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Receiver-operator characteristic curves were plotted,
linking the extracted dose parameters with six patient-
reported clinical endpoints: rectal bleeding, proctitis,
sphincter control, rectal pain, and “How big a problem are
bowels?” (≥Grade 1, ≥Grade 2). Statistical correlations
between planned and accumulated DSMs were compared
using the calculated area under the curve (AUC) presented
on High-Low plots.
Results
For rectal bleeding, the 30, 40, and 60 Gy accumulated
DSM dose-widths were significant predictors (AUC 0.629,
0.621 and 0.643 respectively), where planned dose was
not (Figure 2a). For DSM dose-widths up to 70 Gy, AUC was
greater for accumulated dose than planned dose. EUD was
the strongest predictor of rectal bleeding from both
accumulated (AUC 0.682) and planned (AUC 0.673) DSMs.
The only significant predictor of proctitis was EUD of the
accumulated DSM (AUC 0.673) (Figure 2b). Neither
planned nor accumulated doses were predictive of the
other endpoints
Conclusion
For the first time, it has been possible to quantitatively
demonstrate that accumulated delivered dose to the
rectal wall is more strongly correlated with rectal bleeding
and proctitis in prostate radiotherapy than planned dose.
The results support the hypothesis that incorporating
delivered dose into multi-variable predictive models could
improve toxicity outcomes.
Poster: Physics track: CT Imaging for treatment
preparation
PO-0881 4DMRI for RT planning; novel precise
amplitude binning in the presence of irregular breathing
I. Bones
1
, O.J. Gurney-Champion
2
, A. Van der Horst
1
, A.
Bel
1
, T. Alderliesten
1
, G. Van Tienhoven
1
, K. Ziemons
3
, Z.
Van Kesteren
1
1
Academic Medical Centre, Radiotherapy, Amsterdam,
The Netherlands
2
Academic Medical Centre, Radiotherapy and Radiology,
Amsterdam, The Netherlands
3
FH Aachen University of Applied Sciences, Medical
Physics, Jülich, Germany
Purpose or Objective
Irregular breathing, often the case in clinical practice,
introduces the need for proper outlier handling for 4DMRI
reconstruction. Discarding outliers may lead to
underestimation of the respiratory-induced organ motion.
Our study aimed to develop and evaluate an amplitude
binning strategy that reduces reconstruction artefacts
while improving precision in the presence of irregular
breathing.
Material and Methods
Twelve volunteers and 2 abdominal cancer patients were
scanned with our 4DMRI sequence. In this 6 minute scan,
11 2D coronal slices were acquired repetitively (60 times)
during free breathing, using a T2W TSE sequence
(resolution: 1.3x1.6x5.0 mm
3
). Prior to each slice
acquisition, the position of the diaphragm was assessed
using a 1D acquisition.