ESTRO 2023 - Abstract Book

S1672

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ESTRO 2023

Results The absolute median difference in D0.1cc (EQD2) was 1.13 [0.14 – 2.48] Gy3 and 0.72 [0.32 – 1.64] Gy3 for 4DCT and CBCT doses, respectively, which was not statistically different (p=0.69). However, considering each patient individually, the range of deviations was generally smaller for 4DCT than CBCT (Figure 1 and Figure 2). On a cohort level the deviation for the 4DCT could be affected by a TPCT acquisition in a non-representative breathing phase for a few patients.

Figure 1: 4DCT vs TPCT dose differences and deviation from planned dose in EQD2, planned doses to bronchi for each patient is reported in the legend (Gy3). Each box consists of eight (or ten) data points

Figure 2: CBCT vs TPCT dose differences and deviation from planned dose in EQD2, planned doses to bronchi for each patient is reported in the legend (Gy3). Each box consists of eight data points Conclusion Hypofractionated and in-homogenous dose distributions can lead to large deviations in ‘biological’ delivered doses to the bronchi. When comparing the effect on the dose deviation for bronchi, related to breathing motion and set-up deviations, respectively, these are of similar magnitude in the cohort.

PO-1920 Serial exit dose fluence analysis to detect volume change and implication in adaptive radiotherapy

A. Tiwari 1,2 , V. Pandey 2 , V. Kharade 2 , R. Pasricha 2 , M. Gupta 2 , S. Das 2

1 Postgraduate Institute of Medical Education and Research, Radiotherapy and Clinical Oncology, Chandigarh, India; 2 All India Institute of Medical Sciences, Bhopal, Radiation Oncology, Bhopal, India Purpose or Objective Decisions on adaptive radiotherapy depend on the patient, tumor, and treatment-related factors. Objective parameters for adaptive replanning are sparse. The present study reports tumor volume variation during high-precision radiotherapy and serial exit dose measurement as a patient-specific tool for adaptive radiotherapy.

Materials and Methods