ESTRO 2021 Abstract Book

S1501

ESTRO 2021

Fig1: RGSC variance for lung patients Fig2: DIBH levels for breast patients

Conclusion In summary, this study shows that active RGSC monitoring has a role to play in the management of radiotherapy for thoracal lesions. For lung cancer patients, prediction of motion change is possible: pre- treatment RGSC analysis may help decide whether a time consuming 4D CBCT is needed, saving time and effort to scan, review, and discuss. For breast cancer patients, the study shows that automatic beam holds are advantageous to maintain quality of dose delivery. Still, DIBH variations within each session are seen which may result in slightly lesser CTV2PTV margins. PO-1774 Reproducibility of spirometer-guided DIBH in left-breast treatments with optical surface monitoring C. Romano 1 , M. Craus 1 , P. Viola 1 , V.E. Morabito 1 , F. Deodato 2 , G. Macchia 2 , M. Boccardi 2 , M. Buwenge 3 , S. Cammelli 3 , A.G. Morganti 3 , V. Valentini 4 , S. Cilla 1 1 Gemelli Molise Hospital, Medical Physics Unit, Campobasso, Italy; 2 Gemelli Molise Hospital, Radiation Oncology Unit, Campobasso, Italy; 3 IRCCS Azienda Ospedaliero-Universitaria di Bologna, Radiation Oncology Unit, Bologna, Italy; 4 Fondazione Policlinico Universitario A. Gemelli, IRCCS, Radiation Oncology Department, Roma, Italy Purpose or Objective Deep-inspiration breath-hold (DIBH) has proven to be an highly effective technique to reduce cardiac and lung exposure during left-breast radiotherapy. We evaluated the intra breath-hold and the intra- and inter-fraction reproducibility and stability of spirometer-guided DIBH breast treatments using an optical surface-guided system. Materials and Methods Three left-sided breast cancer patients were treated in DIBH using the Elekta Active Breathing Coordinator spirometer. Patients were treated with a tangential SIB hybrid-IMRT technique. Dose prescription was 50 Gy and 60 Gy in 25 fractions to the breast and axilla/supraclavicular lymph-nodes and to the surgical cavity, respectively. An infrared optical tracking system (AlignRT, VisionRT, London) was used to continuously monitor the interfraction, intrafraction and intrabreath-hold motion in the anterior-posterior (AP), lateral (LL) and superior-inferior (SI) directions during the DIBHs. Mean, median and standard deviations (SD) values together with 95% confidence intervals (CI95%) were used to quantify the metrics stability and reproducibility. Correlations between spirometer and optical surface imaging deviations were investigated.