989 / 1096
S973
ESTRO 36
_______________________________________________________________________________________________
being D the total dose, d the dose per fraction, α/β the
LQ parameter that allows to quantify the sensitivity to the
fractionation of prostate cancer, γ the maximum
normalized dose-response gradient and D
50
the total dose
needed to achieve 50% BC.
To fit the model parameters, and to obtain its
uncertainties, we used Monte Carlo methods.
Results
Firstly, the value of EQD
2
of each program was calculated.
Figure 1 shows the value of BC versus EQD
2
if the currently
accepted value for α/β=1.5 Gy is used in equation (1). The
black square corresponds to the single fraction schedule
[1].
The fit of equation (2) to clinical data produces the results
in figure 2. The confidence intervals of the parameters
correspond to 95%. Figure 2 also shows BC versus the new
EQD
2
values, calculated with α/β=8.7Gy.
From these results, the value of the absorbed dose for an
extreme hypofractionation regime with one fraction in
HDRBT monotherapy, allows us to obtaining a BC=90% at 5
years, is 21.9 [19.6,26.3] Gy.
Conclusion
The α/β value obtained for a range of dose per fraction
between 6 and 19 Gy is much greater than the one
currently estimated for prostate cancer.
The absorbed dose in HDRBT monotherapy for a regime
with one fraction would allow us to obtain a BC=90% is 22
Gy.
The value of α/β obtained here explains well the clinical
data in the region of the doses per fraction considered.
Nonetheless it is important to take into account some of
the limitations of the model, which may be overcame by
adding additional clinical studies, not necessary of
brachytherapy as monotherapy. Those limitations are: the
fit is over conditioned by the only fraction datum, the data
are heterogeneous, and its external validity may be
limited, we do not properly know the associated
uncertainties nor the dose distributions.
References
[1] Prada PJ et al. Radiother Oncol 2016;119:411-6.
EP-1769 Hypofractionated EBRT and single fraction
HDR brachytherapy for patients with prostate cancer.
D.E. Kazberuk
1
, T.M. Filipowski
2
, A. Szmigiel-Trzcińska
3
,
M. Niksa
3
, D. Hempel
4
, J. Topczewska-Bruns
2
, W. Nowik
5
,
B. Pancewicz-Janczuk
6
1
Bialystok Comprehensive Cancer Center, Brachytherapy,
Bialystok, Poland
2
Bialystok Comprehensive Cancer Centre, Radiotherapy,
Bialystok, Poland
3
Bialystok Comprehensive Cancer Centre, Brachytherapy,
Bialystok, Poland
4
Bialystok Comprehensive Cancer Center, Radiotherapy,
Bialystok, Poland
5
Bialystok Comprehensive Cancer Centre, Physics,
Białystok, Poland
6
Bialystok Comprehensive Cancer Centre, Physics,
Bialystok, Poland
Purpose or Objective
To evaluate the short term efficacy, early toxicity and
dosimetric aspects of combined HDR-BT with EBRT in the
radical treatment of prostate cancer patients (PCPs).
Material and Methods
40 PCPs underwent combined treatment including
hypofractionated EBRT (37.5 Gy in 15 fractions over 3
weeks) and conformal HDR-BT between September 2013
and May 2015. The mean age was 69 years with average
PSA 6,7 ng/ml and median Gleason score 6,8. T stage was
distributed from T1 to T2c. Half of the patients received
androgen deprivation. Treatment was delivered
using IMRT with an 6- or 15-MV linear accelerator. HDR
brachytherapy catheter insertion was performed under
spinal anaesthesia. The median number of catheters was
17 (14-18). HDR brachytherapy was delivered using an
Iridum-192 source (Nucletron) and treatment planning
system: SWIFT 2.11.8 and Oncentra Prostate 3.0.9./4.0.
Dose volume constraints included: prostate V 100 ≥95 %,
V150 and V200 below 40%; maximal urethral dose ≤ 120%
and average rectal dose ≤ 85% of the prescription dose.
Patients were monitored weekly during radiotherapy and
in 3 months intervals after treatment. Follow-up visit
included clinical examination and PSA value assessment.
The acute toxicities were graded according to the
EORTC/RTOG scales.
Results
The median V100 was 93% and median D90 was 103%. All
patients finished the scheduled therapy without
interruption. The most common urinary symptoms were:
urgency, frequency, dysuria and nocturia. The rectal
symptoms (urgency, frequency) were rare. No grade 3 and
4 acute toxicities were recorded. No patient developed
clinical or biochemical progression. The constant decrease
of PSA level was observed during follow up.
Conclusion
Single fraction 15 Gy HDR-BT with hypofractionated
EBRT enables dose escalation with excellent dosimetric
parameters for the radical treatment of PCPs. The
treatment was well tolerated by all patients with
satisfactory disease control in the short and medium term.