Dosimetric comparative study of Volumetric Modulated Arc Therapy (VMAT), Intensity Modulated Radiotherapy (IMRT), and ThreeDimensional Conformal Radiation therapy (3DCRT) for post-mastectomy radiotherapy (PMRT) in Left breast cancer patients

Purpose: To evaluate the difference in planning target volume (PTV) coverage and dose to the organs at risk (OAR) by using three different planning methods for the same patient-Volumetric Modulated Arc Therapy (VMAT), Intensity Modulated Radiotherapy (IMRT), and Three-Dimensional Conformal Radiation Therapy (3DCRT) plans after radical surgery for a three-week hypo-fractionated radiotherapy regimen (40 Gy in 15 fractions) for adjuvant left breast radiotherapy. Materials and Methods: A total of 25 patients who received radiation therapy (Volumetric Modulated Arc Radiotherapy-VMAT) for left-sided breast cancer after radical surgery at the State Cancer Institute, Indira Gandhi Institute of Medical Sciences, Patna, India, between September 2021 and November 2022, were included. The prescribed dose was 40 Gy in 15 fractions, administered at a rate of 2.67 Gy per fraction. IMRT and 3D-CRT treatment plans were replanned for each patient on the Eclipse treatment planning system (Version 16.0.1, Varian Medical Systems, Palo Alto, CA). Planning target volume (PTV) parameters, D mean, Homogeneity, and Conformity Indices (HI and CI) were interpreted. The mean doses to organs at risk (OAR), V5, V10, V20, and V25, were generated from the dose-volume histogram (DVH) and compared. Results: PTV 95% coverage in VMAT, IMRT, and 3D-CRT were 93.73, p=0.003; 95.18, p=0.006, and 77.98, respectively. VMAT and IMRT led to improved CI (0.98, in VMAT [p< 0.001], 0.95 in IMRT [p < 0.001], and 0.84 in 3D-CRT, respectively which was statistically significant on pairwise analysis. The homogeneity index (HI) was significantly different for VMAT and IMRT than 3D-CRT (1.07, 1.11 vs 1.21). Maximum PTV doses (Dmax) were 107.87, 105.8, and 106.89 in VMAT, IMRT, and 3D-CRT, respectively. OAR: V25 of the heart was 3.25 (1.25,4.9), 2.75 (1.4,4.25), and 11.75 (3.5,16.3) in IMRT, VMAT, and 3D-CRT, respectively. The mean dose to the heart was lower for the VMAT and IMRT plans as compared to 3D-CRT (16.8 (14.3,18.5), 18.45 (14.3,21.3) vs 21.4 (12.15,26.75). For the ipsilateral lung, V25 was 14.55 (7.8,18.9), 14.45 (6.25,19.5), and 26.35 (8.4,31.05) in IMRT, VMAT, and 3D-CRT, respectively. Conclusion: VMAT and IMRT demonstrated better prescription dose coverage, conformity, and dose uniformity for the target, while also sparing high-dose volumes to OAR, compared to 3D-CRT.