ESTRO 36 Abstract Book

S240 ESTRO 36 _______________________________________________________________________________________________

to variation in arm / shoulder positioning on the breastboard armrests.

Figure 1: Measurement of D LAD Results For proximal, middle and distal LAD, 78%, 72% and 61% of subjects had both the longest D LAD in end-inspiratory (90- 10%) phase and shortest D LAD in end-expiratory (40-60%) phase. The average D LAD in end-inspiratory phase and end- expiratory phase were 13.1±2.0mm, 12.7±1.8mm, 11.6±1.5mm and 10.9±1.5mm, 10.5±1.4mm, 9.5±1.3mm for proximal, middle and distal LAD respectively. While the D LAD decreased from proximal to distal portion of LAD in both phases, the extension of D LAD from end-inspiratory phase to end-expiratory phase were similar in all LAD portions (proximal:2.1±0.9mm; middle: 2.2±0.8mm; distal: 2.1±0.5mm). The average Maxdisp LAD due to cardiac motion were also similar in proximal, middle and distal portion, which were 2.6±0.6mm, 2.4±0.5mm and 2.6±0.7mm respectively. When accounting both cardiac and respiratory motions, D LAD could be shorter than expected. To account the effect of both cardiac and respiratory motions, the shortest distance between LAD and chest wall (D LAD - 0.5 x Maxdisp LAD ) was estimated for end-inspiratory and end-expiratory phase. The averages were 11.8±2.1mm, 11.5±1.8mm, 10.3±1.6mm and 9.6±1.7mm, 9.3±1.4mm, 8.2±1.4mm for proximal, middle and distal LAD respectively. Conclusion Most patients could be benefited from gated radiotherapy using end-inspiratory phase (90-10%). However, the distance between LAD and chest wall could be shorter than expected due to random cardiac motion during actual treatment delivery. Special attention should be put on distal portion of LAD as it had the closest proximity to chest wall. A minimum clearance of 2mm (~0.5 x Maxdisp LAD ) from the LAD to the high dose zone during treatment planning is recommended to compensate for LAD displacement due to cardiac motion for patient receiving gated left breast radiotherapy. OC-0452 Evaluation of a novel field placement algorithm for tangential internal mammary chain radiotherapy A. Ranger 1 , A. Dunlop 1 , M. Maclennan 2 , E. Donovan 3 , E. Harris 3 , B. Brigden 4 , C. Knowles 4 , K. Carr 4 , E. Henegan 4 , J. Francis 4 , F. Bartlett 5 , N. Somiah 1 , I. Locke 1 , C. Coles 6 , A. Kirby 1 1 Royal Marsden Hospital Trust & Institute of Cancer Research, Clinical Oncology, London, United Kingdom 2 Edinburgh Cancer Centre, Clinical Oncology, Edinburgh, United Kingdom 3 Royal Marsden Hospital Trust & Institute of Cancer Research, Physics, London, United Kingdom 4 Royal Marsden Hospital Trust, Radiotherapy, London, United Kingdom 5 Portsmouth Hospital NHS Trust, Clinical Oncology, Portsmouth, United Kingdom 6 Cambridge University Hospitals NHS Trust, Clinical Oncology, Cambridge, United Kingdom

Conclusion With the current patient set up there is a considerable geometric variation in Level 1 in VD direction. Introducing a highly conformal technique requires adaptation of currently used margins for adequate target coverage of both the breast/chest wall and the ALNR. OC-0451 Effect of cardiac motion on displacement of LAD artery in gated left breast treatment using MRI S.Y. Ng 1 , W.K. Fung 1 , K.M. Ku 1 , O.L. Wong 2 , G. Chiu 1 1 Hong Kong Sanatorium & Hospital, Department of Radiotherapy, Hong Kong, Hong Kong SAR China 2 Hong Kong Sanatorium & Hospital, Medical Physics & Research Department, Hong Kong, Hong Kong SAR China Purpose or Objective Respiratory control has been promoted to minimize dose to heart during left sided breast radiotherapy. However, there is limited data to address the effect of intrinsic cardiac motion during actual treatment. This study quantified the effect of both cardiac motion and respiratory motion on variation in distance between left anterior descending artery (LAD) and chest wall, D LAD , for gated left-sided breast radiotherapy using MRI. Material and Methods Eighteen healthy female volunteers aged 32.1±5.0 were scanned in a 1.5T MR simulator (MAGNETOM Aera, Siemens Healthcare) with cine mode for respiratory motion (images resp ) and cardiac triggered cine mode for cardiac motion (images card ), at the middle slice locations of three equal segments of LAD (proximal, middle and distal). The images were sorted into 10 phases for respiratory cycle and cardiac cycle respectively. D LAD was measured in each slice of images resp as shown in Figure 1. The maximum LAD displacement along the direction of D LAD (Maxdisp LAD ) was measured in images card .