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ESTRO 36 2017
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Conclusion
This work presented an application of SOI micodosimeters
for RBE determination in passive and scanning proton and
12
C ion therapy and silicon microdosimetry has
demonstrated a simple and fast method for routine Quality
Assurance in charged particle therapy.
OC-0153 Sensitivity evaluation of prompt γ-ray based
range verification with a slit camera
L. Nenoff
1
, M. Priegnitz
2
, A. Trezza
1
, J. Smeets
3
, G.
Janssens
3
, F. Vander Stappen
3
, L. Hotoiu
3
, D. Prieels
3
, W.
Enghardt
1,4,5,6
, G. Pausch
1,5
, C. Richter
1,4,5,6
1
OncoRay - National Center for Radiation Research in
Oncology, Faculty of Medicine and University Hospital
Carl Gustav Carus- Technische Universität Dresden-
Helmholtz-Zentrum Dresden - Rossendorf, Dresden,
Germany
2
Helmholtz-Zentrum Dresden-Rossendorf, Institute of
Radiation Physics, Dresden, Germany
3
Ion Beam Applications SA, Louvain-la-Neuve, Belgium
4
Faculty of Medicine and University Hospital Carl Gustav
Carus- Technische Universität Dresden, Department of
Radiation Oncology, Dresden, Germany
5
Helmholtz-Zentrum Dresden-Rossendorf, Institute of
Radiooncology, Dresden, Germany
6
German Cancer Consortium DKTK and German Cancer
Research Center DKFZ, Dresden, Germany
Purpose or Objective
The dose distribution and range of proton beams are
exceedingly prone to uncertainties and anatomical
changes, demanding for an in-vivo range verification. A
promising approach is prompt γ-ray imaging (PGI), which
was recently implemented clinically in Dresden using a so-
called PGI slit camera [1,2] in double scattering (DS).
However, the detectability of local range shifts, affecting
only part of the lateral field in DS, is limited. The spot-
wise dose deposition in pencil beam scanning (PBS)
promises a finer spatial resolution of range shifts. The
purpose of this study is to comprehensively investigate the
sensitivity to detect range shifts in DS and PBS using a head
phantom in a clinical setup.
Material and Methods
For a realistic brain tumor treatment, treatment plans in
DS and PBS (2 beams, 60 GyE, 2 GyE/fx), were created.
One beam (1 GyE) was applied to a CIRS head phantom and
monitored with the PGI slit camera. To investigate the
influence of the spot dose, the same beam with 5 GyE was
also delivered and measured. Global and local (5 cm in
diameter) range shifts were introduced and the PGI
profiles (prompt-γ counts over depth) with and without
shifts were compared. Sum profiles containing prompt-γ
counts over the entire fraction were used for the
comparison of DS and PBS. Moreover, PGI profiles
measured in PBS were analyzed spot-wise and will also be
compared with simulated profiles for absolute range
determination.
Results
A good agreement between introduced and measured
global shifts was found in the sum profile evaluation for
both modalities, PBS and DS (Table 1). Relative
differences were below 2, 7 and 12 % for the 10, 7 and 4
mm shifts, respectively. Local shifts are not detectable
using sum profiles. For the applied local shifts, a spot-wise
comparison of PGI profiles in PBS allows the detection and
localization of global and local shifts (Figure 1). For
interpretation, neighboured spots should be clustered, as
shifts detected for single spots are less reliable due to low
statistics. Higher doses (5 vs. 1 GyE) allow the detection
of smaller shifts as shown in Figure 1 for the 4 mm local
shift.
Table 1: Measured global shifts between sum profiles in DS
and PBS with 1 and 5 GyE.
Figure 1: Spot-wise analysis of the determined range
shifts: The points represent PBS spots of one energy layer,
the size corresponds to the dose per spot, the color to the
detected shift between two PGI profiles. Spots influenced
by the local shifts (black ring) are highlighted with a black
edge. Global and local shifts with 1 and 5 GyE were
measured.