S2009 10Gy = 5.05 ⋅ TV 0.803 ) is used to prospectively estimate the expected intermediate-dose spillage (V10Gy) based on the TV alone, prior to definitive treatment planning.2. Risk Conversion and Baseline Risk: The estimated V10Gy is converted intoclinically relevant metrics (e.g., V14Gy), utilizing established dose-volumerelationships [1] to calculate the baseline normal tissue complicationprobability (NTCP) for symptomatic RN.3. Systemic Therapy Adjustment: The influence of concurrent systemic therapy isquantified by applying literature-derived Hazard Ratios (HRs) (e.g., for ICIs or T-DM1) to the baseline probability [2,3].4. Cumulative Risk: For multiple lesions, the overall risk of at least one RN event iscalculated assuming independent events (P total = 1 – Π (1 − P i )). Results: The developed nomogram provides an individualized, quantitative risk prognosis forRN based solely on pre- planning inputs. The visualization clearly illustrates the substantialimpact of systemic agents on RN risk. For example, the model demonstrates howincorporating specific HRs for ICIs can double or triple the baseline NTCP for medium-sizedlesions compared to SRS alone. Furthermore, the tool quantifies the rapid escalation ofcumulative risk when treating multiple metastases. This visualization provides an evidence- based, standardized foundation that not only supports patient consultation but also cruciallyfacilitates interdisciplinary tumor board decisions regarding the risk/benefit trade-off of asystemic therapy pause. Conclusion: This novel tool bridges the communication gap between vague risk statementsand personalized prediction. It translates complex predicted dosimetric and systemic riskfactors into an understandable visual format. This promotes transparency, personalizes theinformed consent process, and strengthens shared decision-making in both patient care andinterdisciplinary strategy planning. References: [1] Milano MT et al., Single- and Multifraction Stereotactic Radiosurgery Dose/Volume Tolerances of the Brain. Int J Radiat Oncol Biol Phys. 2021 May 1;110(1):68-86. doi: 10.1016/j.ijrobp.2020.08.013. Epub 2020 Sep 11. PMID: 32921513; PMCID: PMC9387178.[2] Martin AM et al, Immunotherapy and Symptomatic Radiation Necrosis in Patients With Brain Metastases Treated With Stereotactic Radiation. JAMA Oncol. 2018 Aug 1;4(8):1123-1124. doi: 10.1001/jamaoncol.2017.3993. [3] Koenig JL,Adverse Radiation Effect and Disease Control in Patients Undergoing Stereotactic Radiosurgery and Immune Checkpoint Inhibitor Therapy for Brain Metastases. World Neurosurg. 2019 Jun;126:e1399-e1411. doi: 10.1016/j.wneu.2019.03.110. Keywords: SRS, Radionecrosis, Risk Communication
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Digital Poster 4703
Optimizing heart and left anterior descending artery dose in left breast radiotherapy: is lung V5 limit truly necessary? Taha Erdogan, Feyza Savas Akbulut, Ozveri Tuglu Olcer, Ecem Yigit Department of Radiation Oncology, Afyonkarahisar Health Science University, Afyonkarahisar, Turkey Purpose/Objective: While V20 and mean lung dose (MLD) are recognized as the most important parameters associated with radiation-induced lung injury, the clinical impact of low-dose volumes such as V5 remains controversial. This study aimed to compare treatment plans for left- sided breast cancer generated with an ipsilateral lung V5 ≤ 75% guidance versus plans without V5 limitation, in terms of target coverage and organs of interest doses. Material/Methods: Nine patients treated for left-sided breast cancer at our institution between 2024 and 2025 were retrospectively evaluated. All patients received 50 Gy in 25 fractions to the left breast and regional lymphatics (breast/chest wall, supraclavicular fossa, axilla, internal mammary chain). Intensity-modulated radiotherapy (IMRT) plans with V5 ≤ 75% guidance and alternative volumetric modulated arc therapy (VMAT) plans without V5 limitation were generated. Organs of interest included ipsilateral and contralateral lungs, contralateral breast, heart, and left anterior descending artery (LAD). Statistical analyses were performed using IBM SPSS v23.0. Results: Comparison of clinical target volumes and organs of interest is presented in Table 1. Target coverage did not differ significantly between the two planning approaches. In plans without V5 limitation, ipsilateral lung V5 increased significantly (70.7% vs. 86.6%, p = 0.024), whereas MLD (15.78 Gy vs. 14.96 Gy, p = 0.019) and V20 (28.4% vs. 24.7%, p = 0.002) were significantly reduced. LAD Dmean (17.73 Gy vs. 12.24 Gy, p = 0.024) and Dmax (37.59 Gy vs. 28.1 Gy, p = 0.019) also showed statistically significant reductions, while only trends toward decreased heart Dmean, V25, and V30 were observed. Conversely, contralateral breast Dmean (1.19 Gy vs. 3.2 Gy, p = 0.002) and contralateral lung V5 (12.4% vs. 51.6%, p = 0.001) increased significantly.
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