ESTRO 38 Abstract book

S442 ESTRO 38

Australia ; 4 Calvary Mater Newcastle Hospital, Department of Radiation Oncology, Newcastle, Australia ; 5 Westmead Hospital, Crown Princess Mary Cancer Centre, Sydney, Australia ; 6 Liverpool Hospital, Liverpool and Macarthur Cancer Therapy Centres, Sydney, Australia ; 7 Peter MacCallum Cancer Centre, Department of Physical Sciences, Melbourne, Australia ; 8 Peter MacCallum Cancer Centre, Department of Radiation Oncology, Melbourne, Australia ; 9 University of Sydney, NHMRC Clinical Trials Centre, Sydney, Australia Purpose or Objective Kilovoltage Intrafraction Monitoring (KIM) is an emerging real-time target tracking technology for standard linear accelerators without the need for additional in-room hardware. In the TROG 15.01 Stereotactic Prostate Ablative Radiotherapy (SABR) with KIM (SPARK) trial, KIM was used to enable real-time target tracking in a multi- institutional setting. We test the primary hypothesis that real-time target tracking improves prostate dose distributions. Material and Methods Forty-eight men with prostate cancer were treated with KIM-guided SABR delivering 36.25 Gy to the prostate in five treatments. During treatment the prostate (target) motion was corrected in real-time by implementing KIM- guided beam gating with couch shifts or multileaf collimator tracking. A dose reconstruction method was used to evaluate the dose to the target and organs at risk (OARs) with real-time KIM target tracking. The same dose reconstruction method was used to evaluate the dose that would have been delivered without real-time target tracking. Thus, all cases acted as their own internal controls. A treatment was considered a success if the target and rectal dose with real-time target tracking were closer to the planned dose than the target and rectal dose estimated without real-time target tracking. The prostate dose was represented by the dose to 95% of the planning target volume. The rectal dose was represented by the rectal volume receiving above 30 Gy. The trial was designed with 90% power and 95% confidence to rule in a KIM success rate of 2/3 in favour of the futility rate of 1/3. Results Motion correction via beam gating or multileaf collimator tracking occurred in 51% (121/235) of the treatments where real-time target tracking was performed. The proportion of motion-corrected treatments with an improvement in dose distribution to both the prostate and rectum was 72% (87/121 treatments), significantly higher than the 33% prospectively defined futility cutpoint (p<0.0001, χ 2 ). The prostate dose with KIM was closer to the plan by an average of 4.6% (range -1.7% to 41%). The rectal dose with KIM was closer to the plan by an average of 1.5% (range -1.2% to 9.7%). Waterfall plots of the prostate and rectal doses are shown in Figure 1.

Purpose or Objective After external beam radiotherapy (EBRT) for prostate cancer, the most common site of recurrence is the prostate. The aim was to assess the efficacy and safety of salvage stereotactic body radiotherapy (SBRT) for local prostate cancer recurrence after radiotherapy. Material and Methods We retrospectively reviewed patients with biopsy proven local prostate cancer recurrence after EBRT or brachytherapy in centers from the French Genito-Urinary Group (GETUG) and in the European Institute of Oncology in Milan. Disease extension was assessed by pelvic multiparametric MRI and choline PET in 87% and 94% of patients, respectively. Treatment was proposed by multidisciplinary team in each center and delivered every other day. Median SBRT dose was 36 Gy (range, 25-36.25 Gy) in 6 fractions (range, 5-6). The primary endpoint was second biochemical recurrence-free survival defined according to the Phoenix criteria. Toxicity was assessed according to CTCAE v.4.03. Results Between April 2010 and January 2017, 99 patients were treated with salvage SBRT with a median follow-up of 22.8 months (range 2.4-88.8 months). Twenty-two, 36 and 41 patients presented with low, intermediate and high risk at first diagnosis according to D’Amico classification. All patients presented with biopsy proven recurrence. The median time interval between first radiotherapy and salvage SBRT was 7.5 years (range 2-18 years). Median age at salvage SBRT was 71.2 years (SD 6.4 years) and median PSA at recurrence was 4.3 ng/mL (range, 2-38 ng/mL). Thirty four percent of patients were treated with androgen deprivation therapy for a median duration of 12 months. Whole gland, half prostate and focal treatment was delivered in 48, 18 and 33 patients respectively. Median nadir PSA after salvage SBRT was 0.5 ng/mL, obtained after a median time interval of 10.7 months. Second biochemical recurrence-free survival rates at 2 and 3 years were 72% [95% CI: 60%–81%] and 52% [95% CI: 39%–64%], respectively. Overall survival rates at 2 and 5 years were 96% [95% CI: 87-99] and 87% [95% CI: 71-95], respectively. The initial D’Amico prognostic group was the only prognostic factor of biochemical recurrence-free survival (p=0.025). No patient developed grade ≥ 2 acute gastro-intestinal toxicity; grade 2 and 3 acute genito-urinary toxicity were 8% and 1%, respectively. Late toxicity included urinary events (fifteen grade 2 and one grade 3) and rectal events (two grade 2). One patient presented a neuritis of grade 3. Conclusion With a short follow up, this largest series shows that salvage SBRT allows for good biochemical control and acceptable toxicity, with the key advantage of non- invasiveness of SBRT. This treatment is not a standard, and has to be administered with caution in competent centers. Further prospective studies are necessary to confirm these preliminary results 1 1 https://clinicaltrials.gov/ct2/show/NCT03438552 PO-0842 Real-Time tracking improves treatment: The TROG Stereo Prostate Ablative Radiotherapy with KIM trial P. Keall 1 , D.T. Nguyen 1 , R. O'Brien 1 , E. Hewson 1 , H. Ball 1 , P. Poulsen 2 , J. Booth 3 , P. Greer 4 , P. Hunter 4 , L. Wilton 4 , R. Bromley 3 , J. Kipritidis 3 , T. Eade 3 , A. Kneebone 3 , G. Hruby 3 , T. Moodie 5 , A. Hayden 5 , S. Turner 5 , S. Arumugam 6 , M. Sidhom 6 , N. Hardcastle 7 , S. Siva 8 , K. Tai 8 , V. Gebski 9 , J. Martin 4 1 University of Sydney, ACRF Image X Institute, Sydney, Australia ; 2 Aarhus University Hosptial, Department of Oncology, Aarhus, Denmark ; 3 Royal North Shore Hospital, Northern Sydney Cancer Centre, Sydney,