Physical Wedge Research Articles

Comparison of field-in-field radiotherapy with conformal radiotherapy for unilateral cervical malignant lymphoma.

This study compared field-in-field (FIF) radiotherapy with conformal radiotherapy with physical wedges for the treatment of unilateral cervical malignant lymphoma. Two treatment plans, the FIF technique and conformal RT, were generated for each of 32 patients with unilateral cervical malignant lymphoma. To compare the 2 treatment plans, dose-volume histograms of the planning target volume (PTV), the thyroid, submandibular gland, carotid artery, mucosa, spinal cord, and surrounding normal tissue, and monitor unit (MU) were analyzed. The FIF technique showed significant reduction in the mean dose of thyroid, submandibular gland, carotid artery and mucosa, the maximum dose of the spinal cord and PTV, and the volume receiving＞107% of the prescribed dose of surrounding normal tissue (p＜0.001). In addition, there were gains in the homogeneity index of the PTV for FIF. Furthermore, the total MU was also lower for the FIF technique than for the wedge technique (p＜0.001). Compared with the wedge technique, the FIF technique improved the dose homogeneity of the PTV, reduced the dose to normal structures, and was associated with fewer MUs in the treatment of patients with cervical malignant lymphoma.

SU‐E‐T‐178: Clinical Feasibility of Multi‐Leaf Collimator Based Dynamic Wedge

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.

SU‐E‐T‐362: Enhanced Dynamic Wedge Output Factors for Varian 2300CD and the Case for a Reference Database

Purpose:Dose inhomogeneity in treatment planning can be compensated using physical wedges. Enhanced dynamic wedges (EDW) were introduced by Varian to overcome some of the short comings 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 adding credence to the case of the validity of reference databases.Methods: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.Results:The EDWOF for 6 MV varied from 0.980 for a 5×5 cm 10 degree wedge to 0.424 for 20×20 cm 60 degree wedge. Similarly for 20 MV, the EDWOF varied from 0.986 for 5×5 cm 10 degree wedge to 0.529 for 20×20 cm 60 degree wedge. EDWOF are highly dependent on field size. 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 18MV 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.Conclusion:The consistency of EDWOF across models and institution provide further support that, a standard data set of basic photon and electron dosimetry could be established, as a guide for future commissioning, beam modeling and quality assurance purposes.

Investigating in-field and out-of-field neutron contamination in high-energy medical linear accelerators based on the treatment factors of field size, depth, beam modifiers, and beam type

PurposeWe analysed the effects of field size, depth, beam modifier and beam type on the amount of in-field and out-of-field neutron contamination for medical linear accelerators (linacs). MethodsMeasurements were carried out for three high-energy medical linacs of Elekta Synergy Platform, Varian Clinac DHX High Performance and Philips SL25 using bubble detectors. The photo-neutron measurements were taken in the first two linacs with 18 MV nominal energy, whereas the electro-neutrons were measured in the three linacs with 9 MeV, 10 MeV, 15 MeV and 18 MeV. ResultsThe central neutron doses increased with larger field sizes as a dramatic drop off was observed in peripheral areas. Comparing with the jaws-shaped open-field of 10 × 10 cm, the motorised and physical wedges contributed to neutron contamination at central axis by 60% and 18%, respectively. The similar dose increment was observed in MLC-shaped fields. The contributions of MLCs were in the range of 55–59% and 19–22% in Elekta and Varian linacs comparing with 10 × 10 and 20 × 20 cm open fields shaped by the jaws, respectively. The neutron doses at shallow depths were found to be higher than the doses found at deeper regions. The electro-neutron dose at the 18 MeV energy was higher than the doses at the electron energies of 15 MeV and 9 MeV by a factor of 3 and 50, respectively. ConclusionThe photo- and electro-neutron dose should be taken into consideration in the radiation treatment with high photon and electron energies.

유방암 수술기법에 따른 방사선치료계획 기법의 선택

Techniques, using physical wedge filter and using dynamic wedge filter and FIF(Field in Field) and ISCT(Irregular Surface Compensating Technique), have been developed according to progress of radiation therapy of breast cancer. Measurement of dose was done to judge the usefulness of technique using three cases, non tissue loss after breast conserving operating and tissue loss after breast conserving operating and mastectomy. Dose indexes of breast tissue, CI (Conformity Index), HI (Homogeneity Index) and QOC (Quality of Coverage), dose index of skin, or dose indexes of lung, volume of 50 percent dose and 20 percent dose were estimated and compared. Using dynamic wedge filter is useful plan at non tissue loss allowing for high dose of lung. FIF and ISCT are useful plan at tissue loss. ISCT is useful plan at mastectomy. Henceforth, we need to apply to valid plan and body type and thorax size.

Treatment planning validation for symmetric and asymmetric motorized wedged fields

Purpose: Wedged beam are often used in clinical radiotherapy to compensate missing tissues and dose gradients. The Elekta Precise linear accelerator supports an internal motorized wedge, which is a single large, physical wedge on a motorized carriage. In this study, the dosimetric performance of Elekta precise three dimensional treatment planning system (3DTPS) is evaluated by comparing the calculated and measured doses. Methods: The calculations were performed by the 3DTPS for symmetric as well as asymmetric fields in a source to skin distance (SSD) setup at the depth of maximum dose (d max ) as well as at 5, 10, and 20 cm depths in water phantom using 60° motorized wedges for field sizes of 4 × 4, 10 × 10, and 20 × 20 cm 2 for 6 and 15 MV photon beams. Measurements were produced by Elekta Precise linear accelerator using 0.125 cc volume ionization chamber. Results: Good agreement between the measured and calculated isodose lines were found, with the maximum difference not exceed 5%. The difference between the calculated and measured data increases as the field size decreases, and the deviation in symmetric setting was less than that of asymmetric setting. The increase in wedge angle led to increase in the difference between calculated and measured data. Conclusion: The results from this study showed that the accuracy of Elekta Precise 3DTPS used with the motorized wedges for symmetric and asymmetric fields is adequate for the clinical applications under the studied experimental conditions.

A self-sufficient method for calibration of Varian electronic portal imaging device

Electronic portal imaging device (EPID) is currently used for dosimetric verification of IMRT fields and linac quality assurance (QA). It is critical to understand the dosimetric response and perform an accurate and robust calibration of EPID. We present the implementation of an efficient method for the calibration and the validation of a Varian EPID, which relies only on data collected with that specific device. The calibration method is based on images obtained with five shifts of EPID panel. With this method, the relative gain (sensitivity) of each element of a detector matrix is calculated and applied on top of the calibration determined with the flood-field procedure. The calibration procedure was verified using a physical wedge inserted in the beam line and the corrected profile shows consistent results with the measurements using a calibrated 2D array. This method does not rely on the beam profile used in the flood-field calibration process, which allows EPID calibration in 10 minutes with no additional equipment compared to at least 2 hours to obtain beam profile and scanning beam equipment requirement with the conventional method.

Application of a radiophotoluminescent glass dosimeter to nonreference condition dosimetry in the postal dose audit system.

The purpose of this study was to obtain a set of correction factors of the radiophotoluminescent glass dosimeter (RGD) output for field size changes and wedge insertions. Several linear accelerators were used for irradiation of the RGDs. The field sizes were changed from 5 × 5 cm to 25 × 25 cm for 4, 6, 10, and 15 MV x-ray beams. The wedge angles were 15°, 30°, 45°, and 60°. In addition to physical wedge irradiation, nonphysical (dynamic/virtual) wedge irradiations were performed. The obtained data were fitted with a single line for each energy, and correction factors were determined. Compared with ionization chamber outputs, the RGD outputs gradually increased with increasing field size, because of the higher RGD response to scattered low-energy photons. The output increase was about 1% per 10 cm increase in field size, with a slight difference dependent on the beam energy. For both physical and nonphysical wedged beam irradiation, there were no systematic trends in the RGD outputs, such as monotonic increase or decrease depending on the wedge angle change if the authors consider the uncertainty, which is approximately 0.6% for each set of measured points. Therefore, no correction factor was needed for all inserted wedges. Based on this work, postal dose audits using RGDs for the nonreference condition were initiated in 2010. The postal dose audit results between 2010 and 2012 were analyzed. The mean difference between the measured and stated doses was within 0.5% for all fields with field sizes between 5 × 5 cm and 25 × 25 cm and with wedge angles from 15° to 60°. The standard deviations (SDs) of the difference distribution were within the estimated uncertainty (1SD) except for the 25 × 25 cm field size data, which were not reliable because of poor statistics (n = 16). A set of RGD output correction factors was determined for field size changes and wedge insertions. The results obtained from recent postal dose audits were analyzed, and the mean differences between the measured and stated doses were within 0.5% for every field size and wedge angle. The SDs of the distribution were within the estimated uncertainty, except for one condition that was not reliable because of poor statistics.

SU-E-T-562: Scanned Percent Depth Dose Curve Discrepancy for Photon Beams with Physical Wedge in Place (Varian IX) Using Different Sensitive Volume Ion Chambers

Purpose: To investigate and report the discrepancy of scanned percent depth dose (PDD) for photon beams with physical wedge in place when using ion chambers with different sensitive volumes. Methods/Materials: PDD curves of open fields and physical wedged fields (15, 30, 45, and 60 degree wedge) were scanned for photon beams (6MV and 10MV, Varian iX) with field size of 5×5 and 10×10 cm using three common scanning chambers with different sensitive volumes – PTW30013 (0.6cm3), PTW23323 (0.1cm3) and Exradin A16 (0.007cm3). The scanning system software used was OmniPro version 6.2, and the scanning water tank was the Scanditronix Wellhoffer RFA 300. The PDD curves from the three chambers were compared. Results: Scanned PDD curves of the same energy beams for open fields were almost identical between three chambers, but the wedged fields showed non-trivial differences. The largest differences were observed between chamber PTW30013 and Exradin A16. The differences increased as physical wedge angle increased. The differences also increased with depth, and were more pronounced for 6MV beam. Similar patterns were shown for both 5×5 and 10×10 cm field sizes. For open fields, all PDD values agreed with each other within 1% at 10cm depth and within 1.62% at 20 cm depth. For wedged fields, the difference of PDD values between PTW30013 and A16 reached 4.09% at 10cm depth, and 5.97% at 20 cm depth for 6MV with 60 degree physical wedge. Conclusion: We observed a significant difference in scanned PDD curves of photon beams with physical wedge in place obtained when using different sensitive volume ion chambers. The PDD curves scanned with the smallest sensitive volume ion chamber showed significant difference from larger chamber results, beyond 10cm depth. We believe this to be caused by varying response to beam hardening by the wedges.

Comparison of CCC and ETAR dose calculation algorithms in pituitary adenoma radiation treatment planning; Monte Carlo evaluation

AbstractAimsTo verify the accuracy of two common absorbed dose calculation algorithms in comparison to Monte Carlo (MC) simulation for the planning of the pituitary adenoma radiation treatment.Materials and methodsAfter validation of Linac's head modelling by MC in water phantom, it was verified in Rando phantom as a heterogeneous medium for pituitary gland irradiation. Then, equivalent tissue-air ratio (ETAR) and collapsed cone convolution (CCC) algorithms were compared for a conventional three small non-coplanar field technique. This technique uses 30 degree physical wedge and 18 MV photon beams.ResultsDose distribution findings showed significant difference between ETAR and CCC of delivered dose in pituitary irradiation. The differences between MC and dose calculation algorithms were 6.40 ± 3.44% for CCC and 10.36 ± 4.37% for ETAR. None of the algorithms could predict actual dose in air cavity areas in comparison to the MC method.ConclusionsDifference between calculation and true dose value affects radiation treatment outcome and normal tissue complication probability. It is of prime concern to select appropriate treatment planning system according to our clinical situation. It is further emphasised that MC can be the method of choice for clinical dose calculation algorithms verification.

Impact of respiratory motion on breast tangential radiotherapy using the field-in-field technique compared to irradiation using physical wedges

BackgroundThis study aimed to evaluate whether the field-in-field (FIF) technique was more vulnerable to the impact of respiratory motion than irradiation using physical wedges (PWs).Patients and methodsTen patients with early stage breast cancer were enrolled. Computed tomography (CT) was performed during free breathing (FB). After the FB-CT data set acquisition, 2 additional CT scans were obtained during a held breath after light inhalation (IN) and light exhalation (EX). Based on the FB-CT images, 2 different treatment plans were created for the entire breast for each patient and copied to the IN-CT and EX-CT images. The amount of change in the volume of the target receiving 107%, 95%, and 90% of the prescription dose (V107%, V95%, and V90%, respectively), on the IN-plan and EX-plan compared with the FB-plan were evaluated.ResultsThe V107%, V95%, and V90% were significantly larger for the IN-plan than for the FB-plan in both the FIF technique and PW technique. While the amount of change in the V107% was significantly smaller in the FIF than in the PW plan, the amount of change in the V95% and V90% was significantly larger in the FIF plan. Thus, the increase in the V107% was smaller while the increases in the V95% and V90% were larger in the FIF than in the PW plan.ConclusionsDuring respiratory motion, the dose parameters stay within acceptable range irrespective of irradiation technique used although the amount of change in dose parameters was smaller with FIF technique.

Intensity Modulated Radiotherapy Using Multiple in Fields Compared to Wedged Fields in Breast Irradiation: Clinical Impact on Early Skin Reaction and Organs at Risk Doses

Objective: To measure the impact of multiple fields in filed (MFIF) technique on dose homogeneity, doses to organs at risk (OARs) and acute skin toxicity in comparison to physical wedged (PW) tangential technique. Methods: The study population consisted of 75 patients who had breast-conserving surgery and whole-breast radiation using MFIF. These patients were matched one-to-one to a control group of 75 patients treated with PW tangents, following ethical board approval and signing informed consents. Acute skin reaction was graded by CTCAE 3.0 scoring and multiple regression analysis of covariates was performed. Results: CTCAE grade2 acute skin reaction occurred in 61.3% PW vs. 32% MFIF while grade 3 was encountered in 24% PW vs. 10.7% MFIF patients (P<0.01). Multiple regression analysis confirmed the excessive skin reaction to the related radiation therapy technique (P=0.0002) and whole breast PTV (P<0.001). Homogeneity index within PTV was significantly improved in MFIF plans (0.84 ± 0.7) compared with PW (0.94 ± 0.15) with a (P<0.01). There was also a significant reduction, in lung V20 from 14.3% ± 1.1 to 10.6 % ± 1.4 (P<0.01), heart V30 from 7% ± 5.8 to 6% ± 4.9 (p<0.001). Contralateral breast volume receiving dose more than 2 Gy was also reduced 2.3% ± 0.5 PW to 1.2% ± 0.2 MFIF (P<0.01). Conclusion: The MFIF technique significantly improved PTV dose homogeneity index, while significantly reduced the incidence of grade 2/3 acute skin reaction and doses to OARs when compared to PW tangential fields in whole breast radiotherapy.

Dose Validation of Physical Wedged Asymmetric Fields in Artiste Linear Accelerator

Aim: The purpose of this study was to make a comparison between measured and calculated physical wedge dose distributions using the superposition algorithm. Settings and Design: The accurate determination of absorbed dose is important radiotherapy because of the relatively steep sigmoidal dose response curves for both tumor control and normal-tissue damage. Materials and Methods: High-energy photons (6 and 10 MV) from Artiste Treatment System Linear Accelerator Machine, available at Alexandria Ayadi Al-Mostakbal Oncology Center, were used. Results and Discussion: The results showed that the difference between measured and calculated wedged isodose curves depends on field size, beam energy, and the angle of the used wedge. Conclusion: The results showed that the presence of a wedge alters the primary and scattered components generated by a linear accelerator and causes beam hardening in 6 and 10 MV. The beam hardening increased as the wedge angle increased.

Dosimetric verification of enhanced dynamic wedges by a 2D ion chamber array

Wedge filters are commonly used to achieve dose uniformity in the target volume in radiotherapy and can be categorized as physical wedges (PWs) and enhanced dynamic wedges (EDWs). The EDW generates PW-like dose profiles while moving the upper jaw in the Y directions with a varying dose rate in the treatment beams. Task Group 53 of the AAPM (American Association of Physicists in Medicine) recommended that the dynamic wedge be verified before implementation in the radiation treatment planning (RTP) system. The aim of this study was to use the I’mRT MatriXX to verify the dose profiles of the EDWs manufactured by Varian. We used Pencil Beam Convolution algorithms (eclipse 8.6) for the calculation and I’mRT MatriXX with Plastic Water® phantom MULTICube for dose measurements. The gamma indices of the calculations and the measurements for the EDWs were 84.84% and 86.54% in 2%/2 mm tolerance, and 99.47% and 99.64% in 3%/3 mm tolerance for wedge angles of 15°, 30°, 45° and 60°, respectively. The dose distributions differed between the calculations using the system and the measurements in the penumbra and the outer beam regions of the wedge fields. We confirmed that the dosimetric verifications of the EDW were acceptable when using the criterion for external beam dose calculations of Task Group 53.

SU‐E‐T‐357: Dosimetric Verification of the Enhanced Dynamic Wedges Using a 2D Ion Chamber Array

Purpose: Wedge filters are commonly used to achieve dose uniformity in the target volume in radiotherapy and can be categorized as the physical wedge (PW) and the enhanced dynamic wedge (EDW. The EDW generates PW‐like dose profiles while moving the upper jaw in the Y directions with a varying dose rate in the treatment beams. Task Group 53 of the AAPM (American Association of Physicists in Medicine) recommended that the dynamic wedge should be verified before implementation in the radiation treatment planning (RTP) system in order to ensure the same capabilities between the PW and the dynamic wedge. The aim of this study was to verify the dose profiles of the EDWs manufactured by Varian with the ImRT MatriXX. Methods: The ImRT MatriXX was used to compare the dose distributions between PW and EDW with wedge angles of 15°, 30°, 45° and 60° in the axial plane. The passing criteria of DD and the DTA were selected as 1%/1mm, 2%/2mm and 3%/3mm. The gamma evaluations were performed with the calculated and measured dose distributions for the varied wedge angle in EDW. Results: The gamma index of the calculations and the measurements for the EDWs were 84.84% and 86.54% in 2%/2mm tolerance, and 99.47% and 99.64% in 3%/3mm tolerance for the wedge angles of 15°, 30°, 45° and 60°, respectively. The dose distributions differed between the treatment planning system (TPS) calculations and the measurements in the penumbra and the outer beam regions of the wedge fields. Conclusion: We confirmed that the dosimetric verifications of the EDW were acceptable with an acceptability criterion for external beam dose calculations of Task Group 53. This work has supported by the Yeungnam University Academic Research Fund (212A380146).

SU-D-137-04: Comparison of Treatment Planning Techniques in Treatment of Carcinoma of Left Breast: Second Cancer Risk Perspective

Purpose: To compare the secondary cancer risk (SCR) between different planning techniques for treatment of Ca. Lt.breast patients. Methods: Five treatment plans; 3DCRT tangential fields with physical wedge (PW), enhanced dynamic wedges (EDW), electronic compensator (EC), IMRT tangential fields (ITF) and Rapid-Arc (RA) plan (partial arcs) with 6 MV photon beams were generated for a carcinoma of Lt.breast patient of age 40 to a prescription dose of 50.4Gy in 28 fractions. The SCR was estimated using the organ equivalent dose (OED) concept with a linear exponential, a plateau, and a linear dose response model for OARs. Also, the low dose bath volume (5Gy) was calculated for all the plans. Results: For contralateral breast the SCR relative to PW were (linear, plateau, linear-exponential) (−25.89%, −99.985%, −85.96%) for RA, (−50.12%,−41.94%,−44.57%) for ITF, (−47.78%, −38.43%,−42.05%) for EC and (−32.70%,−26%,−28.31%) for EDW respectively. The relative SCR for heart and Lt-lung were (−89.99% & −89.38%) for RA, (−0.05% & 5.69%) for ITF, (−0.16% & 0.04%) for EC and ( −0.04% & 0.01%)for EDW. In contrast, for skin the relative SCR were 77.68%, −7.71%, −11.11% and −9.04% for RA, ITF, EC and EDW respectively. Also, the 5Gy low dose volume relative to PW for RA was 201.45%, whereas the same for ITF, EC and EDW were −8.41%, −7.33% and −4.2%. Conclusion: Compared to all plans, RA plan showed high conformity for CTV and superior heart, contralateral breast and left lung sparing. But SCR for skin and the low dose volume were significantly high in RA. ITF plan showed relatively better sparing for contralateral breast and heart at the same time has the least low dose bath volume. EC plan shows moderately good sparing for OARs while scoring least SCR value for skin. EDW and PW plans were similar but later had high SCR for contralateral breast.

Multienergetic verification of dynamic wedge angles in medical accelerators using multichannel linear array

BackgroundThe 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. AimThe aim of this study was to perform a multienergetic verification of dynamic wedge angles using the multichannel detector PTW LA48 linear array. Material and methodsThe 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 6MV and 15MV 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). ResultsThe 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 6MV and 15MV, 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 6MV for the angle value of 10° in orientation IN was 1.1% and for energy 15MV in the same case the difference was 3.8%. Thinner wedges exhibit less difference. ConclusionIt 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.

Dose distribution analysis of physical and dynamic wedges by using an intensity-modulated radiotherapy MatriXX

This study investigated differences between the physical wedge and the dynamic wedge distributions of radiation by using an intensity-modulated radiotherapy (ImRT) MatriXX. The linear accelerator used X-rays with energy levels of 6 MV and 10 MV to adjust the collimator by motoring the independent jaws (X1, X2, Y1, Y2) for setting wedge angles of 15, 30, 45, and 60 degrees. The collimator field size was set as 10 × 10 cm2 or 20 × 20 cm2 at the maximum dose point. The dose distribution for each wedge had ±5% and ±11% errors for field sizes of 10 × 10 cm2 and 20 × 20 cm2, respectively. The error was greatest at a wedge angle of 45 degrees and was pronounced at the end of the dynamic wedge where Y1 and Y2 met. Consequently, concluded that the dose distributions were similar for both wedges for the field size of a small beam profile. The beam dose was greatly increased at the end of the dynamic wedge. A more precise estimate of the therapeutic dose of radiation for a dynamic wedge that nearly matches that of the physical wedge can be achieved by correcting of the increasing part of the beam dose. The findings imply that a heavy wedge filter should not be used when calculating the isodose distribution and the therapeutic dose.

Evaluation of Fetal Dose in Breast Radiotherapy With Shielding and Wedges

The fetus may be seriously affected by the peripheral dose when a pregnant woman undergoes breast radiotherapy. To quantify this dose, a humanoid phantom was irradiated at the left breast, simulating breast radiotherapy. The phantom, consisting of an adapted manikin (with internal and external materials having densities close to that of water), was irradiated in a 6-MeV X-ray linear accelerator (Clinac 600CD). A shield of blocks and lead slabs was placed around the abdominal region of the phantom. Two types of wedges were used to modulate the beam: a physical wedge and the enhanced dynamic wedge (EDW), both with 30 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> angulation. Using a cylindrical ionization chamber of 0.6 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> positioned in the phantom's fetal region, at the end of breast treatment, the peripheral doses were 3.90-48.67 cGy with the physical wedge and 1.75-13.78 cGy with the EDW. The doses were 3.5 times greater when the physical wedge was used due to scattering by its attenuator material and the increase in the leakage radiation intensity. The use of a shield around the abdominal region of the phantom and the use of the EDW during simulation of the treatment reduced the peripheral doses to tolerable limits from ICRP and AAPM.

Improvement of dose distribution with irregular surface compensator in whole breast radiotherapy.

Aim of this study was to compare the dosimetric aspects of whole breast radiotherapy (WBRT) between an irregular surface compensator (ISC) and a conventional tangential field technique using physical wedges. Treatment plans were produced for 20 patients. The Eclipse treatment planning system (Varian Medical Systems) was used for the dose calculation: For the physical wedge technique, the wedge angle was selected to provide the best dose homogeneity; for the ISC technique, the fluence editor application was used to extend the optimal fluence. These two treatment plans were compared in terms of doses in the planning target volume, the dose homogeneity index, the maximum dose, ipsilateral lung and heart doses for left breast irradiation, and the monitor unit counts required for treatment. Compared with the physical wedge technique, the ISC technique significantly reduced the dose homogeneity index, the maximum dose, the volumes received at 105% of the prescription dose, as well as reducing both the ipsilateral lung and heart doses (P < 0.01 for all comparisons). However, the monitor unit counts were not significantly different between the techniques (P > 0.05). Thus, the ISC technique for WBRT enables significantly better dose distribution in the planning target volume.