ESTRO 2025 - Abstract Book

S4345

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

1 Medical Physics Unit, IRCCS Istituto Romagnolo per lo Studio dei Tumori (IRST) “Dino Amadori”, Meldola, Italy. 2 Radiotherapy Unit, IRCCS Istituto Romagnolo per lo Studio dei Tumori (IRST) “Dino Amadori”, Meldola, Italy. 3 Biostatistics and Clinical Trials Unit, IRCCS Istituto Romagnolo per lo Studio dei Tumori (IRST) “Dino Amadori”, Meldola, Italy. 4 Medical and Surgical Sciences, University of Bologna, Bologna, Italy. 5 Radiotherapy Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy Purpose/Objective: In breast radiotherapy, a variety of planning techniques such as 3D-CRT, IMRT, VMAT, and hybrid methods are used [1]. The optimal approach is often determined by the planner's and clinician's experience, typically beginning with 3D-CRT and progressing in complexity through a trial-and-error process. This study aims to develop a parameter system to preselect the most effective radiotherapy technique for each patient. Material/Methods: Patients treated with 40.05 Gy in 15 fractions [2] between June 2023 and June 2024 were included. For each patient, three plans—3D-CRT, IMRT (Step-and-Shoot), and a hybrid strategy (3D-CRT+IMRT)—were created and optimized using Pinnacle³ TPS (v16.2.1). Three experienced, blinded radiation oncologists evaluated these plans and assigned scores: “1” for the best choice, “2” for the second, and “3” for the last. The median score determined the optimal plan for each patient; if no plan scored “1,” the patient was added to a test set for parameter signature evaluation.Key anatomical parameters were measured, including 2D metrics such as Maximum Heart Length (MHL), Maximum Heart Distance (MHD), Central Lung Distance (CLD), Maximum Lung Distance (MLD), Maximum Lung Length (MLL), contralateral breast distance, and target length via DRRs (Figure1) and CT images. 3D parameters like heart volume, lung volume, target volume, curvature volume, LAD iso80% volume, and lateral tissue volume were quantified using TPS tools [3;4]. Minimum, maximum, and median values of each parameter set were calculated. Statistical analysis examined the relationship between these parameters and the chosen treatment plan.

Results: Five patients —enrolled from June 2023 to July 2024—were evaluated. The hybrid strategy was optimal for two patients, while IMRT was chosen for three. Despite the small cohort, noticeable differences in the distribution of anatomical parameters were observed between the hybrid and IMRT groups (Figure2 shows an example of MHD