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

Document Type: Research Articles

Authors

1 Department of Radiotherapy, Rajiv Gandhi Cancer Institute and Research Centre, Rohini, New Delhi, India.

2 Department of Physics, VIT University, Vellore, Tamil Nadu, India.

Abstract

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

Keywords

Main Subjects