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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.
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
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
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
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
doses (90Gy) can be achieved in big tumours, and if it is
not used local control can decrease as much as 20%. On
the other hand, smaller volumes can be radiated in
nasopharynx, early bronchial and oesophageal carcinomas
increasing the dose in cases where the tumor control is