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