ESTRO 36 Abstract Book

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S20 ESTRO 36 2017
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We enrolled 8 consecutive patients who were referred to
the Radiological Department of our hospital for ECG-gated
intravenous contrast enhanced CT. All scans were
performed with the same multislice spiral CT
(LIGHTSPEED, General Electric). Patients were asked to
hold their breath after a mild hyperventilation.
Reconstructions were performed in 10% steps over the
entire R-R cycle with a dedicated retrospective ECG-gated
algorithm. For all patients, 10 data sets were created and
the following structures were delineated in the
reconstructed sets: Left main trunk (LMT), left anterior
descending (LAD), left circumflex artery (CX) and right
coronary artery (RC). CA were contoured with inputs from
an experienced radiologist. CA displacements across
different phases of the heart cycle were evaluated in left–
right (X), cranio-caudal (Y) and antero-posterior (Z)
directions with the Van Herk formula (1.3* Σ + 0.5* σ).
Results
The following coronary displacements were found in X, Y
and Z co-ordinates, repectively: 3.6, 2.7 and 2.7 mm for
LMT; 2.6, 5.0 and 6.8 mm for LAD; 3.5, 4.5 and 3.7 mm
for CX; 3.6, 4.6 and 6.9 mm for RC. Figure 1 shows the
axial, coronal and sagittal contours of a right coronary
artery, all retrieved on one of the ten sets created for
each patient.
Conclusion
Our study shows that the CA displacement over the heart
cycle ranges from 2.6 to 6.9 mm, suggesting the need for
an IRV margin to accurately estimate the dose received by
these structures during the planning of a thoracic
irradiation. Based on these findings, we suggest to apply
an isotropic margin of 3-4 mm for LMT and CX and an
isotropic margin of 5-7 mm for LAD and RC.
PV-0046 Comparison of respiratory-induced
diaphragm motion during radiotherapy between
children and adults
S. Huijskens1, I. Van Dijk1, J. Visser1, C. Rasch1, T.
Alderliesten1, A. Bel1
1 Academic Medical Center, Radiation Oncolo gy,
Amsterdam, The Netherlands
Purpose or Objective
Respiratory motion during radiotherapy has been
extensively studied in adults and often 4-dimensional
computed tomography (4DCT) is used to quantify the
respiratory motion prior to treatment in order t o optimize
safety margins. Similar data are not known for paediatric
radiotherapy, and margins are therefore commonly based
on adults data. The purpose of this study is to quantify and
compare respiratory motion in children and adults.
Material and Methods
Respiratory-induced diaphragmatic motion was
retrospectively analysed on repeated Cone Beam CTs
(CBCTs) acquired during the radiotherapy treatment
course of 35 children (mean age 10.7; range 2.2-17.8) and
35 adults (mean age 59.6; range 34.0-93.0). Patients were
included when the diaphragm was visible on upper
abdominal or thoracic free-breathing CBCTs, totaling 359
paediatric CBCTs and 374 CBCTs from adults (mean 12;
range 2-33).
To measure respiratory-induced diaphragmatic motion, a
two-dimensional Amsterdam Shroud image was created for
each CBCT, allowing for selection of the cranio-craudal
position of the end-exhale (EE) and end-inhale (EI)
positions of the top of the right diaphragm. Pixel
coordinates were corrected for the scanner geometry and
translated into millimetres relative to the patients’
isocentre.
The amplitude was defined as the displacement between
EE and EI diaphragm positions. The cycle time described
the time between two consecutive EI peaks. We analysed
the variability of the intrafractional and interfractinoal
respiratory motion. Differences between children and
adults were tested with the Mann-Whitney-U-test,
considering p<0.05 significant.
Results
The differences in respiratory-induced diaphragmatic
motion between children and adults are summarized in
Figure 1. Although the mean amplitude was somewhat
smaller in children than in adults (10.6 mm vs. 11.6 mm),
the difference was small and insignificant. Interfractional
variability in amplitude was significantly smaller in
children compared to adults (p=0.004). Since children
breath faster than adults, the cycle time was significantly
briefer (p=0.000). Additionally, intrafractional variability
in cycle time was also significantly smaller in children
(p=0.002).
Conclusion
We found significant, but small, differences in respiratory-
induced diaphragmatic motion between children and
adults. Large ranges of amplitude and cycle time in both
children and adults confirm that respiratory motion is
patient-specific and requires an individualised approach
to account for. Unexpectedly, overall variability is smaller
in children than in adults, suggesting that a pre-treatment
4DCT for planning purposes will be at least equally
beneficial in children as it is in adults.
PV-0047 Whole lung irradiation in patients with
osteosarcoma and Ewing sarcoma: a systematic review
L. Ronchi1, E. Farina1, A. Zamagni1, V. Panni1, A.
Arcelli1,2, A. Farioli3, A. Paioli4, S. Ferrari 4, G.P. Frezza2,
G. Macchia5, F. Deodato5, M. Ferro5, G. Torre5, S. Cilla6,
A. Ianiro6, S. Cammelli1, A.G. Morganti1
1University of Bologna, Radiation Oncology Center-
Department of Experimental- Diagnostic and Specialty
Medicine - DIMES, Bologna, Italy
2Ospedale Bellaria, Radiotherapy Department, Bologna,
Italy