ESTRO 37 Abstract book

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ESTRO 37

separated by 2 weeks, each with 2 fractions of 9.5 Gy. Finally, they adopted 3 implants, separated by 3 weeks, each with a single fraction of 11.5 Gy. Although their cohort included 25% of intermediate- and 20% of high-risk patients, they reported as high as 94% biochemical control rate at 5 years for the entire cohort. Strouthos et al. recently updated the results for the 3-fraction-in-3- implant cohort with 450 patients, showing a 5-year biochemical control rate of 95% with a prolonged median follow-up of 4.7 years, with late Grade 3 GU toxicity as 0.8% without any late Grade 3 GI toxicity. Similarly, Kukiełka et al. in Poland used 3 separate implants with single fraction per implant, but with 15 Gy each, and 45 Gy in total. Hoskin et al. in the UK started HDR monotherapy with 4-fraction regimen giving 34 or 36 Gy in total. Soon they changed their regimen into 31.5 Gy in 3 fractions, and then into 26 Gy in 2 fractions. Finally, they are investigating a single-fraction regimen. Their indication for HDR monotherapy was almost restricted only to intermediate- or high-risk patients, which is a similar concept to that of Yoshioka et al. in Japan, and also is characterized by a high rate of ADT use. Martinez and Krauss et al. compared 3 regimens, including the aforementioned 38 Gy in 4 fractions, 24 Gy in 2 fractions, and 27 Gy in 2 fractions. They found the acute and late toxicity profiles associated with these 3 HDR monotherapy schedules were similar and were well tolerated. Combined with the fact that the clinical outcomes were similar, they concluded that all 3 regimens may be acceptable options for the management of low- to intermediate-risk prostate cancer. SP-0350 HDR brachytherapy in one fraction vs LDR brachytherapy in the treatment of localized prostate cancer. Early results. P. Agoston 1 , T. Major 1 , K. Jorgo 1 , G. Fröhlich 1 , L. Gesztesi 1 , G. Stelczer 1 , C. Polgár 1 1 National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary Abstract text Aim: We conducted a prospective, randomized clinical trial to compare the toxicity and clinical outcome of a single fraction high dose rate (HDR) monotherapy and low dose rate (LDR) seed brachytherapy (BT) in early, organ confined prostate cancer. We report our early results of the first 100 patients recruited in the study. Study was registered at the national ethical committee with reference number 056501/2013/OTIG and on the clinicaltrials.gov with reference number NCT02258087. Patients and methods: Between January 2015 and June 2017, 100 patients (mean age: 65 years; range: 50-75 years) were randomized to receive either 145 Gy I-125 LDR BT (n=50) or a single fraction of Ir-192 HDR (n=50) BT. In the HDR-BT arm 48 patients were treated with 19 Gy and the last two patients with 21 Gy. Before randomization patients were stratified according to their risk group. Forty-four low risk (LR: PSA≤10, T1-2a, Gleason score≤6) and 56 selected intermediate risk (IR: PSA>10-15ng/ml or T2b-c, or Gleason score 3+4) patients were treated. The mean iPSA was 8.6ng/ml (range:0.5-15 ng/ml). The target volume in LR was the prostate, in IR the prostate with a 3mm margin. Dosimetric parameters for both modality were defined and registered (V100, V150, V200, DHI, COIN for the target, D r 2cm 3 for the rectum, Du10%, Du30% for the urethra). Prior to BT 58% of the patients received neoadjuvant endocrine treatment, which was stopped at the time of brachytherapy. Physical status, toxicity, international prostate symptom score (IPSS), PSA value were checked at 3 and 6 months after BT, than in every 6 months to 3 years and yearly thereafter. Acute side effect was registered within the first three months after BT, and late effects thereafter. Acute and late toxicity were scored based on RTOG toxicity scale. Biochemical relapse

was defined as more than 2 ng/ml increase after the PSA nadir had been reached. The two treatment arms were compared with the Mann-Whitney U test. Results: The median follow up time was 23 months (5-34 months). Four patients had biochemical relapse, two in the LDR (4%) and two (4%) in the HDR BT arm. Three biochemical failures were detected in the IR, and one in the LR group. In all patients with biochemical relapse a local failure was confirmed. No regional or distant metastases were detected. Acute ≥grade2 gastrointestinal (GI) toxicity occurred only in one patient in the LDR arm. Acute ≥ grade2 urogenital (UG) toxicity occurred in 13 patients (26%) in the HDR and in 36 patients (72%) in the LDR group (p<0,001). Acute grade 3 toxicity was only in 1 (2%) patient in the HDR and in two (4%) patients in the LDR group. The mean IPSS score 3 months after BT was significantly better with HDR than with LDR BT (8.9 vs 15.9, p=0,0004), although this difference disappeared in 12 months after BT (8.3 vs 6.9, p=0.3). On the last follow up no ≥ grade2 GI toxicity could be detected, grade 2 UG side effects remained in 7 patients (14%) in the HDR and in 13 patients (26%) in the LDR group. Late grade 3 UG toxicity were detected only in one (2%) patient in the HDR and in two patients (4%) in the LDR group. The V100 was significantly better with LDR than HDR (98.8% vs 97.3%, p<0,001), meanwhile the values of Du10% and Du30% for the urethra were better with HDR compared to LDR technique (114% vs 132%, p<0,001 and 111% vs 128%, p<0,001). Conclusions: In our randomized study there were no differences in biochemical control or local failure rate in patients treated with LDR or single fraction HDR monotherapy for localized prostate cancer. Acute urological side effects were significantly worse with LDR BT, but the difference disappeared by 1 year after BT. More follow up is needed to confirm our results.

Debate: in radiotherapy in the last decade was driven by economics, not clinical needs The technological advancement

SP-0351 For the motion (advancement driven by economics) C. Kirisits Medical University of Vienna, Vienna, Austria

Abstract not received

SP-0352 Against the motion M. Van Vulpen The Netherlands

Abstract not received

Symposium: Applications of machine learning in radiation oncology

SP-0353 Introduction to Machine Learning and its Application in Radiotherapy I. El Naqa 1 1 University of Michigan, Radiation Oncology, Ann Arbor, USA Abstract text With the era of big data and the rapid increase in patient-specific information, there has been burgeoning interest by the radiation oncology community to utilize machine learning (ML) algorithms because of their ability to learn data dependencies from the current environment and generalize into unseen tasks. Application of machine learning currently covers varying