Accelerated vs. Conventional Theta Burst Stimulation for Late-life Depression

The purpose of this trial is to compare the treatment efficacy (change in MADRS scores) of accelerated TBS to conventional TBS in participants with moderate to severe LLD at 4-weeks following accelerated TBS or following 30 once daily treatments of conventional TBS. Accelerated TBS group will receive 5 treatment sessions per day at approximately 1 hour intervals for 4 consecutive days on week 1 and 2 non-consecutive days on week 2. Conventional TBS group will receive 30 once daily treatment (approximately 6 weeks). Each treatment will consist of either 1) cTBS of right DLPFC followed by iTBS of left DLPFC; or 2) iTBS of left DLPFC.