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S393
ESTRO 36
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Purpose or Objective
The use of stereotactic body radiation therapy (SBRT) is
increasing rapidly in patients with bone metastases. This
technique involves high precision dose delivery, for which
accurate gross tumor volume (GTV) contouring is crucial.
This study compares inter-observer agreement in bone
metastases delineated on CT, MR and CT with co-
registered MR imaging.
Material and Methods
Twenty consecutive patients with bone metastases
treated with SBRT were selected. All patients received CT
and MR imaging in treatment position prior to
radiotherapy. CT images were obtained with a Philips
large bore CT scanner (1 mm slice thickness). A Philips 1.5
Tesla MRI scanner was used to acquire T1- and T2-
weighted images in transversal direction. Coronal and/or
sagittal images were acquired, including 3D T1FFE mDIXON
scan (slice thickness 1.1mm) and diffusion weighted
imaging (slice thickness 4 mm). Five observers from three
institutions independently delineated GTV after a training
set of two patients and a consensus meeting. First, GTV
was delineated on CT images only. A second delineation
was based on CT images with co-registered MR images. At
least four weeks after the delineation on CT-MR combined,
the GTV was contoured on MR imaging only. Average
volumes of the contours per patient and imaging modality
were calculated. The generalized conformity index (CI)
was used to quantify inter-observer agreement.
Significant differences between the average volumes and
CI were analyzed by Wilcoxon signed rank test. Observer
count maps were generated for visual comparison of
agreement for each case and imaging modality.
Results
Mean GTV volume delineated on MR (43.4 ± 49.7 cm
3
) was
larger compared to CT-MR (40.2 ± 49.4 cm
3
) and CT (34.8
± 34.8 cm
3
). Compared to CT, the mean volume of GTV
was 11% larger on CT-MR and 35% on MR (Figure 1B). A
large variation in CI was found in all imaging
modalities: CT (range: 0.15-0.75), CT-MR (range: 0.17-
0.71) and MR (0.14-0.80). Mean CI were significantly
higher on CT-MR compared to CT (Table 1). An example of
a count map is shown (case 18, Figure 1B). For this case,
mean volume of the GTV was almost doubled on MR
compared to CT, which might be explained by better
visibility of the extra-osseous disease on MR imaging.
Conclusion
This multicenter contouring study demonstrated large
inter-observer variation in GTV delineation for all
investigated imaging modalities. Delineation of GTV on MR
imaging resulted in larger volumes and marginal better
inter-observer agreement compared to CT only
delineations. These results suggest that future research
should focus on guidelines to improve agreement on GTV
delineation in these spine and non-spine bony metastases.
PO-0747 Setting defaults in palliative radiation: a
value-driven approach to improving care
L. Puckett
1
, L. Lee
1
, I. Zhang
1
, P. Zuvic
1
, P. Gilbo
1
, L.
Potters
1
, B. Bloom
1
1
Northwell Health / Hofstra Northwell School of
Medicine, Radiation Medicine, Lake Success, USA
Purpose or Objective
Single fraction (fx) and hypofractionated (1 or 5 fx)
radiation treatment (RT) provide superior value and
reduced treatment length in the palliation of bone
metastases. Despite data and recent guidelines
recommending reduced treatment duration, there has
been a slow adoption of this practice in the USA and
worldwide. Previous examination of our academic and
community multi-center practice from 2004 - 2016
revealed that single fx RT utilization has remained at 16%
and hypofractionationed courses have remained at 72%
since 2012. We hypothesized that enacting evidence-
based, treatment-guiding defaults would further increase
hypofractionation utilization.
Material and Methods
Institutionally, palliative bone metastasis treatments are
monitored by our Quality Assurance (QA) committee. On
2/29/2016, two distinct consensus-driven and evidence-
based clinical directives were created within our
electronic health system for use with either simple or
complicated bone metastasis, irrespective of primary
histology. The simple and complex treatment directives
had default prescriptions of 8 Gy/1fx or 20 Gy/5fx,