’s not. It’s 20-40$ a day right? (Do you really think mskcc would leave money on the table?) Also I have heard reports of space oar causing severe rectal spasms and pain for several days after placement.

 

[Mandelin Rain]

No it’s not. It’s 20-40$ a day right?

The parking may be free, but the EKG is going to cost you....

 

[RickyScott]

The parking may be free, but the EKG is going to cost you....

If they finally post prices, would love to see how much they charge for those ekgs.

 

[evilbooyaa]

Fiducials whenever possible. It optimizes workflow and improves throughout imo. Plus some therapists simply don't feel comfortable with CBCT and you invariably end up getting called to the machine for every fx

Get better therapists or train them to be better.

We also do spaceOAR and fiducials for every SBRT patient, but if we did that for EVERY prostate patient (including those receiving mod hypofx) we'd need another 1-2 rad oncs probably...
Just unnecessary in the era of CBCT, IMO. CBCT is better than kV/kV to fiducials.
I'd be interested in a head to head comparison of SBRT with spaceOAR vs SBRT without spaceOAR. Some of the dose constraints just seem unachievable without spaceOAR (like rectum V38 < 2cc if doing 40Gy in 5 fractions).

To OP - A modern linac (TrueBeam or equivalent) with CBCT, VMAT is sufficient. Most probably do SpaceOAR (either OG or VUE), likely with a MRI (mandatory if not VUE), + fiducials with every fraction CBCT. 8Gy x 5 or 7.25Gy x 5 are both reasonable.

Rectourethral fistula suggests either the urethra was not contoured as an OAR (which the trials don't but I think most would when doing SBRT dosing) and/or there was an unrecognized error/complication at time of SpaceOAR placement (which has been documented in the literature as well as discussed here and on twitter).

 

[MegaVoltagePhoton]

For those doing cbct alignment only aren’t you concerned about motion during the cbct acquisition and review time? Are you paged when they begin the cbct and get there in minutes?

I saw a webinar with Amar Kishan where he said his workflow was to repeat Fiducial alignment by Kv kv after the cbct was approved for that reason. However I think the therapists there have to get attending sign off on cbct.

 

[Gfunk6]

As posted in other threads, I use SpaceOAR VUE, fiducials, and CyberKnife. Deliver very heterogeneous dosing prescribed to 50-65% of maximum dose. I don't think this is required, but it certainly gives me great confidence in treatment. Also fuse high-resolution MRI mainly to delineate urethra.

I've never had a grade 3+ complication. Of note, I also re-treat previously irradiated prostates.

 

[TheWallnerus]

I saw a webinar with Amar Kishan where he said his workflow was to repeat Fiducial alignment by Kv kv after the cbct

This is actually helpful, at least mathematically, when fraction times (ie fraction doses) get bigger-than-standard-fractionation. I'm a proponent. And have been for ~15 years

 

[thecarbonionangle]

After the UTSW disaster, i would keep dose 36.25/5 to 40/5. My preference is for lower dose with SIB to dominant nodule. SpaceOAR is generally safe. I would use fiducials with a bowel prep before each tx. A good plan does not prevent toxicity, a good set up does folks!

 

[medgator]

Get better therapists or train them to be better.

We also do spaceOAR and fiducials for every SBRT patient, but if we did that for EVERY prostate patient (including those receiving mod hypofx) we'd need another 1-2 rad oncs probably...
Just unnecessary in the era of CBCT, IMO. CBCT is better than kV/kV to fiducials.

Not for efficiency imo. It's so much easier for them to match CBCT when fiducials are in place in my experience. If you're treating 15-20 pts per day on a machine, sure, CBCT all day till the cows come home treating 2-3 pts an hour

 

[TheWallnerus]

After the UTSW disaster

Can you update on that so I don't have to do deep page googling

 

[medgator]

Can you update on that so I don't have to do deep page googling

Hydrogel Spacer Rectal Wall Infiltration Associated With Severe Rectal Injury and Related Complications After Dose Intensified Prostate Cancer Stereotactic Ablative Radiation Therapy

Radiation therapy (RT) for prostate cancer remains associated with a dose-dependent and dose-limiting risk of rectal toxicity.1 Contemporary dose-escalated RT regimens,2-5 have improved biochemical control at the cost of higher rectal toxicity. Temporary hydrogel spacer placement between the...

www.advancesradonc.org

Was all over the airwaves when the publication was released i think

 

[thecarbonionangle]

Can you update on that so I don't have to do deep page googling

DEFINE_ME

They met all constraints too. I commend them for publishing it. I know of places who bury things like this

 

[elementaryschooleconomics]

DEFINE_ME

They met all constraints too. I commend them for publishing it. I know of places who bury things like this

Strongly agree. I really appreciate/respect that crew for doing that.

 

[BobbyHeenan]

As posted in other threads, I use SpaceOAR VUE, fiducials, and CyberKnife. Deliver very heterogeneous dosing prescribed to 50-65% of maximum dose. I don't think this is required, but it certainly gives me great confidence in treatment. Also fuse high-resolution MRI mainly to delineate urethra.

I've never had a grade 3+ complication. Of note, I also re-treat previously irradiated prostates.

I was told by one of the uro groups that the spaceOAR vue in office doesn't reimburse above cost (?or maybe "not enough") so they only use it for patients that can't have an MRI.

Do you have experience with this?

 

[RickyScott]

DEFINE_ME

They met all constraints too. I commend them for publishing it. I know of places who bury things like this

You would need to do like 10,000 space oar placements for the purported benefit to offset the harm of one of these events.

 

[communitydoc13]

DEFINE_ME

They met all constraints too. I commend them for publishing it. I know of places who bury things like this

I recommend everyone look at these MRI images. There is no "oh there's the problem" when you review them and you will see similar MRI features when you review enough pts with SPACEOAR.

 

[tomhobbes]

Before 2020 our group had been doing prostate SBRT with fiducials on Cyberknife. No SpaceOAR. Doses 36.25-40Gy in 5fx. This was done for about 8 years with a few hundred men treated. Outcomes were good. Long term proctitis was rare but did occur in several patients.

Since 2020 we’ve been doing SBRT 40/5 with fiducials and SpaceOAR VUE on Truebeam, daily CBCT. Fiducials with spacer, CT sim, and MRI prostate with T2, high B DWI and ADC sequences, all performed in the same visit. Registration of CT and MRI is straightforward as they are lying in the vaclock both times with the same bladder and rectal anatomy. Makes contouring urethra and any gross intraprostatic disease for treatment planning reliable. As far as treatment times, these plans typically comprise two VMAT arcs of 6 MV FFF and take about 2.5-3 minutes per fraction. We used to do intra-arc kv imaging to verify set up, then reduced frequency to interarc CBCT, and subsequently after finding that these pauses for imaging never resulted in meaningful shifts being applied, now simply CBCT once at the beginning of each fraction.

Like Gfunk, also re-irradiate with this same SBRT set up but to a lower dose of 36.25/5.

Our 60/20 prostates are +/- SpaceOAR. Have not strongly recommended SpaceOAR unless plan for SIB DIL boost and SpaceOAR helps achieve constraints in the context of boost. If we do SpaceOAR we’ll also place fiducials since we’re already there. Otherwise rely exclusively on CBCT for daily set up.

 

[BobbyHeenan]

I recommend everyone look at these MRI images. There is no "oh there's the problem" when you review them and you will see similar MRI features when you review enough pts with SPACEOAR.

I agree with this, It's very subtle. Seen with a retrospectoscope microscope I'm sure after this challenging case.

 

[Gfunk6]

Less net reimbursement for SpaceOAR VUE relative to SpaceOAR, but still marginally profitable. Boston Scientific will stop manufacturing regular SoaceOAR next year as I understand.

Also huge proposed CMS cuts for SpaceOAR placement in 2022 - final decision pending.

I was told by one of the uro groups that the spaceOAR vue in office doesn't reimburse above cost (?or maybe "not enough") so they only use it for patients that can't have an MRI.

Do you have experience with this?

 

[Gfunk6]

Since 2020 we’ve been doing SBRT 40/5 with fiducials and SpaceOAR VUE on Truebeam, daily CBCT. Fiducials with spacer, CT sim, and MRI prostate with T2, high B DWI and ADC sequences, all performed in the same visit. Registration of CT and MRI is straightforward as they are lying in the vaclock both times with the same bladder and rectal anatomy. Makes contouring urethra and any gross intraprostatic disease for treatment planning reliable. As far as treatment times, these plans typically comprise two VMAT arcs of 6 MV FFF and take about 2.5-3 minutes per fraction. We used to do intra-arc kv imaging to verify set up, then reduced frequency to interarc CBCT, and subsequently after finding that these pauses for imaging never resulted in meaningful shifts being applied, now simply CBCT once at the beginning of each fraction.

This sounds like an extremely well-designed, efficient system - kudos.

 

[elementaryschooleconomics]

Less net reimbursement for SpaceOAR VUE relative to SpaceOAR, but still marginally profitable. Boston Scientific will stop manufacturing regular SoaceOAR next year as I understand.

Also huge proposed CMS cuts for SpaceOAR placement in 2022 - final decision pending.

Could you link the proposed cuts? Or is that something you were told verbally?

 

[evilbooyaa]

DEFINE_ME

They met all constraints too. I commend them for publishing it. I know of places who bury things like this

"Meeting" Timmerman constraints (all made up, no prospective validation) is silly given how incredibly lax they are. I'm not saying that the spaceOAR infiltration didn't affect it, but accepting point doses to rectum of > 40Gy is unnecessary, especially in the setting of SpaceOAR. That being said, they contoured the infiltrated rectal wall as spaceOAR so I'm sure it received more (as they mention themselves).

We all love dose escalation but those who fly too close to the sun in terms of aggressiveness of dose escalation are going to get burned sometimes. Rx dose of 40/5 may have avoided this catastrophe. But it's the same story as the OP

 

[Gfunk6]

Could you link the proposed cuts? Or is that something you were told verbally?

Link to Proposed Rate Reductions: CMS-1751-P | CMS

o PFS in-office payment rates for radioprotective spacers will be reduced by 21%.

o The proposed reduced PFS payment rates may have a negative impact on Medicare beneficiaries if rate reductions discourage physicians from implementing a radioprotective spacer, which leaves patients at higher risk of radiation toxicity. Medicare clinicians should be allowed to utilize spacers based on their clinical decision and at their discretion to mitigate risks of reduced quality of life and outcomes when effective prevention of the higher toxicity is available. Radioprotective spacers are fully supported and referenced in the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines 2021)