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Is MLC Tracking Or Gating a Better Real-Time Correction Strategy? An Analysis of the TROG 15.01 Stereotactic Prostate Ablative Radiotherapy with KIM (SPARK) Trial

E Hewson1*, D Nguyen1 , R O'Brien1 , P Poulsen2 , J Booth3 , P Greer4 , T Eade3 , A Kneebone3 , G Hruby3 , T Moodie5 , A Hayden5 , S Turner5 , N Hardcastle6 , S Siva6 , K Tai6 , J Martin4 , P Keall1 , (1) ACRF Image X Institute, University of Sydney, Sydney, NSW, (2) Aarhus University Hospital, Aarhus C (3) Royal North Shore Hospital, St Leonards, NSW, (4) Calvary Mater Newcastle, Newcastle, Newcastle, NSW (5) Crown Princess Mary Cancer Centre, Westmead, NSW, (6) Peter MacCallum Cancer Centre, Melbourne, VIC


(Monday, 7/15/2019) 4:30 PM - 6:00 PM

Room: Stars at Night Ballroom 2-3

Purpose: This study assessed the delivered dose accuracy using multileaf collimator (MLC) tracking or gating as motion correction strategies in conjunction with real-time image guidance for the TROG 15.01 Stereotactic Prostate Ablative Radiotherapy with KIM (SPARK) trial.

Methods: Thirty-nine patients with prostate cancer treated with KIM-guided SABR delivering 36.25Gy to the prostate in five fractions were analysed in this study. During treatment the prostate motion was corrected in real-time using MLC tracking (49 fractions) or beam gating with couch shifts (142 fractions) where intervention occurred when motion exceeded 2mm. A time-resolved motion encoded dose reconstruction method was used to retrospectively evaluate the delivered dose to the target and organs at risk for each fraction.

Results: An independent samples t-test revealed a statistically significant but small difference in discrepancies from the plan between MLC tracking and gating for the CTV D98%, PTV D95% and rectum V30Gy (Δmean=0.32% p=0.04, Δmean=-0.35% p=0.03 and Δmean=-0.38% p=0.02 respectively). No significant differences were found between MLC tracking and gating for the bladder V30Gy (p>0.05). With MLC tracking, the CTV D98% and PTV D95% doses were maintained within 3.2% and 2.3% of the plan. With gating, including 60/142 fractions which required intervention, the CTV and PTV doses were maintained within 4.6% and 5.2%. MLC tracking maintained the bladder V30Gy and rectum V30Gy doses to within 1.3% and 2.5% of the plan, while gating maintained the bladder and rectum doses to within 3.4% and 3.5% of the plan.

Conclusion: MLC tracking and gating was compared for the same prospective patient cohort and were both found to be effective methods to maintain high dose accuracy to the prostate as well as the organs at risk. While both methods were similar dosimetrically, gating requires treatment interruption and manual intervention which is not required with MLC tracking.

Funding Support, Disclosures, and Conflict of Interest: Nguyen is supported by NHMRC and Cancer Institute NSW early career fellowships. O'Brien is supported by a Cancer Institute NSW Career Development fellowship. Keall is supported by an NHMRC Senior Principal Research Fellowship. Keall is an inventor on one licensed patent and one unlicensed patent related to MLC tracking.


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