S291
Clinical - Breast
ESTRO 2026
Purpose/Objective: Postmastectomy radiotherapy (PMRT) in implant- reconstructed breasts presents unique technical challenges due to altered chest wall geometry and implant interfaces, which contribute to dose inhomogeneity and increased exposure of adjacent organs. This study analyzed dosimetric outcomes, planning complexities, and laterality-specific organ-at- risk (OAR) doses, emphasizing the role of Deep Inspiration Breath Hold (DIBH) in achieving adaptive and personalized treatment precision. Material/Methods: Forty-five patients treated between 2019 and 2024 at theDepartment of Radiation Oncology, National Oncology Center, Royal Hospital, Sultanate of Oman following mastectomy with immediate implant reconstruction were retrospectively reviewed.The median age was 40 years (range, 26–54 years).Left- sided patients underwent DIBH during simulation and delivery to optimize cardiac sparing. Histopathology was predominantly invasive ductal carcinoma (95.5%), mainly grade 2 (64%).Chemotherapy regimens were neoadjuvant (68%), adjuvant (26%), or none (4%).Dose regimens included 40Gy in 15 fractions or 45 Gy in 20 fractions, with a uniform 5mm bolus. Treatment techniques comprised 3DCRT-Field-in-Field (84%) and IMRT (11%).Dosimetric indices (PTV V95%, V105%) and mean OAR doses (heart, ipsilateral lung V20, esophagus, contralateral breast, and spinal cord Dmax) were analyzed and correlated with PTV/CTV ratio, laterality, and technique. Results: All plans achieved excellent target coverage (mean PTV V95% = 99.2%).Hotspots (PTV V105% > 30%) were observed in 44.4%, mainly along implant–tissue junctions.IMRT achieved superior dose homogeneity (p = 0.0012), but due to the smaller IMRT cohort and its inherently broader low-dose spread, marginally higher mean doses to adjacent OARs were noted compared with 3DCRT-FIF.Left-sided DIBH substantially reduced the mean heart dose (281.5 cGy) compared with published free-breathing benchmarks (>500 cGy), confirming its efficacy in cardiac sparing.Larger PTV volumes showed a mild correlation with increased heart dose (r = 0.29, p < 0.05).OAR constraint compliance was excellent: heart ≤ 5 Gy (93.3%), lung V20 ≤ 30% (97.8%), and spinal cord ≤ 45 Gy (100%). Conclusion: PMRT in implant-reconstructed breasts requires meticulous balancing of target uniformity and OAR protection. IMRT enhances dose homogeneity,while 3DCRT-FIF with DIBH achieves robust and reproducible cardiac sparing for left-sided cases. The integration of laterality, target volume, and technique-specific parameters supports adaptive PMRT planning, enabling individualized, precision-based radiotherapy
(95% CI, 83.8–97.7%), respectively. In multivariable models, OS was independently associated with receipt of systemic therapy (HR 0.20; p < 0.001) and lesion location (spine vs non-spine: HR 3.35; p < 0.001), see Table 1. Toxicity was low; pathologic fractures occurred in 2.7% of lesions.
Figure 1: Progression-free survival depending on dose concept for SBRT of bone metastasis - Comparison of PFS for spine versus non-spine lesions for the entire cohort and B) depending on the level of mean BED10 ( α / β =10Gy) in gross tumor volume (GTV).
Table 1: Uni- and multivariable Cox proportional hazard regression analyses for overall survival, progression-free survival, and freedom from local
recurrence. Conclusion:
In this multicenter retrospective analysis, SBRT for BoM from breast cancer was well tolerated and provided excellent local control. Prospective studies are warranted to confirm these findings and to define standardized SBRT concepts within multidisciplinary management of oligometastatic breast cancer. Keywords: SBRT Bone Metastates Retrospective
Digital Poster 3037
Postmastectomy Radiotherapy in Implant- Reconstructed Breasts: Towards Adaptive and Personalized Planning with Deep-Inspiration Breath-Hold Precision SATHIYA KRISHNAMOORTHY, THURAYA NASSER SAID AL HAJRI, RUPA DAS, BALAJI SUBRAMANIAN SITARAMAN, BINUKUMAR JOHNSON PICHI, KHALSA ALI AL SHUKAILI, FATMA AL HASHMI, LAILA AL NABHANI RADIATION ONCOLOGY, NATIONAL ONCOLOGY CENTER,ROYAL HOSPITAL, MUSCAT, Oman
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