Single Volumetric Modulated Arc Therapy Research Articles

Deep learning-based inverse mapping for fluence map prediction

We developed a fluence map prediction method that directly generates fluence maps for a given desired dose distribution without optimization for volumetric modulated arc therapy (VMAT) planning. The prediction consists of two steps. First, projections of the desired dose are calculated and then inversely mapped to fluence maps in the phantom geometry by a deep neural network. Second, a plan scaling technique is applied to scale fluence maps from phantom to patient geometry. We evaluated the performance of the proposed fluence map prediction method for 102 head and neck (H&N) and 14 prostate cancer VMAT plans by comparing the patient doses calculated from the predicted fluence maps with the given desired dose distributions. The mean dose differences were 1.42% ± 0.37%, 1.53% ± 0.44% and 1.25% ± 0.44% for the planning target volume (PTV), the region from the PTV boundary to the 50% isodose line, and the region from the 50% to the 20% isodose line, respectively. The gamma passing rate was 98.06% ± 2.64% with the 3 mm/3% criterion. The prediction time for a single VMAT plan was less than one second. In conclusion, we developed an inverse mapping-based method that predicts fluence maps for desired dose distributions with high accuracy. Our method is effectively an optimization-free inverse planning approach, which was orders of magnitude faster than fluence map optimization. Combining the proposed method with leaf sequencing has the potential to dramatically speed up VMAT treatment planning.

Evaluation of geometrical uncertainties on localized prostate radiotherapy of patients with bilateral metallic hip prostheses using 3D-CRT, IMRT and VMAT: A planning study.

Since most radiation treatment plans are based on computed tomography (CT) images, which makes it difficult to define the targeted tumor volume located near a metal implant, this study aims to evaluate and compare three treatment plans in order to optimally reduce geometrical uncertainty in external radiation treatment of localized prostate cancer. Experimental subjects were three prostate patients with bilateral hip prosthesis who had undergone radical radiotherapy. The treatment plans were five-field three-dimensional conformal radiation therapy (3D-CRT), fixed 5-field intensity-modulated radiation therapy (IMRT) using similar gantry angles, and single-arc volumetric modulated arc therapy (VMAT). The monitor units (MUs), dose volume histograms (DVHs), the dose indices of planning target volume (PTV), clinical target volume (CTV) and rectum were compared among the three techniques. The geometrical uncertainties were evaluated by shifting the iso-center (2- 10 mm in the anterior, posterior, left, right, superior, and inferior directions). The CTV and rectum dose indexes with and without the iso-center shifts were compared in each plan. The Conformity Index of PTV were 1.35 in 3D-CRT, 1.12 in IMRT, and 1.04 in VMAT, respectively. The rectum doses in 3D-CRT are also higher than those in IMRT and VMAT. The iso-center shift little affected the CTV dose when smaller than the margin size. The rectum dose increased especially after a posterior shift. Additionally, this dose increase was larger in the VMAT plan than in the 3D- CRT plan. However, the VMAT achieved a superior rectum DVH to that of 3D- CRT, and this effect clearly exceeded the rectum-dose increase elicited by the iso-center shift. For radiotherapy treatment of localized prostate cancer in patients with hip prosthesis, the dose distribution was better in the VMAT and Metal Artifact Reduction (MAR)-CT image methods than the conventional methods. Because the anatomical structure of the male pelvic region is relatively constant among individuals, we consider that VMAT is a valid treatment plan despite analyzing just three cases.

Single-arc VMAT optimization for dual-layer MLC

Dual-layer multi-leaf collimator (DLMLC) has recently attracted renewed interest due to its good balance among resolution, low leakage, and high fabricability. However, existing progressive sampling based volumetric modulated arc therapy (VMAT) algorithm is ineffective for DLMLC, requiring more arcs to achieve dosimetry comparable to VMAT plans with higher resolution single-layer MLC (SLMLC). In this study, we develop a novel single-arc VMAT optimization framework to take advantage of the unique DLMLC characteristics fully. Direct aperture optimization (DAO) for single-arc DLMLC VMAT was formulated as a least square dose fidelity objective, along with an anisotropic total variation term to regulate the fluence smoothness and a single segment term for forming simple apertures. The DAO was solved through alternating optimization approach. The DLMLC deliverability constraint and the MLC leaf speed constraint were formulated as the optimization constraints and solved using a graph optimization algorithm. Feasibility of the proposed framework was tested on a brain, a lung, and a prostate cancer patient. The framework was further adapted for a simultaneous integrated boost (SIB) case. The single-arc DLMLC-10 mm (leaf width) plan was compared against single-arc SLMLC VMAT plans including SLMLC-5mm, SLMLC-10mm, and SLMLC with 10 mm leaf width and 5 mm leaf step size (SLMLC-10mm-5mm). Compared with the SLMLC-10mm plan and the SLMLC-10mm-5mm plan, with the same target coverage, the DLMLC-10 mm plan reduced R50 by 30.7% and 10.0%, the average max OAR dose by 5.79% and 3.7% of the prescription dose, and the average mean OAR dose by 4.18% and 2.1% of the prescription dose, respectively. The plan quality is comparable to that of the SLMLC-5mm plan. The novel single-arc VMAT optimization framework for DLMLC utilizes two MLC layers to improve the effective modulation resolution and afford more sophisticated modulation. Consequently, DLMLC VMAT achieves superior dosimetry to SLMLC VMAT with the same leaf width.

Comparison of dose distribution between VMAT and IMRT in patients with brain metastases during hippocampus-sparing whole brain radiotherapy

Objective To compare the dose distribution between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) in patients with brain metastases receiving hippocampus-sparing whole brain radiotherapy. Methods Forty-six patients with brain metastases admitted to our hospital from 2013 to 2016 were recruited in this study. After fusing the CT and MRI images, the hippocampus was delineated on the fusion images. The three-grade hippocampal avoidance regions were created by using a volumetric expansion of 3, 5 and 10 mm surrounding the hippocampus. The planning target volume (PTV) was calculated by subtracting the 5-mm expansion surrounding the hippocampus from the whole brain. The prescription dose was 30 Gy/10 fractions. The 7-field IMRT and single arc VMAT were designed for each case. The dose distribution of PTV, hippocampus and other organs at risk (OARs) were evaluated in both plans. Results The PTV was statistically compared between VMAT and IMRT: V95: 95.90% and 94.97%(P=0.000); V90: 98.17% and 97.48%(P=0.000); CI: 0.825 and 0.813(P=0.013); HI: 0.277 and 0.289(P=0.025). The hippocampal dose was also compared between VMAT and IMRT: the Dmax of hippocampus was 1 698.9 cGy for VMAT and 1 784.9 cGy for IMRT (P=0.002). The Dmean of hippocampus was 1 183.8 cGy for VMAT and 1 112.7 cGy for IMRT (P=0.000). No statistical significance was observed between IMRT and VMAT in protecting the OARs except the chiasma opticum (3 262.6 cGy and 3 529.3 cGy, P=0.000). The MU and treatment time of VMAT and IMRT were 651 and 2 768(P=0.000), and 188 s and 504 s (P=0.000). Conclusions The dose distribution of PTV in VMAT is significantly better than that in IMRT.VMAT is advantageous in protecting the hippocampus than IMRT.VMAT can significantly shorten treatment time and MU and enhance the equipment utilization. Besides, VMAT can achieve the goal of protecting the hippocampus and meet the prescription dose requirement of PTV. Key words: Neoplasms metastasis, brain/whole brain radiotherapy; Hippocampus-sparing; Neoplasms metastasis, brain/radiotherapy

Organ at risk dose verification in nasopharyngeal cancer VMAT planning with collimator comparison between single arc and double arc

Volumetric modulated arc therapy (VMAT) is an irradiation technique that enables the improvement of the flexibility of dose delivery from a full range of angles with continuous modulation of beam aperture and dose rate. We compared the homogeneity index (HI), conformity index (CI), dose volume histogram (DVH) and dose differentiation of single arc and double arc VMAT delivered for nasopharyngeal cancer (NPC). Planning for gantry rotation angles of 360° counter clockwise and clockwise (double arc) with collimator (0° and 10°) and 360° clockwise (single arc) were created for ten nasopharyngeal cancer cases applied in RANDO phantom with the Eclipse treatment planning system and delivered using Trilogy linear accelerator. The verification was performed by using gafchromic film EBT3 and placed on the RANDO phantom according to the location of the organs at risk. In this study, we evaluated right parotid, left parotid, right eye, left eye and trachea. The measurement of mean dose using gafchromic film and TPS shows that the resulting values were close to TPS results with the difference being −1.51%. From the result of dose measurement using gafchromic film based on the data from RANDO CT phantom use, it can be concluded that double arc VMAT technique with collimator can reduce the dose in the organ at risk.

A Retrospective Review on Stereotactic Radiosurgery Cases Planned with Dynamic Conformal Arcs Versus Volumetric Modulated Arc Therapy

This study aimed to acquire an average value of plan quality metrics by retrospectively analyzing past stereotactic radiosurgery (SRS) treatment plans. The study was also designed to compare the plan quality metrics between single-target Dynamic Conformal Arc (DCA) and multi-target Volumetric Modulated Arc Therapy (VMAT) plans. A total of 253 LINAC-based SRS plans treated in 2017 at our institution were reviewed. A total of 605 lesions were included in these plans as treatment targets. 156 plans were generated with a DCA technique treating single target in each plan, and 97 plans used a VMAT technique to treat multiple targets simultaneously in a single plan. The prescription dose was normalized to 20Gy for all plans for this analysis. Two plan quality metrics, tumor Conformity Index (CI) and normal tissue volume receiving more than 12Gy (V12Gy), were calculated for each target. The results were stratified based on target size and compared between different techniques. For multi-targets VMAT plans, the distance of a target to the nearest other target and the number of targets being treated in the same plan were calculated for each target to evaluate their impact on V12Gy. For the subgroups of target volume < 0.2cc, 0.2-0.5cc, 0.5-1.0cc, 1.0-2.0cc, and 2.0-4.0cc, the mean (±SD) CI were 2.1 (±0.3), 1.9 (±0.2), 1.8 (±0.3), 1.6 (±0.2), and 1.6 (±0.1), respectively, in DCA plans and 1.8 (±0.4), 1.5 (±0.2), 1.4 (±0.2), 1.3 (±0.2), and 1.3 (±0.1), respectively, in VMAT plans. The mean V12Gy were 1.2cc, 1.9cc, 3.5cc, 5.2cc, and 7.4cc, respectively, in DCA plans and 1.3cc, 2.2cc, 3.2cc, 4.7cc, and 7.8cc, respectively, in VMAT plans. The V12Gy for a target in VMAT plan did not show apparent dependence on the distance between targets or the total number of targets in single VMAT plan. The average performance level of CI and V12Gy were established based on previous cases and can be used as benchmark for future SRS planning. The multi-target VMAT plans produced consistently lower CI and kept the normal tissue 12Gy per target comparable to DCA plans.

A Simplified Three-Isocenter VMAT for Craniospinal Irradiation

Craniospinal irradiation (CSI) has become an important treatment method for Central nervous system (CNS) relapse of hematological malignancies. However, conventional CSI is technically very challenging and field edge matching is needed because of the mechanical limitations of standard linear accelerators. We have developed a simple Linac based volumetric modulated arc therapy (VMAT) technique for CSI. The aim of this study is to report initial clinical experience of CSI-VMAT for CNS relapse of hematological malignancies and compare dose homogeneity and dose to organs at risk (OAR) with conventional three-dimensional conformal radiotherapy (3D-CRT) technique. Seven patients with CNS relapse of hematological malignancies were treated with CSI using a novel VMAT technique and seven patients were previously underwent conventional 3D-CRT technique. A dose of 22.5 Gy was prescribed to be delivered in 15 fractions. Planning target volume (PTV) included the whole brain and spinal canal to the S3 vertebral level. Patient is positioned supine and immobilized using a face mask and Vac-Lock in the body. The VMAT plan used three full arcs, each with a unique isocenter (Brain, Superior Spine, Inferior Spine). Spinal two arcs turned off lateral beams (225-315o and 45-135o) to minimize lung dose. Adjacent fields were intentionally overlapped to eliminate the issues of beam edge matching, and the optimization process smoothly integrated the dose inside the overlapped junction. The 3D-CRT plan used edge matching field sets and shifted junctions three times. Comparing the VMAT plan with the 3D-CRT plan, the average simplified homogeneity index (HI=Dmax/Dmin) of PTV was 1.19 ± 0.11 and 1.46 ± 0.13, respectively. Mean doses to avoidable OAR were significantly decreased (for the heart: 5.3 Gy and 11.1 Gy, for the esophagus: 11.6 Gy and 19.7 Gy, for the parotid glands: 8.8 Gy and 20.5 Gy, using VMAT and 3D-CRT, respectively). The lung V5, V10 and Dmean were 28.3%, 5.4%, 3.4 Gy, in VMAT, 20.1%, 15.3 %, 4.6 Gy, in 3D-CRT. The doses of lung except V5 were lower in VMAT. Short term follow-up evaluations revealed no unexpected toxicity associated with this novel VMAT technique. We have developed a simplified three-isocenter Linac based VMAT approach for CSI. The dose to the brain and spine is significantly improved, compared to the conventional 3D-CRT. The single VMAT plan is easier to manage. This new technique simplifies the set up and eliminates the need for shifting junctions during course of CSI treatment and saves OAR of patients with CNS relapse of hematological malignancies.

Log file-based patient dose calculations of double-arc VMAT for head-and-neck radiotherapy

PurposeThe log file-based method cannot display dosimetric changes due to linac component miscalibration because of the insensitivity of log files to linac component miscalibration. The purpose of this study was to supply dosimetric changes in log file-based patient dose calculations for double-arc volumetric-modulated arc therapy (VMAT) in head-and-neck cases. Methods and materialsFifteen head-and-neck cases participated in this study. For each case, treatment planning system (TPS) doses were produced by double-arc and single-arc VMAT. Miscalibration-simulated log files were generated by inducing a leaf miscalibration of ±0.5 mm into the log files that were acquired during VMAT irradiation. Subsequently, patient doses were estimated using the miscalibration-simulated log files. ResultsFor double-arc VMAT, regarding planning target volume (PTV), the change from TPS dose to miscalibration-simulated log file dose in Dmean was 0.9 Gy and that for tumor control probability was 1.4%. As for organ-at-risks (OARs), the change in Dmean was <0.7 Gy and normal tissue complication probability was <1.8%. A comparison between double-arc and single-arc VMAT for PTV showed statistically significant differences in the changes evaluated by Dmean and radiobiological metrics (P < 0.01), even though the magnitude of these differences was small. Similarly, for OARs, the magnitude of these changes was found to be small. ConclusionsUsing the log file-based method for PTV and OARs, the log file-based method estimate of patient dose using the double-arc VMAT has accuracy comparable to that obtained using the single-arc VMAT.

Monaco and film dosimetry of 3D CRT, IMRT and VMAT cases in a realistic pelvic prosthetic phantom

The dosimetry of patients with metallic hip implants during irradiation of pelvic lesions is challenging due to dose distortions caused by implants. This work presents a dosimetric comparison of various multi-field photon-beam dose distributions in the presence of unilateral hip titanium prosthesis (UHTiP) embedded in a unique pelvic phantom made out of water-equivalent nylon slices. The impact of the UHTiP on the accuracy of dose calculations from a Monaco TPS (treatment planning system) using the X-ray voxel Monte Carlo (XVMC) algorithm was benchmarked against measured dose data using Gafchromic EBT3 film. Multi-field beam arrangements including a 4-field box, 5-field 3DCRT (three-dimensional conformal radiation therapy), 6-field IMRT (intensity modulated radiation therapy) and a single-arc VMAT (volumetric modulated arc therapy) plan were set up for 6MV and 15MV beams. These plans were generated for the pelvic phantom that contains the prosthesis with film inserted. Compared to Monaco TPS dose calculations, film measurements showed enhanced dose in the prosthesis which was not predicted by Monaco due to its limitation in relative density assignment. The enhanced prosthesis dose increased with increase in beam energy and decreased with the complexity of the treatment plans, with VMAT giving the least escalated dose. The dose increased between 5% and 19% for 6MV and between 6% and 21% for 15MV. A gamma index analysis showed that 70–92% of dose points (excluding the prosthesis) were within 3% discrepancy. Increasing the number of treatment fields increases target dose coverage and improves the agreement between film and Monaco. When the relative electron density (RED) in the prosthesis was varied between 3.72 and 15 the dose discrepancy between film and Monaco increased from 30% to 57% for 6MV and from 30% to 50% for 15MV. The study indicates that beam weights for fields that pass through the prosthesis should be minimised and its RED must be correct for accurate dose calculation on Monaco.

Volumetric modulated arc therapy (VMAT) to deliver nodal irradiation in breast cancer patients.

To evaluate feasibility, safety, toxicity profile and dosimetric results of volumetric modulated arc therapy (VMAT) to deliver regional nodal irradiation (RNI) after either mastectomy or breast conservation (BCS) in high-risk breast cancer patients. Between January 2015 and January 2017, a total of 45 patients were treated with VMAT to deliver RNI together with whole breast or post-mastectomy radiotherapy. The fractionation schedule comprised 50Gy in 25 fractions given to supraclavicular and axillary apex nodes and to whole breast (after BCS) or chest wall (after mastectomy). Two opposite 50°-60° width arcs were employed for breast ad chest wall irradiation, while a single VMAT arc was used for nodal treatment. Treatment was generally well tolerated. Acute skin toxicity was G2 in 13.3% of patients. Late skin toxicity consisted of G1 induration/fibrosis in six patients (13.3%) and G2 in 1 (2.2%). Dosimetric results were consistent in terms of both target coverage and normal tissue sparing. In conclusion, VMAT proved to be a feasible, safe and effective strategy to deliver RNI in breast cancer patients after either BCS or mastectomy with promising dosimetric results and a mild toxicity profile.

Intelligence artificielle appliquée à la radiothérapie

To investigate, in a prospective phase 1 to 2 trial, the safety and feasibility of delivering external beam radiation therapy in 5 fractions to the breast or thoracic wall, including boost and/or lymph nodes if needed, to women aged ≥65 years with breast cancer.Ninety-five patients aged ≥65 years, referred for adjuvant radiation therapy, were treated in 5 fractions over 12 days with a total dose of 28.5 Gy/5.7 Gy to the breast or thoracic wall and, if indicated, 27 Gy/5.4 Gy to the lymph node regions and 32.5 Gy/6.5 Gy to 34.5 Gy/6.9 Gy to the tumor bed. The primary endpoint was clinically relevant dermatitis (grade ≥2).Mean follow-up time was 5.6 months, and mean age was 73.6 years. Clinically relevant dermatitis was observed in 11.6% of patients and only occurred in breast irradiation with boost (17.5% grade 2-3 vs 0% in the no-boost group). Although doses were high, treatment delivery with intensity modulated radiation therapy was swift, except for complex treatments, including lymph nodes for which single-arc volumetric modulated arc therapy was needed to reduce beam-on time.Accelerated radiation therapy in 5 fractions was technically feasible and resulted in low acute toxicity. Clinically relevant erythema was only observed in patients receiving a boost, but still at an acceptable rate. Although the follow-up is still short, the results on acute toxicity after accelerated radiation therapy were encouraging. A 5-fraction schedule is well tolerated in the elderly and may lower the threshold for radiation therapy in this population.

Highly Accelerated Irradiation in 5 Fractions (HAI-5): Feasibility in Elderly Women With Early or Locally Advanced Breast Cancer

Toinvestigate, in a prospective phase 1 to 2 trial, the safety and feasibility of delivering external beam radiation therapy in 5 fractions to the breast or thoracic wall, including boost and/or lymph nodes if needed, to women aged ≥65years with breast cancer. Ninety-five patients aged ≥65years, referred for adjuvant radiation therapy, were treated in 5 fractions over 12days with a total dose of 28.5Gy/5.7Gyto the breast or thoracic wall and, if indicated, 27Gy/5.4Gy to the lymph node regions and 32.5Gy/6.5Gy to 34.5Gy/6.9Gy to the tumor bed. The primary endpoint was clinically relevant dermatitis (grade ≥2). Mean follow-up time was 5.6months, and mean age was 73.6years. Clinically relevant dermatitis was observed in 11.6% of patients and only occurred in breast irradiation with boost (17.5% grade 2-3 vs 0% in the no-boost group). Although doses were high, treatment delivery with intensity modulated radiation therapy was swift, except for complex treatments, including lymph nodes for which single-arc volumetric modulated arc therapy was needed to reduce beam-on time. Accelerated radiation therapy in 5 fractions was technically feasible and resulted in low acute toxicity. Clinically relevant erythema was only observed in patients receiving a boost, but still at an acceptable rate. Although the follow-up is still short, the results on acute toxicity after accelerated radiation therapy were encouraging. A 5-fraction schedule is well tolerated in the elderly and may lower the threshold for radiation therapy in this population.

Dosimetric Comparison between Single and Dual Arc-Volumetric Modulated Arc Radiotherapy and Intensity Modulated Radiotherapy for Nasopharyngeal Carcinoma Using a Simultaneous Integrated Boost Technique

Backround:Plan quality and performance of dual arc (DA) volumetric modulated arc therapy (VMAT), single arc (SA) VMAT and nine field (9F) intensity modulated radiotherapy were compared using a simultaneous integrated boost (SIB) technique.Methods:Twelve patients treated in Elekta Synergy Platform (mlci2) by 9F-IMRT were replanned with SA/DA-VMAT using a CMS Monaco Treatment Planning System (TPS) with Monte Carlo simulation. Target delineation was conducted as per Radiation Therapy Oncology Protocols (RTOG0225 and 0615). A 70Gy dose prescribed to PTV70 and 61Gy to PTV61 in 33 fractions was applied for the SIB technique. The conformity index (CI) and homogeneity index (HI) for targets and the mean dose and maximum dose for OAR’s, treatment delivery time (min), monitor units (MUs) per fraction, normal tissue integral dose and patient specific quality assurance were analysed.Results:Acceptable target coverage was achieved for PTV70 and PTV61 with all the planning techniques. No significant differences were observed except for D98 (PTV61), CI(PTV70) and HI(PTV61). Maximum dose (Dmax) to the spinal cord was lower in DA-VMAT than 9F-IMRT (p=0.002) and SA-VMAT (p=0.001). D50 (%) of parotid glands was better controlled by 9F-IMRT (p=0.001) and DA-VMAT (p=0.001) than SA-VMAT. A lower mean dose to the larynx was achieved with 9F-IMRT (P=0.001) and DA-VMAT (p=0.001) than with SA-VMAT. DA-VMAT achieved higher CI of PTV70 (P= 0.005) than SA-VMAT. For PTV61, DA-VMAT (P=0.001) and 9F-IMRT (P=0.001) achieved better HI than SA-VMAT. The average treatment delivery times were 7.67mins, 3.35 mins, 4.65 mins for 9F-IMRT, SA-VMAT and DA-VMAT, respectively. No significant difference were observed in MU/fr (p=0.9) and NTID (P=0.90) and the patient quality assurance pass rates were >95% (gamma analysis I3mm, 3%).Conclusion:DA-VMAT showed better conformity over target dose and spared the OARs better or equal to IMRT. SA-VMAT could not spare the OARs well. DA-VMAT offered shorter delivery time than IMRT without compromising the plan quality.

Validation of the relative insensitivity of volumetric-modulated arc therapy (VMAT) plan quality to gantry space resolution.

Volumetric-modulated arc therapy (VMAT) is an efficient form of radiotherapy used to deliver intensity-modulated radiotherapy beams. The aim of this study was to investigate the relative insensitivity of VMAT plan quality to gantry angle spacing (GS). Most previous VMAT planning and dosimetric work for GS resolution has been conducted for single arc VMAT. In this work, a quantitative comparison of dose–volume indices (DIs) was made for partial-, single- and double-arc VMAT plans optimized at 2°, 3° and 4° GS, representing a large variation in deliverable multileaf collimator segments. VMAT plans of six prostate cancer and six head-and-neck cancer patients were simulated for an Elekta SynergyS® Linac (Elekta Ltd, Crawley, UK), using the SmartArc™ module of Pinnacle³ TPS, (version 9.2, Philips Healthcare). All optimization techniques generated clinically acceptable VMAT plans, except for the single-arc for the head-and-neck cancer patients. Plan quality was assessed by comparing the DIs for the planning target volume, organs at risk and normal tissue. A GS of 2°, with finest resolution and consequently highest intensity modulation, was considered to be the reference, and this was compared with GS 3° and 4°. The differences between the majority of reference DIs and compared DIs were <2%. The metrics, such as treatment plan optimization time and pretreatment (phantom) dosimetric calculation time, supported the use of a GS of 4°. The ArcCHECK™ phantom–measured dosimetric agreement verifications resulted in a >95.0% passing rate, using the criteria for γ (3%, 3 mm). In conclusion, a GS of 4° is an optimal choice for minimal usage of planning resources without compromise of plan quality.

Total body irradiation’s dosimetric features by volumetric modulated ARC therapy method

Purpose To compare three different types of volumetric modulated arc therapy(VMAT) planning tecniques using Elekta Versa HD lineer accelerator to deliver total body irradition(TBI) treatment. Methods Five TBI patient’s treatment planning performed using Monaco5.1® treatment planning system with three different VMAT tecniques for each patient.First one was single arc VMAT tecnique, second one was double arc VMAT tecnique and third one was 2 fields arc VMAT tecnique for one isocentre.The VMAT-TBI tecnique consisted of three isocentres and three overlapping arcs.The prescribed dose was 95% of target volume receiving dose of 12 Gy.Mean dose to lung and kidney were restricted less than 9.0 Gy. Results An average total delivery time was determined 835 ± 86 seconds and an average monitor unit (MU)s was determined 2202 ± 254 MUs for double arc VMAT technique. This study demonstrates that double arc VMAT technique has got less MUs than other technique but an average delivery time is %17 more than single arc VMAT technique. When we compared organ at risk (OAR)s, we had less dose and better dose coverage to target with double arc VMAT technique. Conclusion The tecnique for TBI using VMAT was found feasible.The results show that dose coverage of target and OAR’s doses also depend significantly VMAT techniques. Based on the results we have decided to plan TBI in our clinic with double arc VMAT technique.

MO‐AB‐BRA‐01: A Global Level Set Based Formulation for Volumetric Modulated Arc Therapy

Purpose:The current clinical Volumetric Modulated Arc Therapy (VMAT) optimization is formulated as a non‐convex problem and various greedy heuristics have been employed for an empirical solution, jeopardizing plan consistency and quality. We introduce a novel global direct aperture optimization method for VMAT to overcome these limitations.Methods:The global VMAT (gVMAT) planning was formulated as an optimization problem with an L2‐norm fidelity term and an anisotropic total variation term. A level set function was used to describe the aperture shapes and adjacent aperture shapes were penalized to control MLC motion range. An alternating optimization strategy was implemented to solve the fluence intensity and aperture shapes simultaneously. Single arc gVMAT plans, utilizing 180 beams with 2° angular resolution, were generated for a glioblastoma multiforme (GBM), lung (LNG), and 2 head and neck cases—one with 3 PTVs (H&amp;N3PTV) and one with 4 PTVs (H&amp;N4PTV). The plans were compared against the clinical VMAT (cVMAT) plans utilizing two overlapping coplanar arcs.Results:The optimization of the gVMAT plans had converged within 600 iterations. gVMAT reduced the average max and mean OAR dose by 6.59% and 7.45% of the prescription dose. Reductions in max dose and mean dose were as high as 14.5 Gy in the LNG case and 15.3 Gy in the H&amp;N3PTV case. PTV coverages (D95, D98, D99) were within 0.25% of the prescription dose. By globally considering all beams, the gVMAT optimizer allowed some beams to deliver higher intensities, yielding a dose distribution that resembles a static beam IMRT plan with beam orientation optimization.Conclusions:The novel VMAT approach allows for the search of an optimal plan in the global solution space and generates deliverable apertures directly. The single arc VMAT approach fully utilizes the digital linacs’ capability in dose rate and gantry rotation speed modulation.Varian Medical Systems, NIH grant R01CA188300, NIH grant R43CA183390.

An investigation of the dose distribution effect related with collimator angle in volumetric arc therapy of prostate cancer.

To investigate the dose-volume variations of planning target volume (PTV) and organ at risks (OARs) in eleven prostate cancer patients planned with single and double arc volumetric modulated arc therapy (VMAT) when varying collimator angle. Single and double arc VMAT treatment plans were created using Monaco5.0® with collimator angle set to 0°. All plans were normalized 7600 cGy dose to the 95% of clinical target volume (CTV) volume. The single arc VMAT plans were reoptimized with different collimator angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°), and for double arc VMAT plans (0–0°, 15°–345, 30–330°, 45–315°, 60–300°, 75–285°, 90–270°) using the same optimization parameters. For the comparison the parameters of heterogeneity index (HI), dose-volume histogram and minimum dose to the 95% of PTV volume (D95 PTV) calculated and analyzed. The best plans were verified using 2 dimensional ion chamber array IBA Matrixx® and three-dimensional IBA Compass® program. The comparison between calculation and measurement were made by the γ-index (3%/3 mm) analysis. A higher D95 (PTV) were found for single arc VMAT with 15° collimator angle. For double arc, VMAT with 60–300° and 75–285° collimator angles. However, lower rectum doses obtained for 75–285° collimator angles. There was no significant dose difference, based on other OARs which are bladder and femur head. When we compared single and double arc VMAT's D95 (PTV), we determined 2.44% high coverage and lower HI with double arc VMAT. All plans passed the γ-index (3%/3 mm) analysis with more than 97% of the points and we had an average γ-index for CTV 0.36, for PTV 0.32 with double arc VMAT. These results were significant by Wilcoxon signed rank test statistically. The results show that dose coverage of target and OAR's doses also depend significantly on the collimator angles due to the geometry of target and OARs. Based on the results we have decided to plan prostate cancer patients in our clinic with double arc VMAT and 75°–285° collimator angles.

Dosimetric comparison between step-shoot intensity-modulated radiotherapy and volumetric-modulated arc therapy for upper thoracic and cervical esophageal carcinoma

To compare and analyze the dosimetric characteristics of volumetric modulated arc therapy (VMAT) vs step-shoot intensity-modulated radiation therapy (sIMRT) for upper thoracic and cervical esophageal carcinoma. Single-arc VMAT (VMAT1), dual-arc VMAT (VMAT2), and 7-field sIMRT plans were designed for 30 patients with upper thoracic or cervical esophageal carcinoma. Planning target volume (PTV) was prescribed to 50.4Gy in 28 fractions, and PTV1 was prescribed to 60Gy in 28 fractions. The parameters evaluated included dose homogeneity and conformality, dose to organs at risk (OARs), and delivery efficiency. (1) In comparison to sIMRT, VMAT provided a systematic improvement in PTV1 coverage. The homogeneity index of VMAT1 was better than that of VMAT2. There were no significant differences among sIMRT, VMAT1, and VMAT2 in PTV coverage. (2) VMAT1 and VMAT2 reduced the maximum dose of spinal cord as compared with sIMRT (p < 0.05). The rest dose-volume characteristics of OARs were similar. (3) Monitor units of VMAT2 and VMAT1 were more than sIMRT. However, the treatment time of VMAT1, VMAT2, and sIMRT was (2.0 ± 0.2), (2.8 ± 0.3), and (9.8 ± 0.8) minutes, respectively. VMAT1 was the fastest, and the difference was statistically significant. In the treatment of upper thoracic and cervical esophageal carcinoma by the AXESSE linac, compared with 7-field sIMRT, VMAT showed better PTV1 coverage and superior spinal cord sparing. Single-arc VMAT had similar target volume coverage and the sparing of OAR to dual-arc VMAT, with shortest treatment time and highest treatment efficiency in the 3 kinds of plans.

Pancreatic cancer planning: Complex conformal vs modulated therapies

To compare the roles of intensity-modulated radiation therapy (IMRT) and volumetric- modulated arc therapy (VMAT) therapy as compared to simple and complex 3-dimensional chemoradiotherpy (3DCRT) planning for resectable and borderline resectable pancreatic cancer. In all, 12 patients who received postoperative radiotherapy (8) or neoadjuvant concurrent chemoradiotherapy (4) were evaluated retrospectively. Radiotherapy planning was performed for 4 treatment techniques: simple 4-field box, complex 5-field 3DCRT, 5 to 6-field IMRT, and single-arc VMAT. All volumes were approved by a single observer in accordance with Radiation Therapy Oncology Group (RTOG) Pancreas Contouring Atlas. Plans included tumor/tumor bed and regional lymph nodes to 45Gy; with tumor/tumor bed boosted to 50.4Gy, at least 95% of planning target volume (PTV) received the prescription dose. Dose-volume histograms (DVH) for multiple end points, treatment planning, and delivery time were assessed. Complex 3DCRT, IMRT, and VMAT plans significantly (p < 0.05) decreased mean kidney dose, mean liver dose, liver (V30, V35), stomach (D10%), stomach (V45), mean right kidney dose, and right kidney (V15) as compared with the simple 4-field plans that are most commonly reported in the literature. IMRT plans resulted in decreased mean liver dose, liver (V35), and left kidney (V15, V18, V20). VMAT plans decreased small bowel (D10%, D15%), small bowel (V35, V45), stomach (D10%, D15%), stomach (V35, V45), mean liver dose, liver (V35), left kidney (V15, V18, V20), and right kidney (V18, V20). VMAT plans significantly decreased small bowel (D10%, D15%), left kidney (V20), and stomach (V45) as compared with IMRT plans. Treatment planning and delivery times were most efficient for simple 4-field box and VMAT. Excluding patient setup and imaging, average treatment delivery was within 10minutes for simple and complex 3DCRT, IMRT, and VMAT treatments. This article shows significant improvements in 3D plan performance with complex planning over the more frequently compared 3- or 4-field simple 3D planning techniques. VMAT plans continue to demonstrate potential for the most organ sparing. However, further studies are required to identify if dosimetric benefits associated with inverse optimized planning can be translated into clinical benefits and if these treatment techniques are value-added therapies for this group of patients with cancer.

Linac-based extracranial radiosurgery with Elekta volumetric modulated arc therapy and an anatomy-based treatment planning system: Feasibility and initial experience

We reported our initial experience in using Elekta volumetric modulated arc therapy (VMAT) and an anatomy-based treatment planning system (TPS) for single high-dose radiosurgery (SRS-VMAT) of liver metastases. This study included a cohort of 12 patients treated with a 26-Gy single fraction. Single-arc VMAT plans were generated with Ergo++ TPS. The prescription isodose surface (IDS) was selected to fulfill the 2 following criteria: 95% of planning target volume (PTV) reached 100% of the prescription dose and 99% of PTV reached a minimum of 90% of prescription dose. A 1-mm multileaf collimator (MLC) block margin was added around the PTV. For a comparison of dose distributions with literature data, several conformity indexes (conformity index [CI], conformation number [CN], and gradient index [GI]) were calculated. Treatment efficiency and pretreatment dosimetric verification were assessed. Early clinical data were also reported. Our results reported that target and organ-at-risk objectives were met for all patients. Mean and maximum doses to PTVs were on average 112.9% and 121.5% of prescribed dose, respectively. A very high degree of dose conformity was obtained, with CI, CN, and GI average values equal to 1.29, 0.80, and 3.63, respectively. The beam-on-time was on average 9.3 minutes, i.e., 0.36min/Gy. The mean number of monitor units was 3162, i.e., 121.6MU/Gy. Pretreatment verification (3%-3mm) showed an optimal agreement with calculated values; mean γ value was 0.27 and 98.2% of measured points resulted with γ < 1. With a median follow-up of 16 months complete response was observed in 12/14 (86%) lesions; partial response was observed in 2/14 (14%) lesions. No radiation-induced liver disease (RILD) was observed in any patients as well no duodenal ulceration or esophagitis or gastric hemorrhage. In conclusion, this analysis demonstrated the feasibility and the appropriateness of high-dose single-fraction SRS-VMAT in liver metastases performed with Elekta VMAT and Ergo++ TPS. Preliminary clinical outcomes showed a high rate of local control and minimum incidence of acute toxicity.