ESTRO 2023 - Abstract Book

S2091

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ESTRO 2023

Results From 2019/01/01 to 2020/12/30, total 71 non-small cell lung cancer patients with 169 CT scans met our criteria. We have three important findings. (1) In all patient group, we found that volume of radiation pneumonitis (RPv) max and RP grade max was statistically significant (p<0.001). (2) The DVH parameters also affect radiation pneumonitis severity. We found that mean lung dose (MLD), and percentage of normal lung receiving dose, between 1 Gy (V1) to 31 Gy (V31) was significantly correlated to RP. (3) If volume of radiation pneumonitis account for a small percentage of lung, patient may experience no symptoms. We found that cut-off point for symptom occurrence was 4.79% RPv in total lung volume. For this cut-off, the area under the curve (AUC) was 0.779. In the groups with grade 1 and grade 2 radiation pneumonitis, it was found that the radiation dose of 2600cGy covered ≥ 80% of radiation pneumonitis lesions in more than 80% patients.

Conclusion The percentage of radiation pneumonitis lesion volume to total lung volume is a good indicator for quantifying radiation pneumonitis. Radiation pneumonitis lesions can be projected onto the original radiotherapy plan using coverage of 26Gy isodose line to determine whether radiation induced lung injury. This work was supported in part by the National Science and Technology Council, Taiwan under Grant of NSTC 111-2634-F- 006-012

PO-2323 Comparison between single and dual arc VMAT for online adaptive prostate SBRT

S. Moragues-Femenia 1 , C. Laosa-Bello 1 , J.F. Calvo-Ortega 1,2

1 Hospital Quirónsalud Barcelona , Oncología Radioterápica, Barcelona, Spain; 2 Hospital Quirónsalud Málaga, Oncología Radioterápica, Málaga, Spain

Purpose or Objective To compare dose distributions of paired VMAT plans designed for prostate SBRT using one versus two arcs.

Materials and Methods Twenty cases of prostate SBRT were retrospectively included in this study. Dose prescription was 36.25 Gy in 5 fractions according to the PACE-B trial (Lancet Oncol. 2019 Nov;20(11):1531-1543). SBRT plans were designed using the Eclipse v. 16.1 treatment planning system and the VMAT technique. 6 MV FFF photon beams from a Varian TrueBeam linac equipped with a 120 Millennium MLC were used. For each patient case, two plans were designed: the first one consisting of a single arc in a clockwise direction from 160 to 200 degrees, and the second plan was created by adding a second arc in a counterclockwise direction from 200 to 160 degrees (Varian IEC scale). Both plans were optimized using the same objectives and priorities for the targets (prostate and PTV), and organs-at-risk organs (femoral heads, rectum, bladder and penile