ESTRO 36 Abstract Book

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S173 ESTRO 36
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Conclusion
Endoscopic response after EBRT and residual tumor
thickness, circumference and volume at time of HDREBT
were significantly associated with achieving a complete
response. This demonstrates that careful selection of
patients for organ preserving strategies can result in a very
high success rate.
Proffered Papers: Head and Neck
OC-0329 Does margin matter? Distribution of loco-
regional failures after primary IMRT for Head &Neck
cancer
R. Zukauskaite1, C.R. Hansen1, C. Brink1, C. Grau2, E.
Samsøe3, J. Johansen1, E. Andersen3, J. Petersen 2, J.
Overgaard 4, J. Eriksen1
1 Odense University Hospital, Department of Oncology,
Odense, Denmark
2 Aarhus University Hospital, Department of Oncology,
Aarhus, Denmark
3 Herlev Hospital, Department of Oncology, Copenhagen,
Denmark
4 Aarhus University Hospital, Department of Experimental
Clinical Oncology, Aarhus, Denmark
Purpose or Objective
Head and neck squamous cell carcinoma (HNSCC) often
presents as a local or loco-regional disease. Margins are
often added around the gross tumour volume (GTV) during
the planning of curative radiotherapy to cover microscopic
disease. However, there is little evidence available for the
optimal size of the high dose clinical target volume (CTV1)
margin. Until 2013, different margins from GTV to CTV1
were allowed according to the national treatment
guidelines in Denmark, varying from 0 to up to 10 mm. The
objective of this study was to analyse loco-regional
recurrence pattern in a large cohort of patients with
HNSCC treated with curatively intended IMRT. We aimed
at evaluating how the location of CT verified loco-regional
recurrences (LRR) were influenced by different CTV1
margins.
Material and Methods
Patients with larynx, oro-/hypopharynx or oral cavity
HNSCC treated with primary IMRT during 2006–2012 in
three centres were retrospectively identified from
national database. Treatment was given according to
DAHANCA guidelines, primarily 66-68 Gy in 6
fractions/week with concomitant Nimorazole and weekly
cisplatin in loco-regionally advanced cases. The GTV-CTV1
margin was primarily produced by volumetric expansion
that varied from 0-10 mm and eventually modified
according to anatomy. The origin of recurrence was
estimated for all loco-regional treatment failures with
diagnostic CT or PET/CT images available. Assuming that
loco-regional recurrences arise from a few surviving
cancer cells, the possible points of LRR origin (PO) were
identified on diagnostic scans by two independent
observers, and calculated as mass mid-point (MMP) and a
point with maximal surface distance (MSD). A validated
deformable image registration (DIR) propagated the POs
from recurrence-CT to planning-CT. The distance from POs
to the surface of the GTV was calculated and presented as
mean distance from all four POs to the GTV. The patient
specific GTV-CTV1 margin was calculated as median
surface distance from GTV to CTV1. Difference between
LRR distribution in groups with small and large CTV
margins was evaluated using Kolmogorov-Smirnov test
(p<0.05).
Results
In total 1,581 patients were identified and 297 had LRR
within the first 3 years of follow-up; of those, 172 patients
had CT-verified recurrent disease. Among them, 50% had
GTV-CTV1 margin less than 5 mm and 50% larger than 5
mm. There was no difference in sex, tumour site, stage,
tumour differentiation and p16-status between these two
groups. After successful DIR, in total 192 recurrences were
further analysed in the two margin groups; no significant
difference in LRR distribution was found (p=0.6). Of the
POs in the first and the second groups, 58% and 64%
received 95% of the prescription dose, respectively (Figure
1).
Conclusion
The presented data do not suggest any difference in
distribution of loco-regional recurrences in relation to CTV
margins. Such a difference could be expected if the CTV
margin was a key component for loco-regional recurrence
probability.