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Top Line: Real-time intrafraction KV target monitoring is an ultra-fancy way to provide image guidance during ultra-hypofractionated prostate radiation.
The Study: But does it add any value above and beyond initial fiducial alignment via 3D-3D imaging match? That’s what this Aussie single-arm feasibility study (n=48) aims to tell us. First, what’s meant by intrafraction monitoring? During delivery of 7.25 Gy x 5 = 36.25 Gy to the prostate, if continually KV-tracked prostate fiducials moved ≥2-3 mm for ≥5 seconds, either beam gating with couch shifts was manually engaged (the practice at 4 participating institutions) or MLC tracking was automatically engaged (the practice at 1 participating institution). These thresholds were selected based on the smallest planning margins used to create the target. Half of all treatments required such modifications, affecting 88% of patients. To assess the primary outcome of dose delivery accuracy, real-time KV-images were superimposed on the planning CT to calculate what dose was / would have been delivered with / without corrections. In the end, roughly 5% of treatments would have delivered a dose to the clinical target ≥5% less than planned without intrafraction tracking versus none with tracking. On average, the delivered dose to the clinical target was 1% closer to the planned dose with the addition of intrafraction monitoring. Now, back to the original question of adding something of value, it should come as no surprise there was no demonstrable difference in clinical toxicity or patient-reported outcomes when compared to baseline.
TBL: While what we can do continually advances, what we should do remains guided by logic, efficiency, and our best value judgements. | Keall, Int J Radiat Oncol Biol Phys 2020