Wedge Filters Research Articles

Evaluation of lower detection limit and performance analyses related to the incident angle of X-rays and absolute dose using a triple-type dosimeter

When using a wearable active-type dosimeter for real-time dosimetry during X-ray fluoroscopic procedures, medical staff should be aware of the potential for an inaccurate exposure dose due to the large angular dependence. To address this issue, our research group has proposed a triple-type active dosimeter. With this device, the incident angle of scattered X-rays can be determined based on the signal difference between two dosimeters placed side-by-side, in which the wedge filters on the entrance windows are arranged symmetrically. In addition, the absolute dose can be determined from the central dosimeter with angular dependence correction. Although the concept of using wedge filters was proven in a previous study, the wedge filter materials have not been sufficiently studied. In this study, therefore, we sought to determine which of several materials was best suited as a wedge filter material for medical applications: aluminum (Al), titanium (Ti), or copper (Cu). We analyzed the performance of dosimeters with the different wedge filter materials in terms of estimation accuracy and lower detection limit. Using a clinical fluoroscopic system with a tube voltage of 80 kV, the scattered X-rays generated from an elliptical cylinder water phantom were measured while varying the incident direction of the X-rays from −50° to +50° in 10-degree intervals. The experimental results showed that the incident angles were properly determined when using the Ti filter, but the estimation accuracy was slightly lower when using the Al and Cu filters. The accuracy of absolute dose was evaluated from the standard deviation of the absolute dose data between −50° and +50°. As a result, the accuracies when using the Al, Ti, and Cu filters were 3.6%, 3.9%, and 5.9%, respectively. The lower detection limit when using the Cu filter showed a significantly higher value (0.50 μSv/s), but that with the Ti filter was reasonable (0.07 μSv/s). Based on these experimental evaluations, we concluded that the Ti filter would be suitable for use in a triple-type dosimeter. Finally, we investigated the expected dose rates of scattered X-rays in various interventional radiology (IVR) procedures described in the literature and determined that our dosimeter could be used for actual dose measurement.

Wedge Filter Variation on Wedge Factor in Patients Cancer Breast in Sub Installation Radiotherapy RSUP Prof. Dr. I.G.N.G Ngoerah

The aim of the study was to determine the effect of irradiation time, the percentage of the maximum dose, the distribution of doses at the center point, and the wedge factor on wedge filter variations. The research method uses a wedge filter to measure irradiation time, maximum dose percentage, dose distribution at the center point, and the wedge factor. Wedge value factor without wedge, wedge 15 , wedge 30, wedge 45and wedge 60of 1.000, 1.0059, 1.0102, 1.0137, and 1.0092 respectively. The results of the maximum dose percentage values without wedge, wedge 15 , wedge 30 , wedge 45and wedge 60were 106.76%, 106.80%, 106.79%, 106.85%, and 106.81%, respectively. Conclusion is the value of the wedge factor does not comply with the ICRU standard but the percentage of the maximum dose is in accordance with the International Commisson on Radiation Units (ICRU) standard, there is a wedge effect factor, and irradiation time on the variation of the wedge filter, but there is no effect of the maximum dose percentage and distribution at the center point on the variation of the wedge filter.

RADIOTHERAPY GENETIC ALGORITHM PARETO-MULTIOBJECTIVE OPTIMIZATION OF BIOLOGICAL EFECTIVE DOSE AND CLONOGENS MODELS FOR HEAD AND NECK TUMOR ADVANCED TREATMENT

BED model (Biological Effective Dose) for Head and Neck tumors Hyperfractionation TPO was optimizedwith Pareto-Multiobjective (PMO) Genetic Algorithms (GA) software. Artificial Intelligence (AI) with GA is applied on Radiotherapy Treatment Planning Optimization (TPO). Secondly, the review of NEffective (Effective Tumor Population Clonogens Number) model optimization for breast cancer clonogens parameters determination in TPO (Treatment Planning Optimization) is got with 3D Graphical and Interior Optimization methods. Results series comprise PMO imaging process sequences and numerical values of PMO and NEffective model for Head and Neck cancer parameters. Further results demonstrate PMO-GA BED model both with Pareto-Optimal Front detailed graphics, charts and numerical dose fractionation datasets. Supplemental review of new recent applications with 3D Isodoses TPO with AAA (Anisotropic Analytic Algorithm) model wedge filters dose delivery is shown. Advanced RT Head and Neck cancer TPO, and tumors in general for Fractionation-dose protocols are explained.

RADIOTHERAPY GENETIC ALGORITHM PARETO-MULTIOBJECTIVE OPTIMIZATION OF BIOLOGICAL EFFECTIVE DOSE AND CLONOGENS MODELS FOR BREAST TUMOR IMPROVED TREATMENT

BED model (Biological Effective Dose) for Hyperfractionation TPO was optimized with Pareto-Multiobjective Genetic Algorithms (GA) software. Secondly, the NEffective (Effective Tumor Population Clonogens Number) model optimization for breast cancer clonogens parameters determination in TPO (Treatment Planning Optimization) is carried out with 3D Graphical and Interior Optimization methods. BED model (Biological Effective Dose) for Hyperfractionation TPO was optimized with Pareto-Multiobjective GA software. Results comprise imaging process series and numerical values of NEffective model for breast cancer parameters. Additional results demonstrate Pareto-Multiobjective GA BED model both with Pareto-Optimal Front graphics, charts and numerical dose fractionation datasets. For all these findings, supplementary new recent applications with 3D Isodoses TPO with AAA (Anisotropic Analytic Algorithm) model wedge filters dose delivery is shown. Modern RT treatment breast cancer, and tumors in general for Fractionation-dose protocols are explained.

Radiotherapy Wedge Filter AAA Model 3d Simulations For 18 MEV 5cm-Depth Dose with Medical Physics Applications

In a previous study based on series of contributions for Anisotropic Analytic Model (AAA) improvements, several exact/approximated formulations/corrections for wedge filters (WF) photon-dose delivery were presented. Namely, dose delivery correction Omega Factor for 15° WF, Photon Beam Intensity I(z), and Photon Fluence magnitude for 18 Mev for z=15 cm depth-dose. Based on all these algorithms/software, 3D comparative-simulations results with Matlab are developed for AAA model 18 Mev photon-beam, but at superficial depth-dose z=5 cm. The 15° WF corrected AAA photon Beam Intensity I(z) magnitude modification, Standard 18 Mev Fluence and geometrical Omega Factor are implemented. Scatter radiation, tissue inhomogeneities, and contaminating electrons correction are not applied. The calculations with AAA model formulas for these parameters are developed/improved. Findings comprise a number of 3D graphics with 3D Graphical Optimization, and a series of numerical data for AAA WF photon-dose delivery at depth-dose z=15. Results for 4D Interior Optimization imaging-development-approximations are presented in 3D charts, and compared to 3D Graphical optimization photon-dose at z=15 cm depth. Radiotherapy Medical Physics applications for WF usage photon-dose calculations at superficial depth z=5 cm emerge from all the numerical and graphical outcomes. Clinical radiotherapy applications are obtained from 3D graphical simulation series. Radiation Therapy uses for breast cancer at depth-dose z=5 cm are explained and presented.

HOMOGENISASI DENSITAS FOTO VERTEBRAE THORACAL PROYEKSI ANTERO POSTERIOR (AP) DENGAN MENGGUNAKAN FILTER BAJI 7°, 10° DAN 15°

Background: The different thickness of the thoracic vertebrae between the top and bottom causes the radiograph to have uneven density. The use of heel effect anode in the examination of the thoracal vertebrae of the AP projection has not been able to even out the radiograph density, so it is necessary to use a tool in the form of a wedge filter. This study aims to find the correct angle of inclination of the wedge filter to produce a radiograph with a sufficiently even density between the top and bottom of the AP projection thoracic vertebrae. The wedge filter tested tilt angle of 7 °, 10 ° and 15 °.
 Methods: The research used quantitative methods, conducted from January to May 2018. The sample consisted of 4 volunteers and 10 radiographers as respondents.
 Results: The results showed that the examination of the thoracal vertebrae of the AP projection without using a filter obtained an average value of 2.50 from the respondents, while using a wedge filter with a tilt angle of 7 ° got a value of 2.80, with a tilt angle of 10 º got a value of 3.43 and with an angle of inclination. 15 º gets a score of 2.93, so it can be denied that the use of a wedge filter with an angle of 10º is able to produce a more even radiograph density between the top and bottom of the AP projection spine.
 Conclusions : To produce a more even radiograph density between the top and bottom of the thoracal vertebrae, the AP projection can be done using a wedge filter with an angle of 10°.

Recovering the wedge modes lost to 21-cm foregrounds

ABSTRACT One of the critical challenges facing imaging studies of the 21-cm signal at the Epoch of Reionization (EoR) is the separation of astrophysical foreground contamination. These foregrounds are known to lie in a wedge-shaped region of (k⊥, k∥) Fourier space. Removing these Fourier modes excises the foregrounds at grave expense to image fidelity, since the cosmological information at these modes is also removed by the wedge filter. However, the 21-cm EoR signal is non-Gaussian, meaning that the lost wedge modes are correlated to the surviving modes by some covariance matrix. We have developed a machine learning-based method that exploits this information to identify ionized regions within a wedge-filtered image. Our method reliably identifies the largest ionized regions and can reconstruct their shape, size, and location within an image. We further demonstrate that our method remains viable when instrumental effects are accounted for, using the Hydrogen EoR Array and the Square Kilometre Array as fiducial instruments. The ability to recover spatial information from wedge-filtered images unlocks the potential for imaging studies using current- and next-generation instruments without relying on detailed models of the astrophysical foregrounds themselves.

Radiation Doses to Patients Undergoing Osteosynthesis Procedures

Fractures of limbs are most frequent causes of orthopaedic interventions. Especially the older people are exposed to these because of motion disorders and osteoporosis. Most of orthopaedic surgery interventions are performed under X-rays control to achieve an optimal settings the anatomical details and also some artificial implants, if such are necessary. Because if that, X-ray units are common equipment in operational theatre where orthopaedic procedures are performed. As a rule they are mobile C-arm units, which are easy available in any time when are necessary. A consequence of every usage of X-rays an exposure to patient but also to operational medical team [1-3]. They are a number of factors affecting both the patient and staff irradiation. There are three categories: patient dependent, equipment dependent and procedure dependent factors. Patient dependent factors include: body thickness in the beam, complexity of the anatomic structure. Equipment dependent factors include: setting of dose rates in pulsed fluoro- and continuous fluoro mode, last image hold, acquisition, and virtual collimation. The main procedure related factors are: number of radiographic frames per run, collimation, fluoroscopic and radiographic acquisition modes, fluoroscopy time, wedge filter, magnification, distance of patient to image receptor (image intensifier or flat panel detector), distance between X-ray tube and patient, and tube angulations. Very important is also the experience of the operator. In case of patient, this is especially important for the procedures when the primary beam can cover the part of the trunk. Such situation has place in the procedure of osteosynthesis the femoral bone, reconstruction of head of femur and also osteosynthesis the humeral bone. Despite a relatively short time of real exposures, doses to patients undergoing these procedures can achieve quite high values: the entrance skin air kerma (here named the “dose”) over 80 mGy was also recorded. Additionally, in practice the primary X-ray beam incident on the same area patient’ body making a higher risk of radiation detriments. The paper presents collection of doses recorded for patients undergoing the procedures of osteosynthesis the femoral bone and the humeral bone during last moths in the big university clinic.

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.

Hybrid volumetric modulated arc therapy for hypofractionated radiotherapy of breast cancer: a\xa0treatment planning study

PurposeThis study aims to evaluate the best possible practice using hybrid volumetric modulated arc therapy (H-VMAT) for hypofractionated radiation therapy of breast cancer. Different combinations of H‑VMAT—a combination of three-dimensional radiotherapy (3D-CRT) and VMAT—were analyzed regarding planning target volume (PTV), dose coverage, and exposure to organs at risk (OAR).MethodsPlanning computed tomography scans were acquired in deep-inspiration breath-hold. A total of 520 treatment plans were calculated and evaluated for 40 patients, comprising six different H‑VMAT plans and a 3D-CRT plan as reference. H‑VMAT plans consisted of two treatment plans including 3D-CRT and VMAT. During H‑VMAT planning, the use of hard wedge filters (HWF) and beam energies were varied. The reference plans were planned with mixed beam energies and the inclusion/omission of HWF.ResultsCompared to the reference treatment plans, all H‑VMAT plans showed consistently better PTV dose coverage, conformity, and homogeneity. Additionally, OAR protection was significantly improved with several H‑VMAT combinations (p < 0.05). The comparison of different H‑VMAT combinations showed that inclusion of HWF in the base plan had a negative impact on PTV dose coverage, conformity, and OAR exposure. It also increased the planned monitor units and beam-on time. Advantages of using lower beam energies (6-MV photons) in both the base plan and in the VMAT supplementary dose were observed.ConclusionThe H‑VMAT technique is an effective possibility for generating homogenous and conformal dose distributions. With the right choice of H‑VMAT combination, superior OAR protection is achieved compared to 3D-CRT.

The Treatment Planining of Rectum Tumors and The Use of The Wedge Filter for Ensuring The Correct Isodoses

One of the most important issues in the field of radiotherapy is the correct distribution of the dose around the volume of interest or planning target volume (PTV). For making this possible the exact isodose in a treatment plan has to cover the PTV, so it is used the wedge which is a part of the linear accelerator head. Wedge plays the role of a filter and usually it is called wedge filter. The wedge filter is in use almost in all treatment plans, for all the parts of the body. In this paper it is consider the use of the wedge filter for treatment of rectum tumors.&#x0D; The process starts with the scanning of the patient and the deliantion of the interest’s volums in the Monaco system. In the following the imagins have been sent in the treatment planning system for making the nesessary plans for treatment of the rectum. Two plans were done, one with the use of the wedge and the other without using it. The dose volume histogram helps for compering the results of the plans. The best conformity of the isodoses it was for the plan with the use of wedge through volume of interest, which is planning target volume (PTV).

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..

Experimental evaluation of a radiation dose management system-integrated 3D skin dose map by comparison with XR-RV3 Gafchromic® films

ObjectiveTo assess the interactive Skin Dose Map® tool (SDMTool) integrated to the radiation dose management system (RDMS) DoseWatch® with Gafchromic® films for implementation in routine practice. MethodsA retrospective dose estimation software SDMTool was used to calculate Peak Skin Dose (PSD) and display the patient skin dose distribution. PSD was calculated with a triangle mesh of 0.055 cm2 resolution on ICRP 110 male anthropomorphic phantom and with a square ROI of 1 cm2 on flat phantom. The tool uses Radiation Dose Structured Reports (RDSR) data to model exposure events and calculate the PSD per event. The PSD and the skin dose distribution estimated with SDMTool were evaluated in comparison with Gafchromic® films positioned under the PMMA phantom (20 cm) for 13 configurations. Measurements were performed on a Philips system. Statistical analysis were carried out to compare PSDFilm and PSDSDM. ResultsAverage differences between PSDFilm and PSDSDM were 6% ± 6% (range from −3% to 22%) for flat phantom and 5% ± 7% (range from −3% to 25%) for ICRP phantom. Concordance was good between the measured PSDFilm and the estimated PSDSDM with Lin’s coefficient estimation and 95% Confidence Interval of 0.979 [0.875; 0.984] for flat phantom and 0.977 [0.877; 0.985] for ICRP phantom. Dose map representations are concordant for 11 of the 13 tests on PMMA phantom. Disparities arose from the limitations of the RSDR format: table displacement during fluoroscopy events and the use of wedge filter. ConclusionThe results found in this experimental evaluation show that the SDMTool is a suitable alternative to Gafchromic® film to calculate PSD.

Improvements in Simulations for Radiotherapy Wedge Filter dose and AAA-Convolution Factor Algorithms

Analytical-convoluted and numerical Gaussian models have been used in recent decades for radiotherapy treatment planning software/calculations, to perform accurately radiation dose delivery –numerical, analytical, or numerical-analytical. The objective of this evoluted-contribution was to obtain an exact dose delivery, 3D analytical-integral-equation solution, for the triple Gaussian model of wedge filters, since previous/initial 2D approximations of other authors, although correct, were not completely exact. Additionally, to set conceptual and mathematical-geometrical differences between the beam modification created by Multi-Leaf Collimator and Wedge Filters, either standard or Conformal. Ever the precision, from mathematical theory algorithms to real laboratory measurements, a series of simulations are presented. The generic triple Gaussian model of Ulmer and Harder sets an Attenuation Exponential Factor, AEF, well approximated in 2 variables, namely, u and z. This evoluted contribution of the research contribution was specially focused on numerical methods and approximation analysis of the integral equation resolution –with extent details about numerical data, Appendix 3. In this paper we set a detailed spatial-spherical geometry discussion/proof towards the determination of a 3D integral form of the delivery dose in water. In other words, with an AEF for magnitude-values of variables u,v, and z. Simulations, based on these new determinations were shown with sharp presentation of the numerical-computational software and functional programming series development. Computing encode techniques are explained with some practical examples for numerical radiotherapy calculus.

Suitability of a set compost of 2D and a 3D array detectors for the commissioning of dynamic wedge filters

The objective of this work was to evaluate the efficiency of bidimensional array detectors (MatriXX® and QA BeamChecker Plus®) and a tridimensional array detector (ArcCHECK®) in the commissioning of dynamic wedge filters of clinical linear accelerators in order to discuss the convenience and limitation of these devices for such use. The efficiency of MatriXX was investigated in symmetry tests of the collimator jaws, dose linearity, dose rate, filter factor, dose profiles at different depths for 30°, 45°, and 60° dynamic wedge filters, and dose distribution. The efficiency of ArcCHECK was verified in a test of the influence of the gravitational force on the collimator simulating wedges filters. With QA BeamChecker Plus, the 6 MV megavoltage photon beam output constancy was analyzed. In all tests, the three detectors presented good results, indicating that this set of detectors is suitable for the commissioning of dynamic wedge filters.

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.

Quality Assurance Procedure for Linear Accelerators Measuring Direct Tissue Maximum Ratio with a Calibration Water Phantom

In this paper, we proposed an efficient quality assurance method which can measure direct tissue maximum ratio (TMRDir), total scatter factor (Scp, Dir), wedge factor (WFDir), tissue phantom ratio 20/10 (TPR20/10Dir) by using a calibration water phantom and a Farmer chamber. The TMRDir was compared with the calculated TMR (TMRCal) that was calculated from the percentage depth dose at the time of the linear accelerator installation. Scp, Dir, WFDir and TPR20/10Dir calculated from TMRDir were compared with Scp, BD, WFBD, and TPR20/10BD measured at the time of the linear accelerator installation. The difference between TMRDir and TMRCal was approximately within 1% except for using 60° wedge filter. The difference between Scp, Dir and Scp, BD was within 1%, between WFDir and WFBD was within 2%, between TPR20/10Dir and TPR20/10BD was within 1%, these differences were acceptable levels of AAPM TG-142 report. Also, coefficient of variation (CV) of TMRDir, ScpDir, WFDir and TPR20/10Dir when changing days and measuring multiple times were approximately within 1%, these CVs were reference levels of AAPM TG-106 report. We validated that was an efficient quality assurance method by measuring direct tissue maximum ratio, but the propose method has limited in measurable field size.

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.

FLUKA-BASED MONTE CARLO INVESTIGATION OF MICRODOSIMETRIC DISTRIBUTIONS OF TELECOBALT BEAM.

FLUKA-based Monte Carlo calculations of microdosimetric distributions in water phantom involving a walled spherical Tissue-Equivalent Proportional Counter filled with tissue-equivalent propane gas have been studied for an indigenously developed telecobalt machine. The simulated site size considered in the study was 2 μm. In the Monte Carlo calculations, field size was varied from 10 cm × 10 cm to 35 cm × 35 cm and the depth was varied as 5-20 cm. The study also includes calculation of microdosimetric distributions with a 30° wedge filter. The efficiency of the calculations was improved up to a factor of 26 by choosing appropriate cut off values for production and transport of electrons. The calculated microdosimetric distributions of telecobalt machine is distinctly different from that of a bare 60Co source which is attributed to the influence of scattered photons from the machine head and the water phantom.

Therapeutic evaluation between coventional fraction radiotherapy and intensity modulated radiation therapy combined with concurrent chemotherapy for esophageal carcinoma

Objective To evaluate the curative effect between conventional fraction radiotherapy (CFRT) and intensity modulated radiation therapy (IMRT) combined with concurrent chemotherapy for unresectable esophageal carcinoma. Methods 144 patients were enrolled into this study. They were divided into CFRT group and IMRT group. CFRT group (60 cases): irradiation field encompassed primary lesion and mediastinal lymph drainage regin. Neck and thoracic upper segment cases were made front thoraxT field irradiation first, DT 36 Gy/18 f, followed by two front oblique field made Iso-central irradiation, field width was 4.5-5.0 cm, gantry angle 50°-60°, wedge filter 30°, DT added to 66 Gy. For thorax middle or lower segment patients, field width was 6.0-6.5 cm, field length was that the tumor upper and lower each extended 3.0-5.0 cm, vertically irradiated in thoracic front and at the back, after DT 36 Gy/18 f, changed to two back ablique field, made Iso-central irradiation, DT added to 66 Gy. IMRT group (84 cases): GTV was esophageal primary lesion and metastasis lymph node (GTVnd); CTV included GTV, GTVnd and mediastinal lymph drainage region, at GTV around all was widened 0.8-1.0 cm, its upper and lower each extended 3.0-5.0 cm; PTV were in the basis of CTV, all were widened 0.5 cm again. With ≥95% isodose curve covering the PTV and the target dose was prescribed to PTV 60-64 Gy/30-32 f. Organ at risk (OAR): both lungs V20≤30%, spinal cord ≤45 Gy/6 weeks, heart V30≤40%. Chemotherapy of two groups was same, DDP 25-30 mg/m2 × 3-5 days, 5-Fu 450-500 mg/m2 × 5 days civ, 28 days were one period, total 2 period, after 1-3 months, strengthen chemotherapy 3-4 period. Results Leucopenia and radiation-induced esophagitis as shown by the WHO staging system were the most common acute toxicities, but were mainly grade 1 or 2. The incidence rate of leucopenia and radiation-induced esophagitis in CFRT group were 78.3% (47/60) and 83.3% (50/60), IMRT group were 82.1% (69/84) and 79.8% (67/84). After symptomatic treatment, all patients completed the planner treatment. During radiotherapy and after treatment, the patients showed grade 1-2 radiation-induced pneumonitis, CFRT group were 36.7% (22/60), but IMRT group were only 9.5% (8/84) (χ2= 9.99, P < 0.01). In CFRT group and IMRT group, the 1-, 3-, 5-year survival rates were 75.0% (45/60), 36.7% (22/60), 20.0% (17/84) and 79.8% (67/84), 35.7% (30/84), 21.4% (18/84), respectively. Conclusion The overall response and 5-year survival rates of CFRT and IMRT combined with concurrent chemotherapy are similar, however, the incidence of grade 1-2 radiation-induced pneumonitis of IMRT is low, which indicates that IMRT can reduce the lungs irradiational volume and dose. Key words: Esophageal neoplasms; Radiotherapy, intensity-modulated; Drug therapy; Radiation pneumonitis