What can get rid of these Radiesse nodules in my neck? (photos)

Three articles in the literature would form a starting point for discussion of this problem:
The one in the link below is entitled: Foreign Body Granulomas after the Use of Dermal Fillers: Pathophysiology, Clinical Appearance, Histologic Features, and Treatment
Jeong Min Lee and Yu Jin Kim. The point is made that Radiesse (calcium hyddroxyapatite) is highly biocompatible and does not form foreign body granulomas. Lumps are usually nodules from aggregation or too superficial injection (e.g. into the dermis). However, since in this case hyper-diluted Radiesse was used, unless it was infiltrated into the dermis, it should not form nodules. You did not state how long after the second session you developed nodules. If it was shortly after, a month, for example, if this were a hyaluronic acid filler it would be likely to be a delayed hypersensitivity reaction.
Without a history of redness, itching or swelling in this time frame, and because the filler was Radiesse, it seem unlikely in this case to be delayed hypersensitivity.
If these nodules are not due to delayed hypersensitivity or too superficial injection, then there is a possibility that they are foreign body granulomas. Foreign body granulomas due to hyaluronic acid and other fillers have a treatment algorithm that can include three weeks of minocycline (or doxycycline) empirically shown to help, and on the basis that there is some infectious component. Also for foreign body granulomas, fine needle injection with concentrated triamcinolone (kenalog) into the lesions and possibly oral steroids, have been recommended. This would not be appropriate for calcium hydroxyapatite nodules, unless you had one of these nodules biopsied and the histopathology reported that it was a foreign body, giant cell granuloma. Injection of steroid into the thin neck skin would cause atrophy if the injection went outside of the lesion, and it would be difficult to prevent this from occurring.
The second article: Plast Reconstr Surg Glob Open. 2019 Mar 14;7(3):e2160. doi:10.1097/GOX.0000000000002160. eCollection 2019 Mar.
"Consensus Recommendations for the Use of Hyper-diluted Calcium Hydroxyapatite (Radiesse) as a Face and Body Biostimulatory Agent", multiple authors, does not mention the complication you are experiencing. It is a contemporary guide to use of Radiesse in different parts of the body, including neck.
With regard to your question about STS, sodium thiosulfate, it was initially thought to have some clinical benefit, but this study shows that STS has no effect on calcium hydroxyapatite microspheres, and that the clinical benefit is only slightly better than dispersal with saline, but with the additional risk of hemorrhage and skin necrosis.
Clin Cosmet Investig Dermatol. 2020; 13: 1059–1073.
Published online 2020 Dec 31. doi: 10.2147/CCID.S271760
PMCID: PMC7781022
PMID: 33408497
Can Sodium Thiosulfate Act as a Reversal Agent for Calcium Hydroxylapatite Filler? Results of a Preclinical Study.
Since calcium hydroxyapatite is biodegraded over time, it is possible that these nodules will eventually be absorbed.
The article on the use of a fractional CO2 is intriguing. This material in your photograph appears to be superficial, so it might be treatable with that laser. This is not, however, an isolated nodule as described in the article: Calcium Hydroxylapatite Nodule Resolution After Fractional Carbon Dioxide Laser Therapy
Kavitha K. Reddy, MD; Jeremy A. Brauer, MD; Robert Anolik, MD; et al Leonard Bernstein, MD; Lori A. Brightman, MD; Elizabeth Hale, MD; Julie Karen, MD; Elliot Weiss, MD; Roy G. Geronemus, MD
Author Affiliations Article Information
Arch Dermatol. 2012;148(5):634-636. doi:10.1001/archdermatol.2011.3374.
It would seem prudent, if this course is undertaken, to treat a small area only and observe the result.
And before doing anything, it would also seem prudent to get a biopsy, to see if these are calcium hydroxyapatite nodules, foreign body granulomas or a mixture of both.
In any case, an expert second opinion consultation, in difficult cases like this would also be recommended

Radiesse is a stimulatory filler that is an excellent option for patients who desire a longer-lasting filler alternative to hyaluronic acid dermal fillers. In our office, we use Radiesse to complement structural areas of the face and contour bony prominences. Our office also is a center of excellence for filler complication treatments and we see patients who have been treated by other doctors and have undesirable results from Radiesse or other long-lasting fillers. We have treatment options available for Radiesse filler nodules, granulomas, and soft tissue thickening. The first step would be to diagnose the nodularity and determine whether there is an option for surgical vs. non-surgical removal. Surgical excision is a possibility in some patients; whereas others with more diffuse fillers may benefit from intralesional therapy using scar modulators and enzymes and kenalog. Radiesse complications may be long-lasting and prompt action is key. Patients who have no access to an expert in the field should begin gentle massage of the areas of nodularity with Plato’s Scar Serum twice daily. RF and invasive lasers can actually do more damage by stimulating further collagen growth.

Best,
Dr. Karamanoukian
Realself100 Surgeon

this needs steroid/5fu injections and microneedling RF. dermarolling twice weekly. this wasnt injected properly and you werent the best candidate for it. Best, Dr. Emer.