ESTRO 36 Abstract Book

S42 ESTRO 36 _______________________________________________________________________________________________

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 BVH-30 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 +/- 2.0 the MC results. Skin applicator type Output factor (cGyh -1 U -1 ) Flatness (%) Penumbra (mm) BVH-20 0.2215 0.0063 0.1729 0.0049 +/- 1.8 2.0