ESTRO 36 Abstract Book

251 / 1082

S238 ESTRO 36 2017
_______________________________________________________________________________________________
Figure 1: Measurement of DLAD
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 DLAD decreased from proximal to distal portion of LAD
in both phases, the extension of DLAD 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 MaxdispLAD 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 (DLAD - 0.5 x MaxdispLAD) 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. Ranger1, A. Dunlop1, M. Maclennan2, E. Donovan 3, E.
Harris 3, B. Brigden4, C. Knowles4, K. Carr4, E. Henegan4,
J. Francis4, F. Bartlett5, N. Somiah1, I. Locke1, C. Coles6,
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
Purpose or Objective
Published data demonstrate an overall survival benefit
associated with including the internal mammary chain
(IMC) in the radiotherapy target volume (TV) for women
with node positive breast cancer. Implementation of IMC-
RT will be facilitated by development of resource efficient
techniques. However, even relatively simple techniques
rely on time consuming clinician outlining of lymph nodes
to achieve adequate dose to the TV (not well covered by
standard fields based on bony landmarks). In order to
reduce the resource burden of nodal contouring, an
anatomical point based algorithm for guiding field
placement was developed and tested for its ability to
ensure TV coverage.
Material and Methods
We identified six points, representative of regional lymph
node level borders according to ESTRO consensus
guidelines, and tested these for their ability to inform
field placement adequately covering the TV (Table 1).
Written instructions were developed and a cohort of 20
cases identified as a validation group. ‘Gold standard’
nodal volumes (Levels 1-4 and IMC) were delineated
according to ESTRO consensus guidelines by four clinical
oncologists with experience in locoregional breast
radiotherapy. Six independent testers (three clinicians
and three radiographers blinded to the nodal volumes)
were invited to place points and consequently fields on
the cases. In four cases a clinician placed both the points
and fields, in eight cases a clinician placed the points and
radiographer applied the fields and in eight cases points
and fields were placed by a radiographer. Cases were
planned using forward planned techniques. The dose
objective to the nodal PTV was V32Gy ≥90%.
Results
Fourteen of 20 cases met the dose objectives when testers
followed the written algorithm alone (Figure 1). Of the
remaining six cases, four failed due to the subclavian vein
being mistaken for the subclavian artery. Two failed due
to point 3 being placed at the inferior part of the
pectoralis minor muscle resulting in insufficient coverage
of level 3. When the points were re-placed correctly nodal
TVs were well covered.
Conclusion
The results suggest that, in the majority of cases, by
following the algorithm clinicians and radiographers can
appropriately place fields which result in acceptable nodal