Impact of abdominal compression on intra-fractional motion and delivered dose in magnetic resonance image-guided adaptive radiation ablation of adrenal gland metastases

Bernchou, Uffe; Schytte, Tine; Bertelsen, Anders; Lorenzen, Ebbe Laugaard; Brink, Carsten; Mahmood, Faisal

doi:10.1016/j.ejmp.2023.102682

Cited by 4 publications

(1 citation statement)

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“…This way, the tumor displacement measured during a single cine MRI frame (∼350 ms) could be applied to the dose that was delivered when that displacement took place, a more realistic approach than convoluting (or "shaking") the general discussion complete planned dose with all measured motion. 139,154 The 3D cine MRI developed in Chapter 6 allowed for arguably the most physiologically realistic dose accumulation model in this thesis, incorporating volumetric deformations to the time-resolved approach of Chapter 5. However, it can be questioned whether sophisticated imaging like 3D cine MRI is necessary for tumor tracking and dose accumulation.…”

Section: Treatment Planningmentioning

confidence: 99%

Advancing the frontiers of MR-guided radiotherapy for pancreatic cancer

Grimbergen

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Pancreatic cancer is among the deadliest types of cancer, and effective and safe treatment remains challenging. MR-guided radiotherapy, a noninvasive, low-toxic, local treatment, has recently emerged as a new treatment option for inoperable pancreatic cancer. The aim of this thesis was to explore several technical developments for the planning and delivery of radiotherapy for pancreatic cancer on the 1.5 T MR-Linac. These developments are needed to transform contemporary MR-guided radiotherapy into a next-generation treatment for pancreatic cancer, which extensively capitalizes on the capabilities of the 1.5 T MR-Linac. In the first part of this thesis, we focused on (online adaptive) treatment planning. The conventional MRI sequences for online treatment adaptation are prone to blurring artifacts due to respiratory motion, but we found that motion-robust radial MRI sequences can result in much sharper, higher quality images, potentially increasing delineation accuracy and speed. Next, we founded a worldwide consortium of MR-Linac centers to create a consensus protocol on treatment planning for pancreatic cancer. We hope that this collaboration will harmonize the large variations currently found in protocols and strategies between centers around the world that treat pancreatic cancer on the 1.5 T MR-Linac. The second part revolved around intrafraction motion and treatment delivery. The onboard imaging system of the MR-Linac allowed us to fully characterize pancreatic tumor motion during treatment, in terms of respiratory motion, tumor drift, and their respective variations on a day-to-day and patient-to-patient basis. The measured intrafraction motion was used for retrospective dose calculation, thereby allowing us to evaluate whether the tumor motion during irradiation had lead to dosimetric errors such as tumor underdosage or OAR overdosage. We found that this dosimetric impact is generally modest, but small drifts are potentially much more problematic than large respiratory amplitudes. We further developed intrafraction dose accumulation by designing a 3D dynamic MRI scan capable of capturing complete volumetric information in real-time, allowing for advanced deformable dose accumulation. Lastly, we report on the first patients, all with upper abdominal tumors, treated with active motion management on the 1.5 T MR-Linac. This system is capable of fully MR-based respiratory gating, and is enhanced with baseline drift correction capabilities. We showed through dosimetric analysis that this system improves congruence between the planned dose and delivered dose. To conclude, MR-guided radiotherapy has opened the way for a new, safe, local treatment for inoperable pancreatic cancer. The full potential of the MR-Linac, however, has been far from realized. This thesis has shown that MRI is an incredibly versatile tool that can be used in every facet of the online adaptive workflow, allowing us to gain more insight into the treatment and ultimately optimizing the planning and delivery. Ablative radiotherapy for pancreatic cancer with the 1.5 T MR-Linac is one of the most intricate procedures in external beam radiotherapy, and the ongoing developments will only further increase complexity. Therefore, the informal dissemination of clinical experiences and treatment techniques, as well as collaboration between MR-Linac centers, remains crucial for further advancement of radiotherapy for pancreatic cancer.

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Section: Treatment Planningmentioning

confidence: 99%

Advancing the frontiers of MR-guided radiotherapy for pancreatic cancer

Grimbergen

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Intrafraction motion and impact of margin reduction for MR‐Linac online adaptive radiotherapy for pancreatic cancer treatments

Fasala,

Carr,

Surjan

et al. 2024

J of Medical Radiation Sci

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IntroductionOnline adaptive radiotherapy is well suited for stereotactic ablative radiotherapy (SABR) in pancreatic cancer due to considerable intrafractional tumour motion. This study aimed to assess intrafraction motion and generate adjusted planning target volume (PTV) margins required for online adaptive radiotherapy in pancreatic cancer treatment using abdominal compression on the magnetic resonance linear accelerator (MR‐Linac).MethodsMotion monitoring images obtained from 67 fractions for 15 previously treated pancreatic cancer patients were analysed. All patients received SABR (50 Gy in five fractions) on the MR‐Linac using abdominal compression. The analysis included quantification of intrafraction motion, leading to the development of adjusted PTV margins. The dosimetric impact of implementing the adjusted PTV was then evaluated in a cohort of 20 patients.ResultsIntrafraction motion indicated an average target displacement of 1–3 mm, resulting in an adjusted PTV margin of 2 mm in the right–left and superior–inferior directions, and 3 mm in the anterior–posterior direction. Plans incorporating these adjusted margins consistently demonstrated improved dose to target volumes, with improvements averaging 1.5 Gy in CTV D99%, 4.9 Gy in PTV D99% and 1.2 Gy in PTV‐high D90%, and better sparing of the organs at risk (OAR).ConclusionsThe improved target volume coverage and reduced OAR dose suggest potential for reducing current clinical margins for MR‐Linac treatment. However, it is important to note that decreasing margins may reduce safeguards against geographical misses. Nonetheless, the continued integration of gating systems on MR‐Linacs could provide confidence in adopting reduced margins.

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