Abstract
BackgroundOnline magnetic resonance imaging (MRI)-guided radiotherapy of cervical cancer has the potential to further reduce dose to organs at risk (OAR) as compared to a library of plans (LOP) approach. This study presents a dosimetric comparison of an MRI-guided strategy with a LOP strategy taking intrafraction anatomical changes into account.MethodsThe 14 patients included in this study were treated with chemo radiation at our institute and received weekly MRIs after informed consent. The MRI-guided strategy consisted of treatment plans created on the weekly sagittal MRI with 3 mm and 5 mm planning target volume (PTV) margin for clinical target volume (CTV) cervix-uterus (MRI_3mm and MRI_5mm). The plans for the LOP strategy were based on interpolations of CTV cervix-uterus on pretreatment full and empty bladder scans. Dose volume histogram (DVH) parameters were compared for targets and OARs as delineated on the weekly transversal MRI, which was acquired on average 10 min after the sagittal MRI.ResultsFor the MRI_5mm strategy D98% of the high-risk CTV was at least 95% for all weekly MRIs of all patients, while for the LOP and MRI_3mm strategy this requirement was not satisfied for at least one weekly MRI for 1 and 3 patients, respectively. The average reduction of the volume of the reference dose (95% of the prescribed dose) as compared to the LOP strategy was 464 cm3 for the MRI_3mm strategy, and 422 cm3 for the MRI_5mm strategy. The bowel bag constraint V40Gy < 350 cm3 was violated for 13 patients for the LOP strategy and for 5 patients for both MRI_3mm and MRI_5mm strategy.ConclusionsWith online MRI-guided radiotherapy of cervical cancer considerable sparing of OARs can be achieved. If a new treatment plan can be generated and delivered within 10 min, an online MRI-guided strategy with a 5 mm PTV margin for CTV cervix-uterus is sufficient to account for intrafraction anatomical changes.Trial registrationNL44492.018.13.
Highlights
Online magnetic resonance imaging (MRI)-guided radiotherapy of cervical cancer has the potential to further reduce dose to organs at risk (OAR) as compared to a library of plans (LOP) approach
Patient data Of the 17 patients that participated in this study, 14 received at least 3 weekly MRIs and were included in the analysis
A considerable reduction of small bowel toxicity might be achieved with the MRI-guided strategy compared to the LOP strategy, as we found that the dose constraint V40Gy < 350 cm3, suggested by Fiorino et al [24], was satisfied for 9 out of 14 patients for the MRI-guided strategy, compared to 1 patient for the LOP strategy
Summary
Online magnetic resonance imaging (MRI)-guided radiotherapy of cervical cancer has the potential to further reduce dose to organs at risk (OAR) as compared to a library of plans (LOP) approach. Current radiotherapy practice innovation focuses on better local control by better tumour coverage and dose to organs at risk (OAR) reduction [5]. For external beam radiation therapy (EBRT) with volumetric-modulated arc therapy (VMAT), image-guided adaptive radiation therapy with a library of plans (LOP) approach became state-of-the-art care during the last decade, leading to a margin reduction and less dose to OAR [6, 7]. With magnetic resonance imaging (MRI) and adequate brachytherapy target coverage aided by interstitial needles, better local control is achieved while severe toxicity rates are declining [2, 8, 9]. For external beam radiation therapy (EBRT) the importance of determining tumour extension on MRI further increases as margins are being reduced with plan-of-the-day adaptive strategies [11]
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