Hypofractionation Billing and Payer Fraction Limits 2026

Hypofractionation claims are denied for two main reasons. A course that is too short for the code family it was billed under loses a management unit or a physics unit. A course that is one fraction longer than a payer’s policy allows loses payment for the fractions over the cap. Both are avoidable, because the counting rules and the payer caps are published.

This post compares the regimens, the codes and the verifiable caps, then explains how 77427 is counted on a short course.

Keep it as a reference for questions such as whether 16 fractions earns three or four management units.

Two code families, set by the type of course

Stereotactic courses use per-fraction delivery codes limited to 5 fractions and a single management code. CPT 77373 is “stereotactic body radiation therapy, treatment delivery, per fraction to 1 or more lesions, including image guidance, entire course not to exceed 5 fractions,” and 77435 is reported once for the course. Single-session cranial radiosurgery uses 77371 or 77372 with 77432 once. Image guidance is included in these codes, so 77387 is not reported with them, and eviCore bars 77427 and 77431 with SRS or SBRT. Medicare’s SRS and SBRT billing article (A56874) adds that 77373, G0339 and G0340 pay once per day regardless of sessions or lesions and 77435 once per course.

Everything else, whatever the fraction count, uses the conventional family: 77402, 77407 or 77412 once per date of service (twice for BID with modifier 76 or 77 on a separate line), 77387-26 once per date of service when image guidance is justified, 77427 once per five fractions, and 77336 once per five fractions. A 5-fraction whole-breast course is a conventional course that happens to be short; it is not SBRT.

Common regimens, codes and payer caps

Regimen	Delivery and guidance codes	Management	Payer caps verified for this post
5-fraction prostate SBRT (36.25 Gy in 5, NRG-GU005 arm)	77373 x 5	77435 x 1	eviCore: 77373 up to a maximum of 5 fractions for all sites as a complete episode; up to 5 fractions of SBRT alone, not as a boost, for low, intermediate and high-risk disease; SBRT “must be completed in 5 fractions in a single episode of care.” UHC lists 77373 with the 5-fraction descriptor.
5-fraction whole breast (FAST-Forward, 26 Gy in 5)	77407 x 5 (77402 if 2D); 77387-26 x 5 if criteria met	77427 x 1	UHC: IGRT medically necessary for 3D hypofractionated treatment of up to five fractions to the whole breast or chest wall; whole breast cap 21 fractions including boost. eviCore: whole breast up to 16 fractions of 3DCRT plus up to 8 boost fractions.
15 or 16-fraction whole breast (40 Gy in 15; 42.5 Gy in 16)	77407 x 15 or 16; 77387-26 per date when criteria met	77427 x 3	UHC: up to 21 fractions including boost; up to 33 with regional nodes, postmastectomy treatment, prior thoracic RT or connective tissue disorder. eviCore: up to 16 fractions 3DCRT plus up to 8 boost; IMRT only for overlap with a prior field or when an optimized 3D plan exceeds QUANTEC or NCCN organ-at-risk tolerances.
20-fraction prostate (60 Gy in 20)	77407 x 20; 77412 only with active motion management or another Level 3 criterion; 77387-26 x 20 (IGRT with IMRT is a UHC criterion)	77427 x 4	UHC: up to 28 fractions for localized disease; up to 45 with pelvic nodes, post-prostatectomy, inflammatory bowel disease or prior pelvic RT; more than 45 not medically necessary. eviCore: 20 to 28 fractions of IMRT in up to 2 phases; 36 to 45 conventional fractions when treating pelvic nodes.
Bone metastases, 8 Gy in 1 or 20 Gy in 5	77402 or 77407 per fraction; 77387-26 only when a listed criterion applies (for example re-irradiation)	77431 x 1 for a 1 or 2-fraction course; 77427 x 1 for 5 fractions	UHC: up to 10 fractions; more only for a previously treated site. eviCore: 77431 “when the entire treatment course consists of 1-2 fractions”; SBRT for bone metastases not medically necessary except previously irradiated spine or spine metastases from sarcoma, melanoma, hepatocellular or renal cell carcinoma.
Cranial SRS, single session; fractionated SRS, 2 to 5	77371 or 77372 x 1; or 77373 x 2 to 5	77432 x 1; or 77435 x 1	eviCore: 77371 or 77372 only when the whole course is one fraction; 77371 for fraction one followed by 77373 is not allowed; 77373 up to 5 fractions for multi-fraction cranial SRS. Florida Blue 02-77371-02 (reviewed July 23, 2026) lists 77373, 77435, G0339 and G0340 with the 5-fraction descriptor.

Regimens are the published ones; the clinical choice is the physician’s.

How 77427 counts on a short course

The Medicare Claims Processing Manual, chapter 13, section 70.1, is the rule payers follow. “A weekly unit of treatment management is equal to five fractions or treatment sessions,” counted “regardless of the actual time period in which the services are furnished.” At the final billing, “three or four fractions beyond a multiple of five … are paid for as a week,” while “one or two fractions beyond a multiple of five” are not paid. The manual’s own examples: 18 fractions equals 4 units, 8 equals 2, 6 equals 1. eviCore’s coding manual gives 10, 12 and 13 fractions as 2, 2 and 3 units.

Fractions in the course	77427 units	Why
1 or 2	0 (report 77431 x 1)	Course of one or two fractions
3 or 4	1	Three or four fractions count as a week
5	1	One full week
12	2	Two leftover fractions are not paid
13, 15, 16	3	13 has three left over (paid); 15 is exact; 16 has one left over (not paid)
18, 20	4	18 has three left over (paid); 20 is exact

So a 5-fraction whole-breast course earns one unit and a 16-fraction course earns three, not four. The count at final billing governs: a course authorized for 16 that stopped at 13 still earns three units; one that stopped at 12 earns two. eviCore applies the same five-fraction rule to 77336 and bars it for a single-fraction course.

Common causes of denials

Three patterns account for most hypofractionation denials described in payer documents. Billing SBRT past 5 fractions: eviCore’s example is two lung lesions at 3 fractions each, where at 6 total fractions “it is no longer considered SBRT and must be reported with 3D or IMRT treatment codes,” and 77373 as a boost after 28 IMRT fractions is likewise barred. Exceeding a published cap without the qualifying circumstance in the note: UnitedHealthcare’s prostate rule allows 28 fractions by default and 45 only with one of four documented circumstances. Claiming Level 3 because the course was advanced: the level follows delivery facts (multiple isocenters, active motion management, total skin electrons, mixed fields), not fraction count or technique, so a 5-fraction breast course with DIBH may qualify for 77412 while a 20-fraction prostate course with daily CBCT and no tracking does not.

Documentation for a short course

The prescription: total dose, dose per fraction, number of fractions, and the regimen’s name or trial reference where one exists.
For SBRT or SRS: the lesion count and that the entire course is 5 fractions or fewer.
For Level 3 on any course: the criterion and the method, in the physician’s words.
For image guidance: the payer criterion being met (IMRT, re-irradiation, fiducials, DIBH, prone position, the listed 3D indications), and the fraction count at final billing so the 77427 units reconcile.

What to do now

Map every regimen you treat to its code family and unit counts once, and recheck when eviCore or UHC publishes a new edition.
Count 77427 from the fraction count at the end of the course, not from calendar weeks and not from the authorized count.
Base the management lines on the fraction count. Iridium Suite can create 77427 and 77336 automatically from the fraction count, with a billing note, so staff do not calculate units by hand at charge entry; see the claim scrubber for how the frequency rules are applied.
Request the fraction count you will deliver and, for prostate and breast courses above the default cap, name the qualifying circumstance in the authorization request.
Never split a stereotactic plan of 6 or more fractions across SBRT codes. Report it as 3D or IMRT with 77427, or document why the sites are separate episodes.

Hypofractionation billing and payer fraction limits: billing a 5, 15 or 20-fraction course without a denial