Objectives: To determine interobserver variability in axillary nodal contouring in breast cancer (BC) radiotherapy (RT) by comparing the clinical target volume of participating single centres (SC-CTV) with a gold-standard CTV (GS-CTV). Methods: The GS-CTV of three patients (P1, P2, P3) with increasing complexity was created in DICOM format from the median contour of axillary CTVs drawn by BC experts, validated using the simultaneous truth and performance-level estimation and peer-reviewed. GS-CTVs were compared with the correspondent SC-CTVs drawn by radiation oncologists, using validated metrics and a total score (TS) integrating all of them. Results: Eighteen RT centres participated in the study. Comparative analyses revealed that, on average, the SC-CTVs were smaller than GS-CTV for P1 and P2 (by −29.25% and −27.83%, respectively) and larger for P3 (by +12.53%). The mean Jaccard index was greater for P1 and P2 compared to P3, but the overlap extent value was around 0.50 or less. Regarding nodal levels, L4 showed the highest concordance with the GS. In the intra-patient comparison, L2 and L3 achieved lower TS than L4. Nodal levels showed discrepancy with GS, which was not statistically significant for P1, and negligible for P2, while P3 had the worst agreement. DICE similarity coefficient did not exceed the minimum threshold for agreement of 0.70 in all the measurements. Conclusions: Substantial differences were observed between SC- and GS-CTV, especially for P3 with altered arm setup. L2 and L3 were the most critical levels. The study highlighted these key points to address. Advances in knowledge: The present study compares, by means of validated geometric indexes, manual segmentations of axillary lymph nodes in breast cancer from different observers and different institutions made on radiotherapy planning CT images. Assessing such variability is of paramount importance, as geometric uncertainties might lead to incorrect dosimetry and compromise oncological outcome.

Objectives: The aim of this study is to evaluate feasibility of salvage 4-week hypofractionated whole breast radiotherapy (WBRT) in patients with in-breast recurrence after receiving intraoperative radiotherapy with electrons (IOERT) for primary breast cancer (BC). Methods: BC patients who had repeated quadrantectomy underwent modified WBRT with intensity-modulated radiotherapy using Helical Tomotherapy to underdose the IOERT region. This approach, called POLO (Partially Omitted Lobe), excluded the IOERT volume from receiving the full prescription dose. Results: Nine patients were treated with this approach, receiving 45 Gy in 20 fractions. A simultaneous integrated boost of 2.5 Gy in 20 fractions was delivered in 6/9 patients. Dose constraints and planning objectives were reported. No severe toxicity was reported while local control and overall survival were 100%. Conclusion: The POLO approach is technically feasible and capable to achieve a significant reduction of radiation dose delivered to the previous treated IOERT area. Advances in knowledge: The study demonstrates the technical and dosimetric feasibility of conservative salvage whole breast radiotherapy, while sparing the area already treated with IORT, in patients with in-breast recurrence.

Objectives: this study aimed to evaluate the evolution of planned dose distribution quality in two groups of breast cancer patients treated with hypofractionated intensity-modulated radiotherapy (IMRT) using Helical TomoTherapy^® at our institute 5 years apart. Methods: the analysis included two cohorts of patients who underwent implant-based immediate breast reconstruction (IBR) and received post-mastectomy IMRT to the chest wall and infra/supraclavicular lymph nodes, following a 15-fraction regimen (2.67 Gy per fraction). The first group was treated between 2012 and 2015, while the second received treatment between 2019 and 2020. Dosimetric indices derived from dose–volume histograms used in clinical practice were analyzed to assess dose distribution quality. A quantitative scoring system was applied retrospectively to compare the two groups in terms of target coverage and organ-at-risk (OAR) sparing. Additionally, capsular contracture (CC) incidence was examined in both cohorts. Results: A total of 240 patients were included in the study. The percentage of optimal treatment plans increased from 70.8% in the 2012–2015 cohort to 77.5% in the 2019–2020 cohort, while compromised plans decreased from 10.8% to 7.5%. Furthermore, the incidence of moderate-to-severe CC dropped from 54.8% in the earlier cohort to 43.5% in the later one. Conclusions: Helical Tomotherapy^® has demonstrated the ability to achieve a high rate of optimal treatment plans concerning both PTV coverage and OAR sparing in a challenging population of postmastectomy patients with IBR. The learning curve showed that, after 5 years, the rate of optimal plans was increased, accompanied by a reduction in compromised plans and treatment-related toxicity.