CT-guided versus MR-guided radiotherapy: Impact on gastrointestinal sparing in adrenal stereotactic body radiotherapy

Abstract

Background and purpose: To quantify the indication for adaptive, gated breath-hold (BH) MR-guided radiotherapy (MRgRT BH ) versus BH or free-breathing (FB) CT-based image-guided radiotherapy (CT-IGRT) for the ablative treatment of adrenal malignancies. Materials and methods: Twenty adrenal patients underwent adaptive IMRT MRgRT BH to a median dose of 50 Gy/5 fractions. Each patient was replanned for VMAT CT-IGRT BH and CT-IGRT FB on a c-arm linac. Only CT-IGRT FB used an ITV, summed from GTVs of all phases of the 4DCT respiratory evaluation. All used the same 5 mm GTV/ITV to PTV expansion. Metrics evaluated included: target volume and coverage, conformality, mean ipsilateral kidney and 0.5 cc gastrointestinal organ-at-risk (OAR) doses (D 0.5cc ). Adaptive dose for MRgRT BH and predicted dose (i.e., initial plan re-calculated on anatomy of the day) was performed for CT-IGRT BH and MRgRT BH to assess frequency of OAR violations and coverage reductions for each fraction. Results: The more common VMAT CT-IGRT FB , with its significantly larger target volumes, proved inferior to MRgRT BH in mean PTV and ITV/GTV coverage, as well as small bowel D 0.5cc . Conversely, VMAT CT-IGRT BH delivered a dosimetrically superior initial plan in terms of statistically significant (p 0.02) improvements in target coverage, conformality and D 0.5cc to the large bowel, duodenum and mean ipsilateral kidney compared to IMRT MRgRT BH . However, non-adaptive CT-IGRT BH had a 71.8% frequency of predicted indications for adaptation and was 2.8 times more likely to experience a coverage reduction in PTV D 95% than predicted for MRgRT BH . Conclusion: Breath-hold VMAT radiotherapy provides superior target coverage and conformality over MRgRT BH , but the ability of MRgRT BH to safely provide ablative doses to adrenal lesions near mobile luminal OAR through adaptation and direct, real-time motion tracking is unmatched.

Multi-Institutional Outcomes of Stereotactic Magnetic Resonance Image Guided Adaptive Radiation Therapy With a Median Biologically Effective Dose of 100 Gy10 for Non-bone Oligometastases

“… 4 Despite the majority of lesions in our study being in proximity to gastrointestinal luminal OARs, the median prescribed BED was 100 Gy 10 that resulted in excellent 1-year FFLP with minimal severe toxicity, likely facilitated by online adaptive replanning. 25 …”

Hypofractionation and SABR: 25 years of evolution in medical physics and a glimpse of the future

“…In the past, however, there had been very few prospective clinical trials looking into outcome improvement or toxicity reduction from a technology advancement perspective. In recent years, we are seeing more retrospective and prospective clinical trials looking into clinical outcomes from the use of advanced on‐board imaging (i.e., PET‐guidance and MRI‐guidance) and/or online adaptation 89–92 . Early results demonstrate modest toxicity reduction for various cancer indications with the advantage of margin reduction and soft tissue matching using MRI‐guidance, while slow dose rate and inferior plan quality remain as main limitations for commercial MRI‐guided units 93 .…”

“…In recent years, we are seeing more retrospective and prospective clinical trials looking into clinical outcomes from the use of advanced on-board imaging (i.e., PET-guidance and MRI-guidance) and/or online adaptation. [89][90][91][92] Early results demonstrate modest toxicity reduction for various cancer indications with the advantage of margin reduction and soft tissue matching using MRI-guidance, while slow dose rate and inferior plan quality remain as main limitations for commercial MRI-guided units. 93 The ability to perform online adaptation might be beneficial for certain disease sites, i.e.…”

MRI-Linac: the beginning of a new era of personalized medicine in radiotherapy

“…Dans le cas de tumeurs soumises aux mouvements respiratoires, cela permettra de vérifier si elles restent dans le champ de traitement, voire même de délivrer la dose uniquement à certains moments du cycle respiratoire ou de modifier en temps réel la position des champs de traitements afin de suivre la cible pendant tout le cycle respiratoire. Ce sont des techniques de gating ou de tracking respiratoire 9 . Pour les tumeurs de l'abdomen supérieur et les poumons, la différence est parfois importante.…”