
==== Front
Clin Transl Radiat Oncol
Clin Transl Radiat Oncol
Clinical and Translational Radiation Oncology
2405-6308
Elsevier

S2405-6308(24)00118-6
10.1016/j.ctro.2024.100841
100841
Correspondence
Letter to the Editor
Chuong Michael D. michaelchu@baptisthealth.net
a⁎
Hosni Ali b
Kharofa Jordan c
Reyngold Marsha d
Sanford Nina e
Rubio Rodriguez Mamen f
Dawson Laura b
a Miami Cancer Institute, Miami, FL, USA
b Princess Margaret Cancer Centre, Toronto, Canada
c University of Cincinnati, Cincinnati, OH, USA
d Memorial Sloan Kettering Cancer Center, New York, NY, USA
e University of Texas Southwestern, Dallas, TX, USA
f HM Hospitales, Madrid, Spain
⁎ Corresponding author at: Miami Cancer Institute, 8900 North Kendall Drive, Miami, FL 33176, USA. michaelchu@baptisthealth.net
20 8 2024
9 2024
20 8 2024
48 10084128 7 2024
12 8 2024
© 2024 The Author(s)
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
This is a Letter to the Editor in response to the manuscript titled, “Treatment planning for MR-guided SBRT of pancreatic tumors on a 1.5 T MR-Linac: A global consensus protocol” by Grimbergen et al.

Keywords

Pancreatic cancer
MRI
Adaptive
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pmcTo the Editor,

We congratulate Dr. Grimbergen and colleagues on publishing their planning protocol for ablative 5-fraction pancreas MR-guided SBRT on a 1.5 Tesla (T) MR-Linac [1], which will encourage standardization, enhance treatment quality and facilitate collaboration for future trials. This consensus planning document was created with input from multiple intradisciplinary radiation oncology teams.

The authors of this letter, some from centers that contributed to the paper, want to comment on some aspects of our MR-guided SBRT practices that were not a focus of the manuscript although we believe are important to highlight.

There is a growing body of literature describing excellent outcomes of ablative radiation therapy for locally advanced pancreas cancer (LAPC) including higher local control (LC) and overall survival (OS) compared to historical non-ablative outcomes [2], [3], [4], [5]. Advanced image guidance, motion management, and online adaptive radiation therapy (ART) are paramount for the safe delivery of ablative doses. The multi-center phase 2 SMART trial of 136 patients treated with 50 Gy in 5 fractions on a 0.35 T MR-guided device using automatic beam gating and ART reported no acute grade ≥ 3 gastrointestinal (GI) toxicity definitely attributed to SMART and the 2-year LC and OS rates of 78.2 % and 40.5 %, respectively[2], [3]. A CTV was used for most patients.

Although routine use of a CTV for pancreas SBRT is not endorsed by expert guidelines (e.g., ASTRO [6], ESTRO [7], AGITG/TROG [8]), we strongly recommend use of a CTV to cover microscopic regions at risk when treating with SBRT. Multiple series have demonstrated that occult nodal and perineural involvement are present in most pancreatic cancer patients and are independent prognostic factors for OS [9], [10]. Patterns of failure studies have demonstrated a high incidence of marginal recurrences outside of the GTV when SBRT targeted gross disease only [11], [12], [13]. In contrast, an analysis from Miami Cancer Institute among > 100 patients treated with a generous CTV on a 0.35 T MR-Linac demonstrated a low (7 %) in-field recurrence rate within the CTV [14]. Investigators from Johns Hopkins have demonstrated the benefit of electively including the “triangle volume” for patients who are treated with neoadjuvant RT [15]. Lastly, a retrospective analysis from Stanford demonstrated a lower incidence of 24-month locoregional failure in SBRT patients treated with a CTV versus no CTV without a difference in severe toxicity [16]. As systemic therapies evolve to more effectively address metastatic cancer, there is a stronger rationale to use a CTV that encompasses areas at highest risk of harboring microscopic disease.

There is potential for MR-guided adaptive SBRT to improve LC, maintain biliary function and lengthen OS for patients with LAPC. Technical radiation treatment harmonization [1] and consensus target volumes, including a CTV targeting areas at highest risk for microscopic cancer, will help to improve the quality of future trials that could be practice changing. Developing a standardized treatment approach is valuable, and we should leverage the capabilities of MR-Linacs to safely achieve both dose and target volume escalation, because in some situations more is actually better!

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Michael Chuong: Honoraria – ViewRay, Ali Hosni: Leadership position (non-financial) – Elekta, Nina Sanford: Honoraria – AstraZeneca, Signatera, Total Health Conferencing, Jordan Kharofa: none, Mamen Rubio Rodriguez: none, Laura Dawson: none.
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