ESTRO 2021 Abstract Book

S151

ESTRO 2021

Conclusion The proposed novel dose escalation strategy targeting hypoxia and considering a heterogeneous density of clonogens in the tumour based on functional imaging is clinically feasible and may be used for individualised radiation therapy. PH-0218 Functionality-optimised radiotherapy for lung cancer patients using SPECT/CT A. Quinet 1 , Y. Jourani 1 , B. Vanderlinden 1 , P. Fernandes 1 , Z. Paquier 1 , F. Charlier 2 , L. Moretti 2 , P. Flamen 3 , P. Van Houtte 2 , D. Van Gestel 2 , N. Reynaert 1 1 Institut Jules Bordet - Université Libre de Bruxelles, Medical Physics Department, Brussels, Belgium; 2 Institut Jules Bordet - Université Libre de Bruxelles, Radiation Oncology Department, Brussels, Belgium; 3 Institut Jules Bordet - Université Libre de Bruxelles, Nuclear Medicine Department, Brussels, Belgium Purpose or Objective Radiation-induced lung injury is directly related to the dose delivered to well-perfused lungs and is a common treatment-limiting toxicity of radiotherapy in lung cancer. The purpose of this in-silico study is to prospectively investigate the feasibility of SPECT-based functional optimisation in treatment planning for thoracic tumours and to evaluate possible dose improvements. Materials and Methods Twenty-nine patients (36 cases) who underwent a lung perfusion scan on a Symbia T (Siemens Healthcare, Erlangen, Germany) prior to thoracic radiotherapy between January 2016 and September 2020 were included in the study. SPECT images without attenuation correction were used to define functional lung Volumes Of Interest (VOI), segmented with thresholds at the 25 th , 50 th and 75 th functionality percentiles (Perc 25, Perc 50 and Perc 75, respectively) using MIM Maestro (v7.0.3, MIM Software Inc., Cleveland, USA). The contours were then rigidly registered and copied to the planning CT. Two VMAT plans with a 33×2 Gy prescription were calculated using Monaco (v5.5.1, Elekta AB, Stockholm, Sweden), one exclusively optimised on anatomical volumes following our institutional standards, and another for which an ALARA dose constraint was added to the Perc 75 VOI. Statistically significant ( p < 0 . 05) differences for mean dose, V 5 Gy , V 20 Gy , V 40 Gy and max dose between both plans were assessed using a Wilcoxon signed-rank test. Correlations between the PTV volume and changes in dose parameters were also investigated. Results

An example of segmented volumes is shown in figure 1.

A comparison of anatomical and functional DVHs per patient and per VOI showed that, in most cases, a functional optimisation significantly reduces the volume of functional lung receiving low to high doses as illustrated in figure 2a. Fractions of OARs receiving low doses were decreased but highly-irradiated volumes