Comparative Evaluation of a 6MV Flattened Beam and a Flattening Filter Free Beam for Carcinoma of Cervix – IMRT Planning Study

Abstract

Purpose: Intensity modulated radiotherapy (IMRT) plan quality, beam on time and integral dose were compared using<br />6MV FB (Flattened Beam) and FFFB (Flattening filter free beam) for carcinoma of cervix. Materials and Methods:<br />Ten patients with stage II–IIIB cervix cancer (Ca.Cx) were retrospectively identified from the department database.<br />Target volume (TV) and organ at risk (OAR) were delineated as per Radiation Therapy Oncology Group (RTOG) cancer<br />guidelines. Dose prescribed to planning target volume (PTV) was 50.4Gy in 28 fractions. Two plans (6MV FB IMRT<br />and 6MV FFFB IMRT) were generated to achieve 95% of prescription dose to PTV and sparing OAR as per normal<br />tissue guidelines. Numbers of beams and their orientations were the same for all plans. The homogeneity index (HI),<br />conformity index (CI), treatment monitor unit (MU), beam on time (BOT) and non-tumor integral dose (NTID) were<br />chosen for comparison. Results: FFFB generated plans were clinically acceptable. There was a statistically significant<br />difference among the FB IMRT and FFFB IMRT plans with respect to CI, HI, D50%, D2% in PTV coverage, bladder<br />V50Gy, MU, mean NTID and non-tumor low dose volume. Conclusions: 6MV flattened and flattening filter free photon<br />beams produce comparable plans by IMRT . FFF beams allow time efficient treatment delivery and may help reduce<br />the risk of secondary malignances in carcinoma cervix cases.