ESTRO 36 Abstract Book

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S321 ESTRO 36 2017
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purpose of this study is to investigate the accuracy of
delineating microscopic tumor growth on HE stained slices
by comparing it with the gold standard for squamous cell
carcinoma (SCC): immunohistochemical pan-cytokeratin
(CKAE1/3) staining.
Material and Methods
Twenty-seven patients with laryngeal or hypopharyngeal
SCC underwent total laryngectomy (TLE). The laryngeal
specimen was fixated and preserved with formalin and
sliced up into 3 mm thick slices. For each patient, four
subsequent slices with tumor were selected. From each
slice, two 4µm-thick whole-mount sections were obtained
and stained with HE and CKAE1/3. The tumor was
delineated both on the HE and CKAE1/3 stained sections
by a dedicated head-and-neck pathologist using a
microscope. The stained sections were three-
dimensionally reconstructed and rigidly registered to each
other. Registration between CKAE1/3 and HE stainings was
performed by manually selecting 3-5 corresponding
landmarks. The HE-based tumor delineations were
compared with the CKAE1/3-based tumor delineations.
The maximum distance between HE and CKAE1/3 tumor
delineations was measured for each patient. Furthermore,
the conformity index (CI) was measured between the
corresponding delineations.
Results
The 99th percentile distance for microscopic disease
outside the HE sections was 1.7 mm (0.9-3.4). This
distance includes some registration error between HE and
CKAE1/3 stained sections. The coverage of the CKAE1/3
delineated volume by the HE volume (sensitivity) was 0.93
(0.85-0.98) and the positive predictive value (PPV) was
0.89 (0.76-0.95). This shows that the tumor volume
delineated on HE is larger than on CKAE1/3. As the
distances between the contours on HE and CKAE and
reversely between CKAE and HE is comparable, the effect
on the CTV margin might be considered small. The CI was
0.83 (0.73-0.89), which is smaller than the CI for inter-
observer variation in tumor delineation on HE stained
sections. This might be partially attributed to the extra
registration step which is required for the comparison
between HE and CKAE1/3.
Conclusion
Nearly all tumor is delineated on HE within 2 mm accuracy
of the CKAE1/3 delineation. This is comparable with the
interobserver delineation accuracy on HE stained sections.
Consequently, the effect on the CTV margin for
delineations made on MRI or CT is not clinically relevant.
Poster: Clinical track: CNS
PO-0622 Medulloblastoma in adults: a retrospective
single institution analysis
I. Hadi1, O. Roengvoraphoj1, F. Roeder1,2, C. Belka1, S.
Nachbichler1
1Ludwig-Maximilians-Universität München, Radiation
Oncology, München, Germany
2German Cancer Research Center DKFZ, Molecular
Radiation Oncology, Heidelberg, Germany
Purpose or Objective
Adult medulloblastoma is a rare disease. The therapy is
based on pediatric treatment protocols. This retrospective
analysis investigated the clinical outcomes and prognostic
factors of adult patients receiving multimodal therapy in
our institution.
Material and Methods
Treatment charts of patients with medulloblastoma older
than 15 years old, who have been treated in our institution
between 2001 and 2014, were analyzed
retrospectively. Supratentorial tumors were excluded.
Patients‘ demographic parameters, histology, initial