Volumetric Arc Therapy Technique Research Articles

Dosimetric evaluation of volumetric modulated arc therapy for bilateral breast carcinoma

Introduction Patients with bilateral breast carcinoma are usually treated with two sets of tangential beams with different iso-centers. Single iso-center Volumetric Arc Therapy (VMAT) treatment plan can give several logistical advantages, avoiding also the overlapping of tangential fields. Purpose Perform a dosimetric study to evaluate the enforcement of Volumetric Modulated Arc Therapy (VMAT) on bilateral breast carcinoma radiotherapy. Materials and methods Treatment plans for 5 patients, previously treated with 50.4 Gy/28 fractions, using 3D Conformal Radiotherapy planned with a standard tangential field technique, were replanned with VMAT technique. The PTV used in the optimization was expanded 2 cm to the external direction, in order to correct respiratory movement. VMAT plans were optimized with 2-arcs, 3-arcs and 4-arcs, all plans using one iso-center, avoiding angles between 140° and 220°. Results VMAT presents evident logistical advantages for bilateral breast treatment; one iso-center reduces patient setup time, and treatment time. 4-arcs plan and 3-arcs plan had similar dosimetric results, being 2-arcs plan the worst solution. Comparing to the standard tangential field technique, VMAT had better PTV dose coverage (Conformity Index improved in a 13%), avoiding hotspots, which can appear on 3DCRT standard tangential field technique. VMAT also reduces high doses to OARs. On the other hand, VMAT increase lower doses to the whole body, increasing slightly the mean heart dose. Conclusion VMAT technique showed logistical advantages for the treatment of bilateral breast carcinoma, but also dosimetric improvements. 3DCRT had greater high doses to OARs, but save lower doses to the whole body.

17 - Treatment of breast cancer with lymph nodes by volumetric arc therapy (VMAT): Pretreatment and in vivo dosimetry

Introduction: The aim of this study is to clinically implement the COMPASS 3D dosimetry and the MOSFET for pretreatment quality assurance and in vivo dosimetry of breasts cancers treatments by volumetric modulated arc therapy (VMAT). Methods: For this study, 10 patients treated with VMAT technique for breast cancer with lymph nodes were randomly selected. The treatment plans were verified using the COMPASS system with MatriXXEvolution and the collapse convolution superposition algorithm v3.1.6. This system allows on one hand independent verification of dosimetry with a 3D calculation using the patient’s scan, and on the other hand 3D verification of machines dose delivery. In both cases, histograms dose volumes and 3D gamma index were used, in order to evaluate the dose difference between the measurement/ calculation of the COMPASS and the treatment planning system calculation (Eclipse AAA v10.0.28, VARIAN®). For each patient treated with this technique, in vivo dosimetry with MOSFETs was performed during the first session. The detectors were calibrated for measurement of skin dose. Results: Regarding target volumes (lymph nodes and breast), deviations of the mean dose in the calculation of Eclipse TPS and COMPASS, respectively for the 3D independent calculation and measurement is 0.44 ± 1.83% and −0.72 ± 3.07%; and similarly for the parameters D1 (cGy) 3D independent calculation and measurement are −0.37 ± 0.68% et −0.70 ± 1.18%. Significant differences were found on D99 (cGy) parameter, 3D independent calculation: 11.32 ± 22.11%, and for the measurement: −8.69 ± 24.68%. These differences were well within the clinically tolerance level of ±5%, when analyses are done with the breast tumor volume reframed 5 mm from skin. For risk organs (heart, homolateral and contralateral lung), deviations of the mean dose in the calculation of Eclipse TPS and COMPASS for 3D independent calculation are −2.6 ± 1.92 and for measurement are −2 ± 5.6%. Average 3D gammas for target volumes and organ at risks of patients were less than 0.4. Finally, differences between the dose calculated by the TPS and measurement of MOSFETs are −0.23 ± 2.51%. These very good findings result from the fact that measurement are done at the depth of about 3 mm under the skin. Conclusion: The results of this study show that the COMPASS with MatriXXEvolution system and MOSFETs can be used for quality assurance of VMAT treatments in breast cancer.

Clinical Application of a Hybrid Volumetric Arc Therapy Technique for Locally Advanced Lung Cancer

Clinical Application of a Hybrid Volumetric Arc Therapy Technique for Locally Advanced Lung Cancer

SU-E-T-155: Evaluating IMRT and Volumetric Arc Therapy Patient-Specific Quality Assurance by Using Octavius 4D System

Purpose: The goal of this study was to perform and evaluate pre-treatment patient specific verifications of IMRT and volumetric arc therapy(VMAT) plans by using a new, commercially available 2D array Octavius 4D system. Methods: The OCTAVIUS 4D system and its accompanying software (VERISOFT) by PTW were evaluated for the accuracy of the dose reconstruction for patient specific QA. (1)Commissioning of Octavius 4D system for IMRT and VMAT technique was by following the tests suggested in the AAPM TG119 protocol, in order to give a benchmark for optimization process and the calculation accuracy. (2) Verification of total 87 clinical IMRT and VMAT plans, 50 IMRT and 37 VMAT plans were used for the comparison. Comparing treatment planning system calculated versus measured dose using local gamma index analysis (3%, 3 mm criteria). Results: (1)Agreement between calculated and planar doses measured by using Octavius 4D system. It was very good for both modalities. (2)Verifications of pre-treatment clinical plans, showed an average gamma evaluation passing ratio of 97.3±1.9% for 50 IMRT cases and an average pass ratio of 94.94±2.43% for 37 VMAT cases. 2D gamma evaluation for IMRT plans showed 96.82%, 97.5%, 97.93% and 96.94% passing results for head and neck, chest, abdomen and Pelvis sites. Volumetric global gamma evaluation for VMAT plans showed 93.8%, 94.66% and 96.27% passing results for chest, abdomen and Pelvis sites respectively. Conclusion: The TG119 results suggest that it is appropriate to apply patient-specific QA action levels derived from IMRT to VMAT technique. Octavius 4D system together with 2D array 729 is an appropriate and efficient tool for IMRT and VMAT patient specific QA and can potentially improve the data collection and analysis. Further studies will focus on more complex VMAT plans (head and neck treatment plans).

SU‐E‐T‐522: A Multi‐Isocenter VMAT Technique for Cranio‐Spinal Irradiation

Purpose:Develop a matching VMAT field technique and investigate planning feasibility for treating the entire central nervous system (CNS) using Cranio‐Spinal Irradiation (CSI) .Methods:Two patients diagnosed with acute myeloid leukemia (AML) presented with CNS involvement, received CSI, and were included in this study. The patients were treated with the traditional CSI technique: prone position, opposing lateral brain fields, two posterior fields (upper and lower spine), and 5mm junction shifts to improve dose uniformity. The patients were retrospectively re‐planned using volumetric arc therapy (VMAT). The spine and brain were contoured to create the clinical target volume (CTV) as well as normal tissues including kidneys, lung and heart for optimization. Three isocenters were used for planning: brain, upper and lower spine. The beams were allowed to overlap by approximately 10cm. Entire 360 degree rotations were used for the brain fields and posterior 120 degree arcs were used for the spine fields. The dosimetric coverage of the target between the VMAT and traditional plans was compared, as well as the dose to normal tissues.Results:Both VMAT plans achieved improved dose uniformity in the CTV (standard deviation < 2%), and reduced hot spots (<110%). Dose to the heart was reduced, with the V10 being 12.7% and 28.2%, compared to 44.6% and 50.2%, respectively, for the traditional plan. Dose to the total lung V5 increased for the VMAT plans for both patients (21.6% and 27.8% compared to 12% and 13% respectively). The results for the kidneys were mixed with the mean dose increasing for one patient and decreasing for the other .Conclusion:The efficacy of planning CSI treatments using a matching VMAT technique was demonstrated. The developed technique has the potential to improve dose uniformity to the target while at the same time reduce the risk of under or over dosing the spine.

Application of AAPM TG 119 to volumetric arc therapy (VMAT)

The purpose of this study was to create AAPM TG 119 benchmark plans for volumetric arc therapy (VMAT) and to compare VMAT plans with IMRT plan data. AAPM TG 119 proposes a set of test clinical cases for testing the accuracy of IMRT planning and delivery system. For these test cases, we generated two treatment plans, the first plan using 7–9 static dMLC IMRT fields and a second plan utilizing one‐ or two‐arc VMAT technique. Dose optimization and calculations performed using 6 MV photons and Eclipse treatment planning system. Dose prescription and planning objectives were set according to the TG 119 goals. Plans were scored based on TG 119 planning objectives. Treatment plans were compared using conformity index (CI) for reference dose and homogeneity index (HI) (for D5‐D95). F or test cases prostate, head‐and‐neck, C‐shape and multitarget prescription dose are 75.6 Gy, 50.4 Gy, 50 Gy and 50 Gy, respectively. VMAT dose distributions were comparable to dMLC IMRT plans. Our planning results matched TG 119 planning results. For treatment plans studied, conformity indices ranged from 1.05–1.23 (IMRT) and 1.04–1.23 (VMAT). Homogeneity indices ranged from 4.6%–11.0% (IMRT) and 4.6%–10.5% (VMAT). The ratio of total monitor units necessary for dMLC IMRT to that of VMAT was in the range of 1.1–2.0. AAPM TG 119 test cases are useful to generate VMAT benchmark plans. At preclinical implementation stage, plan comparison of VMAT and IMRT plans of AAPM TG 119 test case allowed us to understand basic capabilities of VMAT technique.PACS number: 87.55.Qr

Dosimetric Study of Current Treatment Options for Radiotherapy in Retinoblastoma

To determine the best treatment technique for patients with retinoblastoma requiring radiotherapy to the whole eye. Treatment plans for 3 patients with retinoblastoma were developed using 10 radiotherapy techniques including electron beams, photon beam wedge pair (WP), photon beam three-dimensional conformal radiotherapy (3D-CRT), fixed gantry intensity-modulated radiotherapy (IMRT), photon volumetric arc therapy (VMAT), fractionated stereotactic radiotherapy, and helical tomotherapy (HT). Dose-volume analyses were carried out for each technique. All techniques provided similar target coverage; conformity was highest for VMAT, nine-field (9F) IMRT, and HT (conformity index [CI] = 1.3) and lowest for the WP and two electron techniques (CI = 1.8). The electron techniques had the highest planning target volume dose gradient (131% of maximum dose received [D(max)]), and the CRT techniques had the lowest (103% D(max)) gradient. The volume receiving at least 20 Gy (V(20Gy)) for the ipsilateral bony orbit was lowest for the VMAT and HT techniques (56%) and highest for the CRT techniques (90%). Generally, the electron beam techniques were superior in terms of brain sparing and delivered approximately one-third of the integral dose of the photon techniques. Inverse planned image-guided radiotherapy delivered using HT or VMAT gives better conformity index, improved orbital bone and brain sparing, and a lower integral dose than other techniques.

SU‐E‐T‐820: Comparison of VMAT and IMRT for Stereotactic Body Radiation Therapy (SBRT) of the Adrenal Metastases

Purpose: This study is to compare volumetric arc therapy (VMAT) with intensity modulated radiotherapy (IMRT) for stereotactic body radiation therapy (SBRT) of the adrenal metastases. Methods: For 13 patients who have completed SBRT with conventional IMRT technique, new VMAT plans were generated. Plans were optimized with the aim to protect organs at risk and spare healthy tissue while enforcing highly conformal target coverage of clinical prescriptions. IMRT and VMAT plans were designed on Pinnacle3 Version 9.0. All treatment plans were delivered on Elektaˈs Synergy machine. Plan quality and treatment efficiency for VMAT vs. conventional IMRT were evaluated. Results: all plans designed for conventional IMRT and VMAT techniques fulfilled the specific dose constraints. Both VMAT and IMRT resulted in equivalent target coverage but VMAT had an improved conformity index (CI=0.83±0.02 for VMAT and 0.81±0.02 for IMRT, p=0.025). Normal tissue sparing was comparable in both treatment techniques. The mean dose of the unilateral kidney was 10.5±4.6Gy for VMAT and 10.8±4.8Gy for IMRT (p=0.11). The VMAT reduced the total MUs per fraction by 13.1% (1192±261MU for VMAT and 1371±224MU for IMRT, p<0.001). The treatment delivery time for VMAT was 185± 18 seconds per fraction, while IMRT plans presented higher values with an average of 572±79 seconds. Conclusions: For equivalent target coverage and comparable normal tissue sparing, VMAT plans presented improvement in conformity index, and VMAT demonstrates significantly reduced treatment time and fewer MUs to achieve comparable dosimetric plans.

Total Marrow Irradiation With RapidArc Volumetric Arc Therapy

To develop a volumetric arc therapy (VMAT)-total marrow irradiation (TMI) technique for patients with hematologic malignancies. VMAT planning was performed for 6 patients using RapidArc technology. The planning target volume consisted of all the bones in the body from the head to the mid-femur, excluding the extremities, except for the humerus, plus a 3.0-mm margin. The organs at risk included the lungs, heart, liver, kidneys, bowels, brain, eyes, and oral cavity. The VMAT-TMI technique consisted of three plans: the head and neck, the chest, and the pelvis, each with three 330° arcs. The plans were prescribed to ensure, at a minimum, 95% planning target volume dose coverage with the prescription dose (percentage of volume receiving dose of ≥12 Gy was 95%). The treatments were delivered and verified using MapCheck and ion chamber measurements. The VMAT-TMI technique reported in the present study provided comparable dose distributions with respect to the fixed gantry linear accelerator intensity-modulated TMI. RapidArc planning was less subjective and easier, and, most importantly, the delivery was more efficient. RapidArc reduced the treatment delivery time to approximately 18 min from 45 min with the fixed gantry linear accelerator intensity-modulated TMI. When the prescription dose coverage was reduced to 85% from 95% and the mandible and maxillary structures were not included in the planning target volume as reported in a tomotherapy study, a considerable organ at risk dose reduction of 4.2-51% was observed. The average median dose for the lungs and lenses was reduced to 5.6 Gy from 7.2 Gy and 2.4 Gy from 4.5 Gy, respectively. The RapidArc VMAT technique improved the treatment planning, dose conformality, and, most importantly, treatment delivery efficiency. The results from our study suggest that the RapidArc VMAT technology can be expected to facilitate the clinical transition of TMI.

RapidArc treatment verification in 3D using polymer gel dosimetry and Monte Carlo simulation

The aim of this study was to verify the advanced inhomogeneous dose distribution produced by a volumetric arc therapy technique (RapidArc™) using 3D gel measurements and Monte Carlo (MC) simulations. The TPS (treatment planning system)-calculated dose distribution was compared with gel measurements and MC simulations, thus investigating any discrepancy between the planned dose delivery and the actual delivery. Additionally, the reproducibility of the delivery was investigated using repeated gel measurements. A prostate treatment plan was delivered to a 1.3 liter nPAG gel phantom using one single arc rotation and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using a 1.5 T scanner. The MC dose distributions were calculated using the VIMC-Arc code. The relative absorbed dose differences were calculated voxel-by-voxel, within the volume enclosed by the 90% isodose surface (VOI90), for the TPS versus gel and TPS versus MC. The differences between the verification methods, MC versus gel, and between two repeated gel measurements were investigated in the same way. For all volume comparisons, the mean value was within 1% and the standard deviation of the differences was within 2.5% (1SD). A 3D gamma analysis between the dose matrices were carried out using gamma criteria 3%/3 mm and 5%/5 mm (% dose difference and mm distance to agreement) within the volume enclosed by the 50% isodose surface (VOI50) and the 90% isodose surface (VOI90), respectively. All comparisons resulted in very high pass rates. More than 95% of the TPS points were within 3%/3 mm of both the gel measurement and MC simulation, both inside VOI50 and VOI90. Additionally, the repeated gel measurements showed excellent consistency, indicating reproducible delivery. Using MC simulations and gel measurements, this verification study successfully demonstrated that the RapidArc™ plan was both accurately calculated and delivered as planned.

RapidArc™ treatment verification using polymer gel dosimetry

The aim of this study was to verify a novel volumetric arc therapy technique, RapidArc". Polymer gel dosimetry system was used to measure the advanced inhomogeneous 3D dose distribution produced using the technique RapidArc". A preclinical installation of the novel beam delivery approach was set up on a linear accelerator at Rigshospitalet in Copenhagen. A prostate treatment plan was delivered to a 1.3 l nPAG gel phantom using one single arc rotation from 200 to 160 degrees, and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using the 1.5 T scanner and MATLAB was used for image processing and 3D rendering. The difference in relative absorbed dose between the treatment planning system (TPS) and gel measurement was calculated voxel by voxel within the 80% and the 95% isodose volume, respectively. Measurements agreed well with the TPS within the treated volume. Within both isodose volumes 90% of the voxels showed a deviation less or equal to 5%. This study shows that the 3D gel dosimetry system is a useful tool for dose verification of advanced treatment delivery techniques.