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. 2023 Aug 28;28(4):437-444.
doi: 10.5603/RPOR.a2023.0051. eCollection 2023.

Stereotactic MR-guided adaptive radiotherapy (SMART) for primary rectal cancer: evaluation of early toxicity and pathological response

Alessandra Castelluccia  1 , Domenico Marchesano  2 , Gianmarco Grimaldi  2 , Ivan Annessi  2 , Federico Bianciardi  2   3 , Cristian Borrazzo  2 , Annamaria Dipalma  2 , Randa El Gawhary  2 , Marica Masi  2 , Maria Rago  2 , Maria Valentino  2 , Laura Verna  2 , Maurizio Portaluri  1 , PierCarlo Gentile  2   3
Affiliations

Stereotactic MR-guided adaptive radiotherapy (SMART) for primary rectal cancer: evaluation of early toxicity and pathological response

Alessandra Castelluccia et al. Rep Pract Oncol Radiother. .

Abstract

Background: The purpose of this study is to measure the effects of stereotactic MR-guided adaptive radiotherapy (SMART) for rectal cancer patients in terms of early toxicity and pathological response.

Materials and methods: For this prospective pilot study, patients diagnosed with locally advanced rectal cancer (LARC) with positive lymph node clinical staging underwent SMART on rectal lesion and mesorectum using hybrid MR-Linac (MRIdian ViewRay). Dose prescription at 80% isodose for the rectal lesion and mesorectum was 40 Gy (8 Gy/fr) and 25 Gy (5 Gy/fr), respectively, delivered on 5 days (3 fr/week). Response assessment by MRI was performed 3 weeks after SMART, then patients fit for surgery underwent total mesorectal excision. Primary endpoint was evaluation of adverse effect of radiotherapy. Secondary endpoint was pathological complete response rate. Early toxicity was graded according to the Common Terminology Criteria for Adverse Events (CTCAE v5.0).

Results: From October 2020 to January 2022, twenty patients underwent rectal SMART. No grade 3-5 toxicity was recorded. Twelve patients were eligible for total mesorectal excision (TME). Mean interval between the completion of SMART and surgery was 4 weeks. Pathological downstaging occurred in all patients; rate of pathological complete response (pCR) was 17%. pCR occurred with a prolonged time to surgery (> 7 weeks).

Conclusion: To our knowledge, this is the first study to use stereotactic radiotherapy for primary rectal cancer. SMART for rectal cancer is well tolerated and effective in terms of tumor regression, especially if followed by delayed surgery.

Keywords: MR-guided RT; rectal cancer; stereotactic radiotherapy.

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Conflict of interest statement

Conflict of interest None declared.

Figures

Figure 1
Figure 1
Original plan for rectal stereotactic MR-guided adaptive radiotherapy (SMART): mesorectum is covered by 25 Gy isodose (yellow area), gross target volume (GTV) is covered by 40 Gy isodose (red area)
Figure 2
Figure 2
Inter-fractional motion of GTV: the rectal lesion (in cyan lines) assumes different positions from simulation MR for each fraction (a, b, c, d, e are fractions from first to fifth, respectively)
See this image and copyright information in PMC

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