ESTRO 36 Abstract Book

S312 ESTRO 36 _______________________________________________________________________________________________

Focus on the US Doppler advantages and limitations The 3D Doppler technique allows the evaluation of the hemodynamics by exploiting the Doppler effect. The regions containing moving particles will be shown in false colors according to their velocity. Three main indices are provided, namely the vascularization index (VI), the flow index (FI) and the vascularization flow index (VFI). The VI is the percentage of color pixels in the region of interest and represents the amount of vasculature, while FI is the average (%) color-value of the pixels which were recognized as vessels, indicating the mean flow. The rescaled product of the above equals to the vascularization flow index (00.5) in five cases out of seven. Although non-responsive tumors were more critical to mimic, the model was able to identify their hypoxic status.

arcCHECK. The performance of a dedicated MRI compatible version of the Delta4 and the acrCHECK has been evaluated. Both devices performed well in presence of a 1.5 T magnetic field, and isocentric set-up, with no significant differences relative to conventional linac without magnetic field. Since the MR-Linac aims for online adaptive radiotherapy, online plan QA needs to be developed additional to the offline QA procedures and devices. At the MRI-linac, an IMRT plan will be created online based on the daily anatomy while the patient is on the treatment couch. Therefore, individual plan QA via measurements can’t be performed. As a solution, the use of an independent dose calculation based on 3D collapsed cone dose calculation algorithm was investigated. Although the effect of the magnetic field is not directly incorporated in this algorithm it seems to be sufficient to be used for online QA of the online generated IMRT plan. SP-0595 Modeling the interplay among volume, vascularization and radio-sensitivity in cervical cancer exploiting 3D-Doppler data A. Belfatto 1 , D. Ciardo 2 , A.M. Vidal Urbinati 3 , F. Cattani 4 , R. Lazzari 4 , B.A. Jereczek-Fossa 4 , D. Franchi 3 , R. Orecchia 5 , G. Baroni 1 , P. Cerveri 1 1 Politecnico di Milano University, DEIB, Milano, Italy 2 European Institute of Oncology, Unit of Medical Physics, Milano, Italy 3 European Institute of Oncology, Division of Preventive Gynecology, Milano, Italy 4 European Institute of Oncology, Division of Radiotherapy, Milano, Italy 5 European Institute of Oncology, Scientific Director, Milano, Italy The role of oxygenation in tumor radio-sensitivity The cell damage due to radiation exposure is conveyed by means of both direct effects, and indirect ionization of DNA due to free-radicals (e.g. O-). As a consequence, tumor oxygenation affects the response to radiotherapy by enhancing the radiosensitivity, conversely, hypoxic tumors are likely to be more radio-resistant. Moreover, literature findings suggest a systemic repercussion of changes in oxygen levels in the lesion area, for example hypoxia may reduce the tumor metabolism inducing a quiescent status and preventing the mass development. Mathematical models of tumor growth and response to irradiation are able to mimic the interplay among oxygenation, volume and radiosensitivity addressing the problem as a whole. Tumor data (e.g. volume, PO 2 , necrotic fraction) are mandatory for an accurate and patient-specific model setting. Current methods to assess tumor oxygenation This lecture does not aim to provide an exhaustive overview of the methods currently available for the evaluation of tumor oxygenation, however a brief description of the most used techniques is in order. The Eppendorf probes are still considered the gold standard in the assessment of oxygenation and consist in a direct measure of PO 2 . Despite their accuracy, the electrodes are not always applicable in clinics due to their intrinsic invasiveness and the local nature of the measurements. Alternative methods require the use of radioactive tracers and PET scans or functional MRI (e.g. interleaved BOLD- TOLD protocols). Another option is the 3D Doppler ultrasonography, which is inexpensive and non-invasive, although some restrictions reduces the extent of its application. Symposium: Novel approaches for combining imaging and non-imaging data for radiotherapy response predicition