ESTRO 2023 - Abstract Book

S921

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ESTRO 2023

proton group had reduced incidence of alopecia, dysgeusia, mucositis, and nausea, but higher incidence of skin reaction and fatigue (Figure 1). The proton group maintained a significantly higher lymphocyte count (p = 0.029) (Figure 2). There was a trend to better maintenance of haemoglobin in the proton group, and of neutrophils in the photon group, neither statistically significant. There was no effect of RT type for platelet nadir.

Conclusion This small study illustrates a typical acute toxicity profile and suggests some limited differences in toxicity between proton and photon groups. Study limitations include the retrospective nature and different age profile of the two groups. Further data from larger patient series with detailed toxicity reporting would be needed to justify proton therapy for reduction in acute toxicity.

PO-1151 Robust optimization and variable RBE in proton cranio-spinal irradiation

T. Wiewesiek 1 , M. Durante 2 , C. Graeff 2 , L. Volz 2

1 GSI Helmholtz Centre for Heavy Ion Research, Biophysics, Darmstadt, Germany; 2 GSI Helmholtz Centre for Heavy Ion Research GmbH, Biophysics, Darmstadt, Germany Purpose or Objective Proton cranio-spinal irradiation (pCSI) is advantageous compared to photon therapy due to reduced dose to healthy tissue. However, field sizes are limited and for pCSI several adjacent fields have to be joined not only in the spine (spinal joint), but also in the neck, where opposing lateral fields overlap with the posterior spinal field (cranial joint), making the treatment sensitive to relative shifts between fields. We present new robust optimization strategies for pCSI considering a variable biological effect.