A comparison between 3DCRT, IMRT and VMAT for breast radiotherapy

Stoltz, Abel

A comparison between 3DCRT, IMRT and VMAT for breast radiotherapy

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Division of Medical Physics

Faculty

Faculty of Health Sciences

Abstract

Introduction Breast cancer is the most commonly diagnosed cancer amongst women in low to middle-income countries (LMIC) in Africa. However, LMIC are resource-limited. Optimised planning and treatment strategies are therefore needed. Breast cancer radiotherapy requires an optimal balance between adequate target volume coverage and minimization of dose to surrounding organs at risk (OARs). In large-breasted patients, these challenges are compounded by anatomy and setup variation. This study investigated the dosimetric performance and planning efficiency of four modern techniques: 3D conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT, 2field and 4-field), and volumetric-modulated arc therapy (VMAT and VMAT butterfly, VMATBF), for both left- and right-sided disease. Materials and methods A cohort of 15 patients with right-sided and 15 with left-sided breast cancer, each with separation >25 cm, were replanned on a Varian Eclipse v15.6 treatment planning system (TPS) and Acuros algorithm on a Varian Halcyon 2.0 linear accelerator, using the four techniques. Prescriptions were normalized to a mean PTV dose of 40.05 Gy in 15 fractions. For each plan, indices of conformity (CI), homogeneity (HI), dose coverage (D95, D98, V95), and near maximum dose (D2) were evaluated for the planning target volume (PTV and AutoPTV). OAR endpoints included heart dose and lung exposure (V1.5–V35 Gy). Planning efficiency was assessed by recording planning times during training, first on right-sided and then on left-sided cases, to track competency development. One-way ANOVA and Tukey post-hoc tests were performed to assess statistical significance. Results For right-sided disease, IMRT with four fields (IMRT4F) consistently provided the most robust PTV coverage and homogeneity while maintaining acceptable OAR doses. VMAT techniques offered comparable target coverage and improved conformity but did not significantly reduce OAR exposure. Planning times were moderate for IMRT4F and significantly longer for VMAT/VMATBF. For left-sided disease, sparing of the heart and ipsilateral lung was critical. In this cohort, IMRT4F achieved superior low-dose and comparable high-dose OAR sparing compared with VMAT/VMATBF, while maintaining clinically acceptable target coverage. VMAT techniques produced slightly higher conformity and reduced hotspots, but at the cost of increased low-dose exposure and longer planning times. Across both sides, 3DCRT provided the poorest conformity, often failing to meet modern ICRU coverage standards. Training analysis revealed clear learning effects: planning times decreased as competency improved, yet VMAT remained the slower approach compared to IMRT4F. Conclusion Technique selection should be side-specific. For right-sided patients, IMRT4F is recommended due to a superior balance of coverage, homogeneity, and planning efficiency. For left-sided patients, IMRT4F is preferred for OAR sparing, particularly for the heart and lung, while VMAT or VMAT-BF may be considered only when maximal conformity is required, and additional planning time is acceptable. Overall, 3DCRT remains suboptimal for both sides in this patient group. These results highlight the importance of tailoring technique choice to laterality and clinical priorities, and demonstrate that with training, IMRT4F offers the most consistent and clinically advantageous approach for large-breasted patients, given the limitations of LMIC and planning time.

Keywords

breast cancer

radiotherapy

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