Efficient use of continuous, real-time prostate localization

Abstract

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.

Sensitivity of postplanning target and OAR coverage estimates to dosimetric margin distribution sampling parameters

“…The assumed baseline parameter values ⌺ = = 3 mm are broadly in line with the values reported in literature for setup to external markers. 21 For image-guided setup, interfraction setup errors will be smaller, but in order to properly account for geometric uncertainties, one should also account for intrafraction motion [22][23][24] and delineation errors. 25 The present work did not go to this level of detail.…”

A Failure Detection Strategy for Intrafraction Prostate Motion Monitoring With On-Board Imagers for Fixed-Gantry IMRT

“…Most methods use implanted markers. Current commercially available 3D position monitoring options include stereoscopic x-ray imaging systems (8,16), which consist of two kV x-ray sources (mounted either on the ceiling or on the gantry) respectively paired with opposed x-ray imagers, and an electromagnetic localization system (Calypso) (3,4,10,11,14). Usage of the first method has to be weighed against the additional kV imaging dose to which patients are exposed.…”

“…The prostate is mostly stationary and drifts slowly, with abrupt movement occurring only occasionally (4,(10)(11)(12). Therefore, in contrast with current motion monitoring techniques that seek to accurately and continuously localize a moving target, in a previous study (13), we attempted for the first step to detect only potential motion beyond a predefined threshold.…”

“…This MV-only 3D localization approach would not appear to apply to real-time displacement estimation during fixed-gantry IMRT, however. Although prostate motion is unpredictable, Calypso (Calypso Medical Technologies Inc, Seattle, WA) real-time monitoring data (3,4,10,11,14) demonstrated that it is not completely random. The goal of this study is to develop an MV data processing method that is suitable for the ''failure'' detection scheme during IMRT by incorporating simple assumptions based on prior knowledge of prostate motion without introducing complicated statistical models and requiring neither population-based nor pretreatment patient-specific training data.…”

Clinical development of a failure detection‐based online repositioning strategy for prostate IMRT—Experiments, simulation, and dosimetry study

“…15 The prostate is mostly stationary and drifts slowly with abrupt motion occurring only occasionally. [16][17][18][19][20][21][22][23] In contrast with current motion monitoring techniques, which seek to accurately and continuously localize a moving target, we proposed and simulated a "failure" detection strategy 24 to detect in a first step only motion that is potentially beyond a predefined threshold using treatment beam MV imaging, available at no tracking dose cost. The correlative relationship between directional components of prostate motion [17][18][19] was used for the first step estimation.…”