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Gated Prostate Radiotherapy: Accuracy and Dosimetric Results From First Clinical Study with Kilovoltage Intrafraction Monitoring

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J Booth

J Booth1,2*, J Ng2 , R O'Brien2 , P Keall2 , P Poulsen3 , V Calliet1 , P Juneja2,1 , T Eade1 , A Kneebone1 , (1) Royal North Shore Hospital, St Leonards, ,(2) University of Sydney, Sydney, NSW, (3) Aarhus University Hospital, Aarhus, Aarhus C


TH-AB-303-9 (Thursday, July 16, 2015) 7:30 AM - 9:30 AM Room: 303

Purpose: The purpose of this study is to investigate the localisation accuracy and dosimetric impact of a new real-time IGRT system, kilovoltage intrafraction monitoring (KIM), in a gated prostate cancer radiotherapy clinical trial.
Methods: KIM uses kV fluoroscopy to monitor, in real-time, the 3D position of radio-opaque markers implanted into the prostate target. The real-time target position is used to guide the treatment: if the prostate moves outside the tolerance (displacement exceeding 3mm for 5 seconds) the beam is paused and the patient is repositioned. Localisation accuracy is calculated offline by comparing using triangulation when markers are visible in both kV and MV images (ground truth) with the KIM determined positions. Dosimetric accuracy is calculated for fractions with gating events by comparing reconstructed delivered dose (with or without simulated gating events) against planned doses.
Results: Seven patients have been recruited to the KIM study, with 4 patients completed treatment. Localisation accuracy of KIM from the 126 fractions to date is 0.1±0.5, 0.3±0.3, and -0.5±0.4 mm in the LR, SI and AP directions, respectively. Prostate gating and couch shift correction was applied in 15 fractions, which reduced the mean prostate position error from 3.9±1.4 mm (simulated no gating) to 2.0±1.2 mm. Delivered target doses (PTV D95%) were closer to planned with gating -1.4% compared to simulated no gating 3.2%. Delivered OAR doses were also closer to planned with gating compared to simulated no gating, mean (range) differences were respectively: rectum V65% -3.5 (-9.4, 5.7) & -5.0 (-11.2,18.7); and bladder V65% 3.2 (-0.9, 25.3) & 4.7 (-1.0, 30.5).
Conclusion: KIM gating for prostate radiotherapy has been clinically implemented with sub-millimeter accuracy and improved agreement between the planned and delivered dose distributions. The KIM technology has wide-scale applicability as it is implemented on a standard linear accelerator with little modification.

Funding Support, Disclosures, and Conflict of Interest: Varian Collaborative Research Agreement Cancer Australia NHMRC Australia

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