Superficial Radiation Therapy CPT Codes in Medical Billing: 77436 to 77439 and the End of 77401

Superficial radiation therapy CPT codes are the four 2026 codes for surface radiation treatment of skin tumors: 77436 (planning and simulation-aided field setting), 77437 (superficial delivery, 150 kV or less, per fraction), 77438 (orthovoltage delivery, over 150 to 500 kV, per fraction) and the add-on 77439 (ultrasound image guidance, once per course). They replaced CPT 77401 and HCPCS G6001 on January 1, 2026.

If your practice owns an orthovoltage unit, or you bill for a dermatology group that bought an SRT machine, these codes are new for everyone, including the payers. Here is what is settled and what is not.

Where you see it

Place	What goes there
CMS-1500 box 24D	77436 once at the start of the course; 77437 or 77438 one unit per fraction, with KX where a Medicare LCD applies; 77439 with modifier 26 once per course if ultrasound guidance was used
837P electronic claim	Loop 2400, SV1: 77437, modifier KX (Medicare, LCD jurisdictions), unit count 1 per date of service
Medicare Physician Fee Schedule (RVU26D)	77436 PC/TC indicator 1 (splits into 26 and TC); 77437 and 77438 indicator 3 (technical only, no work RVU); 77439 indicator 1 with the TC line at status B
Medicare MUE table (October 1, 2026)	1 unit per date of service for all four codes
Hospital outpatient claim (OPPS Addendum B, 2026)	77437 and 77438 in APC 5621; 77436 status Q1 in APC 5732; 77439 status N (packaged)
Medicare Coverage Database	LCDs titled “Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)” from five MACs, each with a billing and coding article

The family and what 77401 used to cover

Before 2026 a superficial course was billed as CPT 77401 (radiation treatment delivery, superficial and/or orthovoltage, per day) with CPT 77280 for the simulation and HCPCS G6001 for ultrasound guidance. CMS’s CY 2026 final rule traces the change: G6001 was flagged in October 2020 for high Medicare utilization, the RUC referred it to CPT in January 2021 to build codes that reflect “the different process of care between the two specialties (dermatology and radiation oncology),” and the CPT Editorial Panel created the four-code surface radiation subsection in September 2024.

Code	Descriptor (abridged)	Unit	2026 RVUs (national)	PC/TC
77436	Surface radiation therapy; superficial or orthovoltage, treatment planning and simulation-aided field setting	once per course	2.35 global; 1.25 for 26; 1.10 for TC	1 (splits)
77437	Surface radiation therapy, superficial, delivery, 150 kV or less, per fraction (e.g., electronic brachytherapy)	per fraction	3.28	3 (technical only)
77438	Surface radiation therapy, orthovoltage, delivery, over 150 to 500 kV, per fraction	per fraction	3.31	3 (technical only)
77439	Surface radiation therapy, superficial or orthovoltage, image guidance, ultrasound for placement of radiation therapy fields for treatment of cutaneous tumors, per course of treatment (add-on)	once per course	0.48 global and 26; TC status B	1, TC bundled

Three things to notice. 77436 combines the old planning and simulation into one line, with the physician work (0.77 RVUs) in its 26 component. 77437 and 77438 carry no physician work; the machine’s energy determines the code, and electronic brachytherapy is explicitly included in 77437. And CMS deliberately zeroed the technical component of 77439: bundling the ultrasound “would eliminate financial incentives to provide ultrasound guidance where it may be of questionable value,” so “the use of ultrasound guidance will not vary the payment made under the PFS.” As with 77402, 77407 and 77412, CMS priced the technical side of the family from the OPPS relationship between APCs 5621 and 5732.

Medicare coverage, the LCDs and the KX modifier

Medicare has no national coverage determination for SRT. As of October 2026 the Medicare Coverage Database lists LCDs from CGS (L40179), Noridian (L40176), Palmetto GBA (L40189), WPS (L40193) and Wellpoint Federal (L40168). Noridian’s, effective for services on or after March 1, 2026, covers SRT for basal cell carcinoma, squamous cell carcinoma and squamous cell carcinoma in situ when the record documents that the patient is a nonsurgical candidate, and states that high-resolution ultrasound used to guide SRT “is not considered reasonable and necessary and is not supported by literature.”

Noridian’s billing and coding article A60181 adds the operational rules:

• “When billing 77437 for services covered by the LCD, providers must append the KX modifier.” KX means the requirements specified in the medical policy have been met. Non-covered services are billed with GY or GZ.
• The treating physician must have training and expertise from an accredited residency or fellowship in radiation oncology or dermatology, or be a dermatologist with didactic and clinical radiation treatment experience.
• The record must contain a statement of why the patient is a nonsurgical candidate, a signed treatment plan with dose constraints, and dosimetric verification of setup and delivery signed by the treating physician and the medical physicist.
• The March 1, 2026 revision removed language that had limited SRT payment to the non-facility setting.

The article names 77437 for the KX requirement and does not spell out 77438; ask your MAC before assuming orthovoltage is exempt.

Payer rules, and where they disagree

Rule	eviCore for Cigna (V1.0.2026)	Evolent (January 2026)	Humana (HUM-2632-000)	Medicare (Noridian)
Image-guided SRT	77439-26 once per episode when authorized; 77387 never during an SRT course	77387 not medically necessary with superficial or orthovoltage	Excluded: “Image-guided superficial radiation therapy (eg, SRT performed in conjunction with concurrent or daily imaging)”	Ultrasound guidance not reasonable and necessary
Units of 77437 or 77438	One per date of service “regardless of the number of treatment sites”	Not stated	Not stated	MUE 1 per day
77336 during the course	Cannot be reported	“Should not be billed for a treatment delivery course involving CPT code 77437 or 77438”	Not stated	Article contemplates 77336 and 77370 with SRT; they “must relate to reasonable and necessary services”
Planning, simulation, devices, 77300, 77427	All excluded for the entire course	Clinical planning codes not reported with SRT	Not stated	Not stated

Practices ask about 77336 most often. Payer manuals say no; a Medicare contractor article allows for it; a dermatology vendor webinar tells its users to bill it weekly. Treat it as payer-specific, and when a payer’s policy does not address it, bill it only when a qualified medical physicist actually performed and documented the weekly consultation. Multiple lesions are the other open question: eviCore allows one delivery unit per day no matter how many sites are treated, and no source we could verify says otherwise.

Worked example: a 15-fraction course for a basal cell carcinoma

A 78-year-old Medicare patient with a nasal basal cell carcinoma declines surgery; the radiation oncologist documents why he is a nonsurgical candidate. Fifteen fractions of 100 kV superficial therapy in a freestanding center in a Noridian state, no ultrasound guidance. Illustrative national amounts: RVUs times the 33.4009 conversion factor, before geographic adjustment and sequestration.

Line	Units	Modifier	RVUs	Allowed (national)
77436, planning and field setting	1	none (global)	2.35	78.49
77437, superficial delivery	15	KX	3.28 each	1,643.25
77439, ultrasound guidance	0			0.00
77336, weekly physics	payer-dependent		2.76 each	see text
Course total without 77336				1,721.74

In a hospital department the hospital bills 77437 fifteen times under APC 5621 (104.24 per fraction, 1,563.60 for the course) and the physician bills 77436-26 (41.75). A 77427 line, a 77280 simulation or a 77261 to 77263 planning code anywhere in this course is a denial under eviCore’s rules and uncertain under others.

What to do

• Pick the delivery code by kV, not by machine name. At or below 150 kV is 77437, including electronic brachytherapy; above 150 to 500 kV is 77438. One unit per fraction, one fraction per day.
• Bill 77436 once, at the start. Daily field placement is never a second 77436 or a 77280.
• Append KX on Medicare delivery lines in LCD jurisdictions when the criteria are met and the nonsurgical candidate statement is in the chart; GY or GZ when they are not.
• Report 77439 with modifier 26, once per course, and only when the payer covers image-guided SRT. Humana excludes it; the Noridian LCD calls it not reasonable and necessary.
• Bill 77336 by the payer’s rule, not on a weekly schedule by default.
• Denials to recognize: CARC 96 (non-covered) on 77437 without KX in an LCD state (resubmit with KX only if the criteria were truly met); CARC 97 on 77336, 77280 or 77261 to 77263 during the course (eviCore bundles them, do not appeal); CARC 4 if 77439 is billed without 26 (correct and resubmit); CARC 151 if a second 77437 posts for the same day (the MUE is 1).
• Iridium Suite’s claim scrubber warns when the deleted 77401 or G6001 is entered and checks each 77437 and 77438 line against radiation oncology frequency rules before the claim goes out.

Related terms

• CPT 77427
• 77387 modifier 26
• Modifier 26 and TC
• Radiation oncology modifiers
• Medically unlikely edits
• Radiation therapy prior authorization in 2026

Further reading: CMS Medicare Coverage Database, LCD L40176, Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (Noridian); CMS Medicare Coverage Database, Billing and Coding article A60181 (Noridian); CMS fact sheet, CY 2026 Physician Fee Schedule final rule; CMS PFS Relative Value Files.