ESTRO 36 Abstract Book

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S848 ESTRO 36 2017
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Conclusion
OC resulted to be a parallel organ for mean G≥1.5 OM,
while severe OM was associated to a synergic effect
between PG mean dose and high doses received by small
OC volumes, with BMI acting as a dose-modifying factor.
On the other hand, OC resulted as a fairly serial organ for
G≥2 SD; this could be due to the inclusion of minor salivary
glands in OC contour, that the target often overlaps. Older
age and smoking history were also associated to a SD
increased risk. We did not find a strictly significant
association between G3 dysphagia and dosimetric
features, but the step trend resulting from our model
calibration suggests that the ML model may not describe
well the dose-response relationship in this case, with a
step function possibly being more suitable. Validation of
these models in a larger pts cohort is ongoing.
EP-1595 NTCP models for early toxicities in patients
with prostate or brain tumours receiving proton therapy
A. Dutz1,2, L. Agolli1,3, E.G.C. Troost 1,2,3,4,5, M.
Krause 1,2,3,4,5, M. Baumann 1,2,3,4,5, A. Lühr1,2,3,4, S. Löck1,3,5
1OncoRay - Center for Radiation Research in Oncology,
Faculty of Medicine and University Hospital Carl Gustav
Carus- Technische Universität Dresden, Dresden,
Germany
2Helmholtz-Zentrum Dresden-Rossendorf, Institute of
Radiooncology, Dresden, Germany
3Department of Radiation Oncology, Faculty of Medicine
and University Hospital Carl Gustav Carus- Technische
Universität Dresden, Dresden, Germany
4German Cancer Research Center DKFZ, Heidelberg and
German Cancer Consortium DKTK partner site Dresden,
Dresden, Germany
5National Center for Tumor Diseases, partner site
Dresden, Dresden, Germany
Purpose or Objective
To identify patients who are likely to benefit most from
proton therapy, based on the potential reduction in
normal tissue complication probability (NTCP) compared
to photon therapy. The NTCP models required for this
comparison were developed using clinical data on early
side effects for patients with brain or prostate cancer
having received proton therapy.
Material and Methods
Eighty patients with primary brain tumours and 30 patients
with adenocarcinoma of the prostate who received proton
therapy were included in this study. For the brain tumour
patients, the radiation-induced early toxicities alopecia,
erythema, pain and fatigue were considered, while for
prostate cancer proctitis, diarrhoea, urinary frequency,
urgency and incontinence, obstructive symptoms and
radiation-induced cystitis were investigated. The
occurrence of these side effects was correlated with
different dose-volume parameters of associated organs at
risk. NTCP models were created using logistic regression.
A retrospective comparative treatment planning study was
conducted to predict the potential reduction in NTCP of
proton therapy compared to volumetric modulated arc
therapy using the created models. For patients with brain
tumours different subgroups were defined to identify
patient groups which show a particularly high reduction in
the considered toxicities.
Results
For patients with primary brain tumours significant
correlations between the occurrence of alopecia grade 2
as well as erythema grade ≥ 2 and the dose-volume
parameters D5% and V25Gy of the skin were found. Plan
comparison showed an average reduction in NTCP for
alopecia grade 2 of more than 5 % (see figure) and for
erythema grade ≥ 2 of about 5 % using proton therapy. For
patients with a brain tumour located in the skull base,
with a clinical target volume less than 115 cm³ or with a
prescribed dose less than 60 Gy, a potential reduction in
NTCP for alopecia grade 2 of about 10 % could be achieved.
For patients with prostate cancer significant correlations
between obstructive symptoms grade ≥ 1 and the dose
parameter D30% of the bladder as well as radiation-
induced cystitis grade ≥ 1 and D20% of the bladder were
found. Plan comparison showed an average reduction in
NTCP for obstructive symptoms ≥ grade 1 of about 25 %
and for radiation-induced cystitis about 15 % using proton