From Installation to Treatment: What a Safe Superficial Radiation Therapy Program Requires

Introducing superficial radiation therapy (SRT) involves a series of technical and clinical preparations that begin well before the equipment arrives. Room planning, radiation shielding, equipment acceptance, medical physics commissioning and treatment procedures all need to be addressed before a clinic starts treating patients.

A new professional reference became available on October 30, 2026, when the American Association of Physicists in Medicine (AAPM) published Medical Physics Practice Guideline 18.a, covering superficial radiation therapy using low-energy kilovoltage X-rays. The guideline addresses systems operating at energies up to 100 kVp, with 50–100 kVp representing the typical clinical range discussed in the report.[1]

Its recommendations bring together several aspects of SRT practice that are often handled by different people: equipment performance, radiation protection, treatment calculations, clinical setup and ongoing quality assurance.

For hospitals and dermatology clinics planning an SRT service, these requirements have practical implications for both purchasing and implementation.

Planning the Clinical Service

The intended clinical applications should be established before an SRT system is selected.

Patient assessment, prescription, treatment planning and follow-up require defined clinical responsibilities. The institution also needs to identify who will oversee medical physics, radiation protection and equipment operation.

Medical physics support is particularly important. A Qualified Medical Physicist (QMP), as defined within the AAPM framework, should be involved in equipment commissioning and the development of the quality assurance program. In countries with different professional qualification systems, equivalent responsibilities must be assigned according to local requirements.

The expected treatment workload and available clinical resources also influence equipment configuration. Applicators, beam configurations and positioning arrangements should be evaluated against the procedures the clinic intends to perform.

The clinical role of superficial X-ray radiotherapy in dermatology is another consideration at this stage. Patient selection and treatment indications should guide the service plan rather than equipment availability alone.

Regulatory planning belongs in the same discussion. Requirements for X-ray equipment registration, facility approval, personnel qualifications and radiation protection vary by country. These should be identified before the purchase and installation schedule is finalized.

Site Planning and Radiation Protection

The manufacturer's installation documentation should be reviewed before shipment. Door widths, corridors, elevators, floor space, electrical supply and equipment operating clearances can all affect the installation.

The movement range of the treatment head deserves particular attention. A system may need to approach different anatomical sites while maintaining the positioning and working space required by the clinical team.

Radiation shielding requires a separate assessment by an appropriately qualified medical physicist or radiation shielding professional.

The calculation should consider:

• Maximum beam energy intended for clinical use;

• Expected workload and operating schedule;

• Possible treatment-head orientations;

• Wall, floor and ceiling construction;

• Adjacent occupied areas;

• Doors, viewing windows and access routes;

• Applicable radiation protection limits and design goals.

The beam orientation is especially relevant for mobile superficial X-ray systems. AAPM MPPG 18.a notes that such units may be directed in different directions. Consequently, all walls, the floor and the ceiling may need to be considered as primary barriers, subject to the site-specific shielding assessment. The primary beam should not be directed towards the treatment-room door or viewing window during operation.[1]

There is no universal lead thickness suitable for every SRT room. The required shielding depends on the equipment and the specific installation.

AAPM MPPG 18.a places a comprehensive radiation survey before commissioning activities. Following room construction and equipment installation, a QMP must conduct the post-installation survey using a calibrated survey meter. The assessment is performed under full-scatter conditions, using a large phantom, the highest beam energy and the largest applicator intended for clinical use. Leakage radiation must also be considered.

The results should demonstrate that the established shielding design goals are being met before clinical operation. A written report should document exposure rates in adjacent occupied areas.[1]

These assessments should be coordinated with facility construction and installation planning. Correcting a shielding problem after a treatment room has been completed can involve substantial additional work.

Equipment Acceptance and Medical Physics Commissioning

Equipment installation, acceptance testing and commissioning are separate stages, each producing different information.

Installation covers physical setup, connection and configuration according to the manufacturer's instructions. Basic operating functions and specified safety features are checked as part of this process.

Acceptance testing evaluates whether the delivered system meets the agreed technical and performance specifications. The manufacturer's acceptance procedures and the purchase requirements provide the basis for testing.

AAPM MPPG 18.a states that when a manufacturer offers or requires acceptance testing, it must be conducted by the manufacturer's representative under the oversight of an independent QMP. The report is recommended to be signed by both parties and retained for future reference.[1]

Commissioning establishes the dosimetric information needed for clinical use. AAPM specifies that commissioning measurements must be performed by a QMP.

For a low-energy superficial X-ray system, the commissioning program includes several measurements.

HVL must be measured before absolute output calibration. The measured beam quality is used in the dosimetric calculations required by the AAPM TG-61 protocol.

For absolute output calibration, AAPM MPPG 18.a specifies the TG-61 protocol or an equivalent standard. The commissioning process also requires an appropriately calibrated ionization chamber and the relevant measurements for all energy/filter combinations and applicators intended for clinical use.[1,2]

The calculation method needs the same attention as the equipment measurements. Depending on the system, the clinic may use a treatment-time worksheet, lookup table, treatment planning system or validated software. The selected method must be commissioned and checked before it is used for patient treatment.

AAPM recommends independent verification of reference dosimetry and a comprehensive end-to-end test after commissioning. The latter involves the relevant personnel and uses a phantom to test the workflow from setup simulation through treatment delivery. The commissioning report should document the measurements, procedures and findings.[1]

A clinical implementation report published in 2023 provides a useful example. The authors described commissioning an SRT-100 Vision system using TG-61 reference dosimetry, PDD and beam-profile measurements, timer testing, treatment-time calculations and a routine QA program. They also performed end-to-end testing using a phantom.[3]

This study illustrates the work involved in introducing an SRT service. Its specific equipment measurements and results should not be applied directly to other systems.

Preparing the First Treatment

Low-energy superficial X-ray therapy generally follows a clinical setup workflow rather than conventional CT simulation. The AAPM guideline describes both same-day simulation and treatment and workflows in which treatment takes place at a subsequent visit. The actual arrangement depends on the institution and its clinical procedures.[1]

Patient positioning is established during setup simulation. Clinical and pathology reports, together with physical examination, help the treating physician identify the lesion and mark the treatment area.

The team then determines the applicator size, energy/filter combination, treatment depth where applicable and any required air-gap arrangement. Reproducible positioning is important, particularly for facial lesions and other anatomical sites where small changes in posture can alter the relationship between the skin and treatment applicator.

For open-ended applicators, AAPM recommends that the skin surface be flush with the applicator end. Unintended air gaps should be minimized. If the planned setup requires a gap, the corresponding dosimetric effects must be evaluated and accounted for in the treatment calculation.[1]

The treatment field and nearby critical structures also need consideration. Shielding may be used to protect adjacent lesions or structures such as the eyes and thyroid. Its position must follow the approved treatment setup.

For a closer look at these practical considerations, see our article on why precise positioning matters in superficial radiotherapy.

Prescription and treatment calculations

The treatment prescription should document the information needed to reproduce the planned treatment, including:

• Anatomical treatment site and laterality;

• Treatment modality and energy/filter;

• Applicator size;

• Dose per fraction and total prescribed dose;

• Treatment delivery pattern;

• Prescription depth, where applicable;

• Pretreatment preparation, including shielding;

• Imaging technique and frequency, where applicable.

The treating physician must approve and sign the prescription before treatment.[1]

Treatment time or monitor units (MU), depending on the system, are calculated by appropriately trained personnel using the commissioned dosimetric data. A primary calculation and an independent secondary verification are both required as safety checks under the guideline.

The resulting treatment plan document must be reviewed and signed by the treating physician before delivery. For non-standard setups involving irregular fields or shielding that substantially changes backscatter, patient-specific in-vivo dosimetry may be appropriate to verify dose accuracy.[1]

Before irradiation, the treatment parameters saved in the equipment interface must be checked against the signed treatment plan. Patient identity, treatment site, energy/filter, applicator size and treatment time or MU all need to correspond to the approved documentation.

The treatment record should also include a summary of the parameters actually delivered. AAPM recommends weekly chart review and requires an end-of-treatment chart review within five business days of the final fraction.[1]

Staff preparation

Everyone involved in the SRT program needs training appropriate to their assigned responsibilities.

AAPM MPPG 18.a specifies comprehensive vendor-supported on-site training before patient treatment begins. The training should cover the treatment unit, operating procedures, applicator setup, lead shield use and emergency response. Emergency instructions should be readily available at the treatment console.[1]

General radiation safety education does not replace training on the actual equipment and its clinical procedures. Annual in-service training focused on SRT safety and emergency protocols is also recommended.

Maintaining Equipment Performance Through Routine QA

Commissioning establishes the reference data against which subsequent measurements are compared. Routine quality assurance is used to identify changes in equipment performance and confirm that the system remains within its established action limits.

AAPM MPPG 18.a sets out daily, monthly and annual QA recommendations for the low-energy superficial X-ray systems within its scope.[1]

The following table summarizes representative tests and action limits from Table 3 of the guideline. It is not a substitute for the complete QA schedule.

Additional annual tests include output error associated with beam interruption, timer or MU linearity, timer end-effect error and focal spot size. PDD verification applies where PDD data are used clinically, and beam-profile action limits include field uniformity within ±5% of the commissioning baseline.[1]

Daily and monthly QA can be performed by personnel who have been properly trained and demonstrated competency under the medical physics supervision framework. Annual QA is performed by or under the direct supervision of a QMP.

All QA results must be documented and reviewed independently by a QMP or the facility's radiation safety officer. Following equipment upgrades, repairs, service or relocation, the manufacturer-recommended checks must be completed and QA baselines re-established where necessary.[1]

A 2025 publication reporting three and a half years of QA results from an SRT-100 Vision system offers a useful example of long-term monitoring. The study reviewed dosimetric, mechanical and safety performance and reported results within the recommended tolerances for that particular unit.[4]

The findings demonstrate the value of maintaining a documented QA program over time. They are not a performance guarantee for other equipment models.

Evaluating an SRT System Beyond Its Specifications

Equipment selection should account for the way the system will be used in the clinic.

Positioning range, applicator options, beam-limiting arrangements, control functions and safety features all affect day-to-day operation. Installation requirements, technical documentation, staff training and the manufacturer's after-sales support also deserve attention.

KernelMed's XT-5601 Superficial X-Ray Radiation Therapy System is designed for dermatology and oncology applications. Its published features include robotic arm-assisted positioning, customizable beam limiters, a 12.1-inch touchscreen control console, safety interlocks and programmable timers.

These features are relevant to treatment-head positioning, field configuration and equipment operation. The clinic must still arrange the independent medical physics commissioning, radiation shielding assessment, clinical procedures and QA responsibilities required for its installation.

The AAPM guideline discussed in this article is not a product certification or endorsement. Its specific technical recommendations must be assessed against the verified energy range and configuration of the individual system.

Clinics and distributors evaluating the XT-5601 can find its product configuration and available features on the XT-5601 Superficial X-Ray Radiation Therapy System product page.

Bringing an SRT Service Into Clinical Practice

A functioning SRT service depends on coordinated work by the manufacturer, medical physicist, treating physician and institution.

The equipment must be installed and evaluated. The treatment room must meet its radiation protection requirements. Dosimetric data and treatment calculations must be established, staff must understand their responsibilities, and the clinical workflow must be checked before treatment begins.

Once patients are being treated, the facility continues to monitor equipment performance and review treatment records.

Planning these responsibilities early gives the clinic a clearer route from equipment procurement to routine clinical operation.

Frequently Asked Questions

1. What energy range does AAPM MPPG 18.a cover?

The guideline covers superficial radiation therapy using low-energy kilovoltage X-rays up to 100 kVp. The typical clinical energy range discussed is 50–100 kVp. It does not serve as a universal guideline for electron therapy or high-dose-rate brachytherapy.

2. What must be completed before an SRT clinic treats its first patient?

The clinic should complete the required room preparation, shielding assessment and radiation survey, equipment acceptance testing, medical physics commissioning, staff training and clinical workflow verification. Applicable local regulatory approvals must also be in place.

3. What is the difference between acceptance testing and commissioning?

Acceptance testing checks whether the delivered equipment meets the agreed technical and performance specifications. Commissioning involves dosimetric measurements and validation of the treatment calculation method, establishing the baseline data needed for clinical use and subsequent QA.

4. Who should oversee SRT commissioning?

AAPM MPPG 18.a specifies that commissioning measurements must be performed by a Qualified Medical Physicist (QMP). In other countries, the corresponding professional qualifications and responsibilities should follow the applicable local framework.

5. What measurements are included in SRT commissioning?

The commissioning program includes beam quality (HVL), absolute output calibration, applicator factors, percentage depth dose, beam profiles, field-applicator congruence and focal spot size. Inverse square law validation is also required where an air gap is applicable. The exact measurements depend on the equipment configuration and intended clinical use.

6. Does every SRT treatment room require lead shielding?

The shielding design depends on beam energy, workload, possible beam directions, room construction and occupancy of surrounding areas. A qualified professional must assess the actual installation. Neither a universal lead thickness nor another clinic's shielding design should be adopted without a site-specific evaluation.

7. How often should superficial X-ray therapy equipment undergo QA?

AAPM MPPG 18.a describes daily, monthly and annual QA. Daily and monthly checks cover operational safety, output consistency, timer accuracy and mechanical condition. Annual testing includes more extensive dosimetric and mechanical assessments under QMP supervision. The complete testing schedule and action limits should be applied according to the equipment configuration and relevant local requirements.

8. Does AAPM MPPG 18.a certify or endorse the KernelMed XT-5601?

No. MPPG 18.a is a medical physics practice guideline, not a product certification or manufacturer endorsement. Its recommendations apply to the low-energy superficial X-ray systems within its defined scope. The applicability of individual technical requirements to the XT-5601 must be evaluated using its verified technical specifications and intended clinical configuration.

References

[1] Lee YC, Lim SB, Mondalek PM, et al. AAPM Medical Physics Practice Guideline 18.a: Superficial radiation therapy using low-energy kilovoltage x-rays. Journal of Applied Clinical Medical Physics. 2026;27. First published online October 30, 2026.

https://doi.org/10.1002/acm2.70857

[2] Ma CM, Coffey CW, DeWerd LA, Liu C, Nath R, Seltzer SM, Seuntjens JP. AAPM protocol for 40–300 kV x-ray beam dosimetry in radiotherapy and radiobiology. Medical Physics. 2001;28(6):868–893.

https://doi.org/10.1118/1.1374247

[3] Lee YC, Davis SD, Romaguera W, et al. Implementation of superficial radiation therapy (SRT) using SRT-100 Vision for non-melanoma skin cancer in a Radiation Oncology clinic. Journal of Applied Clinical Medical Physics. 2023;24(6).

https://doi.org/10.1002/acm2.13926

[4] Lee YC, Romaguera W, Davis SD, et al. Initial three-and-a-half-year machine performance assessment of a superficial radiation therapy unit. Journal of Applied Clinical Medical Physics. 2025;26(10).

https://doi.org/10.1002/acm2.70258