Stereotactic Radiosurgery · Cranial
Brain Metastases
The highest-volume indication, and the field that moved decisively from whole-brain radiotherapy to focal radiosurgery
Brain metastases are the most common intracranial tumor and the largest single use of cranial radiosurgery. Over two decades the standard of care shifted from whole-brain radiotherapy toward stereotactic radiosurgery, driven by randomized data showing that adding whole-brain treatment to SRS worsens cognition without extending survival. This page covers the intact-lesion data and the cognition story, how many metastases can be treated focally, postoperative and preoperative cavity radiosurgery, dose by lesion size, and the central late problem of distinguishing radionecrosis from recurrence.
Orientation
Two randomized findings reframed the field. First, adding whole-brain radiotherapy (WBRT) to SRS improves intracranial control but worsens neurocognition and does not improve overall survival — so SRS alone, with MRI surveillance, became standard for limited metastases. Second, the number of lesions that can be treated focally has steadily risen: prospective data show comparable survival treating up to ten metastases with SRS as treating two to four. The clinical task is therefore less "SRS or WBRT" than "how much disease can I control focally while sparing the brain," with cavity radiosurgery after resection and careful late-effect surveillance completing the picture.
Intact Metastases and the Cognition Story
1.SRS alone versus adding whole-brain radiotherapy
Randomized trials established that WBRT added to SRS reduces distant intracranial failure but at a cognitive cost. Chang and colleagues (MD Anderson) found patients receiving SRS plus WBRT had significantly worse learning and memory at four months than SRS alone, and the trial was stopped early. The definitive cognition trial, N0574 (Brown, JAMA 2016), randomized patients with 1–3 metastases and found less cognitive deterioration at three months with SRS alone and no overall-survival difference, concluding SRS alone is the preferred strategy for limited brain metastases amenable to radiosurgery. The trade-off is more frequent distant brain failure with SRS alone, which is managed by serial MRI surveillance and salvage SRS rather than upfront WBRT in most patients.
How Many Metastases Is Too Many?
2.From "limited" to multiple lesions
The historical limit of treating only a few metastases has eroded. JLGK0901 (Yamamoto, Lancet Oncology 2014), a large prospective observational study, showed that overall survival in patients treated with SRS for 5–10 metastases was non-inferior to that for 2–4 metastases, without an excess of adverse events — supporting SRS as a reasonable upfront option well beyond the old three-lesion threshold. Contemporary practice increasingly weights total intracranial tumor volume and patient/systemic factors over a strict lesion count, and randomized trials comparing SRS with WBRT for higher numbers of metastases (e.g., > 4–15) are maturing. The practical point: a high lesion count alone is no longer an automatic indication for WBRT.
Postoperative and Preoperative Cavity Radiosurgery
3.After resection
For a resected metastasis, two randomized trials defined modern practice. Mahajan (MD Anderson, Lancet Oncology 2017) showed that postoperative cavity SRS improves local control versus observation. N107C/CEC.3 (Brown, Lancet Oncology 2017) showed that cavity SRS versus WBRT produces less cognitive decline with no overall-survival difference, establishing cavity SRS as a standard, less-toxic alternative to postoperative WBRT. Cavity SRS is technically harder than intact-lesion SRS: the target is larger and irregular, the dural/surgical margin must be considered, local control is somewhat lower than for small intact lesions, and there is a recognized risk of leptomeningeal disease after resection. Larger cavities are commonly hypofractionated (e.g., 3–5 fractions) to respect normal-brain tolerance.
4.Preoperative SRS — an emerging alternative
Treating the intact metastasis with SRS before resection is an increasingly studied strategy that offers a smaller, better-defined target, potentially lower rates of leptomeningeal spread and radionecrosis, and no need to wait for wound healing. It remains investigational pending randomized confirmation but is a legitimate option at experienced centers and an active trial question.
Dose, Radionecrosis, and Salvage
5.Dose by size, and the radionecrosis problem
Single-fraction marginal dose follows the size-based RTOG 90-05 maximum tolerated doses — 24 Gy for lesions ≤ 20 mm, 18 Gy for 21–30 mm, and 15 Gy for 31–40 mm (the smallest lesions are commonly prescribed toward the upper end, ~20–24 Gy) — with hypofractionation (e.g., 27 Gy/3 or 30 Gy/5) preferred for larger lesions and resection cavities to limit toxicity. The dominant late complication is radionecrosis, whose risk rises with the volume of normal brain receiving 12 Gy (V12Gy) and with prior or concurrent therapy. Distinguishing radionecrosis from tumor recurrence on follow-up imaging is a recurring challenge addressed with serial MRI, perfusion and advanced sequences, and occasionally biopsy; management of symptomatic necrosis includes corticosteroids, bevacizumab, and, in selected cases, laser interstitial thermal therapy or surgery. Repeat SRS is a reasonable salvage option for local or distant failure in appropriately selected patients.
| Scenario | Standard approach | Key trial |
|---|---|---|
| Limited intact metastases (1–3/4) | SRS alone + MRI surveillance (avoid routine WBRT) | N0574 (Brown 2016); Chang 2009 |
| 5–10 metastases | SRS reasonable upfront; weigh total volume | JLGK0901 (Yamamoto 2014) |
| Resected metastasis | Postoperative cavity SRS (not WBRT) | N107C (Brown 2017); Mahajan 2017 |
| Pre-resection | Preoperative SRS (investigational) | Prospective/registry; RCTs ongoing |
| Large lesion / cavity | Hypofractionated SRS (3–5 fx) | Series; HyTEC constraints |
| Lesion / cavity | Typical prescription | Radionecrosis consideration |
|---|---|---|
| ≤ 20 mm | Single-fraction ~20–24 Gy (24 Gy MTD) | Low if V12Gy small; smallest lesions tolerate the upper dose |
| 21–30 mm | Single-fraction 18 Gy, or 3-fraction ~27 Gy | Hypofractionation lowers symptomatic-necrosis risk at this size |
| 31–40 mm | 15 Gy single, or 27 Gy/3 to 30–35 Gy/5 | Hypofractionate; single-fraction 15 Gy gives weak control |
| Resection cavity | Single-fraction by size, or 3–5 fraction for large cavities | Larger cavities favor fractionation; margin on the cavity |
| V12Gy benchmark | — | Symptomatic necrosis ~10% at V12Gy ~5 cc, ~15% at ~10 cc, rising above |
Landmark Trials & Open Controversies
6.The randomized evidence, and what is still argued
Brain metastases are the best-randomized indication in cranial radiosurgery. The trials below define current practice; the debates that follow are genuinely open.
| Trial | What it established |
|---|---|
| Patchell 1990 (NEJM) | Surgery + WBRT beat WBRT alone for a single metastasis (survival, local control) |
| Aoyama 2006 (JAMA) | Adding WBRT to SRS cut intracranial recurrence but did not improve survival |
| Chang 2009 (Lancet Oncol) | SRS + WBRT worsened cognition versus SRS alone |
| EORTC 22952 (Kocher 2011) | Adjuvant WBRT reduced relapse but not survival or functional independence |
| N0574 / Brown 2016 (JAMA) | SRS alone — less cognitive decline, equal survival (1–3 mets) |
| JLGK0901 / Yamamoto 2014 (Lancet Oncol) | SRS for 5–10 mets non-inferior in survival to 2–4 |
| Mahajan 2017 / N107C Brown 2017 (Lancet Oncol) | Cavity SRS improves local control vs observation; less cognitive decline than WBRT |
| NRG CC001 / Brown 2020 (JCO) | Hippocampal-avoidance WBRT + memantine preserves cognition when WBRT is needed |
Open controversies:
- How many metastases is too many? The threshold has drifted from 1–3 toward up to ~10, and total intracranial tumor volume is increasingly viewed as the better selection metric than a raw lesion count.
- Whole-brain avoidance versus distant failure. SRS alone preserves cognition and survival but accepts more new distant metastases; the bargain only holds when paired with surveillance MRI and a willingness to deliver salvage SRS.
- Resection cavity: postoperative versus preoperative SRS. Postoperative cavity SRS is the standard, but carries cavity local failure and leptomeningeal-disease risk; preoperative (neoadjuvant) SRS — a smaller, better-defined target with potentially less leptomeningeal spread and radionecrosis — is promising but still investigational, with randomized trials ongoing.
- Timing with immunotherapy and targeted therapy. Concurrent SRS and CNS-active systemic therapy is common, but the optimal sequencing, the radionecrosis-versus-abscopal balance, and when to defer radiation in asymptomatic patients on effective systemic therapy remain unsettled.
Key points
- Adding WBRT to SRS worsens cognition without improving survival (Chang 2009; N0574/Brown 2016) — SRS alone + MRI surveillance is standard for limited metastases.
- Lesion-number limits have risen: SRS for 5–10 metastases is non-inferior in survival to 2–4 (JLGK0901); total tumor volume increasingly guides selection.
- After resection, cavity SRS improves local control vs observation (Mahajan) and causes less cognitive decline than WBRT with equal survival (N107C) — the postoperative standard.
- Preoperative SRS is a promising, still-investigational alternative (smaller target; potentially less leptomeningeal disease and radionecrosis).
- Dose by size per RTOG 90-05 (24/18/15 Gy MTD; smallest mets often prescribed ~20–24 Gy); hypofractionate large lesions and cavities; radionecrosis risk tracks V12Gy.
- Distinguishing radionecrosis from recurrence (perfusion/advanced MRI, sometimes biopsy) and offering salvage SRS are core to follow-up.
References
- Brown PD, Jaeckle K, Ballman KV, et al. Effect of radiosurgery alone vs radiosurgery with whole brain radiation therapy on cognitive function in patients with 1 to 3 brain metastases: a randomized clinical trial (N0574). JAMA. 2016;316(4):401–409. PubMed
- Yamamoto M, Serizawa T, Shuto T, et al. Stereotactic radiosurgery for patients with multiple brain metastases (JLGK0901): a multi-institutional prospective observational study. Lancet Oncol. 2014;15(4):387–395. PubMed
- Brown PD, Ballman KV, Cerhan JH, et al. Postoperative stereotactic radiosurgery compared with whole brain radiotherapy for resected metastatic brain disease (NCCTG N107C/CEC.3): a multicentre, randomised, controlled, phase 3 trial. Lancet Oncol. 2017;18(8):1049–1060. PubMed
- Mahajan A, Ahmed S, McAleer MF, et al. Post-operative stereotactic radiosurgery versus observation for completely resected brain metastases: a single-centre, randomised, controlled, phase 3 trial. Lancet Oncol. 2017;18(8):1040–1048. PubMed
- Chang EL, Wefel JS, Hess KR, et al. Neurocognition in patients with brain metastases treated with radiosurgery or radiosurgery plus whole-brain irradiation: a randomised controlled trial. Lancet Oncol. 2009;10(11):1037–1044. PubMed
- Aoyama H, Shirato H, Tago M, et al. Stereotactic radiosurgery plus whole-brain radiation therapy vs stereotactic radiosurgery alone for treatment of brain metastases: a randomized controlled trial. JAMA. 2006;295(21):2483–2491. PubMed
- 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
Educational synthesis for neurosurgery and radiation-oncology trainees; doses are representative and not a treatment directive. Landmark trials and guideline references verified during review.