The effect of region of interest strategies on apparent diffusion coefficient assessment in patients treated with palliative radiation therapy to brain metastases

Faisal Mahmood, Helle Hjorth Johannesen, Poul Geertsen, Giske F. Opheim, Rasmus H. Hansen

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Background. Although diffusion-weighted magnetic resonance imaging (DW-MRI) is widely used in radiation therapy (RT) response studies, no standard of delineating the region of interest (ROI) exists. In this retrospective study, we evaluate the effect of four ROI strategies on the apparent diffusion coefficients (ADC) in patients receiving palliative RT to brain metastases.
Material and methods. Twenty-two metastases from nine patients, treated with whole-brain irradiation (30 Gy in 10 fractions) were analyzed. Patients were scanned with a 1T MR system to acquire DW- (eight b-values), T2 * W-, T2Wand T1W scans, before start of RT (pre-RT) and at the 9th/10th fraction (end-RT). The following ROI strategies were applied. ROI b800 and ROI b0 : Entire tumor volume visible on DW(b 800 s/mm 2 ) and DW(b 0 s/mm 2 ) images, respectively. ROI b800vi : Viable tumor volume based on DW(b 800 s/mm 2 ). ROI b800rep : ROI b800 from pre-RT scan replicated to end-RT scan. Delineations were aided by co-registered T1W, T2W and T2 * W images. ADC was estimated with two mono-exponential fits and one bi-exponential fit.
Results. Differences in absolute ADC values were non-signifi cant across ROI strategy independent of fi tting method, while signifi cantly different between fi tting methods. Evaluation of individual metastases showed that ROI strategies
disagreed on the relative ADC change (from pre-RT to end-RT) in 13 of the 22 metastases when all fi tting methods were added up.
Conclusion. The ROI strategies have an effect on the relative ADC change, which may be important for the assessment of individual patient’s response to RT and the interpretation of the current literature.
Original languageEnglish
JournalActa Oncologica
Volume54
Issue number9
Pages (from-to)1529-1534
ISSN0284-186X
DOIs
Publication statusPublished - 2015
Externally publishedYes

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