ESTRO 36 Abstract Book

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S946 ESTRO 36 2017
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2 Karolinska Institutet, Department of Oncology and
Pathology, Stockholm, Sweden
Purpose or Objective
For several decades unidirectional photon-grid therapy
has been a useful tool in radiation oncology. Its main
advantage is to limit the normal tissue toxicity when
irradiating the patients with bulky tumors. In this work
we use proton grid therapy (PGT). PGT delivered with a
crossfiring technique has been used instead of a
unidirectional approach. The physical properties of
proton beams allow for the protection of risk organs
posterior to the target while the crossfiring technique
enables a larger separation between the beams, thus
better preserving the normal tissue. Here we evaluate the
possibility to use PGT as a therapeutic option in certain
clinical situations. For example, due to the ability of
interlaced proton-beam grids to significantly spare normal
tissue, this technique may be useful in re-irradiation cases
not otherwise eligible for radiotherapy treatment because
of too high doses to organs at risk.
Material and Methods
CT data from patients previously treated with
conventional photon therapy at Karolinska Hospital,
Stockholm, were reused in order to create PGT treatment
plans with the TPS Eclipse (Varian Medical Systems).
Patients that could benefit re-irradiations or palliative
care were selected. The aim was to deliver a high and
nearly homogeneous target dose, while keeping the grid
pattern of the dose distribution, made of peak and valley
doses, as close to the target as possible. A low grid dose,
with low peak and valley doses, was also preferable to
better protect the normal tissue. The dosimetric
characteristics of those plans were then evaluated, with a
focus on the overall homogeneity of the target dose, as
well as dose profiles outside of the target (i.e. evaluation
of the grid dose distribution through peak and valley doses
analysis).
Results
All the studied cases presented dose distributions for
which the grid pattern was preserved until the direct
neighborhood of the targets. When normalizing the
minimum target dose to 100%, the valley doses reached
around 5%, while the peak doses were approximately 60-
70%, depending on the grid geometry used. Inside the
targets, a good dose homogeneity could be achieved (σ=
±10 %). The volumes of organs at risk irradiated with high
doses remained small and limited spatially to the dose
peaks of the grids.
Conclusion
PGT produces a combination of nearly homogeneous and
high target dose. The grid pattern can be preserved in the
normal tissue, from the skin to the direct vicinity of the
target, preventing extensive damage to the organs at risk.
The PGT approach could present a therapeutic possibility
in difficult clinical situations where conventional
radiotherapy would fail to provide any suitable option for
the patients.
EP-1744 Failure modes and effects analysis of Total
Skin Electron Irradiation (TSEI) technique
B. Ibanez-Rosello1, J.A. Bautista-Ballesteros1, J.
Bonaque1, J. Perez-Calatayud1,2, A. Gonzalez-Sanchis3, J.
Lopez-Torrecilla3 , L. Brualla-Gonzalez4, M.T. Garcia-
Hernandez4, A. Vicedo-Gonzalez 4, D. Granero4, A.
Serrano4, B. Borderia4, J. Rosello 4,5
1 La Fe University and Polytechnic hospital, Radiotherapy,
Valencia, Spain
2 Clínica Benidorm, Radiotherapy, Benidorm, Spain
3 General University hospital, Radiation Oncology,
Valencia, Spain
4 General University hospital, Medical Physics, Valencia,
Spain
5 University of Valencia, Physiology, Valencia, Spain
Purpose or Objective
A risk analysis of the Total Skin Electron Irradiation (TSEI)
technique was performed. The aim of this study was to
evaluate the safety and the quality of the treatment
process, as well as to adapt the quality assurance program
according to the results.
Material and Methods
This revision has been executed in a reference center in
the TSEI technique, with 80 patients treated following the
method Stanford. The risk analysis was made following the
methodology proposed by the TG-100 of the AAPM, which
is an alternative procedure to the guidelines proposed by
the ESTRO in the ACCIDRAD project. To this end, a
multidisciplinary team developed the process map,
outlining the stages of treatment and steps in which each
stage is divided. The potential failure modes (FMs) of each
step were proposed and evaluated, according their
severity (S), occurrence (O) and detectability (D), with a
scale from 1 to 10. The product of this factors resulted in
its priority number risk (RPN), which enabled ranking the
FMs. Then, the current quality management tools were
examined and the FMs were reevaluated taking to account
these tools. Finally, the FMs with RPN ≥ 80 were studied
and new quality management tools to reduce its RPN were
proposed.
Results
75 steps contained in a total of 12 stages were observed.
361 FMs were evaluated, initially 103 had a RPN ≥ 80 and
41 had S ≥ 8. After, current management tools were
considered, only 30 FMs had RPN ≥ 80 (Figure 1). Thereby,
new control tools were derived from the study of these 30
FMs. The riskiest FMs were associated to the patient's
position during treatment. For the "general body
treatment" stage, the position of the screen and the
patient was marked on the floor (Figure 2a) and some
templates representing the position of the feet were
drawn (Figure 2b). In addition, to facilitate positioning of
the patient's limbs during “hands treatment” and “feet
treatment” stages, the axes must traverse the lasers and
the field size within which should position the extremities
were marked on the sheet (Figure 2c). These new
management tools have begun to be implemented in the
facility.