Impact of flattening filter-free beams on remaining volume at risk in lung cancer treatment.

Modern radiotherapy machines offer a new modality, like flattening filter-free beam (FFF), which is used especially in stereotactic body radiation therapy (SBRT) to reduce treatment time. The remaining volume at risk (RVR) is known as undefined normal tissue, and assists in evaluating late effects such as carcinogenesis. This study aimed to compare the effects of flattening and un-flattened beams on RVR in lung cancer treated by conventional doses using volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT). Twenty-three lung cancer patients with a prescribed dose of 60 Gy delivered in 30 fractions were selected retrospectively. Four treatment plans were generated for each case (VMAT FF, VMAT FFF, IMRT FF and IMRT FFF). Mean doses to RVR and volumes that received low doses (V15Gy, V10Gy and V5Gy) were introduced as RVR evaluation parameters. Variance percentage comparison between flattening filter (FF) and FFF for the RVR evaluation parameters gave 2.38, 1.10, 1.80 and 2.22 for VMAT, and 1.73, 1.18, 1.62 and 1.81 for IMRT. In contrast, VMAT and IMRT RVR evaluation parameters resulted in variance percentage differences of 10.29, 5.02, - 8.84 and - 4.82 for FF, and 11.18, 4.96, - 8.59 and - 4.48for FFF. It is concluded that in terms of RVR evaluation parameters, FFF is clinically beneficial compared to FF for RVR, due to the decrease in mean RVR dose and low-dose irradiated RVR volume. Furthermore, VMAT is preferred in the mean RVR dose and V15Gy, while IMRT is better in V10Gy and V5Gy for RVR.

Alfishawy MM ，Kany AI ，Elshahat KM 《-》

Stereotactic body radiation therapy for prostate cancer: a dosimetric comparison of IMRT and VMAT using flattening filter and flattening filter-free beams.

This retrospective study was performed to evaluate plan quality and treatment delivery parameters of stereotactic body radiation therapy (SBRT) for prostate cancer. The study utilized different isocentric modulated techniques: intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) using 6 MV flattening filter (FF) and 10 MV flattening filter-free beams (FFF). Fifteen retrospective prostate cancer patients were selected for this study. Sixty plans were created with an SBRT-prescribed dose of 36.25 Gy delivered in five fractions. Planning target volume (PTV) coverage, plan quality indices, doses delivered to organs at risk (OARs), and treatment delivery parameters were compared for all plans. It turned out that VMAT plans, particularly those using the FFF beam, provided superior target conformality and a steeper dose gradient as compared to IMRT plans. Additionally, VMAT plans showed better OARs sparing compared to IMRT plans. However, IMRT plans delivered a lower maximum dose to the target than VMAT plans. Importantly, the VMAT plans resulted in reduced treatment delivery parameters, including beam on time (BOT), monitor unit (MU), and modulation factor (MF), compared to IMRT plans. Furthermore, a statistically significant difference was observed in BOT and mean body dose between FF and FFF beams, with FFF beams showing superior performance. Considering all results, VMAT using 10 MV (FFF) is suggested for treating prostate cancer patients with SBRT. This offers the fastest delivery in addition to maintaining the highest plan quality.

El-Sayed SM ，El-Gebaly RH ，Fathy MM ，Abdelaziz DM ... -  《-》

The Effect of Flattening Filter Free on Three-dimensional Conformal Radiation Therapy (3D-CRT), Intensity-Modulated Radiation Therapy (IMRT), and Volumetric Modulated Arc Therapy (VMAT) Plans for Metastatic Brain Tumors from Non-small Cell Lung Cancer.

Shi LW ，Lai YQ ，Lin Q ，Ha HM ，Fu LR ... -  《-》

FFF-VMAT for SBRT of lung lesions: Improves dose coverage at tumor-lung interface compared to flattened beams.

To quantify the differences in dosimetry as a function of ipsilateral lung density and treatment delivery parameters for stereotactic, single dose of volumetric modulated arc therapy (VMAT) lung stereotactic body radiation therapy (SBRT) delivered with 6X flattening filter free (6X-FFF) beams compared to traditional flattened 6X (6X-FF) beams. Thirteen consecutive early stage I-II non-small-cell-lung cancer (NSCLC) patients were treated with highly conformal noncoplanar VMAT SBRT plans (3-6 partial arcs) using 6X-FFF beam and advanced Acuros-based dose calculations to a prescription dose of 30 Gy in one fraction to the tumor margin. These clinical cases included relatively smaller tumor (island tumors) sizes (2.0-4.2 cm diameters) and varying average ipsilateral lung densities between 0.14 g/cc and 0.34 g/cc. Treatment plans were reoptimized with 6X-FF beams for identical beam/arc geometries and planning objectives. For same target coverage, the organs-at-risk (OAR) dose metrics as a function of ipsilateral lung density were compared between 6X-FFF and 6X-FF plans. Moreover, monitor units (MU), beam modulation factor (MF) and beam-on time (BOT) were evaluated. Both plans met the RTOG-0915 protocol compliance. The ipsilateral lung density and the tumor location heavily influenced the treatment plans with 6X-FFF and 6X-FF beams, showing differences up to 12% for the gradient indices. For similar target coverage, 6X-FFF beams showed better target conformity, lower intermediate dose-spillage, and lower dose to the OAR. Additionally, BOT was reduced by a factor of 2.3 with 6X-FFF beams compared to 6X-FF beams. While prescribing dose to the tumor periphery, 6X-FFF VMAT plans for stereotactic single-dose lung SBRT provided similar target coverage with better dose conformity, superior intermediate dose-spillage (improved dose coverage at tumor interface), and improved OAR sparing compared to traditional 6X-FF beams and significantly reduced treatment time. The ipsilateral lung density and tumor location considerably affected dose distributions requiring special attention for clinical SBRT plan optimization on a per-patient basis. Clinical follow up of these patients for tumor local-control rate and treatment-related toxicities is in progress.

Pokhrel D ，Halfman M ，Sanford L 《Journal of Applied Clinical Medical Physics》

Single-fraction flattening filter-free volumetric modulated arc therapy for lung cancer: Dosimetric results and comparison with flattened beams technique.

To report on single-fraction stereotactic body radiotherapy (RT) (SBRT) with flattening filter (FF)-free (FFF) volumetric modulated arc therapy (VMAT) for lung cancer and to compare dosimetric results with VMAT with FF. Overall, 25 patients were treated with 6-MV FFF VMAT (Varian TrueBeam STx LINAC) to a prescribed dose of 24Gy in a single fraction. Treatment plans were recreated using FF VMAT. Dose-volume indices, monitor units (MU), and treatment times were compared between FFF and FF VMAT techniques. Dose constraints to PTV, spinal cord, and lungs were reached in FFF and FF plans. In FFF plans, average conformity index was 1.13 (95% CI: 1.07 to1.38). Maximum doses to spinal cord, heart, esophagus, and trachea were 2.9Gy (95% CI: 0.4 to 6.7Gy), 0.8Gy (95% CI: 0 to 3.6Gy), 3.3Gy (95% CI: 0.02 to 13.9Gy), and 1.5Gy (95% CI: 0 to 4.9Gy), respectively. Average V7Gy, V7.4Gy, and mean dose to the healthy lung were 126.5cc (95% CI: 41.3 to 248.9cc), 107.3cc (95% CI: 18.7 to 232.8cc), and 1.1Gy (95% CI: 0.3 to 2.2Gy), respectively. No statistically significant differences were found in dosimetric results and MU between FF and FFF treatments. Treatment time was reduced by an average factor of 2.31 (95% CI: 2.15 to 2.43) from FF treatments to FFF, and the difference was statistically significant. FFF VMAT for lung SBRT provides equivalent dosimetric results to the target and organs at risk as FF VMAT while significantly reducing treatment time.

Barbiero S ，Rink A ，Matteucci F ，Fedele D ，Paiar F ，Pasqualetti F ，Avanzo M ... -  《-》