ESTRO 36 Abstract Book

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S237 ESTRO 36 2017
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1 Academic Medical Center, Radiotherapie, A msterdam,
The Netherlands
Purpose or Objective
Image-guided radiation therapy (IGRT) for p atients who
will be treated to both the breast/chest wall and the
axillary lymph node region (ALNR) is performed with
Conebeam-CT (CBCT). The position verification is based
on the breast/chest wall registration. The current
planning technique is a combination of a quarter field fast-
forward intensity modulated radiation therapy (IMRT) for
the breast/chest wall with an AP-PA beam technique for
the ALNR. This technique is robust for the daily position
variation of the ALNR but is not very conformal. We are
planning to introduce a volumetric arc therapy (VMAT)
technique which is highly conformal but the margins to
account for daily position variation are not known.
The aim of this study is to determine the daily positional
variation of the ALNR relative to the breast.
Material and Methods
The study population consisted of 20 female patients
treated with locoregional radiotherapy for stage II to IV
breast cancer. For all 20 patients the target volume was
the breast/chest wall and the ALNR level 1 and 2 or level
1 to 4, depending on the TNM classification. A standard
clinical target volume (CTV) to planning target volume
(PTV) margin of 5 mm is used for the entire axilla area and
the delineated breast is the PTV. The patient positioning
was supine with both arms up on a CQual breastboard
including a wedge position combined with a knee support
(CIVCO, USA). The clinical IGRT protocol with CBCT is
based on the position variation of the breast/chest wall.
A bony registration with a region of interest (ROI) on bony
anatomy (ribs and sternum) is used as a surrogate for the
breast position (XVI 4.5, Elekta).
For this study 138 CBCTs were retrospectively registered
on level 1 to 3 and 66 CBCTs on level 4. The CBCT analysis
was based on:
1. registration of the breast/chest wall using a ROI
(figure 1) on bony anatomy of the ribs and sternum;
2. registration of the ALNR using shaped ROI (SROI, figure
1) around level 1, 2, 3 and 4. The SROI is a ROI that can
be designed in the shape of each level separately. No
bony elements were included in these SROIs.
The geometric variation was expressed as the
displacement of the ALNR relative to the breast. The
mean, systematic and random setup errors of the
displacement of level 1 to 4 were calculated.
Results
The mean displacement for each level of the ALNR is small
(table 1). Considerable geometric variation was found for
Level 1 in ventral-dorsal (VD) direction. This may be due
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. Ng1, W.K. Fung1, K.M. Ku 1, O.L. Wong2, G. Chiu1
1Hong Kong Sanatorium & Hospital, Department of
Radiotherapy, Hong Kong, Hong Kong SAR China
2Hong 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, DLAD, 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
(imagesresp) and cardiac triggered cine mode for cardiac
motion (imagescard), 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. DLAD was measured in each
slice of imagesresp as shown in Figure 1. The maximum LAD
displacement along the direction of DLAD (MaxdispLAD ) was
measured in images card.