The THREE-D Trial - iTBS Non-Inferior to Standard rTMS for Depression (Blumberger et al. 2018)
The THREE-D Trial - iTBS Non-Inferior to Standard rTMS for Depression (Blumberger et al. 2018)
What this study was
Who was studied
What the protocol involved
What the results showed
What it means and what it doesn't
Why this study matters for patients
What this study was
The THREE-D trial is the largest randomized controlled trial comparing intermittent theta burst stimulation to standard high-frequency rTMS for major depressive disorder. It was a non-inferiority trial, meaning its primary question was not whether iTBS was better than rTMS, but whether it was at least as good. It was conducted across multiple Canadian sites and published in The Lancet in 2018 by Blumberger, Vila-Rodriguez, Daskalakis and colleagues, one of the most rigorous TMS research groups in the world.
Who was studied
The trial enrolled 414 patients with major depressive disorder across two academic hospital sites. Patients were randomized to receive either iTBS or 10Hz rTMS in a once-daily format over several weeks. It is the largest head-to-head comparison of the two stimulation types published to date.
What the protocol involved
Patients received either: iTBS: 600 pulses per session delivered in the theta burst pattern approximately 3 minutes per session 10Hz rTMS: 3,000 pulses per session delivered at 10 pulses per second approximately 37 minutes per session
Both protocols targeted the left dorsolateral prefrontal cortex. Treatment was delivered once daily, five days per week. Total treatment duration was similar across groups.
What the results showed
iTBS was non-inferior to 10Hz rTMS for depression response and remission meeting the trial's primary endpoint, Response rates were statistically equivalent between the two groups, Session duration: 3 minutes for iTBS versus 37 minutes for rTMS, a clinically meaningful difference in patient burden per session, Adverse event profiles were similar between groups, iTBS was not associated with meaningful increases in side effects, The finding held across subgroups including patients with treatment-resistant depression
What it means and what it doesn't
The THREE-D trial established that iTBS delivers equivalent therapeutic outcomes to the gold standard 10Hz rTMS protocol in a fraction of the session time. This was the foundational evidence that enabled the development of accelerated iTBS protocols you cannot deliver ten 37-minute sessions in a day, but you can deliver ten 3-minute sessions with 30-minute intervals.
The trial used once-daily delivery it did not evaluate accelerated multi-session-per-day protocols. Its non-inferiority finding applies to equivalent session counts delivered once daily. The superiority of accelerated iTBS over traditional rTMS in published trials is a separate finding driven by session density and neuroplasticity window exploitation rather than stimulation type alone.
Why this study matters for patients
The THREE-D trial is the reason iTBS replaced 10Hz rTMS as the standard delivery method for TMS. It demonstrated that the more efficient pulse pattern works just as well and its efficiency is precisely what makes accelerated protocols with multiple daily sessions biologically feasible. Without the THREE-D finding, the SAINT protocol and ONE-D protocol could not exist in their current form.
Full text available at: https://doi.org/10.1016/S0140-6736(18)30295-2
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