Dosimetric Comparison of Three-dimensional Conformal Radiation Therapy (3D-CRT) vs Volumetric Modulated Arc Therapy...

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.

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).

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.

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.