The impact of motion on onboard MRI-guided pencil beam scanned proton therapy treatments

Phys Med Biol. 2024 Mar 27. doi: 10.1088/1361-6560/ad3885. Online ahead of print.ABSTRACTOnline magnetic resonance imaging (MRI) guidance could be especially beneficial for pencil beam scanned (PBS) proton therapy of tumours affected by respiratory motion. For the first time to our knowledge, we investigate the dosimetric impact of respiratory motion on MRI-guided proton therapy compared to the scenario without magnetic field.

Approach. A previously developed analytical proton dose calculation algorithm accounting for perpendicular magnetic fields was extended to enable 4D dose calculations. For two geometrical phantoms and three liver and two lung patient cases, static treatment plans were optimised with and without magnetic field (0, 0.5 and 1.5T). Furthermore, plans were optimised using gantry angle corrections (0.5T+5° and 1.5T+15°) to reproduce similar beam trajectories compared to the 0T reference plans. The effect of motion was then considered using 4D dose calculations without any motion mitigation and simulating 8-times volumetric rescanning, with motion for the patient cases provided by 4DCT(MRI) data sets. Each 4D dose calculation was performed for different starting phases and the CTV dose coverage V95% and homogeneity D5%-D95% were analysed.

Main results. For the geometrical phantoms with rigid motion perpendicular to the beam and parallel to the magnetic field, a comparable dosimetric effect was observed independent of the mag...
Source: Physics in Medicine and Biology - Category: Physics Authors: Source Type: research