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Recent technological advances make it possible to monitor prostate movement during radiation delivery. Using previously published data from 35 patients who underwent continuous localization during prostate cancer treatment, we simulated various interventions to identify the radiation-gating and patient-repositioning strategies that least prolonged the time to complete the daily treatment. Acceptable response protocols were those that resulted in at least 95% of patients' prostates remaining within the planning margins at least 95% of the time. Gating and repositioning were not necessary for margins of 7 or 10 mm because of the rarity of excursions at these margins. However, intervention was routinely necessary for margins of 3 and 5 mm. In simulated interventions for which the therapist could reposition the treatment couch without entering the room, the most time-efficient response protocol was to reposition the couch immediately after the prostate position was outside the treatment margins. In simulations in which the therapist had to enter the room to reposition the couch, overall treatment time could be reduced and accuracy could be increased by manually gating treatment for 11 and 21 s for 3- and 5-mm margins, respectively, before interrupting treatment to reposition the treatment couch.

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