Elekta Volumetric Modulated Arc Therapy Research Articles

Dosimetric evaluation of modern radiation therapy techniques for left breast in deep-inspiration breath-hold

PurposeThe dosimetric differences between four radiation therapy techniques for left sided whole breast irradiation were evaluated side by side in the same patient population. MethodsRadiotherapy treatment plans were retrospectively created with Accuray TomoDirect (TD), Elekta Volumetric Modulated Arc Therapy (E-VMAT), Varian RapidArc (RA) and Field-in-field (FinF) technique for 20 patients, who had received left breast irradiation during deep-inspiration breath-hold. Dose characteristics of planning target volume and organs at risk were compared. ResultsThe E-VMAT, TD and RA treatment plans had higher target coverage (V95%) than FinF plans (97.7–98.3% vs. 96.6%). The low-dose spillage to contralateral breast and lung was smaller with FinF and TD (mean 0.1 and 0.3 Gy) compared to E-VMAT and RA (mean 0.6 and 0.9 Gy). E-VMAT, RA and TD techniques were more effective than FinF in sparing left anterior descending artery (mean 4.0, 4.2 and 4.7 Gy vs. 6.1 Gy, respectively). ConclusionsIn whole breast irradiation TD, E-VMAT and RA plans generated in this study achieved higher dose coverage and sparing of organs from the high dose in the vicinity of the PTV. The advantage of calculated FinF plans is the lowest dose on contralateral organs. The choice of the technique used should be weighted by each institution taking into account the dose characteristics of each technique and its fit with patient anatomy bearing in mind the increased workload of using modulated techniques and the increased beam on time.

Dosimetric Comparison and Evaluation of 4 Stereotactic Body Radiotherapy Techniques for the Treatment of Prostate Cancer.

Purpose:The aim of this study was to compare dosimetric characteristics, monitor unit, and delivery efficiency of 4 different stereotactic body radiotherapy techniques for the treatment of prostate cancer.Methods:This study included 8 patients with localized prostate cancer. Dosimetric assets of 4 delivery techniques for stereotactic body radiotherapy were evaluated: robotic CyberKnife, noncoplanar intensity-modulated radiotherapy, and 2 intensity-modulated arc therapy techniques (RapidArc and Elekta volumetric-modulated arc therapy). All the plans had equal treatment margins and a prescription dose of 35 Gy in 5 fractions.Results:Statistically significant differences were observed in homogeneity index and mean doses of bladder wall and penile bulb, all of which were highest with CyberKnife. No significant differences were observed in the mean doses of rectum, with values of 15.2 ± 2.6, 13.3 ± 2.6, 13.1 ± 2.8, and 13.8 ± 1.6 Gy with CyberKnife, RapidArc, volumetric-modulated arc therapy, and noncoplanar intensity-modulated radiotherapy, respectively. The highest dose conformity was realized with RapidArc. The dose coverage of the planning target volume was lowest with noncoplanar intensity-modulated radiotherapy. Treatment times and number of monitor units were largest with CyberKnife (on average 34.0 ± 5.0 minutes and 8704 ± 1449 monitor units) and least with intensity-modulated arc therapy techniques (on average 5.1 ± 1.1 minutes and 2270 ± 497 monitor units).Conclusion:Compared to CyberKnife, the RapidArc, volumetric-modulated arc therapy, and noncoplanar intensity-modulated radiotherapy produced treatment plans with similar dosimetric quality, with RapidArc achieving the highest dose conformity. Overall, the dosimetric differences between the studied techniques were marginal, and thus, the choice of the technique should rather focus on the delivery accuracies and dose delivery times.

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.

Left-sided breast cancer irradiation using rotational and fixed-field radiotherapy

The 3-dimensional conformal radiotherapy (3DCRT) technique is the standard for breast cancer radiotherapy. During treatment planning, not only the coverage of the planning target volume (PTV) but also the minimization of the dose to critical structures, such as the lung, heart, and contralateral breast tissue, need to be considered. Because of the complexity and variations of patient anatomy, more advanced radiotherapy techniques are sometimes desired to better meet the planning goals. In this study, we evaluated external-beam radiation treatment techniques for left breast cancer using various delivery platforms: fixed-field including TomoDirect (TD), static intensity-modulated radiotherapy (sIMRT), and rotational radiotherapy including Elekta volumetric-modulated arc therapy (VMAT) and tomotherapy helical (TH). A total of 10 patients with left-sided breast cancer who did or did not have positive lymph nodes and were previously treated with 3DCRT/sIMRT to the entire breast were selected, their treatment was planned with Monaco VMAT, TD, and TH. Dosimetric parameters including PTV coverage, organ-at-risk (OAR) sparing, dose-volume histograms, and target minimum/maximum/mean doses were evaluated. It is found that for plans providing comparable PTV coverage, the Elekta VMAT plans were generally more inhomogeneous than the TH and TD plans. For the cases with regional node involvement, the average mean doses administered to the heart were 9.2 (± 5.2) and 8.8 (± 3.0)Gy in the VMAT and TH plans compared with 11.9 (± 6.4) and 11.8 (± 9.2)Gy for the 3DCRT and TD plans, respectively, with slightly higher doses given to the contralateral lung or breast or both. On average, the total monitor units for VMAT plans are 11.6% of those TH plans. Our studies have shown that VMAT and TH plans offer certain dosimetric advantages over fixed-field IMRT plans for advanced breast cancer requiring regional nodal treatment. However, for early-stage breast cancer fixed-field radiotherapy is potentially more beneficial in terms of OAR sparing.

Marvin: an anatomical phantom for dosimetric evaluation of complex radiotherapy of the head and neck

We report on the design of Marvin, a Model Anatomy for Radiotherapy Verification and audit In the head and Neck and present results demonstrating its use in the development of the Elekta volumetric modulated arc therapy (VMAT) technique at the Christie, and in the audit of TomoTherapy and Varian RapidArc at other institutions. The geometry of Marvin was generated from CT datasets of eight male and female patients lying in the treatment position, with removable inhomogeneities modelling the sinuses and mandible. A modular system allows the phantom to be used with a range of detectors, with the locations of the modules being based on an analysis of a range of typical treatment plans (27 in total) which were mapped onto the phantom geometry. Results demonstrate the use of Gafchromic EBT2/EBT3 film for measurement of relative dose in a plane through the target and organs-at-risk, and the use of a small-volume ionization chamber for measurement of absolute dose in the target and spinal cord. Measurements made during the development of the head and neck VMAT protocol at the Christie quantified the improvement in plan delivery resulting from the installation of the Elekta Integrity upgrade (which permits an effectively continuously variable dose rate), with plans delivered before and after the upgrade having 88.5 ± 9.4% and 98.0 ± 2.2% respectively of points passing a gamma analysis (at 4%, 4 mm, global). Audits of TomoTherapy and Varian RapidArc neck techniques at other institutions showed a similar quality of plan delivery as for post-Integrity Elekta VMAT: film measurements for both techniques had >99% of points passing a gamma analysis at the clinical criteria of 4%, 4 mm, global, and >95% of points passing at tighter criteria of 3%, 3 mm, global; and absolute dose measurements in the PTV and spinal cord were within 1.5% and 3.5% of the planned doses respectively for both techniques. The results demonstrate that Marvin is an efficient and effective means of assessing the quality of delivery of complex radiotherapy in the head and neck, and is a useful tool to assist development and audit of these techniques.

VMATにおけるEPID Dosimetryの検討

Recently electronic portal image devices (EPIDs) have been widely used for quality assurance and dose verification. However there are no reports describing EPID dosimetry for Elekta volumetric modulated arc therapy (VMAT). We have investigated EPID dosimetry during VMAT delivery using a commercial software EPIDose with an Elekta Synergy linac. Dose rate dependence and the linac system sag during gantry rotation were measured. Gamma indices were calculated between measured doses using an EPID and calculation made by a treatment planning system for prostate VMAT test plans. The results were also compared to gamma indices using films and a two-dimensional detector array, MapCHECK2. The pass rates of the gamma analysis with a criterion of 3% and 2 mm for the three methods were over 96% with good consistency. Our results have showed that EPID dosimetry is feasible for Elekta VMAT.

Single-Arc Volumetric Modulated Arc Therapy Planning for Left Breast Cancer and Regional Nodes

We have successfully created a single arc volumetric modulated arc therapy (VMAT) plan for treating post-surgical left breast/chest wall and regional nodes using Elekta multileaf collimator (MLC). Dose volume histograms (DVHs) were compared between the VMAT plans and conventional tangential beam plans using a field-in-field technique, leading to significant DVH advantages in the VMAT plans. The difference between Elekta VMAT and Varian RapidArc due to different MLC designs was discussed in terms of the number of arcs required to cover a large target, highlighting a single arc capability of Elekta VMAT for a large target volume which may be less sensitive to unexpected organ motion during dose delivery.

MLC tracking for Elekta VMAT: a modelling study

A model has been developed to simulate volumetric modulated arc therapy (VMAT) delivery for Elekta control systems. The model was experimentally validated for static-tumour VMAT delivery and has been applied to the investigation of motion compensation with dynamic multileaf collimator (dMLC) delivery tracking for a series of VMAT lung treatment plans at various control point spacings for five patients. The relative increase in treatment time with dMLC tracking was calculated for four 1D rigid-body motion trajectories, and the effect of the control point spacing, the MLC leaf speed and an increased number of dose levels on the dMLC tracking delivery time evaluated. It has been observed that a faster leaf speed is advantageous for motion trajectories with shorter time periods and larger amplitudes. The accuracy of dMLC tracking was found to increase with a decreased control point spacing and is dependent on the amplitude and time period of the motion trajectory of the target. dMLC tracking is shown to be a promising emerging technology which can confer advantage over breath-hold motion-compensation techniques which more drastically reduce the efficiency of VMAT and are more invasive for the patient.

A VMAT planning solution for prostate patients using a commercial treatment planning system

Volumetric modulated arc therapy (VMAT) is a rotational delivery technique which offers the potential of improved dose distributions and shorter treatment times when compared to fixed-beam intensity-modulated radiation therapy (IMRT). This note describes the use of an existing treatment planning system (Philips Pinnacle3 v.8.0), supplemented by in-house software, to produce a single-arc VMAT prostate plan. While a number of planning systems for the Elekta VMAT platform are commercially available, the use of an in-house solution has allowed more detailed investigations of VMAT planning, as well as greater control over the optimization process. The solution presented here begins with a static step-and-shoot IMRT approach to provide initial segment shapes, which are then modified and sequenced into 60 equally spaced control points in a 360° arc. Dose–volume histogram comparisons demonstrate that this VMAT planning method offers multiple dose level target coverage comparable to that from a standard IMRT approach. The VMAT plans also show superior sparing of critical structures such as the rectum and bladder. Delivery times are reduced with the VMAT method, and the results of dosimetric verification, resilience and repeatability tests indicate that the solution is robust.

Comparison of Elekta VMAT with helical tomotherapy and fixed field IMRT: Plan quality, delivery efficiency and accuracy

Helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) are arc-based approaches to IMRT delivery. The objective of this study is to compare VMAT to both HT and fixed field IMRT in terms of plan quality, delivery efficiency, and accuracy. Eighteen cases including six prostate, six head-and-neck, and six lung cases were selected for this study. IMRT plans were developed using direct machine parameter optimization in the Pinnacle3 treatment planning system. HT plans were developed using a Hi-Art II planning station. VMAT plans were generated using both the Pinnacle3 SmartArc IMRT module and a home-grown arc sequencing algorithm. VMAT and HT plans were delivered using Elekta's PreciseBeam VMAT linac control system (Elekta AB, Stockholm, Sweden) and a TomoTherapy Hi-Art II system (TomoTherapy Inc., Madison, WI), respectively. Treatment plan quality assurance (QA) for VMAT was performed using the IBA MatriXX system while an ion chamber and films were used for HT plan QA. The results demonstrate that both VMAT and HT are capable of providing more uniform target doses and improved normal tissue sparing as compared with fixed field IMRT. In terms of delivery efficiency, VMAT plan deliveries on average took 2.2 min for prostate and lung cases and 4.6 min for head-and-neck cases. These values increased to 4.7 and 7.0 min for HT plans. Both VMAT and HT plans can be delivered accurately based on their own QA standards. Overall, VMAT was able to provide approximately a 40% reduction in treatment time while maintaining comparable plan quality to that of HT.

SU‐FF‐T‐141: Initial Clinical Experience with Elekta VMAT

Purpose: Elekta recently introduced a new delivery control system called PreciseBeam® VMAT that provides dynamic delivery capabilities including volumetric modulated arc therapy (VMAT). VMAT is a rotational approach to the delivery of IMRT that can be delivered on a conventional linear accelerator. In this study, we report on our initial clinical experience with Elekta VMAT. Method and Materials: The PreciseBeam® VMAT control system has been installed on an Elekta Synergy and an Elekta Precise linear accelerator in our clinic. We have tested the delivery system in conjunction with three inverse planning solutions: (1) an in‐house arc sequencing algorithm that translates optimized fluence maps into deliverable VMAT plans, (2) the Ergo++ planning system that utilizes anatomy based inverse planning, and (3) the SmartArc planning module in the Pinnacle3 treatment planning system. The optimized treatment plans have been verified using phantom irradiations with the IBA MatriXX 2D ion chamber array embedded in a MULTcube phantom. Results: Using our arc‐sequencing algorithm for VMAT planning, we treated our first Elekta VMAT patient under an institutional review board (IRB) protocol in July 2008. In January 2009, we treated our first Elekta VMAT case planned using Ergo++. Our initial focus was on more simple concave targets. More recently, we have opened up VMAT for all clinical sites. Conclusion: Elekta's Precise Beam® VMAT control system can safely and efficiently delivery highly complex VMAT treatment plans. For simple targets such as prostate, pancreatic, and lung cases, single arc VMAT plans are sufficient and be typically delivered in less than 3 minutes. For more complex cases such as head‐and‐neck, the use of multiple arcs provides a dosimetric benefit and plans typically take between 4 and 6 minutes to deliver.Research sponsored in part through a grant from Elekta.

SU-FF-T-247: Influence of Gantry Angle, Multi-Leaf Collimator (MLC), and Jaw Position Errors to Dose Distribution in Volumetric Modulated Arc Therapy (VMAT)

Purpose: To establish a machine quality assurance procedure during VMAT delivery.Method and Materials: A single‐arc VMAT plan with 73 control points (CP) and 5‐degree gantry angle spacing for a prostate cancer patient has been created by ERGO++ TPS (Elekta, 3DLine). Actual multi‐leaf collimator(MLC) and jaw positions, gantry angle and dose rates during prostate VMAT delivery have been recorded in every 0.25 seconds. The dose re‐calculation using these recorded data has been performed and compared with the original plan using the gamma index. Calculated dose distributions in the TPS were also compared with irradiated GafChromic films placed inside a plastic phantom on axial, sagittal, and coronal isocenter planes using the same index. Result: Typical peak errors of MLC position, jaw position, and gantry angle were 3 degrees, 0.6 mm, and 1 mm, respectively. The cumulative MU error was practically negligible because Elekta VMAT delivery was based on MU based servo control. Recalculated dose and original plan agreed well under 2 %–2 mm gamma index criteria. Even in a plan that requires rapid motion of MLCs and jaws, their dynamical parameters were sufficiently well controlled, which was confirmed by comparing film dosimetry and dose calculation with sufficiently small gantry‐angle resampling. Conclusions: Machine quality assurance for VMAT delivery has been performed with a satisfied result.

SU‐FF‐T‐123: Comparison of Elekta VMAT with Tomotherapy: Plan Quality, Delivery Efficiency and Accuracy

Purpose: Helical Tomotherapy and Volumetric Modulated Arc Therapy (VMAT) are arc‐based approaches to IMRT delivery. The objective of this study is to compare VMAT and helical tomotherapy in terms of plan quality, delivery efficiency and accuracy. Method and Materials: Twelve cases including 4 prostate, 4 head &amp; neck, and 4 lung were selected for this study. Tomotherapy plans were developed using a Hi‐Art II planning station. VMAT plans were generated using both the Pinnacle3 SmartArc IMRT module and our home‐grown arc‐sequencing algorithm. The same set of CT images and contours were used for both VMAT and tomotherapy plans. The percentage volume of the PTV that received 95% of the prescribed dose (V95) was used to compare the target coverage. VMAT and tomotherapy plans were delivered using Elekta's PreciseBeam VMAT® control system and TomoTherapy HI_ART II system, respectively. VMAT plan QA was performed using the IBA MatriXX system, and an ion‐chamber and films were used for tomotherapy plan QA. Results: For prostate cases, VMAT provided slightly improved V95 (98.1% vs. 97.6%) and lower dose to the rectum and the bladder. Tomotherapy attained slightly higher target coverage and uniformity in HN cases, with improved V95 (98.9% vs. 98.3%) and reduced standard deviation of the PTV dose (1.2 Gy vs. 1.4 Gy). In lung cases, VMAT provided similar target coverage with improved sparing of the cord and total lung. In terms of delivery efficiency, VMAT plans on average took 2.2 minutes for prostate and lung cases, and 5.4 minutes for HN cases. These values increase to 4.8 and 7.6 minutes for tomotherapy plans. Both VMAT and tomotherapy plans can be delivered accurately based on their own QA standard. Conclusion: VMAT is able to provide ∼40% reduction in treatment time while maintaining comparable plan quality to that of helical tomotherapy. Research supported by Elekta.