ESTRO 36 Abstract Book

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S171 ESTRO 36 2017
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PV-0328 Factors associated with complete response
after brachytherapy for rectal cancer; the HERBERT
study.
E.C. Rijkmans1, R.A. Nout1, E.M. Kerkhof1, A. Cats2, B.
Van Triest 3, A. Inderson4, R.P.J. Van den Ende1, M.S.
Laman 1, M. Ketelaars1, C.A.M. Marijnen1
1 Leiden University Medical Center LUMC, Department of
Radiotherapy, Leiden, The Netherlands
2 The Netherlands Cancer Institute, Department of
Gastroenterology and Hepatology, Amsterdam, The
Netherlands
3 The Netherlands Cancer Institute, Department of
Radiotherapy, Amsterdam, The Netherlands
4 Leiden University Medical Center LUMC, Department of
Gastroenterology and Hepatology, Leiden, The
Netherlands
Purpose or Objective
The HERBERT study was performed to examine the
feasibility of a high hose rate endorectal brachytherapy
(HDREBT) boost after external beam radiotherapy (EBRT)
in elderly patients with rectal cancer who were unfit for
surgery. The primary results and long term clinical
outcomes have been presented at ESTRO 2014 and 2016.
With rising interest for organ preservation, the role of
definitive (chemo)radiotherapy becomes increasingly
important. This current analysis evaluates factors that are
associated with a complete response to treatment.
Material and Methods
A dose finding feasibility study was performed from 2007
to 2013 in inoperable rectal cancer patients. Patients
received 13x3 Gy EBRT followed by three weekly
applications HDREBT of 5 to 8 Gy per fraction. Clinical
target volume (CTV) for HDREBT was defined as residual
scarring or tumor after EBRT. Clinical tumor response was
evaluated based on digital rectal examination and
endoscopy (MRI or biopsy was not routinely performed).
Complete response was determined after serial
assessments. Patient, tumor and treatment
characteristics of complete responders (CR) were
compared to non-complete responders (nCR) using Chi-
square test and the independent samples t-test.
Results
Of the 38 patients included in the study 33 were evaluable
for response evaluation. Seven were treated with 5 Gy per
fraction, four with 6 Gy, 12 with 7 Gy and 10 with 8 Gy per
fraction. In total 20 patients achieved a complete
response. Baseline patient characteristics (age, ASA, WHO
and co-morbidity) and tumor-characteristics (T-stage, N-
stage, cranio-caudal length of the tumor and distance
from anal verge) were not associated with response to
treatment. A trend was observed in complete response
between dose levels; 2/ 7 treated with 5 Gy per fraction;
1/4 with 6 Gy; 9/12 with 7 Gy and 8/10 with 8 Gy per
fraction (p=0.05). The actual planned D98 (dose to 98% of
the CTV) was however not significantly different between
patient with a complete response and no complete
response: 6.25 Gy (range 3.8-8.3 Gy) vs. 5.98 Gy (range
1.2-8.8 Gy) respectively (p=0.63).
Endoscopic evaluation of response after EBRT was
significantly associated with the overall response rate.
Seven patients already had a CR after EBRT, whereas
13/21 patients (62%) with a partial response after EBRT
achieved a CR. None of the five patients with stable
disease achieved a complete response (p=0.002). Mean
residual volume and thickness of residual scarring or tumor
after EBRT were significantly lower in complete
responders (see Figure). In addition, tumors encompassing
less than 1/3 of the circumference were more likely to
achieve a complete response than larger tumors (70% vs
17% respectively, p=0.025).
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. Petersen2, J.
Overgaard 4, J. Eriksen1
1Odense University Hospital, Department of Oncology,
Odense, Denmark
2Aarhus University Hospital, Department of Oncology,
Aarhus, Denmark
3Herlev Hospital, Department of Oncology, Copenhagen,
Denmark
4Aarhus 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