ESTRO 36 Abstract Book

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S939 ESTRO 36 2017
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Figure 1: Planning Study target doses
Material and Methods
Eight clinical cases were identified as part of the initial
planning study and independently re-planned per the RT
trial protocol with and without dose escalation by two
experienced IMRT planners. A single (female) case was
then selected representative of a typical yet challenging
case and used as the planning benchmark.
Ten of the fifteen centres participating in the pilot phase
of the trial completed the benchmark planning case,
planning with dose escalation only. All pilot centre data
was processed with CERR[1] software enabling dose
distribution and dose volume histograms to be assessed.
Results
Dose escalated plans for the initial eight cases showed no
statistically significant increase in dose to the OAR with
dose escalation (p-value>0.1) whilst maintaining PTV
coverage (D95%>95%).
Ten centres participating in the pilot phase completed the
pre-trial exercise. A range of plan beam configurations
were used: 1x 2arc 6 flattening filter free (FFF) MV, 2x
3arc 6MV, 2x 7-field IMRT 6MV, 2x2arc 6MV, 2x
Tomotherapy and 1x 4arc 6MV.
All centres met all trial mandatory dose objectives for the
benchmark planning case and the vast majority of optimal
constraints, see table 1
.
Table 1: Optimal and mandatory dose constraints
Conclusion
Two sequential planning excercises have demonstrated
dose escalation in anal cancer patients is achievable
without sacrifice of OAR sparing. This shows OAR sparing
is achievable across multiple centres using a variety of
planning techniques, giving expectation of consistent
quality plans for trial patients.
Over 30 sites will join the trial in the next phase and will
complete the same RTQA process.
References
[1]A Computational Environment for Radiotherapy
Research, CERR; Online:
EP-1733 Proton grid therapy (PGT): a parameter study
T. Henry 1, A. Valdman2, A. Siegbahn1
1Stockholm University, Department of Medical Physics,
Stockholm, Sweden
2Karolinska Institutet, Department of Oncology and
Pathology, Stockholm, Sweden
Purpose or Objective
Proton grid therapy (PGT) with the use of crossfired and
interlaced proton pencil beams has recently been
proposed by our research group. A clear potential for
clinical applications has been demonstrated. The beam
sizes used in our proof-of-concept study were in the range
7-12 mm, full-width at half maximum (FWHM),
representing the typical range of available proton pencil-
beam widths at a modern proton therapy facility.
However, to further take advantage of the dose-volume
effect, on which the grid therapy approach is based, and
thereby improve the overall outcome of such treatment,
smaller beams are desirable. In this present study, Monte-
Carlo (MC) simulations of a simple PGT treatment were
performed with varying beam sizes and center-to-center
(c-t-c) distances between the beams. The aim was to
determine which combinations of those two parameters
would produce the most therapeutically desirable dose
distributions (high target dose and low valley dose outside
of the target).
Material and Methods
MC calculations were performed using TOPAS version 2.0
in a 20x20x20 cm 3 water tank. The beam grids were aimed
towards a 2x2x2 cm3 cubic target at the tank center. Two
opposing (or 2x2 opposing) grids were used. The target was
cross-fired in an interlaced manner. Grids containing
planar beams (1-D grids) or circular beams (2-D grids) were
considered. Three beam widths (1, 2 and 3 mm FWHM) and