bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐06: Megavoltage CT Imaging Enables CT‐Based Low‐Doserate Brachytherapy Planning Without CT‐Compatible Applicators
Authors: Wagner T , Buchholz D , Langen K , Meeks S , Willoughby T , Kupelian P
Published: June 2005

Purpose: To determine feasibility of megavoltage computed tomography (MVCT) imaging for low dose rate (LDR) brachytherapy for cervical carcinoma. Method and Materials: A helical tomotherapy treatment unit (Tomotherapy HiArt, Tomotherapy Inc., Madison, WI) using a nominal 3.5 MV x‐ray beam was used to image a dosimetry phantom containing standard, non‐CT compatible Fletcher‐Suit applicators and dummy Cs‐137 tube sources (3M Model 6500). The phantom contained several small steel BB markers which were used as dose points. The MVCT images were transferred to a commercially available treatment planning system (CMS XiO 4.2, Computerized Medical Systems, St. Louis, MO). Digitally reconstructed radiographs (DRRs) were generated from the MVCT data set, and doses (dose rates) were calculated at the phantom dose points using standard 2D, film‐based dosimetry methods. Doses were also calculated using a CT‐based, 3D dosimetry technique in which the brachytherapy source tips and ends were localized directly on MVCT images. Separate experiments were performed to verify the spatial accuracy of the MVCT image reconstruction in‐phantom. Results: In‐phantom localization accuracy was 0.6 ± 0.3 mm, slightly less than the size of an axial MVCT image pixel and less than half of the MVCT slice thickness. Point doses in‐phantom calculated by 2D and by 3D methods agreed within an average of 1.5%. The techniques developed for successful MVCT imaging in‐phantom can be used to calculate 3D dose distributions in a human patient undergoing a traditional (non‐CT compatible) Fletcher‐Suit implant. Conclusion: MVCT imaging allows CT‐based dosimetry planning without the use of special, “CT‐compatible” applicators.
SU‐FF‐T‐08: Tomotherapy Megavoltage Imaging for Gynecological Brachytherapy Treatment Planning and IMRT Integration
Authors: Wilson D , Hughes S , Yashar C
Published: June 2005

Purpose: To demonstrate the use of the Tomotherapy IMRT system to image the standard shielded Fletcher‐Suit applicator for CT based brachytherapy dose calculations and to integrate those dose distributions into Tomotherapy treatment plans. Method and Materials: A standard Fletcher‐Suit gynecological applicator was placed in phantom and a megavoltage CT scan was done using the Tomotherapy unit. The images were exported in DICOM format to a Pinnacle treatment planning system. Cesium tubes representing a typical tandem and ovoid loading of the applicator were entered into the planning system, and the dose distribution was calculated. The binary dose matrix was then converted to a CT‐like file by separating the dose values into individual planes, turning the floating point numbers into 12‐bit integers, and adding a header file. Those image files was exported to a Focal Sim viewing station, where the isodose distribution was merged with a phantom CT and contours representing different isosurfaces were drawn. Those contours were exported to the Tomotherapy planning station, were a trial nodal boost volume was drawn in. An IMRT plan was done for this volume, and the resultant Tomotherapy binary dose file was converted to a Pinnacle format in order to be integrated with the brachytherapy plan. Results: The megavoltage CT image accurately showed the source holders, tungsten shielding, and flange of the applicator. Exported doses distributions could be integrated with Tomotherapy IMRT. Conclusion: The Tomotherapy IMRT system will be useful to accurately image Fletcher‐Suit type applicators in actual patients in order to superimpose the dose distributions over the actual patient anatomy. IMRT delivered with Tomotherapy can easily be integrated with brachytherapy with the spread of DICOM dose export. Calculations which take the applicator shielding can be developed because the shielding position is clearly visible.
SU‐FF‐T‐18: A Simple Theoretical Verification of HDR Calculation Dose Using Point and Line Source Approximation
Authors: Shin E , Han Y , Ju S , Huh S
Published: June 2005

Purpose: In order to reduce potential error that can occur in the planning and delivery of brachytherapy treatment, software which is able to be used for three commercial HDR sources was developed. The feasibility of the program was investigated. Method and Materials: This windows based program was developed by Visual‐Basic language. The TG‐43 algorithm was used for the dose computation at interested points. For source geometry, both point source and line source approximations were employed to be capable for most commercial HDR sources. Anisotropy tables for Nucletron microselectron, Gammamed 12i, and Veri Source were included. User is required to select the HDR source type in the beginning of the program, and to enter the number of catheters and dwelling position of a source. The position and the dose at the interested points, such as A and B points, are required to enter. The developed program used the treatment source position and interest point position in the reference frame of the catheters. The computed dose is compared to that in the RTP by calculating the percent dose difference. The accuracy of the code was validated by comparing with commercial RTP computation and hand calculation results for various prototype of treatment ranging from a single catheter to complex multi‐catheter plans as well as clinical plans. Result: The acceptance levels of performed tests were 5.0% for the percent dose difference at each interested point. For few real patient treatment plans using Nucletron sources, results of the developed program agreed with RTP (Plato, Nucletron) results within 3% error. For Veri Source, large difference between the developed program and RTP was observed if anisotropy was not used in the RTP. Discussion: The developed program was adequate for independent dose verification as a part of brachytherapy quality assurance procedure.
SU‐FF‐T‐20: Accuracy of Non‐Coplanar Reconstruction of Shielded Colpostats in Intracavitary Brachytherapy
Authors: Elangovan D , Subramanian S , Vasanthan S , Kushwah R , Shende S , Bansal V
Published: June 2005

Purpose: Presence of shields obscures the radiographic visualization of dummy sources by coplanar imaging. In this study a reconstruction method, using non‐coplanar images, is tested for clinical use. Method and Materials: An isocentric dedicated imaging system with L&C‐arm rotation and networked to a treatment planning system (TPS) is used for filmless planning. Testing done by (1) using a ‘test phantom’ having radiopaque markers separated by known distance (2) using single straight applicator for standardization (3) by orienting the Fletcher‐Suit applicator with non‐shielded and shielded colpostats to simulate clinical situation. Source position reconstruction was done using orthogonal algorithm for coplanar images and ‘IBU reconstruction’ algorithm for coplanar & non‐coplanar images. Treatment length settings & active dwell positions were pre‐fixed . Spatial orientation of dummy source positions, dose‐volume histogram, dwell times, total treatment time were all generated. TPS calculated and delivered dose accuracy for both algorithms was checked for the straight applicator by using a 0.13cc ion chamber in a water phantom at various distances. Results: Distance variation using ‘test phantom’ for IBU method was found to be <1mm in the central region & <1.5mm in the corners of the fluoroscopic image and is comparable to the conventional orthogonal method. IBU method was also found to agree with the orthogonal method applicator with respect to source position co‐ordinates (<0.5mm), dwell time (<0.3%), total treatment time (<0.3%) and dose‐volume histogram analysis. The ratio of measured dose by both algorithms at various distances was close to unity. Reconstructed geometry of shielded colpostats by IBU non‐coplanar method was found to visibly match with the “three dimensional” projection. Conclusion: Non‐coplanar IBU algorithm provides an unambiguous reconstruction method when using shielded colpostats and allows for rapid filmless planning procedure.
SU‐FF‐T‐23: Comparison of Chest Radiographs, Fluoroscopy and Seed‐Migration Detector for the Detection of Embolized Seeds to the Lung
Authors: Morrier J , Chrétien M , Beaulieu L
Published: June 2005

Purpose: To evaluate the efficacy of a seed‐migration detector and to compare its performance to fluoroscopy and to the postoperative chest radiographs generally recommended. Method and Materials: A low energy gamma scintillation survey meter, used together with a count rate meter, was converted to a seed‐migration detector. The detector was used to perform a chest evaluation on 155 patients (8717 seeds) at their first postoperative visit. When the detector showed activity around a patient s chest, it was confirmed by taking an antero‐posterior chest radiograph and by looking at the region with fluoroscopy. Results: 33 patients (21.3%) present at least one embolized seed. That is a 0.47% seed migration rate (41/8717). 37 (90%) of the seeds were visible under fluoroscopy and 28 (68%) appeared on x‐rays. Rapid movement of the seeds, due to breathing or to a location close to the heart or the diaphragm, makes nine seeds to be visible with fluoroscopy but not on the radiograph. Moreover, four seeds were not visible with fluoroscopy neither with radiograph. In comparison to the seed‐migration detector, detection based on fluoroscopy would have led to four false‐negative detections (out of 33 or 12.1%) while the radiograph would have resulted in thirteen (out of 33) false‐negative detections or 39.4%. Finally, standard chest x‐ray would have required a survey, and extra radiation dose to lung, to 100% of the patients rather than the 21.3% who needed it in this study. Conclusion: Because of the high false‐negative rate and the superior efficacy of a scintillator‐based seed‐migration detector, the usual recommendation to perform chest radiographs should be revised. X‐rays should remain for documentation purposes of positive cases only. Our clinical experience also allowed us to conclude that the detector is convenient, cost‐effective and non‐invasive, meaning that it does not require any additional radiation to the patient.
SU‐FF‐T‐30: Dosimetric Comparison of Two Techniques for Prostate Brachytherapy Implants
Authors: Mghari R , Ibrahim‐Ashford K , Bennouna J , Graham NC
Published: June 2005

Purpose: CT based dosimetry was performed one day after prostate cancer treatment by permanent seed implantation. Two techniques were used for implants. To investigate the impact of the two techniques in dose distribution we analyzed several dosimetric ct scans. Method and Materials: Patients with prostate cancer were treated with brachytherapy as monotherapy without neoadjunctive androgen deprivation between 01/00 and 12/04. Patient selection in both groups were staging of T1C, pretreatment PSA <8 and Gleason's score of < 6; the mean age in both groups was 65 years. Ultrasound volume study was performed two weeks prior to implant procedure. The dosimetry results from 40 patients divided into two groups were analyzed after full dose I‐125 implantation. Group one (20 patients) implanted using the Mick Applicator and group two (20 patients) were implanted using the Strand. CT transverse images of the implant volume were collected. Dose volume histogram parameters were analyzed for prostate volume changes, including D 90, V100, and V150. Results: The reference dosimetry was performed post‐implantation, one day after using computed tomography (CT). Variseed software was used for dosimetric evaluation of each implant to compare the D 90, V100, and V150 dose obtained by the two sets of study. The average prostate volume was 35cm cubed (range 25–59). In group one (using the Mick) the median D 90 was 98.4% (range) and was achieved in 9 out of 20 patients. A comprehensive evaluation is shown in table 1. In group two (using the strand) the median D 90 coverage was 108.5% (range) and was achieved in 14out of 20 patients. An elaborate evaluation is shown in Table 2. Conclusion: The above results clearly demonstrate that when we started using the strand we achieved a superior dosimetric outcome that is greater than the minimal therapeutic D 90 value of 140Gy.
SU‐FF‐T‐31: Image Registration of Projected X‐Ray Film and CT Image in Brachytherapy Planning
Authors: Chang J , Suh T , Ji Y , Kim S
Published: June 2005

Purpose: In brachytherapy, film‐based planning commonly used for distinguishing the sources accurately whereas transverse imaging modality like CT used for obtaining the organ structure and dose‐volume histogram (DVH) directly. In this study, to obtain both advantages of projected x‐ray film and CT image, we performed a registration of the coordinates of the film and CT. Method and Materials: The 3D reconstruction algorithm for x‐ray film was based on the semi‐orthogonal method and the registration software developed in IDL 5.5. To verify the registration algorithm, we applied to the humanoid acrylic phantom. The external fiducial marker and the targets, the visible in both films and CT image, attached to the phantom then images acquired. The registration tool provides the coordinates transformation of the pair of orthogonal films and CT image sets. Results: The differences in the coordinates of the targets using registration software showed the within 1.5 mm from all directions in the CT scans. (3 mm slice thickness) As film coordinates of the x and y‐axis derived from the z‐axis of the CT relative to a slice thickness, the uncertainties of x and y was greater than z‐axis. Conclusion: This method provides the exact positions of the sources and organ positions from registration software. Therefore, it can be a useful and reliable method for treatment planning in brachytherapy planning.
SU‐FF‐T‐32: Imaged‐Based Simulation Technique To Determine Stepping Source Dwell Position For MammoSite(r) Brachytherapy Procedures
Authors: Saw C , Komanduri K , Selvaraj R , Chen H , Li F , Heron D
Published: June 2005

Purpose: Incorrect dwell position for the stepping source in MammoSite® radiation therapy system would result in severe dose error to the treated volume. In many centers, CT‐simulators have replaced the fluoroscopic simulators. An alternative method must be developed for this purpose. This project evaluates the feasibility of CT‐based simulation to determine the dwell position for the stepping source of the Nucletron® High‐Dose Rate (HDR) unit. Method and Materials: A MammoSite® balloon applicator is placed in the surgical cavity intraoperatively at the time of segmented mastectomy for breast cancer. The balloon is inflated to near spherical shape with saline solution mixed with a small amount of radiographic contrast to aid in visualization. After recovery, the patient is brought to the radiation oncology facility to determine the quality of the implant and also to determine the stepping source dwell position. A dummy source train is initially inserted in the applicator and pushed to the distal end. The distance is measured using the Nucletron® measuring tool. CT scans of the breast was taken with 1 mm slice thickness. After the images have been acquired, a virtual 3‐dimensional breast is generated. Based on the virtual breast, the path of the dummy source train inside the applicator is assessed. Results: A digitally reconstructed radiography (DRR) that maximizes the projection of the pathway is created. A method is formulated to determine the center of the sphere and marks on the source pathway. The dwell position is determined by subtracting the difference of distance between the distal seed and center of the sphere from the maximum source distance as set on the HDR unit. Conclusion: For institutions where the fluoroscopic simulator has been replaced by a CT‐simulator, imaged‐based simulation allows an effective method of determining the stepping source dwell position for MammoSite® brachytherapy procedures.
SU‐FF‐T‐38: Measurement of the Radial Dose and the Dose Anisotropy Functions for the New 192Ir Varian Source
Authors: Gamboa‐deBuen I , Díaz P , Poitevin A
Published: June 2005

Purpose: To measure the radial dose function and the dose anisotropy functions, used in the AAPM Task Group 43 dose calculation formalism, of the new Varian Source model VS‐2000 utilized in high dose rate brachytherapy. Method and Materials: The measurements were carried out with TLD dosimeters and radiochromic dye films in a 30 × 30 × 30 cm3 acrylic phantom with the source positioned at the center. The new VariSource has an active length of 0.5 cm, and an active diameter of 0.34 mm. Measurements were made for distances between 2 and 7 cm from the source center using TLD‐100 (LiF:Mg,Ti) chips (3.1 × 3.1 × 0.89 mm3) whereas for distances smaller than 2 cm Gafchromic HD‐810 film were used. TLD irradiations for each distance from the source center were made separately at approximately 2 Gy. TLD's were read using a Harshaw 3500 reader. Because of the high gradient dose near the source, HD‐810 films were exposed at three different doses and then digitized in RBG color scale obtaining three images based on the RGB channels. HD‐810 films were calibrated in a beam. Results: Dosimetric characteristics of the new Varian source have been measured in an acrylic phantom using LiF TLD chips and HD‐810 radiochromic film. These measurements were performed following the AAPM TG‐43 task group recommendation. The radial dose and the dose anisotropy functions were measured in the range of 0.25 cm to 1.5 cm using HD‐810 radiochromic film and for distances between 2.0 cm and 7 cm using LiF TLD‐100 chips. The anisotropy function was measured from 5° to 180° relative to the source axis. Conclusion: Dosimetry data were presented for the new Varian HDR source following the AAPM TG‐43 dosimetric formalism, for input and verification purposes in treatment planning systems.
SU‐FF‐T‐41: Monte Carlo Dosimetric Study of the New BEBIG Co‐60 HDR Source
Authors: Perez‐Calatayud J , Granero D , Ballester F , Casal E , Agramunt S , Cases R
Published: June 2005

Purpose: The use of high dose rate brachytherapy (HDR) is a highly extended practice today, being the Ir‐192 the most widely extended isotope used for this type of practice although Co‐60 is also available for HDR. The purpose of this study is to obtain the dosimetric parameters of the Co‐60 source used by the BEBIG MultiSource remote afterloader (BEBIG GmbH, Germany) for which there is no dosimetric data available in the literature. It is recommended that accurate dose distribution data, based on a realistic geometry and on the mechanical characteristics of the source, should be obtained by an appropriate method, experimental or Monte Carlo, to be used as input in the HDR Treatment Planning System. Method and Materials: The Monte Carlo code GEANT4 has been used to obtain the TG43 parameters and the 2‐D rectangular dose rate table of the BEBIG Co‐60 HDR source. Results: The dose rate constant, radial dose function and anisotropy function have been calculated and are presented in tabular form as well as a detailed 2‐D rectangular dose rate table to check the treatment planning systems calculations. Conclusion: A Monte Carlo dosimetric study of the BEBIG HDR source for which no published dosimetric data exists has been done. These dosimetric datasets can be used as input and/or to validate the TPS calculations.
SU‐FF‐T‐43: Objective Comparison of RAPID Strand and Free SelectSeeds Loading for Permanent Prostate Implants Using An Inverse Planning Approach
Authors: Kwa S , Lessard E , Moerland M , Pouliot J
Published: June 2005

Purpose: To quantify differences in treatment plans of permanent implants between RAPID strand™ and free selectSeed™ loading patterns. Method and Materials: The 3‐D US scan and treatment plan from ten patients who have been treated for prostate cancer with the permanent seed implant technique were arbitrary selected. The plans were generated manually by an experienced dosimetrist backed up by a team. Essentially the RAPID strand™ seed‐loading pattern was used. Retrospectively the patients were re‐planned with a commercial 3‐D planning system (SPOT‐PRO™ 3.0) using the new inverse planning algorithm (IPSA). A plan with a RAPID strand loading pattern (IPSA‐R) was generated and a plan with a free seed‐loading pattern (IPSA‐F). Results: The calculation time of IPSA was < 15 s for 400,000 iterations (2.5 GHz PC), which is fast enough to be used intra‐operatively. The target coverage V100 was equal (98–99%) for all plans. The target and urethra DVHs of the manual and the IPSA‐R plan were similar. By contrast the urethra doses D40, D30, D20, D10, and Dmax of the free seed plan IPSA‐F were 27–41 Gy lower than in the RAPID strand plan IPSA‐R. Conclusion: When using free seeds instead of RAPID strands, the urethra dose is significantly reduced. Conflict of Interest: Part of this research was supported by Nucletron B.V., Veenendaal, The Netherlands.
SU‐FF‐T‐48: Prognostic Significance of Perineural Invasion On Biochemical Progression‐Free Survival Following Prostate Brachytherapy
Authors: Adamovich E , Merrick G , Butler W , Galbreath R , Allen Z
Published: June 2005

Purpose: To evaluate the influence of perineural invasion (PNI) in the biopsy specimen on biochemical progression‐free survival in hormone naïve prostate brachytherapy patients. Method and Materials: From 1995 through 2001, 512 consecutive hormone naïve patients (173 low‐risk, 212 intermediate risk, and 127 high‐risk) underwent permanent brachytherapy for clinical stage T1b‐T2c NxM0 prostate cancer. All patients underwent brachytherapy at least 3 years prior to analysis. The median follow‐up was 5.3 years. Biochemical progression‐free survival was defined by a PSA cutpoint ⩽ 0.4 ng/mL after nadir and by the ASTRO consensus definition. PNI was defined as carcinoma tracking along or around a nerve within the perineural space. Clinical, treatment and dosimetric parameters evaluated for biochemical progression‐free survival included PNI, age, PSA, Gleason score, percent positive biopsies, prostate volume, brachytherapy planning volume, V100/150/200, D90, supplemental external beam radiation therapy, tobacco consumption, BMI, hypertension and diabetes. Results: PNI was documented in 133 patients (26.0%). Regardless of which biochemical progression‐free definition was used, 94.0% and 94.9% of patients with and without PNI remained free of biochemical progression. The median time to failure in patients with and without PNI was 17.2 months and 17.9 months respectively. For the entire biochemically disease‐free cohort, the median post‐treatment PSA was < 0.1 ng/mL. In univariate Cox regression analysis, pretreatment PSA, percent positive biopsies, prostate volume and Gleason score predicted for biochemical outcome. PNI did not approach statistical significance (p = 0.671). In multivariate analysis, only pretreatment PSA (p < 0.001) and percent positive biopsies (p < 0.001) maintained statistical significance. Conclusion: In hormone naïve brachytherapy patients implanted with generous periprostatic treatment margins, the presence of PNI in the biopsy specimen did not adversely impact 8‐year biochemical progression‐free survival. PNI is not an independent indicator for ADT in prostate brachytherapy patients.
SU‐FF‐T‐50: Reduction of Computed Tomography Metal Artifacts Due to I‐125 Seeds for Post Implant Analysis in Prostate Permanent Brachytherapy
Authors: Takahashi Y , Mori S , Kozuka T , Gomi K , Osawa A , Yamashita T
Published: June 2005

Purpose: Postimplant analysis in I‐125 permanent brachytherapy for prostate cancer plays important role in improving the techniques of implant. Although American Brachytherapy Society recommends CT based postimplant analysis, the identification of prostate bundle is quite difficult. In addition, metal artifacts from the I‐125 seeds implanted make it more difficult to identify the prostate. Thus accuracy of the dosimetric parameters associated with volume of prostate such as D90 and V100 may be unclear. The purpose of this study is to mitigate CT metal artifacts due to I‐125 seeds to provide more accurate postimplant analysis. Method and Materials: The prostate phantom that was implanted 3 to 10 seeds per a plane was scanned using 16‐detector raw CT. The sinogram was modified by our algorithm that is similar to projection‐interpolation method to CT images containing artifacts from I‐125 seeds. The regions of projection data existing I‐125 seeds were identified by observing differences of X‐ray intensity between the phantom and the seeds. Then the regions were interpolated to remove the metal artifacts. The new images were reconstructed with the corrected sinogram. We compared these with the CT images that are corrected by commercially available metal artifact reduction method. Results: The metal artifacts caused by a small number of I‐125 seeds were completely eliminated by our correcting method. On the other hand, the magnitude of the artifact with the commercially available method was insufficient. With regard to many seeds in the same plane, the metal artifact was mitigated by our method although the contrast of images was degraded. Conclusion: Our method would mitigate metal artifacts caused by I‐125 seeds and be helpful to identify prostate. Although some problems have still remained to improve, our approaches would be adapted to clinical field.
SU‐FF‐T‐53: The Impact of Primary Gleason Grade On Biochemical Outcome Following Brachytherapy for Hormone Naïve Gleason Score 7 Prostate Cancer
Authors: Merrick G , Butler W , Galbreath R , Allen Z , Adamovich E
Published: June 2005

Purpose: Biochemical outcome in Gleason score 7 patients with dominant pattern 4 histology is thought to be inferior to those Gleason score 7 patients with primary Gleason grade 3, based on conclusions from radical prostatectomy studies. In this study, we evaluate the effect of the dominant histologic pattern in Gleason score 7 prostate cancer on biochemical progression‐free survival following prostate brachytherapy. Method and Materials: 273 consecutive Gleason score patients underwent permanent interstitial brachytherapy for prostate cancer without androgen deprivation therapy. All patients underwent brachytherapy more than 3 years prior to analysis. Biochemical progression‐free survival was defined by a PSA cutpoint ⩽ 0.4 ng/mL after nadir or by the ASTRO consensus definition. The median follow‐up was 4.7 years. Clinical, treatment and dosimetric parameters evaluated for biochemical progression‐free survival included primary Gleason grade, clinical T‐stage, pretreatment PSA, risk group, percent positive biopsies, perineural invasion, patient age, isotope, supplemental XRT, prostate volume, brachytherapy planning volume, the percent of the target volume receiving 100%, 150%, and 200% of the prescribed dose (V100/150/200), the minimum percent of the prescribed dose covering 90% of the target volume (D90), tobacco consumption, hypertension and diabetes. Results: The actuarial 8‐year biochemical progression‐free survival rate was 94.5% and 94.8% using either a PSA cutpoint ⩽ 0.4 ng/mL after nadir or the ASTRO consensus definition, respectively. For biochemically disease‐free patients, the median posttreatment PSA was < 0.1 ng/mL. When stratified by the dominant histologic pattern, no statistical difference in outcome was noted for any of the evaluated parameters. In forward conditional Cox regression analysis, pretreatment PSA and percent positive biopsies were statistically significant predictors of biochemical outcome. Conclusion: In hormone naïve Gleason score 7 patients, prostate brachytherapy results in a high probability of 8‐year biochemical progression‐free survival and is independent of Gleason 3+4 versus 4+3 histology.
SU‐FF‐T‐56: Verifying Correct Location of HDR Source Dwell Position in the MammoSite Catheter Using An Integral Linear MOSFET Dosimeter Array
Authors: Vassy D , Hallil A , Stubbs J , Webster M , Turmel J , Salazar B
Published: June 2005

Purpose: Correct centering of the HDR source with the spherical MammoSite balloon is critical for proper brachytherapy delivery. We tested a MammoSite modified to incorporate a linear MOSFET dosimeter array to assess whether real‐time dosimetry measurements could confirm HDR source centering in MammoSite catheters. Method and Materials: A “MammoSite with MOSFETs” was simulated using a linear MOSFET array (Thomson Nielsen) consisting of 2 MOSFETs at the end of a flexible strip spaced 4 cm apart. The MOSFET array was placed along an uninflated 6‐French endobronchial catheter within a water‐equivalent solid phantom. This arrangement simulated having the detectors along the source pathway of a MammoSite, with the detectors within the balloon. The first detector was located at distal end of the “MammoSite” and the second at the proximal balloon collar. The HDR source was programmed to dwell at various positions relative to the “center” and MOSFET readings were obtained. Also, a prototype “MammoSite with MOSFETs” was built with the MOSFET array in a lumen adjacent to the source lumen. The scatter conditions (i.e., variable skin thicknesses) have been assessed by proximal MOSFET readings at various depths in a water phantom. Results: Ratio of the distal and proximal MOSFETs' readings showed high sensitivity to changes in dwell position. The fractional standard deviation of the ratio ranged from 0.9% to 3.2%, while each 1 mm shift from center caused at least 15% change in ratio. These ratios were not strongly affected by dose, dose rate, or nearby scatter media. Conclusion: The “MammoSite with MOSFETs” showed the potential to dosimetrically verify HDR source position with a linear resolution of 1mm or better. Further investigations are warranted to make this a routine clinical tool. Conflict of Interest: AH, Employed by Thomson‐Nielsen. JS, BS, MW, employed by Proxima Therapeutics.
SU‐FF‐T‐57: A COIN‐Based Comprehensive Specification Index for IMRT Treatment Plans
Authors: Barbiere J , Gejerman G , Hanley J
Published: June 2005

Purpose: The purpose of this work is to formulate a single index that can be used to specify the relative merit of an IMRT treatment plan for prostate carcinoma. The index includes components for conformity, tolerance, and uniformity and also serves to analytically determine the optimum normalization required for unbiased plan comparison. Method and Materials: COIN = C1*C2*C3 has been used to evaluate HDR and EBRT plans. C1 and C2 are planning target volume and normal tissue conformity metrics. C3 accounts for the irradiation of critical structures. An ASTRO prostate patient CT and contour data set were used as a case study. Nominal 76 Gy plans were calculated on a commercial system and DVHs exported to a PC using an in‐house program. All IMRT plans were calculated with the same dose‐volume constraints and then normalized to give the maximum COIN value. C3critical is calculated for the specific rectal tolerance dose of 65Gy. The COIN integral is a measure of dose inhomogeneity. A term C4 = [1‐ COINintegral(1.02) / COINintegral(1.00)] is introduced to account for two percent relative hot spots. The Comprehensive Specification Index CSI = C1*C2*C3critical*C4 is the proposed figure of merit. Results: All CSI values were calculated relative to 100 for the 9‐field plan. Respective CSI values for a static 4‐field, ideal fluence 5 and two 7‐field IMRT plans were 44.5, 97.1, 99.6, and 91.8. After conversion to deliverable step‐and‐shoot segments with 0.5 and 1.0 cm MLCs, CSI value for the 9‐field plan was reduced to 75.7 and 53.1. Conclusion: An index CSI was formulated and used to specify the relative merit of analytically normalized prostate IMRT plans. CSI is a sensitive figure of merit capable of distinguishing plans with various field arrangements and able to quantify the effect of converting ideal IMRT fluence to deliverable segments.
SU‐FF‐T‐58: A Comparison Between Helical Tomotherapy and LINAC‐Based Fractionated Cranial Radiosurgery Treatments Utilizing RTOG Guidelines
Authors: Wu H , Akpati H , Rosen L , Katz S , Mirzasadeghi M , Walker J
Published: June 2005

Purpose: An evaluation of helical Tomotherapy fractionated cranial radiosurgery treatment based on RTOG stereotactic radiosurgery indices for dose coverage (C), conformality (CI) and homogeneity (HI). A comparison between helical Tomotherapy and LINAC‐based non‐coplanar arc systems utilizing actual clinical cases. Methods & Materials: Clinical cases presenting with varying target sites, tumor volumes, and risk of complication (i.e. proximity of target to OAR) are evaluated. For each case two separate treatment plans, consisting of the best achievable optimized plan from the Tomotherapy planning system, and from a LINAC‐based radiosurgery planning system (Pinnacle ADAC) are compared. Coverage of the complete (100%) PTV volume is given highest priority during the treatment planning with both systems. Results: The dose coverage obtained from both planning systems is very comparable and range from 97 to 99%. However, in terms of dose conformality and homogeneity the Tomotherapy planning system resulted in superior treatment plans for every patient evaluated in the study. The CI and HI values for the Tomotherapy plans ranged from 1.01 to 1.39 and from 1.02 to 1.12 respectively. Whereas the CI and HI values obtained from the LINAC‐based plans ranged from 1.36 to 2.14, and from 1.88 to 2.98 respectively. Conclusion: For all the cases evaluated the helical Tomotherapy system easily complied with RTOG stereotactic radiosurgery standards for dose coverage, conformality and homogeneity. Whereas target coverage defined as a percentage of the prescribed dose, is comparable between helical Tomotherapy and LINAC‐based non‐coplanar arcs, significantly better conformality and homogeneity are obtained with the Tomotherapy system (especially for large and irregularly‐shaped tumors). The examples presented illustrate a default behavior of the TomoTherapy optimizer that is not employed in conventional radiosurgery planning, specifically the ability to deliver uniform dose to the target volume at the expense of increasing the low doses to the surrounding tissue.
SU‐FF‐T‐59: A Comparison of Forward and Inverse Planned IMRT Treatment of Breast Cancer
Authors: Qin L , Rakfal S
Published: June 2005

Purpose: To compare a forward planning technique with a commercial inverse planning module for breast IMRT treatments. Method and Materials: Currently, our clinic uses the Pinnacle IMRT InvPlan module for left breast IMRT treatment planning. Before the planning, the treatment volume (TV), the heart and the lungs are contoured on the patient CT scans. The isocenter and two tangential fields are defined in our treatment planning system (TPS), and an IMRT treatment plan was then generated using the inverse planning module. For the purpose of this study, we created forward planned IMRT breast plans with the same isocenter and tangential beams. Beam intensities in the forward plan were modulated by adding “control points” (CP), a special functionality provided by Pinnacle TPS. CP combines multiple tangential beams into a step‐and‐shoot IMRT field with multiple segments. A tangential beam in a forward IMRT breast plan typically consists of one open segment and 4 MLC segments blocking hot spots. A typical inverse IMRT breast plan has 6 to 7 segments in each beam. Isodose distributions and DVH's were compared between the breast IMRT plans generated using the forward planning technique and the inverse planning module. The statistical results were examined for the TV volumes receiving 95%, 100% and 105% of the prescription dose, the lung volume receiving more than 20 Gy and the heart volume receiving more than 30 Gy. Results: Five left breast cases were studied. The DVH's generated from both methods were comparable. It was found that the forward planned breast IMRT plans used fewer segments. The average values for V95, V100 and V105 between forward and inverse planed IMRT breast plans were within 2%. Conclusion: The forward planning technique can generate comparable breast IMRT plans and these plans met the clinical constraints used in our IMRT breast protocol.
SU‐FF‐T‐60: A Dosimetric Comparison of Three Commercially Available Carbon Fiber Table Extension Boards
Authors: Gajdos S , Muhieddine L , Chan G , Weinhous M
Published: June 2005

Purpose: To measure and compare the changes in dose distributions produced by the presence of a carbon fiber extension board (used to provide necessary patient extension beyond the gun end of the treatment couch). The tested carbon fiber extension boards are designed to be “radiotranslucent” so that the transmitted radiation beam is not significantly altered. We measured the attenuation due to the boards being placed in the beam's path, compared the relative dose distributions obtained using different boards, and also examined the effect of “build‐up”. Method and Materials: The three boards evaluated were the Med‐Tec Type‐S system, the Brainscan H&N Tx system, and the Orfit HP long baseplate for IMRT. Dosimetric data were obtained for 6 MV photons with an Exradin A12, 0.65 cm3 Farmer ionization chamber, with Kodak EDR film, and with an Exradin P11, 0.62 cm3 plane parallel chamber (for measuring dose buildup in a Gammex RMI solid water phantom). Results: The Orfit board's maximum attenuation was 1.2%. The Med‐Tec Type‐S board's maximum attenuation was 2.3%. The Brainscan board's maximum attenuation was 13.7%. The isodose distribution and profiles for each board will be presented. Conclusion: We determined that the Orfit board did not significantly alter the radiation beam and resulting dose distribution. Its adaptability to various tables was favorable compared to the Med‐Tec system, which is well suited for the Varian Exact couch. The Med‐Tec board is also well suited for therapeutic radiation, but had a higher change in attenuation than the Orfit system. The Brainscan board was sub‐optimal due to non‐air equivalent material used as structural support in the board's interior, which caused significant beam attenuation. Conflict of Interest: Research was supported by equipment loan from Orfit Industries and Med‐Tec, Inc.
SU‐FF‐T‐64: Combined Electron and Photon Intensity Modulated Radiotherapy for the Management of Malignant Pleural Mesothelioma
Authors: Chan M , Chui C , Song Y , Burman C , Schupak K
Published: June 2005

Purpose: This study investigated the feasibility and potential benefits of combining electron and photon intensity modulated radiotherapy (IMRT) for patients with malignant pleural mesothelioma (MPM). Complex‐shaped MPMs are difficult to treat by conventional radiotherapy due to low tolerance doses of the surrounding normal tissues. Even with recent treatment techniques employing photon IMRT, doses to the critical structures are difficult to keep within tolerance. Method and Materials: Two MPM patients after extrapleural pneumonectomy were studied. The patients were planned with photon IMRT alone and photon IMRT combined with electrons. The latter approach incorporated the electron component into the inverse planning optimization. The resulting doses to the planning target volume (PTV) and relevant critical structures were compared. For both plans, 54 Gy was delivered to the PTV that includes non‐uniform margins along the clinical target volume (CTV), ranging from 3 mm along the spine to 6 mm near the ribcage. Results: Target dose coverage for both techniques was optimal (D95, V95 > 98%) while the doses to the critical structures were minimal (liver D50 < 27 Gy, contralateral lung and kidney D80 < 15 Gy, ipsilateral kidney D50 within 15–18 Gy). However, combined electron and photon IMRT exhibited an advantage in reducing the doses to the liver and ipsilateral kidney by an additional 10% while the PTV hot spot was reduced by 10%. The planning and setup time with the addition of electrons is expected to be longer. Conclusion: This study showed that photon IMRT alone or combined with electrons are viable treatment modalities for MPM patients. Both plans can provide excellent target coverage and normal tissue sparing, but with the addition of electron beams the critical structures can be further spared. Additional investigation to optimize the electron contribution to these complicated plans would be expected to result in further improvement.
SU‐FF‐T‐68: Conformal Target Versus Conformal Avoidance IMRT in Patients with Prostate Cancers
Authors: Deng J , Chen Z , Song H , Nath R
Published: June 2005

Purpose: To compare conformal avoidance IMRT with conformal target IMRT for the radiotherapy of prostate cancers. Method and Materials: Twenty patients with prostate cancer who underwent IMRT were selected for this study. For comparison, five plans were generated for each patient with different emphasis on conformal target or conformal avoidance: very conformal target IMRT plan (Plan I, maximum weights for targets and least weights for OARs), conformal target IMRT plan (Plan II, maximum weights for targets and relatively small weights for OARs), balanced IMRT plan (Plan III, maximum weights for targets and medium weights for OARs), conformal avoidance IMRT plan (Plan IV, maximum weights for targets and relatively large weights for OARs) and very conformal avoidance IMRT plan (Plan V, maximum weights for both targets and OARs). All the five plans were designed to deliver 66.6 Gy (prescription dose) to 100% of the CTV. Results: The target dose coverage became worse as plan changed from very conformal target to very conformal avoidance, as 100% isodose line cut more and more through PTV adjacent to rectum. On the other hand, the rectum sparing increased at the same time, due to the increased emphasis on the avoidance of OARs. Overall, all the five plan schemes achieved the goal of delivering 66.6 Gy to the whole CTV. However, Plan IV was slightly better than the rest of plans in terms of largest CTV V100 (99.90%), best homogeneity in CTV dose distributions (smallest difference between Dmax and Dmin) and smallest Rectum D25 (58.88 Gy). Conclusion: For prostate IMRT, practicing conformal avoidance in inverse planning process can achieve better target dose coverage and homogeneity, as well as larger critical structure sparing.
SU‐FF‐T‐70: Dosimetric Comparison of Inhomogeniety Corrections in IMRT Treatment Planning Systems: A Collaborative Study
Authors: Mitra R , Bagala T , Olch A , Das I , Cheng C , Chopra K , Hasson B , Jiang Z , Murphy S , Lian J , Ahnesjo A
Published: June 2005

Purpose: A multi‐institution collaborative study of dosimetric comparison of inhomogeneity corrections in IMRT treatment planning systems. Nine institutions representing twelve IMRT systems participated in this study. Method and Materials: DICOM RT data sets for prostate, lung, and head and neck cases with target volumes and the organ at risks (OAR) already outlined were sent to each collaborative member. Beam arrangements, dose volume constraints and a maximum grid size were kept constant. For the case of prostate, lung and head and neck cases, 7, 5 and 9 equally placed field arrangements, were chosen for treatment planning using a 6 MV beam. Treatment plans were generated and optimized to meet the benchmark clinical endpoints. Each of the cases was calculated with and without inhomogeneity corrections. The calculated DVH's, phantom plans and measured data were collected and analyzed. Results: Traditionally, utilizing modern treatment planning algorithms, there are significant differences in conformal 3D RTP, especially in head and neck and lung cases. Across all of the systems analyzed in this study, however, our data was quite the opposite. DVH analysis of PTV/CTV and critical organs show virtually identical data for homogeneity corrected vs. uncorrected iterations. The ratio of MU's across several IMRT TPS for corrected and uncorrected iterations for lung and head & neck cases were within 5% of each other. Conclusions: The overall conclusion from the data analysis reveals that although the target coverage, total MU's, treatment delivery times etc. may vary significantly from one IMRT TPS manufacturer to another, most systems are able to generate clinically acceptable optimal solutions for both homogeneity corrected and uncorrected calculations. More importantly, the variation in target/critical organ coverage for inhomogeneity corrected vs. uncorrected iterations is minimal and the clinical impact of these variations should also be consequently minimal.
SU‐FF‐T‐74: Effects of Patient Positioning and Treatment Techniques On the Potential for Dose Escalation in Patients with Gynecological Malignancies with Para‐Aortic Lymph Node Involvement
Authors: Levin D , Menhel J , Alezra D , Pfeffer R , Symon Z
Published: June 2005

Purpose: To investigate the effect of patient positioning and treatment technique on the potential for dose escalation in pelvic and para‐aortic irradiation. Method and Materials: 5 patients with gynecological malignancies were CT‐scanned in prone, with belly‐board, and supine positions. For each patient and position 3D and IMRT plans were generated to 45 Gy. The CTV encompassed the pelvis and para‐aortic nodes. PTV was a 3D, 0.6 cm expansion. We contoured kidneys, spine, small bowel, bladder and rectum, and compared the doses distributions. Dose conformity was assessed using the conformity index CI = VT, P / VP, where VT, P is the target volume receiving prescription dose or greater, and VP is the volume receiving the prescription dose. For organs at risk we compared mean (e.g. for kidneys) or maximum (e.g. for spine) doses. Results: Target conformity was significantly improved for IMRT plans as compared to 3D plans. IMRT plans, regardless of position, resulted in superior sparing of spine and bowel compared to 3D plans . For IMRT we found no significant difference in bowel doses between supine and prone belly‐board positions. The kidneys received lower doses in the 3D plans, but IMRT doses were much lower than tolerance. Contrary to small field irradiation, the integral dose in these large‐field IMRT plans was not more than in the 3D plans. Conclusion: IMRT has the potential to allow dose escalation in whole pelvic and para‐aortic radiation as compared to 3D plans, with increased sparing of critical organs. For IMRT, regardless of patient positioning, there is no significant difference in doses to either targets or critical structures. Thus, for reasons of setup reproducibility and patient comfort, supine IMRT would appear to be the better choice. The problem of organ motion in the irradiated area must be addressed before IMRT can be implemented.