Inter-fraction dynamics during post-operative 5 fraction cavity hypofractionated stereotactic radiotherapy with a MR LINAC: a prospective serial imaging study

Hendrick Tan; James Stewart; Mark Ruschin; Michael H Wang; Sten Myrehaug; Chia-Lin Tseng; Jay Detsky; Zain Husain; Hanbo Chen; Arjun Sahgal; Hany Soliman

doi:10.1007/s11060-021-03938-w

Inter-fraction dynamics during post-operative 5 fraction cavity hypofractionated stereotactic radiotherapy with a MR LINAC: a prospective serial imaging study

J Neurooncol. 2022 Feb;156(3):569-577. doi: 10.1007/s11060-021-03938-w. Epub 2022 Jan 3.

Authors

Hendrick Tan^{1

2}, James Stewart¹, Mark Ruschin^{3

4}, Michael H Wang¹, Sten Myrehaug^{1

3}, Chia-Lin Tseng^{1

3}, Jay Detsky^{1

3}, Zain Husain^{1

3}, Hanbo Chen^{1

3}, Arjun Sahgal^{1

3}, Hany Soliman^{5

6}

Affiliations

¹ Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, ON, M4N 3M5, Canada.
² GenesisCare, Perth, WA, Australia.
³ Department of Radiation Oncology, University of Toronto, Toronto, Canada.
⁴ Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, Canada.
⁵ Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, ON, M4N 3M5, Canada. hany.soliman@sunnybrook.ca.
⁶ Department of Radiation Oncology, University of Toronto, Toronto, Canada. hany.soliman@sunnybrook.ca.

PMID: 34981300
DOI: 10.1007/s11060-021-03938-w

Abstract

Purpose/objective(s): This study examined changes in the clinical target volume (CTV) and associated clinical implications on a magnetic resonance imaging linear accelerator (MR LINAC) during hypofractionated stereotactic radiotherapy (HSRT) to resected brain metastases. In addition, the suitability of using T2/FLAIR (T2f) sequence to define CTV was explored by assessing contouring variability between gadolinium-enhanced T1 (T1c) and T2f sequences.

Materials/methods: Fifteen patients treated to either 27.5 or 30 Gy with five fraction HSRT were imaged with T1c and T2f sequences during treatment; T1c was acquired at planning (FxSim), and fraction 3 (Fx3), and T2f was acquired at FxSim and all five fractions. The CTV were contoured on all acquired images. Inter-fraction cavity dynamics and CTV contouring variability were quantified using absolute volume, Dice similarity coefficient (DSC), and Hausdorff distance (HD) metrics.

Results: The median CTV on T1c and T2f sequences at FxSim were 12.0cm³ (range, 1.2-30.1) and 10.2cm³ (range, 2.9-27.9), respectively. At Fx3, the median CTV decreased in both sequences to 9.3cm³ (range, 3.7-25.9) and 8.6cm³ (range, 3.3-22.5), translating to a median % relative reduction of - 11.4% on T1c (p = 0.009) and - 8.4% on T2f (p = 0.032). We observed a median % relative reduction in CTV between T1c and T2f at FxSim of - 6.0% (p = 0.040). The mean DSC was 0.85 ± 0.10, and the mean HD was 5.3 ± 2.7 mm when comparing CTV on T1c and T2f at FxSim.

Conclusion: Statistically significant reductions in cavity CTV was observed during HSRT, supporting the use of MR image guided radiation therapy and treatment adaptation to mitigate toxicity. Significant CTV contouring variability was seen between T1c and T2f sequences. Trial registration NCT04075305 - August 30, 2019.

Keywords: Adaptive radiotherapy; Brain metastases; Hypofractionated stereotactic radiotherapy; Magnetic resonance image-guided radiotherapy.

MeSH terms

Humans
Magnetic Resonance Imaging* / instrumentation
Particle Accelerators
Postoperative Care
Prospective Studies
Radiation Dose Hypofractionation*
Radiotherapy, Image-Guided* / methods

Associated data

ClinicalTrials.gov/NCT04075305