Patterns of practice of adaptive re-planning for anatomic variances during cone-beam CT guided radiotherapy

Michal Stankiewicz; Winnie Li; Tara Rosewall; Tony Tadic; Colleen Dickie; Michael Velec

doi:10.1016/j.tipsro.2019.10.003

Patterns of practice of adaptive re-planning for anatomic variances during cone-beam CT guided radiotherapy

Tech Innov Patient Support Radiat Oncol. 2019 Dec 16:12:50-55. doi: 10.1016/j.tipsro.2019.10.003. eCollection 2019 Dec.

Authors

Michal Stankiewicz^{1

2}, Winnie Li^{1

2}, Tara Rosewall^{1

2}, Tony Tadic^{1

2}, Colleen Dickie^{1

2}, Michael Velec^{1

2

3}

Affiliations

¹ Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network Toronto, Canada.
² Department of Radiation Oncology, University of Toronto, Toronto, Canada.
³ Techna Institute, University Health Network, Toronto, Canada.

Abstract

Purpose: Substantial, unanticipated anatomic variances during cone-beam CT (CBCT)-guided radiotherapy can potentially impact treatment accuracy and clinical outcomes. This study assessed patterns of practice of CBCT variances reported by RTTs and subsequent interventions for multiple-disease sites.

Methods: A chart review was conducted at a large cancer centre for patients treated with daily online CBCT-guided radiotherapy. Patients selected for review were identified via RTT-reported variances that then triggered offline multi-disciplinary assessment. Cases were categorized by the type of anatomic variance observed on CBCT and any further interventions recorded such as un-scheduled adaptive re-planning.

Results: Over a 1-year period, 287 variances from 261 patients were identified (6.2% of the 4207 patients treated with daily CBCT-guided radiotherapy), most often occurring within the first 5 fractions of the treatment course. Of these variances, 21% (59/287) were re-planned and 3.5% (10/287) discontinued treatment altogether. Lung was the most frequent disease-site (27% of 287 variances) reported with IGRT-related variances although head and neck and sarcoma were most frequently re-planned (19% of 59 re-plans for each site). Technical or clinical rationales for re-planning were not routinely documented in patient medical records. All disease-sites had numerous categories of variances. Three of the four most frequent categories were for tumor-related changes on CBCT, and the re-planning rate was highest for tumor progression at 25%. Normal tissue variances were the second most frequency category, and re-planned in 14% of those cases.

Conclusion: RTTs identified a wide range of anatomic variances during CBCT-guided radiotherapy. In a minority of cases, these substantially altered the care plan including ad hoc adaptive re-planning or treatment discontinuation. Improved understanding of the clinical decisions in these cases would aid in developing more routine, systematic adaptive strategies.

Keywords: Adaptive radiation therapy; Cone-beam CT; Image registration; Inter-fraction motion.