Anderle, K.

Bert, C.

Constantinescu, A.

Debus, J.

Durante, M.

Eichhorn, A.

Erbeldinger, N.

Fiedler, F.

Fournier, C.

Graeff, C.

Helmbrecht, S.

Kaderka, R.

Lehmann, H. I.

Lundenbiel, P.

Packer, D. L.

Prall, M.

Richter, D.

Simoniella, P.

Takami, M.

Thomas, D.

GSI Repository

Reproducible immobilization for porcine heart irradiationsM. Prall1, H. I. Lehmann2, A. Constantinescu1, P. Simoniello1, P. Lugenbiel3, D. Richter1, M.Takami2, A. Eichhorn1, N. Erbeldinger1, C. Fournier1, R. Kaderka1, K. Anderle1, S. Helmbrecht4, F.Fiedler4, J. Debus3, D. Thomas3, C. Bert1, M. Durante1, C. Graeff1, and D. L. Packer21GSI Darmstadt (Germany); 2Heart Rhythm Services, Mayo Clinic (USA); 3University of Heidelberg, Germany;4Helmholtz-Zentrum Dresden-Rossendorf, GermanyHadron therapy has already proven to be successful incancer therapy, and might be a non-invasive alternative forthe ablation of cardiac arrhythmias in humans.In order to experimentally investigate this treatmentmodality, scanned carbon beams from the GSI acceleratorwere used to irradiate various targets in beating hearts ofhealthy pigs. Dose ranging from 25 Gy to 55 Gy was ap-plied during breath-hold in the 100 % expiratory phase un-der anesthesia. The alignment and breathing phase duringirradiation had to reproduce the situation of the treatmentplanning CT (TPCT) with an accuracy of a few millimeters.A pig immobilization device (PID) allowing reproducibil-ity of shape and position was designed (cf. Figure 1).Figure 1: A pig in irradiation position in Cave M at GSI.Both, TPCT scans and irradiations were performed dur-ing breath-hold in the 100 % expiratory phase. Animalswere kept in deep anesthesia in order to completely sup-press spontaneous lung motion. A computer-controlledventilator was used (Evita XL by Dra¨ger Medical). Withthis device, animals were ventilated with intermittent pos-itive pressure ventilation with 14 breathing cycles perminute, 350 ml tidal volume, a positive end-expiratorypressure of 0 mbar and an oxygen concentration of 20 %.A LabVIEW interface running on a personal computer wasimplemented for remote control, data logging and commu-nication with the beam application and monitoring systemat GSI.TPCTs where acquired at Heidelberg Ion-Beam TherapyCenter (HIT) and irradiation was applied at GSI Darmstadta few days later. This situation was experimentally simu-lated to estimate the degree of reproducibility: The immo-bilization and TPCT scan of a test animal was repeated atHIT with about one week delay. For the analysis, one ofthe two TPCTs first was shifted such that the PIDs werecoincident in both scans. A displacement vector field relat-ing the two scans was derived using deformable registrationwith the Plastimatch module of the medical image analysissoftware ‘Slicer’ (B-spline deformable registration, regu-larization=0.1, grid size=20). Displacement vectors withan absolute magnitude (AM) of more than 5 mm can onlybe observed in the beating heart. In the remaining volume,the AM is below 5 mm. Throughout the backbone and largeparts of the sternum, AM is below 3 mm. AM up to 4 mmcan be observed in the lateral chest walls.Shortly before irradiation, X-ray images were taken bothin dorsoventral and lateral direction at Cave M. They wereacquired under breath-hold, exactly as during irradiation.Exposure time was about one second. Therefore the targetitself, the beating heart, is smeared out and nearby struc-tures had to be used to verify reproducibility of breath-hold.Pairwise comparison of the positions of selected anatom-ical structures (vertebrae, sternum, diaphragm) was em-ployed. Images were preprocessed using affine and rigidregistration. The plugin Landmark Correspondences of themedical image analysis software ‘ImageJ’ was used. Re-producibility of breath-hold is in the order of 1 mm or be-low for all anatomical sites considered.Based on the available data we estimate that the PIDcombined with a breath-hold, controlled by a clinical ven-tilator, allows to reproduce the geometrical situation of theTPCTs with an accuracy of better than about 5 mm for theanatomy surrounding the heart (backbone, sternum, chestwalls). In irradiations, heart-beat motion was mitigated us-ing the rescanning technique (cf. these proceedings). Wecurrently investigate additional perturbations due to geo-metrical and temporal variability of the heart motion.Irradiated animals were dissected after a follow-up pe-riod of about six months. The desired target regions exhibitfibrotic tissue, suggesting that immobilization and motionmitigation were sufficient. Analysis is ongoing and numer-ous technical and biological factors (cf. these proceedings),still under investigation, will influence the final result.AcknowledgementsThe Helmholtz Association funded this work through theHelmholtz-Portfolio Topic ”Technology and Medicine”.We thank Harry Leidel from the GSI workshop and ElkoSchubert for supporting us with the development of the pigimmobilization device.GSI SCIENTIFIC REPORT 2014 APPA-HEALTH-32DOI:10.15120/GR-2015-1-APPA-HEALTH-32 325

Reproducible immobilization for porcine heart irradiations

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Reproducible immobilization for porcine heart irradiations

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