ESTRO 2020 Abstract book

S108 ESTRO 2020

Material and Methods C57BL/6 mice were irradiated with a single fraction of 16 Gy targeted to the base, middle and apex of the heart, with a 3 x 9 mm field and parallel opposed geometry, using a small animal radiotherapy research platform (SARRP, Xstrahl Life Sciences). Cone beam CT and echocardiography were performed at baseline and at 10 week intervals for 50 weeks after treatment. Left ventricle (LV) wall thickness was quantified from M‐mode parasternal short‐axis scans at the level of the papillary muscles. Fractional shortening (FS) was calculated from the LV end‐diastolic and end‐systolic diameters, and pulse‐ wave Doppler used to quantify mitral valve (MV) flow, expressed as E/A ratio. Structural and functional parameters were correlated with mean heart dose (MHD) All irradiated mice showed a time dependent increase in LV wall thickness detected as early as 10 weeks following treatment, with the most significant and persistent changes occurring in the base irradiated animals. Similarly, differential effects were observed on cardiac function with base irradiated animals showing the most significant decreases in FS, ejection fraction and E/A ratio compared to control animals at 40 and 50 weeks following irradiation. The observed structural and functional changes did not correlate with MHD and V5 indicating that whole heart dosimetry parameters do not predict physiological changes resulting from irradiation of cardiac This is the first report demonstrating structural and functional consequences of subvolume targeting in the mouse heart. Our data are in close agreement with clinical observations indicating the base of the heart as a radiosensitive region and form the basis for further mechanistic investigations. OC-0197 Dose surface maps of the heart identify dose sensitive regions A. McWilliam 1,2 , L. Graham 1 , C. Dootson 1 , A. Abravan 1 , M. Van Herk 1,2 1 University of Manchester, Division of Cancer Science, Manchester, United Kingdom ; 2 The Christie NHS Foundation Trust, Radiotherapy Related Research, Manchester, United Kingdom Purpose or Objective It has become accepted that for lung cancer patients the radiation dose to the heart is an independent predictor of survival. Analysis of dosimetric effects on the heart have investigated volumetric dose statistics, however potential critical cardiac structures are present on the heart surface. Volumetric parameters may not be optimal due to the required inter-patient registration accuracy. In this work we present a methodology for creating cardiac surface dose maps and use these to identify cardiac surface regions where excess dose results in worse patient survival. Material and Methods 648 cardiac surface maps were successfully created with a polar coordinate system with the centre positioned at the centre of mass for the heart contour of each slice in turn. This accounted for the asymmetric nature of the heart and can be considered a modified cylindrical coordinate system. The radiotherapy dose for each patient was sampled on this surface with the described coordinate system. All hearts were normalised to the same superior-inferior dimensions for analysis. For validation of the mapping, and localisation of dosimetric effects, the cardiac chambers were manually delineated and mapped onto the surface maps for 20 patients. A point spread function (PSF) was fitted to the blurred edge of the mapped chambers to quantify uncertainty in the mapping process. To account for this and V5. Results subvolumes. Conclusion

Award Lecture: E. van der Schueren Award Lecture

SP-0194 What´s in a name? M. Leech 1 1 TCD Discipline Of Radiation Therapy, Radiation Therapy, Dublin, Ireland Abstract text ‘What's in a name? That is what we ask ourselves in childhood when we write the name that we are told is ours’ (James Joyce). Names are our titles, our brands and our identities. Consider the name ‘radiation therapy’ or ‘radiotherapy’. Now consider how and if the general public and other healthcare professionals identify with this name, our ‘brand’. Do they really? An ESTRO white paper on seizing the opportunity in cancer care stated that if by 2035, every cancer patient who needs radiation therapy had access to it, almost one million more lives would be saved every year worldwide. Every radiation oncology professional has it within them to contribute to making this happen. Debunking myths about radiation therapy, particularly its safety and efficacy, explaining in plain terms and with simple visual aids the process of radiation therapy and really listening to what patients fear about radiation therapy are ways that all radiation oncology professionals can contribute to this goal, regardless of location and resources. These simple actions are surely within our remit. This presentation urges us to come together as a radiation oncology community to promote and advocate for our specialty, which can only benefit patients globally.

Award Lecture: Jens Overgaard Legacy Award

SP-0195 TBC R. Pötter Medical University of Vienna, Austria

Abstact not available

Proffered Papers: Proffered papers 8: Cardiac toxicity

OC-0196 Cardiac sub-volume targeting demonstrates regional radiosensitivity in the mouse heart K. Butterworth 1 , K. Williams 2 , M. Van Herk 3 , A. McWilliam 3 , M. Aznar 3 , S. McMahon 1 , E. Vasques Osorio 4 , K. Edgar 5 , G. Walls 1 , E. Gill 5 , M. Ghita 1 1 Queen's University Belfast, Centre for Cancer Research and Cell Biology, Belfast, United Kingdom ; 2 University of Manchester, School of Pharmacy, Manchester, United Kingdom ; 3 University of Manchester, Department of Radiotherapy Related Research, Manchester, United Kingdom ; 4 University of Manchester, Division of Molecular and Cancer Science, Manchester, United Kingdom ; 5 Queen's University Belfast, Wellcome-Wolfson Institute For Experimental Medicine, Belfast, United Kingdom Purpose or Objective Radiation induced cardiac toxicity remains one of the most critical dose limiting constraint in radiotherapy and a major cause of mortality amongst cancer survivors. Recent clinical evidence has shown higher doses to the base of the heart are associated with worse overall survival in lung cancer patients receiving curative intent radiotherapy. This work aimed to investigate the impact of subvolume heart irradiation in a mouse model, and to identify critical radiosensitive regions towards developing a mechanistic understanding of regional radiosensitivity.

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