Physical Wedge Research Articles

Dynamic range and optimization strategies for radiochromic film calibration using gradient radiation fields.

This investigation aimed to optimize gradient positioning for radiochromic film calibration to facilitate a uniform distribution of calibration points. The study investigated the influence of various parameters on gradient dose profiles generated by a physical wedge, assessing their impact on the field's dose dynamic range, a scalar quantity representing the span of absorbed doses. Numerical parameterization of the physical wedge profile was used to visualize and quantify the impact of field size, depth, and energy on the dynamic range of dose gradients. This concept enabled the optimization of the gradient positioning and estimation of the necessary number of exposures for the desired calibration dose range. An optimization algorithm based on histogram bin height minimization was developed and presented. The maximum dynamic range was achieved with a 20 20 field size at 5 cm depth. Optimization of wedge gradient positioning yielded the most uniform dose distribution with 7 exposures for the [1,10] Gy range and 8 exposures for the [1,20] Gy range. Film calibration using gradients centered at 1.6, 3, 3.5, and 7 Gy central axis (CAX), obtained through optimized gradient positioning, was showcased. The presented work demonstrates the potential for an improved film calibration process, with efficient material utilization and enhanced dosimetric accuracy for clinical applications. While the method was described for the use of a physical wedge, the methodology can be easily extended to the use of a more convenient dynamicwedge.

Physical wedge as a tool for radiochromic film calibration

Reliable calibration is one of the major challenges in using radiochromic films (RCF) for radiation dosimetry. In this study the feasibility of using dose gradients produced by a physical wedge (PW) for RCF calibration was investigated. The aim was to establish an efficient and reproducible method for calibrating RCF using a PW. Film strips were used to capture the wedge dose profile for five different exposures and the acquired scans were processed to generate corresponding net optical density wedge profiles. The proposed method was compared to the benchmark calibration, following the guidelines for precise calibration using uniform dose fields. The results of the benchmark comparison presented in this paper showed that using a single film strip for measuring wedge dose profile is sufficient for estimating a reliable calibration curve within the recorded dose range. Furthermore, the PW calibration can be extrapolated or extended by using multiple gradients for the optimal coverage of the desired calibration dose range. The method outlined in this paper can be readily replicated using the equipment and expertise commonly found in a radiotherapy center. Once the dose profile and central axis attenuation coefficient of the PW are determined, they can serve as a reference for a variety of calibrations using different types and batches of film. This investigation demonstrated that the calibration curves obtained with the presented PW calibration method are within the bounds of the measurement uncertainty evaluated for the conventional uniform dose field calibration method.

Influence of Percolation effect of additives on the Performance of Conical Textured Porous Hybrid Journal Bearing

Textured bearing surfaces are widely used to reduce the friction in lubricated contacts. Besides the hydrodynamic pressure generated by the physical wedge, micro-textures act as micro-bearings and generates localized pressure. As a result, an additional load carrying capacity is generated. Further, micro-texture also serves as a lubricant reservoir, trapping wear debris and abrasive particles to improve the performance of tribo- pair. In this study, the effect of micro-textures and percolation effect of additives on the performance of hybrid conical porous journal bearings (HCPJBS) has been studied. The interactive effects of permeability parameter, spherical shaped micro-texture, semi cone angle and couple stress lubricant parameter considering the percolation effect parameter of additives on the performance of HCPJBS has been studied. FEM is used to numerically simulate the flow behaviour of couple stress lubricant in the bearing clearance space of a HCPJBS. The results shows that the HCPJBS operating with couple stress lubricant provides enhanced stability margin [Formula: see text] for lower values of permeability parameter [Formula: see text] and semi cone angle [Formula: see text].

Variations in 60Co γ- ray radiotherapy surface dose with physical wedge

Variations in 60Co γ- ray radiotherapy surface dose with physical wedge

Comparison of dosimetric characteristics of physical wedge and enhanced dynamic wedge in inhomogeneous medium using Monte Carlo simulations.

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. A PW and EDW-equipped-linac head was simulated using BEAMnrc code. DOSXYZnrc was used for three-dimensional dosimetry calculation in the CIRS phantom. 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. 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.

Impact of Respiratory Motion on Point Doses for Three Whole-breast Irradiation Techniques after Breast-conserving Surgery

For whole-breast irradiation after breast-conserving surgery, computed tomography simulation (CTS) and irradiation are generally performed during free breathing. In treatment planning, there are three techniques: field-in-field (FIF), physical wedge (PW), and enhanced dynamic wedge (EDW). The aim of this study was to investigate the impact of respiratory motion on doses for these three irradiation techniques. All doses were measured using an ionization chamber in a cylindrical phantom on a respiratory motion platform. Doses for each technique were measured with and without phantom motion. The dose without phantom motion was defined as the reference. The reference was compared to the dose with the phantom motion. The positions of the isocenter with respect to the ranges of phantom motion were set as exhale and intermediate. The phantom motion amplitude was set to 5 mm or 10 mm. The respiratory phase to initiate irradiation was varied as inhale, intermediate-inhale, exhale and intermediate-exhale. When the motion amplitude was 10 mm, the dose differences for the FIF, PW, and EDW techniques were 4.2%, 0.5%, and 0.8%, respectively, at the maximum. However, the dose difference for the FIF technique was -0.5% when the isocenter position was set to the intermediate phase of phantom motion. We found that the dose difference per fraction was reduced when the respiratory phase during CTS image acquisition was set to the intermediate phase. Meanwhile, the dose differences per fraction for the PW and EDW techniques were less affected by the respiratory motion.

Validation of Motorized Wedge Effective Isodose Angle with a 2D Array Detector

Introduction: Elekta Versa HD linear accelerator is equipped with a universal wedge filter which is a single large physical wedge driven by motors; in other words, motorized wedge. It provides a nominal wedge isodose angle of 60° for the field size of 30×40 sq. cm. Motorized wedge isodose distribution generated is a combination of open and wedged beam segments. With this background in mind, the present study aimed to validate the planned wedge effective isodose angle. Material and Methods: The current study validated the planned wedge effective isodose angle for 15°, 30°, 45°, and 60° with 6MV and 15MV for 10x10 sq. cm and 20x20 sq. cm field size. To this end, an analytical formula was applied against a 2D array detector using PTW MultiCheck software. Results: As illustrated by the obtained results, the calculated, measured, and planned wedge effective isodose angle in this work represented a maximum deviation from its pre-set angle (a nominal wedge angle) of 9° for a 6MV photon energy and 5° for 15MV for field sizes of 10×10 sq. cm and 20×20 sq. cm. Conclusion: In the present study, we validated the planned wedge effective isodose angle for field sizes of 10x10sq. cm and 20x20sq. cm for 6MV and 15MV photon energies using an analytical method and 2D array detector with a reasonable agreement.

Characterization of Wedge Factors and Dose Distributions in Radiotherapy with Symmetric and Asymmetric Physical Wedged Beams of 6 MV Photon Beam

Introduction: Physical wedge by modify photon beam shape and intensity has been utilized in radiotherapy to obtain uniformly dose distribution in tumor site with reduced hot spots. Calculation of dosimetric parameters for both symmetric and asymmetric wedged fields is proved necessary during linear accelerator (Linac) commissioning. The present study aimed to achieve output factors and dose profiles for symmetric and asymmetric wedged fields of 6 MV beams. Material and Methods: The Siemens PRIMUS Linac head for 6 MV beam was simulated by BEAMnrc and all dose calculations were performed by DOSXYZnrc code. Percentage depth dose (PDD) and profiles for open and wedged (15° and 45°) fields were compared with corresponding measurements. Wedge factors for 10 x 10 cm2 field were obtained as a function of lateral distance as well for half beam wedged fields. Results: Based on the results of the present study, the calculated doses were in agreement with the measured data. The output factors on the central axis of symmetric wedged beams decreased to 0.693 and 0.307 for 15˚, and 45˚ wedges. The total photon fluence of 15˚ and 45˚ physical wedged fields reduced to 71.6% and 27.7% of open field, respectively. Conclusion: The output factor for asymmetric wedged fields was found to be lower than corresponding symmetric open and wedged fields, particularly at field edges. Lack of scattering photons near the half beam edges resulted in dose fall-off in these regions possible to be overestimated by treatment planning system and consequently caused cold spots at target volume.

Installation, commissioning, and performance evaluation of Bhabhatron-II TAW – An Indian-made telecobalt unit

Aim: The aim of this study was to report commissioning and performance evaluation of Bhabhatron-II TAW (an Indian made machine). Materials and Methods: Commissioning comprises of following quality assurance (QA) (a) electrical QA, (b) mechanical QA, (c) radiation QA and (d) survey of installation. Electrical QA were done for various components of the unit for its functionality. Mechanical QA were done and the measured data were verified as per guidelines of Atomic Energy Regulatory Board (AERB), India and vendor's specified values. Cylindrical ionization chamber, electrometer, ready pack films, water phantom, thermometer and barometer were used during radiation QA and survey of installation procedures. Moreover, the data so generated were fed to treatment planning system (TPS) for dose calculation and also kept in proper tabular manner for clinical use. Results: Couch and collimator parameters were found to comply the tolerance criteria. Source strength of 172.2 roentgen per minute at 1 meter (RMM) was measured with an absolute dose rate of 225.76 cGy/min at dmax for 10cm x 10cm field size at normal treatment distance (NTD). Shutter timer error of 0.004 min was measured and incorporated in the clinical data. A maximum of 3.66 % variation was noted for 300 (15W × 20) physical wedge transmission factor between measured and vendor specified value. Radiation leakage through beam limiting device (BLD) and outside BLD were found to be within the limits prescribed by AERB. Conclusion: Commissioning is a prerequisite process after installation of a radiation therapy machine for medical purpose. Bhabhatron-II machine has several advantages over other telecobalt machine. Features like high source storage capacity of machine head, one pair of asymmetric jaw, closure of jaws to 0 cm x 0 cm during radiation emergency and presence of one motorized wedge filter makes it unique and yet cost effective telecobalt machine..

Measurement of the photon and thermal neutron doses of contralateral breast surface in breast cancer radiotherapy

AbstractIntroduction and purpose:During the radiation therapy of tumoral breast, the contralateral breast (CB) will receive scattered doses. In the present study, the photon and thermal neutron dose values received by CB surface during breast cancer radiation therapy were measured.Materials and methods:The right breast region of RANDO phantom was considered as CB, and the measurements of photon and thermal neutron dose values were carried out on this region surface. The phantom was irradiated with 18 MV photon beams, and the dose values were measured with thermoluminescent dosimeter (TLD-600 and TLD-700) chips for 11 × 13, 11 × 17 and 11 × 21 cm2 field sizes in the presence of physical and dynamic wedges.Results:The total dose values (photon + thermal neutron) received by the CB surface in the presence of physical wedge were 12·06%, 15·75% and 33·40% of the prescribed dose, respectively, for 11 × 13, 11 × 17 and 11 × 21 cm2 field sizes. The corresponding dose values for dynamic wedge were 9·18%, 12·92% and 29·26% of the prescribed dose, respectively. Moreover, the results showed that treatment field size and wedge type affect the received photon and thermal neutron doses at CB surface.Conclusion:According to our results, the total dose values received at CB surface during breast cancer radiotherapy with high-energy photon beams are remarkable. In addition, the dose values received at CB surface when using a physical wedge were greater than when using a dynamic wedge, especially for medial tangential fields.

Performance Evaluation of a Transmission Reference Detector for Commissioning Beam Data in a Wedge Field

The purpose of this study is to evaluate the performance of a “stealth chamber” as a novel reference detector for measuring the commissioning beam data for a wedge field. The stealth chamber is a transmission ionization chamber intended to be used as a reference chamber for relative dosimetry. The percentage depth doses (PDDs) and the dose profiles of 6-, 8-, and 10-MV photon beams of four wedge filters were measured using the stealth and the CC13 chambers as reference detectors. The PDD and the profile measurements were performed under various field sizes ranging from 4 × 4 cm2 to 20 × 20 cm2. For the evaluate of the performance of the stealth chamber in fields with a physical wedge, all measurement data obtained using the stealth chamber as a reference detector were compared with those measured using two CC13 chambers as both field and reference detectors. For the PDDs, the differences in dosimetric parameters such as the depth of maximum dose (dmax) and the PDD at 10 cm (D10) and 5 cm (D5) were analyzed for both reference detectors. In addition, the root-mean-square error (RMSE) was calculated to measure the agreement of the profiles at dmax and a 10 cm depth. The percentage differences in D10 and D5 between both detectors were less than 1% for all energies and fields with four wedges. Furthermore, the RMSEs of the profiles at dmax and 10-cm depth in both chambers were within 1% for all energies and fields except for the 60° wedge angle. This study found that the use of a stealth chamber to measure the commissioning beam data for a wedge field is feasible, although a relatively large difference in the PDD was observed in the build-up region. However, we recommend careful verification of the PDDs and dose profiles for large field size and wedge angle before clinical use.

Measurement of the contralateral breast photon and neutron dose in breast cancer radiotherapy: A Monte Carlo study.

This study aimed to calculate the photon and neutron doses received to the contralateral breast (CB) during breast cancer radiotherapy for various field sizes in the presence of a physical wedge. Varian 2100 C/D linear accelerator was simulated using a MCNP4C Monte Carlo code. Then, a phantom of real female chest was simulated and the treatment planning was carried out on tumoral breast (left breast). Finally, the received photon and neutron doses to CB (right breast) were calculated in the presence of a physical wedge for 18 MV photon beam energy. These calculations were performed for different field sizes including 11 cm × 13 cm, 11 cm × 17 cm, and 11 cm × 21 cm. The findings showed that the received doses (both of the photon and neutron) to CB in the presence of a physical wedge for 11 cm × 13 cm, 11 cm × 17 cm, and 11 cm × 21 cm field sizes were 9.87%, 12.91%, and 27.37% of the prescribed dose, respectively. In addition, the results showed that the received photon and neutron doses to CB increased with increment in the field size. From the results of this study, it is concluded that the received photon and neutron doses to CB in the presence of a physical wedge is relatively more, and therefore, they should be reduced to as low as possible. Therefore, using a dynamic wedge instead of a physical wedge or field-in-field technique is suggested.

Quantification the dosimetric parameters of asymmetric physical wedged-6MV photon beam

Introduction: Physical wedge as a useful tool has been utilized in radiotherapy to modify photon beam shape and intensity such that it distributes dose uniformly in tumor site and reduces hot points. Since during Linac commissioning dosimetric parameters like output factors and lateral dose profiles are measured only for symmetric open and wedged fields, so calculation the parameters for asymmetric wedged fields become necessary. The study aims to achieve output factors and dose profiles for symmetric and asymmetric wedged fields of 6 MV photon beams. Materials and Methods: The Siemens PRIMUS Linac head for 6 MV photon beam was simulated by BEAMnrc and all dose calculations were performed by DOSXYZnrc code. Percentage depth dose (PDD) and profiles for open and wedged (15° and 45°) fields were compared with corresponding measurements. Wedge factors for 10 x 10 cm2 field size as a function of lateral distance from central axis were obtained as well for half beam (negative or positive Y jaws were closed) wedged fields. All mesurments were carried out using 0.125 cm3 Farmer type ionization chamber with DOSE1 electrometer (FC65G, Scanditronix-Wellhofer, Germany) at the depth of 10 cm with source to surface distance (SSD) of 100 cm in 50 cm3 PTW-Blue water phantom and processed by dosimetry software RFAplus (Version 5.2, Scanditronix-Wellhofer, Germany). Results: The calculated doses were in agreement with measured data that confirmed the simulated MC model. The output factors on the central axis of symmetric wedged beams decreased to 0.693 and 0.307 for 15˚ and 45˚ wedges, respectively. The total photon fluence of 15˚ and 45˚ physical wedged fields reduced to 71.6% and 27.7% of fluence for open field, respectively. It was found that the output factor for asymmetric wedged fields is lower than ones from symmetric fields, particularly at field edges. Conclusion: The presences of physical wedge across the beamline decrease the photon fluence and cases beam hardening both for symmetric and asymmetric wedged fields. Lack of scattering photons near the half beam edges in asymmetric wedged field causes a dose fall off in these regions where have potential to overestimate the calculated dose by treatment planning system and consequent cold spots at target volume. Our calculated correction coefficients are recommended to calculate doses by TPS in case of asymmetric wedged fields.

Evaluation of Three-dimensional Treatment Planning System (TPS) performance in dose calculation of virtual wedged fields using film dosimetry

Introduction: Nowadays radiotherapy plays an important role in cancer treatment. Different radiotherapy techniques improvement emphasizes on using of the precise ، appropriate and useful algorithms. one of these techniques are wedged which is used in radiotherapy to compensate missing tissues and create a uniform dose distribution in tissues. The Siemens Artiste linear accelerator supports a virtual wedge ، that this wedge creates a dose distribution similar to a physical wedge without the use of any extra accessory and wedged profiles are produced moving collimator jaw during irradiation with a constant speed but varying the dose rate. In this study ، TPS performance is evaluated in virtual wedged fields by comparing the calculated and measured results. Materials and Methods: The calculations were performed by the collapsed cone superposition algorithm based TPS for two tangent fields in anthropomorphic slab phantom using 15، 30، 45، 60 virtual wedges for field size of 20 × 20 cm2 for 6 and 15 MV photon beams. Measurements were produced by Gafchromic EBT films and reading exposed films with scanner. Results: Good agreement between the measured dose with film dosimetry and calculated dose with collapsed cone superposition algorithm based TPS with using virtual wedge in heterogeneous environment and different energies were found ، with the maximum difference not exceed 3 -5%. The increase in wedge angle due to increase in the difference between calculated and measured data. Conclusion: : The results from this study showed that the accuracy of collapsed cone superposition algorithm based TPS used with the virtual wedges for two tangent fields is enough for the clinical usage under the studied experimental conditions.

Determination of an Effective Wedge Angle by Combination of Two Arbitrary Universal Wedge Fields in Radiation Therapy of Cancer Patients with Megavoltage Photon Beams.

Introduction: Wedge filters are commonly used in radiation oncology for eliminating hot spots and creating a uniform dose distribution in optimizing isodose curves in the target volume for clinical aspects. These are some limited standard physical wedges (15°, 30°, 45°, 60°), or creating an arbitrary wedge angle, like motorized wedge or dynamic wedge, ... The new formulation is presented by the combination of wedge fields for determining an arbitrary effective wedge angle. The isodose curves also are derived for these wedges. Materials and Methods: we performed the dosimetry of Varian Clinac 2100C/D with Scanditronix Wellhofer water blue phantom, CU500E, OmniPro - Accept software and 0.13cc ionization chamber for 6Mv photon beam in depth of 10cm (reference depth) for universal physical wedges (15°, 30°, 45°, and 60°) and reference field 10x10cm2. By combining the isodose curve standard wedge fields with compatible weighting dose for each field, the effective isodose curve is calculated for any wedge angle. Results: The relation between a given effective wedge angle and the weighting of each combining wedge fields was derived. A good agreement was found between the measured and calculated wedge angles and the maximum deviation did not exceed 3°. The difference between the measured and calculated data decreased when the combined wedge angles were closer. The results are in agreement with the motorized single wedge appliance in the literature. Conclusion: This technique showed that the effective wedge angle that is obtained from this method is adequate for clinical applications and the motorized wedge formalism is a special case of this consideration.

156. Dosimetric comparison between 3D-CRT, Field in Field and VMAT techniques in the adjuvant radiotherapy treatment of breast cancer

Purpose To compare 3D-CRT, Field-in-Field (FIF) and VMAT for adjuvant radiotherapy of breast cancer. Methods 26 patients (13 with left-sided breast cancer, 13 with right-sided) treated to a prescribed dose of 40 Gy (2.667 Gy/fraction; normalized to the target mean) were considered. For all patients a 3D-CRT and a VMAT plan were simulated. 3D-CRTs were planned with 2 primary tangential fields with physical wedges and 2 additional low weighted segments. VMAT plans were performed with a Rapid Arc (RA) technique using 2 partial arc. In a subgroup of 15 patients FIF technique was implemented, combining two open fields with 2–3 segments in two tangential beam directions, without using wedges. Comparisons were performed in terms of PTV coverage and OARs dose-volume histogram (DVH) parameters, considering optimal/acceptable constraints of RTOG-1005 protocol. The dosimetric value of omolateral (lung/heart) OARs were related to the OARs volume included in the chest concavity and to OAR’s inclusion maximum depth. Results Concerning PTV, coverage was similar for the three techniques. The mean dose to OARs are summarized in the table. RA was sub-optimal for all contralateral OARs because mean doses were significantly (p Conclusions The FIF (3D-CRT) technique is similar to RA for PTV data and presents the best results all contralateral OARs. Only when (omolateral) lung and heart have an inclusion in chest concavity >1.5 cm, RA significantly reduces dose in the high DVH region.

Toward invivo dosimetry in external beam radiotherapy using x-ray acoustic computed tomography: A soft-tissue phantom study validation.

To study, using phantoms made from biological tissues, the feasibility and practical challenges of monitoring the position of the radiation beam and the deposited dose by x-ray acoustic computed tomography (XACT) during external beam radiotherapy delivery. A prototype XACT system with a single immersion ultrasound transducer, which was positioned around the target sample driven by a motor-controlled rotation stage, was used to acquire the x-ray acoustic (XA) signals produced by a medical linear accelerator (Linac) to form an XACT image of the irradiated phantom. To investigate the feasibility of XACT in tracking the position of radiation dose, a large piece of veal liver with embedded fat tissue was imaged and beam misalignments were measured. Next, we explored the sensitivity of XACT in monitoring and quantifying the delivered dose, in which a block of porcine gel was embedded with equally spaced lard cylinders and imaged. The doses on the lard cylinders modulated by physical wedges were quantified from the XACT image and were verified by comparison to measurements from radiochromic films as the gold standard. Then, to simulate how XACT can perform in a targeted tissue in the human body, a porcine gel phantom with lard cylinders covered by different materials (bone, muscle, and air gap, respectively) was also imaged. The reconstructed XACT images of the phantoms show congruence with the boundaries of the beam field and the interfaces between the different tissue materials. The beam displacement from the target was tracked properly by the reconstructed XACT images. An intensity difference as small as 2.9% in delivered dose region can be measured from XACT images P=0.02. The intensities of XACT images were highly correlated to the film measurements with an R2 better than 0.986. The expected variances of dose delivered to different target regions as a result of the difference in attenuation were successfully captured by the XACT images. This study validated the feasibility of XACT in accurately obtaining relative dose maps of tissue-mimicking phantoms. XACT offers a practical method for verifying the beam position against the target and quantifying the relative dose delivered to the target during external beam radiotherapy.

Dosimetric verification of the Elekta motorized wedge

Elekta linear accelerator is equipped with a motorized wedge which produces the wedge angles of less than 60° continuously by the combination of a wedged field and an open field with appropriate proportions. The effective wedge angles for various field sizes and depths were calculated using an analytical formula and a 2-D array detector data. The validity of the effective wedge angles has been done by determining wedge angles in accordance with ICRU-24. The effect of the field size on the wedge angle and wedge factor was investigated for motorized wedge. The maximum difference between planned and measured angles was found to be about 10. The planned dose for different wedge angles and field sizes compared with measured doses and their differences were found to be less than 3%. The calculating wedge factor throughout linear interpolation method for all field sizes from a few selected measurements had been proved for physical wedge beforehand. This method was applied to obtain the wedge factors with field size and compared with measured data for motorized wedge. The errors were in agreement with ICRU proposed error and less than treatment planning system error. The linear relation between wedge angle and output factor and depth were investigated and the linear interpolation method was proved to calculate wedge angle for any output factor and depth.

An analysis of hydrodynamic ferrofluid lubrication of an inclined rough slider bearing

The present study aims at analysing the effects of surface roughness, porosity and magnetic field on an inclined slider bearing. The slider bearings mainly are designed for supporting transverse load in an engineering system and enjoy a priority due to its physical wedge pressure generating mechanism. The ferrofluid is being used as lubricant which becomes strongly magnetised in the presence of external magnetic field in a plane inclined rough slider bearing with slip velocity. The earlier studies were related to ferrofluid lubrication based on Shliomis model and it was concluded that the adverse effect of surface roughness was reduced due to magnetisation under the influence of proactive slip parameter. In the present study a space dependent magnetic field of the form has been considered rather than sinusoidal type H2 = KL2 sin (πX). The analysis brings out some interesting results due to change in pattern of magnetic field strength. The pattern of variation of magnetic field considered in the present study contributes to an increase in pressure and load capacity by and load by our conventional lubricant i.e. as that of magnetised lubricant. One interesting finding reported here is that, the adverse effect of slip parameter, reported in earlier studies over load carrying capacity turns rather sinusoidal to be favourable which may be due to the pattern of variation of magnetic field considered in the present study.

Dosimetric Comparison of Treatment Plans Using Physical Wedge and Enhanced Dynamic Wedge for the Planning of Breast Radiotherapy.

The aim of this study is to compare the physical wedge (PW) with enhanced dynamic wedge (EDW) to determine the difference in the dose distribution affecting the treated breast and the contralateral breast, lungs, heart, esophagus, spine, and surrounding skin in the radiotherapy of breast cancer. Computed tomography (CT) data sets of 30 breast cancer patients were selected from the database for the study. The treatment plans which were executed with PW were re-planned with EDW without changing the beam parameters. Keeping the wedge angles same, the analytic anisotropic algorithm (AAA) with heterogeneity correction was used for dose calculation in all plans. The prescription was 50 Gy in 25 fractions. The dose- volume histogram (DVH) of the planning target volume (PTV) and critical structures of both PW and EDW plans were analyzed. The analysis showed that the maximum dose within the target volume is higher in EDW plan compared to PW plan. However the PTV conformity index (CI) remained the same in both plans. For all the critical structures, the EDW technique offered less dose compared to PW technique. The effect of volume of the contralateral breast on the dose to contralateral breast and the effect of volume of PTV breast for patients with carcinoma left breast on the dose to heart were studied and analyzed for the two wedges. No correlation between volumes and dose parameters was found for the two techniques. The number of monitor units to deliver a particular dose with EDW field is less than that of PW field due to change in wedge factor. As EDW produces less scattered dose to structures outside the treatment field, the risk of a second malignancy can be reduced with this technique.