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ESTRO 36 2017
_______________________________________________________________________________________________
Purpose or Objective
Medical error rates are a leading cause of death in the
United States. Health leaders have advocated for incident
learning systems (ILS) to prevent errors, but there is
limited evidence demonstrating that ILSs improve patient
safety. Herein, we report a long term retrospective
review of 2273 prospectively collected and analyzed
incident learning system reports for the brachytherapy
practice at a large academic institution for the years 2007-
2015.
Material and Methods
This nine-year ILS intervention extended reporting beyond
the institutional pathway for near-misses. An ILS was
established in 2007 for the entire department to report all
standard operating procedures deviations, including low
risk deviations that do not reach the patient but could
indirectly impact patient care. A multidisciplinary
committee continually measured risk to patients by
assigning root causes and composite-risk-scores to all
incidents. Primary outcomes were decreased dose risk and
composite risk scores. Incidents were scored from 1 (low)
to 5 (high) in five categories: likelihood of recurrence,
likelihood of quality assurance failure, likelihood of non-
dose related severity, likelihood of dose related severity
or violation of radiation safety policy, and staff or patient
time wasted. A composite-risk-score was calculated from
the multiplicative product of the aforementioned scores
(minimum score = 1
5
,maximum score = 5
5
). Secondary
outcomes included safety culture metrics such as
improved communication and written procedure quality.
Risk scores were used to identify needed practice changes.
Relevant incidents were communicated to all
staff. Significance was tested using Chi-squared and
Spearman statistical methods.
Results
For 5258 brachytherapy procedures performed between
January 1, 2007 and December 31, 2015, participation in
the incident learning system increased remarkably
between 2007 (0.12 submissions/procedures) to 2011
(1.58 submissions/procedures) and has remained stable
since 2011. Since 2011, risk of dose error or radiation
safety policy violation decreased by 60% (p<0.001), and
frequency of composite-risk-scores greater than 50 (the
ILS threshold for immediate action) decreased by 69%
(p<0.001). Significant decreases were observed in
incidents with root causes of poor communication (57%
decrease, p<0.001) and poor quality of written procedures
(56% decrease, p<0.001) as a result of practice
improvement.
Conclusion
Patient safety was significantly improved in brachytherapy
through use of a comprehensive incident learning system
that captured both low and high risk incidents. Incident
learning systems may be effective in promoting a culture
of safety and preventing medical error.
OC-0082 Novel Valencia-type skin applicators:
Dosimetry and implementation of a TG-43 hybrid
technique
D. Baltas
1
, G. Anagnostopoulos
2
, M. Andrassy
3
1
Universitatsklinik Freiburg, Medical Physics - Radiation
Oncology, Freiburg, Germany
2
pi Medical Ltd, Medical Physics, Athens, Greece
3
Eckert&Ziegler GmbH, Medical Physics, Berlin, Germany
Purpose or Objective
To determine the relative dose rate distribution in water
for the novel Bebig 20 mm (BVH-20) and 30 mm (BVH-30)
skin applicators. Results for both skin applicators are also
provided in the form of a hybrid TG-43 dosimetry
technique. Furthermore, the radiation leakage around
both skin applicators, as well as the impact of the
geometrical uncertainties on the dose delivery are studied
and reported.
Material and Methods
MC simulations were performed using the MCNP5 v.1.6
code, which was benchmarked against dosimetry data for
the Bebig Ir2.A85-2
192
Ir source and the dose data for the
two Elekta Valencia skin applicators. The dose
distributions for both Bebig applicators in a water
phantom were calculated. The dosimetric quantities
derived according to a hybrid TG-43 dosimetry technique
were incorporated in a TPS and the accuracy of the dose
calculation in comparison to MC results was assessed.
Furthermore the air- kerma rate in air was simulated in
the vicinity of each skin applicator to assess the radiation
leakage of both skin applicators. For the assessment of the
geometrical uncertainties impact on the dose
administered to the PTV, the tolerance limit values of all
skin applicator parts and source offset positions were
modelled and calculated. The dose percentage difference
is shown with the aid of colormap figures.
Results
Results from MC-simulations of both skin applicators are
presented in form of figures, dose rate tables and with the
aid of the quantities defined in the hybrid TG-43 dosimetry
technique. Their output factors, flatness and penumbra
are presented in Table 1. Their radiation shielding was
adequate for their clinical employment with the 10%
isokerma line in air confined within 1cm from the skin
applicator shielding surface as illustrated in Figure 1. The
TPS dose rate values calculated with the hybrid TG-43
technique were within 2% with the MC dose rate values in
the dose flattened regions. The geometrical uncertainties
impact on the PTV showed a 3% over-/underdosage at the
prescription depth of d=0.3cm. The geometrical
uncertainties impact on dosimetry are more profound at
the applicator periphery projection in the high dose
gradient regions outside of the PTV extension and could
reach a value of up to 14% dose difference. Further work
is currently performed for the experimental verification of
the MC results.
Skin applicator
type
Output factor
(cGyh
-1
U
-1
)
Flatness
(%)
Penumbra
(mm)
BVH-20
0.2215
+/-
0.0063
1.8
2.0
BVH-30
0.1729
+/-
0.0049
2.0
2.2
Table 1.
The output factors, flatness and penumbra of the
novel Bebig skin applicators evaluated at the reference
depth of d= 0.3cm from the MC simulations
Conclusion
The Bebig skin applicators are suitable for the treatment
of skin lesions and their dosimetric data can be entered in
the form of hybrid TG-43 dose datasets in the TPS, so as
to enable 3D dose calculations. The user is advised to
perform autoradiography prior to the clinical use because
a potential source shift could result to the over-/
underdosage of the PTV and the OARs.
OC-0083 High-dose-rate surface brachytherapy for
basal cell cancer
P. Wojcieszek
1
, M. Szlag
2
, A. Cholewka
2
, S. Kellas-
Ślęczka
1
, A. Pruefer
2
, M. Fijałkowski
1
, B. Białas
1
1
MSC Memorial Cancer Center and Institute of Oncology
Gliwice Branch, Brachytherapy, Gliwice, Poland
2
MSC Memorial Cancer Center and Institute of Oncology
Gliwice Branch, Radiotherapy Planning, Gliwice, Poland
Purpose or Objective
To evaluate efficacy of high-dose-rate (HDR) surface
brachytherapy with individual moulds and flaps in the
treatment of basal cell cancer.
Material and Methods
One hundred sixty two skin cancer patients were treated
with HDR surface brachytherapy from 01.01.2008 to
31.12.2009 in our department. Patients with
pathologically confirmed basal cell cancer were enrolled
into this study. We excluded patients with relapse after