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Stereotactic treatment gives a very high dose in one to a few sessions to a small target, so a small error matters more than in ordinary radiotherapy. The team uses a firm head frame or a close-fitting mask or body cushion, checks the plan with an independent calculation, takes images to confirm the target's position before every treatment, and has a physicist present for the first session.
AAPM-RSS MPPG 9.b (2025) sets minimum practice for linac SRS and SBRT in the United States. The service needs standard operating procedures for every step, a safety checklist, participation in an incident learning system, at least two radiation therapists at every session (one trained in the technique), 4D CT for thoracic and abdominal SBRT, and MRI and PET fusion. At simulation the therapists prepare immobilisation and document set-up after the radiation oncologist approves position, images and target localisation. In planning, prior radiotherapy plans are obtained for re-irradiation and cumulative dose reported; brain metastases are named with the MRI date so new and old targets cannot be confused; a calculation grid of 2 mm or finer is used (1 mm for targets of 1 cc or less); the radiation oncologist signs the plan; an independent dose calculation and a physicist's plan and chart review are done before treatment. At delivery a pre-treatment QA check including a dry-run collision check is done, target localisation is verified by imaging before every treatment, imaging-to-treatment isocentre coincidence must be within 1 mm for SRS and 1.5 mm for SBRT (tested daily on treatment days), and a qualified medical physicist personally supervises the first session and directly supervises the rest (new in 9.b). For frameless intracranial SRS, open-face masks let surface guidance use the face. In one randomised trial of SRS for brain metastases, a 1 mm margin around the visible tumour gave similar local control to 3 mm with less radionecrosis (5 of 6 biopsy-proven cases in the 3 mm arm, P=.10), and the authors judged 1 mm more appropriate.
Why: Checklists catch the slips that matter most when the whole dose is given in one or a few sessions.
“Establishment of a comprehensive safety checklist to act as a guide for the entire treatment process, and determine appropriate methods for the clinic's QA committee to monitor the SRS-SBRT program.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: The position at the planning scan has to be repeatable to within a millimetre or two at treatment.
“For each simulation session, prepare immobilization devices, position the patient, and acquire images for treatment planning in accordance with the clinic's SRS-SBRT procedure and the patient-specific instructions, and document treatment setup parameters after the radiation oncologist has approved the positioning, images, and target localization.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: Tumours in the chest and upper abdomen move with breathing, and the plan must account for it.
“Four-dimensional computed tomography (4D CT) capability (for thoracic and abdominal SBRT services).”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: Treating the wrong lesion, or overdosing an area treated before, are known stereotactic errors.
“In the case of multiple brain metastases and re-irradiation, a target naming convention that makes clear which targets are new and which are old must be utilized; for example, include the date of the MR scan at the end of the target structure's name.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: Small targets and steep dose fall-off need a fine calculation to be accurate.
“The use of an isotropic calculation grid size of 2 mm or finer should be utilized.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: A second, separate check of a high-dose plan is the main protection against a planning error reaching the patient.
“An independent dose calculation check must be performed prior to treatment.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: Stereotactic beams often come from unusual angles close to the patient.
“This should include a “dry run” collision check where the potential for collision exists.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: A few millimetres off can mean missing the tumour or hitting a nearby organ with a very high dose.
“Pre-treatment verification of target localization must always be performed; the criteria for intra-treatment image guidance should be clearly described.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: The images are only useful if the machine treats exactly where the images say.
“AAPM MPPG 2.b states that the composite tolerance of the imaging-treatment isocenter coincidence and table repositioning accuracy must be ≤1 mm for SRS and ≤1.5 mm for SBRT, tested daily when SRS-SBRT treatments are conducted.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: Experienced eyes at the machine catch problems before the beam is switched on.
“For the first treatment session the QMP must provide personal supervision of the session.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
Why: Learning from near misses prevents the next real error.
“Facilitation and management of the clinic's participation in an incident learning system to ensure a transparent, structured evaluation of all “near miss” and actual deviations in the planning and treatment delivery process.”
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · Minimum practice guideline (ungraded)
How care is usually carried out, read from the guidelines and standards cited. Your own team's protocol and their judgement come first; this page is for understanding it, not for doing it yourself.
AAPM-RSS MPPG 9.b (2025) is the most recent and most detailed guideline read: written procedures and a checklist for every step, an independent dose calculation and physicist plan review before treatment, imaging verification of the target before every treatment, daily isocentre coincidence within 1 mm (SRS) or 1.5 mm (SBRT), at least two trained therapists at every session and a physicist personally present at the first, and participation in incident learning. For brain metastases treated with image-guided linac SRS, one randomised trial supports a 1 mm rather than a 3 mm margin. European and UK guidance (ESTRO ACROP for lung SBRT, the UK SABR Consortium) cover the same ground; they were read only as an abstract or not at all, so differences in detail could not be compared.
American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 · International Journal of Radiation Oncology, Biology, Physics (Kirkpatrick et al.) 2015 · ESTRO ACROP (Guckenberger et al., Radiotherapy and Oncology) 2017 · American Association of Physicists in Medicine (Benedict et al., Medical Physics) 2010
Where it differs: A stereotactic head frame is fixed to the skull under local anaesthetic on the day of treatment; frameless SRS uses a thermoplastic mask (often open-face, with surface guidance on the exposed face) and image guidance. MPPG 9.b requires the procedure, tolerances and supervision for each treatment type to be written down and notes that open-face masks let the face serve as a reference surface for frameless SRS.
Evidence: No comparative trial was read here; MPPG 9.b treats both as acceptable when commissioned and verified.
Where it differs: A European consensus of eight institutions found only 8 of 57 technologies and techniques mandatory and 32 optional, but half of quality assurance items mandatory, and agreed risk-adapted doses of 3 x 15 Gy for peripheral lesions and 4 x 12 Gy for lesions with broad chest wall contact.
Evidence: Questionnaire-based expert consensus; read as an abstract.
ESTRO ACROP (Guckenberger et al., Radiotherapy and Oncology) 2017
| Recommendation | Grade, as printed | Source |
|---|---|---|
| A 1 mm margin is more appropriate than 3 mm for image-guided SRS of brain metastases “However, given the higher potential risk of RN with a 3-mm margin, a 1-mm GTV expansion is more appropriate.” | Single randomised trial (49 patients, 80 metastases) | International Journal of Radiation Oncology, Biology, Physics (Kirkpatrick et al.) 2015 |
| Personal physicist supervision for the first session is new in the 2025 guideline “The new language requires personal supervision for the first treatment session of SRS-SBRT and direct treatment supervision after the initial fraction.” | Minimum practice guideline (ungraded) | American Association of Physicists in Medicine and Radiosurgery Society (Journal of Applied Clinical Medical Physics) 2025 |
| European consensus treats few techniques but many QA items as mandatory “Only 8/57 technologies and techniques were identified as mandatory for SBRT while 32/57 were considered as optional.” | Expert consensus (questionnaire, 8 institutions) | ESTRO ACROP (Guckenberger et al., Radiotherapy and Oncology) 2017 |
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Shares Surface-guided radiotherapy (SGRT), Respiratory motion management (4D-CT, gating, breath-hold, tracking), In-room imaging for radiotherapy (cone-beam CT, ExacTrac, CT-on-rails, HyperSight).
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Shares In-room imaging for radiotherapy (cone-beam CT, ExacTrac, CT-on-rails, HyperSight), CyberKnife robotic radiosurgery, Stereotactic radiosurgery (Gamma Knife, CyberKnife, linac SRS), SBRT / SABR (stereotactic radiotherapy).
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