ESTRO 36 Abstract Book

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S439 ESTRO 36
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Gustav Carus- Technische Universität Dresden-
Helmholtz-Zentrum Dresden – Rossendorf, Dresden,
Germany
2 University Hospital Carl Gustav Carus- Technische
Universität Dresden, Department of Radiation Oncology,
Dresden, Germany
3 German Cancer Consortium DKTK, partner site Dresden,
Dresden, Germany
4 Helmholtz-Zentrum Dresden – Rossendorf, Institute of
Radiooncology, Dresden, Germany
5 National Center for Tumor Diseases, partner site
Dresden, Dresden, Germany
Purpose or Objective
To compare 4 different proton pencil beam scanning (PBS)
treatment approaches for unilateral head and neck cancer
(HNC) targets in terms of robustness, including anatomical
changes during the treatment course.
Material and Methods
Eight patients with unilateral HNC treated with double
scattered proton therapy were selected. Each patient
dataset consists in a planning CT and several control CTs
acquired by an in-room CT scanner during the treatment
course. Four different proton PBS plans with simultaneous
integrated boost and dose prescriptions of 50.3 Gy(RBE) to
the low-risk CTV and 68 Gy(RBE) to the high-risk CTV in 34
fractions were calculated: conventional PTV-based single-
field (SFO) and multifield optimization (MFO), and
robustly optimized SFO and MFO plans on CTV level,
considering ±3 mm and ±3.5% of setup and range
uncertainty,respectively.
The treatment plans were recalculated on the registered
control CTs and the cumulative doses calculated and
compared with the nominal plan.
For robustness evaluation, perturbed doses using a
probabilistic scenario-wise approach obtaining random
setup shifts through Gaussian sampling, and range
uncertainties of 0, +3,5% and -3,5% were calculated, using
planning and control CTs, considering both anatomic
changes and uncertainties. Cumulative doses from 30
different perturbed treatment courses were generated for
each plan.
Results
The target coverage for the four nominal plans was
similar, fulfilling the clinical specification of D98≥95% of
the prescribed dose (range 96.9-100.5% for low-risk CTV,
97.4-100.8% for high-risk CTV), being slightly lower on the
robust optimized plans. The doses to the organs at risk
were similar for all plans; however, for the ipsilateral
parotid, higher median doses up to 5 Gy were found on the
SFO approaches (Table 1), whereas the contralateral
parotid is completely spared. The target coverage
throughout the treatment course with slightly changing
anatomy remains in general constant.
In terms of robustness evaluation, PTV-based MFO showed
reduced robustness against both anatomical changes and
uncertainties, i.e. wider DVH bands and a disagreement
between planned and summed dose, whereas the robust
MFO is less influenced. Both SFO approaches resulted in
robust plans on the CTVs (Figure 1).
Conclusion
The PTV-based MFO approach showed less robustness
against uncertainties in setup and range, as well as for
anatomical changes during the treatment course. Both
SFO plans are robust in terms of CTV coverage; however,
they present higher doses to the ipsilateral parotid gland.
Robust MFO approach presents the lowest doses to the
ipsilateral parotid and more robustness against
uncertainties.
The dose to more organs at risk and the difference in
normal tissue complication probabilities for the 4 planning
approaches will be presented as well.
PO-0820 Full automation of radiation therapy
treatment planning
L. Court1, R. McCarroll1, K. Kisling 1, L. Zhang1, J. Yang 1,
H. Simonds2, M. Du Toit2, M. Mejia3, A. Jhingran4, P.
Balter1, B. Beadle4
1MD Anderson Cancer Center, Department of Radiation
Physics, Houston, USA
2Stellenbosch University, Radiation Oncology,
Stellenbosch, South Africa