Purpose: Flattening filter free beam is a modern modality used in new radiotherapy machines, especially in SBRT cases to consuming treatment time. The remaining volume at risk (RVR) is known as undefined normal tissue, and it assists in evaluating very late effects like carcinogenesis.The present study is aimed to compare between the effect of flattening and unflattening 6MV beams on (RVR) in the lung cases that treated by conventional dose for volumetric modulated arc therapy (VMAT) and Intensity modulated radiation therapy IMRT.
Methods: Eleven lung cancer cases with prescribed dose 60Gy in 30 fractions were selected retrospectively for this study. Four plans were generated for each case (VMAT FF, VMAT FFF, IMRT FF and IMRT FFF plan). Plans are developed using Eclipse treatment planning system and Truebeam linear accelerator HD MLC. Two arcs for VMAT plan and five coplanar fields are selected according to lesion volume and location for IMRT plans. RVR mean dose, V15Gy, V10Gy and V5Gy are introduced in this study as RVR evaluation parameters.
Results: The study revealed that the variance percentage comparison between FFF and FF for the RVR evaluation parameters are (2.95, 1.1, 1.95 and 2.6), (1.95, 0.9, 1.6 and 2.15) for VMAT and IMRT respectively. However, for the comparison between VMAT and IMRT in RVR evaluation parameters study shows that variance percentage is (1.74, 2.06, -7.8 and -4.8), (2.86, 2.28, -7.2 and -4.4) for FF and FFF respectively.
Conclusion: The study present that using FFF is clinically benefit than FF for all RVR evaluation parameters in addition to consuming time. On the other hand VMAT is preferred in RVR mean dose and V15Gy while oppositely in the V10Gy and 5Gy.