Document Type : Research Articles
Authors
1
Department of Radiation Oncology, All India Institute of Medical Sciences (AIIMS), Bibinagar, Hyderabad, Telangana, India.
2
Department of Radiation Oncology, Vydehi Institute of Medical Sciences & Research Centre, Bengaluru, India.
3
Department of Radiation Oncology, Kamineni Academy of Medical Sciences and Research Centre, Hyderabad, Telangana, India.
Abstract
Background: Advances in radiotherapy planning have led to better dose delivery and protection of organs at risk (OAR) in malignant brain tumors. Though three-dimensional conformal radiotherapy (3D-CRT) is still commonly used, Volumetric modulated arc therapy (VMAT) delivers highly precise doses with dynamic adjustments. This study compares dosimetric differences prospectively between 3D-CRT and VMAT in primary malignant brain tumors. Methods: Fifty (50) patients with confirmed malignant primary brain tumors who received postoperative or definitive radiotherapy were assessed. Each patient had CT simulations, target and OAR contouring, and two distinct plans: 3D-CRT and VMAT using 6 MV photons. Treatment was delivered as per VMAT planning. The dosimetric endpoints included PTV coverage (D2%, D50%, D98%), conformity index (CI), homogeneity index (HI), and OAR doses (optic nerves, optic chiasm, brainstem, cochlea, retina, lens, pituitary, and spinal cord). Results: VMAT delivered significantly lower doses to some OARs compared to 3D-CRT. The Dmax to the right and left optic nerves was significantly lower with VMAT (24.77 Gy vs. 32.34 Gy, p=0.002; 27.35 Gy vs. 32.86 Gy, p=0.032). For the optic chiasm, both the Dmax and Dmean doses were significantly lower with VMAT (31.28 Gy vs. 36.32 Gy, p=0.036; 24.27 Gy vs. 30.77 Gy, p=0.019). The Dmean for the right cochlea was greatly reduced (7.27 Gy vs. 15.97 Gy, p=0.007). Differences in doses to the brainstem, pituitary, retina, and lens were minimal and not statistically significant. The PTV metrics (D2%, D50%, D98%) showed no significant differences between the techniques. The conformity index was acceptable for both plans (VMAT 0.903; 3D-CRT 1.089). Homogeneity indices were similar. Conclusion: VMAT offers better sparing of several critical OARs, such as the optic pathways and cochleae, while maintaining similar PTV coverage compared to 3D-CRT. Both techniques meet acceptable dose limits, but VMAT may be preferred for tumors near sensitive structures.
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