ESTRO 2024 - Abstract Book

S4619

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

The median voxel-by-voxel dose difference between the BDO- and DECT-based treatment plans was within 0.2% for all patients. The gamma passing rates for 2%/2mm were 92.4, 93.3 and 99.8%, and for 3%/3mm 96.8, 96.2, 100% in patients 1-3, respectively. The target coverage of the CTV deteriorated up to 0.5 Gy and 0.1 Gy for D98% and D2%, respectively (Figure 2). The D50% of the CTV varied within 0.1%. For patient #2, the HI changed from 9.5% for the DECT to 10.6% for the BDO-based plan, while for others the difference was within 0.1%. For the organs at risk, the D2% for the fibula increased up to 5.5%, and for the tibia up to 7.1%.

Figure 2. Dose-volume histogram parameters for the BDO-based (left, darker bar) and DECT-based treatment plans (right, lighter bar) for the fibula, tibia, and the CTV for the 3 patients.

Conclusion:

For soft-tissue tumors of the extremities MRI-only based proton dose calculation accuracy of BDO is comparable to DECT-based planning. Gamma passing rates for all treatment plans are within clinical acceptance limits. Therefore, BDO can be used for treatment planning of soft-tissue tumors of the extremities based on daily MR imaging, allowing for daily plan adaptation. A density override of the muscle and a voxel-wise based override is expected to further improve the dose calculation accuracy [3]. More patients are needed to confirm the initial findings of this study.

Keywords: MR-only, proton therapy

References:

[1] Hoffmann A, Oborn B, Moteabbed M, Yan S, Bortfeld T, Knopf A, Fuchs H, Georg D, Seco J, Spadea MF, Jäkel O, Kurz C, Parodi K. MR-guided proton therapy: a review and a preview. Radiat Oncol. 2020 May 29;15(1):129. doi: 10.1186/s13014-020-01571-x. PMID: 32471500; PMCID: PMC7260752.