ESTRO 2024 - Abstract Book

S4244

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

ESTRO 2024

Stereotactic body radiotherapy (SBRT) has shown promise as an effective and non-invasive treatment option for ventricular tachycardia (VT) patients. Accurate target definition is vital to minimize dose to healthy heart tissue, considering the cardiac and respiratory motions. We simulated and compared dosimetric effects of expiration breath hold (EBH), inspiration breath-hold (IBH) and free breathing (FB) with and without abdominal compression (AC) in SBRT for VT using a surrogate lung cancer patient cohort.

Material/Methods:

4DCT scans were acquired with and without AC for 10 patients. A standardized clinical target volume (CTV), corresponding to an occlusion of the left anterior descending artery, was delineated in the FB mid-position phase of the 4DCT without and with AC, respectively. Then, the same CTV was delineated in the max expiration phase and the max inspiration phase, to correspond to a simulated EBH and IBH, respectively. The two FB CTVs were expanded to an internal target volume (ITV) based on all phases in each 4DCT. Breath-hold (BH) CTVs were expanded by 5 mm and FB ITVs were expanded by 3 mm to create planning target volumes (PTVs). Organs at risk (OARs) delineated were the heart, esophagus, stomach, bowel, and both lungs. Dose constraints to the OARs were prioritized higher than target dose coverage. The PTV-stomach distance and overlap were assessed, and treatment plans were created for the five patients with largest overlap. The treatment plans consisted of two arcs with a 10 MV flattening filter free beam and a prescribed dose of 25 Gy in one fraction.

Results:

The distance between the PTV and stomach was generally larger in BH compared to FB. The stomach was the OAR was the only OAR that caused a compromised PTV dose. A large compromise of the PTV coverage was observed for two patients, for one of them the FB treatment plan without AC and for the other in the FB treatment plan with AC (Figure 1). Due to the larger separation between the PTV and stomach in the BH plans, these plans had smaller PTV volumes receiving <25 Gy and <20 Gy.

Conclusion: