European Journal of Cardiovascular Medicine

Breast cancer is the most frequently diagnosed malignancy among women worldwide and represents a major public health challenge. According to the World Health Organization and International Agency for Research on Cancer estimates, breast cancer accounts for a substantial proportion of cancer incidence and mortality among women globally. Radiotherapy plays a crucial role in the multidisciplinary management of breast cancer, particularly following breast-conserving surgery and in selected cases after mastectomy. It significantly reduces the risk of local recurrence and improves overall survival (1,2).

Despite its therapeutic benefits, radiotherapy for breast cancer inevitably exposes surrounding normal tissues such as the heart, lungs, and contralateral breast to radiation. These organs at risk (OARs) are susceptible to radiation-induced toxicities, including radiation pneumonitis, cardiac morbidity, and secondary malignancies (3). Therefore, the optimization of radiotherapy techniques is essential to maximize tumor control while minimizing radiation exposure to normal tissues.

Over the past few decades, radiotherapy techniques have evolved considerably. Conventional three-dimensional conformal radiotherapy (3D-CRT) has been widely used for breast irradiation due to its simplicity and effectiveness. However, advanced techniques such as intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) have been developed to improve dose conformity and homogeneity while reducing the radiation dose to adjacent organs at risk (4,5). These modern techniques allow better shaping of radiation beams and more precise dose distribution, potentially decreasing treatment-related complications.

Several dosimetric studies have compared different radiotherapy techniques in breast cancer treatment, demonstrating variations in target coverage and dose distribution to organs at risk. While IMRT and VMAT may improve dose homogeneity and conformity, concerns remain regarding increased low-dose radiation exposure to surrounding tissues (6). Hence, careful evaluation of these techniques is required to determine the most suitable approach that balances adequate target coverage with minimal OAR exposure.

In developing countries, including India, resource availability, treatment planning expertise, and patient load may influence the choice of radiotherapy technique. Comparative dosimetric analysis can provide valuable evidence for selecting the optimal treatment modality in routine clinical practice (7).

Justification of the Study

Although advanced radiotherapy techniques such as IMRT and VMAT are increasingly used in breast cancer treatment, their dosimetric advantages over conventional techniques remain a subject of ongoing research. A systematic comparison of different radiotherapy techniques is necessary to evaluate their impact on dose distribution to organs at risk, particularly the heart and lungs. Such studies are essential for optimizing treatment planning, reducing radiation-induced toxicities, and improving the overall quality of cancer care.

Aim

To compare the dosimetric parameters of three different radiotherapy techniques in breast cancer patients and evaluate their impact on organs at risk.

Objectives

1. To evaluate target volume coverage achieved by three different radiotherapy techniques.
2. To compare dose distribution parameters such as conformity index and homogeneity index among the techniques.
3. To assess and compare radiation doses delivered to organs at risk including the heart, ipsilateral lung, contralateral lung, and contralateral breast.
4. To identify the radiotherapy technique that provides optimal target coverage with minimal radiation exposure to surrounding normal tissues.

Study Design and Study Setting This was a prospective dosimetric comparative study conducted in the Konaseema Institute of Medical Sciences, Amalapuram, in the Department of Radiotherapy. The study was carried out over a period of 18 months. The aim was to compare the dosimetric parameters of three different radiotherapy techniques used in the treatment of breast cancer and to evaluate their impact on organs at risk (OARs). Study Population Patients diagnosed with histologically confirmed carcinoma breast who were planned for adjuvant radiotherapy after breast conserving surgery or modified radical mastectomy were included in the study. Sample Size A total of 30 patients with carcinoma breast who met the inclusion criteria were included in the study. For each patient, three different radiotherapy treatment plans were generated for comparison. Inclusion Criteria 1. Patients with histologically confirmed breast cancer. 2. Patients who underwent breast conserving surgery or modified radical mastectomy. 3. Patients planned for adjuvant external beam radiotherapy. 4. Age ≥18 years. 5. Patients who provided informed consent. Exclusion Criteria 1. Patients with metastatic disease. 2. Patients who had received previous thoracic radiotherapy. 3. Pregnant patients. 4. Patients with incomplete imaging or treatment planning data. Simulation and Imaging All patients were immobilized in the supine position using a breast board with both arms raised above the head. A planning computed tomography (CT) scan was performed from the level of the mandible to the upper abdomen with a slice thickness of 3–5 mm. The CT images were transferred to the treatment planning system (TPS) for contouring and planning. Target Volume Delineation Target volumes and organs at risk were contoured according to the guidelines of the European Society for Radiotherapy and Oncology. • Clinical Target Volume (CTV): Included the whole breast or chest wall depending on the type of surgery. • Planning Target Volume (PTV): Generated by adding an appropriate margin (usually 5–7 mm) around the CTV to account for setup uncertainties. Organs at Risk (OARs) The following organs at risk were contoured: • Heart • Ipsilateral lung • Contralateral lung • Contralateral breast • Spinal cord (when applicable) Treatment Planning Techniques For each patient, three different radiotherapy plans were generated using the same CT dataset: 1. Three-Dimensional Conformal Radiotherapy (3D-CRT) 2. Intensity Modulated Radiotherapy (IMRT) 3. Volumetric Modulated Arc Therapy (VMAT) All treatment plans were designed to deliver a prescribed dose of 50 Gy in 25 fractions over 5 weeks to the planning target volume. Dosimetric Parameters Evaluated For Target Volume (PTV): • D95 (dose covering 95% of PTV) • Dmax (maximum dose) • Homogeneity Index (HI) • Conformity Index (CI) For Organs at Risk: • Mean dose to heart • Heart V25 • Mean dose to ipsilateral lung • Ipsilateral lung V20 • Mean dose to contralateral lung • Mean dose to contralateral breast Dose–volume histograms (DVHs) were generated for each plan to evaluate dose distribution. Plan Evaluation All three radiotherapy plans were compared based on target coverage, dose homogeneity, conformity index, and dose to organs at risk. The optimal plan was identified based on superior PTV coverage with minimal exposure to surrounding normal tissues. Statistical Analysis All collected data were entered into Microsoft Excel and analyzed using statistical software (SPSS version 22). Continuous variables were expressed as mean ± standard deviation. Differences in dosimetric parameters between the three radiotherapy techniques were analyzed using analysis of variance (ANOVA). A p-value <0.05 was considered statistically significant.

A total of 30 patients with carcinoma breast were included in the dosimetric analysis. For each patient, three radiotherapy plans were generated using Three-Dimensional Conformal Radiotherapy (3D-CRT), Intensity Modulated Radiotherapy (IMRT), and Volumetric Modulated Arc Therapy (VMAT). The plans were compared based on planning target volume (PTV) coverage, homogeneity index, conformity index, and dose received by organs at risk (OARs).

All three techniques achieved acceptable target coverage; however, IMRT and VMAT demonstrated improved dose conformity and homogeneity compared with 3D-CRT. Advanced techniques also showed better sparing of critical organs such as the heart and ipsilateral lung.

Table 1: Comparison of PTV Dosimetric Parameters Among Radiotherapy Techniques

IMRT and VMAT demonstrated better conformity and improved homogeneity compared to 3D-CRT. VMAT showed the highest conformity index, indicating better target coverage with reduced dose spillage.

Table 2: Comparison of Dose to Organs at Risk (OARs)

VMAT and IMRT significantly reduced radiation exposure to the heart and ipsilateral lung compared with 3D-CRT. However, slightly higher low-dose exposure to the contralateral lung and breast was observed with IMRT and VMAT.

Radiotherapy is an integral component in the management of breast cancer, particularly after breast-conserving surgery and in selected post-mastectomy patients. The primary goal of radiotherapy planning is to achieve optimal planning target volume (PTV) coverage while minimizing radiation exposure to surrounding organs at risk such as the heart, ipsilateral lung, and contralateral breast. Advances in radiation delivery techniques such as Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) have significantly improved dose conformity and homogeneity compared with conventional Three-Dimensional Conformal Radiotherapy (3D-CRT).

In the present study, a comparative dosimetric evaluation of 3D-CRT, IMRT, and VMAT was performed in breast cancer patients. The results demonstrated that IMRT and VMAT achieved better target coverage and improved homogeneity index compared to 3D-CRT. These findings are consistent with previous studies that have reported improved dose distribution with advanced radiotherapy techniques (8,9). Improved dose homogeneity is important in breast irradiation as it reduces the occurrence of hot spots within the breast tissue, thereby minimizing radiation-induced skin toxicity and improving cosmetic outcomes.

Our study showed that VMAT provided the highest conformity index among the three techniques, indicating superior ability to shape the radiation dose around the target volume while sparing adjacent normal tissues. Similar results were reported by Nicolini et al., who demonstrated that VMAT achieved superior conformity and treatment efficiency compared to conventional techniques (10).

One of the major concerns in breast radiotherapy is radiation exposure to the heart, particularly in left-sided breast cancers. Several epidemiological studies have shown that even small increases in cardiac radiation dose may increase the long-term risk of ischemic heart disease. In the present study, both IMRT and VMAT significantly reduced the mean heart dose compared to 3D-CRT. This observation is supported by the work of Taylor et al., who highlighted the importance of modern radiotherapy techniques in reducing cardiac toxicity in breast cancer patients (11).

The ipsilateral lung is another critical organ at risk during breast irradiation. High radiation doses to the lung may lead to complications such as radiation pneumonitis and pulmonary fibrosis. In our study, the mean dose and V20 of the ipsilateral lung were lower with IMRT and VMAT compared with 3D-CRT, indicating improved lung sparing. These findings are in agreement with the study by Haciislamoglu et al., which demonstrated reduced lung dose with IMRT techniques (12).

However, the present study also showed that IMRT and VMAT resulted in slightly higher low-dose radiation exposure to contralateral lung and contralateral breast compared with 3D-CRT. This phenomenon is attributed to the use of multiple beam angles and rotational delivery in advanced radiotherapy techniques. Similar findings have been reported by other investigators who observed increased low-dose spread with IMRT and VMAT (13). Although the clinical significance of this low-dose exposure remains uncertain, it may theoretically increase the risk of secondary malignancies, particularly in younger patients.

Overall, the results of the present study suggest that VMAT provides the most favorable dosimetric profile, achieving superior target coverage and better sparing of critical organs such as the heart and ipsilateral lung. However, careful patient selection and treatment planning are necessary to balance the benefits of improved conformity with the potential risk of increased low-dose radiation exposure.

The present dosimetric study demonstrates that advanced radiotherapy techniques such as IMRT and VMAT provide improved target coverage and better dose homogeneity compared with conventional 3D-CRT in breast cancer radiotherapy. Among the three techniques evaluated, VMAT showed the best conformity index and the lowest radiation dose to the heart and ipsilateral lung. However, IMRT and VMAT were associated with slightly increased low-dose exposure to contralateral organs compared with 3D-CRT. Therefore, careful treatment planning is essential to optimize the balance between adequate tumor coverage and protection of normal tissues. In conclusion, VMAT appears to be a promising radiotherapy technique for breast cancer treatment, offering superior dosimetric advantages and improved organ sparing. Further clinical studies with long-term follow-up are recommended to evaluate the impact of these dosimetric improvements on treatment outcomes and late radiation-induced toxicities.

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