Impact of Daily Plan Adaptation on Organ-At-Risk Normal Tissue Complication Probability for Adrenal Lesions undergoing Stereotactic Ablative Radiation Therapy: NTCP advantages of adaptive MR-guided adrenal SABR

Hanbo Chen, Famke L Schneiders, Anna M E Bruynzeel, Frank J Lagerwaard, John R van Sornsen de Koste, Paul Cobussen, Omar Bohoudi, Berend J Slotman, Alexander V Louie, Suresh Senan, John R. van Sörnsen de Koste

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Introduction: Stereotactic ablative radiotherapy (SABR) can achieve good local control for metastatic adrenal lesions. Magnetic resonance (MR)-guidance with daily on-table plan adaptation can augment the delivery of SABR with greater dose certainty. The goal of this study was to quantify the potential clinical benefit MR-guided daily-adaptive adrenal SABR using the normal tissue complication probability (NTCP) framework. Methods: Patients treated with adrenal MR-guided SABR at a single institution were retrospectively reviewed. Lyman-Kutcher-Burman NTCP models were used to calculate the NTCP of upper abdominal organs-at-risk (OARs) at simulation and both before and after daily on-table plan adaptation. Differences in OAR NTCPs were assessed using signed-rank tests. Potential predictors of the benefits of adaptation were assessed by linear regression. Results: Fifty-two adrenal MR-guided SABR courses were analyzed. The baseline simulation plan underestimated the absolute stomach NTCP by 10.0% on average (95% confidence interval: 4.7–15.2%, p < 0.001). Daily on-table adaptation lowered absolute NTCP by 8.7% (4.2–13.2%, p < 0.001). The most significant predictor of the benefits of adaptation was lesion laterality (p = 0.018), with left-sided lesions benefitting more (13.3% [6.3–20.4%], p < 0.001) than right-sided lesions (2.1% [−1.6–5.7%], p = 0.25). Sensitivity analyses did not change the statistical significance of the findings. Conclusion: NTCP analysis revealed that patients with left adrenal tumors were more likely to benefit from MR-guided daily on-table adaptive SABR using current dose/fractionation regimens due to reductions in predicted gastric toxicity. Right-sided adrenal lesions may be considered for dose escalation due to low predicted NTCP.

Original languageEnglish
Pages (from-to)14-20
Number of pages7
JournalRadiotherapy and oncology
Early online date31 Jul 2021
Publication statusPublished - 1 Oct 2021


  • Adaptive radiotherapy
  • Adrenal
  • Magnetic resonance
  • Normal tissue complication probability
  • Stereotactic ablative radiotherapy
  • Stereotactic body radiation therapy

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