880 / 1096
S864
ESTRO 36
_______________________________________________________________________________________________
Conclusion
Proper analysis of pixel-based data mining showed that
lung pixel density outside the GTV did not predict for
survival. The method we proposed allows pixel-based data
mining based on distance to an organ. For such analysis,
one should be well aware of confounding variables such as
tumour size and mediastinal attachment.
EP-1602 Treatment planning individualisation based on
18F-HX4 PET hypoxic subvolumes in NSCLC patients
E. Lindblom
1
, A. Dasu
2
, J. Uhrdin
3
, A. Even
4
, W. Van
Elmpt
4
, P. Lambin
4
, I. Toma-Dasu
5
1
Stockholm University, Medical Radiation Physics-
Department of Physics, Stockholm, Sweden
2
The Skandion Clinic, The Skandion Clinic, Uppsala,
Sweden
3
RaySearch Laboratories AB, RaySearch Laboratories AB,
Stockholm, Sweden
4
Maastricht University Medical Center, Department of
Radiation Oncology- GROW-School for Oncology and
Developmental Biology, Maastricht, The Netherlands
5
Stockholm University and Karolinska Institutet, Medical
Radiation Physics- Department of Physics and
Department of Oncology and Pathology, Stockholm,
Sweden
Purpose or Objective
Pre-treatment functional imaging of tumour hypoxia
enables the identification of patients at greater risk of
treatment
failure,
and,
potentially,
allows
individualisation of treatment to overcome the increased
radioresistance of hypoxic tumours. Treatment
individualisation based on tumour hypoxia aims at
identifying and prescribing higher doses to radioresistant
hypoxic subvolumes based on the relative uptake of
hypoxia-specific tracers. This study aimed to perform
hypoxic target volume delineation and dose-prescription
calculation for non-small cell lung cancer (NSCLC) patients
using a novel hypoxic PET tracer,
18
F-HX4.
Material and Methods
Six non-small cell lung cancer (NSCLC) patients imaged
with
18
F-HX4 PET/CT were included in the study. The
hypoxic target volumes (HTV) were determined based on
a non-linear conversion between tracer uptake and pO2,
using a threshold of 10 mmHg. Assuming a clonogenic cell
density of 10
8
per cm
3
in the CTV, the HTV doses required
to achieve 95% local control (LC) were calculated based on
a previously developed radiobiological model (Toma-Dasu
et al 2009, 2012) accounting for the dynamic tumour
oxygenation due to changes in acute hypoxia not visible in
PET images. The total doses were calculated assuming
that the treatment involves 24, 30 or 35 fractions.
Results
The non-linear conversion function and hypoxic threshold
of 10 mmHg resulted in hypoxic subvolumes identified in
five out six patients. Three out of six patients had a
hypoxic subvolume > 3cm
3
. In two of the patients, the
delineated HTV was not entirely confined within the
primary CTV. For a treatment delivered in 30 fractions,
the prescribed dose required to achieve 95% local control
for the two patients with the largest HTVs of 32.74 and
38.29 cm
3
respectively were 75.52 and 75.67 Gy, both
corresponding to an EQD2 of almost 79 Gy10. For the third
patient with a smaller HTV of only 12.37 cm
3
, the total
dose in 30 fractions for 95% LC was 72.35 Gy. If the total
dose would be delivered in 35 fractions instead, the
prescribed doses would increase with about 2.2% of the
dose prescribed in 30 fractions for all three cases. The
relative decrease in the total dose if the total dose will be
delivered in only 24 fractions is about 3.5% for all three
HTVs. For all patients and for all treatment fractionation
schemes the dose levels required for achieving 95% tumour
control probability accounting for local changes in the
oxygenation of the tumour are below the levels of dose
boosts proved to be feasible to be delivered without extra
dose burden to the OARs on a previous study carried out
on the same patients.
Conclusion
HX4-based delineation of hypoxic target volumes and
calculation of required boost doses for a predefined
tumour control probability appears to be feasible. HX4 is
thus a potentially suitable tracer for the purpose of
treatment individualisation in NSCLC.
EP-1603 Atlas of complication incidence to explore
dosimetric contributions to osteoradionecrosis
L. Humbert-Vidan
1
, S. Gulliford
2
, V. Patel
3
, C. Thomas
1
,
T. Guerrero-Urbano
4
1
Guy's & St Thomas' NHS Foundation Trust, Radiotherapy
Physics, London, United Kingdom
2
The Institute of Cancer Research and Royal Marsden NHS
Foundation Trust, Joint Department of Physics, London,
United Kingdom
3
Guy's & St Thomas' NHS Foundation Trust, Oral Surgery,
London, United Kingdom
4
Guy's & St Thomas' NHS Foundation Trust, Clinical
Oncology, London, United Kingdom
Purpose or Objective
Mandibular osteoradionecrosis (ORN) is one of the most
severe complications in patients with head and neck
cancer undergoing radiation therapy (RT). Potential risk
factors include primary tumour site and stage, radiation
dose, pre- and post-RT dental extractions and mandibular
surgery, chemotherapy, dental hygiene, smoking or
alcohol.
This pilot study aims to assess the contribution of radiation
dose to the mandible to the incidence of ORN and
investigates the effect of different risk factors using the
atlas of complication incidence (ACI) method to
summarise dose-volume histograms and toxicity data.
Material and Methods
This retrospective study included 80 patients with head
and neck cancer with a median age of 62 (range 35-86)
treated with radical IMRT. Primary tumour sites included
a majority of oropharynx cases (42), oral cavity (26),