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When I was offered my very first Ga68 PET/CT at a 6 monthly surveillance meeting in May 2018, I was both excited and apprehensive. Let me explain below why I had a mix of emotions. You can read about my Ga68 PET experience here.
I was diagnosed in 2010 with metastatic NETs clearly showing on CT scan, the staging was confirmed via an Octreotide Scan which in addition pointed out two further deposits above the diaphragm (one of which has since been dealt with). In addition to routine surveillance via CT scan, I had two further Octreotide Scans in 2011 and 2013 following 3 surgeries, these confirmed the surveillance CT findings of the remnant disease. The third scan in 2013 highlighted an additional lesion in my thyroid (still under a watch and wait regime, biopsy inconclusive but read on….).
In 2018, my 6 monthly CT scans seem to have been adequate surveillance cover and all my tumour and hormone markers remain normal. I was reasonably fit and well for a (then) 62-year-old.
Then I ventured into the unknown
I wrote a comprehensive post about the Ga68 PET entitled “…. Into the unknown” – so named because that is how I felt at the time. It’s well-known that the Ga68 is a far superior nuclear scan to the elderly Octreotide type, showing much greater detail with the advantage of providing better predictions of PRRT success if required downstream. It has been a game-changer for many and if you look below and inside my article, you will see statistics indicating just how it can ‘change the game’ in somatostatin receptor-positive Neuroendocrine Cancer diagnostics and treatment.
The excitement of the Ga68 PET
I was going to get the latest ‘tech’ and thought it could be useful confirmation of what I already knew. I also felt lucky to get one, they are limited in UK and there has to be a clinical need to get access. I was excited because it might just rubber-stamp the stability I’ve enjoyed for the 5 or so years since my last surgery in 2012.
The apprehension of the Ga68 PET
I also felt apprehensive because of the ‘unknown’ factor with cancer, i.e. what is there lurking in my body that no one knows about, and which might never harm me, but this scan will light it up demanding attention. I was also apprehensive in case this more detailed scan found something potentially dangerous. As we know, NETs are mostly slow-growing but always sneaky. Of course, any new tumours found may not actually be new, they were just not seen until the Ga68 PET was able to uncover them. How annoying!
Is the Ga68 PET Scan a game-changer?
To confirm the advantages of SSTR PET over Octreotide scans, a study comprising 1,561 patients reported a change in tumour management occurred in over a third of patients after SSTR PET/CT even when performed after an Octreotide scan.
- Overall, change in management occurred in 44% (range, 16%-71%) of NET patients after SSTR PET/CT.
- In 4 of 14 studies, SSTR PET/CT was performed after an 111In-Octreotide scan. In this subgroup, additional information by SSTR PET/CT led to a change in management in 39% (range, 16%-71%) of patients.
- Seven of 14 studies differentiated between inter and intramodality changes, with most changes being intermodality (77%); intramodality, (23%). (note: intermodality means changes within the same treatment, intramodality means a change to another treatment).
In an older study, this slide from a NET Research Foundation conference shows some more interesting statistics:
Was Ga68 PET a game changer for me?
Not sure. I’m now in the ‘bone met club’ and although that single metastasis has probably been there for some time, it’s not a ‘label‘ I was keen to add to my portfolio. The scan has brought more light to my thyroid issue. In fact, it indicates even more potential issues above the diaphragm including what looks like a new sighting around my left pectoral lymph nodes. The scan also lights up a known and potential issue in the left clavicle lymph nodes first pointed out via Octreotide scan in 2010 and biopsy negative. Two subsequent CT scans since this Ga68 PET would indicate the lymph node uptakes of the supraclavicular and sub-pectoral nodes are not reflected in a pathologically enlarged problem, indicating these are physiological or ‘reactive’ in nature.
In addition to a nuclear scan update (routine surveillance), it also formed part of an investigation into the progression of my retroperitoneal fibrosis (initially diagnosed 2010 but potential growth spotted on recent surveillance CT). The Ga68 PET doesn’t make fibrosis light up (it’s not cancerous) but there are some hotspots in the area of the aorta close to the fibrosis, a potential source of the cause. Surgery is on hold for now as my kidney function is fine following a renal MAG3 scan which reported no blockages.
The 2018 Ga68 PET Scan confirmed:
Bone Metastases. The report indicates “intense focal uptake” on my 11th right rib. It always amazes me that people can be thankful for having an extra tumour. I’m thankful I only have a single bone metastasis. I had read so many stories of those who got their first Ga68 PET and came back with multiple bone metastases. I’ll accept one and add to my NET CV. I have no symptoms of this bone metastasis and it will now be monitored going forward. I’m annoyed that I don’t know how long it’s been there though!
Confirmation and a better understanding of the following:
- Thyroid lesion There is some uptake showing. A 2014 Biopsy of this lesion was inconclusive and the actual 2018 Ga68 PET report infers physiological uptake. I’m already diagnosed hypothyroidism, possibly connected. (Edit – on ultrasound in Jan 2019, looks slightly smaller than the previous check), most recent CT describes it as an adenoma (benign tumour).
- Left Supraclavicular Fossa (SCF) Nodes lighting up “intense uptake“. I’ve had an exploratory biopsy of the SCF nodes, 5 nodes removed all tested negative. Nothing is ‘pathologically enlarged’ in this area. Monitored every 6 months on CT, annually on ultrasound. I had 9 nodes removed from the left axillary in 2012, 5 tested positive for NETs and this area did not light up. This whole area on the left above the diaphragm continues to be controversial. My surgeon once said I had an unusual disposition of tumours. (Edit: Nothing sinister or worryingly enlarged showing on Jan 2019 ultrasound – measuring 6mm). The latest CT describes them as not pathologically enlarged.
- The report also highlights left subpectoral lymph nodes which is new. The subpectoral area is very interesting as from my quick research, they are closer to the left axillary (armpit) nodes than they are to the SCF nodes. I’m hoping to get an ultrasound of these in January at my annual thyroid clinic (Edit: nothing sinister showing on ultrasound in Jan 2019), nothing sinister showing on the latest CT scan Nov 2019 or Nov 2020 or Jun 2022).
- My known liver metastases lit up (remnant from liver surgery 2011) – not marked as intense though. The figure of 3 seems to figure highly throughout my surveillance scans although the PET report said “multiple” and predominately right-sided which fits.
- Retroperitoneal area. This has been a problem area for me since diagnosis and some lymph nodes are identified (the ‘intense’ word not used). This area has been highlighted on my 3 octreotide scans to date and was first highlighted in my diagnosis trigger scan due to fibrosis (desmoplasia) which was surrounding the aorta and inferior venous cava, some pretty important blood vessels. I wrote an article on the issue very recently – you can read it by clicking here. So, this scan confirms there are potentially active lymph nodes in this area (see 2021 update below), perhaps contributing to further growth of the fibrosis threatening important vessels – read below.
The 2021 Ga68 PET Scan confirmed:
That the above findings are pretty much the same and everything looks stable. I appear to have a dominant retrocaval node which is unchanged in size since 2018 and the SUV is less than it was in 2018 (22). It’s now coming out as 19.5. I realise SUVs are not an exact science. This is a strange area for lymph node spread in a NET and when I search, it’s all related to genito-urinary cancers such as ovarian and testicular.
Note: The radiologist noted I had some right-side axillary node reaction (armpit) which will have been due to a recent COVID vaccination. I had my 2nd vaccine at the end of March and on the right arm. Read about this phenomena by clicking here.
As this partly triggered the Ga68 PET, I’ve learned so much about desmoplasia since this issue arose and I now fully understand why I had to have radical surgery back in 2010 to try to remove as much of the fibrosis as possible from the aortic area. You can read more about this in my article. Desmoplasia via fibrosis is still very much of an unknown and mystery condition in NETs. I now know that my fibrosis is classed as clinically significant and according to the Uppsala study of over 800 patients inside my article, I’m in 5% of those affected in this way (2% if you calculate it using just the retroperitoneal area).
It appears this problem may have come back with new fibrosis or growth of existing fibrosis threatening to impinge on blood vessels related to the kidneys and also my ureters (kidney to bladder urine flow). The Ga68 PET doesn’t make fibrosis light up but there are some hotspots in the area of the aorta close to the fibrosis. This is being closely monitored.
I didn’t expect this particular problem to return – it was a bit of a shock. My hormone markers have been normal since 2011 and this just emphasises the importance of scans in surveillance.
Conventional Imaging is still important though
There’s still quite a lot of hype surrounding the Ga68 PET scan and I get this. However, it does not replace conventional imaging (CI) such as CT and MRI scans which still have their place in routine surveillance and also in diagnostics where they are normally at least the trigger for ‘something is wrong’. For the vast majority, a CT/MRI scan will find tumours and be able to measure reductions and progress in regular surveillance regimes. In fact, the retroperitoneal fibrosis has appeared on every CT scan since diagnosis, but the changes were highlighted on my most recent standalone CT and it triggered the Ga68 PET (although my new Oncologist did say I was due a revised nuclear scan). It’s not a ‘functional’ issue (although it is caused by functional tumours). In fact, the fibrosis is not mentioned on the Ga68 PET because it is not lighting up – but the lymph nodes surrounding it are mentioned and they are under suspicion of being active.
Appropriate Use Criteria for Somatostatin Receptor PET Imaging in Neuroendocrine Tumors
There are actually recommended usages for the Ga68 PET scan and other SSTR PETs here. For example, it is not recommended for routine surveillance in place of CI. I see people who are getting 3 or 6 monthly Ga68 PETs which seems odd and not as per the aforementioned recommendations.
Scans – ‘horses for courses’
Read a summary of all conventional scans and nuclear scans by clicking here. In my own experience it can be a case of now you see them, now you don’t, and radiologists and specialists experienced in how best to use and interpret every type of scan to get the best views of NETs is a really important factor. And I cannot emphasise enough that interpreting scans for NETs is a bit of a dark art.
My game has changed a bit. However, at least my medical team and I now know what WE are dealing with, and the risks vs benefits of intervention are under review. I’m heavily involved in that.
Understanding your Somatostatin Receptor (SSTR) PET scan reports
None of us are radiologists (unless you are a radiology professional reading this of course!). But I hope this overview may help you understand some of the written report from SSTR PETs.
The “Copper” PET
All of the above most likely applies to any other variant of somatostatin receptor (SSTR) PETs being deployed. The other approved radioligand used in SSTR PET for Neuroendocrine Cancer is the 64Cu DOTATATE which is said to pick more lesions (perhaps including some that were always there but not visible on Ga68). Read about the “copper scan” here.
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