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or 345°) and posterior (165° or 195°) beam for the lateral
periclavicular and axillary regions ( Fig. 1.).
For the VMAT technique tangential arcs of 24 degrees
were chosen as these provide the best sparing of lung and
heart and further minimize the low dose delivery to the
rest of the body (integral dose). We analyzed PTV
coverage including the conformation number (CN) and
dose to the OARs to compare the techniques.
Results
Results: Table 1 shows the results. Mean V95% for the PTV
was 95,3% for 3D-CRT and 97,5% for VMAT.
CN was higher for the VMAT technique, indicating that
PTV-coverage has improved at the same time as limiting
the volume receiving a lower dose. Coverage was
especially better with VMAT for lymph node levels 3-4.
This came at a cost of a slightly higher dose to the thyroid
gland. Dose to the lungs as well as the heart were lower
with VMAT.
Conclusion
Conclusion: We developed a VMAT-only planning method
for locoregional breast irradiation, which is
straightforward, robust, can be combined with respiratory
control and creates very conformal and homogeneous
treatment plans with improved PTV coverage and low
doses to the organs at risk.
EP-1566 Biologically optimized IMRT plans for prostate
cancer using population-based tumour biology
E.J. Her
1
, M.A. Ebert
1,2
, H.M. Reynolds
3,4
, A. Kennedy
2
, A.
Haworth
5
1
The University of Western Australia, School of Physics,
Perth, Australia
2
Sir Charles Gairdner Hospital, Department of Radiation
Oncology, Perth, Australia
3
The Peter MacCallum Cancer Centre, Department of
Physical Sciences, Melbourne, Australia
4
University of Melbourne, Sir Peter MacCallum
Department of Oncology, Melbourne, Australia
5
University of Sydney, School of Physics, Sydney,
Australia
Purpose or Objective
The standard approach to treating prostate cancer with
EBRT involves delivery of a high dose of radiation to the
entire gland. However, the capability of IMRT planning
with dose based objectives fails to exploit the potential to
deliver a highly non-uniform dose distribution based on
patient/tumour-specific data. A personalised approach to
prostate RT is proposed, which aims to deliver a dose
distribution sculpted by specific biology, including the
spatial distribution of clonogen densities and degree of
hypoxia [1, 2], using in vivo multiparametric imaging. The
aim of this study was to explore the feasibility and
benefits of using a TCP model utilising population-based
tumour biology to guide IMRT for prostate cancer, to
maximize TCP while simultaneously minimizing NTCP of
normal tissues.
Material and Methods
Four intermediate-risk prostate cancer patients were
selected from an established trial patient cohort that
underwent conventional 3D conformal radiation therapy
(3DCRT). This study compared the delivered 3DCRT plan
with a conventional uniform-dose and a biologically-
optimized IMRT plan. IMRT planning was carried out on
matRad (German Cancer Research Centre, Heidelberg,
Germany) and was modified to include biological
optimization. The conventional IMRT treatment planning
objectives and clinical acceptance criteria were based on
the recommendations of Pollack et al [3]. The biologically-
optimized plans were created to achieve TCP of at least
0.70. The TCP model included a non-uniform clonogen cell
density within the CTV, variation in radiosensitivity
parameters within a patient population and repopulation
effect. TCP was first calculated for the biologically-
optimized plan, then the dose for the other two treatment
plans was scaled to match the same TCP. Rectum and
bladder NTCP were used for comparison.
Results