Mitigation on bowel loops daily variations by 1.5-T MR-guided daily-adaptive SBRT for abdomino-pelvic lymph-nodal oligometastases

Abstract

We report preliminary dosimetric data concerning the use of 1.5-T MR-guided daily-adaptive radiotherapy for abdomino-pelvic lymph-nodal oligometastases. We aimed to assess the impact of this technology on mitigating daily variations for both target coverage and organs-at-risk (OARs) sparing. MethodsA total of 150 sessions for 30 oligometastases in 23 patients were analyzed. All patients were treated with MR-guided stereotactic body radiotherapy (SBRT) for a total dose of 35Gy in 5 fractions. For each fraction, a quantitative analysis was performed for PTV volume, V35Gy and Dmean. Similarly, for OARs we assessed daily variations of volume, Dmean, Dmax. Any potential statistically signi cant change between baseline planning and daily-adaptive sessions was assessed using the Wilcoxon signed-rank test, assuming a p-value< 0.05 as signi cant. ResultsAverage baseline PTV, bowel, bladder and single intestinal loop volumes were respectively 8.9cc (range, 0.7-41.2cc), 1176cc (119-3654 cc), 95cc (39.7-202.9 cc), 18.3cc (9.1-37.7 cc). No signi cant volume variations were detected for PTV (p=0.21) bowel (p=0.36), bladder (p=0.47), except for single intestinal loops, which resulted smaller (p=0.026).Average baseline V35Gy and Dmean for PTV were respectively 85.6% (72-98.8%) and 35.6 Gy (34.6-36.1 Gy). We recorded a slightly positive trend in favor of daily-adaptive strategy vs baseline planning for improved target coverage, although not reaching statistical signi cance. (p=0.11 and p=0.18 for PTV-V35Gy and PTV-Dmean).Concerning OARs, a signi cant difference was observed in favor of daily-adapted treatments in terms of single intestinal loop Dmax [23.05 Gy (13.2-26.9 Gy) at baseline vs 20.5 Gy (12.1-24 Gy); p-value=0.0377] and Dmean [14.4 Gy (6.5-18 Gy) at baseline vs 13.0 Gy (6.7-17.6 Gy); p-value=0.0003].Speci cally for bladder, the average Dmax was 18.6 Gy (0.4-34.3 Gy) at baseline vs 18.3 Gy (0.7-34.3 Gy) for a p-value=0.28; the average Dmean was 7.0 Gy (0.2-16.6 Gy) at baseline vs 6.98 Gy (0.2-16.4 Gy) for a p-value=0.66. Concerning the bowel, no differences in terms of Gy) vs 5.6 Gy (1.4-10.5 Gy); p-value=0.23] were observed between after daily-adapted sessions. A statistically signi cant difference was observed for bowel Dmax [26.4 Gy (7.7-34 Gy) vs 25.8 Gy (7.8-33.1 Gy); p-value=0.0086]. ConclusionsDaily-adaptive MR-guided SBRT reported a signi cantly improved single intestinal loop sparing for lymphnodal oligometastases. Also bowel Dmax was signi cantly reduced with daily-adaptive strategy. A minor

1.5T MR-Guided Daily-Adapted SBRT on Lymphnode Oligometastases from Prostate Cancer

“…However, especially in the abdominal-pelvic area, target identification may not be always optimal with cbCT IGRT methods due to lower resolution than conventional CT and low soft tissue contrast. (14,15).…”

“…This latter is a crucial issue especially in the case of targets close to healthy structures, which are more influenced by daily anatomical variations, such as bowel loops. (14,18,22). The aim of our study was to evaluate the efficacy and toxicity of a daily-adaptive MR-guided SBRT on 1.5 T MR-linac in patients affected by lymphnode oligometastases from PCa.…”

“…The widespread use of metabolic imaging in the very early phase of the PCa metastatic disease have permitted the early identification of metastatic lesions, also infracentimetrical (13). Despite image-guided radiotherapy significantly increased treatment accuracy, there might be some dosimetrical and imaging limitations when lesions are small or close organs at risk or vessels (14,15). Moreover, standard radiotherapy on conventional linac don't allow clinicians to modify treatment plans in case of lesions displacement of when OARs (i.e.…”

“…The recent introduction of MR-linac might overcome this problem by allowing for daily treatment adaptation and exploiting the high tissue contrast provided by MR images (16). Recent evidence showed dosimetrical improvement to bowel loops in lymphnode metastases treated with SBRT on a 1.5T MR-linac (14). However, to date clinical data are limited by small retrospective series and short follow-up (17,18), therefore little is known regarding the clinical impact of MR-guided radiotherapy (MRgRT).…”

Vas deferens metastasis from prostate adenocarcinoma treated with daily-adaptive MR-guided SBRT on 1.5T MR-linac

“…Baseline treatment plans were generated using static field intensity-modulated radiotherapy (IMRT) delivered with 16 beams. Constraints for planning approval were the following: (1) for the rectum: V18Gy ≤ 35%, V28Gy ≤ 10%, V32Gy ≤ 5%, Dmax ≤ 35Gy; (2) for the bladder and bowel loops: Dmax ≤ 35Gy [ 6 , 7 ]. The average treatment duration was 23 minutes.…”