ESTRO 2024 - Abstract Book

S4258

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

Internal drifts with a magnitude exceeding the external 2 mm gating window occurred frequently across all time scales. Interestingly, the smallest drift motion occurred between repeated BHs (inter-BH drift), which is similar to the motion typically assessed during the planning phase by repeated DIBH CT scans. Both the intra-BH drift and the pre to-post CBCT drift were considerably larger than the inter-BH motion. It indicates that repeated DIBH CT scans can underestimate the actual motion during DIBH treatments. The systematic cranial-posterior drift observed on the longer time scale from pre-CBCT to post-CBCT agrees with previous studies of mediastinal LN drift motion in free breathing [2]. It may be ascribed to gravity changing from caudal to posterior direction when a patient lies down in supine position. Although excluded from this abstract for brevity, the data set also provides detailed information on the intra-BH and intra-fraction motion magnitude, cardiac motion during BHs, differential motion in patients with multiple markers and setup errors for mediastinal LNs in DIBH after image-guided setup on the primary lung tumor.

Keywords: DIBH, lung cancer, tumor motion

References:

[1] Aznar M, et al. ESTRO-ACROP guideline: Recommendations on implementation of breath-hold techniques in radiotherapy. Radiother Oncol 2023: 185; 109734.

[1] Schmidt ML, et al. Systematic intrafraction shifts of mediastinal lymph node targets between setup imaging and radiation treatment delivery in lung cancer patients. Radiother Oncol 2018: 126; 318-324.

1406

Digital Poster

Improved lung sparing with MRgRT: a systematic dosimetric assessment of lung radiotherapy

Michael Lauria, Jack Neylon, Kevin Jimenez, Andrew Krupien, Minsong Cao, Trudy Wu, Alan Lee, Drew Moghanaki, X. Sharon Qi

UCLA, Department of Radiation Oncology, Los Angeles, USA

Purpose/Objective:

Respiratory motion has always posed a difficult problem in thoracic radiotherapy. In conventional external beam treatments, radiation oncologists add an internal margin (IM) to tumors to account for physiological motion, thus creating a larger planning target volume (PTV) that includes all probable locations of the tumor during free breathing. This ensures adequate target coverage, but results in additional normal lung being irradiated with treatment dose. With the advent of MR-guided radiation therapy (MRgRT), real-time tumor tracking has enabled clinicians to use gated treatments to treat the PTV when it enters a region of interest at a fixed breathing state, for example, at end inhalation. However, these MR-linacs have more limitations on planning technique due to the technical challenge of housing a linac within an MRI machine. For example, they are only commercially capable of step-and-shoot Intensity Modulated Radiation Therapy (IMRT) rather than continuous Volumetric Modulated Arc Therapy (VMAT) treatments.