Stereotactic Radiosurgery · Quick Reference

Quick Reference

Recommended imaging sequences, marginal doses, single-fraction limits, and organ-at-risk constraints at a glance

A consolidated reference for day-to-day planning: the MRI sequences worth acquiring per indication, the representative marginal/prescription doses for the main cranial and spine targets, the single-fraction maximum tolerated doses by lesion size, and the commonly cited organ-at-risk constraints. Every value here is a starting point for multidisciplinary planning, not a prescription; final dose and technique are individualized and follow the current constraint set adopted by your physics and radiation-oncology team.

Timoteo Almeida, MD, MSc, PhD, FCNS | Departments of Neurological Surgery and Radiation Oncology

Orientation

This page is deliberately tabular. The detailed reasoning, evidence, and citations behind each number live on the corresponding disease and technical pages; here the goal is fast retrieval. Read the caveats in each caption: doses are representative ranges from the literature and converge differently across centers and platforms. The full decision framework is on the Dose Selection & Fractionation page.

Part I

Recommended Imaging

1.MRI sequences by indication

Representative high-yield planning studies. Use a thin, contiguous stereotactic protocol, adapt to the validated local workflow, and obtain imaging as close to treatment as practical.
Indication	Core planning imaging	Adjunct / problem-solving imaging
Brain metastases	≤1 mm isotropic pre/post-contrast 3D T1 (MPRAGE, SPGR/BRAVO, or TFE); T2/FLAIR; DWI	3D TSE/black-blood (SPACE, CUBE, or VISTA); delayed post-contrast acquisition
Vestibular / cranial-nerve schwannoma	Thin post-contrast 3D T1 plus CISS/FIESTA/SPACE for nerve and cochlea	Thin CT for internal auditory canal, cochlea, or skull-base bone
Meningioma	Volumetric post-contrast 3D T1; T2/FLAIR	CT for hyperostosis/bone; selected somatostatin-receptor PET for complex disease
Pituitary / parasellar	Dedicated thin sellar pre/post-contrast T1; T2; precise optic-apparatus contouring	Dynamic contrast for microadenoma; fat suppression after grafting
Trigeminal neuralgia	High-resolution heavily T2-weighted cisternography (CISS/FIESTA) through nerve and REZ	Thin post-contrast 3D T1; TOF-MRA when vascular anatomy needs clarification
Tremor / thalamotomy	Isotropic stereotactic 3D T1 with AC-PC definition; FGATIR	DRTT tractography as an adjunct; coordinate/atlas targeting remains primary
AVM	Stereotactic DSA plus MRI/MRA	TOF/time-resolved MRA; CTA for selected angioarchitecture or embolic material
Cavernous malformation	T2 plus GRE/SWI to define lesion and hemosiderin boundary	Post-contrast 3D T1 and DVA assessment
Epilepsy / hypothalamic hamartoma	Isotropic 3D T1 plus thin coronal T2/FLAIR oriented to the hippocampi or lesion	Dedicated epilepsy-protocol functional/metabolic studies as indicated
Spine SBRT	Thin T1 and T2 co-registered to planning CT for cord/thecal sac and target	CT myelogram if MRI is inadequate, contraindicated, or degraded by hardware

Image age matters Use planning imaging that still represents the anatomy at treatment. For brain metastases, aim for MRI within 7 days of SRS; same-day imaging is ideal in frame-based workflows. Repeat sooner for large or rapidly changing lesions, recent cavities, changing edema or corticosteroid dose, or new neurologic findings.

Part II

Marginal / Prescription Doses

2.Cranial single-fraction targets

Representative single-fraction starting ranges. Individualize by size/volume, location, prior RT, normal-tissue exposure, and treatment intent; use fractionation when a safe single-fraction plan is not achievable.
Target	Representative dose	Convention / dominant modifier
Brain metastasis <2 cm	20–24 Gy / 1 fx	Prescription dose; reduce or fractionate for OAR proximity or excessive normal-brain dose
Brain metastasis 2–4 cm	15–18 Gy / 1 fx or commonly 27 Gy / 3 fx to 30 Gy / 5 fx	Size, volume, location, symptoms, and V12Gy favor fractionation as targets enlarge
Vestibular schwannoma	12–13 Gy	Margin dose; baseline hearing and cochlear dose dominate
Other cranial-nerve schwannoma	~11–14 Gy	Margin dose; nerve, brainstem, cochlear, and optic proximity
Meningioma, presumed WHO grade I	~12–16 Gy (often 13–15)	Margin dose; fractionate perioptic targets; higher grade is a different treatment problem
Pituitary, nonfunctioning	~14–16 Gy	Margin dose for control; optic apparatus limits feasibility
Pituitary, functioning	~18–30 Gy	Margin dose for biochemical remission; subtype and optic dose matter
Craniopharyngioma	~12–15 Gy in selected single-fraction cases	Cyst dynamics and optic proximity often favor fractionation
Hemangioblastoma	~15–18 Gy	Treat the solid nodule; cyst behavior and VHL disease affect strategy
Glomus / paraganglioma	~13–16 Gy	Margin dose; goal is durable control and cranial-nerve preservation
AVM	~16–25 Gy (often 18–21)	Nidus margin dose; volume and eloquent location dominate
Cavernous malformation, selected	~12–13 Gy	Margin dose; only for carefully selected, surgically inaccessible hemorrhagic lesions
Trigeminal neuralgia	~80–90 Gy maximum	Maximum dose through a 4-mm shot; target position trades pain control against numbness
Vim thalamotomy	~130–140 Gy maximum (series span 130–150 Gy)	Maximum lesioning dose through a 4-mm shot; unilateral, delayed, irreversible

The prescription isodose percentage is intentionally omitted: Gamma Knife, LINAC, and robotic plans normalize differently. Report the clinically meaningful prescription or maximum dose, target coverage, hotspot, conformity, gradient, and normal-tissue exposure rather than treating a platform-specific isodose percentage as a disease dose.

3.Single-fraction MTD by size (RTOG 90-05)

RTOG 90-05 maximum tolerated single-fraction doses by maximum tumor diameter (previously irradiated brain; widely used as a ceiling reference).
Maximum diameter	Single-fraction dose
≤ 20 mm	24 Gy
21–30 mm	18 Gy
31–40 mm	15 Gy

4.Spine SBRT schedules

Common spine schedules (choose by tumor, cord proximity, prior RT, and postoperative status; cord limits are protocol-specific).
Schedule	Note
16–24 Gy / 1 fx	High local control; steepest cord challenge, higher fracture risk
24 Gy / 2 fx	SC.24 regimen with randomized pain benefit
27 Gy / 3 fx	Common for larger volumes / postoperative beds
30–40 Gy / 5 fx	When cord or long segment limits hypofractionation; common postop

Part III

Organ-at-Risk Constraints

5.Commonly cited limits

Representative single-fraction OAR constraints (use the current adopted constraint set, e.g., TG-101/HyTEC; fractionated limits differ).
Structure	Representative single-fraction limit
Optic apparatus (nerves/chiasm)	Single-fraction planning goal is Dmax under 10 Gy. HyTEC recommends no more than 10 Gy in 1 fx, 20 Gy in 3 fx, and 25 Gy in 5 fx without prior RT, each at roughly 1% RION risk; after prior irradiation a >10% risk is anticipated at those same doses
Brainstem	Protocol- and volume-specific; many single-fraction plans use a point maximum in the ~12.5–15 Gy range
Spinal cord / thecal sac	Do not interchange true-cord, thecal-sac, and PRV limits; de novo HyTEC tolerance estimates are not automatic planning constraints
Cochlea (hearing preservation)	Mean below about 4 Gy when hearing is serviceable; keep as low as feasible without compromising target coverage
Lens	As low as reasonably achievable
Radionecrosis predictor (brain)	Track V12Gy (volume receiving ≥12 Gy)

Starting points, not prescriptions Every dose and constraint on this page is a representative literature value for orientation. Final prescription, fractionation, and OAR limits are individualized and must follow current guidance and consensus documents (TG-101, QUANTEC, HyTEC), the dose ceilings established by RTOG 90-05, and the constraint set your center has adopted. Cord and optic limits in particular are tighter in the reirradiation setting.

Key points

Imaging: use ≤1 mm isotropic post-contrast 3D T1 for metastases, acquire it within 7 days of treatment when practical, and add indication-specific sequences rather than relying on one generic tumor protocol.
MPRAGE, SPGR/BRAVO, and TFE are vendor-specific implementations of the core 3D T1 role; 3D TSE/black-blood imaging can complement them for small metastases.
FGATIR adds patient-specific thalamic and capsular anatomy for tremor targeting, but remains an adjunct to validated coordinate/atlas methods and, when used, tractography.
Representative cranial doses: small metastasis 20–24 Gy/1 fx, VS 12–13 Gy, benign meningioma 12–16 Gy, nonfunctioning pituitary 14–16 Gy (functioning 18–30), AVM 16–25 Gy, TN 80–90 Gy maximum, Vim thalamotomy ~130–140 Gy maximum.
RTOG 90-05 single-fraction ceiling: 24 / 18 / 15 Gy for ≤20 / 21–30 / 31–40 mm.
Spine: 16–24 Gy/1 fx, 24 Gy/2 fx (SC.24), 27 Gy/3 fx, 30–40 Gy/5 fx; cord Dmax limits are protocol-specific and tighter on reirradiation.
OAR limits require the exact metric and contour: the single-fraction optic planning goal is a Dmax under 10 Gy, the dose HyTEC ties to about 1% radiation-induced optic neuropathy without prior RT; brainstem and cord constraints depend on exposed volume, true structure versus surrogate/PRV, fractionation, and prior RT.

References

Gondi V, Bauman G, Bradfield L, et al. Radiation therapy for brain metastases: an ASTRO clinical practice guideline. Pract Radiat Oncol. 2022;12(4):265–282. PubMed
Grishchuk D, Dimitriadis A, Sahgal A, et al. ISRS technical guidelines for stereotactic radiosurgery: treatment of small brain metastases (≤1 cm in diameter). Pract Radiat Oncol. 2023;13(3):183–194. PubMed
Kaufmann TJ, Smits M, Boxerman J, et al. Consensus recommendations for a standardized brain tumor imaging protocol for clinical trials in brain metastases. Neuro Oncol. 2020;22(6):757–772. PubMed
Shaw E, Scott C, Souhami L, et al. Single-dose radiosurgical treatment of recurrent previously irradiated primary brain tumors and brain metastases (RTOG 90-05). Int J Radiat Oncol Biol Phys. 2000;47(2):291–298. PubMed
Benedict SH, Yenice KM, Followill D, et al. Stereotactic body radiation therapy: AAPM Task Group 101. Med Phys. 2010;37(8):4078–4101. PubMed
Milano MT, Grimm J, Niemierko A, et al. HyTEC: single- and multifraction SRS dose/volume tolerances of the brain. Int J Radiat Oncol Biol Phys. 2021;110(1):68–86. PubMed
Milano MT, Grimm J, Soltys SG, et al. Single- and multifraction stereotactic radiosurgery dose tolerances of the optic pathways (HyTEC). Int J Radiat Oncol Biol Phys. 2021;110(1):87–99. PubMed
Sahgal A, Weinberg V, Ma L, et al. Probabilities of radiation myelopathy specific to stereotactic body radiation therapy to guide safe practice. Int J Radiat Oncol Biol Phys. 2013;85(2):341–347. PubMed

Educational quick reference for neurosurgery and radiation-oncology trainees; not a treatment directive. All values are representative literature ranges; defer to current consensus documents and your center's adopted constraint set. Detailed evidence and citations are on the corresponding disease and technical pages.