ESTRO 2021 Abstract Book

S429

ESTRO 2021

Figure 1. Average and SD of the Jacobians for PTVs and OARs. Daily dose coverage for the target volumes were maintained. The relevant OARs constraints were also respected without major deviation from the planning values, while no significant differences were found between the Body or Mask based processing (Figure 2). Accumulated dose remained comparable to the planned one as well.

Figure 2. Daily DVH parameters using Mask and Body based deformation.

Conclusion We demonstrated the feasibility of daily and accumulated dose determination for pancreas SABR using residual error assessment and deformable registration. The clinical plausibility is granted with visual and quantitative evaluation of deformation. As the accumulated DVHs also met our dose constrains, our results reassuring the safe administration of pancreas SABR using our current margins of 3mm. PH-0546 Proton therapy guidelines for treating targets with adjacent cardiac implantable electronic devices L.B. Stick 1 , P.M.T. Lægdsmand 1 , H.L. Bjerre 1,2 , M. Høyer 1 , M.F. Jensen 1 , B.V. Offersen 1,3 , C.J.S. Kronborg 1 1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Cardiology, Aarhus, Denmark; 3 Aarhus University Hospital, Department of Experimental Clinical Oncology & Department of Oncology, Aarhus, Denmark Purpose or Objective Cardiac implantable electronic device (CIED) malfunctions can be induced by secondary neutrons from treatment with proton therapy. A recent in-vitro study at the Danish Centre for Particle Therapy (DCPT) investigated secondary neutron exposure (SNE) of CIEDs up to 7 mSv per fraction (calculated as ambient dose equivalent H*(10)) and found a low risk of malfunctions, which were clinically manageable. The amount of SNE in the CIEDs depends on the number of protons, the beam energy and their distances from the beam. This study defines the DCPT guideline for selection of breast and head & neck (H&N) cancer patients with CIEDs adjacent to target for pencil beam scanning proton therapy based on Monte Carlo simulations of SNE and the 7 mSv threshold. Materials and Methods Ten breast and five H&N cancer patients were included in the study. Five breast cancer patients received photon therapy with CIED and proton plans were retrospectively created. Five breast and five H&N cancer patients received proton therapy without CIED and a worst-case position of a virtual CIED were retrospectively delineated. Two breast cancer patients received breast only irradiation with an ipsilateral CIED and eight