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NCT Number: NCT07687147

Daily Adjustment of the Radiation Dose in MRI-guided Stereotactic Radiotherapy for Tumors in the Abdominal and Pelvic Regions

SBRT delivers high-dose radiation to precisely defined target volumes and is an effective locally ablative treatment option for both primary tumours and oligometastases in various settings, including lesions in the abdomen or pelvis. However, SBRT in these regions faces considerable challenges such as inter-fractional organ motion and anatomical deformation, which can compromise treatment precision.

MR-guided SBRT offers a solution, providing superior soft-tissue contrast and enabling real-time, online treatment plan adaptation over the course of SBRT. This approach reduces the risk of geographical miss and overdose to adjacent, vulnerable OARs. Currently, MR-guided SBRT uses a fixed dose per fraction, only adjusting target volume and OAR contours for anatomical changes when performing plan adaptation. However, overlaps between planning target volumes (PTVs) and dose-limiting OARs regularly require compromises in PTV coverage. To address this, AF aims to also adjust dose per fraction based on daily PTV-OAR overlap. With this approach, more dose is applied on treatment days with less PTV-OAR overlap while less dose is applied on days with more PTV-OAR overlap. This trial assesses the feasibility of AF in MR-guided SBRT for abdominal and pelvic tumours that show PTV-overlap with one or more dose-limiting OARs, ultimately aiming to enhance PTV dose coverage without increasing toxicity.

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Key information

Conditions

Abdominal Tumor Abdominal Neoplasms Neoplasms Neoplasms by Site Pelvic Neoplasms Pelvic Tumor

Age range

18 year and older

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

University Hospital Zurich

Zurich, Canton of Zurich, 8091, Switzerland

Location status: Recruiting

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Karnofsky performance status ≥70
  • Abdominal or pelvic malignancy (primary or secondary) with previous histological confirmation of the primary tumour, amenable to SBRT in 5 fractions (excluding SBRT to primary tumour in patients with prostate cancer) Note: patients with primary prostate cancer are eligible, but SBRT to the primary tumour in the prostate cannot be performed within the study
  • Total prescribed SBRT dose > 30 Gy (constraint for dose-limiting OAR) over 5 treatment fractions
  • Distance of the GTV ≤ 1 cm from at least one dose-limiting OAR (bowel / duodenum / stomach) in the available diagnostic images
  • Patients able to tolerate long (approximately 60 minutes) treatment time according to clinical evaluation of the treating radiation oncologist
  • Patients willing and able to comply with scheduled visits, treatment, and other trial procedures

Exclusion criteria

  • Previous radiation therapy directly overlapping with planned SBRT (type I re-irradiation)
  • More than one PTV irradiated in the same plan
  • Contraindications for MRI, e.g., patients with metal fragments or implanted devices that are not MR compatible such as certain types of pacemakers and aneurysm clips or severe claustrophobia
  • SBRT not indicated or not possible
  • Inability to follow the procedures of the trial, e.g. due to language problems of the participant

Treatment and study plan

SBRT with adaptive fractionation

Radiation

The fraction dose to the PTV will be adapted based on the volume overlap of PTV and the dose-limiting OAR(s) (bowel / duodenum / stomach) on the planning MRI scan of the day ("geometry-of-the-day"). The treatment plan is then approved by the treating physician and independently verified according to department-internal standard. MR-guided fraction dose adaptation will be repeated at each of the 5 fractions, until the prescribed total dose is reached.

Standard of Care (SOC)

Radiation

Patients that qualify for inclusion in the study but for whom AF is no viable treatment due to lacking PTV/OAR overlap in the planning scans. These patients are treated according to clinical standard of care (SoC), i.e. without dose adaptation, and function as a control group.

Primary outcomes

  1. Proportion of patients with successful daily dose adaptation

    Time frame: from enrollment to end of treatment at 1-2 weeks

    Proportion of patients treated with daily dose-adapted treatment, who received at least one fraction of non-uniformly fractionated treatment with expectation of a benefit in PTV-coverage of ≥ 1ccGy

Secondary outcomes

  1. Acute treatment toxicities

    Time frame: during treatment (1-2 weeks) and until 90 days after

    Acute treatment toxicities for all included patients measured with Common Terminology Criteria for Adverse Events

  2. Interfractional variation in PTV/OAR overlap volume

    Time frame: during treatment (1-2 weeks)

    interfractional variation in PTV/OAR overlap volume, in cc

  3. Interfractional variation in GTV/OAR distance

    Time frame: during treatment (1-2 weeks)

    interfractional variation in GTV/OAR distance, in mm

  4. Dosimetric difference in PTV-coverage between algorithm-based calculation and the reference plan

    Time frame: after end of treatment (2 weeks after last fraction)

    PTV coverage quantified as the area above the dose-volume-histogram curve measured in cc x Gy

Study contacts

Contact information is provided by the study sponsor or research team.

Jan Unkelbach, Prof. Dr. rer. nat.

CONTACT

[email protected]

+41 44 255 85 49

Lena Kretzschmar, Dr. med.

CONTACT

[email protected]

Sponsors and collaborators

Lead sponsor

University of Zurich

Other

Registry information

Official study title

Adaptive Fractionation in Online MR-guided SBRT for Abdominal and Pelvic Target Volumes

Acronym: ACTION

Important dates

Study start
2026
Primary completion
2028
Study completion
2028
First posted
Jul 7, 2026
Registry last updated
Jul 7, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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