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. A 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 five 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 significant change between baseline planning and daily-adaptive sessions was assessed using the Wilcoxon signed-rank test, assuming a p value < 0.05 as significant. Average baseline PTV, bowel, bladder, and single intestinal loop volumes were respectively 8.9cc (range 0.7-41.2cc), 1176cc (119-3654cc), 95cc (39.7-202.9cc), 18.3cc (9.1-37.7cc). No significant 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 35.6Gy (34.6-36.1Gy). We recorded a slightly positive trend in favor of daily-adaptive strategy vs baseline planning for improved target coverage, although not reaching statistical significance (p = 0.11 and p = 0.18 for PTV-V35Gy and PTV-Dmean). Concerning OARs, a significant difference was observed in favor of daily-adapted treatments in terms of single intestinal loop Dmax [23.05Gy (13.2-26.9Gy) at baseline vs 20.5Gy (12.1-24Gy); p value = 0.0377] and Dmean [14.4Gy (6.5-18Gy) at baseline vs 13.0Gy (6.7-17.6Gy); p value = 0.0003]. Specifically for bladder, the average Dmax was 18.6Gy (0.4-34.3Gy) at baseline vs 18.3Gy (0.7-34.3Gy) for a p value = 0.28; the average Dmean was 7.0Gy (0.2-16.6Gy) at baseline vs 6.98Gy (0.2-16.4Gy) for a p value = 0.66. Concerning the bowel, no differences in terms of Dmean [4.78Gy (1.3-10.9Gy) vs 5.6Gy (1.4-10.5Gy); p value = 0.23] were observed between after daily-adapted sessions. A statistically significant difference was observed for bowel Dmax [26.4Gy (7.7-34Gy) vs 25.8Gy (7.8-33.1Gy); p value = 0.0086]. Daily-adaptive MR-guided SBRT reported a significantly improved single intestinal loop sparing for lymph-nodal oligometastases. Also, bowel Dmax was significantly reduced with daily-adaptive strategy. A minor advantage was also reported in terms of PTV coverage, although not statistically significant.
Highlights
The role of stereotactic body radiotherapy (SBRT) for the treatment of oligometastases is gaining a growing attractiveness in the oncological community. [1]The use of SBRT represents a non-invasive ablative local treatment for both oligorecurrent or oligoprogressive disease in several anatomical sites, and its use is favorably reported in combination with novel systemic treatments such as immunotherapy. [2, 3]SBRT allows clinicians to deliver high doses to small volumes in few sessions with a rapid dose fall-off outside the target, minimizing the involvement of the nearby healthy structures
We report preliminary dosimetric data concerning the use of 1.5-T MR-guided daily-adaptive radiotherapy for abdomino-pelvic lymph-nodal oligometastases
Daily-adaptive MR-guided SBRT reported a significantly improved single intestinal loop sparing for lymphnodal oligometastases
Summary
The role of stereotactic body radiotherapy (SBRT) for the treatment of oligometastases is gaining a growing attractiveness in the oncological community. [1]The use of SBRT represents a non-invasive ablative local treatment for both oligorecurrent or oligoprogressive disease in several anatomical sites, and its use is favorably reported in combination with novel systemic treatments such as immunotherapy. [2, 3]SBRT allows clinicians to deliver high doses to small volumes in few sessions with a rapid dose fall-off outside the target, minimizing the involvement of the nearby healthy structures. Especially in the abdominal-pelvic region, target identification may be suboptimal with conventional cone beam CTimaging due to the low soft tissue contrast In this scenario, the recent introduction of MR-Linacs represents a potential paradigm shift for the implementation of lymph-nodes SBRT. Based on a superior anatomy visualization, MR-Linacs are supposed to refine target volumes and organs at risk (OARs) identification, with a improved inter- and intra-fraction precision. This is a crucial issue especially in the case of targets very close to healthy structures, which are more influenced by daily anatomical variations, such as bowel loops. The MRI-based daily position verification minimizes the risk of target missing and the use of MR-guided online adaptive workflows allows a safe delivery of the treatment, which is calculated on real-time anatomy conditions. [9,10,11,12]
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