In the Context of Treating Breast Cancer, Which Dosimetric Advantages do Volumetric Intensity- Modulated Radiotherapy by Arc Therapy and 3D Conformal Radiotherapy Offer?

Volumetric intensity-modulated arc therapy (VMAT) is gaining popularity in external beam radiotherapy to optimize tumor coverage while sparing healthy tissue. The objective of this study is to compare the dosimetry between the VMAT technique and the conventional 3D tangential technique in the treatment of breast cancer.  Methods and Materials : The study is based on a dosimetric analysis of 35 breast cancer patients treated at the Radiotherapy Department of the National Institute of Oncology in Rabat, Morocco, between March 2024 and September 2024. Target volumes (PTV) and organs at risk (heart, lungs, and spinal cord) were delineated on CT images according to ESTRO recommendations. 3D tangential treatment plans and VMAT plans were created for each patient, allowing for a comparative assessment of dosimetric parameters, including PTV coverage (V95), maximum dose (Dmax), as well as mean doses and irradiated volumes of critical organs.  Results: The results show significant differences in dose distribution between the two techniques:  Target volume coverage (PTV): The 95% coverage of the target volume (V95) is almost identical for both techniques.  Maximum dose in the target volume (PTV Dmax): The maximum dose delivered to the PTV is lower in VMAT (48.98 Gy) than in 3D (50.87 Gy), suggesting that VMAT can reduce hotspots within the target volume. This reduction in Dmax with VMAT could improve local tolerance and reduce side effects in the target volume. 3. 2% PTV: The dose received by 2% of the PTV is also more controlled in VMAT (46.50 Gy) compared to 50.97 Gy in 3D, indicating that VMAT manages to limit the high dose in critical regions of the PTV, which is favorable for dose homogeneity.  Mean dose to the heart and coverage of V17: The mean dose received by the heart is significantly higher in VMAT (3.94 Gy) compared to the 3D technique (2.32 Gy). Similarly, the cardiac volume receiving a dose greater than 17 Gy (V17) is slightly higher with VMAT (2.95%) compared to 3D (2.84%). These results indicate that 3D radiotherapy is more advantageous in terms of cardiac protection, a crucial parameter for patients with cardiovascular risks. 5. Maximum spinal cord dose: The maximum dose achieved in the spinal cord is higher with VMAT (8.58 Gy) than with 3D (4.03 Gy), suggesting that the 3D tangential technique may offer better spinal cord preservation.  Lung dose (V26 and V17): The results show that VMAT reduces pulmonary exposure: the lung volume receiving 26 Gy (V26) is reduced to 13.7% with VMAT, compared to 16.5% with 3D. However, the lung volume receiving 17 Gy (V17) is slightly higher with VMAT (24.6%) compared to 3D (21.2%). This reduction in V26 in VMAT could potentially reduce the risk of long-term pulmonary toxicity, although the increase in V17 requires careful assessment according to each patient's specific risks.  Conclusion : This analysis shows that the VMAT technique offers notable advantages, such as reduced maximum and high doses to the target volume, as well as reduced irradiated lung volume at a high dose. However, the VMAT technique increases the average dose to the heart and the maximum dose to the spinal cord compared to 3D radiotherapy. The choice of technique must therefore be guided by dosimetric priorities, particularly the protection of organs at risk, based on each patient's characteristics and risk factors.