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S526
ESTRO 36 2017
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the use of predictive biomarkers for assessing
radiotherapy related toxicity.
Poster: Radiobiology track: Radiobiology of proton and
heavy ions
PO-0960 Radiobiological effectiveness and its role in
modelling secondary cancer risk for proton therapy
A. Madkhali
1,2
, C. Timlin
1
, M. Partridge
1
1
University of Oxford, Oncology, Oxford, United Kingdom
2
King Saud University, Medicine, Riyadh, Saudi Arabia
Purpose or Objective
In proton therapy, a radiobiological effectiveness ratio
(RBE) of 1.1 (RBE
1.1
) is often used. In reality, RBE depends
on dose, linear energy transfer (LET), biological end point,
and tissue type. Using a value of RBE that may be not
accurate may affect dose calculation and hence,
outcome.
Material and Methods
We used an in-house built code for modelling malignant
induction probability (MIP) from voxel-by-voxel dose map
(Timlin 2014) and implement a published model to
calculate structure-specific RBE, recalculate dose and
MIP, and compare the outcomes with initial calculations
using RBE
1.1
. MIP was calculated using linear quadratic
(LQ), linear (LIN), and linear-no-threshold (LNT) models
for proton therapy plans for an adult and a teenage
patient diagnosed with medulloblastoma (MB). The MIP
was then re-calculated using the RBE model by Dale and
Jones which is a function of dose (d), α and β and RBE
min
and
RBE
max:
Results
Results are shown in Table 1. The difference in MIP by
using RBE
1.1
and RBE
MinMax
is ~2-3%. The effect on mean
dose varies between different organs and is between 6%
and 8%. Clinical implications due to difference in RBE
depend on beam characteristics, dose, structures
concerned, and the volume irradiated.
Conclusion
Using RBE
1.1
makes proton therapy dose and dose-
dependent predictions less accurate. Our results using a
RBE calculation model show that decreased accuracy may
have clinical implications, which agrees with published
literature (Jones 2012; Jones, 2014), and may affect
secondary cancer risk and normal tissue complication
probability calculations as well.
PO-0961 DNA damage and repair influence tumor
sensitivity to diffusing alpha emitters radiation therapy
Y. Keisari
1
, R. Etzyoni
1
, H. Bittan
2
, E. Lazarov
2
, M. Efrati
1
,
M. Schmidt
2
, T. Cooks
1
, L. Arazi
2
, I. Kelson
2
1
Tel-Aviv University / Faculty of Medicine, Clinical
Microbiology and Immunology, Tel-Aviv, Israel
2
Tel Aviv University, School of Physics and Astronomy-
Sackler Faculty of Exact sciences, Tel Aviv, Israel
Purpose or Objective
We developed an alpha radiation based brachytherapy,
which provides efficient ablation of solid tumors by alpha
radiation. This treatment termed,
Diffusing Alpha
emitters Radiation Therapy
(DaRT) utilizes radium-224
loaded wires, which when inserted into the tumor release
by recoil short-lived alpha-emitting atoms. These atoms
disperse in the tumor, and spray it with highly destructive
alpha radiation.
DaRT achieved substantial tumor growth retardation,
extended survival, and reduced lung metastases in mice
bearing various mouse and human derived tumors. Better
tumor control was achieved when DaRT was applied with
chemotherapy. Furthermore, tumor ablation by DaRT
boosted anti-tumor immune responses.