bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐10: Coils, a New Twist for Treatment of Prosate Cancer by Brachytherapy
Authors: Gladstone D , Hartford A , Hug E
Published: June 2005

Purpose: Pd‐103 sources have recently been produced in coil form. These coils offer advantages over conventional seeds including high stability in tissue, better visualization under ultrasound, and more homogeneous dose distribution. We report the first use of Pd‐103 coils for treatment of prostate cancer. Method and Materials: Fully TG‐43 compliant parameters for a 1 cm long source were entered into the treatment planning system and multiples of these 1 cm sources were used to model coils of lengths up to 5 cm. Dosimetry was compared between Theragenics Pd‐103 seeds and the new RadioCoil sources. Plans were compared with equivalent geometries, unlike sources placed with their centers matched. Ten patients have been implanted with Pd‐103 coils. Intraoperative treatment planning was performed and needles were custom loaded as with conventional seeds. Results: The dosimetry of coils is roughly comparable to that of seeds. Required activity of the coils is approximately 8% higher than that of seeds to achieve the same minimum target dose. Even with effectively higher activity per cm, coils deliver a more homogeneous dose distribution with maximum doses to tissues significantly lower than that delivered by seeds. Conclusion: Coils are an interesting new source for delivery of therapeutic doses by brachytherapy. They promise better stability in tissues, higher dose homogeneity, and better visualization under ultrasound compared to conventional seeds. Fully compliant TG‐43 algorithms are required for accurate dose calculation.
SU‐FF‐T‐12: Experimental and Theoretical Dosimetric Characterization of ADVANTAGETM Pd‐103 Brachytherapy Source
Authors: Koona R , Rachabatthula V , Awan S , Meigooni A
Published: June 2005

Purpose: Recently, a new design of 103Pd brachytherapy source namely ADVANTAGE™ Pd‐103 source has been introduced by IsoAid for interstitial prostate implants. In this project, the dosimetric characteristics of this new source were determined using experimental and theoretical methods, following the updated TG43U1 recommendations. Method and Materials: The experimental procedures were performed in Solid Water™ phantoms using LiF TLD dosimetry technique, while the theoretical calculations were performed both in water and Solid Water™ phantom materials using the PTRAN version 7.43, Monte Carlo simulation code. The photon cross section used for these simulations was DLC‐146, distributed by the Radiation Sciences Information Computing Center at Oak Ridge National Laboratory. The dose rate constant, radial dose function, 2D and 1D anisotropy functions of the source were obtained following the TG‐43U1 recommendations. Results: The results of Monte Carlo simulations indicated a dose rate constant of 0.69 ± 3% cGyh−1U−1 and 0.67 ± 3% cGy−1U−1 in water and Solid Water™, respectively. The measured dose rate constant in Solid Water™ was found to be 0.66 ± 8% cGyh−1U−1, which is in good agreement with the Monte Carlo results to within the experimental uncertainty. Moreover, the dose rate constant of the new source in water medium, calculated for clinical applications was found to be in excellent agreement with the dose rate constants of the other commercially available sources. A very good agreement between the measured and Monte Carlo simulated, radial dose functions and anisotropy functions were observed. Conclusion: The dosimetric characteristics of the newly designed ADVANTAGE™ Pd‐103 source were determined as per the TG‐43U1 recommendations. The radial dose function, 2D anisotropy function, and dose rate constant were also compared to the other available commercial sources. An excellent agreement was observed on comparison.
SU‐FF‐T‐13: Monte Carlo Calculation of the TG‐43 Dosimetric Parameters of a New BEBIG Ir‐192 HDR Source
Authors: Ballester F , Casal E , Granero D , Perez‐Calatayud J , Agramunt S , Cases R
Published: June 2005

Purpose: High dose rate (HDR) brachytherapy is a highly extended practice in clinical brachytherapy today. Quality dose rate distribution datasets of the HDR sources used in a clinical treatment are required. Because of the different source designs, a specific dosimetry dataset is required for each source model. In the recently published BRAPHYQS‐ESTRO Report, an overview of available dosimetric data for all HDR Ir‐192 sources is given, pointing out the lack of data for one of the sources, the used by the BEBIG MultiSource afterloading system (BEBIG GmbH, Germany). The purpose of this study is to obtain detailed dose rate distributions in liquid water media around this source. Material and methods: The MC code GEANT4 was used to estimate dose rate in water and air‐kerma strength around the Ir‐192 source. All the details of the stainless steel encapsulated BEBIG HDR 1.1 mm in external diameter has been included in the simulation. Results: A complete dosimetric dataset for the BEBIG Ir‐192 HDR source is presented. TG43 dosimetric functions and parameters have been obtained as well as a 2‐D rectangular dose rate table, consistent with the TG43 dose calculation formalism. Conclusion: The dosimetric parameters and functions obtained for the BEBIG HDR source have been compared with that obtained in the literature for others HDR sources, showing that the use of specific datasets for this new source is justified. This dataset can be used as input in the TPS and to validate its calculations. As policy of BRAPHYQS‐ESTRO task group, this dataset will be incorporated to the website: http://www.uv.es/braphyqs available to users in excel format.
SU‐FF‐T‐14: Monte Carlo Derivation of TG‐43 Dosimetric Parameters for Radiation Therapy Resources and 3M Cs‐137 Sources
Authors: Casal E , Granero D , Ballester F , Perez‐Calatayud J , Agramunt S , Cases R
Published: June 2005

Purpose: In clinical brachytherapy dosimetry a detailed dose rate distribution of the radioactive source in water is needed to make a quality treatment planning. Two Cs‐137 sources are considered in this study the Radiation Therapy Resources 67–800 source (Radiation Therapy Resources Inc., Valencia, CA) and the 3M model 6500/6D6C source. Material and methods: A complete dosimetric dataset for both sources has been obtained by means of the Monte Carlo GEANT4 code. Results: Dose rate distributions are presented in two different ways, following the TG43 formalism and in a 2D rectangular dose rate table. Conclusion: This 2D dose rate table is helpful for the TPS quality control and it is fully consistent with the TG43 dose calculation formalism. In this wok, several improvements to the previously published data for these sources have been included: the source asymmetries were taken explicitly into account in the MC calculations, TG43 data were derived directly from MC calculations, the data radial range was increased, the angular grid in the anisotropy function was increased and TG43 data is now consistent with the along and away dose rate table as is recommended by the TG43 Update.
SU‐FF‐T‐17: 3D Monte Carlo‐Based Treatment Planning Evaluation of Intracavitary HDR Balloon Catheter Brachytherapy
Authors: Lerma F , Le Y , Kelley J , Arthur D , Williamson J
Published: June 2005

Purpose: To evaluate the dosimetric effects of missing tissue and tissue heterogeneities on intracavitary HDR balloon‐catheter brachytherapy using a novel 3D Monte Carlo‐based treatment planning study. Method and Materials: The PTRAN Monte Carlo (MC) photon transport code is used to generate 3D calculations of the doses arising from an HDR 192 Ir source in; Anatomy‐based MC simulations modeling the dosimetric effects of missing tissue beyond the skin surface and tissue heterogeneities (such as air pockets) adjacent to the balloon catheter (Mammosite); and in a large water phantom representing those calculations achievable with a conventional 3D brachytherapy RTPS. Each MC simulation employs a track length estimator scoring method in a 3D grid, with 2mm resolution in a 12cm×11cm×8cm volume, scoring 8×106 primary photon histories. The dose matrices from all MC simulation are registered (in the external beam module of a commercial RTPS) to a single, modeled patient CT, which is identical in location, scale, and shape to the patient volume described in the anatomy‐based MC simulations. Several target volumes (e.g. a 1cm margin on the Mammosite balloon) and a skin‐surface contour, are created. Dose‐volume histograms (DVH's) are computed for each volume, per each plan. Comparisons of the resultant DVH's quantify the dosimetric errors expected from routine clinical planning of Mammosite applications. Results: The missing tissue beyond the skin surface reduces target coverage by 1.5–3.5% and skin doses by 8–20%, when compared to calculations achievable with conventional 3D brachytherapy treatment planning systems. A 10cc airpocket neighboring the Mammosite balloon reduces doses to adjacent tissues <0.5%. Conclusion: A detailed 3D Monte Carlo‐based brachytherapy RTP study of the dose prediction errors in balloon catheter HDR applications shows that the missing tissue beyond the skin surface reduces skin doses by as much as 20% and target coverage by as much as 3.5%.
SU‐FF‐T‐19: A Study of the Effects of Seed Migration On Prostate Post‐Seed Dose Plan Evaluation
Authors: Gao M , Samsami N , Woollard J , Kanellitsas C , Wang J , Gupta N
Published: June 2005

Purpose: Brachytherapy using permanent seed implants has been an effective treatment for prostate cancer. It is a known fact that the seeds will migrate after implant, thus making the evaluation of long‐term (e.g. a few weeks) dose distribution difficult. We have performed a sensitivity analysis to determine the impact of seed migration on post‐seed dose plan evaluation parameters. Method and Materials: The CMS Interplant system and loose Pd‐103 seeds are used for the implant. The prostate is implanted with direct ultrasound visualization. CT scan and radiographs are taken 3 hours after the implant. Dosimetric studies are done using Nucletron's Theraplan Plus treatment planning system based on CT images. The migrations of the seeds are randomly modeled according to Gaussian distribution. The mean migration is taken to be 0.5 cm and the sigma to be 0.25 cm. These numbers are close to latest clinical observations published. To test the sensitivity, an extreme case with mean migration of 1.0 cm and sigma of 0.5 cm is also modeled and compared. Patients are divided into 3 groups according to the prostate size. For each patient, the seed locations are modeled 10 times for a given mean migration, and the resulting 10 DVHs from the 10 trials are compared. Data are summarized according to prostate size and mean migration. Results: Preliminary results shows that D100 and D90 for prostate change about 3.5% and 2.5% respectively, V100 for prostate changes by about 25%, V100 and V150 for urethra change by about 20% and 50% respectively, and V50 for rectum changes by about 15%. Conclusion: Dose distribution changes as seed migrate, especially for the volume coverage. This effect should be taken into account when evaluating post‐seed plans. Quantitative knowledge of this effect may also factor into the seed distribution in the pre‐plan.
SU‐FF‐T‐21: Analysis of Three Optimization Techniques in a Treatment Planning System
Authors: Hu Z , Chu J
Published: June 2005

Purpose: To develop the biological and dosimetric based tools for the evaluation of the treatment plans. Method and Materials: We have developed a set of treatment planning evaluation tools based on the equivalent uniform dose(EUD), Coverage Index(CI), Homogeneity Index(HI) and Overdose Index(OI) to evaluate the HDR brachytherapy treatment plans. Three different optimization techniques in PLATO treatment planning system are used for CT based 3D conformal brachytherapy: geometric optimization(GO), inverse optimization(IO), and the optimization to the dose points on the surface of the tumor volume(SO). All reference doses are prescribed to the points on the PTV surfaces. Treatment plans of 10 patients are analyzed. Results: The GO techniques has the best dose uniformity(mean HI=0.60) but poorest target volume coverage(mean CI=0.71). The SO method provides the best coverage(mean CI=0.85) and lowest homogeneity(mean HI=0.62). The IO plans show a compromise between coverage and dose homogeneity(mean CI=0.52 and HI=0.43). CI and EUD show close correlation for plans produced by all three optimization techniques. Conclusion: Our study suggests that these dosimetric indices could be useful tools in the evaluation of the CT based 3D conformal brachytherapy planning.
SU‐FF‐T‐24: Comparison of Endobronchial HDR Brachytherapy Using CT Imaging and Conventional Simulator Filming
Authors: Tsai J , Cardarelli G , Corrao A , Hiatt J , Shearer D , Bradford C , DiPetrillo T , Puthawala Y , Wazer D
Published: June 2005

Purpose: To compare the clinical merit of endobronchial HDR based on CT imaging and conventional simulator films. Method and Materials: The tumor locations within the lung and trachea were first identified and defined with bronchoscopy (FigA). Next a catheter was inserted in conjunction with a dwell position x‐ray marker. Subsequently, the patient underwent either simulator filming or CT scanning for HDR treatment planning. For simulator filming, two orthogonal films were taken to define the tumor location and dose reference points (FigB&C). For CT, the area containing the bronchial target was scanned (FigD). Unlike simulator filming, 3D contouring of the tumor and the reference dose points can be obtained with CT in compliance with actual clinic requirements. Isodose distributions and tumor dose volume histograms (DVH) in both techniques were compared. Results: The simulator filming technique has an advantage of time efficiency. FigC shows the isodose distribution using simulator films. The treatment time durations on each dwell position are fairly constant. Since the tumor volume was defined by estimation, DVHs have little significance. Also, there is a magnification deviation of the tumor volume if the catheter is not always along the gantry axis. For large patients (lateral separation > 40cm), image quality diminishes resulting in uncertainty of isodose distribution coincidence to the tumor. FigE illustrates the CT images isodose distribution. The isodose distribution in each CT image changes from slice to slice and conformal to the tumor, thus reducing dose toxicity to adjacent tissues. It is in contrast to the monotonic one of the simulator films plan. The DVH is now more significance for analysis. Conclusions: Despite procedure time and cost saving with conventional simulator filming, CT imaging is favored for endobronchial HDR in terms of isodose conformity to the tumor and normal functional tissue toxicity reduction.
SU‐FF‐T‐25: Comparison of Intra‐Operative Computer Optimized and Nomogram‐Based Total Implant Activities in Prostate I‐125 Seed Implants
Authors: Yaparpalvi R , Guha C , Kahan N , Minsky L , Danish A , Shah S , Engler M , Kalnicki S
Published: June 2005

Purpose: Nomograms correlating total I‐125 seed activity, prostatic volume and prescription dose have been published in the literature. In this study, we have retrospectively compared our institutional patient I‐125 seed implant activity data with nomogram‐based calculations. Our objectives were: (a) to identify if our computer optimized implanted activity data followed any particular nomogram, and (b) to evaluate if implanting adequate activity guaranteed good post‐implant dosimetric results. Method and Materials: The charts of 255 patients with clinically localized prostate cancer who underwent TRUS guided I‐125 seed implantation of the prostate were reviewed. The median pre‐implant US prostate volume was 35 cc (range 14 – 82 cc) and the median total activity was 30.9 mCi (range 14.76 – 64.17 mCi). In 95% of the cases, intra‐operative computerized dosimetric planning was performed to optimize the needles, seeds and seed positions. For each patient, a CT‐study obtained 1‐month after the procedure was used for post‐implant dosimetry. Results: Our patient implanted activity data was within the range predicted by various nomograms, except in cases where intra‐operative computer planning was not used (Fig 1). Implanted activities were dispersed and did not follow activity curve of any specific nomogram. Implanting adequate activity did not always result in good post‐implant dosimetry (median D90 value 108.8 Gy, range 31.64 – 256.6 Gy, p<0.0001) (Fig 2). CT/US volume ratio >1.5 was associated with decreased D90 (median CT/US ratio 1.51, range 1 – 3.3) (p<0.0001) (Fig 3). Conclusion: Nomogram calculated and computer optimized activities complement each other, however, intra‐operative computerized activity optimization should continue to be the gold standard in prostate seed brachytherapy. Even in properly implanted prostates, discrepancies caused by contouring prostate on US and CT‐ based images, plus any real volume changes due to edema, significantly influence post‐implant dosimetric quality. CT/US‐fusion featured on newer planning systems should lessen these contouring uncertainties.
SU‐FF‐T‐26: Comparison of PDR Iridium and LDR Cesium Through Monte Carlo Simulation
Authors: Vass H , Ibbott G
Published: June 2005

Purpose: Pulsed dose rate (PDR) 192Ir has been proposed as a substitute for intracavitary 137Cs brachytherapy because it radiobiologically mimics LDR treatments. Monte Carlo calculated doses to the ICRU 38 reference points show that PDR delivers a dose distribution that is comparable to that delivered by LDR 137Cs. Method and Materials: After validation of the Monte Carlo model using published data for a single source and radiochromic film measurements around a single shielded ovoid, the tandem and ovoid applicator system were modeled using Monte Carlo geometries. Treatment plans using the PDR source were created in Varian's Brachyvision software simulating the isodose shapes produced in a typical Cesium plan. These plans were recreated in Monte Carlo input files. A shielded and an unshielded version of each patient's treatment plan was created to ascertain the effect of the shields on the reference points. Results: The results showed that Monte Carlo calculations for the unshielded model to the standard ICRU 38 reference points agreed well with Brachyvision's calculations to these points. Results from the shielded model showed no significant affect to points A and B, but significant change to the bladder and rectal points. An average shielding effect of 12.7% was observed for the bladder point and an average effect of 29.4% was observed for the rectal point. The results were compared with data from a previous Cesium study involving the same patients. Doses to points A and B were similar. The shielding showed greater effectiveness with PDR for the bladder and rectum. Conclusion: A Monte Carlo model was developed to simulate representative clinical dose distributions from a PDR Iridium source in a shielded GYN applicator. The calculations demonstrate that PDR Iridium can be substituted for conventional LDR Cesium brachytherapy.
SU‐FF‐T‐27: Detailed Urethral Dosimetry in the Evaluation of Prostate Brachytherapy‐Related Urinary Morbidity
Authors: Allen Z , Merrick G , Butler W , Kurko B , Anderson R , Murray B , Galbreath R
Published: June 2005

Purpose: To evaluate the relationship between post‐prostate brachytherapy urinary morbidity and urethral doses calculated at the base, mid‐prostate, apex and urogenital diaphragm. Method and Materials: 186 consecutive patients with no history of transurethral resection underwent monotherapeutic prostate brachytherapy (no external beam radiation or androgen deprivation) with urethral sparing techniques (average urethral dose 100–140% of prescribed dose). The median follow‐up was 45.5 months. Urinary morbidity was defined by time to International Prostate Symptom Score (IPSS) resolution, maximum increase in IPSS, catheter dependency, and the need for postimplant surgical intervention. An α‐blocker was initiated approximately 2 weeks prior to implantation and continued until the IPSS returned to baseline. Evaluated parameters included overall urethral dose, doses to the base, mid‐prostate, apex and urogenital diaphragm, patient age, clinical T‐stage, preimplant IPSS, ultrasound volume, isotope, D90 and V100/150/200. Results: Of the 186 patients, 176 had the urinary catheter permanently removed on the day zero and only 1 patient required a urinary catheter > 5 days. No patient developed a urethral stricture, and only two patients required a postbrachytherapy TURP. For the entire cohort, mean IPSS peaked 2 weeks following implantation, and the median time to IPSS resolution of 3 weeks. For the entire cohort, only isotope predicted for IPSS resolution, while neither overall average prostatic urethra nor segmental urethral dose predicted for IPSS resolution. The maximum postimplant IPSS increase was best predicted by preimplant IPSS and the maximum apical urethral dose. Conclusion: With the use of prophylactic α‐blockers and adherence to urethral sparing techniques, urethral dosimetry did not improve the ability to predict urinary morbidity. Neither the average dose to the prostatic urethra nor urethral doses stratified into base, mid‐prostate, apex, and urogenital diaphragm segments predicted for IPSS normalization. Radiation doses of 100–140% mPD are well tolerated by all segments of the prostatic urethra.
SU‐FF‐T‐28: Dose Perturbation Effects in Brain Implant Brachytherapy with I‐125 Radioactive Seeds
Authors: Mobit P , Badragan I
Published: June 2005

Purpose: Use Monte Carlo simulations to determine the dose perturbation effects of a single column of radioactive seeds implanted in the brain. Material and Methods: The EGSnrc Monte Carlo simulation code together with an EGSnrc user code (BRACHYDOSnrc) was used to investigate dose perturbation effects in brain implant brachytheray using 125I. Dose perturbation effects resulting from the mutual attenuation or shielding of other seeds in the implant consisting between 8 and 12 seeds were investigated. The dose perturbation effects were calculated as the difference between the full Monte Carlo simulations taking into account the inhomogeneity caused by the presence of the seeds and the single seed superposition model which ignores the perturbation caused by other seeds in the implant. The seeds were arranged in a single column in a Perspex tubing (end‐to‐end) and calculation medium was water. Results: The results show that for 125I. seeds implanted into the brain, with no spacing between seeds, the single superposition dose calculation models underestimates the dose along the longitudinal direction of the seeds by up to 20%. The shielding effects of other seeds causes the dose perturbation which occur generally in the longitudinal direction of the seeds. The volume occupied by the difference in the dose distribution between the full Monte Carlo simulations and simple superposition model increases with increasing number of seeds as expected. The differences in the rest of the calculation grid was generally with ± 5%. Conclusions The differences between the full Monte Carlo simulations and the single seed superposition dose calculation is not clinically significant as differences occur close to the column of seeds where the dose is already high.
SU‐FF‐T‐33: Introduction to 3‐D Image‐Based Treatment Planning for Complex Brachytherapy of Soft Tissue Sarcoma
Authors: Proffitt J , Coffey C , Teng M
Published: June 2005

Purpose: To introduce CT‐based treatment planning for brachytherapy of soft tissue sarcoma utilizing 3‐D graphics, and to examine resulting improvements in dosimetry and efficiency for complex cases. Method and Materials: This procedure begins with a CT scan (Picker PQ 5000) following surgical catheter placement. CT data is transferred to the treatment planning workstation and imported into BrachyVision 6.5 (Varian) software. The catheters are defined as applicators utilizing the combination of 2‐D transverse, coronal, and sagittal CT views and 3‐D image reconstruction. This type of applicator definition creates automatic seed placement and spacing along the catheter. Ir‐192 seeds (Best Industries, Inc.) with TG‐43 data are used for dose calculation. Dosimetry is optimized using 3‐D dose visualization. This planning procedure has been performed and analyzed on seven LDR and two HDR clinical cases. Two LDR cases were planned with both the previous 2‐D method of orthogonal films and the new 3‐D CT‐based method. The two methods were compared on 3‐D versus 2‐D (volume versus planar), dosimetry optimization, and clinical feasibility. Results: There are significant benefits of using CT‐based 3‐D planning for sarcoma brachytherapy. CT plane views allow accurate catheter definition and seed placement. 3‐D visualization permits an assessment of catheter distribution in more than one plane, and enhances dose optimization for tumor bed dose, hot/cold spots, and normal tissue doses. The process is no more time consuming, and gives more confidence in source placement, more choices in source activity, and improved displays of isodose distributions. Conclusion: 3‐D compatible planning software with CT imaging has allowed this clinic to improve visualization and dosimetry optimization while reducing uncertainty in seed positioning for complex cases of sarcoma brachytherapy. Use of CT additionally creates the potential of combining dose distributions from external beam treatment and brachytherapy to produce composite dose evaluation.
SU‐FF‐T‐35: Is High‐Dose Rate (HDR) “better Than” and Low‐Dose Rate (LDR) Prostate Brachytherapy? A Dosimetric Study Using Retrospective Data
Authors: Sankreacha R , Morton G , Al‐Hebshi A
Published: June 2005

Purpose: To compare high‐dose rate (HDR) and low‐dose rate (LDR permanent seeds) prostate brachytherapy using dosimetric parameters. Method and Materials: From January 2003 to August 2004, 102 HDR prostate implants were planned on the Nucletron PLATO Brachytherapy with subsequent treatment using Nucletron afterloader (I192 stepping source). During this time period, 72 LDR implants were pre‐planned on Varian Variseed Brachytherapy with subsequent treatment using I125 seeds (a combination of loose and stranded seeds). The HDR implants were forward planned using a combination of manual dwell time adjustments and graphical optimization on patient CT images. The LDR implants were pre‐planned based on ultrasound images and post‐implant dosimetry was assessed at one month from CT. For this study, post‐plans were analyzed using Nucletron PLATO Brachytherapy Seeds. Parameters used for comparison included: Conformal index (COIN), Homogeneity Index (HI), Natural Dose Ratio (NDR) as well as volume and dose coverage indices. Maximum dose contribution to critical structures was reported. Results: Our results show the V100 for HDR with a mean of 96.1% is higher than LDR (post‐plan) with a mean of 81.8% (p<0.001). Conformal Index for HDR was 0.701 compared to LDR pre‐plan (COIN=0.627, p<0.001) and post‐plan (0.534, p<0.001). The homogeneity index showed a significant difference between techniques (HDR HI=0.628, LDR pre‐plan HI=0.518, HI post‐plan HI=0.425). The Natural Dose Ratio did not show a large difference (HDR NDR=1.025, LDR pre‐plan NDR=1.041, LDR post‐plan NDR=0.915). Conclusion: It has been shown high‐dose rate brachytherapy for prostate treatment delivers a more conformal and uniform dose throughout the target than low‐dose rate permanent seeds. The dose contribution to the rectum and urethra is much less with high‐dose rate than low‐dose rate. Dose contribution to the target can be tailored using existing optimization routines and newer algorithms for inverse planning that will make the planning procedure simpler.
SU‐FF‐T‐36: MammoSite Dosimetry Under Condition of Insufficient Buildup and the Proximity of the Balloon to the Lung
Authors: Cheng C , Das I , Mitra R
Published: June 2005

Purpose: Brachytherapy dose planning for MammoSite assumes full scatter buildup. Clinically, MammoSite dosimetry is affected by the buildup condition between the balloon and the skin and the reduced backscatter contribution from the lung. We attempted to answer the following questions: what is the effect of insufficient buildup? What is the dose to the lung? Method and Materials: A breast phantom consisting of polystyrene slabs and Styrofoam blocks is constructed. The thickness of slabs may vary to simulate the varying tissues thickness between the balloon surface and skin. Kodak EDR2 films are mounted parallel to the MammoSite catheter between the polystyrene slabs and the Styrofoam blocks. For each thickness of polystyrene slab above the base, the films are irradiated with the same dose. The films are scanned and analyzed by the RIT software. Results: The insufficient dose buildup and the lack of backscatter contribution may lead to underdosage at the prescription depth. With only 1 cm tissue above the balloon surface, the minimum dose at the prescription depth is only 75% of the dose under full scatter buildup. Even with 3.5 cm tissue, the dose at 10 mm is only 85%. The lung dose, on the other hand, exhibits a buildup behavior, which varies with the thickness of tissue. As much as 180% of the prescribed dose may be delivered to the lung in the vicinity to the balloon surface. Conclusion: The insufficient dose buildup and the presence of lung lead to undersage at the prescription distance which is not revealed in all existing planning system since full scatter buildup without heterogeneity correction is assumed. For correct MammoSite dosimetry, the above issues should be addressed properly. The excessive lung dose even under insufficient dose buildup is may be avoided in some cases by careful placement of the balloon.
SU‐FF‐T‐37: Measurement of Cranio‐Caudal Catheter Displacement Between Fractions in CT‐Based HDR Brachytherapy of Prostate Cancer
Authors: Kim Y , Hsu I , Pouliot J
Published: June 2005

Purpose: To measure the cranio‐caudal displacement of catheters occurring between consecutive fractions of transrectal ultrasound (TRUS) guided high dose rate (HDR) prostate brachytherapy. Method and Materials: Ten consecutive patients were treated with 2 fractions of 9.5 Gy TRUS guided HDR brachytherapy using dental putty for the fixation of catheters. For each patient, a CT scan with 3 mm slice thickness was acquired before each of the two fractions. Two different references were employed to measure the catheter displacement between fractions: the ischial bone as a bony marker (BM) and the center of two gold markers (COGM) implanted in the prostate. The catheter displacement was calculated by multiplying the thickness of CT slice with the difference in number of CT slices between the reference slice and the slice containing the tip of a catheter. Results: The average (range) magnitude of caudal catheter displacement was 4.1 mm: 2.7 mm (−6.0 to 13.5 mm) for BM method and 5.4 mm (−3.75 to 18.0 mm) for COGM method, respectively. The measurement results obtained from BM and COGM methods verified that both prostate movement and catheter displacement independently occurred between fractions. The most anterior and medial two catheters (catheter position 8 and 12) had the greatest tendency to be displaced in the caudal direction because they were located at the most distant position from the fulcrum, susceptible to the rotation of the dental putty in lateral plane due to patient movement between fractions. Conclusion: The catheter displacement using dental putty for the fixation of catheters is smaller than the conventional technique using pre‐fabricated template. The use of both BM and COGM methods for catheter displacement measurement can demonstrate the prostate movement relative to the catheter displacement between fractions.
SU‐FF‐T‐39: Mono‐Energetic Brachytherapy Sources
Authors: Gueye P , Britten R , Keppel C
Published: June 2005

Purpose: Determination of the energy dependence of human cell inactivation (i.e., loss of reproductive capacity) following exposure to β radiation. Method and Materials: A dipole magnet was constructed from two 5.08cm × 5.08cm × 2.54cm niobium permanent magnets separated by a distance of about 2cm. This dipole has a highly non‐uniform field that reaches about 5 kG at the center. A 1cm × 1cm collimated electron beam exiting a radioactive source (300 Ci, max energy: 662 keV) was placed at the entrance face of the dipole magnet. Separation of the different energies was ensured by placing a second identical collimator perpendicular to the dispersive plane. The setup provides an energy resolution of about 10%. Four normal human fibroblast (AGO1521, AGO1522, GM06419 and WI‐38) and one human breast cancer (MDA231) cell line were exposed to electrons of defined energy for approximately 1 hour (∼3.5 Gy). Radiation induced changes in clonogenic survival were determined and protein samples collected for subsequent proteomic analysis using 2D gel electrophoresis, coupled with Mass Spectroscopic identification of candidate proteins. Results: Examination of the Relative Biological Effectiveness of the various electron beam energies on human cell lines indicates an energy dependence of cell inactivation. The radiation exposure time variation and the type of cell lines play a non‐negligible role in the experimental outcome. Preliminary Monte Carlo simulation data of the process at the molecular level compare fairly well with experimental results. Conclusion: This work indicates the potential efficacy of providing mono‐energetic radioactive sources for Brachytherapy treatments. Characteristic responses of tumor cells to well defined kinetic energies of β particles could reduce the incidence of unwanted side effects associated with ineffective radiation dose. The methodology will be used in future investigations on small animals to establish in‐vivo applicability of the technique.
SU‐FF‐T‐44: Optimized Source Selection for Low Dose Rate Brachytherapy
Authors: Nurushev T , Kim J
Published: June 2005

Purpose: To introduce the method of the optimized source selection for the LDR Brachytherapy, and investigate its effectiveness as compared to the regular trial and error source selection. Method and Materials: An in‐house method of optimized source strength ratios was developed to replace the trial and error guess work for the LDR therapy with sealed Sc‐137 sources. Inverse treatment planning philosophy was applied to the whole process. The desired dose to the reference points is first specified. The corresponding optimal plan is then defined, and the source selection program is run to produce an actual loading plan with the available sources. These actual sources are then used to calculate the final dose distribution. Treatment plans obtained with this method were compared to the plans obtained with the regular technique. Also optimal plans produced by our method were compared to the actual plans selected by the segmentation algorithm. Results: The difference between the optimal and the actual plans is determined by the available inventory. In our tests we achieved a relative difference a few percent at the expense of the dose rate. We noticed a significant difference between the regular plans and optimized plans. The regular method produced clinically acceptable plans after several iterations. The results depend on the personal experience. With our method the desired 3D dose distribution was achieved at a first try. Conclusion: Utilizing our source selection method treatment plans closest to the clinically optimal can be produced in a short amount of time. The results are independent of the personal experience and the most limiting factor was the discreteness of the available inventory. Keeping the statistics on the frequently requested source strengths for the optimal plans helps in ordering the clinically relevant replacement or additional sources, and minimizing the quantity of idle sources in the inventory.
SU‐FF‐T‐47: Phantom Study of Radiation Dose Reduction to the Contralateral Breast Using Lead Shielding When Treating with the MammoSite Applicator
Authors: Hansen J , Stewart A , O'Farrell D , Rodenbush R , Devlin P , Cormack R
Published: June 2005

Purpose: Accelerated intracavitary partial breast irradiation can be delivered using an Ir‐192 HDR afterloader with a MammoSite™ applicator. Over the course of a 3400 cGy treatment the contralateral breast can receive total radiation doses exceeding 200 cGy. Placing shielding between the breasts might reduce the dose to the contralateral breast. Phantom measurements were performed to investigate the feasibility and benefit of this shielding. Method and Materials: Treatments were simulated using doses of 340 cGy. Dose measurements were performed using an ion chamber in a homogeneous solid water phantom. The ion chamber was calibrated is solid water 5 cm from a known Ir‐192 source. The phantom was simulating a geometrically simple patient with 5 cm tissue from the center of the MammoSite balloon to the medial breast surface, 10 cm of air between the breasts, and 1 cm to the measurement point in the contralateral breast. 1.6 mm lead sheets were used in single or double layers. The simulations were repeated in a Rando™ anthropomorphic phantom with simulated breasts created from BolxII™. Results: Contralateral breast shielding is strongly dependant upon the position of the Ir‐192 source and the lead shield. Using 1.6 mm and 3.2 mm of lead reduced the contralateral breast dose behind the shield by approximately 45% and 65% respectively. In our Rando™ experiments, using 3.2 mm of lead, the dose 1 cm below the skin would decrease from 190 cGy to 57 cGy and the dose at the center of the breast from 101 cGy to 39 cGy Conclusion: A 3.2 mm lead shield decreases the dose to the contralateral breast by more than 60%. This may be clinically significant for a reduction in the risk of radiation‐induced second malignancies. Shielding may be of best use if treating the patient in a prone or sitting position.
SU‐FF‐T‐49: Prostate Brachytherapy‐Induced Urethral Strictures
Authors: Galbreath R , Merrick G , Butler W , Anderson R , Allen Z
Published: June 2005

Purpose: To determine the incidence and to identify clinical, treatment and dosimetric parameters associated with the development of urethral strictures following permanent prostate brachytherapy. Method and Materials: From April 1995 through May 2003, 1186 consecutive patients underwent permanent prostate brachytherapy for clinical stage T1b‐T3a NxM0 (2002 AJCC) prostate cancer. Nine hundred and twelve patients (76.9%) were implanted with Pd‐103 and 204 (23.1%) with I‐125. The median follow‐up was 4.3 years. Follow‐up was calculated from the date of implantation. Clinical, treatment and dosimetric parameters evaluated for bulbomembranous urethral strictures included patient age, prostate volume, the use of supplemental XRT, isotope, androgen deprivation therapy (ADT), duration of ADT, prostate V100/150/200, D90, prostatic urethral dose (mean, median and maximum), bulbomembranous urethral dose (mean, median and maximum), tobacco use, hypertension, diabetes and BMI. Results: Twenty‐nine patients developed brachytherapy‐induced strictures and all occurred within the first 5 years following brachytherapy. All strictures involved the bulbomembranous urethra. The 9‐year actuarial risk of bulbomembranous urethral strictures was 3.6% with a median time to development of 34 months. The radiation dose to the bulbomembranous urethra was significantly greater in patients with strictures than those without (p < 0.001). In addition, the urethral dose 15 mm distal to the prostate apex was significantly greater in patients with strictures (p < 0.001). In multivariate analysis, only the bulbomembranous urethral dose and the duration of ADT (> 6 months) predicted for the development of a urethral stricture. All patients were successfully managed by either a urethral dilatation or internal optical urethrotomy. Conclusion: Brachytherapy‐related urethral strictures are related to overaggressive implantation of the periapical region and prolonged (> 6 months) treatment with ADT. Careful attention to preplanning and intraoperative execution, along with the judicious use of ADT, is essential to minimize the incidence of brachytherapy‐related strictures.
SU‐FF‐T‐51: Relationship Between Isotope, Prostate Volume and Urinary Morbidity Following Prostate Brachytherapy
Authors: Butler W , Niehaus A , Merrick G , Allen Z , Galbreath R , Adamovich E
Published: June 2005

Purpose: To evaluate the influence of isotope and prostate size on International Prostate Symptom Score (IPSS) normalization, catheter dependency and the need for surgical intervention following permanent prostate brachytherapy. Method and Materials: 976 consecutive patients underwent permanent brachytherapy for clinical stage T1b‐T3a prostate cancer. Of these, 789 were implanted with Pd‐103 and 187 with I‐125. Patients were stratified into size cohorts ⩽ 25.0 cm3, 25–35 cm3, 35–45 cm3, and > 45.0 cm3. 418 received androgen deprivation therapy (ADT). 486 received supplemental external beam radiation therapy (XRT). In all patients, an α‐blocker was initiated prior to implantation and continued until the IPSS returned to baseline. The median number of IPSS determinations per patient was 21. Clinical, treatment and dosimetric parameters evaluated included patient age, pretreatment PSA, Gleason score, clinical T‐stage, percent positive biopsies, preimplant IPSS, ultrasound volume, planning volume, isotope, V100/150/200, D90, urethral dose, supplemental XRT, ADT, and the duration of ADT (⩽ 6 months versus > 6 months). Results: For both isotopes and all size cohorts, IPSS peaked 1 month following implantation and returned to baseline at a mean of 1.9 months. Stratification of prostate size cohorts by isotope resulted in no significant differences in prolonged catheter dependency, IPSS resolution or postimplant surgical intervention. In Cox regression analysis, IPSS normalization was best predicted by preimplant IPSS, XRT and any need for a catheter following brachytherapy. Catheter dependency correlated with prostate volume, while the need for surgical intervention was related to catheter dependency, maximum urethral dose, ADT and maximum IPSS increase. Conclusion: When stratified by prostate size, the choice of isotope did not impact IPSS resolution, catheter dependency or the need for postbrachytherapy surgical intervention. While prostate size did predict for short‐term (< 5 day) catheter dependency, it did not influence IPSS resolution or the need for surgical intervention.
SU‐FF‐T‐54: Treatment Planning in HDR Intracavitary Brachytherapy: Comparison of Critical Organ Doses as Estimated by Orthogonal Radiographs Based Planning and Image Based Planning
Authors: Ganesh T , Subramani V , Joshi R , Aruna T , Sharma R , Gopishankar N , Rath G
Published: June 2005

Purpose: Doses to rectum, bladder and Point‐A in patients who received intracavitary HDR brachytherapy treatment were calculated by both orthogonal radiographs reconstruction method and by image based reconstruction method and were compared. Method and Materials: Twenty‐five patients of carcinoma cervix who received intracavitary brachytherapy treatment by micro‐Selectron HDR unit were included in this study. For these patients, in Plato treatment planning system, reconstruction of sources, applicator, organs at risk and Point‐A were done using conventional orthogonal radiographs and by using 1 mm thick CT scan images. Bladder was identified on radiographs through a Foley's catheter inserted into it filled with 7 cc of radio‐opaque fluid and the rectum through a rectal marker. Doses were calculated at 5 points each on bladder and rectum, for the treatment dose of 7 Gy to Point‐A (right & left). On CT images, these organs were delineated with the radiologists help and from dose‐volume‐histograms, doses to 1, 2 and 5 cc of these organs were calculated besides dose to Point‐A (right & left). Results: The critical organ doses estimated by the CT method were consistently higher when compared to those by the radiographs method. When compared to the radiographic dose maximum for bladder, doses to 1, 2 and 5 cc of bladder were higher by 89%, 69.7% and 41.6% on an average respectively. For rectum, the corresponding values were 36.6%, 21.7% and 0.4%. However dose to Point‐A did not differ by more than 3% between the two methods. Conclusion: The conventional orthogonal radiography based reconstruction method consistently underestimates the doses to critical organs while the doses to reference points are comparable in these two methods. Long‐term follow‐up in such patients can identify the threshold volumes for these critical organs beyond which complication rates are bound to rise.
SU‐FF‐T‐61: A Pseudo‐Tangential IMRT Technique for the Whole Large Left Breast Radiation Therapy Using Helios/Eclipse System
Authors: Guan H , Hammoud R , Pradhan D , Yin F , Kim J , Ajlouni M , Movsas B
Published: June 2005

Purpose: A pseudo‐tangential IMRT (PT‐IMRT) technique was developed to achieve high dose uniformity for the whole large left breast (separations >24 cm and volumes > 1200cc) radiation therapy and to reduce the early and late skin and subcutaneous reactions. Method and Materials: The proposed PT‐IMRT technique basically combines two pairs of tangential beams with two additional beams angled less than 10 degree from each side. In most situations, the two additional beams were angled anterior to the tangential plane. An additional OAR was drawn around the high dose (>110%) area at the lateral side. The PT‐IMRT is an inverse planning approach. After the optimization, 2 cm skin flash was added to each beam. Multiple static segments were used for the IMRT delivery. For comparison purpose, four other plans were also run for each patient: an inverse tangential‐IMRT plan (T‐IMRT), a 3D plan, a forward field‐in‐field (FIF) plan and a forward electronic compensator (EC) plan (all use the tangential beams only.) In‐homogeneity correction was included in all plans. Dose volume histogram (DVH) was used for the evaluation of all plans. Results: The PT‐IMRT provided the best dose volume uniformity for PTV. The dose volume to heart and left lung for doses less than 15 Gy was 2–3% higher for PT‐IMRT, but was 2–3% lower for doses larger than 25 Gy. The dose increment to a point 1 cm deep and 5 cm right to the mid‐sternum inside the right breast was 2–5% higher compared to other four plans. The normal tissue volume for doses larger than 105% was significantly reduced with the PT‐IMRT compared to the other four plans. Conclusion: The PT‐IMRT resulted in the most homogenous dose distribution among all the five techniques and has the potential to reduce the early and late skin and subcutaneous reactions.