ESTRO 36 Abstract Book

S309 ESTRO 36 _______________________________________________________________________________________________

SP-0585 Hypofractionation in prostate cancer: a word of caution S.Bentzen 4 University of Maryland Greenebaum Cancer Center, Division of Biostatistics and Bioinformatics, Baltimore, USA 5 University of Maryland School of Medicine, Department of Epidemiology and Public Health, Baltimore, USA

have been expected from radiobiological models (HFRT 80.5% vs. CFRT 77.1%) and not statistically significant. The relatively unfavourable side effect profiles may be due to the higher HFRT doses delivered. The trial failed to demonstrate either superior efficacy or non-inferior side effects for HFRT. These 3 studies were undertaken in predominantly intermediate and high risk localised PCa. 1092 men were included in RTOG trial 0415 (4) which tested the non-inferiority of HFRT in low risk PCa. Daily schedules of SFRT (73.8Gy/1.8Gyf) were compared with HFRT (70Gy/2.5Gyf). The cumulative incidence of biochemical recurrence at 5 years was 8% and 6% in SFRT and HFRT groups respectively which met the protocol- specified non-inferiority criterion but late gastrointestinal and genitourinary side effects were increased with HFRT. There was no certain improvement in the therapeutic ratio. Together the 4 trials provide a rich source of data to further explore the radiobiology of prostate cancer response and hint that there may be a time factor resulting from tumour repopulation. Without a time factor the CHHiP and PROFIT trials suggest the α/β ratio is low and between 1.3-1.9 Gy although higher values of 3.5-6.9 Gy are suggested by HYPRO and RTOG-0415. However if time factors are included “best fit” estimates of the α/β ratio increase and cluster between 3.8-5.4 Gy. These estimates are associated with wide confidence intervals and should be treated with considerable caution. Much remains to be learnt about PCa radiobiology which may have significant impact on the on-going development of more extreme hypofractionation schedules. The clinical trial results are adequately robust to recommend a change in prostate cancer fractionation to 60Gy in 20 fractions with the key proviso that high quality IMRT is delivered meeting appropriately defined normal tissue dose constraints. 1. Dearnaley D, Syndikus I, Mossop H, et al. Lancet Oncol. 2016; 17:1047-1060. 2. Catton C, Lukka H, Julian J, et al. J Clin Oncol. 2016; 34 (suppl; abstr 5003). 3. Incrocci L, Wortel R, Alemayehu W, et al. Lancet Oncol. 2016; 17;1061-1069. 4. Lee W, Dignam J, Amin M, et al. J Clin Oncol. 2016; 34:2325-2332. SP-0584 Extreme hypofractionation – the future of prostate care or repeating past mistakes? A. Loblaw 1 1 Odette Cancer Centre - Sunnybrook Health Science, Department of Radiotherapy, North York- Toronto, Canada Based on in vivo and clinical observations, it was hypothesized in the late 1990’s and early 2000’s that the radiobiology of prostate cancer favored hypofractionation. There have since been a number of randomized studies published that confirm that moderate hypofractionation (doses per day of 2.1 – 5Gy) is non- inferior and isotoxic compared to conventional fractionated regimes. With the high precision available with newer stereotactic systems (non-coplanar, tomotherapy and gantry-based) interest developed in testing the feasibility, tolerability and efficacy of extreme hypofractionation (> 5Gy per day) protocols. A number of small to medium-sized prospective and retrospective studies have been published with medium follow- up. These studies suggest that with moderate doses (35- 40Gy in 5 fractions), biochemical disease-free survival is similar to brachytherapy with low rates of severe toxicities. There is emerging data that rectal and bladder toxicities are highly sensitive to the volume of normal tissues in the high dose region. There are two ongoing phase 3 studies (SPCG, PACE, HEAT) which are comparing extreme and conventionally fractionated / mild hypofractionated regimens.

Abstract not received

Symposium: Is there any ground for boost brachytherapy in the time of high precision IGRT/IMRT?

SP-0586 The efficacy of IGRT/IMRT simultaneous integrated boost (SIB) in gynaecology and breast E.M. Ozsahin 1 1 Centre Hospitalier Universitaire Vaudois, Department of Radiation Oncology, Lausanne Vaud, Switzerland Brachytherapy (BT) has been the standard of care for cervical cancer since the discovery of X-rays. In advanced cervical carcinoma, radiation treatment is typically external-beam irradiation (EBRT) to the pelvis followed by intracavitary brachytherapy boost to the cervix. Breast brachytherapy is increasingly used as an accelerated partial breast irradiation (APBI) modality in selected patients undergoing breast-conserving surgery. With the advent of advanced external beam radiation therapy techniques, including volumetric modulated arc therapy (VMAT), helical Tomotherapy (HT), and protontherapy (PT); and stereotactic body radiotherapy (SBRT) techniques such as CyberKnife (CK) or VMAT SBRT, many attempts have been made to substitute the BT boost with SBRT or SIB using VMAT, HT, or PT in cervical cancer; or to substitute BT with VMAT, HT, PT, or CK in APBI of breast cancer. The presentation will focus on the use of SBRT or SIB-EBRT techniques in the boost treatment cervical cancer or in APBI. SP-0587 Dose gradients: the effect of high doses inside the CTV comparing boost brachytherapy with SIB D.Baltas 1 University Medical Centre, Division of Medical Physics- Department of Radiation Oncology, Freiburg, Germany Brachytherapy (BT) is an effective treatment with a century of antiquity but remains the best way to give a high dose of radiation to small volumes. The development of radiosurgery displaced the use of BT in brain tumors, avoiding the aggressiveness of inserting catheters through surgery. Stereotactic body radiation therapy (SBRT) is achieving new indications and optimal outcomes in small volume tumors avoiding the invasiveness and discomfort of BT. The question is open, and the debate is between invasiveness and results, comfort and accuracy. We can show that BT has always a better conformity, with a steep dose gradient, with higher doses inside the volume and shorter overall time of treatment. But the most important issue is the evidence of long-term outcomes: BT has been used for years and those data are known; SBRT must have a longer follow-up to be sure that it is an alternative and can replace BT. We will review long-term clinical evidence supporting the use of brachytherapy boost in multiple sites. BR is mandatory in cervical tumors, because higher Abstract not received SP-0588 Why use invasive techniques for boost if IGRT is more comfortable for the patient? J.L. Guinot 1 1 Fundación Instituto Valenciano de Oncologia, Department of Radiation Oncology, Valencia, Spain