ESTRO 36 Abstract Book

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S481 ESTRO 36 2017
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Conclusion
The availability of MRI images during target delineation of
pancreatic cancer on 3DCT and 4DCT improved the
interobserver variation. Furthermore, delineated volumes
are smaller on CT+MRI than on CT only. An approach of
3DCT GTV delineation with margins may be preferable to
4DCT iGTV delineation since the latter increases
uncertainty.
Poster: Physics track: (Quantitative) functional and
biological imaging
PO-0885 Assess Tumor Voxel Dose Response (SF2) Using
Multiple FDG PET Images
D. Yan 1, S. Chen2, D. Krauss2, P. Chen 2, G. Wilson2
1 Beaumont Health System, Radiation Oncology, Royal
Oak MI, USA
2 Beaumont Health system, Radiation Oncology, Royal
Oak- MI, USA
Purpose or Objective
To determine human tumor voxel dose response with using
bio-marker (SF2) derived from multiple FDG PET images
and evaluate the pattern of tumor local radioresistance
and failure.
Material and Methods
Multiple FDG PET/CT images obtained at the pre- and
weekly during the treatment (35x2Gy) for 15 HN cancer
patients were used for the study. from 0 to 70Gy, for each
tumor voxel, v, such that TMR(v, d) = SUV(v, d)/SUV(v, 0).
TMR of each patient was constructed following voxel-by-
voxel deformable PET/CT image registration. Assuming
ln(TMR(v, d)) = k . ln(SF(v, d)), the optimal linear
regression with unknown break-points was used to
determine the tumor voxel survival fraction, SF at
different treatment dose levels. Therefore, SF2(v, d), the
tumor voxel survival fraction after 2Gy, was obtained and
used as the tumor voxel dose response marker. Tumor
voxel SF2 distribution at different treatment dose level
was analyzed to evaluate the pattern of tumor voxel dose
response, specifically the tumor local radioresistant
pattern; meanwhile the effects of tumor voxel
reoxygennation and proliferation with respect to tumor
local failure were also evaluated. The tumor volumes with
different SF2 cutoffs were also correlated to treatment
outcome.
Results
Human tumor has significant inter- and intra-tumor
variations in their voxel dose response (Table). Tumor
voxels with the mean SF2 > 0.7 shows significant
prediction power (p < 0.01) after the treatment dose of
20~40Gy on tumor local failure. Tumor local recurrence
showed strong correlation to the tumor local
radioresistance determined using SF2 (Figure). Two of 3
failures showed a clear reoxygennation effect after 20Gy,
therefore could be potentially controlled by escalating
dose to destroy the local radioresistant niches. One failure
had a small (< 1cc) local radioresistant sub-volume and
showed the minimal reoxygennation, therefore it may
need a local ablation.
Conclusion
Tumor voxel metabolic ratio determined us ing multiple
FDG PET images can be used to assess tumor voxel dose
response, SF2, which shows an excellent predictive value
for tumor local radioresistance and failure. Our results
demonstrate that a heterogeneous dose distribution in
tumor should be prescribed to optimize cancer
radiotherapy. Tumor voxel TMR determined at the early
treatment will be good bio-parametric matrix to
determine a new tumor dose prescription function at the
voxel level for the treatment of adaptive dose-painting-
by-number.
PO-0886 Early changes of FDG-PET markers predict the
outcome after chemo-radiotherapy for pancreatic
cancer
S. Broggi1, P. Passoni2, E.G. Vanoli3, C. Fiorino1, G.M.
Cattaneo1, C. Gumina2, P. Mapelli3, E. Incerti3, L.
Gianolli3, N. Slim2, M. Picchio3, R. Calandrino1, N.G. Di
Muzio2