ESTRO 2025 - Abstract Book

S1313

Clinical - Lung

ESTRO 2025

structures, Toxicity, and survival in ultra central lung tumor patients treated with SBRT. Clin Transl Radiat Oncol. 2023 Sep 13;43:100675.

1049

Digital Poster Implementation of treatment planning using 4D CT-based lung ventilation imaging to avoid radiation pneumonitis. takeshi ito radiation oncology, japanease red cross society nagaoka hospital, nagaoka, Japan Purpose/Objective: The occurrence of radiation pneumonitis is a major limitation in the radiation therapy of lung cancer. However, it is not clear what lung areas and at what dose levels radiation pneumonitis occurs. Recent advances in CT have made respiratory-synchronised 4DCT easy to perform, and it has been applied to CT for radiation thrapy planning. This 4DCT can be used to produce lung function images reflecting pulmonary ventilation from two time phases during maximal expiration and maximal inspiration. We studied the sites of radiation pneumonitis after irradiation of lung cancers for which 4DCT was taken during treatment planning, with the aim of confirming that the hyperventilated region is the preferred site of radiation pneumonitis. Material/Methods: A retrospective study was conducted on 50 patients who underwent radiotherapy between January 2023 and June 2024 at this hospital, had 4DCT for treatment planning and developed radiation pneumonitis after treatment.The treatment planning CT was Somatom go (SiemensAG, Germany), and the chest wall position monitoring system was Abchess( Apexmedical Inc.,Japan). Pulmonary ventilation images were produced from the obtained 10 times phases of maximal expiration and maximal inspiration. Ventilation images were created in JACOBIAN BASED METRIC and calculated on a MIM software inc. workstation. This method is used as an indicator of lung ventilation volume, as the Jacobian Determinant(JD) reflects the increase or decrease in volume after fusion of two time-phase CT images with Deformable image registration. JD established areas above 1.1 as hyperventilated lung regions, in accordance with reports from previous studies 1 . Pulmonary stereotactic irradiation is performed using coplanar rotational intensity modulated radiotherapy(IMRT) with a dose of 48 Gy in 4 Fractions, and in some cases respiratory synchronous IMRT is performed using Radixact synchrony system (Acuuray Inc.,USA).

Results:

JD>=1.1

JD<1.1

total

ChiSQTest

Pneumonitis(+)

24

6

30

0.015<5%

Pneumonitis(-)

1

9

10

0.017<5%

total 40 The table shows the results of the classification of cases of possible radiation pneumonitis shadows in lung tissue irradiated with 20 Gy or more, with JD = 1.1. A chi-square test showed a difference in incidence with a 5% significance difference at JD > 1.1. Conclusion: It is possible to incorporate high-ventilation areas into the dose constraints of IMRT to reduce the irradiation dose as much as possible, but it remains to be seen whether a reduction in clinical radiation pneumonitis incidence can be achieved.The use of breath-synchronised irradiation is also expected to increase the robustness of dose distribution. 25 15