BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Comparison of tangential-intensity modulated radiotherapy (t-IMRT) and volumetric modulated arc therapy (VMAT) for different sizes of left b reast cancer DTSTART;VALUE=DATE-TIME:20260518T123300Z DTEND;VALUE=DATE-TIME:20260518T124100Z DTSTAMP;VALUE=DATE-TIME:20260624T105828Z UID:indico-contribution-3815@indico.tlabs.ac.za DESCRIPTION:Speakers: Abuobaida Ahmed (North-West University)\nBackground: Radiotherapy is an essential part of the management of left-sided breast cancer\, and this requires an optimal balance in target volume coverage an d organs at risk\, such as the ipsilateral lung and the heart. Advanced te chniques such as tangential-intensity modulated radiotherapy (t-IMRT) and volumetric modulated arc therapy (VMAT) are commonly used. However\, the d osimetric performance of t-IMRT and VMAT for varying breast sizes has been poorly characterized. \nAim: To compare the effectiveness of tangential-I MRT and VMAT for hypo-fractionated left-sided breast cancers across small\ , medium\, and large breast sizes.\nMaterials & Methods: A total of 30 CT datasets from female patients with left-sided breast cancer\, acquired bet ween 2020 and 2025\, were analyzed. Patients were divided into groups base d on breast volume\, with a mean volume of 781.00 cc. For each patient\, t wo treatment plans were designed using the Monaco treatment planning syste m\, which uses the Monte Carlo method. A dose of 26 Gy in 5 fractions was prescribed according to the FAST-Forward hypo-fractionated protocol. Evalu ation of the dosimetric parameters included the Planning Target Volume (PT V) coverage indices D2%\, D5%\, D95%\, Homogeneity Index (HI)\, Conformity Index (CI)\, and doses to the heart (V7 and V1.5 Gy)\, as well as the ips ilateral lung volume receiving V8 Gy. A two-way ANOVA was performed\, with a significance (p < 0.05).\nResults: VMAT showed superior target coverage \, conformity\, and dose homogeneity compared to t-IMRT across all breast sizes (p < 0.05). PTV D95% coverage with the VMAT plans was 99.8%\, 98.3%\ , and 97.0% for small\, medium\, and large breasts\, respectively\, wherea s the t-IMRT plans failed to achieve the required coverage of ≥95% and r esulted in 89.2-90.0% coverage across all the breast sizes. Also\, the hom ogeneity and conformity indices were improved with the VMAT plan. Both pla ns satisfied the PTV hotspot constraints of D2% < 107% and D5% < 105%. Alt hough the t-IMRT plans resulted in lower hotspot doses for small and mediu m breasts\, the VMAT plans resulted in slightly better hotspot dose contro l for large breasts. However\, the differences were not clinically signifi cant\, as they were within 1%. However\, the t-IMRT plans resulted in supe rior OAR sparing\, with lower ipsilateral lung V8 Gy and lower high-dose c ardiac exposure (Heart V1.5 Gy: 0.9 - 1.1 Gy)\, compared to the VMAT plan s\, which resulted in higher high-dose cardiac exposure (2.9 - 3.3 Gy)\, e xceeding the tolerance limit\, though the VMAT plans resulted in lower low -dose cardiac exposure (Heart V7 Gy).\nConclusion: VMAT provided superior target coverage\, conformity\, and homogeneity across all breasts compared to t-IMRT\, achieving the required PTV D95% ≥ 95% in all cases. Both te chniques were able to meet the PTV hotspot requirements\, with slightly im proved control for larger breasts with VMAT\, while this may not have a cl inically significant impact. However\, t-IMRT showed superior sparing of O ARs\, particularly the ipsilateral lung and high-dose cardiac areas. In co ntrast\, VMAT showed increased dose to high-dose cardiac areas and decreas ed dose to low-dose cardiac areas.\nKeywords: VMAT\, Tangential-IMRT\, Lef t-sided Breast radiotherapy\, Breast sizes\, UK FSAT-Forward protocol.\n\n https://indico.tlabs.ac.za/event/139/contributions/3815/ LOCATION:NRF-iThemba LABS\, Old Faure Road\, Cape Town Auditorium URL:https://indico.tlabs.ac.za/event/139/contributions/3815/ END:VEVENT END:VCALENDAR