S2159
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Conclusion: Pre-trial planning on emulated cases demonstrated the technical feasibility of RANGER’s response-adapted sequential SBRT strategy. An 8 mm PTV gap preserves robust dosimetric coverage for both prostate fossa and pelvic nodes, supporting the trial’s design. This approach enables selective intensification without compromising safety or efficacy, offering a personalized salvage radiotherapy pathway that balances treatment aggressiveness with toxicity reduction. Keywords: prostate cancer, field match Proffered Paper 3561 MR-Guided Radiotherapy (MRgRT) for Personalized Ultrafractionated Stereotactic Adaptive Radiotherapy (PULSAR) in Advanced Metastatic Cervical Cancer Yesenia Gonzalez 1 , Justin Visak 1 , Thomas Banks 1 , Viktor Iakovenko 1 , Tsuicheng Chiu 1 , Mu-Han Lin 1 , Robert Timmerman 1 , Chika Nwachukwu 2 , Kevin Albuquerque 1 1 Radiation Oncology, UTSW, Dallas, USA. 2 Radiation Oncology, UTSD, San Diego, USA Purpose/Objective To report our institutional experience delivering personalized ultra-fractionated stereotactic adaptive radiotherapy (PULSAR) with MR-guidance (MRgRT) stereotactic) for patients with large primary cervical tumors and synchronous metastatic disease (Stage IVB). PULSAR enables treatment of primary cervix tumors and bulky nodes in the setting of metastatic disease for patients who otherwise may have limited options by leveraging normal tissue recovery and biologic response within the tumor microenvironment. This report evaluates technical implementation of a novel trial and assesses dosimetric outcomes and longitudinal tumor response. Material/Methods Twelve Stage IVB cervical cancer patients were treated on MR-linac with a total dose of 40–42.5 Gy delivered in 3-5 adaptive pulses spaced about three weeks apart to integrate with systemic therapy under an IRB- approved protocol. The primary planning target volume (PTV) included cervical tumor defined by MRI with 3-5mm margin. Nodal targets, were added at physician discretion. Tumor response was evaluated by clinical target volume (CTV) measurements at each adaptive fraction. Dosimetric differences between reference plan and adaptive fractions were analyzed using HyTEC/SBRT and EMBRACE II criteria. Tracking data were recorded at each adaptive fraction in an integrated spreadsheet that enabled the treating team to review cumulative dose information and adjust subsequent plans as needed. This practical and novel
approach supported efficient dose accumulation assessment and more informed adaptive decisions throughout the MRgRT workflow. Results In total, 39 pulses were delivered to patients, 9 patients received at least 3 pulses. The average CTV cervix volume reduction throughout their course of treatment was 58.3±71.8cc (range:9.7-252.5Gy). On average, coverage was maintained for all fractions to primary and nodal tumor volumes. Maximum D2cc(Gy) improvement was observed in the sigmoid with an average sparing of 3.2±9.0Gy (range:-3.9- 28.3Gy) where other OAR D2cc(Gy) were modestly improved/maintained with bladder, small bowel and rectum reporting sparing as 1.2±2.4Gy(range:-2-
3.92Gy), -0.1±3.9Gy (range:-4.9-9.3Gy), and 0.0002±10.3(-17.0-19.9Gy), respectively. Conclusion
This work demonstrates the feasibility and dosimetric value of delivering ultra-fractionated adaptive MRgRT for advanced cervical cancer using the PULSAR paradigm. The ultra-interfraction interval enables measurable tumor regression between pulses and provides opportunities to refine adaptive plans based on evolving anatomy. Several patients showed meaningful OAR dose reductions and significant tumor shrinkage, confirming that PULSAR can safely exploit biologic recovery while maintaining ablative intent. These findings suggest that MR-guided PULSAR represents a promising and novel treatment strategy for patients with advanced metastatic cervical cancer who otherwise have limited therapeutic options.
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