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 0.3 cm 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 44.41 ± 0.12, 44.38 ± 0.13, 44.59 ± 0.14, and 44.49 ± 0.19 Gy for IMRT 6MV&#95;FFB, IMRT 6MV&#95;FFFB, VMAT 6MV&#95;FFB, and VMAT 6MV&#95;FFFB respectively. 6MV&#95;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&#95;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.