ESTRO 2023 - Abstract Book

S1657

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ESTRO 2023

resulting in 6 scenarios including the original per patient. Target delineations were adjusted to maintain 5mm separation between CTVp_breast and simulated skin surface. Dose was recalculated using density override for each scenario and evaluated for 7 ROIs. Results The breast coverage, heart and lung dose is constant as shown in tabel 1. For the intermediastinal chain (CTVp_IC1-3) V90% increases, which is an improvement to the original dose. However, for the locoregional lymph nodes (CTVp_periclav) V90% decreases, and with a reduction of 5 mm or more the clinical effect of the treatment may be compromised. Hotspots increase for the breast CTV as shown in figure 1. The DBCG criteria V107% < 2% is exceeded when the reduction is 5 mm or more.

Conclusion The impact of tissue reduction on the dose for breast RT shows that a reduction of 4mm or less results in an acceptable dose distribution for at full course when V105% < 2% is planned. For further tissue reduction V107% in the breast increase significantly and coverage of locoregional lymph nodes decrease significantly and thus adaption might be required taking the number of fractions, where the reduction occurs, into account. The dose to heart and ipsilateral lung is overall unchanged and acceptable even with major tissue reduction. The current study suggests a guidance ROI extending to 4 mm below the original skin surface with respect to tissue reduction.

PO-1909 Clinical evaluation of Exactrac Dynamic surface guided pre-positioning system for cranial treatments

J. Alonso Muriedas 1 , R. Fabregat Borras 1 , R. Astudillo Olalla 1 , M. Gutiérrez Ruiz 1 , F. Gómez Enríquez 1 , D. Bruzos López 1 , S. Ruiz Arrebola 1 , G. Camacho de la Vega 1 , A. Reguilón Martín 1 , V. Cañón García 1 , M. Ferri Molina 1 , A.L. Rivero Pérez 1 , J. Albendea Roch 1 , F. Pinto Guevara 1 , M. García Lamela 1

1 Hospital Universitario Marqués de Valdecilla, Radiotherapy, Santander, Spain

Purpose or Objective