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

Purpose: In this study, the authors have quantified the two-dimensional (2D) perspective of skindose increase using EBT filmdosimetry in phantom in the presence of patient immobilization devices during conventional and IMRTtreatments. Methods: For 6 MV conventional photon field, the authors evaluated and quantified the 2D bolus effect on skindoses for six different common patient immobilization/support devices, including carbon fiber grid with Mylar sheet, Orfit carbon fiber base plate, balsa wood board, Styrofoam, perforated AquaPlast™ sheet, and alpha-cradle. For 6 and 15 MV IMRT fields, a stack of two film layers positioned above a solid phantom was exposed at the air interface or in the presence of a patient alpha-cradle. All the films were scanned and the pixel values were converted to doses based on an established calibration curve. The authors determined the 2D skindose distributions, isodose curves, and cross-sectional profiles at the surface layers with or without the immobilization/support device. The authors also generated and compared the dose area histograms (DAHs) and dose area products from the 2D skindose distributions. Results: In contrast with 20% relative dose [(RD) dose relative to d max on central axis] at 0.0153 cm in the film layer for 6 MV 10 × 10 cm 2 open field, the average RDs at the same depth in the film layer were 71%, 69%, 55%, and 57% for Orfit, balsa wood, Styrofoam, and alpha-cradle, respectively. At the same depth, the RDs were 54% under a strut and 26% between neighboring struts of a carbon fiber grid with Mylar sheet, and between 34% and 56% for stretched perforated AquaPlast™ sheet. In the presence of the alpha-cradle for the 6 MV (15 MV) IMRT fields, the hot spot doses at the effective measurement depths of 0.0153 and 0.0459 cm were 140% and 150% (83% and 89%), respectively, of the isocenter dose. The enhancement factor was defined as the ratio of a given DAH parameter (minimum dose received in a given area) with and without the support device. For 6 MV conventional 10 × 10 cm 2 field, the enhancement factor was the highest (3.4) for the Orfit carbon fiber plate. As for the IMRT field, the enhancement factors varied with the size of the area of interest and were as high as 3.8 (4.3) at the hot spot of 5 cm 2 area in the top film layer (0.0153 cm) for 6 MV (15 MV) beams. Conclusions: Significant 2D bolus effect on skindose in the presence of patient support and immobilization devices was confirmed and quantified with EBT filmdosimetry. Furthermore, the EBT film has potential application forin vivo monitoring of the 2D skindose distributions during patient treatments.

The goal of IMRT is to achieve an isodose distribution conformed to the tumor while avoiding the organs at risk. For these tasks several gantry angles are selected, each one containing a series of different leaf configurations for the multileaf collimator (MLC) (segments). Verifying the relative distributions as well as the absolute doses is an important step for quality assurance issues. We have observed that an accurate modeling of the transmission of the primary x-ray fluence through the jaws and MLC as well as the head scatter is crucial for a precise calculation of relative doses and monitor units. Also, an inaccurate calculation of the output factor for small size segments can lead to important differences in the absolute dose for points under these segments. Incorrect models could lead to systematic errors of around 5% to 10% in the calculated monitor units and a shift in the isodose curves.

The use of high dose levels in CT Scan Brain produce distribution scattered radiation originating from the patient. This study was conducted to determine the distribution of scattered radiation at a particular point on the CT scan to obtain the curve isodose. Using Experimental Methods researchers conducted measurements of the distribution of the scattering radiation at 128 Slice CT Scan of the Brain CT examination. Thermoluminescent dosimeter (TLD) is used to measure the distribution of scattered radiation and use as a phantom object head. Eksposi parameters used are Brain CT program. Take 19 points to be measured. Using a point distance of 1, 2 meters, 3 meters from the gantry CT Scan. The results showed a minimum value of the distribution of the scattering radiation at the measurement point at a distance of 1 meter, 2 meters. 3 meters is at point A is the right side of the gantry and a maximum distribution at point C which is the examination table. Key words : CT Scan, distribution of scattered radiation, isodose curves

The analysis of treatment plans generated following prostate implants (post plans) is an essential part of the patient's treatment regimen. The results are used to determine the adequacy of the individual implant and, just as importantly, to provide an evaluation of the institution's brachytherapy technique. Compiled post plan results can be used to compare data from different institutions and help determine guidelines that should be established as dosimetric goals. Sector analysis, or spatial dose mapping, is a novel method of analyzing brachytherapy results that has been developed for this purpose. The display of isodose curves provides spatial information pertaining to the dosimetric evaluation of post plans but is an unwieldy tool; ill suited to the creation of general conclusions for comparative efforts. Dose-volume histogram (DVH) analysis is an excellent tool for examining dosimetric results, but the spatial information is lost. Sector analysis bridges the gap between isodose curves and DVH analysis in post plan analysis. To perform sector analysis we divide the gland into three regions in the cranial-caudal direction (base, midgland, and apex) and four regions on each transverse slice (anterior, posterior, left and right). This gives twelve sectors, each identified by its location in the cranial-caudal direction and position on the transverse slice, e.g., posterior midgland. DVH analysis is performed for each region separately and compiled for display. We present an example of the use of this technique wherein we have analyzed a sequential series of 118 implants performed by a single practitioner (BRP) at two institutions over a calendar year. The implants were performed using two different techniques at the two institutions. Sector analysis was used to compare the results of the implants at the two institutions.

The International Commission on Radiation Units and Measurements recommends the use of 60 Gy isodose volumes for reporting doses in the intracavity treatment of carcinoma of the uterine cervix. This study was aimed at determining the variation in isodose volumes while using different sizes of intrauterine tubes and ovoids, with different applicator geometries. It was based on the treatment plans of 175 patients with cervical cancer, treated with low dose rate intracavitary brachytherapy with or without additional external beam radiotherapy. The volumes encompassed by the 60 Gy isodose curves were calculated using the Nucletron planning system. Applicator positions in 15 patients who were treated to the same point A dose, using 6 cm intrauterine tube and medium ovoids, were recorded. This was to discover how variations in applicator geometry influences isodose volumes. The 60 Gy isodose volumes increased with increasing point A dose. For a constant point A dose prescription, reference isodose volume increased with ovoid applicator size used, but showed no consistent variation with the length of intrauterine tube. There were individual variations in the isodose volumes within a standard set-up (same sized intrauterine tube and ovoids and same point A dose), due to variations in applicator geometry. Displacement of the ovoids changed the volumes encompassed by the reference isodose. There are significant variations in the volumes encompassed by the 60 Gy isodose during intracavitary treatment using a standard set-up, while treatment using applicators of different sizes can give equivalent values of 60 Gy isodose volume. 60 Gy isodose volumes may hence be useful in dosimetric comparisons but have a limited role in predicting clinical response.

Introduction Dosimetry in external radiotherapy is based on tomodensitometry images that are required to be previously calibrated and assume that the electron density is comparable to the mass density. In Magnetic Resonance Imaging, and in particular diffusion sequence, significant heterogeneities have been shown. These heterogeneities result in density variations within the tumor, e.g. glioblastomas. Purpose The aim of this study is to evaluate slight influence of mass density variations within the tumor via a dosimetric study. This can then be used to quantify the impact of those variations on modifications of dose 3D distribution. Materials and methods This study is devoted to dosimetric calculations realization using TPS Eclipse AAA used in clinical. Treatments were carried out with 5 X-ray beams of 6 MeV, in optimized dynamic Intensity-Modulated-Radiotherapy. Mass density changes of GTV for the same treatment plans have been tested from 1.04 (default tumor density) to 1.8 g.cm−3 in steps of 0.1. Results Dose-volume-histograms and profiles studies show a slight dose increase in surface GTV for the highest densities with significant changes isodose curves. Conversely, upon leaving the GTV, an under dosage of the tumor has been observed from a density variation from 1.04 to 1.2 g cm−3. It was noted that density differences of 0.5 and 0.8 g cm−3 caused failure to respect the prescribed dose limits of ± 3% in brain volumes of 1.5 and 25 cm3, respectively. Conclusion Dose distributions variations were recorded by densities changes. From a change of 0.5 g/cm3 within the tumor, dose prescriptions limits are not any more guarantees.

Purpose: Computed tomography (CT) exam rooms are shielded more quickly and accurately compared to manual calculations using RadShield, a semi-automated diagnostic shielding software package. Last year, we presented RadShield's approach to shielding radiographic and fluoroscopic rooms calculating air kerma rate and barrier thickness at many points on the floor plan and reporting the maximum values for each barrier. RadShield has now been expanded to include CT shielding design using not only NCRP 147 methodology but also by overlaying vendor provided isodose curves onto the floor plan. Methods: The floor plan image is imported onto the RadShield workspace to serve as a template for drawing barriers, occupied regions and CT locations. SubGUIs are used to set design goals, occupancy factors, workload, and overlay isodose curve files. CTDI and DLP methods are solved following NCRP 147. RadShield's isodose curve method employs radial scanning to extract data point sets to fit kerma to a generalized power law equation of the form K(r) = ar^b. RadShield's semiautomated shielding recommendations were compared against a board certified medical physicist's design using dose length product (DLP) and isodose curves. Results: The percentage error found between the physicist's manual calculation and RadShield's semi-automated calculation of lead barrier thickness was 3.42% and 21.17% for the DLP and isodose curve methods, respectively. The medical physicist's selection of calculation points for recommending lead thickness was roughly the same as those found by RadShield for the DLP method but differed greatly using the isodose method. Conclusion: RadShield improves accuracy in calculating air-kerma rate and barrier thickness over manual calculations using isodose curves. Isodose curves were less intuitive and more prone to error for the physicist than inverse square methods. RadShield can now perform shielding design calculations for general scattering bodies for which isodose curves are provided.

A set of standard wedge filters has been modified for use with half-collimated beams of a 6 MV linear accelerator. The position of the standard size wedge filter has been shifted as far to one side of the wedge plate to ensure optimum half-collimated field coverage (up to 20 x 30 cm) required in certain clinical situations. Dosimetric parameters were normalized at 1.5 cm depth and at an off-axis reference point (3.5 cm from the central axis of the collimator at 100 cm SSD. The shapes of the wedged profile and isodose curves of the modified wedges remained similar to those of standard wedges. Data presented include wedge transmission factors, wedge angles, beam profiles, and isodose distributions. The clinical advantages of using modified wedge filters (larger field size, larger transmission, and smaller weight) over standard large wedges is discussed.

A method of producing “flat” X-ray isodose curves at any given depth in a phantom by means of “stepped” copper filters, is described. Details of these filters as fitted in a variety of applicators are given. A specimen isodose curve is shown and the effects of the filter on the surface dose and dose distribution, and on the central percentage depth dose values, are discussed.

In order to initiate the use of a multileaf collimator (MLC) in the clinic, a set of technical procedures needs to be available sufficient to create MLC leaf settings and to deliver an accurate dose of radiation through the MLC-shaped field. Dosimetry data for clinical use of the MLC were measured. Dosimetric characteristics included central axis percent depth dose, output factors, and penumbra. In this paper, it has been concluded that a dose control monitor unit calculation procedure that has been applied to the use of conventional secondary field-shaping blocks can be applied to the multileaf collimator dosimetry. The multileaf collimator penumbra (20% to 80%) is only slightly wider (1-3 mm) than the penumbra of the conventional collimator jaws. Beam's-eye-view comparisons made between the isodose curves in fields shaped by conventional Cerrobend blocks and isodose curves in fields shaped by the multileaf collimator demonstrated that the 50% isodose line at 10-cm depth exhibited the discrete steps of the multileaf collimator leaves, but that the 90% and 10% isodose curves of the multileaf were close to those shaped by Cerrobend blocks.

High dose rate (HDR) remote afterloading is increasingly being used to replace many conventional low dose rate (LDR) brachytherapy procedures. Implementation of the microSelectron-HDR with Ir-192 at our facility necessitated this study to obtain equivalent dosimetric distributions with those of our LDR Cs-137 techniques using our current treatment planning system. Three anatomical sites are presented: nasopharynx, esophagus, and uterine cervix. Attention must be given to the anisotropy of Cs-137 tubes when converting to Ir-192; for linear geometries, total equivalent activity may be preserved but the shapes of the resulting isodose curves for Ir-192 are longer than those of Cs-137. In the case of Fletcher-Suit intracavitary treatments of the uterine cervix, the longer contours for Ir-192 in the vaginal ovoids results in higher isodose levels reaching the bladder and rectum. Maintaining the traditional dose levels to these organs is accomplished by modifying the loading of the ovoids to approximately 85% of the corresponding Cs-137 activity. Computerized dosimetry is presented, along with a chart we have devised to easily convert a standard LDR treatment to HDR dwell times. Our results are especially suitable to those users who will continue to make use of their present computer treatment planning system.

In a beam accessory configuration for a linear accelerator using a prototype multileaf collimator, newly designed wedges were mounted beyond the blocking tray. The isodose curves, depth of maximum dose, surface dose, and wedge transmission factors were measured for the wedges designed for this unique configuration. The same set of wedges was used for both 6‐ and 18‐MV x rays. The shape of the wedged isodose curves was essentially unchanged from those produced by the conventional wedges located above the blocking tray. The isodose curves exhibited the desired wedge angles over the range of field sizes from 5×5 to 15×40 cm. In the 10×10‐cm field, the average difference between the observed wedge angle and the desired wedge angle was 3.8°. The surface doses ranged from 18% to 35% for the wedged 10×10‐cm fields as compared with about 15% for the same open field. Dosimetrically the wedges were acceptable for clinical use.

One of the methods currently being used to treat choroidal melanoma employs an episcleral plaque containing I-125 radioactive seeds. However, comprehensive dosimetry studies on the plaque are scarce and controversial. For this work, we use film to study the dosimetry outside the lip of the gold shield of the eye plaque. This lip around the gold shield was made to protect the critical structures behind and adjacent to the lesion. Since the changes of energy spectrum of I-125 in tissue are negligible, film dosimetry seems to be a logical choice because of high spatial resolution required around the lip of the gold plaque. For this study, we first established an H and D curve with dose expressed in a unit of specific dose rate constant. This avoids absolute dose measurements. All film density measurements are made with a 1-mm aperture scan, normalized to the density at the prescription point for tumor of 3--5-mm apical height, i.e., 5 mm from the interior surface of sclera, and converted to percentage isodose curves. With a gold shield, it is found that when the plaque is placed against the optical nerve, the optical disk and macula, located at 2 mm outside the lip, onmore » the exterior surface of sclera, may receive 85% of the prescription dose for a 12-mm plaque and 58% for a 16-mm plaque. For tumors of 8-mm apical height, the optical nerve would receive more than the prescription dose.« less

Dose distribution studies were carried out using different dosimetric techniques for the purpose of transferring the respective methodologies to a semi-industrial Gamma Irradiation plant (UTR GAMA-Pi). The work was performed using a Cobalt-60 experimental source (Graviner, England - initial activity - 1/3/71 - 3.7X10 14 Bq), and different dosimetric systems (Fricke system, ethanol monochlorobenzene and polymethyl methacrylate). The dose distribution in the irradiation chamber, with a volume of 65X50X20 cm 3 , was calculated using a two-dimensional B-Spline interpolation method.

Dosimetric studies in mammography are addressed by means of a Monte Carlo simulation program. The core of this program (DOSIS: dosimetry simulation studies) is a simulation model developed using FORTRAN 90, enriched with a graphical user interface developed in MS Visual Basic. User defined mammographic technique parameters affecting breast dose are imported to the simulation model and the produced results are provided by means of both absolute (surface dose, exposure at detector plane) and relative quantities (percentage depth dose, isodose curves). The program functionality has been demonstrated in the evaluation of various mammographic examination techniques. Specifically, the influence of tube voltage and filtration on the surface dose and the exposure at detector plane has been studied utilizing a water phantom. Increase of tube voltage from 25 to 30 kVp for a Mo/Mo system resulted in a 42% decrease of the surface dose for a thick breast (6 cm), without changing the exposure at the detector plane. Use of 1.02 mm Al filter for a W anode system operating at 30 kVp resulted in a 19.1% decrease of the surface dose delivered to a 5 cm water equivalent breast. Overall, W/Al systems appear to have improved dosimetric performance, resulting up to a 65% decrease of surface dose compared to Mo/Mo systems, for identical exposures at the detector plane and breast thicknesses.

Purpose: The interactive dose shaping (IDS) planning paradigm aims to perform interactive local dose adaptations of an IMRT plan without compromising already established valuable dose features in real‐time. In this work we introduce an interactive isodose curve manipulation tool which enables local modifications of a dose distribution by intuitively dragging an isodose curve. Methods: We developed an in‐house IMRT TPS framework consisting of a 3D GUI for dose manipulation and visualization. Dose calculations are performed with an adapted pencil beam algorithm, enabling ultra‐fast dose calculation for local fluence map changes. Starting point of our planning approach is a homogeneous, conformal dose of the target volume at the prescribed dose level. This initial dose distribution will be interactively modified by our isodose curve manipulation tool, which induces a dose modification as a direct change of dose in one or more voxels. This modification is incrementally obtained by fluence adjustments. These will naturally lead to unintended and unwanted dose features outside the vicinity of modified dose. A subsequent recovery step identifies these voxels and aims to recover their original dose by selecting and modifying an orthogonal set of fluence amplitudes that does not alter the initially achieved dose modification. Results: We evaluated the proposed tool by adapting the dose distribution of a prostate case (9 beams, coplanar). The initial homogeneous, conformal dose distribution led to a severe over dosage of the rectum. By manipulation of isodose curves it was possible to reduce the dose in the rectum to clinically acceptable values. Dose modification for one dragged point on the isodose curve took about 1 second, subsequent recovery of 25 points took 2 seconds. This time includes approximately 300 local fluence updates per beam as well as 300 dose calculations. Conclusions: We proposed, implemented and successfully tested an isodose curve manipulation tool.

Purpose: Extending MVCT's potential for daily patient position and anatomy verification, we investigated the feasibility of using MVCT to assess the daily delivered dose for head and neck patients treated with proton beams. Method and Materials: A Rando head phantom was scanned on a Philips Brilliance Big Bore CTscanner to obtain the planning kVCT images. The corresponding MVCT images were acquired on a helical Tomotherapy unit. To establish CT‐electron density curves, a Gammex RMI 465 electron density phantom was scanned on both kVCT and MVCT scanners. A typical 4‐field plan was created for the phantom and dose distribution was calculated using pencil beam algorithm from the XIO treatment planning system. After MVCT and kVCT images manually registered, kVCT‐based treatment plan with structure contours and beam configuration including beam shaping devices was mapped to MVCT images for dose re‐computation. Dose map, isodose curves, dose profiles, gamma maps, and dose‐volume histograms were used for dose comparison. Results: Although the noise level in MVCT images is higher than that with the comparabl kVCT the dose distribution computed on MVCT image is comparable to the dose distribution computed on the kVCT images. The dose comparison showed an agreement of higher than 97% between the two plans given the criteria of 3% dose difference and 3 mm distance to agreement. The biggest dose difference between two plans occurred around the periphery of the target. There was negligible difference in the DVH comparison. Conclusions: MVCT images acquired for daily setup verification in image‐guidedproton therapy are feasible for assessment of daily deliveredproton dose distributions with accuracy comparable to that of kVCT‐based dose calculation. The original treatment plan based on kVCT can be transferred to the daily MVCT image set to evaluate the actual dose distribution for adaptive proton therapy.

Purpose: Recently, there has been a renewed interest in the delivery of arcbased IMRT using conventional linear accelerators. Elekta and Varian have developed linear acceleratorcontrol systems that are capable of delivering rotational IMRT by combining gantry rotation, dynamic MLC leaf motion, and a variable dose rate. Elekta's new Precise Beam Infinity™ control system has been installed in our clinic and acceptance testing and plan verifications have been performed. In this study, we will report on our initial experiences with volumetric modulated arc therapy (VMAT) delivered using an Elekta Precise linear accelerator.Method and Materials: VMAT is a radiotherapydelivery technique that combines the dosimetric advantages of rotational delivery with the dose painting capabilities of IMRT. We have developed an arc sequencing algorithm that translates optimized fluence maps into deliverable VMAT treatment plans. In this investigation, one head‐and‐neck and five prostate plans have been delivered in an effort to quantify the efficiency and accuracy of the VMAT delivery system. Results: A complex head‐and‐neck plan involving two targets and a simultaneous boost was delivered in 5 minutes 29 seconds. For this three‐arc head‐and‐neck plan, the point dose agreed within 1.9%. Additional measurements for 5 prostate cases demonstrated an average delivery time of 3 minutes 28 seconds with all ion chamber measurements agreeing within 3%. Film measurements demonstrated close agreement between the predicted and measured isodose curves. Measurements have also been performed to quantify efficiency of single‐arc versus multi‐arc VMAT deliveries.Conclusion: Elekta's Precise Beam Infinity control system can safely and efficiently delivery highly complex VMAT treatment plans. In our initial investigation, all plans delivered in less than 5.5 minutes. Numerous additional plan verifications will be performed as we move towards an anticipated clinical implementation of VMAT in May 2008. Research sponsored in part through a grant from Elekta.

Current methods for evaluating modern radiation therapy treatment planning (RTP) systems include the manual superposition of calculated and measured isodose curves and the comparison of a limited number of calculated and measured point doses. Both techniques have significant limitations in providing quantitative evaluations of the large number of dose data generated by modern RTP systems. More sophisticated comparison techniques have been presented in the literature, including dose-difference and distance-to-agreement (DTA) analyses. A software tool has been developed that uses superimposed isodose plots, dose-difference, and DTA distributions to quantify errors in computed dose distributions. Dose-difference and DTA analyses are overly sensitive in regions of high- and low-dose gradient, respectively. The logical union of locations that fail both dose-difference and DTA acceptance criteria, termed the composite evaluation, is calculated and displayed. The composite evaluation provides a method for the physicist to efficiently identify regions that fail both the dose-difference and DTA acceptance criteria. The tool provides a computer platform for the quantitative comparison of calculated and measured dose distributions.

A prototype multi-rod collimator for producing irregular fields in photon radiation therapy has been designed and built. The mechanical details of the design and operation of the multi-rod collimator are discussed. Beam profiles for an approximately 10 x 10 cm2 field have been measured at various depths in phantom, and compared with profiles obtained using the secondary collimator jaws alone and with cast metal blocks. The ability of the collimator to produce irregular fields is demonstrated with reference to some commonly encountered therapy fields and the ability to produce central blocks and island blocks is discussed. Isodose curves for selected irregular fields are presented.

A procedure is described to calculate the monitor unit ratios required to produce effective wedge fields having a desired wedge angle by combining an internal 60 degrees wedge with an open field. Complementary procedures are derived and demonstrated for calculating the effective wedge dose distributions with wedge angles of 15 degrees, 30 degrees, and 45 degrees using the central axis depth dose data and off-axis ratios of the open field and the 60 degrees wedged field. Measurements at five points on and off the central axis within each field and measurements of the effective wedge factor demonstrated that the calculated wedge distributions were correctly delivered to within 2% in all cases.

Purpose: Ophthalmic plaque radiotherapy using I‐125 radioactive seeds in removable episcleral plaques is often used in management of ophthalmic tumors. The goal of this study was to develop a Monte Carlo simulation method for treatment planningoptimization of eye plaques. Method and Materials: MCNP4C Monte Carlo Code was used to calculate the percent depth dose curves, dose profiles and isodose curves created by three different plaques. The plaques used were Collaborative Ocular Melanoma Study‐12mm (C0MS‐12mm) with eight model 6702 seeds, COMS‐20mm with three model 6711 seeds, and University of Southern California (USC) #9 with nine model 6711 seeds. Dosimetric characteristics of I‐125 model 6702 and 671 seeds, were calculated according to recommendations of AAPM Task Group 43 protocol. Then, the geometry of each plaque was simulated and dose calculations were performed using F6 tally card in a 12mm radius spherical water phantom. Results: The comparison of calculated central axis depth doses to reported measured values, showed the deviation up to %10 for C0MS‐12mm, %3 for COMS‐20mm and %1 for USC#9. For off‐axis dose profiles the deviation was up to %9 for C0MS‐12mm, at 7mm depth, %6 for COMS‐20mm at 10mm depth and %1 for USC#9 at 17 mm depth. The results of this study show that C0MS‐12mm and COMS‐20mm plaques are suitable for treatment of symmetrical tumors with thickness‐diameter (base) of 8mm‐14mm and 4mm‐12mm, respectively. However, a USC#9 plaque is suitable for treatment of non‐symmetrical tumors with 8mm thickness and 16mm base diameter. Conclusion: The user code developed in this study can be used as an optimization tool within a few millimeters of the plaque surface. It can also be used to design custom made plaques for treatment of ocular tumors with various sizes, shapes and locations.

Purpose: The purpose of this investigation is to compare quality of plan, treatment time, monitor units (MUs) and dose delivery capability between dynamic and segmental IMRT for combination of Varian 21iX‐S and CMS XiO. Method and Materials: Head and neck (HN) and prostate IMRT were planned in both dynamic and segmental fashion using same dose objectives in the optimization process. Quality of plans was evaluated with isodose curves and dose‐volume‐histograms. Treatment time defined as time from the first beam‐on to the last beam‐off and MUs were compared. Dose rate of segmental and dynamic were 500 and 300 MU/min, respectively. Dosimetric verification was performed with 0.6 cc ionization chamber for point dose measurement and radiographic film for dose distribution. Results: In HN cases, dose conformity for PTV were slightly superior, however doses to parallel organs (e.g. parotid gland) were higher in dynamic delivery. MUs with dynamic delivery were lager by 20% for HN and prostate cases. Therefore, larger MUs lead more transmitted dose from MLC to parallel organs. Some reports mentioned that with dynamic delivery using other than XiO, treatment time could be shortened by half. But our results showed only 20% reduction for HN and comparable for prostate. The MLC sequence file of dynamic delivery was fairly large (320 control points/port), on the other hand, that of segmental was 1/6 of dynamic. Therefore, beam was kept off while treatment console read MLC sequence file (approximately 20 s/port for dynamic and 5 s/port for segmental, respectively). For HN cases, dose delivery capability was better in both point dose and dose distribution for segmental delivery. Due to higher MUs, dynamic delivery needs precise modeling especially for MLC transmission is required. Conclusion: Delivery performances are superior in segmental delivery, except for treatment time. To conclude, segmental delivery could be suitable for IMRT.

Purpose: Investigate physical aspects of silvernanoparticle (AgNp) application in iodine therapy aiming increase dose conformality in Nuclear Medicine treatments of thyroid disease. Material and Methods: AgNp (2–3nm size) were considered uniformly embedded in thyroid tissue in 1% mass concentration. PENELOPE‐2008 Monte Carlo code was used to perform the simulations. A faithful neck geometry was described in PENGEOM‐2008 code, considering air cavity, spinal cord and all relevant tissues present in clinical cases. Iodine‐131 radioactive events inside thyroid volume were simulated considering beta and photon energy spectrums. Monte Carlo spectrometry was applied inside thyroid volume to identify components with high probability of interaction with silver atoms that increase dose locally due to AgNP presence. Dose increase in thyroid volume was calculated as the ratio between total dose deposited with and without AgNp (DEF = D without AgNp /D with AgNp ) and comparing total doses deposited in studied volumes. Dose conformality increase was evaluated from changes in dose‐profiles and isodose curves inside the neck. Results: The DEF was 1.19 to thyroid volume (target) and 0.40, 0.56, 0.77 and 0.63 to spinal cord, spinal bone, parotids and sublingual base, respectively. In non‐target regions, DEF lower than 1 indicate that the dose decrease, resultant from high absorptions of fluency that occurs locally in target volume. Total dose in thyroid volume increases from 32.43Gy to 38.40Gy due to AgNp presence, representing 18.4%. In axial and longitudinal profiles is possible to observe that the doses not only increase in target region, but also decrease in healthy volumes, contributing to more conformai treatment. Conclusions:Silvernanoparticle added to Iodine therapy can contribute to dose increase changing dose conformality in benefic therapeutic levels. Monte Carlo simulation is a powerful tool to investigate metal nanoparticle applications in Nuclear Medicine cases. Future investigations will asses nanoparticle atomic number and concentration variations.

Purpose: The aim of this study was to dosimetrically evaluate various intraluminal brachytherapy applicators for the Gammamed high dose rate afterloading system. Materials and methods:Dosimetric evaluation was carried out for 8 mm, 10 mm, 12 mm and 14 mm diameter intraluminal applicators available with the Gammamed high dose rate afterloading system. Treatment planning for these applicators was carried out with abacus treatment planning system for active source length and 8 cm, 10 cm and 12 cm. All evaluations were carried out for prescription dose of 5 Gy at the reference point of 1cm from source axis. Reference volume length (RVL), Treated volume (TV), Hyper dose sleeve radius (HSR) were noted down from the isodose plans. Iterative, geometric and equal times optimization routines were carried out for all evaluations with step size of 0.5cm. Results: The isodose curves showed tapering pattern towards the distal and proximal regions. The reference volume lengths were larger than active source lengths for 8mm and 10mm diameter applicators. Reference volume lengths were smaller than active source length for 12mm and 14mm diameter applicators hyper dose sleeve radius decreases with increase in diameter of the applicator. For 14mm diameter applicators, the hyper dose sleeve radius was smaller than the radius of the reference isodose. Iterative optimization routine gave better average in terms of reference volume length few are four diameter applicators. Conclusions: We evaluated the dosimetric parameters for various intraluminal applicators available with the Gamma med high dose rate remote after loading system. The values of RVL and HSR were within acceptable limits for the four applicators considered in this study.

Purpose: Relative shifts in isodose curves were noted between post‐operative and intra‐operative 131 Cs prostate seed plans. This study examines the dose differences between intra‐operative and post‐operative plans and evaluates regions of prostate to determine the direction of the shift. Materials and Methods: 103 patient plans done with 131 Cs seed implants were examined. Each intra‐operative plan was derived in realtime via TRUS. Loose seeds (mean activity of 2.1U) were implanted to deliver a peripheral dose of 115Gy. Post‐operative studies were evaluated via CT at 4 weeks post implant. Intra‐operative and post‐operative prostate D90, D100 and V100 were compared. 50 patients were randomly selected and had two additional volumes contoured, Anterior‐Prostate (AP) and Posterior‐Prostate (PP). D90, D100 and V100 values for these additional regions were also compared. Results: Comparing intra‐operative and post‐operative plans, significant differences (p = 10% in 73.8% of patients. V100 prostate quantities dipped in post‐operative plans >= 4% in 64.1% patients. For the additional regions contoured, intra‐operative AP D90, D100 and V100 values were >=10% higher than their corresponding post‐operative values in 74.0%, 64.0% and 68.0% of patients, respectively. Intra‐operative to post‐operative dose reductions of at least 5% to the PP D90 and D100 values were noted for 56% and 64% of patients. Conversely, 62% experienced increased post‐operative PP V100 values of at least 5%. Conclusion: These findings confirm significant prostate dose discrepancies between intra‐operative and post‐operative plans. Specifically, the dose to anterior prostate was consistently overestimated in intra‐operative plans. Discrepancies are believed to be due to the probe deforming the prostate during the implant. However, further evaluation is needed to provide conclusive results.

Purpose: To establish a protocol for directly measuring spatial dose deposition and activity distribution of beta particles emitted by Re‐186 transported by liposomes in a HNSCC Xenografts in Nude Rats using HS GafChromic dosimetry media. Method and Materials: Nude rats (n=3) at 4–5 weeks age (75–100 g) bearing a tumor with an average volume of 1.73±0.37 cm3 were injected intratumorally with 0.29±0.05 ml of 18.5±2.7 MBq (0.50±0.09 mCi) 186Re‐liposomes, which contained 4.0±0.7 mg of DSPC and cholesterol. The 186Re‐liposome dose was equally divided and delivered to several separate locations of the tumor.SPECT and CTimages in vivo were acquired using a micro‐SPECT/CT scanner. The rats were sacrificed six hours after liposome injection, and tumor lobes were excised and sectioned in slices (3 mm thickness). HS films were placed between each slice and the tumor lobe was reassembled to its original shape. Film calibration was performed between 0–40 Gy using 60Co γ rays. Film response was measured using a flatbed scanner in 36 bits RGB transmission mode. Dose distributions were extracted from the red and green components. Results: The 2D spatial dose distributions are highly heterogeneous with dose regions above 40 Gy. Dose gradients up to 40 Gy in distances smaller than 2 mm in the center of the slice tumor were found. While comparing dose distributions between the 3 different tumors, significant differences in the volumes (larger than 30%) covered by the isodose curves of 1 Gy were observed. Conclusion: The method to measure direct dose distributions produced by Re‐186 transported by liposomes using GafChromic HS film has proved to be adequate for the large dose gradients produced. The use of the different components of the scanned image (red and green) allows us to extend the sensitivity range of the HS film without loss of precision.

Purpose: To quantify the effect of the curvature of flexible applicators on the dose distribution in high‐dose‐rate intraoperative radiation therapy (HDR‐IORT). Method and Materials:Treatment planning was performed with flat Harrison‐Anderson‐Mick applicators using 192 Ir as the radioactive source, and dwell times were optimized using dose‐pointoptimization techniques. These optimized dwell times were then used for the curved applicators, and the dose distributions that would actually be delivered to patients were determined. Shallow, moderate, and steep curvatures were considered. The discrepancies in dose distribution resulting from the applicator's curvature were quantified, and the regions receiving significant underdoses or overdoses were identified. Results: The dose directly below the central catheter was strongly dependent on the curvature of the applicator. Steep parabolic curves caused underdoses as large as 19% at the prescribed depth of 1 cm normal to the convex side of the applicator surface. The rate of dose reduction with increasing distance from the applicator surface was also greatly affected by applicator curvature. The local dose distribution was not greatly affected by the number of catheters. On the concave side of the applicator, curvature pushed the isodose curves from the applicator surface, causing overdosing. Data from these experiments could be used to create a simple library of treatment plans for curved geometries to complement existing libraries for flat applicators. Conclusion: The curvature of the applicator profoundly affects dosimetry and can be exploited to optimize coverage of the target during HDR‐IORT procedures. To ensure accurate dosedelivery, these dose perturbations must be accounted for in the planning process. We recommend maintaining a dosimetry atlas of various applicator sizes and curvatures in addition to one for flat applicators.

A β-ray source collimator has been suggested to reduce the lenticular dose associated with the treatment of eye lesions. A new design of collimator for a plane source which could completely avoid the irradiation of the lens epithelium for post-operative radiotherapy of keratoplasty is illustrated. A field-limiting device for spherical shell type of applicators which would reduce the lens epithelium dose and the extent of the irradiated area of the lens epithelium is also presented. Percentage depth dose and isodose curves with these collimators and field-limiting devices are presented for plane and spherical sources respectively.

We present a uniform method for selecting an optimum implant geometry by presenting techniques for evaluating the therapeutically significant maximum dose rate (herein referred to as the ‘‘maximum dose rate’’), the reference isodose (85% of the maximum dose rate), and the area enclosed by the reference isodose contour. The therapeutic performances of planar iridium implants may be compared by evaluating their respective maximum dose rates, reference isodoses, and areas within the reference isodose contours. Because these parameters are mathematically defined, they reproducibly describe each implant geometry. We chose a small microcomputer to develop these comparison algorithms so that the radiotherapist need not have large, expensive computer facilities available to conduct his own studies. The development of these algorithms led to some significant conclusions and recommendations regarding the placement of interstitial implants. Using seeds that are centrally located in the array to evaluate the maximum dose contour avoids underestimating the array’s maximum dose rate. This could occur if edge or corner seeds were used. Underestimating the maximum dose rate (and hence the reference isodose contour area) may have a serious therapeutic outcome, because the actual total treatment dosage may be excessive. As ribbon spacing is increased, there is a point beyond which the reference isodose contours become decoupled. At this point, a single relatively uniform reference isodose contour separates into several contours. This effect not only complicates the planimetry calculations, but it also adversely affects the therapeutic efficacy of the implant by producing therapeutically ‘‘cold’’ regions.

The Therac 20 medicallinear accelerator produces electron beams of 6, 9, 13, 17, and 20 MeV. We measured depth dose, isodose curves, and output factors for small electron fields using an ionization chamber, film, and thermoluminescent dosimeters. Tables and graphs were generated from these measurements for accurate treatment planning of various blocked and open fields.

A semi-automated procedure for the calculation of point doses and isodose distributions for a curved multi-wire implant is described. A dose optimisation method has been developed for producing acceptable dose distributions from non-ideal implants and the dosimetry of such implants is discussed. Source preparation, handling and stock control methods are described which facilitate the re-use of the encapsulated wire with consequent benefits in the reduction of staff radiation exposure and the costs of treatment.

Rad 8 is a small, in-house computer system for calculating radiotherapy dose distributions, both for multiple field and rotational external beam techniques and for interstitial and intracavitary redium treatments. Implementing the system has its difficulties, particularly in obtaining the necessary beam profile information. Several approaches have been tried and finally a separate profile generator program was written. Other difficulties encountered with beam data storage were overcome by making minor changes to the system programs. The various calculation techniques have been evaluated, and in general found to be satisfactory, and suitable factors to be used in the inhomogeneity correction for 4 MV X rays have been calculated based on previously published measured data. An option to change beam weightings exists and this can be used to renormalize dose distributions to give percentage isodose curves relative to the prescribed tumour dose. If this procedure is followed dose homogeneity over the target volume can readily be assessed, and the exposure times may easily be calculated from the new weightings. Certain shortcomings in the rotating beam program and the radium program may easily lead to error if extreme care is not exercised.

Some of the physical parameters necessary in electron beam treatment planning are investigated for 5- to 45-MeV electrons extracted from a Brown-Boveri betatron. The percent depth ionization (PDI) curves are compared with the empirical relation given by Laughlin's equation, and an extension of Laughlin's equation is described. The modified absorption coefficient (MAC) method is introduced to correct the isodose distributions for the presence of inhomogeneities, such as lung, with the actual density of lung and the location of the inhomogeneity taken into consideration. Experimental data from measurements made in a water-cork phantom are presented, and the results are compared with the various calculated methods.

Dose tables and isodose curves for several commercially available platinum filtered caesium-137 tubes and needles are presented and shown to be more closely related to those of radium sources than to stainless steel filtered 137Cs sources. Alternative definitions of the concept of exposure equivalent milligrams of radium as a method of specifying the activity of 137Cs sources are discussed. An activity correction factor characteristic of each source is introduced as a function of the active length and the source filter material and thickness. Application of this factor facilitates conversion to millicuries from units of milligrams of radium equivalent when the latter unit is based on the equivalence of the exposure dose rates, in air at 25 cm distance, of the caesium source and a point source of radium screened by 0·5 mm platinum.

Aus experimentell ermittelten Tiefendosisverteilungen von energiereichen Elektronen wurde eine Formel zur mathematischen Beschreibung des Tiefendosisverlaufs im Energiebereich 0,5–3 MeV entwickelt, die als Grundlage zur Berechung von Dosis- und Vernetzungsgradverteilungen im bestrahlten Material dienen kann. Als Beispiel werden einige Verteilungen diskutiert, die sich bei Mehrseitenbestrahlung von zylindrischen Absorbern mit energiereichen Elektronen ergeben.

A modification of the conventional extrapolation chamber to perform absolute dose measurements from surfaces of spherical beta applicators (type SIA.I, SIA.3, SIA.6) is described. A stack of Ilford N 550 films has been used in a spherical geometry to obtain the variation of surface dose, the depth dose data and the isodose curves. The results obtained are compared with data available in the literature.

Electron beam therapy is usually employed for the treatment of tumours located at or near the surface of the body, because the electron beam gives a high dose near the surface, but falls off rapidly with increasing depth beyond the level of the 80% depth dose. Isodose curves for radiotherapy have been obtained using physical methods, but have rarely been investigated on the basis of living human cells. In the present study, lymphocyte chromosome analysis was employed as a biological dosemeter for comparison with the isodose curve measured physically. The peripheral blood was exposed to a 14 MeV electron beam in a plastic tube set in a specially made test-tube stand immersed in a water tank. The chromosome aberration frequencies induced by irradiation of about 95% of peak dose at a depth of 31 mm were found to be higher in value than those induced at a depth of 17 mm where the peak dose had been determined physically. Three gray of irradiation given to whole blood in the presence of contrast medium gave rise to a slight enhancement of radiation-induced chromosome aberration frequencies in the lymphocytes exposed at a depth of 17 mm, but a slight decrease at 31 mm.

The determination of isodoses in a facility, which enables the gamma irradiation of samples with good reproducibility and uniformity, is described. Two examples of applications, with catheters and cork stoppers, are presented.

The characteristics of wedged fields which affect their clinical use have been examined for the 10-MV x-ray beam from the Clinac-18. The methods used for obtaining and analyzing the wedged-field data are discussed. These characteristics have been examined in terms of (a) the wedge angle, (b) the variation of the wedge angle with field size, (c) the variation in the angle through which isodose curves between the approximate depths of 5 and 15 cm are turned relative to the central axis as a function of depth, and (d) the variation of wedge central-axis transmission factor with field size. Analysis of the data pertinent to these categories is presented for the 15-, 30-, 45-, and 60-deg wedges. In addition, the effect of the 60-deg wedge upon the position of maximum dose on the central axis was determined.

Es wird eine Meβanordnung zur Bestimmung der Beta-Dosisleistung ebener und gewolbter medizinischer Applikatoren vorgestellt. Die mit der Anordnung gemessenen Isodosen differieren bis zu 35% im Vergleich mit entsprechenden Messungen an der Extrapolationskammer. Die Meβergebnisse werden in Verbindung mit berechneten Beta-Dosis-Absorptionskurven fūr 90Y und 106Rh diskutiert.

The first Mitsubishi medicallinear accelerator in the United States was commissioned in April 1985. This unit EXL‐8 (marketed by Mitsubishi International Corporation) produces 8‐MeV electron beams in addition to 6‐MV x rays. It is a 100‐cm source–axis distance isocentric machine. Acceptance testing and performance evaluation of this accelerator were completed. Our measurements included beam characteristics and dosimetry parameters for both modalities. Central axis % depth dose (% DD), tissue‐maximum ratio, field size output factors, wedge factors, etc., for this Linac 6‐MV beam are reported. Characteristics of the 8‐MeV electron beam, namely % DD data, isodose curves, and cone ratios for various electron applicators are presented.

We have studied the dosimetry of an independent jaw system (provided with the Varian Clinac 2500) using ionometric measurements performed both in air and in a water phantom. Our study shows that the effect of the independent jaw on the dose distribution is similar to that of secondary blocking except for changes produced in the collimator scatter. A system of dose calculation was developed which takes into account the changes in the collimator scatter as well as in the isodose distribution. A method is described to correctly generate isodose curves for fields shaped by an independent jaw using a modified AECL TP11 treatment planning system. The primary modification in the program consists of correcting the zero‐area tissue–maximum ratios for the off‐axis variation in beam quality.