ESTRO 37 Abstract book

ESTRO 37

S453

12 University Clinic of Radiotherapy and Oncology, Dept. of Radiation Oncology, Skopje, Macedonia Former Yugoslav Republic 13 National Cancer Centre, Dept. of Radiation Oncology, Ulaanbaatar, Mongolia 14 Clinical Centre of Montenegro, Radiotherapy Dept., Podgorica, Montenegro 15 Nuclear Medicine- Oncology and Radiotherapy Institute, Dept. of Radiation Oncology, Islamabad, Pakistan 16 Institute of Nuclear Medicine and Oncology, Dept. of Radiation Oncology, Lahore, Pakistan 17 Centro de Radioterapia de Lima, Dept. of Radiation Oncology, Lima, Peru 18 ONCOSUR, Dept. of Radiation Oncology, Florida, Uruguay 19 ESTRO, ESTRO School, Brussels, Belgium 20 IAEA, Applied Radiation Biology and Radiotherapy Section- Division of Human Health, Vienna, Austria Purpose or Objective One of the challenges in modern radiotherapy (RT) is variability in contouring of target volumes (TVs) and organs at risk (OARs). Interactive online teaching has shown immediate improvement of homogeneity of delineation but the long-term effect is unknown. The aim of the present multicenter study was to evaluate the short- and long-term impact of online learning on homogeneity in contouring for 3D RT planning and to evaluate the feasibility of blended learning in centers from low- and middle-income countries (LMIC) who have recently transitioned from 2D to 3D RT. Material and Methods Radiation Oncologists (ROs) from 14 centers in 13 countries from Costa Rica in the West to Mongolia in the East were invited. The online teaching consisted of three lectures, one week and one month in between. Participants delineated TVs and OARs on a treatment- planning scan available in the FALCON-EduCase online system. Four delineations were done: before and during the teaching-period (three lectures separated by one week and one month) and again without teaching six months later. As soon as one teaching program had finished a new program started for another site. In total 12 delineations for three cases of head and neck cancer, cervical cancer and lung cancer were delineated over a period of one year. Participants were not aware of which structures were evaluated. The DICE index and defined qualitative measures were used as endpoints. Results Of the 60 ROs invited, 57 were included and delineated: 77% were specialists, 68% female and 80% worked in public hospitals. The compliance to the whole program varied from site to site but were in general good (>50%). The majority (88%) used 3D RT on a routine basis. For the head and neck part of the program, significant increases were seen in homogeneity of delineation for both TVs and OARs (table 1). For example delineation of the elective CTV in the neck (no pathology involved), DICE increased immediately during the teaching sessions and remained high even six months after teaching (p<0.0001, figure 1). That was also reflected in the levels chosen by the participants changing from 4% delineating level II-IV to 94% delineating the levels suggested by the guidelines after 6 months. Similar results were recorded for OAR, like for DICE of the right parotid gland (p<0.0001, table 1) and with an increase from 71% to 100% of the ROs who remembered to include the deep lobe of the gland from first delineation to the last, six months later. The general trends summarized here were also reflected for the other tumor sites.

Conclusion Online teaching in LMIC seems feasible and with an acceptable compliance to the learning program. The learning obtained on a short-term basis was shown to be sustainable six month after teaching. PO-0865 Unconventional radiotherapy for bulky tumors exploiting the bystander and abscopal effects. S. Tubin 1 , W. Raunik 1 1 KABEG Klinikum- Landeskrankenhaus, Strahlentherapie und Radioonkologie, Klagenfurt, Austria Purpose or Objective Even if radiotherapy has benefited tremendously from a long series of advances, the prognosis of bulky tumor patients treated with conventional radiotherapy remains poor. Trying to improve the outcomes we developed an unconventional radiotherapy method applying to such a clinical situation the generation of bystander (BE) and abscopal effect (AE). In our pre-clinical studies on the induction of BE/AE, partial (vs. whole) tumor irradiation, targeting hypoxic (vs. normoxic) tumor segment with high dose radiotherapy correlated with strongest BE/AE. Those findings were recently translated to a clinic with the aim to evaluate the hypothesis that partial high-single-dose irradiation of the hypoxic tumor segment leads to the induction of BE/AE improving the therapeutic ratio. The primary endpoint was to assess the efficacy of this method in terms of local control by generating BE/AE. The secondary endpoints included the assessment of toxicity and symptoms control. Material and Methods This prospective study included 25 oligometastatic, symptomatic patients with bulky tumors of the lung, head and neck, kidney, skin, adrenal glands and lymph nodes. For definition of the hypoxic tumor segment (“bystander tumor volume”-BTV, Fig.1), PET-CT in combination with contrast-enhanced CT was used. All bulky masses were irradiated partially by targeting exclusively BTV with 10 or 12Gy in single fraction prescribed to the 70% isodose line (Dmax: 15 or 18 Gy, respectively). Treatment was delivered with VMAT by 6MV flattening filter free photon beams with a dose rate up to 1400 MU/min. A SBRT plan was calculated on Monaco TPS (Monte Carlo algorithm). Before every treatment, a kilovoltage cone-beam CT was performed. Chemotherapy and immunotherapy were not