Flattening Filter Free Beams Research Articles

Investigation of low and high dose rate X-ray effects on histopathological changes and prognostic importance of Ki-67 in laryngeal cancer radiotherapy

The aim of this study is to analyze the effect on histopathological changes and Ki-67 expression levels of Flattening Filter (FF) and Flattening Filter Free (FFF) beams to investigate the radiobiological mechanisms underlying laryngeal cancer (LCa) post-radiotherapy (RT) on mice models.Forty adult NOD SCID gamma (NSG) mice models were randomly divided into four groups; the sham, LCa, FF-RT and FFF-RT groups. The head and neck region of mice in FF-RT and FFF-RT groups (LCa plus RT groups) were irradiated with a single dose of 18 Gy at 400 MU/min and 1400 MU/min. The NSG mice received radiotherapy 30 days after tumor transplantation and sacrificed 2 days after radiotherapy for analysis of histopathology parameters and K-67 expression levels.Comparing the LCa, FF-RT and FFF-RT groups with the sham group, statistically significant differences were observed in histopathological parameters depending on tumor tissue and dose rate (p < 0.05). When the histopathological effects of FF-RT beam on LCa tissue were compared with FFF-RT beam, it was observed that statistically significant differences occurred (p < 0.05). Comparing the LCa group with the sham group, it was observed that the Ki-67 level affected significantly depending on the development of cancer (p < 0.01).It was concluded that FF and FFF beams caused significant changes in the histopathological parameters and Ki-67 expression levels. When the effects of FFF beam on Ki-67 levels, cell nucleus and cytoplasmic findings were compared with FF beam, significant radiobiological differences were observed.

Assessment of Treatment Plan Quality between Flattening Filter and Flattening Filter Free Photon Beam for Carcinoma of the Esophagus with IMRT Technique.

As compared to the flattened photon beam, removing the flattening filter (FF) from the head of a gantry decreases the average energy of the photon beam and increases the dose rate, leading to an impact on the quality of treatment plans. This study aimed to compare the quality of intensity-modulated radiation therapy (IMRT) treatment plans for esophageal cancer with and without a flattened filter photon beam. In this analytical study, 12 patients, who had already been treated with a 6X FF photon beam, were treated based on new IMRT methods using a 6X the flattening filter-free (FFF) photon beam. Both 6X FF IMRT and 6X FFF IMRT plans used identical beam parameters and planning objectives. All plans were evaluated with planning indices and doses for organs at risk (OARs). Insignificant dose variation was for HI, CI, D98%, and V95% between FF and FFF photon beam IMRT plans. FF-based IMRT plan delivered a 15.51 % and 11.27% higher mean dose to both lungs and heart than the FFF plan, respectively. The integral dose (ID) for the heart and lungs was 11.21% and 15.51%, respectively, less in the IMRT plan with an FFF photon beam. In contrast to the FF photon beam, a filtered photon beam-oriented IMRT plan provides significant OAR sparing without losing the quality of the treatment plan. High monitor units (MUs), low ID, and Beam on Time (BOT) are major highlights of the IMRT plan with FFF beam.

Quantification of the role of lead foil in flattening filter free beam reference dosimetry

To quantify the potential error in outputs for flattening filter free (FFF) beams associated with use of a lead foil in beam quality determination per the addendum protocol for TG-51, we examined differences in measurements of the beam quality conversion factor kQ when using or not using lead foil. Two FFF beams, a 6 MV FFF and a 10 MV FFF, were calibrated on eight Varian TrueBeams and two Elekta Versa HD linear accelerators (linacs) according to the TG-51 addendum protocol by using Farmer ionization chambers [TN 30013 (PTW) and SNC600c (Sun Nuclear)] with traceable absorbed dose-to-water calibrations. In determining kQ , the percentage depth-dose at 10cm [PDD(10)] was measured with 10×10 cm2 field size at 100cm source-to-surface distance (SSD). PDD(10) values were measured either with a 1 mm lead foil positioned in the path of the beam [%dd(10)Pb ] or with omission of a lead foil [%dd(10)]. The %dd(10)x values were then calculated and the kQ factors determined by using the empirical fit equation in the TG-51 addendum for the PTW 30013 chambers. A similar equation was used to calculate kQ for the SNC600c chamber, with the fitting parameters taken from a very recent Monte Carlo study. The differences in kQ factors were compared for with lead foil vs. without lead foil. Differences in %dd(10)x with lead foil and with omission of lead foil were 0.9±0.2% for the 6 MV FFF beam and 0.6±0.1% for the 10 MV FFF beam. Differences in kQ values with lead foil and with omission of lead foil were -0.1±0.02% for the 6 MV FFF and -0.1±0.01% for the 10 MV FFF beams. With evaluation of the lead foil role in determination of the kQ factor for FFF beams. Our results suggest that the omission of lead foil introduces approximately 0.1% of error for reference dosimetry of FFF beams on both TrueBeam and Versa platforms.

Benchmarking a New Circular Cone-based Radiosurgery System against Clinically Tested Radiosurgery System on the same Novel Digital Linear Accelerator Platform.

To examine the dosimetric characteristics of circular cones, the accuracy of dose modeling and overall treatment delivery of two radiosurgery systems integrated on a linear accelerator (Linac). The dosimetric characteristics of circular cones (4-17.5 mm) from Varian (VC) and BrainLAB (BLC) were measured for 6 MV flattening filter free beam from Edge linac using stereotactic field diode and 0.65 cc ionization chamber following established protocols. The Eclipse and iPlan modeled dose distribution for VCs and BLCs were validated with EBT3-film measurement. End-to-end tests were performed using stereotactic phantom having PTW 60008 diode connected to a Dose-1 electrometer. The depth at dose maximum, TRP2010 and dose at 10cm depth of the same size VC and BLC agree within ± 0.7 mm, ± 0.71% and ± 0.81% respectively. Full width at half maximum (FWHM) of any cone beyond 15 mm depth increases at 1% of nominal cone size per 10 mm depth. The penumbra of 4mm and 17.5mm VC at 15 mm depth was 1.1 mm and 1.50 mm. At 300 mm depth, penumbra increased by around 0.4 mm for 4 mm cone and up to 1 mm for cone size ≥12.5 mm. The VCs penumbra values were within ±1mm of the corresponding BLCs. Scatter factors for VCs varies from 0.609 to 0.841 and were within ± 1.0% of corresponding values of BLCs. Agreement between the Eclipse and iPlan computed dose fluence and the EBT3-film measured dose fluence was >98% (γ: 1%@1 mm), and the absolute dose difference was ≤ 2.2%, except for the 4 mm cone in which it was >96% and ≤4.83%. Target localization using cone-beam computed tomography was accurate within ± 0.8 mm and ± 0.3° in translation and rotation. The end-to-end dose delivery accuracy for both radiosurgery systems was within ± 3.62%. The dosimetric characteristics of Varian and BLC cones of same diameter was comparable. Both Eclipse and iPlan cone planning system modeled dose fluences agree well with the EBT3 film measurement. The end-to-end tests revealed an excellent target localization accuracy of Edge linac with satisfactory and comparable absolute dose agreement between Varian and BLC radiosurgery systems and hence these can be interchanged on edge linac.

Dosimetric Parameters in Hypofractionated Stereotactic Radiotherapy for Brain Metastases: Do Flattening Filter-Free Beams Bring Benefits? A Preliminary Study.

This study aimed to compare the dosimetric results of flattening filter-free (FFF) vs. flattened (FF) treatment plans for fractionated stereotactic radiotherapy (fSRT), with the goal to highlight potential advantages of FFF beams. A group of 18 patients with brain metastases treated with fSRT (30 Gy delivered in 5 fractions) were included. The dosimetric parameters evaluated were: (1) physical dosimetric parameters (number of monitor units (MUs), conformity index (CI), dose gradient index (DGI), beam on time (BOT)); (2) clinical dosimetric parameters pertaining to target volume (PTV) and organs at risk (OARs). Two treatment plans were performed for all patients: one used 6 MV FFF beams and the other used 6 MV flattened beams. A slight increase in MUs was observed for the FFF mode (+23.3 MUs). The CI showed a difference of -2.7% for the FF plans (p = 0.28), correlated with a poorer coverage of the PTV. DGI values reported in terms of PTV are in line with international recommendations and showed a +1.9% difference for FFF plans. An average BOT of 90.3 s was reported for FFF plans, which was 2.3 times shorter than that required for FF plans delivery (p ≤ 0.001). A slight decrease of PTV coverage (-1.26%, p = 0.036) for FF plans can be considered relevant, but no other significant differences were observed between the two optimizations. No statistically significant benefit of using FFF beams to reduce V20 for normal brain could be demonstrated. These dosimetric results encourage the implementation of fSRT with standard flattened beams in centers where FFF linacs are not available.

Linac primary barrier transmission: Flattening filter free and field size dependence.

There is widespread consensus in the literature that flattening filter free (FFF) beams have a lower primary barrier transmission than flattened beams. Measurements presented here, however, show that for energy compensated FFF beams, the barrier transmission can be as much as 70% higher than for flattened beams. The ratio of the FFF barrier transmission to the flattened beam barrier transmission increases with increasing barrier thickness. The use of published FFF TVL data for energy compensated FFF beams could lead to an order of magnitude underestimate of the air kerma rate. There are little data in the literature on the field size dependence of the barrier transmission for flattened beams. Barrier transmission depends on the field size at the barrier, not at isocenter Measurements are presented showing the relative dependence of barrier transmission on the field size, measured at the barrier, for 6MV and 10MV beams. An analytical fitting formula is provided for the field size dependence. For field sizes greater than about 150cm in side length, the field size dependence is minimal. For field sizes less than about 100cm, the transmission declines rapidly as the field size decreases.

Delivery of a VMAT technique with flattening filter (FF) and flattening filter free (FFF) mode for whole breast irradiation with five fractions (FAST-Forward trial).

To investigate the feasibility of volumetric modulated arc therapy (VMAT) delivery for whole breast irradiation with a 5-fraction regimen according to the FAST-Forward trial. Recently, we treated 10 patients with carcinoma of the left breast after breast conserving surgery. The dose prescription to the PTV was 26 Gy in 5 fractions. Treatment plans were produced using a VMAT technique with the Eclipse treatment planning system for 6 MV flattening filter (FF) and FF free (FFF) beams. Dose volume histograms (DVHs) for the PTV and the organs at risk (OARs), the ipsilateral lung and heart, were compared with the dose constraints specified in the FAST-Forward trial (PTV, D95 > 95%, D5 < 105%, D2 < 107% and Dmax < 110%; ipsilateral lung, D15 < 8Gy; Heart, D30 < 1.5Gy and D5 < 7Gy). Furthermore, conformity index (CI), homogeneity index (HI) and dose to the heart, contralateral lung, contralateral breast, and left anterior descending artery (LAD), were also assessed. Mean ± SD D95(%), D5(%), D2(%), and Dmax (%) for PTV were 97.75 ± 1.12, 105.2 ± 0.82, 105.90 ± 0.89, 109.36 ± 1.00 (FF) and 96.46 ± 0.75, 103.97 ± 0.97, 104.70 ± 1.09, 108.58 ± 1.33 (FFF) respectively. The mean ± SD CI was 1.07 ± 0.05 (FF), 1.048 ± 0.06 (FFF) and HI was 0.11 ± 0.02 (FF), 0.10 ± 0.02 (FFF). Dose constraints for OARs were met for both treatment techniques. However, D15 (Gy) for ipsilateral lung was 3.0% lower with FFF beams. In contrast, D5 (Gy) for heart was 9.0% higher with FFF beams. The dose difference between FF and FFF beams for other OARs such as contralateral lung-D10 (Gy) contralateral breast-D5 (Gy) and LAD was up to 6.0%. Both FF and FFF methods met the acceptable criteria. However, the treatment plans with FFF mode were more conformal and provided greater target homogeneity.

Assessment of Monitor Units and Gamma Pass Rate for 6 MV and Flattening Filter Free (FFF) Beams in Volumetric Modulated Arc Therapy (VMAT)

Background: In linear accelerators, the treatment field’s uniform intensity is achieved by including a flattening filter in the beam. However, to produce more conformal dose distributions, contemporary radiotherapy practice now frequently uses fluence and aperture modifying techniques, such as volumetric modulated arc therapy. In these circumstances, the flattening filter in the beam manufacturing process is no longer required. It is therefore necessary to compare the monitor units of 6 MV and flattening filter free plans and how it influences the gamma pass rates to determine which is best for treating cervical cancer with pelvic lymph node metastasis. Methods: VMAT plans for fifteen patients with cervical cancer with pathological pelvic lymph node metastasis were included in this study. Each patient had two VMAT plans using conventional 6 MV beam with flattening filter and one with flattening filter free beam (FFF). The VMAT plans were made using two arcs, and then recalculated to give the planned dose distribution to the detectors in a Delta4 phantom. The VMAT plans were irradiated on the Delta4 phantom using an Elekta linear accelerator (6 MV). Results: The mean monitor unit for the 6 MV plans was 506.3 MU and a standard deviation of 48.6 while that of the FFF plans had a mean MU of 701.5 with a standard deviation of 87.6. The total monitor units (MUs) for the FFF plans were significantly greater than the 6 MV plans (p = 6.1 × 10-5). Conclusion: Flattening filter free (FFF) plans require more numbers of monitor units in comparison to conventional 6 MV filtered beams for external radiation of cervical cancer with pelvic lymph nodes involvement.

Overcoming Problems Caused by Offset Distance of Multiple Targets in Single-isocenter Volumetric Modulated Arc Therapy Planning for Stereotactic Radiosurgery.

The purpose of the study is to investigate the impact of large target offset distances on the dose distribution and gamma passing rate (GPR) in single-isocenter multiple-target stereotactic radiosurgery (SIMT SRS) using volumetric modulated arc therapy (VMAT) with a flattening filter-free (FFF) beam from a linear accelerator. Two targets with a diameter of 1 cm were offset by "±2, ±4, and ±6 cm from the isocenter in a verification phantom for head SRS (20 Gy/fr). The VMAT plans were created using collimator angles that ensured the two targets did not share a leaf pair from the multi-leaf collimator. To evaluate the low-dose spread intermediate dose spill (R50%), GPRs were measured with a criterion of 3%/2 mm using an electronic portal imaging device and evaluated using monitor unit (MU), modulation complexity score for VMAT (MCSv), and leaf travel (LT) parameters. For offsets of 2, 4, and 6 cm, the respective parameters were: R50%, 4.75 ± 0.36, 5.13 ± 0.36, and 5.11 ± 0.33; GPR, 95.01%, 93.82%, and 90.67%; MU, 5893 ± 186, 5825 ± 286, and 5810 ± 396; MCSv, 0.24, 0.16, and 0.13; and LT, 189.21 ± 36.04, 327.69 ± 67.01, and 430.39 ± 114.34 mm. There was a spread in the low-dose region from offsets of ≥4 cm and the GPR negatively correlated with LT (r = -0.762). There was minimal correlation between GPR and MU or MCSv. In SIMT SRS VMAT plans with an FFF beam from a linear accelerator, target offsets of <4 cm from the isocenter can minimize the volume of the low-dose region receiving 10 Gy or more. During treatment planning, it is important to choose gantry, couch, and collimator angles that minimize LT and thereby improve the GPR.

Validating TG119 VMAT Commissioning on a Volumetric Phantom

<h3>Purpose/Objective(s)</h3> The present work adapts AAPM TG119 on a volumetric detector array and evaluates its feasibility for VMAT commissioning for two different Treatment Planning Systems (TPS). <h3>Materials/Methods</h3> TG119 describes a group of test plans for standard structure sets following prescription and dose constraints objectives. These plans were calculated and evaluated using both Elekta Monaco V5.0 (Montecarlo) and Varian Eclipse v15.6 (AAA algorithm) TPS. TG119 structure sets were inserted on virtual CT images for volumetric Quality Assurance (QA) phantom. A set of plans calculated on both TPS were delivered on a 6MV photon beam on an Elekta Synergy Linac. A set of plans was generated only on Eclipse for a Varian Halcyon Linac with 6MV Flattening Filter Free beam. Generated plans were delivered, dose distribution was concurrently measured with Ion Chamber (IC) point doses using a cavity plug holder inserted on the QA phantom. Dose constraints and goals comparison between TPS was executed. Gamma analysis was performed for 3%3mm and 3%2mm global gamma index and Confidence Limits (CL) according to the TG119 definition of Normal quantile were calculated. Measured and planned point doses on relevant positions were compared. <h3>Results</h3> TG119 goals were mostly satisfied except for some critical situations: PTV D99 goal on head & neck plan calculated on Eclipse TPS and Superior Target D10 goal on Multitarget Plan for Monaco TPS calculation. Gamma Analysis for 3%3mm range of passing rate was 96.8% to 100% while CLs range between 4.1% and 4.7% for a Normal quantile for Monaco TPS. For Eclipse TPS range of passing rate achieved was among 97.2% and 99.9%, CLs range was between 3.2% and 3.1%. For Eclipse plans delivered on Halcyon, the passing rate range was among 98.6% and 99.8%, CLs between 1.6% and 1.7%. 3%2mm global gamma index analysis shows a range of passing rate of 93.5% and 100% for Monaco TPS while CLs range between 4.8% and 8.3%. For Elekta plans on Eclipse TPS range of passing rate was 95.6% and 98.8%, CLs range was between 5.1% and 4.5%. The gamma passing rate range for Halcyon plans was between 94.5% and 99.3 and CLs between 3.4% and 6.0%. IC measurements for Synergy Linac showed an average dose difference of 0.84% between measured and calculated plans on Monaco, range among -3.15% and 7.01%, the greatest differences were found on C-Shape plan for high gradient regions measurements. For Eclipse TPS, the average dose difference was 1.28%, range between -1.04% and 10.26%, the highest difference was found in high gradient region C-Shape plan. For Halcyon plans, IC measurements showed an average dose difference of 0.74%, ranging between -0.27% and 3.38%. <h3>Conclusion</h3> CLs agreed with TG119 reference values even when stricter requirements were used. New criteria are more appropriate for modern treatments, but TG119 methodology remains a valid procedure for VMAT. The methodology described for commissioning VMAT technique on a volumetric QA phantom shows to be robust and consistent for various TPS and lilacs.

Target volume size effect on comparison of dynamic arc treatment plans computed using flattened and unflattened 6MV beams

Introduction/backgroundIn conventional linear accelerators, to obtain flat profiles leading to uniform dose distribution in homogeneous medium, the flattening filter is usually applied on the beam path. In recent years, to obtain higher dose rates, there have been the options of flattening filter free (FFF) beams and it has been noticed that these have many advantages. The aim of this study was to clearly underline the advantages and the drawbacks of flattened filter free (FFF) beams in comparison with the flattening filter (FF) beams for different clinical contexts (planning target volumes locations). MethodsTwo groups (planned with auto-planning VMAT, full and partial arcs) of eight patients each were analyzed: Group I (small planning target volume PTV, with average volume 48.9 ±44.4 cm3), Group II (large PTV, with average volume 532.4 ±368.8 cm3). Both beam modalities 6MV and 6MVFFF were compared in terms of Dmax, D95%, D1cc, D2cc, homogeneity index (HI), number of monitor units (MU), treatment delivery time. ResultsUsing the 6MVFFF, the treatment delivery time was significantly reduced (p<0.05). For larger PTVs, the number of MU increased by more than twice, and the p-value shown a significant difference (p= 0.008). The value of Dmax increased by 4%. On the contrary, for small volumes, the results were quite similar from 6MVFFF to 6MV except some differences in terms of MU. ConclusionIt is recommended to use 6MVFFF beam with small PTV volumes. Dose distributions are almost the same as with 6MV and there is a significant reduction of the treatment delivery time up to 57%. Due to the dose profile shape in FFF mode, the dose is lowered beyond the central axis for the FFF beams, and the additional MU allows the dose to be delivered away from the beam axis.

HyperArc Planning for Benign Intracranial Pathologies: A Prospective Analysis on Plan Quality, Delivery, Control and Toxicity

<h3>Purpose/Objective(s)</h3> This study reviews a treatment planning system (TPS) that automates both treatment planning and delivery of single-isocenter VMAT radiosurgery (SRS). The TPS was intended for complex multi-metastasis cases, for which it generates high quality, rapidly-deliverable plans. The effectiveness of treating benign intracranial pathologies (BIP) with TPS was unknown. Under an IRB-approved prospective registry, we collected data on the treatment planning and delivery as well as clinical outcomes of BIP managed with SRS since deployment of TPS. <h3>Materials/Methods</h3> Patients included received SRS between October 2017 and November 2021 using TPS. Patients with less than 3 months follow-up (FU) were censored. For all targets, full prescription dose was normalized to ≥ 99% of target volume without additional PTV expansion. All treatments were delivered on a linear accelerator with 10MV flattening-filter free beam at 2400 MU/min with high-definition (2.5mm) multi-leaf collimator. Descriptive statistics related to SRS treatment, pathology, and prior therapy determined at the time of or prior to treatment were analyzed. Post-treatment imaging, toxicities, and standard pathology-specific outcomes were assessed during FU visits. Significant toxicity was defined as ≥ Grade 3 by CTCAE. <h3>Results</h3> 245 targets (min=0.1cc, max=58.9cc) in 235 patients (53.5% female, median age=59) were treated with TPS. The most common pathologies were meningiomas (134), AVMs (43), pituitary adenomas (30), and acoustic schwannomas (23). 45% of patients were treated due to recurrent, residual, or persistent disease after prior treatment with 15% having prior radiation. A majority (53.5%) were treated in a single fraction (12-22Gy), and 46.5% were treated with fractionated SRS (24-35Gy). A majority (74%) were treated with 3 arcs with median (MED) total treatment and beam-on time lasting 10.4 and 2.3 minutes, respectively. MED RTOG CI and Paddick GI were 1.12 and 3.28, respectively. MED FU was 1.1 years. Excluding AVMs, 11 of 202 (5.4%) benign tumors progressed on FU imaging. Among those that progressed, MED time to failure was 1.14 years. Of those, 9 were WHO grade 2+ meningiomas with prior surgery. Of all patients, significant CNS toxicity was reported in 13 (5.6%, G3=9, G4=4), most of whom had persistent cerebral edema after steroids. Of those with BIP near cochlea (> 3 Gy dose max) without severe hearing loss prior to SRS (n=65), 14% subjectively reported decreased hearing after SRS and 3.5% did not preserve hearing. Of those with BIP near the optics (> 3 Gy dose max, n=81), visual preservation was 100%. <h3>Conclusion</h3> Although developed for multi-metastasis SRS, TPS is capable of generating and efficiently delivering high quality plans characterized by excellent conformality and rapid fall-off. Early clinical outcomes appear congruent with historical controls.

Dosimetric Impact of Intrafraction Prostate Motion in Dose-Escalated Linac-Based SBRT

<h3>Purpose/Objective(s)</h3> The aim of this study was to investigate the impact of observed intrafraction prostate motion on dose metrics and the effect of beam gating and motion correction using a novel electromagnetic (EM) tracking device in dose-escalated Linac-based SBRT. <h3>Materials/Methods</h3> Thirteen patients (56 fractions) with organ-confined prostate cancer received 40 Gy in 5 fractions or 38 Gy in 4 fractions using VMAT technique with flattening filter-free (FFF) arcs. The EM tracking device consisted of an integrated Foley catheter with a transmitter and provided real-time 3D prostate motion data. Treatment was interrupted when the signals exceeded a 2 mm threshold in any of the three spatial directions and, unless the offset was transient, target position was re-defined by repeating a ConeBeam-CT (CBCT). Prostate trajectories with and without beam gating and motion correction events were reconstructed and analyzed. Both actually delivered treatments (case A) and non-gated treatments (case B) were simulated by incorporating the observed prostate motion for each fraction into the patient original treatment plan with an isocenter shift method. Target and organs at risk (OARs) dosimetric parameters of the two motion-inclusive plans were compared to planned values and protocol dose constraints. <h3>Results</h3> Treatment interruptions were needed in 25 fractions (45%) because of target motion beyond the predefined threshold. The prostate was found within 2 mm from its initial position in 96% of the treatment time, i.e., in 94% of the time during the setup, and in 98% during the delivery. In non-gated treatments, the prostate would have been found outside the tolerance in 8% of the total session time, in 4% of the time during the setup, and in 14% during beam-on. The predominant motion pattern was posterior and its probability increased with time, with a mean motion ≤ 2 mm occurring within 10 minutes. Mean relative dose differences respect to original plans were -0.1% [-1.8 – 1.0] for CTV D99% and -0.2% [-1.6 – 0.7] for PTV D95% in case A. The same values were -1.2% [-8.8 – 0.8] and -1.2% [-5.9 – 0.7] in case B. In both cases, urethra planning organ at risk volume was slightly degraded after taking motion into account, and the rectum and bladder dose metrics showed a favorable underexposition of rectum and an undesirable overdose to bladder. Nevertheless, no protocol dose constraints violations were observed. <h3>Conclusion</h3> Our findings showed that the majority of the observed prostate motion was modest; however, there were a non-insignificant number of fractions with motion exceeding the predetermined threshold. The current CTV to PTV margins, the robustness of original treatment plans, and the fast FFF beams delivery led to minimal degradations of dose metrics for the target and OARs in both cases. Anyway, real-time monitoring with beam gating and motion correction ensured superior results and are recommended in dose-escalated prostate SBRT.

A Comprehensive Evaluation of Single Isocenter Multiple Target SRS Plans and the Analytical Relationship between Plan Quality Indices with the Number and Volume of Targets.

To study the relationship of plan quality indices with the number and volume of target for 5 to 10 brain metastases treated with LINAC-based Single Isocenter Multiple Target (SIMT) Stereotactic radiosurgery (SRS) planning and to determine the maximum volume of spherical targets treated without exceeding the normal tissue tolerances. Spherical targets of 5 to 10 numbers per plan, with individual target volumes ranging from 0.025 cc to 11.5 cc, were simulated with randomly drawn planning target volumes (PTVs) within the brain. SIMT SRS plans were generated for the 21 Gy prescription dose with a 6 MV Flattening Filter Free photon beam. Target coverage, organ at risk sparing, plan quality indices, R50%, and gradient measure were studied. Mean brain dose, V12 for Brain minus PTV (BmP), V10, V12, V15, V18, V20, and V24 for brain volume were evaluated. Equations relating the gradient index, mean brain dose, and V12 (BmP) to the given number and volume of the targets were constructed. PTV coverage D98 was 98.77 ± 1.37 %. The mean CIRTOG, QRTOG, HIRTOG, CIP, GI, and R50% of the individual targets were 1.02 ± 0.08, 0.94 ± 0.02, 1.49 ± 0.11, 0.91 ± 0.06, 4.74 ± 2.3, and 4.95 ± 2.67, respectively. The gradient measure achieved was in the range of 0.49 to 1.35 cm. The mean brain dose was in the range of 1.62 to 6.69 Gy. The mean V12 (BmP) per target obtained was 3.85 ± 2.83 cc. Equations relating the number and volume of targets to the gradient measure, mean brain dose, V12 (BmP), and V10-24 can serve as a baseline for multiple brain metastases SIMT planning. The target volume for 5, 6, 7, 8, 9, and 10 targets that can be treated without exceeding V12 (BmP) is 6, 5, 4.7, 4, 3.7, and 3.4 cc, respectively, for the 21 Gy prescription dose.

Assessment of Organ Dose Reduction Using Dynamic Conformal Arc and Static Field with FFF Beams for SBRT in Lung Cancer

Background The aim of this study is to compare the dose delivered to the organs at risk (OAR), using static beams (SF) and a dynamic conformational arc (DCA) with flattening filter free (FFF) beams, for lung stereotactic body radiation therapy (SBRT). Methods 100 patients with lung cancer were treated with SBRT, using FF beams (TrueBeam STx, 6 MV, IQ = 0.67, 600 MU/min), separated into two groups: DCA (50 patients) and SF (50 patients). These patients were retrospectively re-planned using 6XFFF beams, IQ = 0.63, 1400 MU/min. The beam-on time and dosimetric gain on planning target volume (PTV) and OARs (heart, spinal cord, planning risk volume (PRV) of spinal cord, esophagus, lungs and ribs) were analyzed according to tumor location. The comparison of median values was performed using the non-parametric Wilcoxon test (significance level: p < 0.05). Results PTV coverage was 98.90% versus 98.40% (DCA) and 98.8% versus 98.3% (SF) for the FF and FFF beams, respectively. The median dosimetric gain to the heart, spinal cord, PRV spinal cord, esophagus and lungs was 6% (4–11%) in the central region and 8% (2–23%) in the peripheral region, using FFF (p < 0.05). The dose received by the ribs decreases by 5–6 Gy, using FFF beams. The median gain in beam-on time ranged from 31% to 34% for SF and from 44 to 52% for DCA using FFF beams. Conclusions The FFF beams reduce the dose received by all OARs, regardless of the used technique or tumor location, reducing treatment delivery time as well.

Feasibility and Short-Term Toxicity of a Consecutively Delivered Five Fraction Stereotactic Body Radiation Therapy Regimen in Early-Stage Breast Cancer Patients Receiving Partial Breast Irradiation.

BackgroundFor appropriately selected patients with early-stage breast cancer (ESBC), accelerated partial breast irradiation (APBI) yields equivalent rates of ipsilateral breast tumor recurrence with mixed results in patient-rated cosmesis compared with whole-breast radiotherapy depending on the technique utilized. When utilizing external beam radiotherapy for APBI, techniques to reduce target margins and overall treatment volume are potentially important to decrease rates of long-term adverse cosmesis. Stereotactic body radiotherapy (SBRT) is a promising technique to deliver APBI because of its increased accuracy and sparing of uninvolved breast tissue. We report the initial results of a prospective clinical trial investigating feasibility, safety, and cosmetic outcomes of a daily five-fraction SBRT regimen for APBI.MethodsTwenty-three patients with ESBC after lumpectomy who met APBI suitability were enrolled. During lumpectomy, a bioabsorbable three-dimensional fixed array tissue marker (BioZorb™, Hologic, Marlborough, MA) was placed for enhanced visualization of the cavity boundaries. Clinical target volume (CTV) was defined as the delineable cavity plus a 1-cm isotropic expansion followed by a 3-mm isotropic planning target volume (PTV) expansion. Patients received 30 Gy delivered in five planned consecutive daily fractions in either prone or supine positioning depending on individual anatomy. Two patients completed the five-fraction treatments in 9-day interval and 11-day interval due to external circumstances. A maximum PTV of 124cc was allowed to minimize incidence of fat necrosis. Plans utilized 10-MV flattening filter–free beams delivered on a Varian Edge linear accelerator. Local control, toxicity, and nurse/patient-scored cosmesis at pre-treatment baseline, 1 month post-treatment, and at subsequent 6-month intervals were recorded.ResultsTwenty-three patients were accrued at the time of submission with median follow-up of 6 months. No patients experienced grade ≥3 acute toxicity. Of the 10 events reported probably related to SBRT, nine were grade 1 (n = 9/10, 90%). There was no evidence of difference, deterioration, or change in patient or nurse-scored cosmesis from baseline to 1 and 6 months post-treatment. One patient developed nodal failure shortly after APBI.ConclusionsAlthough longer follow-up is needed to assess long-term toxicity and local control, this study demonstrated a five-fraction SBRT regimen delivered over consecutive days is a safe, efficient, well-tolerated, and cosmetically favorable means of delivering APBI in suitable women.Clinical Trial Registrationhttps://www.clinicaltrials.gov/ct2/show/NCT03643861, NCT03643861.

DNA strand breaks based on Monte Carlo simulation in and around the Lipiodol with flattening filter and flattening filter-free photon beams.

BackgroundThe current study aims to investigate the DNA strand breaks based on the Monte Carlo simulation within and around the Lipiodol with flattening filter (FF) and flattening filter-free (FFF) photon beams.Materials and methodsThe dose-mean lineal energy (yD) and DNA single- and double strand breaks (DSB/SSB) based on spatial patterns of inelastic interactions were calculated using the Monte Carlo code: particle and heavy ion transport system (PHITS). The ratios of dose using standard radiation (200 kVX) to the dose of test radiation (FF and FFF of 6 MV X-ray (6MVX) and 10 MVX beams) to produce the same biological effects was defined as RBEDSB. The RBEDSB within the Lipiodol and in the build-up and build-down regions was evaluated.ResultsThe RBEDSB values with the Lipiodol was larger than that without the Lipiodol at the depth of 4.9 cm by 4.2% and 2.5% for 6 MVX FFF and FF beams, and 3.3% and 2.5% for 10 MVX FFF and FF beams. The RBEDSB values with the Lipiodol was larger than that without the Lipiodol at the depth of 6.5 cm by 2.9% and 2.4% for 6 MVX FFF and FF beams, and 1.9% and 1.4% for 10 MVX FFF and FF beams. In the build-down region at the depth of 8.1 cm, the RBEDSB values with the Lipiodol was smaller than that without the Lipiodol by 4.2% and 2.9% for 6 MVX FFF and FF beams, and 1.4% and 0.1% for 10 MVX FFF and FF beams.ConclusionsThe current study simulated the DNA strand break except for the physical dose difference. The lower and FFF beam occurred the higher biological effect.

Efficient method for whole-breast irradiation therapy using Halcyon linear accelerators.

BackgroundThe Halcyon is a linear accelerator‐based treatment machine designed for a high‐throughput simplified workflow. The machine features a compact jawless design, dual‐layer multileaf collimators, and a single 6‐MV flattening filter‐free (FFF) beam. However, the machine's 6‐MV FFF beam may restrict its applicability to conventional techniques, such as field‐in‐field (FiF) radiotherapy, for breast cancer treatment. This study developed a practical and efficient hybrid method for imaging, planning, and irradiation procedures for whole‐breast irradiation using Halcyon linear accelerators.Materials and methodsThe proposed method involves five major steps: (1) field arrangement, (2) planning target volume (PTV) generation and evaluation, (3) basal plan generation, (4) inverse planning intensity–modulated radiation therapy plan generation, and (5) plan evaluation and irradiation. The PTV is generated using isodose curves plotted on the basis of tangential fields, which are applied to create a basal plan. Subsequently, a basal‐dose‐compensation approach is applied to further optimize the treatment plan. This efficient workflow necessitates executing only one onboard cone‐beam computed tomography procedure. This study included 10 patients with early‐stage breast cancer who were treated at our center. The performance of the proposed method was evaluated by comparing its corresponding irradiation time and dose statistics with those derived for a dynamically flattened beam‐based FiF (DFB‐FiF) method.ResultsAll plans were normalized to ensure that 98% of the prescribed dose covered 95% of the PTV. On average, the global maximum doses in the proposed and DFB‐FiF methods were lower than 106%. The homogeneity index for right‐sided (left‐sided) breast cancer was 0.053 (0.056) in the proposed method and 0.073 (0.076) in the DFB‐FiF method. The dose statistics of normal tissues, including the contralateral breast, heart, and lungs, were comparable between the methods. However, the irradiation time per monitor unit in the proposed method was approximately five times faster than that in the DFB‐FiF method, but the planning time and complexity were similar between the methods.ConclusionsThis study developed and evaluated an efficient and practical hybrid method for whole‐breast irradiation using the Halcyon. This method can significantly reduce the irradiation time, while providing comparable dose statistics to the DFB‐FiF method.

Monte Carlo computation of photon energy spectra in central axis of flattened and unflattened beams and doses in critical organs in a water phantom model of prostate radiotherapy

A thorough understanding of the energy spectra for clinical linear accelerators is essential in modern cancer treatment planning. We aimed to determine the radiation spectra and out-of-field doses in a water phantom under the conditions of prostate radiotherapy in beams with a flattening filter (FF) and without (FFF). Monte Carlo simulations were performed to determine the energy spectra and doses outside the irradiated volume. Doses were registered in locations corresponding to critical organs (kidneys, lungs, and thyroid) and the spectra was determined in the central axis (prostate gland). Simulations were conducted for 6 MV and 10 MV for FF and FFF beams. The out-of-field doses were calculated at selected points from the field edge for 6 MV photon beams (FF and FFF), and for 10 and 15 MV beams (FFF only). Compared to FF beams, we found that the mean energy for the photon spectra of FFF beams was lower. For 6 MV FF beams, the relative doses for the critical organs (kidneys, lungs and thyroid) were 0.7%, 1.2%, 0.6% versus 1.6%, 1.2%, 1.3% for the unflattened beams. For 10 MV FF beams, the out-of-field doses to the organs were 0.1%, 0.4% and 0.4% versus 0.4%, 0.2% and 0.3% with the FFF beam. FFF beams had a higher photon fluence, indicating less scattered radiation. Removal of the filter leads to lower doses in the areas surrounding the irradiated volumes, especially at large distances from the treatment field. These findings are consistent with previous reports, indicating that flattening filter free beams are likely to improve clinical outcomes. The reduction in scattered radiation lowers the probability of inducing second cancers.

Retrospective study of random and systematic errors in Head and Neck cancer Patients with Image guided Helical Intensity Modulated Radiation Therapy

The Precision of radiotherapy is checked based on the matching of pre-treatment 2D portal imaging/CBCT to the reference image. The objective of this study is to find inter-fractional systematic and random setup errors (mm) for head and Neck cancer patients and also find setup margin for Planning Target Volume (PTV) at Mohan Dai Oswal Cancer Hospital Ludhiana Punjab. Inter-fractional motion errors were quantified for 10 Head and neck cancer patients who underwent image guided helical intensity modulated radiation therapy with Radixact X9 machine. One hundred fan beam computed tomography scans of 2mm slice thickness, 3.5 MV average energy and flattening filter free beam has been used to collect the data for the calculation of systematic and random errors. After patient immobilization, patient accuracy is checked with registration of pre-treatment image with reference planning image with the help of Accuray Precision image guidance protocol. For every patient 10 fan beam computed tomography images has been taken. Translational errors have been calculated in X, Y and Z direction to find systematic error (∑) and random error (σ). The final PTV margin is calculated by van Herk’s equation (2.5∑ + 0.7σ). The results of this study shows that mean translational errors varies from -2.3 mm to 3.3 mm in lateral direction (X), -3.6 mm to 1.7 mm in longitudinal direction (Y), -2.7 mm to 1.5 mm in vertical direction (Z). The mean and standard deviation (SD) for systematic errors are 1.467, 0.8, 0.923 and random error 0.0595, 0.02266, 0.03824 in X, Y and Z direction has been calculated. The Total Margin for CTV to PTV which include setup margin (mm) in X, Y and Z direction are 3.7 mm, 2.02 mm and 2.33 mm. In addition to that, a PTV margin of 5.00 mm is the appropriate margin for Mohan Dai Oswal Cancer Hospital’s patients. This work conclude that CTV to PTV margin of 5.00 mm is suitable for image guided helical intensity modulated radiation therapy for Head and neck patients to ensure the minimum 95% coverage of dose to target