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S557
ESTRO 36 2017
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Large dose differences between planned and delivered
doses may be observed in the rectum and in the bladder,
resulting from anatomical variation in the course of
prostate IMRT. The objective of this study was to compare
dosimetrically an original approach of Dose Guided
Adaptive Radiotherapy (DGART) to the standard IGRT
(CBCT daily repositioning).
Material and Methods
Based on a series of 24 patients with daily CBCT, planned
and delivered dose were compared in manually delineated
structures (prostate, rectum and bladder), using dose
accumulation process after estimation of the fraction dose
[Nassef et al, Radiother Oncol 2016]. The four patients
with the most important overdose in the rectum wall and
the bladder wall were selected to estimate the DGART
benefit compared to the standard IGRT.
The DGART strategy (Figure 1) was based on replanning(s)
triggered by monitoring the cumulated doses to the
prostate, the rectum wall and the bladder wall. Thereby,
the first step consisted in estimating the relative excess
of the cumulated dose compared to the planned dose after
every fraction for the prostate D
99
, the rectum wall V
72
and
the bladder wall V
70
. After an observation phase of 5
fractions, the adaptation was triggered (i.e. a replanning
was performed), if a 2 % underdose of D
99
for prostate or
an overdose of 10 % on V
72
for the rectum wall or V
70
for
the bladder wall occurred.
If a replanning was triggered at the fraction n, the CBCT
chosen for the replanning corresponded to the anatomy
leading to the highest dose drift compared to the planned
dose. For that, for every fraction x (x=1..n), an index (see
figure 2) was calculated to select the morphology leading
to the highest dose drift compared to the planned dose. If
the relative excess was compensated by the replanning,
no other adaption was needed and the new replanning was
used for the rest of the fractions. If the relative excess
was not compensated, the replanning process was
repeated in case of a new CBCT leading to a higher index
value. An example of DGART implementation is provided
in Figure 2, showing the benefit of DGART to decrease the
dose to the bladder.
Results
For the four patients, the DGART resulted to only one
replanning during the first week of treatment. For the
rectum wall V
72
, the overdose was on average reduced of
50% (100% maximum) and the mean dose reduced of 4.5
Gy compared to standard IGRT. For the bladder wall V
70
,
the overdose was on average reduced of 19% (37%
maximum) and the mean dose reduced of 6.6 Gy compared
to standard IGRT. For the prostate, the D
99
was on average
0.5 Gy higher (0.7 Gy maximum) using DGART compared
to standard IGRT.
Conclusion
DGART with only one replanning applied to a selected sub-
group of patients may reduce the rectum and bladder
overdose in prostate IGRT.
Poster: RTT track: Patient care, side effects and
communication
PO-1018 Improvement of radiation-induced late
toxicity after hyperbaric oxygen treatment
R. Roncero
1
, J. Pardo
1
, E. Jimenez-Jimenez
1
, D. Morera
2
,
N. Aymar
1
, I. Ortiz
1
, M. Vidal
1
1
Hospital Universitari Son Espases, Radiation Oncology,
palma de mallorca, Spain
2
Hospital Universitari Son Espases, Medical Physics,
palma de mallorca, Spain
Purpose or Objective
To assess the efficacy of hyperbaric oxygen therapy
(HBOT) in the management of patients with radiation-
induced late effects, in which more conservative
treatments have failed
Material and Methods
We retrospectively reviewed the clinical records of 33
patients treated at our Department, from 2012 to 2016,
who developed late toxicity (Grade IV CTCAE4.0) and
which did not respond to conservative treatment, and
recorded the variation, if occurred, in the degree of
toxicity after hyperbaric treatment. The average age of
the patients was 61 +/- 12 years and the mean dose
delivered during the radiotherapy treatment was 52 +/-
12Gy with standard fractionation. Regarding HBOT, they
received an average of 61 sessions. The patients presented
the following toxicities: enteritis/proctitis in 33%, bone
necrosis and sacroileitis in 30%, skin injury 9%, Cystitis 6%
and others 9% (neurocognitive impairment, dysphagia and
xerostomy).
In order to its evaluation, responses were classified into
three groups according the CTCAE4.0 scoring:
Major Response Group
: Improvement of toxicity from
Grade IV to Grade I or 0 (without toxicity, or minor toxicity
not requiring medical treatment),
Minor Response Group
: Improvement from Grade IV to
Grade III/II (permanent toxicity controlled with medical
treatment) and
No Response Group
. The statistical study was carried out
by using SPSS_22.
Results
Ninety-one percent of the patients (30) completed the
treatment sessions with hyperbaric chamber scheduled (2
patients didn´t start the treatment and 1 patient stopped
after 4 sessions). Statistical significant toxicity
improvement (p<0.05) was observed after the hyperbaric
oxygen treatment. 60% of the patients presented a Major
Response, and 18% presented a Minor Response. 9% (3) of
our patients were no responders. In our patients, no
relationship was founded between the response and the
age, the number of sessions of HBOT, or the time relapsed
since radiation treatment to the indication of the HBOT.
Table 1 presents the patients outcomes according the
toxicity.