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in-field plans were not (poor homogeneity). Our original
clinical plans were generally more homogeneous than
those created for the prototype MLC design. The optimal
treatment plans for treatments that are typically treated
with two beam angles (breast, whole brain) used IMRT
with the conventional beam angles. For large breasts, 2
additional IMRT fields were needed to improve coverage
and
homogeneity
(see
figure)
The best VMAT plans created with the prototype MLC were
typically less homogeneous but more conformal than IMRT
plans, when 4 or more arcs were used (see figure
comparing IMRT (left) and VMAT (right)). Based on our
current experience, we suggest the use of IMRT for this
prototype MLC design - because these plans are
significantly faster to optimize, and usually give the best
treatment plans (for this MLC)
.
Beam modulation was similar for IMRT and VMAT (3.2 vs
3.4 MU/cGy. When comparing the calculated dose and
delivered dose the average gamma passing rate (3%/3mm)
was 99.5% (range: 91%-100%) and 99.0% (97.7%-100%) for
IMRT and VMAT, respectively.
Conclusion
It was possible to plan and deliver clinically acceptable
plans for all treatment sites using the prototype 1.0cm
MLC design. Initial experience was that IMRT plans
outperform the VMAT plans in terms of homogeneity.
EP-1572 Feasibility study of prone position in
radiotherapy of breast with regional lymph nodes
E. Pawlowska
1
, A. Prawdzik
1
, M. Narkowicz
1
, M.
Damięcka
1
, R. Zaucha
1
1
Medical University of Gdansk, Department of Oncology
and Radiotherapy, Gdansk, Poland
Purpose or Objective
Prone position radiotherapy has been successfully used to
treat breast cancer in women with large, pendulous
breasts. The benefit of this technique comes from
decreased doses in organs at risk (OAR). Simultaneous
irradiation of regional lymph nodes (RLNs) is done only in
supine position, losing this beneficial effect. We have
performed a feasibility study of irradiating large (> 780 ml)
breasts with RLNs in prone setup.
Material and Methods
Target volumes including breast, supra-, infraclavicular,
Rotter’s, axillary lymph nodes with or without internal
mammary (IM) chain were contoured on six tomography
scans of 5 patients immobilized in prone position using two
commercial breast boards. Delineation was done in
accordance with European Society for Radiotherapy and
Oncology (ESTRO) consensus. Radiotherapy plans using
static (3D CRT) and dynamic (IMRT) conformal techniques
were prepared. Dose-volume limits were based on
QUANTEC review.
Results
In all plans mean doses to the heart, lung (ipsilateral,
contralateral and both), left descending artery (LAD) were
obtained. Volumes receiving more than 20 and 25 Gy were
reported in lungs and heart, respectively. Mean values
from all plans are presented in Table 1.
Radiotherapy to breast and RLNs with IM was associated
with significantly higher doses in all OARs independently
of the technique used. 3D CRT plans resulted in lower
doses than IMRT to nearly all structures.
Image 1 presents differences in dose distribution between
IMRT (bottom) and 3D CRT (top). PTV includes breast and
RLNs with IM
Conclusion
Irradiation of breast and RLNs without IM in prone position
in women with large, pendulous breasts is feasible and
safe. Including IM chain in radiotherapy plan significantly
increases doses in lungs and heart but acceptable values
may be achieved in some of patients. Dynamic techniques
show no benefit in comparison to 3D CRT.