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BACKGROUND: The aim of the modern radiotherapy is to get a homogenous dose distribution in PTV, which is obtained by using for example physical or dynamic wedges. The using of a physical wedge has provided such isodose distributions but their use resulted in detrimental dosimetric consequences, for example beam hardening effects and practical consequences of filter handling or possible misalignment. Linear accelerators are now equipped with collimator jaws systems and controlled by modern computers and it is possible to generate wedge shaped isodose distributions dynamically. Because of a more comfortable use of a dynamic wedge, there are alternatives to the standard physical wedge. During the treatment, different segments of the treatment field can be exposed to the primary beam at different intervals of time. This process of shrinking the field while modulating the collimator jaw velocity and dose rate creates the desired wedge-shaped isodose gradient across the treatment field. Dynamic wedges can replace physical wedges but they need more precise dosimetry and quality control procedures. AIM: The aim of this study was to perform a multienergetic verification of dynamic wedge angles using the multichannel detector PTW LA48 linear array. MATERIAL AND METHODS: The measurements of angle value of dynamic wedges were performed for Clinac 2300 C/D accelerators (Varian). The accelerator was equipped with the EDW option for 6 MV and 15 MV photon beams. In this case, 7 wedge angle values were used: 10°, 15°, 20°, 25°, 30°, 45° and 60°. The dynamic wedges are realized by continuous movement of one collimator jaw. The field size is gradually reduced until the collimator is almost completely closed or the field increases, while the beam is on. The measurements were divided in two steps: in the first step, the dynamic wedges were verified with the recommended values and in the second step there the planned and measured angles of dynamic wedges were compared. Measurements were made by means of LA48 linear array of ionization chambers (PTW). The results of the measurements were compared with the reference profile produced by the treatment planning system ECLIPSE 8.5 (Varian). RESULTS: The results showed differences between measured and calculated angle of dynamic wedges. The differences were observed for both energies in the case of a small angle value. For energies 6 MV and 15 MV, almost all percentage difference between the measured and calculated profile was lower than 5%. The biggest difference was observed in the first step of measurements when the angle of Dynamic Wedge was verified. The comparison between the planned and measured angle value of Dynamic Wedge showed the difference between 0.1% and 4.5%. The difference for 6 MV for the angle value of 10° in orientation IN was 1.1% and for energy 15 MV in the same case the difference was 3.8%. Thinner wedges exhibit less difference. CONCLUSION: It is necessary to provide comprehensive quality control procedure for enhanced dynamic wedges. Verification measurements should be an obligatory procedure in the recommendation for the testing of medical accelerators. These results are the preliminary results to provide measurements in other Polish Cancer Centres.
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Buildup region dose calculation of Pinnacle3 (version 9.0), a treatment planning system (TPS) commissioned using cylindrical ionization chamber measurements, have been verified experimentally. Dose values measured using Attix parallel plate ionization chamber were compared with those calculated by Pinnacle3 for a variety of clinical setups involving: 6 MV and 15 MV photon beams, open fields, enhanced dynamic wedges, physical wedges, block tray, 85, 100 and 120 cm source-to-surface distances, and square field sizes ranging from 3 × 3 to 30 × 30 cm2 . The dose difference (DD) and distance-to-agreement (DTA) techniques were used to evaluate the discrepancy between measured and calculated dose values. Based on the criteria of DD less than 2% or DTA less than 2mm, 93.7% of 1,710 dose points for the 6 MV and 96.1% of 2,244 dose points for 15 MV passed. Dose points that failed were mostly for open fields, block tray fields, and physical wedges (15 and 30 degrees) fields; this is attributed to high electron contamination (EC) associated with these fields. The levels of discrepancies between measured and calculated dose values were greatly reduced after remodeling the EC in Pinnacle3 using Attix chamber measurements, an indication that the EC equation in Pinnacle3 may be adequate for modeling EC in the dose buildup region, and the commissioning of a TPS using cylindrical ionization chamber measurements may not provide accurate buildup region dose calculation. Attix chamber measurements were validated using GafChromic EBT2 film; the disagreement was less than 3% for 89.9% of dose values compared.
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The aim of this study is to compare the dosimetry of the physical wedge (PW) and enhanced dynamic wedge (EDW) in radiotherapy of rectal cancer. Two wedge angles of 45° and 60° were used in the comparison due to the size of the pelvis contour. 6 and 15 MV photon beams produced from a Varian 21 CD linear accelerator were used. Thirty rectum patients were investigated using the three-field technique. Treatment plans using the PWs and EDWs were created using the Eclipse treatment planning system. Monitor units, plan normalization value, maximum and minimum doses in the planning target volume (PTV), dose conformity index, dose homogeneity index and uniformity index were determined for each treatment plan. The average dose coverage for the PTV with EDW and PW plans were compared. The PTV received prescription doses of 100.9±0.74%, 101.01±1.63% for the EDW (45°, 60°) compared to 101.2±1.65%, 101.3±1.33% for the PW (45°, 60°). Homogeneity indices were (0.11±0.02%, 0.11±0.05%) for the EDW (45°, 60°), and (0.15±0.1%, 0.16±0.11%) for the PW (45°, 60°), respectively. The EDW at 45° had better target coverage with higher conformity index value of 0.98 ± 0.01 compared to the other wedges. A statistically significant (p < 0.01) change in plan normalization values and fewer monitor units were found using the EDW at 45°. We conclude that the EDW at 45° results in an improvement to the plan evaluation parameters presented and thus increases dose efficacy for radiotherapy of rectal cancer.
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PURPOSE: To study the effect of the virtual wedge and physical wedge filters on the surface and build-up region doses for 6 and 15MV high-energy photon beams for different field sizes and various source to surface distance(SSD). METHODS: The measurements were made in water equivalent (PMMA) solid phantom in the build-up region at various SSD for various field sizes using virtual and physical wedge filters having different angles. A parallel-plate ion chamber (Markus) was used to measure the percent depth doses at surface and buildup region. Plane parallel ion chamber with fixed plate separation on the surface and buildup region would perturbate the dose measured, to get the proper dose over response correction factor was used. RESULTS: The percentage depth dose at surface (PDD0) increased as the field size increased for open, virtual, and physical wedged beams. For open, 30 degree physical, and virtual wedged beams, the surface doses were found to be 15.4%, 11.2%, and 15.2% with 6-MV photons and 11.2%, 9.4%, 11.2% with 15-MV photons, respectively, at 10 × 10 cm2 field size at 100cm SSD.As SSD increases percentage depth dose at surface (PDD0) decreases for open,physical and virtual wedge field. CONCLUSIONS: Percentage depth dose at surface (PDD0) of virtual wedged beams were similar to those of open beams. PDD0 of physical wedged beams were lower than those of open and virtual wedged beams. Surface doses for both PW and VW increases with field size and small increase in surface dose for both PW and VW fields as wedge angle increases especially for large fields.
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PURPOSE: To compare an advantage/disadvantage between Field-in-Field (FIF) technique and conventional physical wedge (PW) technique for a whole breast (WB) tangential field irradiation. METHODS AND MATERIALS: Total 86 patients were included in this study. 46 of them were left breast cancer cases. FIF/PW plans were created by Eclipse (V7.3, Varian) with 6MV or 6MV mixed with 18MV. Plans had a same ioscenter location, beam setup and normalized isodose line selection for each case. Varian 21EX Linac with 120 MLC was used for beam delivery. Two plans were compared by PTV encompassed by 95% isodose line (V95), dose inhomogeneity (DI), dose received by 10% volume of lung (D10), mean lung dose (MLD), dose received by 5% volume of heart (D5), Mean heart dose (MHD), total MU, maximum dose in the plan and the number of field needed for each fraction. RESULTS: Comparing with PW plan, FIF plan showed an average percentage improvement of V95 was 0.1±1.6, DI was 0.6±5.0, MLD was 1.5±4.2, D5 was 2.0±8.8, MHD was 3.2±4.6. However, D10 increased by 1.4%±0.050. FIF lowered an average daily MU by 28.5%±0.080, maximum dose by 0.5%±0.018, and increased number of treatment field by 1.50±0.356. There were 12 cases treated with mixed beam in PW technique vs 10 in FIF technique. CONCLUSION: The advantages of FIF technique included: (1) Reduce radiation contamination to contra lateral breast and Linac room induced activity by remove the PW, lower MU and diminish a higher energy. (2) Time saving was not only from less MU but also from not need go into the treatment room for a wedge adjustment. (3) Reduced the therapist work load. (4) Regular MU 2nd check was applied because there was not FIF merge involved in the treatment field. With a MLC to shape the field and treatment record/verification system to control the treatment, increasing number of treatment field didn't show as a problem.
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PURPOSE: To evaluate impact on surface dose, Depth of dose maximum (dmax) and depth dose distribution due to physical wedge filters for different wedge angle were studied for 6MV flattened (6MV FB) and 7MV unflattened (7MV UFB) photon beams. METHODS: The flattening filter and primary collimator are the major sources of producing the scattered radiation and these parameters affect the surface dose, dmax and dose distribution. In this study, open fields surface dose, dmax and depth dose distribution values were compared with physical wedge filter for 6MV FB and 7MV UFB .The measurement carried out in Siemens - ARTISTE linear accelerator with diode detector along the central axis of the beam at 100 cm source to surface distance using IBA blue water phantom for 6MV FB and 7MV UFB x-ray beams. RESULTS: The surface dose increased as the field size increased for open and physical wedge fields for 6MV FB and 7MV UFB beams. For open fields, Surface doses relative to the dose at dmax ranged from 0.443 to 0.569 and 0.463 to 0.668 for field sizes of 5 × 5 to 20×20 cm2 for the 7MV UFB and 6MV FB beam respectively. The measured surface dose for 150, 300,450 and 600 wedge field values are 0.396 to 0.504, 0.366 to 0.484, 0.342 to 0.464 and 0.347 to 0.47 respectively for 7MV UFB and 0.424 to 0.566, 0.398 to 0.555, 0.3860 to 0.5430 and 0.389 to 0.55 respectively for 6MV FB. CONCLUSIONS: We found that dmax of wedged beams were higher than those open beams for field size up to 10 × 10 cm2 , Surface doses of wedged beams were lower than those of open beams for 7MV UFB and 6MV FB. Surface dose of the 7MV UFB were lower than the 6MV FB for open and wedged beams.
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As the first Canadian users of the Velocity™ program offered by Siemens, we would like to share our experience with the program. The Velocity program involves the measurement of the commissioning data by an independent Physics consulting company at the factory test cell. The data collected was used to model the treatment beams in our planning system in parallel with the linac delivery and installation. Beam models and a complete data book were generated for two photon energies including Virtual Wedge, physical wedge, and IMRT, and 6 electron energies at 100 and 110 cm SSD. Our final beam models are essentially the Velocity models with some minor modifications to customize the fit to our liking. Our experience with the Velocity program was very positive; the data collection was professional and efficient. It allowed us to proceed with confidence in our beam data and modeling and to spend more time on other aspects of opening a new clinic. With the assistance of the program we were able to open a three-linac clinic with Image-Guided IMRT within 4.5 months of machine delivery.