Comparison of MR‐guided radiotherapy accumulated doses for central lung tumors with non‐adaptive and online adaptive proton therapy

Abstract

Background: Stereotactic body radiation therapy (SBRT) of central lung tumors with photon or proton therapy has a risk of increased toxicity. Treatment planning studies comparing accumulated doses for state-of -the-art treatment techniques, such as MR-guided radiotherapy (MRgRT) and intensity modulated proton therapy (IMPT), are currently lacking. Purpose: We conducted a comparison of accumulated doses for MRgRT, robustly optimized non-adaptive IMPT, and online adaptive IMPT for central lung tumors. A special focus was set on analyzing the accumulated doses to the bronchial tree, a parameter linked to high-grade toxicities. Methods: Data of 18 early-stage central lung tumor patients, treated at a 0.35 T MR-linac in eight or five fractions, were analyzed. Three gated treatment scenarios were compared: (S1) online adaptive MRgRT, (S2) non-adaptive IMPT, and (S3) online adaptive IMPT. The treatment plans were recalculated or reoptimized on the daily imaging data acquired during MRgRT, and accumulated over all treatment fractions. Accumulated dose-volume histogram (DVH) parameters of the gross tumor volume (GTV), lung, heart, and organs-at-risk (OARs) within 2 cm of the planning target volume (PTV) were extracted for each scenario and compared in Wilcoxon signed-rank tests between S1 & S2, and S1 & S3. Results: The accumulated GTV D 98% was above the prescribed dose for all patients and scenarios. Significant reductions (p < 0.05) of the mean ipsilateral lung dose (S2: -8%; S3: -23%) and mean heart dose (S2: -79%; S3: -83%) were observed for both proton scenarios compared to S1. The bronchial tree D 0.1cc was significantly lower for S3 (S1: 48.1 Gy; S3: 39.2 Gy; p = 0.005), but not significantly different for S2 (S2: 45.0 Gy; p = 0.094), compared to S1. The D 0.1cc for S2 and S3 compared to S1 was significantly (p < 0.05) smaller for OARs within 1-2 cm of the PTV (S1: 30.2 Gy; S2: 24.6 Gy; S3: 23.1 Gy), but not significantly different for OARs within 1 cm of the PTV. Conclusions: A significant dose sparing potential of non-adaptive and online adaptive proton therapy compared to MRgRT for OARs in close, but not direct proximity of central lung tumors was identified. The near-maximum dose to the bronchial tree was not significantly different for MRgRT and non-adaptive IMPT.

The role of online MR-guided multi-fraction stereotactic ablative radiotherapy in lung tumours

“…Conversely, we are currently investigating dosimetry benefits and clinical outcomes of online plan adaption in our cohort of patients treated exclusively to ultra-(central) locations. The results of this analysis and further investigations at the level of accumulated dose using the approach by Rabe et al would certainly be of interest and could complement the current literature and aid in future clinical decision making in this setting [51] .…”

Automatic lung segmentation of magnetic resonance images: A new approach applied to healthy volunteers undergoing enhanced Deep-Inspiration-Breath-Hold for motion-mitigated 4D proton therapy of lung tumors

“…The DSCs of neural network segmentations applied to 3D-MRI acquisitions using fast ultra-short echo time sequences were higher than those of our algorithm. DSCs of 0.97 with a 95 %-CI [0.96, 0.97] for the right lung and 0.96 with a 95 %-CI of [0.96, 0.97] for the left lung were found in [42] using manual segmentations complemented by the region growing algorithm of [38] as reference. In [44] a total DSC of 0.967 ± 0.076 was observed for lung tissue when using manual segmentation by an experienced radiologist as a reference.…”

“…Our MRI-based study has shown that TLC conditions under eDIBH provide excellent reproducibility of lung topology, including potential tumor locations and adjacent structures [21] . Accurate LV determination by reliable, effective contouring is paramount to accurately quantify e.g., D mean and V20% [38] . For its use in online-adaptive, conventional radiotherapy (RT) under image guidance, such as MR-guided RT (MRgRT), computational speed could also be crucial [39] .…”

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

“…To date, however, only a limited number of treatment planning studies have investigated the clinical benefits associated with onboard MRI guidance for proton therapy. Moreover, these studies, which encompassed pediatric (Acharya et al 2020), liver (Moteabbed et al 2021a), prostate (Moteabbed et al 2021b), and lung cancer patients (Rabe et al 2023), did not consider the effect of the magnetic field on the proton dose distributions. In another study, Kurz et al (2017) used MC-based treatment planning to investigate the robustness against setup errors and anatomical changes for prostate treatment plans optimised with and without a magnetic field.…”