77427 Billing Rules: How to Count Fractions and Bill Weekly Treatment Management Correctly

Despite its “weekly” label, radiation treatment management is not billed by the calendar. 77427 billing follows the treatment count: one unit for every five fractions delivered, whether they fall in one week or spread across two.

At the end of a course, 3 or 4 leftover fractions earn one more unit, while 1 or 2 leftover fractions do not. A course of only one or two fractions uses 77431 instead, and stereotactic courses use 77432 or 77435. Each unit also needs a documented face-to-face visit with the radiation oncologist.

What CPT 77427 Covers

CPT 77427 radiation treatment management pays the radiation oncologist for overseeing external beam treatment, five fractions at a time. Each unit covers a face-to-face evaluation plus reviews of on-treatment images, dosimetry and patient setup.

Only the physician bills it, since Medicare treats 77427 as a professional-only service. So 77427 modifier 26 is usually unnecessary; add it only when a payer’s policy asks. Also, brachytherapy and stereotactic courses use their own management codes.

When Another Management Code Replaces 77427

Some courses skip 77427 altogether. So before counting, confirm it is the right code by asking these questions in order:

1. Is it stereotactic? Cranial SRS in one session uses 77432. In contrast, SBRT of up to five fractions, or fractionated cranial stereotactic treatment, uses 77435 once per course. These 77432 77435 stereotactic management codes replace 77427, and stereotactic fractions never count toward it.
2. Is the whole course one or two fractions? Then bill 77431 once. The 77431 one or two fractions code fits, for example, a single palliative bone treatment.
3. Was radiation delivered during surgery? Intraoperative radiation management uses 77469 instead.
4. Did the case need unusual extra effort? Payers often group the 77469 77470 special treatment codes together, but 77470 is different: it reports extra work such as twice-daily treatment or concurrent chemotherapy, generally once per course. It is billed alongside 77427, not instead of it, and many payers require a written rationale.

If every answer is no, 77427 applies, and the fraction count decides the units. For the planning and delivery codes billed alongside it, see our oncology coding guidelines.

77427 Billing by Fraction Count

The five fractions rule is simple: count delivered fractions, not days or weeks. As the BCBS Mississippi policy notes, the five do not need to be consecutive, so a holiday or a missed day simply pushes the unit later. Bill the unit once the fifth fraction is complete, with dates of service that span the first and fifth treatments.

Use this table to check any course total:

For any total, divide by five, then add one unit if the remainder is 3 or 4. For example, a 28-fraction prostate course is five full units plus 3 leftover fractions, so it bills six units.

Leftover Fractions at the End of a Course

Most courses do not divide evenly by five, so the last few fractions need a decision.

When the remaining 3 or 4 fractions finish the course, they count as one more 77427 unit. So an 8-fraction or 9-fraction course bills two units.

When only 1 or 2 fractions remain, they fold into the last full unit. In that case, the final unit’s dates stretch to cover the extra treatments, and a 6-fraction or 7-fraction course still bills one unit.

However, never bill 77431 for those 1 or 2 leftover fractions. That code is reserved for a complete course of one or two fractions, and adding it to a longer course is a common audit finding.

When to Bill Each Unit and Which Date to Use

Once the count is right, timing is the next step. A unit is earned only after its fifth fraction is delivered, so never bill it at the start of the week or in advance of treatment.

For the date of service, most payers expect a span from the first to the fifth fraction of that unit. Some ask for a single date instead, usually the face-to-face visit or the fifth fraction, so follow each payer’s rule. In either case, report one unit per line, because 77427 allows only one unit per date.

Finally, close out each course on the last treatment day. That is when the 3 or 4 leftover fractions become a unit, and it is also the moment most often missed, as this radiation oncology coding audit shows.

Three Scenarios That Change the Count

Real courses rarely run five days a week without interruption. These three cases cause most counting questions.

Twice-Daily Treatment

A head and neck patient receives two fractions a day. Payers apply a twice-daily fractions distinct break rule: when a clear gap separates the two sessions, each one counts as its own fraction. So five fractions are reached by the middle of the third day, and the first unit is billed then. The extra effort may also support 77470 once per course.

A Break in the Middle

A patient finishes three fractions, then pauses treatment for two weeks because of skin toxicity. The count simply resumes when treatment restarts, and fractions four and five complete the first unit. As a result, that unit’s dates of service span the break. If the patient never returns, the 3 delivered fractions still support one unit.

Sequential Boost

A breast patient receives 25 whole-breast fractions, followed by a 5-fraction boost. Because the boost is part of the same course, count all 30 fractions together, which gives six units. By contrast, a new course for a different site months later starts a fresh count.

Multiple Treatment Sites and Covering Physicians

Extra sites or shared care do not change the basic count.

Two sites treated in the same session still count as one fraction. Only a separate session after a distinct break adds another. So daily treatment of two sites for five days supports one 77427 unit.

Likewise, when partners cover a patient, each five-fraction period supports only one unit. Assign it to the physician who held the face-to-face visit, and make sure no partner bills the same dates.

Documentation and Audit Findings for 77427

In 77427 billing, each unit must stand on its own record. Good weekly treatment management documentation includes a dated face-to-face visit with the radiation oncologist inside that five-fraction period, a requirement the RadMD coding standard spells out. It also shows the review of on-treatment images, dosimetry and setup, plus the fraction numbers the unit covers. A second visit in the same period does not create a second unit.

Charge audits of 77427 billing tend to find the same problems:

• Missed units: fractions delivered but no unit billed, often at the end of a course. Our post on missing radiation oncology charges shows where these slip through.
• Calendar billing: one unit per week regardless of fractions, which overbills short weeks.
• 77431 added to a long course: used for 1 or 2 leftover fractions instead of folding them in.
• Stereotactic fractions counted: SBRT sessions added to a 77427 total.
• No visit note: a unit billed without a face-to-face encounter in that period.

To catch these before submission, compare fraction logs from the treatment system against billed units each week. Our oncology charge capture checklist offers a broader review routine.

Fractions, Not Weeks, Drive Every Management Unit

Correct 77427 billing comes down to one habit: count delivered fractions and let the total decide the units. Five fractions make one unit, 3 or 4 leftovers make one more, and 1 or 2 leftovers fold in. Meanwhile, stereotactic courses and one- or two-fraction courses use their own codes. With a visit note behind each unit, radiation oncology practices and hospital-based physicians can bill every management unit they earn and defend it later.

Small counting gaps add up across a full patient load. For fraction-level charge review, explore our radiation oncology billing services.

77427 Billing FAQs