2D-ARRAY Seven29 Research Articles

Comparison of Gamma Index Passing Rate in Several Treatment Planning System Algorithms

The verification of dose calculation algorithm in a new Treatment Planning System (TPS) can be evaluated by comparing the passing rate of the gamma index analysis of the evaluated algorithm and the clinically implemented algorithms. In the present investigation, the gamma index passing rates was investigated as the reference data in the verification of the new three-dimensional TPS. The algorithms which are used in this study are Pencil Beam Convolution (PBC) version 11.0.31 and Anisotropic Analytical Algorithm (AAA) version 11.0.31 in Eclipse v.11 TPS, and Fast Convolution (FC), Adaptive Convolution (AC), and Collapsed-Cone Convolution (CCC) in Pinnacle 3 v.7.6c TPS. The 6 MV X-ray beam configurations were varied in the depth of measurement points, field sizes, source-to-surface distances, and wedge angles. The dose measurement was done using MatriXX Evolution and PTW 2D-array seven29. Then, OmniPro ImRT and Verisoft 3.1 software were chosen to analyze the gamma index from varied gamma criteria (3 %/3mm, 2 %/3mm, 3 %/2mm, and 2 %/2mm). Overall, the passing rate of AAA is the highest rate obtained of all algorithms. For gamma criterion of 2 %/2mm, the passing rate of AAA was 93.18 % ± 7.21 %, the passing rate of PBC was 89.76 % ± 7.21 %, and the passing rate of convolution algorithms was 76.84 % ± 11.10 %. 800x600 Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif;}

Comparative Study and Dose Evaluation of Photon Beam for water phantom,2D-array and Treatment Planning System in Small Field sizes

This study assessed the clinical usefulness of the 2D-Array Seven29 ,which may compensate for the of the water phantom, by comparing the radiological doses between the two depending on five field sizes. The experimental equipment used was a linear accelerator for medical use, treatment planning system (TPS) , water phantom, 2D-Array, solid phantoms,( Semiflex , Pinpoint) types ion chamber and electrometer. The field size was 10 x 10 cm2 and the radiation energies of the photon beam were 6 MV and 15 MV, The field size involved (1×1, 2×2, 3×3, 4×4, 5×5,) for each energy. The relative deviation ratio of the TPS to both chamber in water phantom and TPS to 2darray in the solid phantom was calculated. The measured doses in standard phantom were less than the TPS values for small field dimensions for fields less than 3×3 cm2, The measured data by 2D-Array data for fields 2×2 and 3×3cm2 this difference within ±2% is due to good accuracy of measurement planning system for field size 1×1cm2. The measured in standard phantom were less than the TPS values for small field dimensions and the measured data by 2D-Array for 6 MV shows mild differences between the TPS and the experimental data. Small difference existed between the TPS and the experimental data using 2D-Array for 15 MV the results were the same for TPS and measured data, at only field dimension of 1×1cm2. Measured data was increased as field area enlarged from 2×2 to 5×5cm2 by constant value of 4%.

Validation of the Octavius 4D measuring system in verifying advanced external beams radiotherapy techniques

The development of advanced techniques as Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are characterized by their numerous steep dose gradient using the dynamic MLC modality and these requires specific quality assurance (QA) to meet this complexity. The conventional dosimetery techniques, such as ionization chamber, point dose measurements and film dosimetry, are gradually being replaced by detector arrays which can produce accurate results immediately. There are many commercial detector arrays one of them is 2D-ARRAY seven29 (PTW, Freiburg, Germany). We used the Octavius 4 D measuring system with its detector array, ionization chamber. The accuracy of the synchronizing motion of the phantom was validated. It was found that the detector array response is stable after warming up with 800 MU, the dose rate measurements and the dose response is linear with R2=0.929. The gamma index for the clinical IMRT plans were found to be 93.3%, 98.0 %, 95.5% and 96.2% for head and neck, prostate, breast and brain cases, and for VMAT plans are 96.3%, 99.4 %, 98.1% and 98.6% for head and neck, prostate, breast and brain, respectively, using gamma criteria 3%/3 mm. The aim of this work is to characterize and validate the Octavius 4D measuring system for 6MV beams. Also, to verify clinical IMRT and VMAT plans, the volumetric dose matrix of the clinical plans, dose line profiles and to study the factors affect the gamma index.

IMRT plan verification with EBT2 and EBT3 films compared to PTW 2D-ARRAY seven29

The aim of this study was to compare dosimetry with Gafchromic EBT2 and EBT3 films to the ion chamber array PTW seven29 in terms of their performance in clinical IMRT plan verification.A methodology for film processing and calibration was developed. Calibration curves were obtained in MATLAB and in FilmQA Pro. The best calibration curve was then used to calibrate EBT2 and EBT3 films for IMRT plan verification measurements. Films were placed in several coronal planes into an RW3 slab phantom and irradiated with a clinical IMRT plan for prostate and lymph nodes using 18MV photon beams. Individual fields were tested and irradiated with gantry at 0°. Results were evaluated using gamma analysis with 3%/3mm criteria in OmniPro I’mRT version 1.7. The same measurements were performed with the ion chamber array PTW seven29 in RW3 slabs (different depths) and in the OCTAVIUS II phantom (isocenter depth only; both original and nominal gantry angles). Results were evaluated in PTW VeriSoft version 3.1 using the same criteria. Altogether, 45 IMRT planes were tested with film and 25 planes with the PTW 2D-ARRAY seven29. Film measuerements showed different results than ion chamber matrix measurements. With PTW 2D-ARRAY seven29, worse results were obtained when the detector was placed into the OCTAVIUS phantom than into the RW3 slab phantom, and the worst pass rates were seen for rotational measurements. EBT2 films showed inconsistent results and could differ significantly for different planes in one field. EBT3 films seemed to give the best results of all the tested configurations.

Multichannel film dosimetry vs 2D-array seven29 for vmat lung sbrt

Introduction Volumetric Modulated Arc Therapy (VMAT) can achieve high conformation and gradient levels required to deliver Stereotactic Body Radiation Therapy (SBRT). Quality Assurance (QA) usually includes a 2D gamma analysis. Here we compare two different QA procedures for VMAT lung SBRT treatments. Materials and methods Fourteen patients were selected. Dose per fraction ranged between 7.5 and 18 Gy. OCTAVIUS phantom (PTW) was used in both QA arrangements: 1. PTW 2D-ARRAY seven29 consists of a matrix of 729 cubic vented ionization chambers spaced 1 cm. To duplicate the resolution from 1 to 0,5 cm the “Merge” algorithm included in Verisoft software was used. 2. EBT3 radiochromic film with multichannel dosimetry was used. Also we applied the “efficient protocol” (Lewis, Mike and Yu, 2012) that provides specific calibration curves for each individual irradiation. Scanning was made with an Epson 10000XL, resolution was 72 dpi. Dose maps were created with Matlab. Gamma analysis criteria of 3%/3 mm and 2%/2 mm relative to maximum (MD) and local (LD) doses were performed. Results 3%/3 mm criteria: MD analysis produced averaged pass rates of 100% in both test. LD analysis gave 99.1% for EBT3 and 97.2% for 2D-array. A. 2%/2 mm criteria: MD analysis for EBT3 gave 98.9% and 90.8% for 2D-array. Also LD analysis gives 93.5% and 86.8% respectively. EBT3 provides more resolution and gives higher pass rates compared with 2D array. 3%/3 mm seems not to be an appropriate criterion. 2%/2 mm was more sensitive and gives pass rates above 96% and 91% for maximum and local dose respectively. Conclusion 2%/2 mm local dose gamma analysis of EBT3 using multichannel dosimetry gives excellent results for VMAT lung SBRT. Disclosure None.

Evaluation of a novel susceptibility weighted imaging MRI sequence for neonate brain scanning

Evaluation of a novel susceptibility weighted imaging MRI sequence for neonate brain scanning

Clinical evaluation of inter-fractional organ motion using 3D ultrasound image-guided radiotherapy for positioning prostate cancer patients

Clinical evaluation of inter-fractional organ motion using 3D ultrasound image-guided radiotherapy for positioning prostate cancer patients

Pre-Treatment Dose Verification of Imrt Using Gafchromic Ebt3 Film and 2DArray

Purpose: The present work deals with pre-treatment dosimetric verification of 10 prostate intensity-modulated radiotherapy (IMRT) plans obtained by Gafchromic EBT3 film and 2D-Array seven29 to establish quality control protocol for the delivery of prostate IMRT in our clinic. Methods: 10 prostate patients were irradiated according to IMRT techniques with 6 MV photon beams produced by a Varian DHX linear accelerator. Dose plans were computed using Eclipse 8.9 (version8.9, Varian, Palo Alto, CA, United States) treatment planning system (TPS). Pre-treatment dosimetric verification was carried out on field-perfield and total IMRT plan basis measuring 2D dose distributions in RW3 solid water phantom (PTW-Freiburg, Germany). For 10 patient plans, the dose distribution was re-calculated with the phantom CT scan and delivered to the phantom with the original and 0 degrees gantry, collimator and table angles. Thus IMRT quality control (QC) plans were generated. Dose distribution measurements were measured with Gafchromic EBT3 film and 2D-Array seven29 (PTW-Freiburg, Germany) two dimensional ionization chamber system. Verification measurements of total IMRT plans and each individual beams were compared with expected dose maps, and differences were evaluated by Verisoft program (PTW-Freiburg, Germany). To provide comparisons of multidimensional dose distributions, dose comparison tools such as gamma dose distribution, distance- to- agreement (DTA) and dose difference (DD) have been developed. The gamma dose distribution tool was used in our study. Three different gamma criteria of dose difference (DD) and distance to agreement (DTA) (3%/3 mm, 4%/4 mm and 5%/5 mm DD / DTA) are selected. These criteria are evaluated while suppressing the dose of 5% from dose distribution. Criterion validity accepted as section with gamma value less than or equal to 1 (γ ≤ 1) to be 90%. Results: In the comparison of dose distributions obtained from TPS and the results of PTW 2D-Array seven29 and Gafchromic EBT3 film dosimetry systems, it was showed that the compatibility of both methods were above 90% with respect to 3% DD and 3mm DTA criteria. PTW 2D-Array seven29 results compared to the results of the film was closer to the TPS data and this difference was statistically meaningful (p 0.05). Conclusions: The measurements performed with PTW 2D-Array seven29 were closer to the TPS data than film measurements and it takes less time during clinical use, so it could be preferred for routine use. The present results suggest the gamma criteria of 3%/3 mm as the most suitable criteria for prostate IMRT quality assurance.

Analysis of the impact of wedge filters on the dose profile symmetry in external radiotherapy

Context A bibliographic review, following a symmetry defect discovered on a radiation therapy accelerator, reveals a lack of results on the analysis of asymmetries created on the depth dose profiles with wedge filters. To deal with this issue, we propose an experimental and theoretical study. Material and methods Measurements of the dose profiles for different wedge angles (15° to 60°) are performed in the reference conditions (SSD = 90 cm, SAD = 100 cm, 10 × 10 cm 2 field), for a 18 MV photon beam with a VARIANO 2100C accelerator. Two types of detectors are used: 0.3 cc Semiflex ionization chambers in a PTW MP3 water tank, and a PTW 2D-Array seven29 detector array. These profiles are compared with the data of both TPS Oncentra Master Plan and the Monte-Carlo simulations results, performed with the BEAMnrc code. The combination of multiple wedges is also analysed. Results The dose profile symmetry differs according to the nature of the filter (physical or dynamic) and depends on experimental conditions, such as the measurement depth or the field size. The combination of two wedges in series (physical and dynamic) has also been modelized. It enables to check that the ‘‘equivalent” wedge angle resulting from these two filters is not a linear combination of these two angles. Conclusion The results obtained in reference conditions, which should be complemented by a dosimetric evaluation, were used to quantify the symmetry defects in output beams.

Simulation of respiratory motion effect on dose distributions in three-dimensional radiotherapy

Objective To evaluate the effects of respiratory on dose distributions in threedimensional conformal radiotherapy (3 DCRT) and intensity-modulated radiotherapy (IMRT).Methods The dose distributions were measured with a PTW 2D-ARRAY seven29 placed on a home-made moving platform to simulate the respirator.Dosimetric comparisions for 3DCRT and IMRT plans were performed by means of Gamma analysis with 3％ and 3 mm,respectively.Dose distribution measured for static treatment plans.Results The respiratory could reduce the target does and conformal index.The r pass rate (3％3 mm in 3 DCRT was greater than it in IMRT ((53.58 ± 0.74) ％,(30.71 ± 1.00) ％,t =57.91,P ＜ 0.01).The failed points were mainly near the field edge,but located in the whole target volumes for IMRT plans.Conclusions It is undesirable to use IMRT techniques for tumors with large motion amplitude.3DCRT can give a reliable dose distribution by reasonably selecting the PTV margin. Key words: Respiratory motion; Three-dimensional conformal radiotherapy; Intensitymodulated radiotherapy; Dose distribution

SU-E-T-134: Patient Specific Quality Assurance of RapidArc Pre Treatment Plans Using Semiflex 0.125 Cc Ionization Chamber.

To evaluate the Patient specific pre-treatment quality assurance for hundred RapidArc plans using semiflex (0.125cc) ionization chambers. Absolute point dose were measured for head and neck, thorax and abdomen cases using semiflex (0.125 cc) ionization chamber. Verification plan was created for each treatment plan in eclipse 8.6 treatment planning system with the semiflex ionization chamber and the octavius phantom. Measurements were performed on a Varian Clinac2100C/D linear accelerator equipped with a millennium 120 leaf collimator. All the results were compared with the fluence measurements using 2D Seven29 ion chamber array combined with octavius phantom. Positive absolute mean dose variation of 0.56 % was observed with thorax cases with a standard deviation (SD) of ± 1.13 between the plans with a range of -1.78% to 2.70%. Negative percentage dose errors were found with head and neck and abdomen cases, with a mean variation of -0.43 % (SD ± 1.50), (range -3.25 % to 2.85 %) and -0.35 % (SD ± 1.48), (range -3.10 % to 2.65 %) for head and neck and abdomen cases respectively. Relative dose measurements with 2D array agreed well with the TPS calculate for all the cases. The maximum percentage value failed in gamma analysis was found to be 4.95, 4.75, and 4.88 for head and neck, thorax, and abdomen cases respectively. In all the cases analysed the percentage dose points failed the gamma criteria was less than 5%. On the basis of the studies performed it can be concluded that the semiflex ionization chamber having a volume of 0.125cc can be used efficiently for measuring the pre-treatment quality assurance of RapidArc plans for all the sites. The results provide an overall accuracy when compared to fluence measurement done using 2D array seven29.

SU-E-T-488: Dose Calculation Model Using the Simplified Monte Carlo Method with an Initial Beam Model Adapted to a Beam-Wobbling System

We have developed an accurate dose calculation model based on a simplified Monte Carlo (SMC) method adapted to a beam-wobbling delivery system at National Cancer Center Hospital East (NCCHE). We used an initial beam model specific to the beam-wobbling system to reproduce accurately different dose distributions in two lateral directions (x- and y-directions) perpendicular to each other. The SMC calculates a dose distribution by tracking individual protons. The SMC starts tracking protons at an entrance of a range compensator. Protons are generated in an initial phase space adapted to the wobbler system. Since two wobbling-magnets are located at separate places with different distances from the iso-center, different dose distributions are formed in x- and y-directions. We derived an initial phase space distribution for the beam-wobbling system using an analytical method. We used the SMC method with the initial beam model to calculate dose distributions accurately. To verify accuracy of the calculation method, we measured the dose distribution in a homogeneous phantom formed by 235 MeV protons passing through a L-shaped range compensator. We used a 2D-array of parallel-plate ionization chambers (2D Array seven29®) to measure dose distributions with a sampling period of 5 mm. The measured dose distribution in the x-direction was different from that in the y-direction. Our calculation model reproduces the measurement results well in both lateral directions. In addition, the calculation reproduced the dose increments in edge regions contributed by edge-scattered protons in collimator. It indicates the advantage of the SMC. A dose calculation model has been developed based on the simplified Monte Carlo method applied to a beam-wobbling system. By adapting the initial beam model to the wobbling system, the SMC method is found to reproduce observed different dose distributions in x- and y-directions well.

SU-E-I-107: Suitability of Various Radiation Detectors Used in Radiation Therapy for X-Ray Dosimetry in Computed Tomography.

Assessment of suitability for X-ray dosimetry in computed tomography of various ionization chambers, diodes and two-dimensional detector arrays primarily used in radiation therapy. An Oldelft X-ray simulation unit was used to irradiate PTW 60008, 60012 dosimetry diodes, PTW 23332, 31013, 31010, 31006 axial symmetrical ionization chambers, PTW 23343, 34001 plane parallel ionization chambers and PTW Starcheck and 2D-Array seven29 as well as a prototype Farmer chamber with a copper wall. Peak potential was varied from 50 kV up to 125 kV and beam qualities were quantified through half-value-layer measurements. Energy response was investigated free in air as well as in 2 cm depth in a solid water phantom and refers to a manufacturer calibrated PTW 60004 diode for kV-dosimetry. The thimble ionization chambers PTW 31010, 31013, the uncapsuled diode PTW 60012 and the PTW 2D-Array seven29 exhibit an energy response deviation in the investigated energy region of approximately 10% or lower thus proving good usability in X-ray dosimetry if higher spatial resolution is needed or rotational irradiations occur. It could be shown that in radiation therapy routinely used detectors are usable in a much lower energy region. The rotational symmetry is of advantage in computed tomography dosimetry and enables dose profile as well as point dose measurements in a suitable phantom for estimation of organ doses. Additional the PTW 2D-Array seven29 can give a quick overview of radiation fields in non-rotating tasks.

A method to enhance spatial resolution of a 2D ion chamber array for quality control of MLC

This work introduces a new method for verifying MLC leaf positions with enough spatial resolution to replace film‐based methods in performing QA tests. It is implemented on a 2D ion chamber array, and it is based on the principle of varying signal response of a volumetric detector to partial irradiation. A PTW 2D‐ARRAY seven29 (PTW‐729 2D) array was used to assess a Siemens OPTIFOCUS MLC. Partial volume response curves for chambers in the array were obtained by irradiating them with the leaves of the MLC, progressively covering varying portions of the chambers correlated with the leaf positions. The readings from the array's chambers are processed with an in‐house program; it generates a reference response that translates readings into leaf positions. This principle allows discriminating errors in pairs of opposing leaves that could combine to cancel their detection with other tools.Patterns of leaf positions, similar to the Bayouth test but with different, purposefully introduced errors, were generated and used to test the effectiveness of the method. The same patterns were exposed on radiographic film and analyzed with the RIT software for validation. For four test patterns with a total of 100 errors of ±1 mm, ±2 mm and ±3 mm, all were correctly determined with the proposed method. The analysis of the same pattern with film using the Bayouth routine in the RIT software resulted in either somewhat low true positives combined with a large fraction of false positives, or a low true positive rate with a low false positive ratio, the results being significantly affected by the threshold selected for the analysis.This method provides an effective, easy to use tool for quantitative MLC QA assessment, with excellent spatial resolution. It can be easily applied to other 2D arrays, as long as they exhibit a partial volume detector response.PACS number: 87.55.Qr

Characterization of responses of 2d array seven29 detector and its combined use with octavius phantom for the patient-specific quality assurance in rapidarc treatment delivery

A commercial 2D array seven29 detector has been characterized and its performance has been evaluated. 2D array ionization chamber equipped with 729 ionization chambers uniformly arranged in a 27 × 27 matrix with an active area of 27 × 27 cm2 was used for the study. An octagon-shaped phantom (Octavius Phantom) with a central cavity is used to insert the 2D ion chamber array. All measurements were done with a linear accelerator. The detector dose linearity, reproducibility, output factors, dose rate, source to surface distance (SSD), and directional dependency has been studied. The performance of the 2D array, when measuring clinical dose maps, was also investigated. For pretreatment quality assurance, 10 different RapidArc plans conforming to the clinical standards were selected. The 2D array demonstrates an excellent short-term output reproducibility. The long-term reproducibility was found to be within ±1% over a period of 5 months. Output factor measurements for the central chamber of the array showed no considerable deviation from ion chamber measurements. We found that the 2D array exhibits directional dependency for static fields. Measurement of beam profiles and wedge-modulated fields with the 2D array matched very well with the ion chamber measurements in the water phantom. The study shows that 2D array seven29 is a reliable and accurate dosimeter and a useful tool for quality assurance. The combination of the 2D array with the Octavius phantom proved to be a fast and reliable method for pretreatment verification of rotational treatments.

SU-GG-T-223: Characterization of Responses of 2D-Array Seven29 Detector and Its Combined Use with Octavius Phantom for the Patient Specific Quality Assurance in Rapid Arc Treatment Delivery

Purpose: To study the dosimetric characteristics of 2D Seven29 ion chamber array and henceforth to perform the patient specific QA for RapidArc treatment delivery in combination with Octavius phantom. Method and Materials: The dosimetric characteristics of PTW 2D seven29 array such as linearity, reproducibility, dose rate, output factors, and directional dependency were evaluated for 6 and 15 MV X‐rays using CLINAC 2100. Performance of detector for measuring clinical dose maps for open and wedge modulated fields and MLC QA were studied. The pre‐treatment patient specific QA of RapidArc for ten different clinical cases was performed. Results: The detector response to dose was linear within the range of 2–500 MUs. Standard deviation for short and long term (5 months) reproducibility were 0.1% and ±1% respectively. The detector response to dose rates was independent with a standard deviation of ±0.7 for 6MV and ±0.5 for 15MV. Output factor showed no significant deviation. The directional dependency for static fields is found to be less than 1.0% when the array is irradiated from the front side. Variation of −4.9% for 6MV and − 5.95% for 15MV was found when the array is irradiated parallel to the beam axis. Less than 4% variation was observed when the beam is incident through the rear of the array for both the energies. MLC and wedge modulated fields matched very well with ion chamber and film measurements. For pre‐treatment QA of RapidArc, Gamma analysis shows that 95% of evaluated dose points in planned and delivered fluence agree for 3mm DTA, 3% dose difference (except for two studies). Conclusion: This study concludes that 2D Array Seven29 is a reliable and accurate dosimeter. The combination of 2D Array with Octavius phantom proved to be a fast and reliable method for pretreatment verification of RapidArc with a satisfactory accuracy for clinical practices.

Characterization of a 2D ion chamber array for the verification of radiotherapy treatments

In this study we investigated the characteristics of a commercial ion chamber array and its performance in the verification of radiotherapy plans. The device was the 2D Array Seven29™ model (PTW, Freiburg, Germany). This is a two-dimensional detector array with 729 ionization chambers uniformly arranged in a 27 × 27 matrix with an active area of 27 × 27 cm2. The detector short-, medium- and long-term reproducibility have been tested through an extensive set of repeated measurements. Short-term reproducibility was well within 0.2%. Medium- and long-term reproducibility were within 1%, including set-up reproducibility errors and linac output fluctuations. Dose linearity was also assessed. The system response to dose was verified to be linear within the range 2–500 MU. Output factors matched very well pinpoint chamber measurements performed in the same experimental conditions with a maximum local percentage difference of 0.4%. Furthermore, the 2D Array sensitivity to millimetric collimator positional changes and to perturbation effect of irradiated area was tested. The comparison with ion chamber data carried out in water was very satisfying. Finally, measurements of wedge-modulated fields and IMRT beam sequence matched very well ion chamber dose profiles acquired in a water tank. The extensive tests performed in this investigation show that the 2D Array Seven29 is a reliable and accurate dosimeter and that it could be a useful tool for the quality assurance and the verification of radiotherapy plans.