Showing papers on "Dose profile published in 2001"

Dosimetric characteristics of tissue equivalent thermoluminescent solid TL detectors based on lithium borate

Abstract: This paper presents the main dosimetric characteristics of newly prepared, complete tissue-equivalent thermoluminescent dosimeters Li2B4O7:Cu,In, and Li2B4O7:Cu, in the form of sintered pellets. The dosimetric characteristics of lithium borate thermoluminescent dosimeters examined in this study, include glow-curve shapes, TL sensitivity, photon dose response, minimum detectable dose, relative photon energy response, fading, reproducibility, precision of dose measurements and annealing procedure.

A miniature "scintillator-fiberoptic-PMT" detector system for the dosimetry of small fields in stereotactic radiosurgery

Abstract: Linear accelerator-based stereotactic radiosurgery is an important modality in the management of localized intracranial abnormalities and often is the only option for treatment of certain lesions. The quantification of the absorbed radiation doses delivered for this modality has been a challenge due to the small size of the treatment fields (typically 5-30 mm collimated fields) and the type of detectors presently available. This paper presents comparative dose measurements performed using a miniature (1.6/spl times/10/sup -3/ cm/sup 3/) plastic scintillator detector to the commonly used detectors for the dosimetry of small photon fields used for stereotactic radiosurgery. The spatial resolution of the plastic scintillator detector was compared to that of a p-type Si diode and a 0.1-cm/sup 3/ ionization chamber. Small field dosimetry parameters (beam profiles, percent depth doses, and dose output factors) using the scintillation detector, the 0.1-cm/sup 3/ ionization chamber, the p-type Si diode, and radiographic film are presented. This comparative study shows that designing a miniature scintillator detector system is feasible and when compared to other benchmark detectors is an appropriate detector for the dosimetry of small stereotactic radiosurgery photon fields.

Radiation therapy treatment method

Abstract: Radiation therapy planning uses a beam commissioning tool and a Monte Carlo dose calculation tool. In the beam commissioning, measured dose data are input into a data processor. The measured dose data are derived from exposing a phantom to radiation from a source; and measuring the radiation dose to obtain a measured dose in the phantom resulting from the exposing step. The dose is measured at a plurality of points within the phantom, at least some of said points being axial points located at positions along a substantially central axis of the radiation source and others of said points being transverse points located at positions along an axis transverse to the central axis. The method further performs a Monte Carlo simulation of the radiation source to determine a simulated dose at the plurality of points; and further models the radiation source using the simulated dose and the measured dose.

Digital radiography of scoliosis with a scanning method: initial evaluation.

Abstract: PURPOSE: To evaluate the radiation dose, image quality, and Cobb angle measurements obtained with a digital scanning method of scoliosis radiography. MATERIALS AND METHODS: Multiple images were reconstructed into one image at a workstation. A low-dose alternative was to use digital pulsed fluoroscopy. Dose measurements were performed with thermoluminescent dosimeters in an Alderson phantom. At the same time, kerma area-product values were recorded. A Monte Carlo dose calculation also was performed. Image quality was evaluated with a contrast-detail phantom and visual grading system. Angle measurements were evaluated with an angle phantom and measurements obtained on patient images. RESULTS: The effective radiation dose was 0.087 mSv for screen-film imaging, 0.16 mSv for digital exposure imaging, and 0.017 mSv for digital fluoroscopy; the corresponding kerma area-product values were 0.43, 0.87, and 0.097 Gy · cm2, respectively. The image quality of the digital exposure and screen-film images was about equa...

Collimator scatter and 2D dosimetry in small proton beams

Abstract: Monte Carlo simulations have been performed to determine the influence of collimator-scattered protons from a 150 MeV proton beam on the dose distribution behind a collimator. Slit-shaped collimators with apertures between 2 and 20 mm have been simulated. The Monte Carlo code GEANT 3.21 has been validated against one-dimensional dose measurements with a scintillating screen, observed by a CCD camera. In order to account for the effects of the spatial response of the CCD/scintillator system, the line-spread function was determined by comparison with measurements made with a diamond detector. The line-spread function of the CCD/scintillator system is described by a Gaussian distribution with a standard deviation of 0.22 mm. The Monte Carlo simulations show that protons that hit the collimator on the entrance face and leave it through the wall of the aperture make the largest scatter contribution. Scatter on air is the major contribution to the extent of the penumbra. From the energy spectra it is derived that protons with a relative biological effectiveness greater than 1 cause at most 1% more damage in tissue than what would be expected from the physical dose.

Narrow stereotactic beam profile measurements using N-vinylpyrrolidone based polymer gels and magnetic resonance imaging

Abstract: In this work, polymer gel-MRI dosimetry (using VIPAR gels), radiographic film and a PinPoint ion chamber were used for profile measurements of 6 MV x-ray stereotactic beams of 5 and 10 mm diameter. The VIPAR gel-MRI method exhibited a linear dose response up to 32 Gy. VIPAR gels were found to resolve the penumbra region quite accurately, provided that the in-plane image resolution of the related T2-map is adequate (≤0.53 mm). T2-map slice thickness had no significant effect on beam profile data. VIPAR measurements performed with a spatial resolution of 0.13 mm provided penumbra widths (80%-20% distance) of 1.34 and 1.70 mm for the 5 and 10 mm cones respectively. These widths were found to be significantly smaller than those obtained with the film (2.23 mm for the 5 mm cone, 2.45 mm for the 10 mm cone) and PinPoint (2.25 mm for the 5 mm cone, 2.52 mm for the 10 mm cone) methods. Regarding relative depth dose measurements, good correlation between VIPAR gel and PinPoint data was observed. In conclusion, polymer gel-MRI dosimetry can provide relatively accurate profile data for very small beams used in stereotactic radiosurgery since it can overcome, to some extent, the problems related to the finite size of conventional detectors.

Comparison of the IAEA TRS-398 and AAPM TG-51 absorbed dose to water protocols in the dosimetry of high-energy photon and electron beams

Abstract: The International Atomic Energy Agency (IAEA TRS-398) and the American Association of Physicists in Medicine (AAPM TG-51) have published new protocols for the calibration of radiotherapy beams. These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standards laboratory's reference quality beam. This paper compares the recommendations of the two protocols in two ways: (i) by analysing in detail the differences in the basic data included in the two protocols for photon and electron beam dosimetry and (ii) by performing measurements in clinical photon and electron beams and determining the absorbed dose to water following the recommendations of the two protocols. Measurements were made with two Farmer-type ionization chambers and three plane-parallel ionization chamber types in 6, 18 and 25 MV photon beams and 6, 8, 10, 12, 15 and 18 MeV electron beams. The Farmer-type chambers used were NE 2571 and PTW 30001, and the plane-parallel chambers were a Scanditronix-Wellhofer NACP and Roos, and a PTW Markus chamber. For photon beams, the measured ratios TG-51/TRS-398 of absorbed dose to water Dw ranged between 0.997 and 1.001, with a mean value of 0.999. The ratios for the beam quality correction factors kQ were found to agree to within about +/-0.2% despite significant differences in the method of beam quality specification for photon beams and in the basic data entering into kQ. For electron beams, dose measurements were made using direct N(D,w) calibrations of cylindrical and plane-parallel chambers in a 60Co gamma-ray beam, as well as cross-calibrations of plane-parallel chambers in a high-energy electron beam. For the direct N(D,w) calibrations the ratios TG-51/TRS-398 of absorbed dose to water Dw were found to lie between 0.994 and 1.018 depending upon the chamber and electron beam energy used, with mean values of 0.996, 1.006, and 1.017, respectively, for the cylindrical, well-guarded and not well-guarded plane-parallel chambers. The Dw ratios measured for the cross-calibration procedures varied between 0.993 and 0.997. The largest discrepancies for electron beams between the two protocols arise from the use of different data for the perturbation correction factors p(wall) and p(dis) of cylindrical and plane-parallel chambers, all in 60Co. A detailed analysis of the reasons for the discrepancies is made which includes comparing the formalisms, correction factors and the quantities in the two protocols.

Differences in effective dose estimation from dose–area product and entrance surface dose measurements in intravenous urography

Abstract: In this study, measurements of dose-area product (DAP) and entrance surface dose (ESD) were carried out in a sample of 25 adult patients who underwent intravenous urography (IVU). These measured quantities were used to estimate the effective dose E from the IVU examination, a quantity closely correlated to radiation risk. Estimating E involves the use of conversion coefficients that have been determined for specific X-ray views in a mathematical phantom. These are obtained under conditions which are not usually met in clinical practice. As a result, the E estimates using the two different measurable quantities can be quite different. Analysis of the calculation procedure suggests that the E estimate using the DAP measurements, in addition to being more practical, could be more accurate than using ESD measurements, as DAP is sensitive to the X-ray field size settings. Furthermore, it is shown that in the absence of the appropriate equipment, a reliable E estimate can be obtained from the ESD calculated using the exposure data for each X-ray view.

Experimental determination and verification of the parameters used in a proton pencil beam algorithm

Abstract: We present an experimental procedure for the determination and the verification under practical conditions of physical and computational parameters used in our proton pencil beam algorithm. The calculation of the dose delivered by a single pencil beam relies on a measured spread-out Bragg peak, and the description of its radial spread at depth features simple specific parameters accounting individually for the influence of the beam line as a whole, the beam energy modulation, the compensator, and the patient medium. For determining the experimental values of the physical parameters related to proton scattering, we utilized a simple relation between Gaussian radial spreads and the width of lateral penumbras. The contribution from the beam line has been extracted from lateral penumbra measurements in air: a linear variation with the distance collimator-point has been observed. Analytically predicted radial spreads within the patient were in good agreement with experimental values in water under various reference conditions. Results indicated no significant influence of the beam energy modulation. Using measurements in presence of Plexiglas slabs, a simple assumption on the effective source of scattering due to the compensator has been stated, leading to accurate radial spread calculations. Dose measurements in presence of complexly shaped compensators have been used to assess the performances of the algorithm supplied with the adequate physical parameters. One of these compensators has also been used, together with a reference configuration, for investigating a set of computational parameters decreasing the calculation time while maintaining a high level of accuracy. Faster dose computations have been performed for algorithm evaluation in the presence of geometrical and patient compensators, and have shown good agreement with the measured dose distributions.

Implementation of an in vivo diode dosimetry program and changes in diode characteristics over a 4-year clinical history.

Abstract: An in vivodosimetry system that used n-type semiconductor diodes with integral build-up caps was introduced into the clinic. Measurements were made on the entrance surface of the patient and were compared to calculated diode readings expected from monitor units delivered by each beam. A method is given for calibration and correction for changes in diode sensitivity, dose-per-pulse effects, collimated field-size (head-scatter factor), wedges, compensators, and scatter from blocks and block trays. Clinically relevant temperature corrections are determined based on temperature measurements made with the diode used as a thermistor. Changes in diode characteristics over 4 years of clinical use are presented. With proper correction for clinical variables it is shown that difference between calculated and measured diode readings are within ±1% for phantom measurements and within ±3% for clinical measurements at a 95% confidence level. The correlation of dose measurements on the patient surface to dose inside a target volume is discussed.

Wide dynamic dose range of VIPAR polymer gel dosimetry.

Abstract: In this work the extent of the linear dose response and the dynamic dose range of N-vinylpyrrolidone-argon based (VIPAR) polymer gels were investigated. VIPAR gels were irradiated using a 6 MV linear accelerator up to 60 Gy and a Nucletron microSelectron 192Ir HDR brachytherapy source to much higher doses to cover a dose range of two orders of magnitude. They were then MR scanned at 1.5 T to obtain T2-maps. VIPAR gel measurements obtained from the two irradiation regimes were calibrated against ion chamber measurements and dose calculations derived using the AAPM TG-43 protocol respectively. A satisfying agreement between the calibration results derived using the 6 MV x-rays and the 192Ir source was found for doses up to 60 Gy, implying that the response of the VIPAR gels is independent of photon energy and dose rate. A linear R2 dose response up to ~40 Gy and a dynamic dose range up to at least ~250 Gy were observed. VIPAR gel dose measurements derived using the monoexponentially fitted brachytherapy calibration data were found to be quite accurate.

An iterative EPID calibration procedure for dosimetric verification that considers the EPID scattering factor

Abstract: There has been an increasing interest in the application of electronic portal imaging devices (EPIDs) to dosimetric verification, particularly for intensity modulated radiotherapy Although not water equivalent, the phantom scatter factor of an EPID, Spe, is generally assumed to be that of a full phantom, Sp, a slab phantom, Sps, or a mini phantom This assumption may introduce errors in absolute dosimetry using EPIDs A calibration procedure that iteratively updates Spe and the calibration curve (pixel value to dose rate) is presented The EPID (Varian Portal Vision) is irradiated using a 20 x 20 cm2 field with different beam intensities The initial guess of dose rates in the EPID is calculated from ionization chamber measurements in air, multiplied by Sp or Sps The calibration curve is obtained by fitting EPID readings from pixels near the beam central axis and dose rates in EPID to a quadratic equation The Spe is obtained from EPID measurements in 10 X 10 cm2 and 20 x 20 cm2 field and from the calibration curve, and is in turn used to adjust the dose rate measurements and hence the calibration curve The above procedure is repeated until it converges The final calibration curve is used to convert portal dose to dose in the slab phantom, using the calibrated Spe, or assuming Spe = Sp or Spe=Sps The converted doses are then compared with the dose measured using an ionization chamber We also apply this procedure to off-axis points and study its dependence on the energy spectrum The hypothesis testing results (on the 95% significance level) indicate that systematic errors are introduced when assuming Spe = Sp or Spe=Sps and the dose calculated using Spe is more consistent with ionization chamber measurements Differences between Spe and Sps are as large as 2% for large field sizes The measured relative dose profile at dmax using the EPID agrees well with the measured profile at dmax of the isocentric plane using film in a polystyrene phantom with full buildup and full backup, for open and wedged fields, and for a broad range of field sizes of interest The dependence of the EPID response on the energy spectrum is removed once the calibration is performed under the same conditions as the actual measurements

Treatment planning for heavy-ion radiotherapy: biological optimization of multiple beam ports.

Abstract: A crucial task in radiotherapy is dose conformation to the prescribed target volume whilst sparing the surrounding healthy tissue around as much as possible. One of the best approaches so far is active dose shaping in three dimensions using scanned beams of charged particles, like carbon ions. Besides their inverse dose profile and minimal lateral scattering, carbon ions have the advantage that their RBEs increase towards the end of their range. An active beam-delivery system for intensity-modulated carbon-ion beams has been operational at GSI since December, 1997. In order to ensure dose conformation, inverse treatment planning with respect to the biologically effective dose distribution must be applied. A typical patient irradiation comprises two singly optimized opposing fields. This paper discusses the superposition of biologically effective dose distributions for radiotherapy with 12C ions, which is non-trivial due to the nonlinear nature of the dose response of biological systems. Sum rules for the nonlinear addition of singly optimized fields are derived. This method is being used clinically, and has been successfully applied to more than 50 patients.

A translational couch technique for total body irradiation.

Abstract: We have constructed a computer controlled translational couch to administer total body irradiation reproducibly and safely. The system has replaced the previous stationary anterior-posterior technique in our institution and 30 plus patients have been treated with it so far. In this technique, patients comfortably lie on a couch in supine and prone positions and are transported slowly through a narrow beam with the gantry in an upright position. Dose to the patient is determined by the couch velocity that is calculated based on physical parameters such as patients dimensions, beam geometry, and machine dose rate. In our design, the couch velocity is continuously updated to compensate for machine dose rate fluctuations. The translational couch technique provides better dose uniformity within the patient compared to fixed beam techniques, and allows a more precise shielding block placement for organs at risk. At the same time, it presents a special challenge for dosimetry calculations. A dosimetry parameter is introduced that converts the moving beam output to the fixed beam output factor. Based on this factor, a simple dosimetry calculation method has been developed that takes advantage of conventional dosimetry parameters, eliminating extensive dosimetry measurements. Multiple point dose measurements within a phantom confirmed the validity of the calculation method. 2001 American College of Medical Physics.

A simplified shielding approach for limiting fetal dose during radiation therapy of pregnant patients.

Abstract: Purpose: To investigate the effectiveness of a simple and practical shielding device to reduce fetal dose for a patient undergoing radiation therapy of nasopharyngeal carcinoma. Methods and Materials: Using 5-cm-thick lead bricks and a heavy-duty steel cart, a 50 × 50-cm portable shield was designed and fabricated to reduce fetal dose due to collimator scatter and head leakage radiation. With the gantry at 90°/270° the shield can be easily positioned between the machine head and the fetus to reduce peripheral dose. Dose measurements for 6-MV X-rays and 9-MeV electrons have been made, utilizing a Rando phantom, to quantify the effect of the shield. Results: Measurements show that the peripheral dose to the fetus can be reduced by 60% when the simple shielding device is used.

A measured data set for evaluating electron-beam dose algorithms.

Abstract: The purpose of this work was to develop an electron-beam dose algorithm verification data set of high precision and accuracy. Phantom geometries and treatment-beam configurations used in this study were similar to those in a subset of the verification data set produced by the Electron Collaborative Working Group (ECWG). Measurement techniques and quality-control measures were utilized in developing the data set to minimize systematic errors inherent in the ECWG data set. All measurements were made in water with p-type diode detectors and using a Wellhofer dosimetry system. The 9 and 20 MeV, 15 x 15 cm2 beams from a single linear accelerator composed the treatment beams. Measurements were made in water at 100 and 110 cm source-to-surface distances. Irregular surface measurements included a "stepped surface" and a "nose-shaped surface." Internal heterogeneity measurements were made for bone and air cavities in differing orientations. Confidence in the accuracy of the measured data set was reinforced by a comparison with Monte Carlo (MC)-calculated dose distributions. The MC-calculated dose distributions were generated using the OMEGA/BEAM code to explicitly model the accelerator and phantom geometries of the measured data set. The precision of the measured data, estimated from multiple measurements, was better than 0.5% in regions of low-dose gradients. In general, the agreement between the measured data and the MC-calculated data was within 2%. The quality of the data set was superior to that of the ECWG data set, and should allow for a more accurate evaluation of an electron beam dose algorithm. The data set will be made publicly available from the Department of Radiation Physics at The University of Texas M. D. Anderson Cancer Center.

Accurate in vivo dosimetry of a randomized trial of prostate cancer irradiation

Abstract: Purpose: To guarantee an accurate dose delivery, within ± 2.5%, in a Phase III randomized trial of prostate cancer irradiation (68 vs. 78 Gy) by means of a comprehensive in vivo dosimetry program. Methods and Materials: Prostate patients are generally treated in our clinic with a 3-field isocentric technique: an 8-MV anteroposterior beam and 2 18-MV wedged laterals. All fields are shaped conformally to the PTV. Patients were randomized between two dose levels of 68 Gy and 78 Gy. During treatment, the entrance and exit dose were measured for each patient with diodes. Special 2.5-mm thick steel build-up caps were applied to make the diodes appropriate for measurements in 18-MV photon beams as well. Portal images were used to verify the correct position of the diodes and to detect and correct for gas filling in the rectum that may influence the exit dose reading. Entrance and exit dose measurements were converted to midplane dose, which was used in combination with a depth dose correction to obtain the dose at the specification point. An action level of 2.5% was applied. Results: The added build-up for the diodes in the 18-MV beams resulted in correction factors that were only slightly sensitive to changes in beam setup and comparable to the corrections used in the 8-MV beams for diodes without extra build-up. The calibration factor increased almost linearly with cumulative dose: 0.7%/kGy for the 8-MV and 1.2%/kGy for the 18-MV photon beams. The introduction of average correction factors made the analysis easier, while keeping the accuracy within acceptable limits. In a period of 3 years, 225 patients were analyzed, from which 8 patients needed to be corrected. The average ratio of measured and prescribed dose was 1.009 (standard deviation [SD] 0.012) for the total group treated on two linear accelerators. When the results were analyzed per accelerator, the ratios were 1.002 (SD, 0.001) for Accelerator A and 1.015 (SD, 0.001) for Accelerator B. This difference could be attributed to the cumulative effect of three small imperfections in the performance of Accelerator B that were well within the limits of our quality assurance program. Conclusion: Diodes can be used for accurate in vivo dosimetry during prostate irradiation in high-energy photon beams. The dose delivery in this randomized trial is guaranteed within the 2.5% limits on an individual patient basis. This could not be achieved without the in vivo dosimetry program, despite our high-standard quality assurance program of treatment delivery.

The START trial-measurements in semi-anatomical breast and chest wall phantoms.

Abstract: This paper describes dosimetry measurements performed prior to departments entering patients into the START Trial, a breast fractionation trial. Absolute and relative doses were measured in semi-anatomical breast and chest wall phantoms, as part of a quality assurance programme visit. Doses were measured using an ionization chamber and the resulting distributions were compared with those calculated by the department. The mean ratio of measured to calculated dose at the START reference point was found to be 0.981 for the breast phantom and 0.978 for the chest wall phantom. This average measured dose was significantly less than the prescribed dose (p < 0.001). Differences were found between 2D and 3D planning systems and for departments using cobalt 60 beams. A number of departments had deviations of greater than 4%, which was the tolerance applied for this trial. It is essential for dose measurements of this type to be performed for randomized clinical trials involving radiotherapy, particularly where dose fractionation regimes are being compared.

Extrapolation chamber response in low-energy x radiation standard beams

Abstract: Measurements of absorbed dose rates in air and tissue produced by low-energy x radiation are often difficult to obtain with accuracy. The recommended instruments for these applications are extrapolation chambers. The performance of an extrapolation chamber, developed at IPEN, was studied in low energy x radiation standard beams in relation to its response linearity, extrapolation curves and energy dependence. The results obtained indicate that the developed chamber is suitable for x radiation measurements.

Dosimetry of low-energy protons and light ions

Abstract: For the vertical beam facility at the 14 MV Munich tandem accelerator, various techniques for dosimetry were tested for radiation fields of low-energy protons and light ions (4He, 12C and 16O). A reference dose was determined from the fluence of particles by counting individual particles. A parallel-plate Markus chamber with a small sensitive air volume was used for beam dosimetry applying the ICRU protocol. The doses measured with the ionization chamber were compared with doses evaluated from the fluence measurements. Alternative dose measurements were performed using MTS-N LiF:Mg, Ti thermoluminescence detectors (TLDs) and a photometrically evaluated Fricke chemical dosimeter. An uncertainty of 8% was found in the determination of the dose relative to the reference method. Effects of an inhomogeneous energy loss and a finite track length of the projectiles in the sensitive detector volume of the dosimeters had to be taken into account.

A stereotactic device for experimental rat and mouse irradiation using gamma knife model B--technical note.

Abstract: Background. For radiobiological experiments using the Gamma Knife model B, we constructed a stereotactic device to irradiate rat and mouse brains and verify the absorbed dose at the target using thermoluminescence dosimetry and a head phantom. Methods. Our stereotactic device is primarily designed for rats using the fixation principles of a stereotactic atlas. A head-fixation adapter for a mouse was constructed to enable targeted irradiation of mouse brains. We built simple phantoms to simulate rat and mouse heads. We placed thermoluminescent dosimeters at various positions on the phantom for dose measurements. Dose planning employed the Leksell Gamma Plan version 4.11 software, assuming a spherical skull geometry for all calculations. Findings. The measurements demonstrated that the actual absorbed dose agreed with our calculations within the errors of thermoluminescence dosimetry and the accuracy of our irradiation technique and dose calculations. Interpretation. This device provides an accurate method for irradiating rat and mouse brains using the Gamma Knife model B.

The properties of the ultramicrocylindrical ionization chamber for small field used in stereotactic radiosurgery

Abstract: Accurate dosimetry of small-field photonbeams tends to be difficult to perform due to the presence of lateral electronic disequilibrium and steep dose gradients. In stereotactic radiosurgery(SRS), small fields of 6–30 mm in diameter are used. Generally thermoluminescencedosimetry chips, Farmer, Thimble ion chamber, and film dosimetry are not adequate to measure dose in SRSbeams. These techniques generally do not provide the required precision due to their energy dependence and/or poor resolution. It is necessary to construct a small, accurate detector with high spatial resolution for the small fields used in SRS. The ultramicrocylindrical ionization chamber (UCIC) with a gold wall of 2.2 mm in diameter and 4.0 mm in length has dual sensitive volumes of air (8.0 mm3) and borosilicate (2.6 mm3) cavity. Reproducibility, linearity, and radiation damage with respect to absorbed dose, beam profile of small beam, and independence of dose rate of the UCIC are tested by the dose measurements in high energy photon (5, 15 MV) and electron (9 MeV) beams. The UCIC with a unique supporting system in the polystyrene phantom is demonstrated to be a suitable detector for the dose measurements in a small beam size.

Three-dimensional radiotherapy of head and neck and esophageal carcinomas: a monoisocentric treatment technique to achieve improved dose distributions.

Abstract: The specific aim of three-dimensional conformal radiotherapy is to deliver adequate therapeutic radiation dose to the target volume while concomitantly keeping the dose to surrounding and intervening normal tissues to a minimum. The objective of this study is to examine dose distributions produced by various radiotherapy techniques used in managing head and neck tumors when the upper part of the esophagus is also involved. Treatment planning was performed with a three-dimensional (3-D) treatment planning system. Computerized tomographic (CT) scans used by this system to generate isodose distributions and dose-volume histograms were obtained directly from the CT scanner, which is connected via ethernet cabling to the 3-D planning system. These are useful clinical tools for evaluating the dose distribution to the treatment volume, clinical target volume, gross tumor volume, and certain critical organs. Using 6 and 18 MV photon beams, different configurations of standard treatment techniques for head and neck and esophageal carcinoma were studied and the resulting dose distributions were analyzed. Film validation dosimetry in solid-water phantom was performed to assess the magnitude of dose inhomogeneity at the field junction. Real-time dose measurements on patients using diode dosimetry were made and compared with computed dose values. With regard to minimizing radiation dose to surrounding structures (i.e., lung, spinal cord, etc.), the monoisocentric technique gave the best isodose distributions in terms of dose uniformity. The mini-mantle anterior-posterior/posterior-anterior (AP/PA) technique produced grossly non-uniform dose distribution with excessive hot spots. The dose measured on the patient during the treatment agrees to within +/- 5 % with the computed dose. The protocols presented in this work for simulation, immobilization and treatment planning of patients with head and neck and esophageal tumors provide the optimum dose distributions in the target volume with reduced irradiation of surrounding non-target tissues, and can be routinely implemented in a radiation oncology department. The presence of a real-time dose-measuring system plays an important role in verifying the actual delivery of radiation dose.

Range-Modulated Pencil Beam Algorithm for Proton Dose Calculations

Abstract: The range-modulated pencil beam algorithm (RMPBA) has been developed for proton treatment planning on the basis of the pencil beam algorithm (PBA) to reduce the calculation time yet realize sufficient accuracy. It uses the depth-dose distribution of the range-modulated beam as a central-axis term of pencil beams. The spread of the range-modulated pencil beam is derived by assuming that the protons pass through the average thickness of the ridge-filter. The accuracy of dose calculations by the RMPBA is verified by comparison with dose measurements in water performed using a silicon semiconductor detector. The results of the measured dose distributions agree well with those of the calculations using the RMPBA. Furthermore, the calculation time required by the RMPBA is one-sixth of that required by the PBA in the case of the six-step ridge-filter. Therefore, the dose-calculation method by the RMPBA will be useful and applicable to actual treatment planning of proton therapy.

Verification of the accuracy of 3D calculations of breast dose during tangential irradiation: measurements in a breast phantom.

Abstract: This report specifically describes the use of a unique anthropomorphic breast phantom to validate the accuracy of three-dimensional dose calculations performed by a commercial treatment-planning system for intact-breast tangential irradiation. The accuracy of monitor-unit calculations has been corroborated using ionization chamber measurements made in this phantom. Measured doses have been compared to those calculated from a variety of treatment plans. The treatment plans utilized a 6-MV x-ray beam and incorporated a variety of field configurations and wedge combinations. Dose measurements at several clinically relevant points within the breast phantom have confirmed the accuracy of calculated doses generated from the variety of treatment plans. Overall agreement between measurements and calculations averaged 0.9980.009. These results indicate that the dose per monitor-unit calculations performed by the treatment-planning system can be confidently utilized in the fulfillment of clinical dose prescriptions. 2001 American College of Medical Physics.

Integral and pulse mode silicon dosimetry for dose verification on radiation oncology modalities

Abstract: Radiation oncology is an important part of cancer therapy. In 1996 a Committee of the Australian National Health and Medical Research Council recommended that 50-55% of all the new cancers include radiotherapy as part of their treatment. Cancer patients are treated with different radiation oncology modalities and while most are treated by conventional x-ray therapy a growing number is treated by hadron therapies such as fast neutron therapy (FNT), brachytherapy, proton therapy, heavy ion therapy and boron neutron capture therapy (BNCT). A new radiation oncology modality, microbeam radiation therapy (MRT), is currently under development. The outcome of radiation treatment in a hadron therapy is highly dependent on an accurate knowledge of both dose distribution and the quality of the radiation beam. Aim of this project was to develop new semiconductor probes for applications in hadron therapy and in synchrotron M R T and for validation of quality assurance on these modalities. A. Metal oxide semiconductor field effect transistor (MOSFET) dosimeters have been investigated in this study and new applications for dosimetry in radiation oncology have been introduced. • A novel dual use of a MOSFET detector has been proposed, which is based on simultaneous mini and microdosimetry by a single M O S F E T detector. • The count mode response of a M O S F E T detector has been investigated for correlation with its integral response in a high lineal energy transfer (LET) radiation field for separation, by a single M O S F E T detector, of low and high L E T doses in a mixed radiation field. • A paired integral M O S F E T detector technique, for dosimetry in a thermal neutron field, has been proposed and investigated. This technique has allowed determination of a relative boron depth dose in B N C T and evaluation of the boron enhancement in FNT. • A novel "edge-on" M O S F E T mini dosimetry has been introduced, investigated and its micron scale spatial resolution proven. It was successfully demonstrated that the "edge-on" M O S F E T probe can be used for accurate measurements of the dose profile of a 30 urn wide synchrotron microbeam for MRT. • The role of a M O S F E T package for detector response was investigated for xray beams with energy range from 20 keV to 6 M V . • High spatial resolution M O S F E T dosimetry, in strong electron nonequilibrium x-ray fields of a conventional medical linac, has been proved using optimal packaging. B. A pulse method has been introduced for neutron clinical dosimetry • A small sized ion-implanted silicon detector with a thick 23 U converter, for absolute thermal neutron dosimetry, has been theoretically simulated and developed.