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The Identification of Sea Lamprey Pheromones Using Bioassay-Guided Fractionation
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Overlap guided adaptive fractionation.

Yoel Samuel Pérez Haas1, Lena Kretzschmar1, Bertrand Pouymayou1

  • 1Department of Radiation Oncology, University Hospital of Zurich, Zurich, Switzerland.

Physics in Medicine and Biology
|January 30, 2026
PubMed
Summary
This summary is machine-generated.

Overlap-guided adaptive fractionation (AF) improves target coverage in MR-guided SBRT for abdominal tumors by adjusting daily doses based on tumor and organ overlap. Patients with greater overlap variation experience the most significant benefits.

Keywords:
MR-guidanceMR-linacSBRTadaptive radiotherapydose adaptationinterfractional motion management

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Area of Science:

  • Radiation Oncology
  • Medical Physics
  • Image-Guided Therapy

Background:

  • Magnetic-Resonance-(MR)-guided radiotherapy on hybrid MR-linear accelerators enables stereotactic body radiotherapy (SBRT) for abdominal/pelvic tumors with significant interfractional motion.
  • Overlaps between planning target volume (PTV) and dose-limiting organs at risk (OARs) frequently necessitate compromises in PTV coverage during SBRT.
  • Online-adaptive radiotherapy (ART) strategies are crucial for optimizing treatment delivery in the presence of anatomical variations.

Purpose of the Study:

  • To assess the potential benefits of overlap-guided adaptive fractionation (AF) in improving PTV coverage for MR-guided SBRT of abdominal/pelvic tumors.
  • To evaluate the dosimetric gain achieved by leveraging daily variations in PTV/OAR overlap to administer variable fraction doses.
  • To determine the relationship between PTV/OAR overlap variation and the magnitude of benefit from AF.

Main Methods:

  • Analysis of 58 patients undergoing 5-fraction MR-guided SBRT for abdominal/pelvic tumors with PTV-OAR overlap in at least one fraction.
  • Dose-limiting OARs (bowel, duodenum, stomach) constrained to 1cc ≤ 6Gy per fraction, leading to underdosed overlapping PTV volumes.
  • Optimal fraction doses determined via dynamic programming (Markov decision process) to maximize PTV coverage based on measured daily overlap volume.

Main Results:

  • A substantial variation in PTV/OAR overlap volume (standard deviation: 0.02 - 5.76cc) was observed across patients.
  • Overlap-guided AF demonstrated a benefit in PTV coverage for 55 out of 58 patients, with a mean cohort benefit of 2.93ccGy.
  • A positive correlation was found between higher PTV/OAR overlap variation and a larger AF benefit, ranging from -4.44 to 22.42ccGy.

Conclusions:

  • Overlap-guided AF is a promising strategy for enhancing PTV coverage in abdominal/pelvic SBRT without compromising OAR sparing.
  • The mean cohort advantage of AF is modest due to low overlap variation in many patients, but selected individuals with significant variation benefit considerably.
  • Further prospective studies are warranted to evaluate the clinical feasibility and benefits of adaptive fractionation.