Vienna, Austria

ESTRO 2023

Session Item

May 15
10:30 - 11:30
Business Suite 1-2
Pelvic cancers
Li Tee Tan, United Kingdom
Poster Discussion
Toxicity outcomes of dose-escalated MR-guided radiation therapy for abdominal and pelvic tumors
Rupesh Kotecha, USA


Toxicity outcomes of dose-escalated MR-guided radiation therapy for abdominal and pelvic tumors

Roberto Herrera1, Tugce Kutuk2, Michael Chuong2, Kathryn Mittauer2, Martin Tom2, Jessika Contreras2, Adeel Kaiser2, Matthew Hall2, James McCulloch2, Diane Alvarez2, Minesh Mehta2, Alonso Gutierrez2, Rupesh Kotecha2

1Miami Cancer Institute, Radiation Onocology, Miami, USA; 2Miami Cancer Institute, Radiation Oncology, Miami, USA

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Purpose or Objective

Magnetic Resonance Image-guided Radiation Therapy (MRgRT) offers improved soft tissue visualization compared to CT-based techniques, intra-fraction real-time fiducial-free tracking, and ability to adapt the treatment plan, facilitating dose-escalated radiotherapy (RT) for abdominal and pelvic tumors. In this study, we report our institutional MRgRT toxicity results.

Material and Methods

Consecutive patients treated on a 0.35T MR-linac for primary and metastatic tumors in the abdomen and pelvis from April 2018 to September 2022 were evaluated. All were treated without fiducial markers and with real-time MR-based soft tissue tracking and automated beam gating, allowing for intra- and inter-fraction visualization of both the target and the critical organs-at-risk (OARs). The biologic effective dose with α/β of 10 Gy (BED10) was calculated for each treatment. The Common Terminology Criteria for Adverse Events (CTCAE) v5.0 criteria was used to score treatment-related toxicities by the treating physicians. Any toxicity within the first 3 months from completion of MRgRT was scored as “acute” and thereafter was scored as “late.”


335 patients with a median age of 68 years (range, 28-94) met the inclusion criteria. The most common treatment sites were pancreas (n=157, 47%), abdominopelvic lymph nodes (LNs) (n=70, 21%), adrenal glands (n= 48, 14%), and liver/hepatobiliary tract (n=44, 13%). All patients had ECOG 0-1 performance status. 208 (62%) patients were treated for primary tumors and 127 (38%) were treated to metastatic sites. The median prescribed RT dose was 50 Gy (range, 20-76 Gy) in 5 fractions (range, 1-30) over 7 days (range, 1-50 days), the median prescribed BED10 dose was 100 Gy10 (range, 34-158 Gy10), and 184 (55%) patients were treated with 100 Gy10 or higher. 1190 of 1893 prescribed fractions (63%) required plan adaptation. The median follow-up was 11 months (range, 1-52 months). Acute grade 2 or 3 toxicity occurred in 52 (16%) and 6 (2%) patients, respectively. Late grade 2 or 3 toxicity occurred in 24 (7%) and 6 (2%) patients, respectively. Grade 2+ toxicity rates were not different for daily compared to every other day treatments (24% vs. 17%, p=0.3). For 159 patients with more than 1 year follow-up (median 22 months), the 1-year rate of Grade 2+ toxicity was 15% (95% CI: 10.6-19.4%). There were no acute or late grade 4 toxicities, and 1 acute grade 5 toxicity was observed in a pancreatic cancer patient post Whipple procedure, possibly related to RT.


Dose-escalated RT delivered on a 0.35T MR-linac has been very well tolerated in this large series of consecutively treated patients, with acute or late grade 3+ toxicity being rare even with daily treatment delivery.  This is notable given our frequent use of ultra-hypofractionation, frequent use of the adaptive workflow, and ablative dosing in most patients to sites close to gastrointestinal OARs.