Dosimetric Analysis of Unflattened (FFFB) and Flattened (FB) Photon Beam Energy for Gastric Cancers Using IMRT and VMAT-a Comparative Study

Purpose To evaluate the feasibility of flattening filter free beam (FFFB) for the treatment of gastric tumors and to review their benefits over 6MV flatten beam (6MV_FFB). Methods Fifteen patients with histologically proven gastric carcinoma were selected. CT scans with slice thickness of 0.3cm were acquired and planning target volume (PTV) and organ at risk (OAR) were delineated. Plans were made retrospectively for each patient for the prescription dose of 45 Gy/25 fractions to the PTV. Four isocentric plans were compared in the present study on Varian TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, CA, USA). Results PTV D98% was 44.410.12, 44.38 +/- 0.13, 44.59 +/- 0.14, and 44.49 +/- 0.19 Gy for IMRT 6MV_FFB, IMRT 6MV_FFFB, VMAT 6MV_FFB, and VMAT 6MV_FFFB respectively. 6MV_FFFB beam minimizes the mean heart dose D-mean (P = 0.001). VMAT dominates over IMRT when it came to kidney doses V-12Gy (P = 0.02), V-23Gy (P = 0.015), V-28Gy (P = 0.011), and D-max (P < 0.01). VMAT has significantly reduced the doses to kidneys. It was analyzed that 6MV_FFFB significantly reduces the dose to normal tissues (P = 0.006 and P = 0.018). VMAT significantly reduces the TMU, which is required to deliver the similar dose by IMRT (P < 0.01). Conclusions Unflattened beam spares the organs at risk significantly to avoid the chances of secondary malignancies and reduces the intra-fraction motion during treatment due to provision of higher dose rate. Hence, we conclude that 6MV unflattened beam can be used to treat gastric carcinoma.