Radiation Oncology Modifiers in Medical Billing: The 2026 Cheat Sheet for 26, TC, 59, 76, Q6, KX and the Rest

Radiation oncology modifiers are the two-character suffixes that tell a payer which component of a service was performed (26, TC), that a service was distinct from another on the same day (59, XE, XS, XP, XU), repeated (76, 77), furnished by a substitute (Q5, Q6), medically necessary under a policy (KX), supervised in a teaching setting (GC, GE), delivered by telehealth (place of service 02 or 10, with 95 where a payer requires it), or involved drug waste (JW, JZ).

Most radiation oncology claims carry one modifier or none, so the rarely used ones are the ones most often coded wrong. Here is the set, by code family, as it stands for 2026.

Where you see it

Place	What goes there
CMS-1500 box 24D	Up to four modifiers after the CPT code
837P electronic claim	Loop 2400, SV1 segment, modifier positions 1 through 4
Medicare Physician Fee Schedule (RVU26D)	The PC/TC indicator column shows whether 26 and TC can be used with a code
Remittance advice	CARC 4 (procedure code inconsistent with the modifier) when a modifier is wrong; CARC 236 when a procedure or procedure-modifier combination conflicts with another procedure the same day

26 and TC: follow the PC/TC indicator

Indicator	Meaning	Radiation oncology codes
2	Professional component only; “modifiers 26 and TC cannot be used”	77261, 77262, 77263, 77427, 77431, 77432, 77435
3	Technical component only	77336, 77370, 77371, 77372, 77373, 77402, 77407, 77412, 77437, 77438, 77520, 77522, 77523, 77525
1	Splits into a professional (26) and technical (TC) component; global when one entity bills both	77280, 77285, 77290, 77293, 77295, 77300, 77301, 77306, 77307, 77316, 77317, 77318, 77321, 77331, 77332, 77333, 77334, 77338, 77387, 77436, 77439, 77470, 77750 to 77789
9	Concept does not apply	77417 (status B, bundled)

Two 2026 exceptions within indicator 1: the TC lines of 77387 and 77439 exist in the file but carry status B and zero RVUs, so the only payable form is 77387-26 and 77439-26, in every setting. Freestanding centers that used to bill 77387 global now bill it with 26 and nothing else.

59 and the X modifiers

Modifier 59 (distinct procedural service) and its replacements XE (separate encounter), XS (separate structure), XP (separate practitioner) and XU (unusual non-overlapping service) bypass an NCCI pair edit when two services really were separate. The NCCI manual gives radiation oncology two uses and one prohibition:

• 77336 with a planning code on the same date. The edits block weekly physics against 77261 to 77295, 77301 to 77318 and 77332 to 77334, but “because radiation planning procedures may occasionally be repeated during a course of radiation treatment, the edits allow modifiers 59 or XE, XP, XS, XU to be appended to CPT code 77336” when both fall on one date.
• A device later in an IMRT course. IMRT planning includes most devices, but a patient “occasionally require[s] an additional treatment device at a later date due to decreased tumor volume or patient weight,” reportable with 77332 to 77334.
• Never on 77427. “Modifier 59 shall not be used with code 77427.”

Use the X modifier that describes the situation and 59 only when none fits. Simulation with 77301 is the opposite case: the manual says that edit “shall not be circumvented” by moving the simulation to another date, and no modifier overrides it.

76 and 77: the second fraction of the day

Medicare pays “multiple treatment sessions on the same day … as long as there has been a distinct break in therapy services, and the individual sessions are of the character usually furnished on different days” (Claims Processing Manual, chapter 13, section 70.3). The second fraction goes on a separate line with modifier 76 (repeat procedure by the same physician) or 77 (repeat by another physician). eviCore’s 2026 manual says the same: two units of 77402, 77407 or 77412 are allowed on a BID day, and “CPT 77412 with modifier 76 or 77 is allowed for the second treatment.” The MUE for the three delivery codes is 2 per day, which is the maximum.

Q6, Q5, KX, GC, 95, JW and JZ

Modifier	When	Rule
Q6	A substitute covers the regular radiation oncologist under a fee-for-time compensation arrangement (the term that replaced locum tenens in 2017)	The regular physician bills under his or her own NPI with Q6 on each professional line; the substitute may not cover Medicare patients “over a continuous period of longer than 60 days,” with an exception for active military duty (Claims Processing Manual, chapter 1, section 30.2.11)
Q5	Two physicians cover each other occasionally	Reciprocal billing arrangement, chapter 1, section 30.2.10
KX	77437 in a superficial therapy LCD jurisdiction	“When billing 77437 for services covered by the LCD, providers must append the KX modifier” (Noridian article A60181); KX attests that the requirements of the medical policy have been met; GY or GZ for non-covered services
GC	A teaching physician bills a service involving a resident	Certifies compliance with the teaching physician rules in chapter 12, section 100; goes on professional lines including 77427 and 26 components. GE is the primary care center exception and does not arise in radiation oncology
POS 02 or 10 (and 95)	77427 furnished by real-time video	77427 is on the CY 2026 Medicare telehealth list. Medicare professional claims identify telehealth by place of service: 02 when the patient is not at home, 10 when the patient is at home (MLN booklet 901705). Many commercial payers want modifier 95 on the line as well. 77431, 77432 and 77435 are not on the list. Audio-only does not qualify; CMS’s permanent direct supervision definition requires real-time audio and video, “excluding audio-only”
JW and JZ	A separately payable Part B drug from a single-dose container	JW on a second line reports the discarded amount; JZ attests nothing was discarded and is required “on all claims that bill for drugs from single-dose containers” separately payable under Part B (CMS discarded drugs policy). Radiopharmaceuticals and imaging agents are among the exceptions to the refund policy

The table by code family

Family	Codes	Component modifiers	Other modifiers you may need
Clinical treatment planning	77261 to 77263	None (indicator 2)	Q6, GC
Simulation	77280 to 77293	26 or TC, or global	None; no modifier separates them from 77301
Dosimetry and planning	77295, 77300, 77301, 77306 to 77321, 77331	26 or TC, or global	None in the ordinary course
Devices	77332 to 77334, 77338	26 or TC, or global	59 or XU on a device added later in an IMRT course
Physics	77336, 77370	None (indicator 3)	59 or XE, XP, XS, XU on 77336 when planning repeats the same day
Image guidance	77387, 77439	26 only (TC is status B)	None
Treatment delivery	77402, 77407, 77412, 77437, 77438, 77520 to 77525	None (indicator 3)	76 or 77 on the second same-day fraction; KX on 77437 in LCD states
SRS and SBRT delivery	77371 to 77373	None (indicator 3)	None
Management	77427, 77431, 77432, 77435	None (indicator 2)	Q6, Q5, GC; POS 02 or 10 (and 95 if the payer wants it) for telehealth 77427; never 59
Brachytherapy procedures	77750 to 77789	26 or TC, or global	59 or X modifiers per the NCCI pair
Drugs	J codes	None	JW, JZ

Modifiers no longer used in 2026

• TC on 77387 and on 77439. Status B, zero RVUs. The codes are 77387-26 and 77439-26 everywhere.
• Anything on 77417. Port films are status B in 2026; the line is not separately paid.
• G-code conventions. G6001 to G6017 were deleted January 1, 2026, along with 77385, 77386, 77401 and 77014; the IMRT and IGRT modifier conventions for those codes no longer apply.

Worked example: a BID head and neck day with a new device

Hyperfractionated IMRT, hospital department, Monday of week four. Two fractions six hours apart; a new bite block built because of weight loss; weekly physics performed. Illustrative national professional amounts (RVUs times 33.4009, before geographic adjustment); the hospital’s technical lines are listed without amounts.

Line	Modifier	Units	Who bills	Allowed (national)
77412	none	1	Hospital	APC 5623
77412	76	1	Hospital, separate line	APC 5623
77387	26	1	Physician (one per date under eviCore)	36.41
77334	26	1	Physician	60.12
77334	TC	1	Hospital	APC
77336	XU	1	Hospital (technical only; the X modifier separates it from the same-day device)	APC
77427	none	counts 2 fractions toward the next unit	Physician	195.40 per unit

A freestanding center bills the same lines globally: 77334 without a modifier (126.26), 77336 with XU (92.19), 77412 twice (443.56 each, the second with 76), 77387-26 (36.41).

What to do

• Look up the PC/TC indicator before adding 26 or TC. Indicators 2 and 3 take neither; indicator 1 takes one or the other unless you bill global.
• Put 76 or 77 on the second same-day fraction, on its own line, with the break between sessions in the note.
• Reserve 59 and the X modifiers for 77336 with repeated planning and for devices added mid-course; never on 77427.
• Use Q6 within 60 continuous days, KX on 77437 in LCD states, and POS 02 or 10 for telehealth 77427 (77431, 77432 and 77435 in person).
• Denials to recognize: CARC 4 on 77427-26 or 77412-TC (correct and resubmit); CARC 97 on a second same-day 77412 without 76 (resubmit with the modifier and the break documented); CARC 236 when 77336 is billed with a planning code without an X modifier (append it only if the planning was truly repeated).
• Iridium Suite’s claim scrubber requires the 26 modifier on 77387 and warns when a second BID treatment is entered without 76, before the claim is sent.

Related terms

• Modifier 26 and TC
• Modifier Q6 and locum tenens billing
• 77387 modifier 26
• CPT 77427
• Place of service codes
• Superficial radiation therapy CPT codes

Further reading: CMS PFS Relative Value Files (RVU26D, with the PC/TC indicator definitions); CMS Medicare NCCI Policy Manual, 2026; CMS Medicare Claims Processing Manual, Chapter 12 (teaching physicians, telehealth); CMS, Discarded drugs and the JW and JZ modifiers.