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Due to rarity of the disease, our data did not show
significant improvement of LC after RT. GTR should be
pursued and adjuvant RT after STR is a resonable approch.
Further investigations are needed to determine the
optimal therapeutic strategy.
Electronic Poster: Clinical track: Paediatric tumours
EP-1379 Heart volume reduction in paediatric cancer
patients during radiotherapy
I. Van Dijk
1
, J. Visser
1
, J. Wiersma
1
, J. Van Boggelen
1
, B.
Balgobind
1
, L. Feijen
2
, S. Huijskens
1
, L. Kremer
2
, C.
Rasch
1
, A. Bel
1
1
Academic Medical Center, Radiation Oncology,
Amsterdam, The Netherlands
2
Academic Medical Center, Pediatric Oncology- Emma
Children's Hospital, Amsterdam, The Netherlands
Purpose or Objective
Radiation to the heart is associated with adverse cardiac
effects in long-term cancer survivors. In adult patients
with oesophageal cancer, a decrease in heart volume was
observed already early during radiotherapy. Based on this
observation we investigated whether similar heart volume
changes occur during radiotherapy in paediatric cancer
patients as well. Therefore, we retrospectively assessed
heart volume change during thoracic radiotherapy in
paediatric cancer patients.
Material and Methods
We included 13 females and 14 males who received
radiotherapy to the thoracic region for a primary
paediatric cancer, a recurrence, or metastatic disease
between 2010 and 2016; median age at treatment was
11.0 (range 4.0-17.3) years. Median height and weight
were 1.4 (range 1.0-2.0) meter and 40 (range 14-69)
kilogram, respectively. Primary cancer diagnoses included
CNS tumours (n=15), bone tumours (n=4), lymphomas
(n=3), rhabdomyosarcomas (n=2), neuroblastomas (n=2),
and 1 blastoma.
Heart contours were delineated and volumes were
measured on cone beam (CB)CTs, considering an interval
of at least 3 treatment days between the scans. Relative
volume changes were determined by normalizing the
volumes with respect to the volume as measured on the
first CBCT (i.e., baseline 100%). Cardiac radiation doses
were converted into equivalent doses of 2 Gy per fraction
(EQD2 for α/β = 3 Gy), after which radiation dose
parameters were calculated from dose volume histograms.
Chemotherapy was administered to 23 of the 27 children
(in 13 cases concurrently with radiotherapy), and was
categorized as follows: anthracyclines, alkylating agents,
vinca-alkaloïds, and other.
We tested possible correlations between heart volume
change and patient characteristics (gender, age, height,
weight), cardiac radiation dose, and category of
chemotherapy.
Results
Heart volumes were measured on 90 CBCTs (range 2-6 per
patient). Figure 1A shows the volume change during the
radiation course. The overall median volume reduction
from the first to the last CBCT was 3.6% (IQR 0.3-8%)
(Figure 1B) this reduction was significant (Wilcoxon
signed-ranks tests, p<0.01).
No correlations were found between the reduction of the
heart volume and patient characteristics, cardiac
radiation dose, or category of chemotherapy.
Conclusion
We found a significant heart volume reduction in children
during thoracic radiotherapy for cancer. Correlations with
patient- or treatment-characteristics were not found.
Elucidation of the underlying mechanism and clinical
relevance of early heart volume reduction during thoracic
radiotherapy require a prospective follow-up study.
EP-1380 Impact of radiobiological models in decision
making to individualize proton and photon radiotherapy
A. Chaikh
1
, J. Balosso
2
, J. Blouzard
3
, J. Bondiau
4
1
CHU de Grenoble - A.Michallon, Radiothérapie et
physique médicale, Grenoble, France
2
University Hospital of Grenoble- University Grenoble-
Alpes, Department of Radiation Oncology and Medical
physics, Grenoble, France
3
IPNL, France HADRON national research infrastructure,
Lyon, France
4
Centre Antoine Lacassagne, Department of Radiation
Oncology, Nice, France
Purpose or Objective
The aim of this study is to assess the impact of
radiobiological models and their clinical parameters on
the medical decisions. This include TCP, NTCP, UTCP
(substitute of QALY) and secondary cancer risk estimation
in pediatric patients.
Material and Methods
17 pediatric patient’s cases with medulloblastoma were
studied. Two treatment plans were generated with
conformal photon radiotherapy and proton therapy. The
same dose prescriptions for posterior fossa and
craniospinal irradiation were used for both plans. Two
radiobiological models were used for NTCP (LKB and
Niemierko) and the EUD model for TCP. The organ
equivalent dose model was used to estimate secondary
cancer risk. The in-silico dose based estimation of toxicity
and cancer risk derived from dose volume histogram
(DVH). Wilcoxon paired test was used to calculate p-value.
Results
Overall, proton plans achieved lower dose for most of the
OARs. Consequently, the NTCPs were significantly lower,
p < 0.05. However, the variation, due to the model and
radiobiological parameters choice, showed a significant
impact on UTCP based on TCP/NTCP regarding medical
decision. Similarly the variation of TCP/NTCP can reach
20-30% and 100% for secondary cancer, depending on the
model.
Conclusion
The considerable impact of radiobiological model on the
radiotherapy outcomes urges us, once again, to measure
specific (CTCAE scale) and global (QoL as EQ-5D) clinical
outcomes, to tune the parameters of TCP/NTCP