Proton Therapy CPT Codes in Medical Billing: 77520 to 77525, Contractor Pricing and the APCs

Proton therapy CPT codes are 77520, 77522, 77523 and 77525, the four per-fraction codes for proton treatment delivery, graded from simple without compensation to complex. They describe only the technical delivery; the radiation oncologist’s work is reported with the same planning, image guidance and management codes used for photon courses.

Proton billing uses two payment systems that pay very differently, and coverage comes entirely from local policy. Both are easier to follow when you compare them side by side.

Where you see it

Place	What goes there
CMS-1500 box 24D (freestanding center)	77520, 77522, 77523 or 77525, one unit per fraction, no modifier (technical-only code, PC/TC indicator 3)
837P electronic claim	Loop 2400, SV1: 77525, unit count 1 per date of service
Medicare Physician Fee Schedule (RVU26D)	Status C (contractor priced), 0.00 RVUs, PC/TC indicator 3, global XXX
Medicare MUE table (October 1, 2026)	2 units per date of service for all four codes
Hospital outpatient claim (OPPS Addendum B, 2026)	77520 status S, APC 5623; 77522, 77523 and 77525 status S, APC 5625
Medicare Coverage Database	LCDs L35075, L36658 and L33937, with billing and coding article A56827 under L35075

The four codes

Code	Descriptor	Hospital APC (2026)	APC national rate	PFS
77520	Proton treatment delivery; simple, without compensation	5623, Level 3 Radiation Therapy	564.51	Contractor priced
77522	Proton treatment delivery; simple, with compensation	5625, Level 5 Radiation Therapy	1,276.81	Contractor priced
77523	Proton treatment delivery; intermediate	5625	1,276.81	Contractor priced
77525	Proton treatment delivery; complex	5625	1,276.81	Contractor priced

The APC rates are from the CY 2026 OPPS Addendum B; the national unadjusted copayment is 112.91 for APC 5623 and 255.37 for APC 5625. The hospital receives one APC payment per fraction. For comparison, 77412, the Level 3 photon delivery code, is in the same APC 5623 as 77520.

Why professional fees are contractor-priced

Under the fee schedule the proton codes have never had RVUs. CMS said why again in the CY 2026 final rule: “we have not previously established RVUs for these services due to the unique nature of the equipment costs associated with these services compared to other capital costs addressed by our usual PE methodology.” Each MAC prices the codes itself, so a freestanding center’s allowed amount depends on which contractor processes its claims.

For 2026 CMS asked whether it should price the proton codes nationally the way it had just priced 77402, 77407 and 77412 from hospital cost data. It received “many thoughtful comments” and said it “will consider it as part of future rulemaking.” The CY 2027 proposed rule, published July 16, 2026 (91 FR 43842; comments closed September 14), carried that forward. CMS cited 2024 claims for 77525 with allowed charges that “ranged from $122.15 to $1,374.26” across contractors and proposed to:

• use the total allowed charges the MACs paid for 77520 to 77525 as the pool of practice expense RVUs for the family, and
• allocate that pool to the four codes using the relationship between the APC 5625 and APC 5623 relative weights under the OPPS.

If finalized, the 2027 fee schedule would carry national practice expense RVUs for proton delivery for the first time. The final rule normally appears in early November; until it does, bill against your MAC’s published amount.

The rest of the claim is ordinary

Service	Code	Notes
Clinical treatment planning	77261 to 77263	Professional only (PC/TC indicator 2)
Simulation	77280 to 77290, with 77293 when a 4D data set is needed	Complex simulation lists particle therapy as a qualifying item
Dosimetry plan	77295 or 77301	Evolent’s standards say a 3D plan “may be appropriate for proton beam therapy,” one per course unless a new data set shows meaningful anatomic change
Devices and calculations	77300, 77332 to 77334, 77338	Standard rules
Image guidance	77387-26	eviCore allows one unit per date of service with 77520 to 77525 and bundles the technical component of IGRT into the proton delivery codes
Management	77427	One unit per five fractions; 77432 or 77435 for stereotactic courses
Physics	77336, 77370	Standard rules

Coverage: no NCD, so read the LCD

Medicare has no national coverage determination for proton beam therapy, a point UnitedHealthcare’s Medicare Advantage policy states before directing providers to the LCDs. As of October 2026 three LCDs are current on the Medicare Coverage Database.

LCD	Contractor and states	Structure
L35075, Proton Beam Therapy (revision effective April 1, 2026)	Wellpoint Federal (formerly National Government Services): Illinois, Minnesota, Wisconsin, New York and New England	Group 1 diagnoses that “frequently support the use of PBT” (ocular tumors, skull base tumors, unresectable CNS tumors, hypofractionated hepatocellular cancer, pediatric tumors and others); Group 2 (including non-metastatic prostate, breast, lung, pancreas and re-irradiation) “limited to providers who have demonstrated experience in data collection and analysis”; normal tissue DVHs “must be demonstrably improved with a PBT plan”
L36658, Proton Beam Therapy (revision effective October 8, 2026)	CGS: Kentucky and Ohio	Same two-group design; for prostate it finds “no good comparative data to determine whether or not Proton Beam Therapy for prostate cancer is superior, inferior, or equivalent to external beam radiation, IMRT, or brachytherapy” and requires physician documentation of patient selection criteria; for metastatic lesions “An IMRT or 3-D radiotherapy plan will need to be generated and compared to the Proton plan”
L33937, Proton Beam Radiotherapy (effective December 16, 2019)	First Coast, Part B	Not read for this article

The billing and coding article under L35075 (A56827) requires a treatment prescription and plan signed by a physician, “verification of planned dose distribution via independent dose calculation or physical measurement,” and the referring physician’s name and NPI on the claim.

Commercial and Medicare Advantage plans add their own rules, and those rules matter most for prostate. Aetna’s Clinical Policy Bulletin 0270 states: “Aetna considers proton beam radiotherapy and IMRT clinically equivalent for localized cancer of an intact prostate.” In practice a prostate proton request may come back approved as IMRT, and the center must decide whether to treat under the approved code set or appeal with a comparative plan.

Worked example: a 28-fraction prostate course in two settings

Hospital-based proton center, traditional Medicare, Group 2 LCD criteria met and documented. Illustrative amounts: APC national rates from the 2026 Addendum B; physician amounts are RVUs times 33.4009, before geographic adjustment and sequestration.

Line	Who bills	Units	Rate	Total
77525 (APC 5625)	Hospital	28	1,276.81	35,750.68
77387-26	Physician	28	36.41	1,019.48
77427 (28 fractions is 5 units plus 3 leftover fractions, so 6 units)	Physician	6	195.40	1,172.40
Planning, simulation and devices	Both, split 26 and TC			per code

Freestanding proton center, same course. The 77387-26 and 77427 lines are identical. The 28 units of 77525 are paid at whatever the center’s MAC has published, with no national floor; CMS’s own 2024 figures put the spread across contractors at more than tenfold. Two centers treating the same patient the same way can be paid very differently for the technical side, which is the problem CMS says the 2027 proposal is meant to fix.

What to do

• Pull your MAC’s current proton fee schedule and load it as the expected allowed amount for 77520 to 77525; there is no national figure to fall back on in 2026.
• Bill one delivery unit per fraction, no modifier, and never 26 or TC: the codes have no professional component.
• Keep 77387 on its own line with 26 on every treatment date the physician reviews the images; the technical side is included in the proton code in both settings.
• Match the diagnosis to the LCD group before the first fraction, and for Group 2 sites hold the data collection documentation the LCD requires.
• For prostate, read the plan’s equivalence language before requesting authorization, and expect to supply a comparative IMRT plan when the LCD or plan asks for one.
• Denials to recognize: CARC 96 (non-covered) with a coverage remark when the LCD group is not supported (appeal with the DVH comparison and selection criteria); CARC 4 if a modifier is billed on 77525 (correct and resubmit); CARC 151 when a third unit posts in one day (the MUE is 2).
• Iridium Suite’s site-of-service billing selects the global, professional or technical component from the treatment location, so a hospital-based physician’s 77387-26 and a freestanding center’s technical 77525 come out of the same charge entry; see why Iridium Suite for radiation oncology.

Related terms

• CPT 77427
• 77387 modifier 26
• Facility vs non-facility
• Radiation oncology modifiers
• 2027 Medicare proposed rules for radiation oncology
• Radiation therapy prior authorization in 2026

Further reading: CMS Medicare Coverage Database, LCD L35075, Proton Beam Therapy; CMS, CY 2027 Physician Fee Schedule proposed rule (CMS-1848-P) page; CMS OPPS Addendum A and B quarterly updates; Aetna Clinical Policy Bulletin 0270, Proton Beam, Neutron Beam, and Carbon Ion Radiotherapy.