Abstract
Background and purposeMagnetic resonance (MR)-guided linear accelerator (MR-Linac) systems have changed radiotherapy workflows. The addition of daily online contour adaptation allows for higher precision treatment, but also increases the workload of those involved. We train radiation therapists (RTTs) to perform daily online contour adaptation for MR-Linac treatment of prostate cancer (PCa) patients. The purpose of this study was to evaluate these prostate contours by performing an interfraction and interobserver analysis. Materials and methodsClinical target volume (CTV) contours generated online by RTTs from 30 low-intermediate risk PCa patients, treated with 5x7.25 Gy, were used. Two physicians (Observers) judged the RTTs contours and performed adaptations when necessary. Interfraction relative volume differences between the first and the subsequent fractions were calculated for the RTTs, Observer 1, and Observer 2. Additionally, interobserver dice’s similarity coefficient (DSC) for fraction 2–5 was calculated with the RTTs- and physician-adapted contours. Clinical acceptability of the RTTs contours was judged by a third observer. ResultsMean (SD) online contour adaptation time was 12.6 (±3.8) minutes and overall median (interquartile range [IQR]) relative volume difference was 9.3% (4.4–13.0). Adaptations by the observers were mostly performed at the apex and base of the prostate. Median (IQR) interobserver DSC between RTTs and Observer 1, RTTs and Observer 2, and Observer 1 and 2 was 0.99 (0.98–1.00), 1.00 (0.98–1.00), and 1.00 (0.99–1.00), respectively. Contours were acceptable for clinical use in 113 (94.2%) fractions. Dose-volume histogram (DVH) analysis showed significant CTV underdosage for one of the seven identified outliers. ConclusionDaily online contour adaptation by RTTs is clinically feasible for MR-Linac treatment of PCa.
Highlights
The clinical introduction of magnetic resonance (MR)-guided linear accelerator (MR-Linac) systems has led to major changes in the workflows for treatment of various types of cancer [1,2]
The pre-treatment contours are propagated to the daily MR scan, followed by manual adaptation to make them perfectly fit the anatomy of the day
Dose-volume histogram (DVH) for four exemplary outlier cases are displayed in Fig. 5 and Clinical target volume (CTV) D99% is presented in Supplementary Table S1
Summary
The clinical introduction of magnetic resonance (MR)-guided linear accelerator (MR-Linac) systems has led to major changes in the workflows for treatment of various types of cancer [1,2]. The pre-treatment contours are propagated to the daily MR scan, followed by manual adaptation to make them perfectly fit the anatomy of the day. This so called ‘Adapt-toShape’ (ATS) workflow is aimed at delivering the highest precision treatment to the patient, thereby potentially reducing toxicity and improving oncological outcomes [4,5]. We train radiation therapists (RTTs) to perform daily online contour adaptation for MR-Linac treatment of prostate cancer (PCa) patients. Conclusion: Daily online contour adaptation by RTTs is clinically feasible for MR-Linac treatment of PCa
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