Filter Free Volumetric Modulated Arc Research Articles

Single Fraction (30 Gy) Stereotactic Body Radiation Treatment of Peripheral Lung Lesions using Flattening Filter Free Volumetric Modulated Arc Therapy (FFF-VMAT): Early Clinical Outcomes

To present early clinical outcomes utilizing stereotactic body radiation therapy (SBRT) to mid lung or peripheral lung lesions, delivering a dose of 30 Gy in a single fraction with flattening filter free volumetric modulated arc therapy (FFF-VMAT). Twenty-four lesions were identified from twenty-three patients with either early stage non-small cell lung cancer (lesions n = 17) or isolated, limited, thoracic progression from a known metastatic cancer diagnosis (lesions n = 2 head and neck, n = 2 rectal, n = 3 lung). Patients were prescribed a single dose of 30 Gy, delivered using FFF VMAT with noncoplanar 6MV beams and cone beam CT image guidance. Four-dimensional (4D) CT based treatment plans were generated using an advanced Acuros-based dose calculation engine for heterogeneity corrections. Plan quality and delivery efficiency were reported. Outcomes evaluated include local control, radiation-induced pneumonitis, and rib toxicity. Median follow-up time was 9 months (range: 1 to 38 months). Mean planning target volume (PTV) was 17.6 ± 13.9 cc. All plans met RTOG requirements for target coverage and dose to organs at risk (OAR). Average values of the conformity index, gradient index, maximum dose at 2 cm away from the PTV, normal lung V20Gy, and normal lung V10Gy were 1.06 ± 0.1, 5.4 ± 1.4, 49.5 ± 4.5%, 0.8 ± 0.5% and 3.2 ± 1.9 %, respectively. All OAR doses were well below RTOG compliance criteria. Average beam on time was 6.6 ± 1.3 min. Four patients were lost to follow up. One patient has initial post-treatment imaging pending. During the follow up period, all patients demonstrated local control of the treated lesion. Six patients developed new distant metastases, 4 of whom had prior stage 4 disease. All patients developed asymptomatic radiographic changes surrounding the treated lesion, though there were no reports of grade 2+ pneumonitis or chest wall pain and no radiographic evidence of rib fracture. Stereotactic delivery of 30 Gy in a single fraction using cone-beam CT image guidance with a non-coplanar FFF-VMAT plan is a fast, safe, and effective treatment modality for managing small mid-lung or peripherally located lung lesions. Local control is excellent and no symptomatic adverse events were noted over the follow up period. This is a promising strategy for rapidly delivering a meaningful oncologic dose to patients unable to tolerate a multi-fraction regimen due to discomfort, medical comorbidities, or socio-economic barriers hindering treatment compliance. Longer clinical follow up in a larger patient cohort is ongoing to further validate these outcomes.

Standardized flattening filter free volumetric modulated arc therapy plans based on anteroposterior width for total body irradiation.

In this work, the feasibility of using flattening filter free (FFF) beams in volumetric modulated arc therapy (VMAT) total body irradiation (TBI) treatment planning to decrease protracted beam‐on times for these treatments was investigated. In addition, a methodology was developed to generate standardized VMAT TBI treatment plans based on patient physical dimensions to eliminate plan optimization time. A planning study cohort of 47 TBI patients previously treated with optimized VMAT ARC 6 MV beams was retrospectively examined. These patients were sorted into six categories depending on height and anteroposterior (AP) width at the umbilicus. Using Varian Eclipse, clinical 40 cm × 10 cm open field arcs were substituted with 6 MV FFF. Mid‐plane lateral dose profiles in conjunction with relative arc output factors (RAOF) yielded how far a given multileaf collimator (MLC) leaf must move in order to achieve a mid‐plane 100% isodose for a specific control point. Linear interpolation gave the dynamic MLC aperture for the entire arc for each patient AP width category, which was subsequently applied through Python scripting. All FFF VMAT TBI plans were then evaluated by two radiation oncologists and deemed clinically acceptable. The FFF and clinical VMAT TBI plans had similar Body–5 mm D98% distributions, but overall the FFF plans had statistically significantly increased or broader Body–5 mm D2% and mean lung dose distributions. These differences are not considered clinically significant. Median beam‐on times for the FFF and clinical VMAT TBI plans were 11.07 and 18.06 min, respectively, and planning time for the FFF VMAT TBI plans was reduced by 34.1 min. In conclusion, use of FFF beams in VMAT TBI treatment planning resulted in dose homogeneity similar to our current VMAT TBI technique. Clinical dosimetric criteria were achieved for a majority of patients while planning and calculated beam‐on times were reduced, offering the possibility of improved patient experience.

Interaction between CIEDs and modern radiotherapy techniques: Flattening filter free-VMAT, dose-rate effects, scatter radiation, and neutron-generating energies

Background and purposeProviding evidence for radiotherapy (RT)-induced effects on cardiac implantable electric devices (CIEDs) with focus on flattening filter free-volumetric modulated arc therapy (FFF-VMAT) at 6 and 10 MV as well as 3D-conformal radiotherapy (3D-CRT) at 18 MV. Materials and methods68 CIEDs (64 implantable cardioverter-defibrillators (ICDs) and 4 cardiac pacemakers (PMs)) were located on the left chest position on a slab phantom and irradiated under telemetrical surveillance either directly, or distant to 3D-CRT or FFF-VMAT, dose-rate 2500 cGy/min, and target dose of 150 Gy. Devices were placed within, close by (2.5 cm and 5 cm), and distant (35 cm) to the radiation field. Scatter radiation (SR) and photon neutrons (PN) were recorded. CIEDs were investigated in following groups: 1a) 18 MV 3D-CRT − 4 ICDs/4 PMs out of radiation field, 1b) 18 MV open field − 4 ICDs/4 PMs within radiation field, 2) 6 MV FFF-VMAT, 15 ICDs in 35 cm distance to VMAT, 3) 10 MV-FFF VMAT, 15 ICDs in 35 cm distance to VMAT, 4) 6 MV FFF-VMAT, 15 ICDs in 2.5 cm distance to VMAT, 5) 10 MV FFF-VMAT, 15 ICDs in 2.5 cm distance to VMAT. ResultsNo incidents occurred at 6 MV FFF. 10 MV FFF-VMAT and 18 MV 3D-CRT resulted in data loss, reset, and erroneous sensing with inhibition of pacing (leading to inadequate defibrillation) in 8/34 ICDs and 2/4 PMs which were not located within radiation. Direct radiation triggered instantaneous defibrillation in 3/4 ICDs. Conclusions6 MV FFF-VMAT is safe even at high dose-rates of 2500 cGy/min, regardless whether CIEDs are located close (2.5 cm) or distant (35 cm) to the radiation beam. CIEDs should never be placed within radiation and energy should always be limited to 6 MV. At 6 MV, VMAT at high dose-rates can be used to treat tumors, which are located close to CIEDs.

High-quality Linac-based Stereotactic Body Radiation Therapy with Flattening Filter Free Beams and Volumetric Modulated Arc Therapy for Low–Intermediate Risk Prostate Cancer. A Mono-institutional Experience with 90 Patients

AimsThe aim of this phase II study was to evaluate the efficacy and toxicity of stereotactic body radiotherapy in patients with low or intermediate risk prostate cancer. Materials and methodsBiopsy-confirmed prostate cancer patients were enrolled, provided that they had the following characteristics: initial prostate-specific antigen (PSA) ≤ 20 ng/ml, Gleason Score < 7, International Prostate Symptom Score < 7. The treatment schedule was 35 Gy in five fractions, delivered with volumetric modulated arcs with flattening filter free beams. Toxicity was recorded according to CTCAE criteria v4.0. Biochemical failure was calculated according to the Phoenix definition. The Expanded Prostate Cancer Index Composite questionnaire was used to record health-related quality of life. ResultsBetween December 2011 and March 2015, 90 patients were enrolled (53 low risk, 37 intermediate risk). The median age was 71 years (range 48–82). In total, 58 (64.5%) of the patients had Gleason Score=6, the remaining had Gleason Score=7.The median initial PSA was 6.9 ng/ml (range 2.7–17.0). Acute toxicity was mild, with 32.2 patients presenting grade 1 urinary toxicity and 32.2% of patients presenting grade 2 urinary toxicity, mainly represented by urgency, dysuria and stranguria. Rectal grade 1 toxicity was found in 15.5% of patients, whereas grade 2 toxicity was recorded in 6.6% of patients. Regarding late toxicity, grade 1 proctitis was recorded in 11.1% of patients and grade 1 urinary in 38.8%; only two events of grade 2 urinary toxicity were observed (transient urethral stenosis, resolved by a 24 h catheterisation). At a median follow-up of 27 months (6–62 months) only two intermediate risk patients experienced a biochemical failure. Health-related quality of life revealed a slight worsening in all the domains during treatment, with a return to baseline 3 months after treatment. ConclusionsStereotactic body radiotherapy delivered using linac-based flattening filter free volumetric modulated arc radiotherapy in low and intermediate risk prostate cancer patients is associated with mild toxicity profiles and good patient-reported quality of life.

SU‐F‐T‐87: Comparison of Advanced Radiotherapy Techniques for Post‐ Mastectomy Breast Cancer Patients

Purpose:To determine if bolus electron conformal therapy (Bolus‐ECT) combined with intensity modulated x‐ray therapy (IMXT) and flattening filter free volumetric modulated arc therapy (FFF‐VMAT (6x and 10x)) can maintain equal or better dose coverage than standard volumetric modulated arc therapy (Std‐VMAT) while reducing doses to organs at risk (OARs).Methods:Bolus‐ECT with IMXT, FFF‐VMAT, and Std‐VMAT treatment plans were produced for ten post‐mastectomy radiotherapy (PMRT) patients previously treated at our clinic. The treatment plans were created on commercially available treatment planning system (TPS) and all completed treatment plans were reviewed and approved by a radiation oncologist. The plans were evaluated based on planning target volume (PTV) coverage, tumor control probability (TCP), dose homogeneity index (DHI), conformity index (CI), and dose to organs at risk (OAR).Results:All techniques produced clinically acceptable PMRT plans. Overall, Bolus‐ECT with IMXT exhibited higher maximum dose compared to all VMAT techniques. Bolus‐ECT with IMXT and FFF‐VMAT10x had slightly improved TCP over FFF‐VMAT6x and Std‐VMAT. However, all VMAT techniques showed improved CI and DHI over Bolus‐ECT with IMXT. All techniques showed very similar mean lung dose. Bolus‐ECT with IMXT exhibited a reduced mean heart dose over Std‐VMAT. Both FFF‐VMAT techniques had higher mean heart dose compared to Std‐VMAT. In addition, Bolus‐ECT with IMXT was able to reduce mean dose to the contralateral breast compared to Std‐VMAT and both FFF‐VMAT techniques had comparable but slightly reduced dose compared to Std‐VMAT.Conclusion:This work has shown that Bolus‐ECT with IMXT produces clinically acceptable plans while reducing OAR doses. Both FFF‐VMAT techniques are comparable to Std‐VMAT with slight improvements. Even though all VMAT techniques produce more homogenous and conformal dose distributions, Bolus‐ECT with IMXT is a viable option for treating post‐mastectomy patients possibly leading to reduced risks of normal tissue complications.

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

PurposeTo 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. Methods and materialsOverall, 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. ResultsDose 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. ConclusionsFFF VMAT for lung SBRT provides equivalent dosimetric results to the target and organs at risk as FF VMAT while significantly reducing treatment time.

Frameless high dose rate stereotactic lung radiotherapy: Intrafraction tumor position and delivery time

Intrafraction change in tumor position (Δ) was evaluated for stereotactic lung radiotherapy delivered with flattening filter free volumetric modulated arc therapy. In 140 fractions from 32 patients mean Δ (±SD) was −0.7±1.4mm (vertical), −0.7±1.3mm (longitudinal) and +0.2±1.2mm (lateral) with mean vector 2.1±1.2mm. Mean delivery time was 4.4±3.4min (mean beam-on 1.9±0.4min).