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Background: Widely used physical wedges in clinical radiotherapy lead to beam intensity attenuation as well as the beam hardening effect, which must be considered. Dynamic wedges devised to overcome the physical wedges (PWs) problems result in dosimetry complications due to jaw movement while the beam is on. This study was aimed to investigate the usability of physical wedge data instead of enhanced dynamic wedge due to the enhanced dynamic wedge (EDW) dosimetry measurement hardships of Varian 2100CD in inhomogeneous phantom by Monte Carlo code as a reliable method in radiation dosimetry. Materials and methods: A PW and EDW-equipped-linac head was simulated using BEAMnrc code. DOSXYZnrc was used for three-dimensional dosimetry calculation in the CIRS phantom. Results: Based on the isodose curves, EDW generated a less scattered as well as lower penumbra width compared to the PW. The depth dose variations of PWs and EDWs were more in soft tissue than the lung tissue. Beam profiles of PW and EDW indicated good coincidence in all points, except for the heel area. Conclusion: Results demonstrated that it is possible to apply PW data instead of EDW due to the dosimetry and commissioning hardships caused by EDW in inhomogeneous media.

Aim of Study: Physical wedges (PWs) are widely used in radiotherapy to obtain tilted isodose curves, but they alter beam quality. Dynamic wedges (DWs) using moving collimator overcome this problem, but measuring their beam data is not simple. The main aim of this study is to obtain all dosimetric parameters of DWs produced by Varian 2100CD with Monte Carlo simulation and compare them to those from PWs. Subjects and Methods: To simulate 6 MV photon beams equipped with PW and DW, BEAMnrc code was used. All dosimetric data were obtained with EDR2 films and two-dimensional diode array detector. Results: Good agreement between simulated and measured dosimetric data for PW and DW fields was obtained. Our results showed that percentage depth dose and beam profiles at nonwedged direction for DWs are the same as open fields and can be used to each other. Conclusion: From Monte Carlo simulations, it can be concluded that DWs in spite of PW do not have effect on beam quality and are good options for treatment planning system which cannot consider hardening effect produced by PWs. Furthermore, BEAMnrc is a powerful code to acquire all date required by DWs.

Background: Across the history of radiotherapy, wedges are generally used to modify the shape of isodose lines to achieve desired clinical dose coverage to the target and to reduce the hot spot as well. Aim: The main aim of this study was to analyse and compare the dosimetric properties of Varian’s physical and enhanced dynamic wedges, and their dosimetric impact on radiotherapy plan (3D-Conformal). Materials and Methods: All plans were generated and evaluated in Varian’s eclipse planning system. For comparing the isodose line alteration, the plans were prepared in water phantom with field of size 10 cmx 10 cm. Wedges of angle 15°, 30°, 45° and 60° were used for generating isodose lines in the current study. All wedge factors were measured in water phantom using FC65 farmer type chamber. Discussion: In the current study, the dosimetric characteristics of EDW and PW were analyzed and compared. For analyzing the impact of EDW and PW, 22 patients were taken into consideration, and 50 Gy dose was prescribed to PTV in 25 fractions. Conclusion: The analysis of EDW and PW shows slightly different dosimetric features. EDW gives better target’s coverage, less hyper dose and comparatively less MUs as compare to PW. Hence the use EDW in 3D-conformal radiotherapy plan is a prudent practice.

Dose inhomogeneity in treatment planning can be compensated using physical wedges. Enhanced dynamic wedges (EDW) were introduced by Varian to overcome some of the shortcomings of physical wedges. The objectives of this study were to measure EDW output factors for 6 MV and 20 MV photon energies for a Varian 2300CD. Secondly, to review the literature in terms of published enhanced dynamic wedge output factors (EDWOF) for different Varian models and thereby add credence to the case of the validity of reference databases. The enhanced dynamic wedge output factors were measured for the Varian 2300CD for both 6 MV and 20 MV photon energies. Twelve papers with published EDWOF for different Varian linac models were found in the literature. Comparing our results with the published mean, we found an excellent agreement for 6 MV EDWOF, with the percentage differences ranging from 0.01% to 0.57%, with a mean of 0.03%. The coefficient of variation of published EDWOF ranged from 0.17% to 0.85% and 0.1% to 0.9% for the for 6 MV and 18 MV photon energies, respectively. This paper provides the first published EDWOF for 20 MV photon energy. In addition, we have provided the first compendium of EDWOFs for different Varian linac models. The consistency of value across models and institution provide further support that a standard dataset of basic photon and electron dosimetry could be established as a guide for future commissioning, beam modeling, and quality assurance purposes. PACS numbers: 87.50, 87.55

The purpose of this work was to study the dosimetric properties of the enhanced dynamic wedge using a Seven29 ion chamber array. The PTW Seven29 ion chamber array and solid water phantoms were used for the study. Primarily, the solid water phantoms with the two-dimensional (2D) array were scanned using a computed tomography scanner at different depths. Using these scanned images, planning was performed for different wedge angles at 6 and 15 MV. A dose of 100 CGy was delivered in each case. For each delivery, the required monitoring units (MUs) were calculated. Using the same setup with a Varian Clinac iX, the calculated MU was delivered for different wedge angles. Subsequently, the different wedged dose distributions that had been obtained were analysed using Verisoft software. A shoulder-like region was observed in the profile; this region reduced as depth increased. The percentage deviation between the planned and measured doses at the shoulder region fell within the range of 0·9–4·3%. The standard deviation between planned and measured doses at shoulder region in the profile fell within 0·08±0·02 at different depths. The standard deviations between planned and measured wedge factors for different depths (2·5, 5, 10 and 15 cm) were 0·0021, 0·0007, 0·0050 and 0·0001 for 6 MV and 0·0024, 0·0191, 0·0013 and 0·0005 for 15 MV, respectively. On the basis of the studies that we performed, it can be concluded that the 2D ion chamber array is a good tool for enhanced dynamic wedge dosimetry.

Junctions of fields are known to be susceptible to developing cold or hot spots in the presence of even small geometrical misalignments. Reduction of these dose inhomogeneities can be accomplished through decreasing the dose gradients in the penumbra, but currently it cannot be done for enhanced dynamic wedges (EDW). An MLC‐based penumbra softener was developed in the developer mode of TrueBeam linacs to reduce dose gradients across the side border of EDWs. The movement of each leaf was individually synchronized with the movement of the dynamic Y jaw to soften the penumbra in the same manner along the entire field border, in spite of the presence of the dose gradient of the EDW. Junction homogeneity upon field misalignment for side‐matched EDWs was examined with the MV imager. The fluence inhomogeneities were reduced from about 30% per mm of shift of the field borders for the conventional EDW to about 2% per mm for the softened‐penumbra plan. The junction in a four‐field monoisocentric breast plan delivered to the Rando phantom was assessed with film. The dose inhomogeneities across the junction in the superior‐inferior direction were reduced from about 20% to 25% per mm for the conventional fields to about 5% per mm. The dose near the softened junction of the breast plan with no shifts did not deviate from the conventional plan by more than about 4%. The newly‐developed softened‐penumbra junction of EDW (and/or open) fields was shown to reduce sensitivity to misalignments without increasing complexity of the planning or delivery. This methodology needs to be adopted by the manufacturers for clinical use.

In this study the interplay effects for Enhanced Dynamic Wedge (EDW) treatments are experimentally investigated. Single and multiple field EDW plans for different wedge angles were delivered to a phantom and detector on a moving platform, with various periods, amplitudes for parallel and perpendicular motions. A four field 4D CT planned lung EDW treatment was delivered to a dummy tumor over four fractions. For the single field parallel case the amplitude and the period of motion both affect the interplay resulting in the appearance of a step function and penumbral cut off with the discrepancy worst where collimator-tumor speed is similar. For perpendicular motion the amplitude of tumor motion is the only dominant factor. For large wedge angle the dose discrepancy is more pronounced compared to the small wedge angle for the same field size and amplitude-period values. For a small field size i.e. 5 × 5 cm2 the loss of wedged distribution was observed for both 60° and 15° wedge angles for parallel and perpendicular motions. Film results from 4D CT planned delivery displayed a mix of over and under dosages over 4 fractions, with the gamma pass rate of 40% for the averaged film image at 3%/1 mm DTA (Distance to Agreement). Amplitude and period of the tumor motion both affect the interplay for single and multi-field EDW treatments and for a limited (4 or 5) fraction delivery there is a possibility of non-averaging of the EDW interplay.

Intensity Modulated Radiotherapy (IMRT) is increasing its use r ecently due to its benefits of minimizing the dose on surrounding normal organs and being able to target a hi gh dose specifically to the tumor. The study aims to measure and evaluate the dose distribution according to its dynamic changes in Mapcheck.In order to verify the dose distribution by EDW angle(10 ˚,15˚,20˚,25˚,30˚,45˚,60˚), field size (asymmetric field) and depth changes (1.5 cm, 5.0 cm)using IMRT in Clinac i x, a solid phantom was placed on the Mapcheck and 100MU was exposed by 6 MV, 10MV X-ray. Using a 6MV, 10MV energy, the percentage depth dose according to a dynamic changes at a maximum dose depth (1.5 cm) and at 5.0 cm depth showed the value difference of maximum 0.6%, less than 1%, which was calculated by a treatment program device considering the maximum dose depth at the center as 100%, the percentage de pth dose was in the range between 2.4% and 7.2%. Also, the maximum value difference of a percentage de pth dose was 4.1% in Y2-OUT direction, and 1.7% in Y1-IN direction. When treating a patient using a wedge, it is considered that using an enhanced dynamic wedge is effective to reduce the scattered dose which i nduces unnecessary dose to the surroundings. In particular, when treating a patient at clinic, a treatment m ust be performed considering that the wedge dose in a toe direction is higher than the dose in a heel direction.

The purpose of this work is to study dose non-linearity in medical linear accelerators used in conventional radiotherapy and intensity-modulated radiation therapy. Open fields, as well as the enhanced dynamic wedge ones, were used to collect data for 6 MV and 15 MV photon beams obtained from the VARIAN linear accelerator. Beam stability was checked and confirmed for different dose rates, energies, and application of enhanced dynamic wedge by calculating the charge per monitor unit. Monitor unit error was calculated by the two-exposure method for open and enhanced dynamic wedge beams of 6 MV and 15 MV photons. A significant monitor unit error with maximum values of ±2.05931 monitor unit and ±2.44787 monitor unit for open and enhanced dynamic wedge beams, respectively, both energy and dose rate dependent, was observed both in the open photon beam and enhanced dynamic wedge fields. However, it exhibited certain irregular patterns at enhanced dynamic wedge angles. Dose monitor unit error exists only because of the overshoot phenomena and electronic delay in dose coincident and integrated circuits with a dependency on the dose rate and photon energy. Monitor unit errors are independent of the application of enhanced dynamic wedge. The existence of monitor unit error demands that the dose non-linearity of the linear accelerator dosimetry system be periodically tested, so as to avoid significant dosimetric errors.

Introduction. Enhanced dynamic wedges (EDW) are known to increase drastically the radiation therapy treatment efficiency. This paper has the aim to compare linear array measurements of EDW with the calculations of treatment planning system (TPS) and the electronic portal imaging device (EPID) for 15 MV photon energy. Materials and methods. The range of different field sizes and wedge angles (for 15 MV photon beam) were measured by the linear chamber array CA 24 in Blue water phantom. The measurement conditions were applied to the calculations of the commercial treatment planning system XIO CMS v.4.2.0 using convolution algorithm. EPID measurements were done on EPID-focus distance of 100 cm, and beam parameters being the same as for CA24 measurements. Results. Both depth doses and profiles were measured. EDW linear array measurements of profiles to XIO CMS TPS calculation differ around 0.5%. Profiles in non-wedged direction and open field profiles practically do not differ. Percentage depth doses (PDDs) for all EDW measurements show the difference of not more than 0.2%, while the open field PDD is almost the same as EDW PDD. Wedge factors for 60 deg wedge angle were also examined, and the difference is up to 4%. EPID to linear array differs up to 5%. Conclusions. The implementation of EDW in radiation therapy treatments provides clinicians with an effective tool for the conformal radiotherapy treatment planning. If modelling of EDW beam in TPS is done correctly, a very good agreement between measurements and calculation is obtained, but EPID cannot be used for reference measurements.

This study was designed to investigate variation in Varian′s Physical and Enhanced Dynamic Wedge Factors (WF) as a function of depth and field size. The profiles for physical wedges (PWs) and enhanced dynamic wedges (EDWs) were also measured using LDA-99 array and compared for confirmation of EDW angles at different depths and field sizes. WF measurements were performed in water phantom using cylindrical 0.66 cc ionization chamber. WF was measured by taking the ratio of wedge and open field ionization data. A normalized wedge factor (NWF) was introduced to circumvent large differences between wedge factors for different wedge angles. A strong linear dependence of PW Factor (PWF) with depth was observed. Maximum variation of 8.9% and 4.1% was observed for 60° PW with depth at 6 and 15 MV beams respectively. The variation in EDW Factor (EDWF) with depth was almost negligible and less than two per cent. The highest variation in PWF as a function of field size was 4.1% and 3.4% for thicker wedge (60°) at 6 and 15 MV beams respectively and decreases with decreasing wedge angle. EDWF shows strong field size dependence and significant variation was observed for all wedges at both photon energies. Differences in profiles between PW and EDW were observed on toe and heel sides. These differences were dominant for larger fields, shallow depths, thicker wedges and low energy beam. The study indicated that ignoring depth and field size dependence of WF may result in under/over dose to the patient especially doing manual point dose calculation.

This work assessed the dosimetric performance of an amorphous silicon electronic portal imaging device (EPID) for measurement and quality assurance of enhanced dynamic wedge (EDW) profile and wedge factor. EPID measurements of EDW profiles were corrected for pixel sensitivity variation and spectral over-response relative to ion chamber and compared to ion-chamber and diode-array measurements. The dependence of EPID measurements on wedge direction and source to EPID distance was assessed. The long-term stability was investigated by weekly measurement of EDW profiles and wedge factors over a seven month interval. An empirical correction method was developed to improve EPID profile agreement with diode-array measurements. The EPID profiles differed from conventional measurements by up to 5%. Backscatter from the EPID housing was also found to affect measurements by up to 4%, resulting in changes in EPID measured profile with the direction of the moving jaw and source to EPID distance. EPID profile measurements varied by a maximum of 0.3% (1 SD) within the umbra, and wedge factors varied by 0.3% (1 SD) over the seven month interval. The correction function improved agreement between EPID and diode array to within 2% for all wedge angles and energies. Due to the ease of use and reproducibility of the EPID-measured EDW profiles the device is highly suited to regular measurement of EDW.

Dynamic techniques for dose delivering used in external radiotherapy such as modulated radiation intensity (IMRT) and enhanced dynamic wedges (EDW) tend to be used with more frequency due to the benefits in terms of higher treatment does to the tumor while preserving the exposure of healthy tissues and reduction in treatment times needed in wedged beam techniques, respectively. In seeking to ensure accuracy in dose delivery in dynamic techniques are several the measurement methods and systems developed.

Dynamic wedges have been used in clinical practice for many years. Obvious superiority of dynamic over physical wedges is accompanied by the increased overhead involved in verifying the accuracy and reliability of their use. Contrary to very limited QA required to ensure proper functioning of the physical wedges, dynamic wedges, like any other dynamic treatment, require a robust QA program. This work expands upon previous suggestions and describes a comprehensive QA program for Varian enhanced dynamic wedges (EDWs) and presents the results of an 18‐month evaluation of these wedges. The QA program includes daily, monthly, and yearly tests and individual treatment QA at the onset of use of the EDWs. The results of the 18‐month evaluation show reproducibility in the wedge factors of better than 1% and in dose profiles of better than 2% on a monthly basis. Daily output measurements are generally within 2% of expected values. PACS numbers: 87.53.Xd, 87.56.Fc

We proposed a formula for the enhanced dynamic wedge (EDW) factor in the half-field (HF) that combined the formula proposed by Liu et al. in 1998 and their formula in 2003. When the EDW was used for irradiation to the tangent line of the HF breast, the values calculated by our formula and the measured values were consistent within 0.5%. We showed that our proposed formula was useful, easy to use, and more accurate than the conventional formula. The purpose of this study was to examine the available range of the wedge factor of symmetrical and asymmetric EDW calculated by our formula. As a result of the examination, the values calculated by our formula and the measured values were consistent within 2% except for highly asymmetric EDW. We created a spreadsheet to calculate the wedge factor easily and accurately. We will examine the reason why the calculated and measured values were greater than 2%, and improve our formula so that it can be used in a wider range.

The method presented by Liu et al. in 1998 has generally been used in Japan to calculate the wedge factor of the enhanced dynamic wedge (EDW). When the points used to evaluate the dose exist outside the central beam axis in the half field (HF), however, a difference of about 3% can occur between the values calculated by this method and the measured values. In 2003, Liu et al. presented a new general formula for calculating MU using the EDW. We modified the formula for calculating the wedge factor by combining the conventional calculation formula and the formula of Liu et al., presented in 2003, and compared the calculated values of the wedge factor of the EDW in the HF with the measured values. Our formula employs a very simple method in which only the normalized golden segmented treatment table (NGSTT) on the center of the radiation field and the central beam axis are added to the existing formula. The values calculated by our formula and the measured values were consistent within 1% in most combinations of energy, wedge angle, and size of radiation field. When the EDW was used for irradiation to the tangent line of the HF breast, in particular, the values calculated by our formula and the measured values were consistent within 0.5%, and it was possible to calculate the wedge factor with a higher degree of accuracy than that calculated with the existing formula.

The purpose of this study is to describe and evaluate a new analytical model for Varian enhanced dynamic wedge factors at off-center points. The new model was verified by comparing measured and calculated wedge factors for the standard set of wedge angles (i.e., 15 deg., 30 deg., 45 deg. and 60 deg.), different symmetric and asymmetric fields, and two different photon energies. The maximum difference between calculated and measured wedge factors is less than 2%. The average absolute difference is within 1%. The obtained results indicate that the suggested model can be useful for independent dose calculation with enhanced dynamic wedges.

Some serious radiation accidents have occurred around the world during the delivery of radiotherapy treatment. The regrettable incident in Panama clearly indicated the need for independent monitor unit (MU) verification. Indeed the International Atomic Energy Agency (IAEA), after investigating the incident, made specific recommendations for radiotherapy centres which included an independent monitor unit check for all treatments. Independent monitor unit verification is practiced in many radiotherapy centres in developed countries around the world. It is mandatory in USA but not yet in Australia. This paper describes development of an independent MU program, concentrating on the implementation of the Enhanced Dynamic Wedge (EDW) component. The difficult case of non centre of field (COF) calculation points under the EDW was studied in some detail. Results of a survey of Australasian centres regarding the use of independent MU check systems is also presented. The system was developed with reference to MU calculations made by Pinnacle 3D Radiotherapy Treatment Planning (RTP) system (ADAC - Philips) for 4MV, 6MV and 18MV X-ray beams used at the Newcastle Mater Misericordiae Hospital (NMMH) in the clinical environment. A small systematic error was detected in the equation used for the EDW calculations. Results indicate that COF equations may be used in the non COF situation with similar accuracy to that achieved with profile corrected methods. Further collaborative work with other centres is planned to extend these findings.

The generalized monitor unit (MU) calculation equation for the Varian enhanced dynamic wedge (EDW) is derived. The assumption of this MU calculation method is that the wedge factor of the EDW at the center of the field is a function of field size, the position of the center of the field in the wedge direction, and the final position of the moving jaw. The wedge factors at the center of the field in both symmetric and asymmetric fields are examined. The difference between calculated and measured wedge factors is within 1.0%. The method developed here is easy to implement. The only datum required in addition to the standard set of conventional physical wedge implementation data is the off-axis output factor for the open field in the reference condition. The off-center point calculation is also examined. For the off-center point calculation, the dose profile in the wedge direction for the largest EDW field is used to obtain the relative off-center ratio in any smaller wedge field. The accuracy of the off-center point calculation decreases when the point of calculation is too close to the field edge.

Enhanced dynamic wedges can be very useful in increasing radiation therapy treatment efficiency. A drawback to their use is finding a factor analogous to a conventional wedge factor to calculate the dose to a point in a dynamically wedged field. A formalism has previously been published J. Gibbons, Med. Phys. 25, 14111418 (1998) to determine this factor at the central point of a dynamically wedged field. This paper expands the use of the previous formalism to show efficacy at any point under a dynamically wedged field, provided the point is not in a penumbra region. Results of measurements taken with four clinically relevant field sizes, both symmetric and asymmetric, are given. These results show acceptable correlation between the original formalism and its expanded use to noncentral points. 2003 American College of Medical Physics.

The Enhanced Dynamic Wedge (EDW) presents many advantages over the physical wedge. However, in order to calculate monitor units (MUs) necessary to deliver a certain dose at a certain point, EDW factors (EDWFs) need to be determined. In this work, based on analysis of the golden segmented treatment table (GSTT) and the MU fraction model, an empirical analytic formula has been developed to calculate EDW factors for symmetric and asymmetric fields. This formalism is an extension of the MU fraction model. However in comparison with previous studies [J. P. Gibbons, Med. Phys. 25, 1411-1418 (1998) and M. Miften et al., Med. Dosim. 25, 81-86 (2000)], this formula is simpler, and easier to use. It is applicable to EDW fields of different sizes, wedge angles and different photon energies. For 6 and 18 MV beams from a Varian 21EX accelerator with 7 EDW angles (Varian Oncology Systems, Palo Alto, CA), more than 250 measured EDWFs for symmetric and asymmetric fields with different off-axis distances and field sizes were compared with model calculations. Results show that 80% and 98% of calculated EDWFs match corresponding measured values to within 0.5% and 1.0%, respectively, the maximum deviation being 1.3%.

Introduction: Using physical wedges (PWs) to modify dose distribution and more homogeneous target coverage is a well-established technique. However, there are many problems with PWs known as beam hardening, which made them problematic. This can be overcome by dynamic wedges which do not filter beam. Comparison of physical properties of physical and enhanced dynamic wedges (EDWs) restricted to homogeneous medium. Hence, the main aim of this study is to compare dosimetric properties of physical and EDWs at bladder inhomogeneous phantom as a most common case implementing wedges. Materials and Methods: An inhomogeneous pelvic phantom with homogeneities of uterus, femur, soft tissue, rectum, and bladder was designed. Eclipse treatment planning system with the aim of bladder target was used for calculations. All dose distributions were measured with EBT3 films. Results: Comparison between beam profiles of physical and EDWs at wedged and nonwedged directions shows a greater difference at near inhomogeneous soft tissue interface and also at heel side of wedges. Conclusion: Little difference observed between dose distribution of physical and EDWs shows neglectable effect of beam hardening produced by PW compared to EDW at inhomogeneous medium. Furthermore, EBT3 films present good feature to measure dose distributions at EDW fields.

Enhanced dynamic wedge factors (EDWF) are characterized by a strong field size dependence. In contrast to physical wedge factors, the EDWF decrease as the field size is increased: for 6 MV 60 degrees wedge, the EDWF decreases by 50% when the field size is increased from 4 x 4 cm2 to 20 x 20 cm2. A method that eliminates the field size dependence of EDWF was developed and investigated in this work. In this method, the wedged field shape is determined by a multileaf collimator. The initial position of the moving Y jaw is determined by the field size and the stationary Y jaw is kept fixed at 10 cm for field sizesor = 20 cm in the wedged direction. For all other fields, the stationary Y jaw setting is determined by the field size. The modified method results in EDWF that are independent of field size, with no change in the wedge dose distribution when compared with the conventional use of EDW.

An enhanced dynamic wedge (EDW) is one of the latest technical innovations frequently used in the radiotherapy department. Its usage is enthusiastically supported by radiation therapists. Intensity modulated radiotherapy (IMRT) is the other, which has become popular within the past several years. Its usage is not as straightforward as the EDW. However, its ability to further increase dose conformity to the target and to spare the surrounding normal tissues has been evidenced. Both of these treatment modalities demand sophisticated software, which controls precision motion and speed of jaws or multileaf collimators as well as dose rate. This paper deals with the question of how accurately the EDW profiles and IMRT dose distributions be maintained when the additional constraint of linear accelerator gating is invoked. For this, square pulses mimicking breathing were used in gated and nongated modes for film dosimetry and ion chamber measurements using the Varian 2100C linear accelerator. The results show no observable difference between gated and nongated EDW profiles and IMRT dose distribution regardless of the machine repetition rate. Also studied in this paper are the "fuzzy" dose distributions caused by realistic finite gate window settings.

Zusammenfassung In dieser Arbeit wurde der Einsatz des erweiterten Monitor Unit Fraction Models fur die Berechnung von dynamischen Keilfilterfaktoren im klinischen Einsatz untersucht. Die Parameter des erweiterten Monitor Unit Fraction Model wurden anhand von Messungen an die individuellen Gerateverhaltnisse fur quadratisch-symmetrische Keilfelder angepasst. Die Keilfillerfaktoren wurden hierzu am Linearbeschleuniger Clinac 600c mit einer Mikrokammer im Wasserphantom gemessen. Die Abweichungen der berechneten Keilfilterfaktoren fur die symmetrischen Felder sind kleiner als 0.33 % fur alle Keilwinkel und alle Feldgrossen. Mit dem erweiterten MU Fraction Model konnen Keilfilterfaktoren fur asymmetrische Felder in einfacher Weise berechnet werden. Die Abweichungen der berechneten Keilfilterfaktoren von den gemessenen Werten fur asymmetrische Felder sind kleiner als 1.1 %. Fur asymmetrische Feldverkleinerungen um 8 cm betragen die Abweichungen fur einen 60° Keil bis zu 2.6 %. Das erweiterte Monitor Unit Fraction Model eignet sich in der klinischen Anwendung zur einfachen Bestimmung der Keilfilterfaktoren von dynamischen Keilfeldern.

A method is introduced to calculate wedge factors for an enhanced dynamic wedge (EDW). An analytic formula has been derived that allows the determination of wedge factors at the center of symmetric and asymmetric photon fields. The formalism is an extension of the "MU fraction approximation," which holds that the dynamic wedge factor is equal to the fraction of MU delivered to the point of calculation. Extensive data are presented, comparing measured enhanced dynamic wedge factors with the current method and the MU fraction model for both symmetric and asymmetric fields. For both 6 and 18 MV photons, the current method demonstrates improved results: Agreement to within 1% is obtained in all symmetric fields and within 2% for all asymmetric fields compared with discrepancies of up to 4% obtained with the MU fraction model.

The output factor for an enhanced dynamic wedge (EDW) field, like that for a dynamic wedge field, is a complex function of the field dimension in the wedge direction. The large change in output for different field sizes (varying more than 40% for a 60 degrees wedge angle) is due to rescaling of the golden segmented treatment table (GSTT), which specifies the cumulative monitor unit weighting as a function of moving jaw position. The rescaling of the GSTT results in increased output on the central axis with a decrease in the value of the final moving jaw position in the wedge plane. The output factor (in air or in water) on the central axis of an EDW field can be predicted to within 1% by multiplying the output factor (in air or in water) of an open field of the same size with the ratio of the normalized GSTT (NGSTT) value at 4.5 cm, which corresponds to a 10 cm x 10 cm square field, to the NGSTT value at the final moving jaw position for the EDW field. Once the NGSTT factor is separated from the output for EDW fields, the field-size-dependent wedge factor varies less than 1%. This approach allows a simple and accurate determination of the output factor for rectangular and asymmetric EDW fields. The equivalent square method for determining output for rectangular fields applies to EDW fields with the same precision as it does to open fields. The output for EDW fields strongly depends on the final moving jaw position. Every 5-mm change in the final moving jaw position causes 3.5-5.4% error in monitor unit calculation.

The article discusses how to use the standard utility program on Theraplan to create physical wedges which are equivalent to each of the enhanced dynamic wedges. The user must first create segmented treatment tables for each wedge, using a spreadsheet, and then convert these tables to equivalent thicknesses of an arbitrary wedge material. These thicknesses are then supplied to Theraplan. The paper discusses the agreement achieved between Theraplan and measured data, and the quality assurance procedures which should be adopted.

An EDW field is in principle a sum of fields with different sizes. The Helax TMS 3.1 dose planning system uses pre-existing open beam data and information specific to the geometry of the accelerator treatment head including flattening filter and collimators to generate open fields. These open fields are then summed using the Segmented Treatment Tables (STT) to generate the Enhanced Dynamic Wedge fields. Verification of predicted fields and output factors against measured data are discussed for different wedge angles, asymmetric fields and shaped fields.

Dynamic wedge distributions are produced by closing one jaw continuously while simultaneously controlling dose as each position of the jaw. This method of producing wedge distributions requires more frequent Quality Assurance checks, such as verification of wedge profile, wedge factor and verification of the accuracy of the digital position readout for the jaws used for dynamic wedge. “Hard” wedges require only the verification of wedge factor and the verification of reproducibility of mechanical position in the beam. This paper will discuss methods and equipment used for the Quality Assurance of Enhanced Dynamic Wedges.

This paper investigates the accuracy of the two available calculation algorithms of the Oncentra MasterPlan three‐dimensional treatment planning system (TPS) – the pencil beam method and collapsed‐cone convolution – in modeling the Varian enhanced dynamic wedge (EDW). Measurements were carried out for a dual high energy (6–15 MV) Varian DHX‐S linear accelerator using ionization chambers for beam axis measurements (wedge factors and depth doses), film dosimetry for off‐axis dose profiles measurements, and a diode matrix detector for two dimensional absolute dose distributions. Using both calculation algorithms, different configuration of symmetric and asymmetric fields varying the wedge's angle were tested. Accuracy of the treatment planning system was evaluated in terms of percentage differences between measured and calculated values for wedge factors, depth doses, and profiles. As far as the absolute dose distribution was concerned, the gamma index method (Low et al. (13) ) was used with 3% and 3 mm as acceptance criteria for dose difference and distance‐to‐agreement, respectively. Wedge factors and percentage depth doses were within 1% deviation between calculated and measured values. The comparison of measured and calculated dose profiles shows that the Van Dyk's acceptance criteria (Van Dyk et al. (14) ) are generally met; a disagreement can be noted for large wedge angles and field size limited to the low dose‐low gradient region only. The 2D absolute dose distribution analysis confirms the good accuracy of the two calculation algorithms in modeling the enhanced dynamic wedge. PACS number: 87.53.Bn, 87.55.kn, 87.56.ng

Purpose: A multi-leaf collimator (MLC) based dynamic wedge (MDW), which provide similar dose profile of physical wedge (PW) along x-jaw direction while significant monitor unit (MU) reduction, was developed and investigated for clinical use. Methods: A novel technique was used to create the wedge profile using MLC. A modification was applied to the DICOM-RT format file of the plan made with the PW to replace PW with MDW. The Varian enhanced dynamic wedge profile was used to produce MLC sequence, while the MU of the wedged field was recalculated using PW factor and fluence map. The profiles for all possible MDWs to substitute PWs were verified in 6/15 MV x-ray irradiations. New plans with MDWs were compared with the original plans in 5 rectal, 5 RT breast and 5 liver cases. Results: The wedge profile of the MDW fields were well matched with those of PWs inside the fields while less scatter than PW out of the fields. For plan comparisons of the clinical cases no significant dose discrepancy was observed between MDW plan and PW’s with the dose volume histograms. The maximum and mean doses in PTVs are agreed within 1.0%. The Result of OARs of MDW plans are slightly improved in the maximum doses (3.22 ∼ 150.4 cGy) and the mean doses (17.18 ∼ 85.52 cGy) on average for all cases while the prescribed doses are 45 Gy for rectal cases, 40 or 45 Gy for liver cases and 50 Gy for breast cases. The MUs of the fields which replace PW with MDW are reduced to 68% of those of PW. Conclusion: We developed a novel dynamic wedge technique with MLC that shows clinical advantage compared to PW.

Purpose: To study the dosimetric properties of Enhanced Dynamic Wedge (EDW) using PTW Seven29 ion chamber array Methods: PTW Seven29 ion chamber array and Solid Water phantoms for different depths were used for the study. The study was carried out in Varian Clinac ix with photon energies, 6MV & 15MV. Primarily the solid water phantoms with the 2D array were scanned using a CT scanner (GE Optima 580) at different depths. These scanned images were used for EDW planning in an Eclipse treatment planning system (version 10). Planning was done for different wedge angles and for different depths for 6MV & 15MV. A dose of 100 CGy was delivered in each cases. For each delivery, calculated the Monitoring Unit (MU) required. Same set-up was created before delivering the plans in Varian Clinac-ix. For each clinically relevant depth and for different wedge angles, the same MU was delivered as calculated. Different wedged dose distributions where reconstructed from the measured 2D array data using the in-house developed excel program. Results: It is observed that the shoulder like region in the profile which reduces as depth increases. For the same depth and energy, the percentage difference between planned and measured dose is lesser than 3%. For smaller wedge angles, the percentage difference is found to be greater than 3% for the largest wedge angle. Standard deviation between measured doses at shoulder region for planned and measured profiles is 0.08 and 0.02 respectively. Standard deviations between planned and measured wedge factors for different depths (2.5cm, 5cm, 10cm, and 15cm) are (0.0021, 0.0007, 0.0050, 0.0001) for 6MV and (0.0024, 0.0191, 0.0013, 0.0005) for 15MV respectively. Conclusion: The 2D Seven29 ion chamber array is a good tool for the Enhanced Dynamic Wedge (EDW) dosimetry.