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ESTRO 36
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Purpose or Objective
The aim of this study was to evaluate the acute and late
toxicities and biochemical disease-free survival and
overall survival after high-dose-rate brachytherapy as a
salvage modality for locally recurrent prostate
radiotherapy failure.
Material and Methods
Between 2007 and 2014, we retrospectively analyzed 20
consecutively patients. Median age of first treatment was
62 years (range 51-73). The majority of the patients in
this study (65%) were low risk. 5p received hormonal
blockade. 11p received treatment with low-dose-rate
brachytherapy (LDR-BT) and 9p received treatment with
external beam radiotherapy with median dose of 75Gy (70-
78Gy). Time to biochemical recurrence was 62 months
(range 14-119). Median presalvage PSA was 3.72 (range
1,83-12,29). After biochemical relapse, we confirm local
recurrence with biopsy. Patients received high-dose-rate
brachytherapy (HDR-BT). The schedule was three
implantations, every two weeks, with 10,5Gy per implant.
By the time of salvage BT, only 1p received ADT. Acute
and late genitourinary and gastrointestinal toxicities were
graded using Common Terminology Criteria for Adverse
Events (CTCv4.0). Overall survival (OS) and biochemical
(bDFS) control were calculated using Kaplan-Meier
method.
Results
After first treatment, acute toxicities consisted of
genitourinary toxicities grade 1 (3p) and grade 3 (1p). Not
late gastrointestinal toxicities.
After HDR-BT, acute toxicities consisted of genitourinary
grade 1 (4p), grade 2 (5p) and grade 3 (3p),
gastrointestinal toxicities grade 1 (3p) and grade 2 (4p)
and impotence in 4p. Not acute toxicities grade 4 were
reported.
Late toxicities consisted of genitourinary grade 3 were
observed in 2p. Not grade 4 complications.
With a median follow-up after salvage HDR-BT of 47
months (range 11-112 months), local control was achieved
on PSA levels in all patients.
Among 20 patients studied, 1 lost follow-up and he was
excluded from the survival analysis.
Using Kaplan-Meier analysis the 2-year and 5-year OS were
100% and 84,2%, respectively. The 2-year and 5-year
biochemical disease-free survival (bDFS) were 85% and
81%, respectively.
Conclusion
Prostate BT is an effective salvage modality in some
selected prostate local recurrence patients after radiation
therapy.
HDR-BT is a good choice to deliver high-dose radiation in
prostate recurrence tumors after external beam
radiotherapy or LDR-BT. This treatment offers adequate
locoregional control with acceptable range of
complications.
OC-0176 Identifying Patients Who Benefit the Most
from Salvage HDR Brachytherapy
G. Valdes
1
, A.J. Chang
1
, O. Kenton
1
, A. Cunha
1
, T.D.
Solberg
1
, H. I-Chow
1
1
University of Californ ia UCSF, Radiation Oncology, San
Francisco CA, U SA
Purpose or Objective
To use mac hine learning to better identify patients that
could benefit from prostate salvage HDRB (HDR
brachytherapy).
Material and Methods
Data was analyzed for
52 consecutively accrued patients
that underwent salvage HDRB between 1998 and 2009 for
locally recurrent prostate cancer following previous
definitive radiation therapy at the University of California,
San Francisco (UCSF). All patients were treated with 36
Gy in 6 fractions after pathologic confirmation of locally
recurrent disease without evidence of metastatic
disease. Determination of biochemical failure after
salvage HDRB was based on the Phoenix definition. All
non-failure patients were followed for a minimum of 5
years. Eighteen different clinical risk features were
collected from each patient. Machine Learning was used
to identify subpopulations that would most likely to
remain biochemically disease free after the
treatment. Decision tree algorithms were constructed
using Matlab R 2011a. The complexity of the decision tree
was fine-tuned by selecting the optimum number of
observations per terminal node that minimized
the “Leave One Out Cross-Validation” estimation of the
deviance. Results were compared to those obtained using
Ensemble Methods. Random permutation experiments
were also performed to estimate the probability that the
tree found was the result of random variations.
Results
A subpopulation of patients with a high risk of biochemical
failure after salvage HDRB was identified. Those patients
with a fraction of positive nodes from those sample that
was greater than 0.354 and disease free interval less than
4.12 years had a failure rate after salvage HDRB of 0.75 vs
0.38 for the remainder of the population,
Figure 1
. The
probability that the conclusions reached in this paper are
not due to random fluctuations is 0.7,
Figure 2
.
Figure1.
The Optimal Decision Tree obtained for
predicting failure after Salvage HDRB.
Figure 2.
Random permutation of output labels. 1000
iterations were created in each case were the outcome of
was randomly permuted. Not correlation between
features and outcome should be present in this case. The
probability of obtaining a cross-validated leave one out
error smaller than the one obtained by the tree in Figure
1 was calculated.
Conclusion
Patients with a fraction of positive nodes higher than 0.35
and a disease free interval bigger than 4.12 years are at
higher risk of biochemical failure after salvage HDBR.
Machine Learning is effective in identify subtle variables
that can affect the treatment outcome.