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S182
ESTRO 36
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3
The Royal Marsden NHS Foundation Trust, Radiation
Oncology, Sutton, United Kingdom
4
Institute Curie, Radiation oncology, Paris, France
5
West German Proton Therapy Center Essen, Clinic for
Particle Therapy, Essen, Germany
6
Instituto nazionale dei tumori, radiation oncology,
Milano, Italy
7
Radboud university medical center, Department of
Radiation Oncology, Nijmegen, The Netherlands
8
Addenbrooke's Hospital, Radiation Oncology,
Cambridge, United Kingdom
9
Hygeia Hospital, Medical physics department, Athens,
Greece
10
Radboud university medical center, radiation oncology,
Nijmegen, The Netherlands
11
Aarhus University Hospital, radiation oncology, Aarhus,
Denmark
12
Oslo University Hospital, Radiation oncology, Oslo,
Norway
13
The Christie NHS Foundation Trust, Radiation oncology,
Manchester, United Kingdom
14
AMC, radiation oncology, Amsterdam, The Netherlands
15
Timone hospital, radiation oncology, Marseille, France
16
Hygeia Hospital, MEidcal Physics, Athens, Greece
17
Santa Chiara Hospital, Proton therapy Center, Trento,
Italy
18
Aarhus University Hospital, Medical Physics, Aarhus,
Denmark
19
University Medical Center Utrecht, Radiation Oncology,
Utrecht, The Netherlands
Purpose or Objective
The craniospinal irradiation (CSI) is challenging due to the
long target volume and the need of field junctions. The
conventional 3D-CRT technique (two lateral opposed
cranial fields matched to a posterior field) is still widely
adopted. Modern techniques (MT) like IMRT, VMAT,
Tomotherapy and proton pencil beam (PBS) are used in a
limited number of centres.
A multicentre dosimetric analysis of five techniques for CSI
is performed using the same patient, set of delineations
and dose prescription. We aimed to address two questions:
Is the use of 3D-CRT still justifiable in the modern
radiotherapy era? Is one technique superior?
Material and Methods
One 14 year-old patient with medulloblastoma underwent
a CT-simulation in supine position. The CTV and OARs were
delineated in one centre. A margin for PTV was added to
CTV: 5 mm around the brain and spinal levels C1-L2, 8 mm
for levels L3-S3. Fifteen SIOP-E linked institutes, applying
3D-CRT, IMRT, VMAT, Tomotherapy, or PBS (three centres
per technique), were asked to return the best plan
applicable for their technique: high weighting for PTV
coverage (at least 95% of PTV should receive 95% of the
prescribed dose) and low weighting for OAR sparing. Plans
for a prescription dose of 36 Gy were compared within and
between techniques, using a number of dose metrics:
Paddick conformity (range 0-1, with 1 being highly
conformal), and heterogeneity (range 0-1, with 1 being
highly heterogeneous) indices for brain and spine PTVs,
OAR mean doses and non-PTV integral doses.
Results
Conformity- (range 0.75-0.90) and homogeneity (range
0.06-0.08) indices of brain PTV were similar among all
techniques. However for the spinal PTV inferior indices
(CI: 0.30 vs 0.61 HI: 0.18 vs 0.08) are observed for 3D-CRT
with respect to modern techniques (Figure 1). Compared
to more advanced photon techniques, 3D-CRT increased
mean dose to the heart (13Gy vs 8Gy), thyroid (28Gy vs
15Gy), and pancreas (17Gy vs 12Gy) but decreased dose to
both kidneys (4Gy vs 6Gy) and lungs (6Gy vs 8Gy) (Figure
2). PBS reduced the mean dose to the OARs compared to
all photon techniques: a decrease of more than 10Gy was
found for parotid glands, thyroid and pancreas; between
5-10Gy for lenses, submandibular glands, larynx, heart,
lungs, intestine and stomach; smaller than 5Gy for scalp
and kidneys (Figure 2). Moreover, protons provide the
smallest non-PTV integral doses (V1Gy: 53% 3D-CRT, 69%
photons MT, 15% PBS; V5Gy: 23% 3D-CRT, 43% photons MT,
12% PBS). A considerable variation in PTV and OAR
dosimetry was observed within a certain technique.
Conclusion
Modern radiotherapy techniques demonstrate superior
conformity and homogeneity, and reduced mean dose the
OARs compared to 3D-CRT.
PBS produced the case with the lowest mean dose for each
OAR and integral doses. However, the variability among
centres using the same technique means it is not possible
to clearly identify the best technique from this
data. Efforts should be made to improve inter-centre
consistency for each technique.
OC-0346 Multicentre audit of SBRT oligometastases
plan quality
J. Lee
1
, R. Patel
1
, C. Dean
2
, G. Webster
3
, D.J. Eaton
1
1
Mount Vernon Cancer Centre, National Radiotherapy
Trials QA RTTQA Group, Northwood, United Kingdom
2
Barts Health NHS Trust, Radiotherapy Physics, London,
United Kingdom
3
Worcestershire Oncology Centre, Radiotherapy Physics,
Worcester, United Kingdom
Purpose or Objective
SBRT for oligometastases is currently being used to treat
patients at 17 centres in England, as part of the NHS
England “Commissioning through Evaluation” programme.
The national trials QA group conducted QA for the
programme, which included establishing appropriate
clinical plan quality metrics for auditing submitted SBRT
plans. The purpose of the audit was to inform future
guidance on plan quality metric tolerances and help
centres determine whether a given plan is optimal.
Material and Methods
Plans included were either benchmark plans using pre-
delineated CT images planned by all cen tres prior to
patient recruitment; or plans of initial patients reviewed
prior to treatment. VODCA software (Medical Software
Solutions) was used for independent plan review. Lung
plans were analysed separately due to the inherent