The Benefit of Individualized Custom Bolus in the Postmastectomy Radiation Therapy:Numerical Analysis with 3-D Treatment Planning / 대한방사선종양학회지

PURPOSE: To reduce the irradiation dose to the lungs and heart in the case of chest wall irradiation using an oppositional electron beam, we used an individualized custom bolus, which was precisely designed to compensate for the differences in chest wall thickness. The benefits were evaluated by comparing the normal tissue complication probabilities (NTCPs) and dose statistics both with and without boluses. MATERIALS AND METHODS: Boluses were made, and their effects evaluated in ten patients treated using the reverse hockey-stick technique. The electron beam energy was determined so as to administer 80% of the irradiation prescription dose to the deepest lung-chest wall border, which was usually located at the internal mammary lymph node chain. An individualized custom bolus was prepared to compensate for a chest wall thinner than the prescription depth by meticulously measuring the chest wall thickness at 1 cm2 intervals on the planning CT images. A second planning CT was obtained overlying the individualized custom bolus for each patient's chest wall. 3-D treatment planning was performed using ADAC-Pinnacle3 for all patients with and without bolus. NTCPs based on "the Lyman-Kutcher" model were analyzed and the mean, maximum, minimum doses, V50 and V95 for the heart and lungs were computed. RESULTS: The average NTCPs in the ipsilateral lung showed a statistically significant reduction (p<0.01), from 80.2+/-3.43% to 47.7+/-4.61%, with the use of the individualized custom boluses. The mean lung irradiation dose to the ipsilateral lung was also significantly reduced by about 430 cGy, from 2757 cGy to 2,327 cGy (p<0.01). The V50 and V95 in the ipsilateral lung markedly decreased from the averages of 54.5 and 17.4% to 45.3 and 11.0%, respectively. The V50 and V95 in the heart also decreased from the averages of 16.8 and 6.1% to 9.8% and 2.2%, respectively. The NTCP in the contralateral lung and the heart were 0%, even for the cases with no bolus because of the small effective mean radiation volume values of 4.4 and 7.1%, respectively. CONCLUSION: The use of an individualized custom bolus in the radiotherapy of postmastectomy chest wall reduced the NTCP of the ipsilateral lung by about 24.5 to 40.5%, which can improve the complication free cure probability of breast cancer patients.

Patients Setup Verification Tool for RT (PSVTs): DRR, Simulation, Portal and Digital images / 대한방사선종양학회지

PURPOSE: To develop a patients' setup verification tool (PSVT) to verify the alignment of the machine and the target isocenters, and the reproducibility of patients' setup for three dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT). The utilization of this system is evaluated through phantom and patient case studies. MATERIALS AND METHODS: We developed and clinically tested a new method for patients' setup verification, using digitally reconstructed radiography (DRR), simulation, portal and digital images. The PSVT system was networked to a Pentium PC for the transmission of the acquired images to the PC for analysis. To verify the alignment of the machine and target isocenters, orthogonal pairs of simulation images were used as verification images. Errors in the isocenter alignment were measured by comparing the verification images with DRR of CT images. Orthogonal films were taken of all the patients once a week. These verification films were compared with the DRR were used for the treatment setup. By performing this procedure every treatment, using humanoid phantom and patient cases, the errors of localization can be analyzed, with adjustments made from the translation. The reproducibility of the patients' setup was verified using portal and digital images. RESULTS: The PSVT system was developed to verify the alignment of the machine and the target isocenters, and the reproducibility of the patients' setup for 3DCRT and IMRT. The results show that the localization errors are 0.8+/-0.2 mm (AP) and 1.0+/-0.3 mm (Lateral) in the cases relating to the brain and 1.1+/-0.5 mm (AP) and 1.0+/-0.6 mm (Lateral) in the cases relating to the pelvis. The reproducibility of the patients' setup was verified by visualization, using real-time image acquisition, leading to the practical utilization of our software. CONCLUSION: A PSVT system was developed for the verification of the alignment between machine and the target isocenters, and the reproducibility of the patients' setup in 3DCRT and IMRT. With adjustment of the completed GUI-based algorithm, and a good quality DRR image, our software may be used for clinical applications.

Independent Verification Program for High-Dose-Rate Brachytherapy Treatment Plans / 대한방사선종양학회지

PURPOSE: The planning of High-Dose-Rate (HDR) brachytherapy treatments are becoming individualized and more dependent on the treatment planning system. Therefore, computer software has been developed to perform independent point dose calculations with the integration of an isodose distribution curve display into the patient anatomy images. MATERIALS AND METHODS: As primary input data, the program takes patients' planning data including the source dwell positions, dwell times and the doses at reference points, computed by an HDR treatment planning system (TPS). Dosimetric calculations were performed in a 10x12x10 cm3 grid space using the Interstitial Collaborative Working Group (ICWG) formalism and an anisotropy table for the HDR Iridium-192 source. The computed doses at the reference points were automatically compared with the relevant results of the TPS. The MR and simulation film images were then imported and the isodose distributions on the axial, sagittal and coronal planes intersecting the point selected by a user were superimposed on the imported images and then displayed. The accuracy of the software was tested in three benchmark plans performed by Gamma-Med 12i TPS (MDS Nordion, Germany). Nine patients' plans generated by Plato (Nucletron Corporation, The Netherlands) were verified by the developed software. RESULTS: The absolute doses computed by the developed software agreed with the commercial TPS results within an accuracy of 2.8% in the benchmark plans. The isodose distribution plots showed excellent agreements with the exception of the tip region of the source's longitudinal axis where a slight deviation was observed. In clinical plans, the secondary dose calculations had, on average, about a 3.4% deviation from the TPS plans. CONCLUSION: The accurate validation of complicate treatment plans is possible with the developed software and the quality of the HDR treatment plan can be improved with the isodose display integrated into the patient anatomy information.

CT Simulation Technique for Craniospinal Irradiation in Supine Position / 대한방사선종양학회지

PURPOSE: In order to perform craniospinal irradiation (CSI) in the supine position on patients who are unable to lie in the prone position, a new simulation technique using a CT simulator was developed and its availability was evaluated. MATERIALS AND METHODS: A CT simulator and a 3-D conformal treatment planning system were used to develop CSI in the supine position. The head and neck were immobilized with a thermoplastic mask in the supine position and the entire body was immobilized with a Vac-Loc. A volumetric image was then obtained using the CT simulator. In order to improve the reproducibility of the patients' setup, datum lines and points were marked on the head and the body. Virtual fluoroscopy was performed with the removal of visual obstacles such as the treatment table or the immobilization devices. After the virtual simulation, the treatment isocenters of each field were marked on the body and the immobilization devices at the conventional simulation room. Each treatment field was confirmed by comparing the fluoroscopy images with the digitally reconstructed radiography (DRR)/digitally composite radiography (DCR) images from the virtual simulation. The port verification films from the first treatment were also compared with the DRR/DCR images for a geometrical verification. RESULTS: CSI in the supine position was successfully performed in 9 patients. It required less than 20 minutes to construct the immobilization device and to obtain the whole body volumetric images. This made it possible to not only reduce the patients' inconvenience, but also to eliminate the position change variables during the long conventional simulation process. In addition, by obtaining the CT volumetric image, critical organs, such as the eyeballs and spinal cord, were better defined, and the accuracy of the port designs and shielding was improved. The differences between the DRRs and the portal films were less than 3 mm in the vertebral contour. CONCLUSION: CSI in the supine position is feasible in patients who cannot lie on prone position, such as pediatric patients under the age of 4 years, patients with a poor general condition, or patients with a tracheostomy.

Improved Breast Irradiation Techniques Using Multistatic Fields or Three Dimensional Universal Compensators / 대한방사선종양학회지

PURPOSE: In order to improve dose homogeneity and to reduce acute toxicity in tangential whole breast radiotherapy, we evaluated two treatment techniques using multiple static fields or universal compensators. MATERIALS AND METHODS: 1) Multistatic field technique : Using a three dimensional radiation treatment planning system, Adac Pinnacle 4.0, we accomplished a conventional wedged tangential plan. Examining the isodose distributions, a third field which blocked overdose regions was designed and an opposing field was created by using an automatic function of RTPS. Weighting of the beams was tuned until an ideal dose distribution was obtained. Another pair of beams were added when the dose homogeneity was not satisfactory. 2) Universal compensator technique : The breast shapes and sizes were obtained from the CT images of 20 patients who received whole breast radiation therapy at our institution. The data obtained were averaged and a pair of universal physical compensators were designed for the averaged data. DII (Dose Inhomogeneity Index : percentage volume of PTV outside 95-105% of the prescribed dose), Dmax (the maximum point dose in the PTV) and isodose distributions for each technique were compared. RESULTS: The multistatic field technique was found to be superior to the conventional technique, reducing the mean value of DII by 14.6% ( p value<0.000) and the Dmax by 4.7% ( p value<0.000). The universal compensator was not significantly superior to the conventional technique since it decreased Dmax by 0.3% ( p value=0.867) and reduced DII by 3.7% ( p value=0.260). However, it decreased the value of DII by maximum 18% when patients' breast shapes fitted in with the compensator geometry. CONCLUSION: The multistatic field technique is effective for improving dose homogeneity for whole breast radiation therapy and is applicable to all patients, whereas the use of universal compensators is effective only in patients whose breast shapes fit inwith the universal compensator geometry, and thus has limited applicability.

Development of Conformal Radiotherapy with Respiratory Gate Device / 대한방사선종양학회지

PURPOSE: 3D conformal radiotherapy, the optimum dose delivered to the tumor and provided the risk of normal tissue unless marginal miss, was restricted by organ motion. For tumors in the thorax and abdomen, the planning target volume (PTV) is decided including the margin for movement of tumor volumes during treatment due to patients breathing. We designed the respiratory gating radiotherapy device (RGRD) for using during CT simulation, dose planning and beam delivery at identical breathing period conditions. Using RGRD, reducing the treatment margin for organ (thorax or abdomen) motion due to breathing and improve dose distribution for 3D conformal radiotherapy. MATERIALS AND METHODS: The internal organ motion data for lung cancer patients were obtained by examining the diaphragm in the supine position to find the position dependency. We made a respiratory gating radiotherapy device (RGRD) that is composed of a strip band, drug sensor, micro switch, and a connected on-off switch in a LINAC control box. During same breathing period by RGRD, spiral CT scan, virtual simulation, and 3D dose planing for lung cancer patients were performed, without an extended PTV margin for free breathing, and then the dose was delivered at the same positions. We calculated effective volumes and normal tissue complication probabilities (NTCP) using dose volume histograms for normal lung, and analyzed changes in doses associated with selected NTCP levels and tumor control probabilities (TCP) at these new dose levels. The effects of 3D conformal radiotherapy by RGRD were evaluated with DVH (Dose Volume Histogram), TCP, NTCP and dose statistics. RESULTS: The average movement of a diaphragm was 1.5 cm in the supine position when patients breathed freely. Depending on the location of the tumor, the magnitude of the PTV margin needs to be extended from 1 cm to 3 cm, which can greatly increase normal tissue irradiation, and hence, results in increase of the normal tissue complications probability. Simple and precise RGRD is very easy to setup on patients and is sensitive to length variation (+2 mm), it also delivers on-off information to patients and the LINAC machine. We evaluated the treatment plans of patients who had received conformal partial organ lung irradiation for the treatment of thorax malignancies. Using RGRD, the PTV margin by free breathing can be reduced about 2 cm for moving organs by breathing. TCP values are almost the same values (4-5% increased) for lung cancer regardless of increasing the PTV margin to 2.0 cm but NTCP values are rapidly increased (60-70% increased) for upon extending PTV margins by 2.0 cm. CONCLUSION: Internal organ motion due to breathing can be reduced effectively using our simple RGRD. This method can be used in clinical treatments to reduce organ motion induced margin, thereby reducing normal tissue irradiation. Using treatment planning software, the dose to normal tissues was analyzed by comparing dose statistics with and without RGRD. Potential benefits of radiotherapy derived from reduction or elimination of planning target volume (PTV) margins associated with patient breathing through the evaluation of the lung cancer patients treated with 3D conformal radiotherapy.

Dose Planning of Forward Intensity Modulated Radiation Therapy for Nasopharyngeal Cancer using Compensating Filters / 대한방사선종양학회지

PURPOSE: To improve the local control of patients with nasopharyngeal cancer, we have implemented 3-D conformal radiotherapy and forward intensity modulated radiation therapy (IMRT) to used of compensating filters. Three dimension conformal radiotherapy with intensity modulation is a new modality for cancer treatments. We designed 3-D treatment planning with 3-D RTP (radiation treatment planning system) and evaluation dose distribution with tumor control probability (TCP) and normal tissue complication probability (NTCP). MATERIALS AND METHODS: We have developed a treatment plan consisting four intensity modulated photon fields that are delivered through the compensating filters and block transmission for critical organs. We get a full size CT imaging including head and neck as 3 mm slices, and delineating PTV (planning target volume) and surrounding critical organs, and reconstructed 3D imaging on the computer windows. In the planning stage, the planner specifies the number of beams and their directions including non-coplanar, and the prescribed doses for the target volume and the permissible dose of normal organs and the overlap regions. We designed compensating filter according to tissue deficit and PTV volume shape also dose weighting for each field to obtain adequate dose distribution, and shielding blocks weighting for transmission. Therapeutic gains were evaluated by numerical equation of tumor control probability and normal tissue complication probability. The TCP and NTCP by DVH (dose volume histogram) were compared with the 3-D conformal radiotherapy and forward intensity modulated conformal radiotherapy by compensator and blocks weighting. Optimization for the weight distribution was performed iteration with initial guess weight or the even weight distribution. The TCP and NTCP by DVH were compared with the 3-D conformal radiotherapy and intensitiy modulated conformal radiotherapy by compensator and blocks weighting. RESULTS: Using a four field IMRT plan, we have customized dose distribution to conform and deliver sufficient dose to the PTV. In addition, in the overlap regions between the PTV and the normal organs (spinal cord, salivary grand, pituitary, optic nerves), the dose is kept within the tolerance of the respective organs. We evaluated to obtain sufficient TCP value and acceptable NTCP using compensating filters. Quality assurance checks show acceptable agreement between the planned and the implemented MLC (multi-leaf collimator). CONCLUSION: IMRT provides a powerful and efficient solution for complex planning problems where the surrounding normal tissues place severe constraints on the prescription dose. The intensity modulated fields can be efficaciously and accurately delivered using compensating filters.

Fabrication of Backscatter Electron Cones for Radiation Therapy / 대한방사선종양학회지

PURPOSE: Irradiation cones by using backscatter electrons are made for the treatment of superficial small lesions of skin, oral cavity, and rectum where a significant dose gradient and maximum surface dose is desired. METHODS AND MATERIALS: Backscatter electrons are produced from the primary electron beams from the linear accelerators. The design consists of a cylindrical cone that has a thick circular plate of high atomic number medium (Pb or Cu) attached to the distal end, and the plate can be adjusted the reflected angle. Primary electrons strike the metal plate perpendicularly and produce backscatter electrons that reflect through the lateral hole for treatment. Using film and a parallel plate ion chamber, backscatter electron dose characteristics are measured. RESULTS: The depth dose characteristic of the backscatter electron is very similar to that of the hard x-ray beam that is commonly used for the intracavitary and superficial lesions. The basckscatter electron energy is nearly constant and effectively about 1.5 MeV from the clinical megavoltage beams. The backscatter electron dose rate of 35~85 cGy/min could be achieved from modern accelerators without any modification. and the depth in water of 50% depth dose from backscatter electron located at 6mm for 45degrees angled lead scatter. The beam flatness is dependent on the slit size and the depth of treatment, but is satisfactory to treat small lesions. CONCLUSIONS: The measured data for backscatter electron energy, depth dose flatness dose rate and absolute dose indicates that the backscatter electrons are suitable for clinical use.

Use of Respiratory Motion Reduction Device (RRD) in Treatment of Hepatoma / 대한방사선종양학회지

PURPOSE: Planning target volume (PTV) for tumors in abdomen or thorax includes enough margin for breathing-related movement of tumor volumes during treatment. Depending on the location of the tumor, the magnitude of PTV margin extends from 10 mm to 30 mm, which increases substantial volume of the irradiated normal tissue hence, resulting in increase of normal tissue complication probability (NTCP). We developed a simple and handy method which can reduce PTV margins in patients with liver tumors, respiratory motion reduction device (RRD). MATERIALS AND METHODS: For 10 liver cancer patients, the data of internal organ motion were obtained by examining the diaphragm motion under fluoroscope. It was tested for both supine and prone position. A RRD was made using MeV-Green and Styrofoam panels and then applied to the patients. By analyzing the diaphragm movement from patients with RRD, the magnitude of PTV margin was determined and dose volume histogram (DVH) was computed using AcQ-Plan, a treatment planning software. Dose to normal tissue between patients with RRD and without RRD was analyzed by comparing the fraction of the normal liver receiving to 50% of the isocenter dose. DVH and NTCP for normal liver and adjacent organs were also evaluated. RESULTS: When patients breathed freely, average movement of diaphragm was 12+/-1.9 mm in prone position in contrast to 16+/-1.9 mm in supine position. In prone position, difference in diaphragm movement with and without RRD was 3+/-0.9 mm and 12 mm, respectively, showing that PTV margins could be reduced to as much as 9 mm. With RRD, volume of the irradiated normal liver reduced up to 22.7% in DVH analysis. CONCLUSION: Internal organ motion due to breathing can be reduced using RRD, which is simple and easy to use in clinical setting. It can reduce the organ motion-related PTV margin, thereby decrease volume of the irradiated normal tissue.

Measurements of Setup Error and Physiological Movement of Liver by Using Electronic Portal Imaging Device in Patients with Hepatocellular Carcinoma / 대한방사선종양학회지

PURPOSE: The goal of this study was to improve the accuracy of three-dimensional conformal radio therapy (3-D CRT) by measuring the treatment setup error and physiological movement of liver based on the analysis of images which were obtained by electronic portal imaging device (EPID). MATERIALS AND METHODS: For 10 patients with hepatocellular carcinoma, 4-7 portal images were obtained by using EPID during the radiotherapy from each patient daily. We analyzed the setup error and physiological movement of liver based on the verification data. We also determined the safety margin of the tumor in 3-D CRT through the analysis of physiological movement. RESULTS: The setup errors were measured as 3 mm with standard deviation 1.70 mm in x direction and 3.7 mm with standard deviation 1.88 mm in y direction respectively. Hence, deviation were smaller than 5 mm from the center of each axis. The measured range of liver movement due to the physiological motion was 8.63 mm on the average. Considering the motion of liver and setup error, the safety margin of tumor was at least 15 mm. CONCLUSION: EPID is a very useful device for the determination of the optimal margin of the tumor, and thus enhance the accuracy and stability of the 3-D CRT in patients with hepatocellular carcinoma.

Understanding the Response Characteristics of X-ray Verification Film / 대한방사선종양학회지

PURPOSE: This study is intended to understand the sensitometric charac teristics and the emulsion properties of the commercially available CEA TVS film in comparison with the Kodak X-Omat V film. MATERIAL AND METHODS: For this purpose, we have formulated an analytic expression of the characteristic curves for x-ray film exposed to mixed radiation of electrons, photons, and visible light. This mathematical expression was developed based on reaction-rate and target-hit theories. Unlike previous expressions, it relates optical density to emulsion properties such as grain size and silver bromide content. We have also developed a quantity which characterizes the film response to visible light relative to that to photons and electrons. This quantity could be expressed as a function of grain area. Thus, we have developed mathematical expressions and quantities with which the emulsion properties of the films can be revealed based on the sensitometric characteristics. Demonstrating the use of this analytical study, we exposed CEA and Kodak verification films to the mixed radiation of electrons, photons, and visible light, and interpreted the experimental results accordingly. RESULTS: We have demonstrated that: (1) the saturation density increases as the silver bromide content increases, (2) the time required to reach the threshold dose (to which the film begins to respond) when films are exposed to visible light decreases as the grain size increases, and (3) the CEA film contains more silver bromide, whereas the Kodak film contains larger grains. These findings were supported by the data provided by the manufacturers afterward. CONCLUSION: This study presented an analytical and experimental basis for understanding the response of X-ray film with respect to the emulsion properties.

Objective Analysis of the Set-up Error and Tumor Movementin Lung Cancer Patients using Electronic Portal Imaging Device / 대한치료방사선과학회지

PURPOSE: The aim of this study is to investigate the random and systematic errors and tumor movement using electronic portal imaging device in lung cancer patients for the adequate margin in the treatment planning of 3-dimensional conformal therapy. METHODS AND MATERIALS: The electronic portal imaging device is matrix ion chamber type(Portal Vision, Varian). Ten patients of lung cancer treated with chest irradiation were selected for this study. Patients were treated in the supine position without immobilization device. All treatments were delivered by an 10 MV linear accelerator that had the portal imaging system mounted to its gantry. AP or PA field portal images were only analyzed. Radiation therapy field included the tumor, mediastinum, and supraclavicular lymph nodes. A total of 103 portal images wereanalyzed for set-up deviation and 10 multiple images were analyzed for tumor movement because of respiration and cardiac motion. RESULTS: The average values of setup displacements in the x, y direction was 1.41 mm, 1.78 mm, respectively. The standard deviation of systematic component was 4.63 mm, 4.11mm along the x,y axis, respectively while the random component was 4.17 mm in the x direction and 3.31 mm in the y direction. The average displacement from respiratory movement was 12.2 mm with a standard deviation of 4.03 mm CONCLUSION: The overall set-up displacement includes both random and systematic component and respiratory movement. About 10 mm, 25 mm margins along x,y axis which considered the set-up displacement and tumor movement were required for initial 3-dimensional conformal treatment planning in the lung cancer patients and portal images should be madeand analyzed during first week of treatment, individually.

Skin Dose Distrubution with Spoiler of 6 MV X-ray for head and Neck Tumor / 대한치료방사선과학회지

PURPOSE: This study was performed for adequate irradating tumor area when 6 MV linear accerelator photon was used to treat the head and neck tumor. The skin surface dose and maximum build-up ragion was measured by using a spoiler which was located between skin surface and collimator. METHODS: A spoiler was made of tissue equivalent materials and the skin surface dose and maximum build-up region was measured varing with field size, thickness of spoiler and interval between skin and collimator. The results of skin surface dose and maximum build-up dose was represented as a build-up ratio and it was compared with dose distribution by using a bolus. RESULTS: The skin surface dose was increased with appling spoiler and decreased by distance of the skin-spoiler separation. The maxium build-up region was 1.5 cm below the skin surface and it was markedly decreased near the skin surface. By using a 1.0-cm thickness spoiler, Dmax moved to 5, 10.2, 12.3, 13.9 and 14.8 mm from the skin surface by separation of the spoiler from the skin 0, 5, 10, 15, 20 cm, respectively. CONCLUSION: The skin surface dose was increased and maximum build-up region was moved to the surface by using a spoiler. Therefore spoiler was useful in treating by high energy photon in the head and neck tumor.

The Role of Intraluminal Brachytherapy in Management of Esophageal Cancer / 대한치료방사선과학회지

PURPOSE: To evaluate our clinical experience with the combination of teletherapy and intraluminal brachytherapy in patients with unresectable or inoperable esophageal cancers. MATERIALS AND METHODS: From Nov. 1989 to Mar. 1993, twenty patients with esophageal cancer were treated with radical radiotherapy and intraluminal brachytherapy at Yonsei Cancer Center. All patients had squamous histology and stage distribution was as follows: stage II, 4(20%) patients; III, 15(75%) patients; IV, 1(5%) patients. A dose of 5-12 Gy/1-3 weeks with intraluminal brachytherapy (3-5 Gy/fraction) to 5mm from the outside of the esophageal tube using high dose rate iridium-192 reotely afterloading bracytherapy machine was given 2 weeks after a total dose of 59-64Gy with external radiotherapy. Induction chemotherapy using cisplatin and 5-FU was performed in 13 patients with median 3 cycles(1-6 cycles). Response rate, local control rate, survival and complications were analysed retrospectively. RESULTS: Two-year overall survival rate and median survival were 15.8% and 13.5 months. Resonse rates were as follows: complete remission(CR) 5(25%); partial remission a(Pra) 7(35%); partial remission b(PRb) 7(35%); no response(NR) 1(5%). Patterns of failure were as follows : local failure 13(65%), local and distant failure 3(15%), distant failure 0(0%). Ultimate local control rate was 20%. Treatment related complications included esophageal ulcer in two patients and esophageal stricture in one. CONCLUSION: Though poor local control rate, median survival was improved as compared with previous results of radiation therapy alone(8months) and chemo-radiation combined treatment(11months) in Yonsei Cancer Center. High-dose-rate intraluminal brachytherapy following external irradiation is an effective treatment modality with acceptable toxicity in esophageal cancer.

Optimization of Dose Distribution for High Dose Rate Intraluminal Therapy / 대한치료방사선과학회지

The use of high dose rate remote afterloading system for the treatment of intraluminal lesions necessitates the need for a more accurate of dose distributions around the high intensity brachytherapy sources, doses are often prescribed to a distance of few centimeters from the linear source, and in this range the dose distribution is very difficult to assess. Accurated and optimized dose calculation with stable numerical algorithms by PC level computer was required to treatment intraluminal lesions by high dose rate brachytherapy system. The exposure rate from sources was calculated with Sievert integral and dose rate in tissue was calculated with Meisberger equation. An algorithm for generating a treatment plan with optimized dose distribution was developed for high dose rate intraluminal radiotherapy. The treatment volume becomes the locus of the constrained target surface points that is the specified radial distance from the source dwelling positions. The treatment target volume may be alternately outlined on a x-ray film of the implant dummy sources. The routine used a linear programming formulism to compute which dwell time at each position to irradiate the constrained dose rate at the target surface points whiles minimizing the total volume integrated dose to the patient. The exposure rate and the dose distribution to be confirmed the result of calculation with algorithm were measured with film dosimetry, TLD and small size ion chambers.

Verification of Dose Distribution for Stereotactic Radiosurgery with a Linear Accelerator / 대한치료방사선과학회지

The calculation of dose distribution in multiple arc stereotactic radiotherapy is a three-dimensional problem and, therefore, the three-dimensional dose calculation algorithm is important and the algorithm's accuracy and reliability should be confirmed experimentally. The aim of this study is to verify the dose distribution of stereotactic radiosurgery experimentally and to investigate the effect of the beam quality, the number of arcs of radiation, and the tertiary collimation on the resulting dose distribution. Film dosimetry with phantom measurements was done to get the three-dimensional orthogonal isodose distribution. All experiments were carried out with a 6 MV X-ray, except for the study of the effects of beam energy on dose distribution, which was done for X-ray energies of 6 and 15 MV. The irradiation technique was from 4 to 11 arcs at intervals of from 15 to 45 degrees between each arc with various field sizes with additional circular collimator. The dose distributions of square field with linear accelerator collimator compared with the dose distributions obtained using circular field with tertiary collimator. The parameters used for comparing the results were the shape of the isodose curve, dose fall-offs from 90% to 50 % and from 90% to 20% isodose line for the steepest and shallowest profile, and A= (90% idsose area) /( 50% isodose area - 90% isodose area (modified from Chierego)). This ratio may be considered as being proportional to the sparing of normal tissue around the target volume. The effect of beam energy in 6 and 15 MV X-ray indicated that the shapes of isodose cuties were the same. The value of ratio A and the steepest and shallowest dose fall-offs for 6 MV X-ray was minimally better than that for 15 MV X-ray. These data illustrated that an increase in the dimensions of the field from 10 to 28 mm in diameter did not significantly change the isodose distribution. There was no significant difference in dose gradient and the shape of isodose cutie regardless of the number of arcs for field sizes of 10, 21, and 32 mm in diameter The shape of isodose cuties was more circular in circular field and square in square field. And the dose gradient for the circular field was slightly better than that for the square field.

The Enhancement of Skin Sparing by Tray Materials for High Energy Photon Beam / 대한치료방사선과학회지

The skin sparing effect associated with high energy x-ray or gamma ray beams may be reduce or lost under certain conditions of treatment. Current trends in using large fields. Shield carrying trays, compensating filters, and isocentric methods of treatment have posed problems of increased skin dose which sometimes become a limiting factor in giving adquate tumor doses. We used the shallow ion chamber to measure the phantom surface dose and the physical treatment variables for Co-60 gamma ray, 4MV and 10 MV x-ray beam. The dependence of percent surface dose on field sizes, atomic number of the shielding tray materials and its distance from the surface for 4, 10MV x-rays and Co-60 gamma ray is qualitatively similar. The use of 2 mm thick tin filter is recommended for situations where a low atomic number tray is introduced into the beam at distances less than 15 cm from the surface and with the large field sized for 4 MV x-ray beam. In case of Co-50 gamma ray, the lead glass tray is suitable for enhancement of skin sparing. Also, the filter distance should be as large as possible to achieve substantial skin sparing.

The dosimetric Properties of Electron Beam Using Lyon Intraoperative Device for Intraoperative Radiation Therapy / 대한치료방사선과학회지

We have studied the dosimetric properties of electron beam using Lyon intraoperative device for intraoperative radiation therapy. The dosimetry data had compiled in such a way that a quick and correct decision regarding the cone shape, energy, and accurate calculations could be made. Using 3 dimensional water phantom, we have got the following data: cone output ratios, surface dose, dmax, dgo, flatness, symmetry, beam profiles, isodose curve, and SSD correction factors. The cone output ratios were measured with straight and bevelled cone, respectively. As the cone size and the energy were reduced, the cone output ratios decreased rapidly. With the flattening filter, the surface dose increased by electron beam to 85.3%, 89.2%, and 93.4%, for 6MeV, 9MeV, and 12MeV, respectively. It is important to increase the surface dose to 90% or more. Inspite of diminishing dose rate and beam penetration, this flattening filter increases the treatment volume significantly. With the combination of the three levels collimation and the flattening filter, we achieved good homogeneity of the beam and better flatness and the diameter of the 90% isodose curve was increased. It is important to increase the area that is included in the 90% isodose level. The value of measured and calculated SSD correction factors did not agree over the clinically important range from 100cm to 110cm .

Dosimetry for Total Skin Electron Beam Therapy in Skin Cancer / 대한치료방사선과학회지

Increasing frequency of skin cancer, mycosis fungoides, Kaposi's sarcoma etc, it need to treatment dose planning for total skin electron beam (TSEB) therapy. Appropriate treatment planning for TSEB therapy is needed to give homogeneous dose distribution throughout the entire skin surface. The energy of 6 MeV electron from the 18 MeV medical linear accelerator was adapted for superficial total skin electron beam therapy. The energy of the electron beam was reduced to 4.2 MeV by a 0.5cm x90cm x180cm acryl screen placed in a feet front of the patient. Six dual field beam was adapted for total skin irradiation to encompass the entire body surface from head to toe simultaneously. The patients were treated behind the acryl screen plate acted as a beam scatterer and contained a parallel-plate shallow ion chamber for dosimetry and beam monitoring. During treatment, the patient was placed in six different positions due to be homogeneous dose distribution for whole skin around the body. One treatment session delivered 400 cGy to the entire skin surface and patients were treated twice a week for eight consecutive weeks, which is equivalent to TDF value 57. Instrumentation and techniques developed in determining the depth dose, dose distribution and bremsstrahlung dose are discussed.