Coding for surface radiation therapy in dermatology: A practical guide

Surface radiation therapy (SRT), previously referred to as superficial radiation therapy, has become an increasingly employed modality for treating cutaneous tumors such as nonmelanoma skin cancers and select benign lesions in dermatology. With the 2026 CPT^® changes, the SRT code set has been modified and streamlined, and is now directly clinically relevant for dermatology practices. Understanding when and how to use new surface radiation therapy CPT codes 77436, 77437, 77438, and 77439, as well as services not to be reported in conjunction with the new codes, is essential for compliance and preventing inadvertent claim denial.

This comprehensive guide provides you with all you need to know to successfully report SRT, including clinical indications, accurate code application, documentation essentials, and payer expectations.

Understanding surface radiation therapy (SRT)

The AMA CPT coding manual describes surface radiation therapy as the delivery of low-energy X-rays (≤500 kV) to treat tumors or lesions on or near the skin surface. Radiation therapy of skin cancers is principally performed with X-rays of ≤150 kV energy. Such low-energy X-rays do not penetrate deep into the body and transmit most of their energy into the skin, and are therefore used for the treatment of skin cancers.

Low-energy X-rays are stratified into superficial (SXT) and orthovoltage or deep (DXT) X-rays. Superficial and orthovoltage radiotherapy utilize low-energy ionizing radiation to treat cancer and other conditions that occur either within or close to the skin surface.

Superficial delivery utilizes ≤150 kV X-rays to treat various benign and malignant skin lesions on or near the surface of the skin. CPT lists these X-rays as penetrating tissue <1.5-2 cm from the skin surface.

This technique is commonly used to treat nonmelanoma skin cancers (e.g., basal cell carcinoma, squamous cell carcinoma) and select benign conditions (treated less often than cancers, depending on guideline support).

2026 CPT codes for surface radiation therapy

This code represents the initial setup and planning for SRT, target delineation (defining where radiation will be delivered), simulation or imaging to identify field size and settings, and treatment field layout.

Please note that this code is reported once per course of treatment, not per session. It is separate from the actual radiation delivery codes and includes simulation-aided field settings. In other words, do not report separate simulation codes.

Please review specific CMS Billing and Coding: Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC) guidance which states in part: CPT 77436 is not typically repeated with each treatment except when clinically indicated and documentation supports additional simulation requirements.

This is the primary delivery code most dermatology practices will use when treating skin tumors. Billed per fraction (each treatment session), it applies to each SRT treatment delivery fraction and is typically used for skin cancers that require multiple fractions over multiple visits.

Each radiation “fraction” (session) is reported with a unit of CPT code 77437 reflecting the technical work of radiation delivery.

Do not report separate basic dosimetry or simulation codes during the SRT sessions.

This code is not likely to be used by dermatologists, who typically would utilize surface radiation therapy devices.

This code specifies ultrasound image guidance is used in conjunction with radiation therapy delivery.

This is an add-on code to CPT 77436 and 77437 and is reported once per entire treatment course, NOT per treatment day.

Image guidance done with anything other than ultrasound is not separately reportable.

Avoid claim denials

One of the biggest sources of claim denials or audits will be due to inappropriate code reporting or bundling. The 2026 CPT guidelines explicitly state that the following services should not be reported separately with SRT codes 77436 - 77439:

• Clinical treatment planning (77261, 77262, 77263)

• simulation (77280, 77285, 77290, 77295)

• Basic or special dosimetry calculation (77300, 77331)

• Isodose planning (77306 -77307, 77316 -77318)

• Treatment devices (77332, 77333, 77334)

• Simulation (77280–77290)

• megavoltage (MeV) (77402, 77407, 77412)

• Treatment delivery codes like 77401 (deleted) and others

• Radiation treatment management (77427, 77431, 77432, 77435, 77469, 77470, 77499)

• Hyperthermia, externally generated (77600, 77615, 77620)

• Intracavitary radiation source application (77761, 77762, 77763)

• Remote after loading high dose rate radionuclide skin surface brachytherapy, includes basic dosimetry, when performed (77767, 77768, 77770, 77771, 77772)

• Interstitial radiation source application (77778)

• Surface application of low dose rate radionuclide source (77789)

Choosing the right CPT code for SRT treatment

A practical way to select the correct SRT code is to ask yourself:

Pre-treatment considerations

SRT often requires prior authorization with major payers. Many plans list codes CPT 77437 - 77439 as requiring pre-service review in 2026. Being proactive with pre-authorization can prevent claim rejection once the service is rendered at a later date.

The following best practices before providing the service are advisable:

• Submit the treatment plan and rationale with the pre-authorization request.

• Use precise and accurate ICD-10-CM diagnosis codes that tie the encounter clearly to the planned service and define the medical necessity for the service rendered.

• Clearly describe why the use of SRT is medically necessary (especially if image guidance will be employed), e.g., surgical contraindication, tumor location, etc.

• Check and verify specific payer coverage and payment policies to ensure compliance before providing the service. Some payers may interpret image guidance differently.

Accuracy in SRT coding is best supported by using updated coding resources and understanding coding guidance and policies. The AAD Coding and Billing Manual provides you with the most recent specialty-specific coding guidance that helps prevent claim denials and inadvertent audits.

SRT codes (77436 –77439) replace older superficial codes, such as 77401, and deleted Category III codes like 0394T. Do not unbundle and report dosimetry and simulation services separately. Documentation must support every service reported on the claim. It is recommended that pre-authorization be obtained from the payer, as it is becoming increasingly necessary before the service is provided.

Most importantly, mastering the correct way to report this service will reduce claim denials, ensure clinical accuracy, and support efficient dermatology practice operations in 2026.

In summary:

CMS resources

Several Medicare Administrative Contractors (MACs), including Noridian, NGS, CGS, Palmetto GBA, and WPS, are implementing new Local Coverage Determinations (LCD) and Billing and Coding Articles (BCAs) to address reporting and coverage of SRT effective March 1, 2026. Dermatologists are encouraged to review payer-specific documentation and payment requirements. The LCDs and BCAs may be accessed on the CMS website as well as on the individual MAC websites, below:

• Future National Government Services: (L40168) Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)

  • A60176 - Billing and Coding: Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC) (Future)

• Future Noridian Healthcare Solutions: (L40176) Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)

  • A60181 - Billing and Coding: Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)

• Future Palmetto GBA: (L40189) Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)

  • A60211 - Billing and Coding: Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC) (Future)

• Future CGS Administrators: (L40179) Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)

  • A60185 - Billing and Coding: Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC) (Future)

  • A60357 - Response to Comments: Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)

• Future WPS Government Services: (L40193) Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC)

  • A60213 - Billing and Coding: Superficial Radiation Therapy (SRT) for the Treatment of Nonmelanoma Skin Cancers (NMSC) (Future)