bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐142: Sensitivity of Treatment Assessment to Different PET Normalization Techniques
Authors: Jallow N , Vanderhoek M , Barbee D , Song C , Jeraj R
Published: April 2010

Purpose: Assessment of treatment outcome based on PET imaging requires accurate and robust patient‐specific normalization of tracer uptake. This study investigates the sensitivity of treatment response as a function of various PET imaging normalization methods. Materials and Methods: Fourteen patients undergoing molecular targeted therapy received [18F]FLT (cellular proliferation marker) PET/CT scans that were acquired pre, mid and post therapy. SUV normalization was performed using body weight (BW), body surface area (BSA), and lean body mass (LBM). Dependence of treatment response outcome on the normalization technique was evaluated both experimentally and analytically. Additional normalization of the SUVs was performed using an external reference source comprised of Ge‐68 to reduce the inherent variations in scanner stability. Robustness of treatment response outcome was assessed by evaluating ratios of both corrected and uncorrected SUVs. Results: The absolute mean values of the SUVs were 2.3 ± 0.8, 1.4 ± 0.4, and 0.05±0.02 for BW, LBM, and BSA respectively. Despite a substantial difference in their values, the treatment response ratios between the post and pre scans were found to be within 0.3% on average for all types of SUV normalizations. For the largest weight change of about 6%, the difference between treatment response ratios was less than 1% for SUVs based on BSA versus LBM and it was about 3%for SUVs based on BSA versus BW. After reference source normalization, the treatment response ratios shifted by 5.5%. For post and mid scans, the treatment response ratios shifted by −2.4% after reference source normalization. Conclusions: The type of SUV normalization technique used does not affect treatment response assessment unless there is a significant change in weight. On the other hand, the treatment response is influenced by normalization with the external reference source.
SU‐FF‐J‐155: The Influence of Material Assignment On Monte Carlo Dose Calculations for Kilovoltage Small Animal Radiotherapy
Authors: Bazalova M , Zhou H , Keall P , Graves E
Published: April 2010

Purpose: To investigate the sensitivity of tissue assignment for Monte Carlo (MC) dose calculations using a kilovoltage beam for small animal radiotherapy, and to test the feasibility of dual energy microCT (DEmCT) imaging for material determination. Method and Materials: MC dose calculations for 34 ICRU‐44 tissue types were performed in the EGSnrc/DOSXYZnrc code, using a 120kVp x‐ray beam. Each tissue type was modeled as a 5mm diameter spherical inhomogeneity in a soft tissue cylindrical phantom and a treatment plan with five 5mm diameter isocentric beams was simulated. The mean absorbed dose as a function of tissue density (r) and atomic number (Z) was studied. Two phantoms with five known materials were scanned with 70kVp and 120kVp beams and the r and Z of these materials were extracted. DEmCT tissue segmentation was also applied on 70kVp and 120kVp CT images of a euthanized mouse. Results: The MC simulations demonstrate that inaccurate tissue segmentation can result in large dose calculation errors, up to 40% if adipose is assigned as soft tissue. The MC simulations also show a strong correlation between the Z of a tissue and the dose to the tissue. Preliminary results indicate that DEmCT material extraction using a microCT scanner is feasible; the mean error on the r and Z extraction of the five materials was 2.5% and 3.4%, respectively. The mouse DEmCT extracted tissues follow the data of ICRU‐44 tissues. Conclusions: It was demonstrated that tissue segmentation is one of the key steps in Monte Carlo treatment planning for small animal radiotherapy using a microCT scanner. Preliminary results indicate that dual energy microCT extraction has the potential to increase the accuracy of the conventional tissue segmentation scheme.
SU‐FF‐J‐160: Spatially Fractionated Radiation Therapy (GRID) On Implanted Tumors Using a Small Animal Conformal Radiation Therapy System
Authors: Sharma S , Webber J , Nathan K , Griffin R , Moros E , Corry P
Published: April 2010

Purpose: To deliver spatially fractionated (GRID) radiation fields to murine tumors using a high precision small animal conformal radiation therapy device (SACRTD). Method and Materials: The SACRTD is a “gantry” based image‐guide system with a special collimating assembly that allows field sizes down to 0.5 mm in diameter at isocenter. The precise positioning of the target/beam is achieved by a six‐degree of freedom robotic system (Adept Technology, Pleasanton, CA) which has positional repeatability of ±0.020mm in XYZ directions. The system can be used to deliver small GRID fields with varying open‐to‐close area ratios. Immunohistochemistry for DNA damage after 10 Gy to a 1cm depth GRID therapy was performed in B16 murine melanoma tumors. The GRID pattern consisted of an array of 7 beams of 1 mm in diameter at isocenter with center‐to‐center separation of 2 mm. Tumor growth rates and cell survival were assessed. Results: The exit dose recorded by Gafchromic film confirmed that the GRID radiation pattern was delivered with high precision. Histology showed the radiation induced DNA strand breaks in the open regions of the GRID field. Approximately 55% of clonogenic cells in the B16 tumors were killed by the single GRID dose. Interestingly, mice receiving GRID alone did not have significant tumor growth delay compared to untreated tumors. However, in the group that received GRID therapy followed by Anginex anti‐angiogenic peptide for 5 days there was a noticeable delay in tumor growth compared to tumors receiving 10 Gy GRID alone. Conclusion: This preliminary biological study shows the usefulness and flexibility of the SACRTD to deliver precise radiation patterns to implanted tumors in small animals. The system facilitates in vivo radiobiological studies and promotes translational research in radiation oncology.
SU‐FF‐J‐162: In Vivo Biological Evaluation of Micro‐CT Based 3D Conformal Radiotherapy System
Authors: Nelson G , Rodriguez M , Zhou H , Lee A , Wu J , Tran P , Felsher D , Keall P , Graves E
Published: April 2010

Purpose: Typically small animal irradiation is performed in the laboratory using single field techniques using lead blocks for beam shaping. This method is incapable of the accuracy of dose distribution and delivery to small regions possible in an average cancer center. To mitigate this, a collimator was installed in a microCT system which made the system capable of accurate dose delivery. By collimating the x‐ray beam from the CT, we are able to shape the beam down to 1mm at the isocenter of the system. With a bed capable of 3d movement, we are able to move the target to the isocenter of the system for treatment. We evaluated the effectiveness of dose delivery in vivo and tracked the biological effects of various doses and targets. Methods: Using multiple mice, we tested several aspects of the system. We evaluated the ability to treat a small target by using a small aperture and delivering dose to spontaneous lung tumors grown in transgenic mice. Immediately after treatment the mice were sacrificed, the tumor regions sliced for histology, and H2AX stained to evaluate double strand DNA breaks. In addition, subcutaneous teratomas expressing luciferase were also irradiated and monitored with bioluminescence imaging to assess radiation response. Results: The system is capable of accurate dose delivery, as verified by phantom and in vivo studies. It is able to deliver dose to targeted areas while avoiding dose to others, and produce biological effects measurable by both histologic and macroscopic imaging methods. Dose fractionation allows the system to deliver a greater total dose within the dose rate constraints. Conclusion: The microCT/RT system is capable of dose delivery closely related to clinical systems. This opens many possibilities to perform pre‐clinical studies related to radiotherapy.
SU‐FF‐J‐166: The Development of a Precise Electron Irradiator for Small Animal Studies
Authors: Chao T , Lee C , Chen A , Tu S , Tung C
Published: April 2010

Purpose: This study focuses on the development, validation, and evaluation of a precise MV‐electron irradiator. Compared with all other prototypes which use photons to irradiate small animals, an electron irradiator has many advantages in its shallow dose distribution. Method and Materials: Two major approaches including simulation and measurement were used to evaluate the feasibility of an electron animal irradiator. These simulations/measurements were taken in three different fields (a 6 cm square field, and 30 and 4 mm diameter circular fields) and with two different energies (6 and 18 MeV). A PTW Semiflex chamber i n a PTW‐MP3 water tank, a PTW Markus chamber type 23343, a PTW diamond detector type 60003, and KODAK XV films were used to measure PDDs, lateral beam profiles, and output factors for either optimizing parameters of Monte Carlo simulation or to verify Monte Carlo simulation in small fields. Results: Results show good agreement for the comparisons of PDD (⩽ 2.5% for 6 MeV e; ⩽ 1.8% for 18 MeV e) and profiles (FWHM ⩽ 0.5 mm) between simulations and measurements on the 6 cm field. Greater deviation can be observed in the 4 mm field due to the partial volume effects of detectors. The output factor for the 18 MeV electron beam is 0.970 in the 30 mm field, and 0.610 in the 4 mm field; the FWHM of profiles for the 18 MeV electron beam is 32.6 mm in the 30 mm field, and 4.7 mm in the 4 mm field at the d90. Two different digital phantoms were also constructed, including a homogeneous cylindrical water phantom and a CT‐based heterogeneous mouse phantom, and were implemented into Monte Carlo to simulate the dose distribution with different electron irradiations. Conclusion: These results ensure that our proposed electron irradiator is feasible for precise small animal irradiation.
SU‐FF‐J‐169: A Hybrid Deformable Registration Method to Warp Image with Contrast
Authors: Lian J , Foskey M , Rosenman J , Tracton G , Chang S
Published: April 2010

Purpose: The delineation of the prostate on CT images is crucial for radiotherapy treatment planning. In order to help identify the prostate, contrast is often injected to the bladder when acquiring CT. Deformable image registration is used for dose accumulation, but unfortunately, all intensity driven algorithms fail to handle images with contrast. In addition, significant shape change of organs makes image registration less accurate. The purpose of this work is to develop a hybrid method to register images with contrast and large organ deformation. Method and Materials: Six pairs of CT images, one planning CT with bladder contrast and one daily treatment CT without any contrast, were retrospectively selected for this study. The prostate, bladder and rectum were contoured on both images. The contrasted bladder was replaced by pixel intensities of a Gaussian distribution. On each image, a ring of 3mm thickness was generated inward from the outline of contours of the bladder and rectum. The ring was masked with Hounsfield number −500 and 500 for the bladder and rectum, respectively. A fluid‐based deformable image registration method and a rigid body‐based method (for comparison purposes) were used to register pre‐processed images. The accuracy of registration was estimated by the coincidence index (CI). Results: The fluid image registration tool maps treatment day CT onto the contrasted planning CT with relatively high accuracy. The overlap of contours reached CI 89.5% for the prostate, 95.1% for the bladder and 83.9% for the rectum. The rigid body method resulted in CI 50.1% for the prostate, 52.1% for the bladder and 31.7% for the rectum. Conclusion: We develop a novel hybrid tool to register the images with contrast. It relatively accurately overlaps the organ with large deformation, which makes it a promising tool for dose accumulation.
SU‐FF‐T‐01: Investigation of Pagat Gel Dosimeter Application in Lowe Dose Rate Brachytherapy by Detemination of TG‐43 Parameters of Selectron Cs‐137 Source
Authors: Zehtabian M , Faghihi R , Meigooni A , Mosleh‐Shirazi M , Zahmatkesh M , Mehdizadeh S , Sina S , Nili M , Mansouri K
Published: April 2010

Purpose Nowadays, medical physicists need a dosimeter that can detect three‐dimensional (3‐D) dose distributions with high spatial resolution. To date, in combination with Magnetic Resonance Imaging (MRI), polyacrylamide gel (PAG) polymers are the most promising gel dosimetry systems that have the potential to verify 3‐D dose distributions delivered by clinical radiotherapy equipment. The purpose of this research is to investigate the application of PAGAT gel in dosimetry of a low dose rate (LDR) brachytherapy source, by simulation and experimental measurements of TG‐43 report parameters. Material and method Selectron Cs‐137 source, an LDR brachytherapy used in remote afterloading systems, is composed of active and dummy spherical pellets 2.5 mm in diameter. The gel was manufactured using the PAGAT gel dosimetry recipe of Venning et al. (2005). The gel dosimeter was manufactured inside a fume hood and under normal atmospheric conditions. Dosimetry of a spherical active source was done by means of the PAGAT gel. Results The results of Monte Carlo simulations are in good agreement with measurements and simulations of other investigators. The results of a 36 hour irradiation of PAGAT gel for measurement of F(r, θ) and g(r) showed that the measured R2 parameters were almost the same for different distances although the near points had been expected to receive more dose than the far points. In this experiment, 5 vials containing PAGAT gel were placed at different distances from the Cs‐137 teletherapy source and exposed to an equal dose (5 and 20 Gy). The results indicated that in dose rates less than 0.98 Gy/hr, the gel dosimeter did not respond while in high dose rates, the response of the gel dosimeter was reliable. Conclusion The experimental results of gel dosimetry suggest that PAGAT gel dosimeter does not have a suitable response in low dose rates.
SU‐FF‐T‐15: Comparison of Various Monte Carlo Codes for Brachytherapy Source Dosimetry
Authors: Meigooni A , Luerman C , Perez‐Calatayud J , Ballester F , Rivard M , Sowards K , Zehtabian M , Walmsley J
Published: April 2010

Purpose: Monte Carlo simulations are used for dosimetric evaluation of brachytherapy sources. Various investigators had demonstrated good agreement between the measured and simulated data while some others have shown discrepancies between the two methods. These discrepancies were attributed to the errors in cross section data, differences in phantom and source geometry and composition. However, the exact causes of these differences have not yet fully explored. The goal of this project is to verify the differences among the widely available Monte Carlo codes for brachytherapy source dosimetry. Material and method: These investigations are based on VariSource , Model VS2000, IsoAid Advantage Model IA1‐125A, and Best Industries Model Best2335 sources. TG‐43 parameters of these sources have been determined using 6 different commonly utilized Monte Carlo codes. All the simulations would be performed in water and number of photons would be selected to provide statistical fluctuations better than better than 1%. Dose rate constant, radial dose functions and anisotropy function at 2 cm distance will be simulated for each source by each Monte Carlo code. Results: The results of these investigations indicate the more recent Monte Carlo code with the updated cross section data are in excellent agreement with each other for producing all of the TG‐43 parameters except 2D anisotropy functions at small angles (<10 degree). The older Monte Carlo codes or older cross section data have larger uncertainty in their results. Conclusion: The TG‐43 dosimetric parameters of the brachytherapy source can be simulated with the one of the Monte Carlo codes. It would be recommended to use one of the well established codes as a benchmark code for establishment of other codes in parameterization of the brachytherapy sources.
SU‐FF‐T‐23: Analysis of Dosimetric Quantities Associated with Partial Breast Brachytherapy
Authors: O'Farrell D , Steward A , Racine M , Lyatskaya Y , Devlin P , Cormack R
Published: April 2010

Purpose: Radiation dose to the heart and lung are a concern in accelerated partial breast irradiation (APBI). This work presents an analysis of the metrics inherent to high dose rate APBI using a brachytherapy source. Method and Materials: Five patients receiving APBI brachytherapy, and 4 patients, who were simulated in both supine and prone position for XRT, were contoured. Dose to the heart and lung were calculated for all potential dwell locations within the contoured breast for a range of potential dwell times. Summary volume and dose metrics were calculated for heart and lung as function of minimum distance (dmin) to the normal structures. The distribution of minimum distances was then compared for the prone and supine patients. Results: Dose metrics such as the D10cc were patient specific and not well suited to parameterization. Volume metrics such as V10Gy tend to have similar behavior and may be characterized as a function of dmin. The characterization provides a measure of the normal tissue dose parameters that are achievable as a function of dmin. While prone position shift the distribution of lung to breast distances towards greater value, the distribution of heart to breast distances is shifted to smaller distances. Conclusion: Characteristic curves of the achievable volume metrics as a function of minimum distance from implant to normal structures are presented. These curves may be helpful in the decision to use APBI brachytherapy based on the location of the cavity. The choice of treatment position affects the distribution of breast tissue, though the effect on distance to heart and lung differs.
SU‐FF‐T‐27: Dosimetric Evaluation of a Redesigned High‐Dose Rate (HDR) Vaginal Applicator for Treatment of Cervical Cancer with Extension Into Lower Vagina
Authors: Cheng Harry
Published: April 2010

Purpose: The vaginal applicator was redesigned to reduce the rectal and bladder dose to optimal level for patient having cervical cancer with extension into the lower vagina without compromising the dose to the point A. Compared with the Miami applicator; it can be implanted easily without affecting by necrotic nature of the tumour around cervix. Method and Materials: The original set of the vaginal applicator consists of different lengths of intrauterine tube with different angles and different diameters of cylinder. Six cylindrical holes were drilled at 30°, 90°, 150°, 210°, 270° and 330° positions where are located 5 mm away from the surface of the cylinder. Six OncoSmart ProGuide Needles (Nucletron) were placed into the holes to form a multi‐channel vaginal applicator which allows dose optimization to the area of interest. The applicator was anchored by a Perspex lock and affixed to a base plate to prevent displacement. A set of CT images were taken to reconstruct the applicator. Using HDR brachytherapy planning system, the standard dose distribution was adjusted to achieve the prescribed dose which is 7 Gy at point A and 5 mm away from the cylinder surface. After insertion in the patient, one set of orthogonal films was taken to localize the ICRU points with reference to the applicator. Doses to the bladder and rectum are optimized to approximately 80% and 75% respectively of the prescribed dose. The biologically effective dose (BED) to all ICRU points was compared. Results: The redesigned multi‐channel cylinder with intrauterine tube allows much better control than the original vaginal applicator. The BED of the rectum and target decreased by 20% and increased by 24% respectively during brachytherapy. Conclusions: The redesigned multi‐channel vaginal applicator enables conformal isodose shaping and dose control to organs at risk without compromising the dose to the target.
SU‐FF‐T‐31: Time Dependence of Energy Spectra of Brachytherapy Sources and Its Impact On Their Half and the Tenth Value Layers
Authors: Yue N , Chen Z , Hearn R , Rodgers J , Nath R
Published: April 2010

Purpose: To investigate the impacts of spectral time dependence of brachytherapy source on shielding requirements and the Nth value layers NthVL). Method and Materials: The photon energy spectrum of brachytherapy sources is influenced by several factors including radionuclide purity. Existence of impurities in radionuclide substrate may not only alter the spectrum but also cause time dependent changes in the spectrum. A semi‐empirical formalism was established to take this time dependence into account and was used to calculate the NthVL thicknesses for Model 200 seed. Originally, the was purified to a level less than 0.006% of the total activity, consisting of impurity that emits high energy photons and has longer half‐life of 244 days which leads to spectral time dependence. The time dependence of the NthVL and shielding requirements were analyzed. Results: The 1st HVL and 1st TVL steadily increased with time for about 200 days and then reached a plateau. The increases at plateau were more than 1000 times. The 2nd and 3rd TVLs reached their plateaus in about 100 and 60 days, respectively, and the increases were about 1900% and 233%, respectively. All the TVLs demonstrated a similar time dependence pattern; with significant increases and eventual approach to a plateau. Conclusions: The time dependence of emitted photon spectra from brachytherapy sources may introduce significant variations of the NthVL with time if impurities are present. The importance of these variations should not be underestimated in considerations of radiation protection and detection. It should also be noted that the use of new processing technologies since 2005, the likelihood of existence of impurities in seeds is dramatically reduced, as demonstrated in the measured spectra from current Model 200 seeds. This study points out the importance of performing periodic photon spectroscopy of manufactured radioactive seeds.
SU‐FF‐T‐37: Contura Multilumen Balloon (MLB) Registry Trial: Initial Dosimetric Experience
Authors: Todor D , Vicini F , Arthur D , Julian T , Lyden M
Published: April 2010

Purpose: The Contura MLB registry trial is a prospective, non‐randomized, multiple site accelerated partial breast irradiation (APBI) study designed to compare the dosimetric efficacy of the Contura™MLB against a single central lumen balloon device. The preliminary dosimetric comparisons, based on the first 74 patients are presented. Materials and Methods: All patients are enrolled prior to Contura™MLB placement based on eligibility criteria. After successful post lumpectomy placement of the Contura MLB is confirmed by CT scan, three dosimetric plans are generated: 1)multi‐lumen(ML), 2)central‐lumen/multi‐dwell(CL‐MD) and 3)central‐lumen/single‐dwell(CL‐SD). For similar target coverage (D95>95%), V150, V200 and maximum skin and ribs dose of the three plans are compared. Results: The ML plans succeeded in meeting all dosimetric criteria in 78% of the cases whereas the CL‐MD and CL‐SD plans only succeeded in 54% and 40%, respectively. The ML plan delivered max skin dose ⩽125% in 92% of cases as compared to 79.7% and 69.9% for the CL‐MD and CL‐SD plans generated for the same patients. When the balloon‐skin spacing measured ⩽7mm, the ML plan delivered a reduced max skin dose in 28.8% of cases compared to CL‐MD plans and 34.2% of cases using CL‐SD. The mean skin dose reduction was 17.2% and 29.4% respectively. When the rib distance measured ⩽5mm, the ML plan delivered reduced dose to the closest rib in 27.4% of cases compared to CL‐MD plans and 32.9% when compared to CL‐SD. The mean rib dose reduction was 12.2% and 31.8% respectively. Conclusion: This initial comparison supports the hypothesis that using multiple offset lumens allows optimization of target coverage while minimizing dose to skin and chest wall. Completion of this trial is needed for the confirmation of this hypothesis, and to explore the clinical scenarios where the Contra MLB can provide the safest solution while extending PBI use in breast conserving therapy.
SU‐FF‐T‐41: A Study of Effectiveness of Dose Volume Histogram Based Multi‐Solutions Optimization Algorithm in High Dose Rate Brachytherapy for the Prostate
Authors: Pokharel G , Sadeghi A , Prestidge B
Published: April 2010

Purpose: To investigate the effectiveness of multi‐solutions dose volume histogram based optimization (MDVHO) for high dose rate (HDR) brachytherapy for the prostate. Method and Materials: This study consists data from 20 patients who underwent ultrasound based real time HDR brachytherapy for the prostate using the treatment planning system (TPS) called Oncentra Prostate (vs. 3) by Nucletron. The treatment plans for all the patients treated were optimized using graphical optimization (GRO). The GRO is the on screen manipulation of isodose lines slice by slice manually and quality of plan heavily depends on planner expertise and experience. Later, treatment plans were created and optimized using MDVHO algorithm with same set of dose constraints, same number of catheters as in GRO. MDVHO is an anatomic based deterministic optimization algorithm. Several Pareto optimal solutions were obtained by varying the weighting factors of composite objective function in finite steps with adequate resolutions. These solutions were then stored in the database of TPS and final solution that best fulfilled the clinical goal was selected from the pool of alternative solutions using decision engine. Results: The mean dose to 100% of planning target volume (PTV) V100 due to MDVHO and GRO were 95.03% and 97.56% of prescription dose respectively which was not statistically significant (P = 0.066) using student pair t‐test at 5% level of significance. The mean conformal index (0.65 vs. 0.50) was statistically higher (P = 0.002) with MDVHO in comparison to GRO. The mean dose (Dmean) and dose to 10% volume (D10) of critical structures such as urethra, bladder and rectum were comparable with MDVHO and GRO. Conclusion: MDVHO algorithm can provide conformal plans with comparable dosimetric indexes to PTV and critical structures in comparison to GRO within clinically reasonable amount of time independent of planner experience and expertise.
SU‐FF‐T‐45: Sensitivity of the 50 KVp Xoft Axxent Electronic Brachytherapy Skin Applicator to Flattening Filter Design, Source‐Filter Position, Applicator Alignment and Surface Collimation
Authors: Holt R , Axelrod S
Published: April 2010

Purpose: The Xoft Axxent Electronic Brachytherapy Skin Applicator and miniature x‐ray source combination can be used for superficial skin or surface treatments. The applicator is a 25 mm SSD cone (1.0–5.0 cm diameter) with an embedded flattening filter. The applicator and source are decoupled, which could lead to variations in dose profile. Several potential problems are investigated for this system. Method and Materials: Dose profiles of the 35 mm diameter cone were measured in solid water using GAFChromic EBT film and in water using a stereotactic diode. Two flattening filter designs were examined. The effect of rotating the source or applicator independently, tilting the applicator with respect to the surface, modifying the source‐filter distance, and skin collimation from 10 to 30 mm by means of tungsten aperture cutouts were examined. Results: The stepped disk filter design had flatness and asymmetry of 8.3% and 3.1%. The chamfered filter was 14.8% and 0.7% respectively. Rotation of the source and applicator produced a minimal change in flatness and asymmetry, with less than 2% change in flatness or asymmetry. The stepped‐disk filter flatness changed by up to 7% with filter source displacement. Tipping the applicator off of the perpendicular axis by 6 degrees changed the symmetry by 14%. Beam profiles for cutouts ranging from 1.0–3.0 showed little change in flatness and asymmetry, and the sharp edges of the PTW were retained. Conclusion: The stepped filter design is superior. The source‐filter is sufficiently concentric to prevent profile shifts, but the dose is very sensitive to the filter‐source distance, as predicted by the geometric model. Small tilts of up to 2 degrees, or a 1 mm gap on one side of the cone, can be tolerated. Skin collimation preserves both profile and penumbra. Research Sponsored by Xoft, Inc.
SU‐FF‐T‐46: Dosimetric Comparison of Superficial X‐Rays and a Custom HDR Surface Applicator for the Treatment of Superficial Cancers
Authors: Merz B , Feldmeier J , Parsai E
Published: April 2010

Purpose: The purpose of this study was to design and characterize a custom HDR applicator for the treatment of cancers in the region 0–5 mm, comparing it to the dosimetric properties of the Maxima R‐100 superficial x‐ray unit. Accelerator produced electrons of energy 4–6 MeV with the addition of a buildup bolus are in competition with superficial X‐rays and are very well suited for the treatment of shallow lesions as the maximum dose, Dmax, is brought to the surface. With this applicator, HDR may be a modality suited for treatment of Basal and squamous cell carcinomas, Kaposi's sarcoma, and Merkel cell carcinomas. Method and Materials: The superficial machine was characterized in terms of percent depth dose, beam profiles, and dose rate. Similar measurements were taken from a Varian Varisource HDR unit applying a newly designed copper HDR applicator. Both data sets were compared in terms of dosimetric properties and clinical efficacy. Results: The applicator alone had an unacceptably large dose inhomogeneity across the the HDR beam so a primary filter, modified filter, and secondary lead collimator were designed and manufactured to help shape the dose into a profile similar to the superficial applicator. Beam flatness and width were nearly replicated but beam divergence was more pronounced for the HDR applicators. Conclusions: Percent depth dose measurements for the HDR applicator showed a dose fall‐off nearly identical to superficial x‐rays rather than the assumed inverse square dose fall‐off. Flatenning the HDR beam through this filtered applicator provides means to deliver uniform dose to surface lesions with superior treatment delivery while implementing the HDR billing codes.
SU‐FF‐T‐47: Automated Planning Volume Definition for HDR Brachytherapy: Application to Intraluminal Treatment of the Bile Duct
Authors: Lee E , Cha K , Zaider M
Published: April 2010

Purpose: Although surgery remains the treatment of choice, patients with carcinoma of the extrahepatic bile duct who are not candidates for surgical resection(∼75%) are treated palliatively with radiation therapy and/or chemotherapy. Intraluminal LDR or HDR brachytherapy has the well‐documented advantage of delivering a large target dose, while significantly sparing surrounding healthy tissues. Typically, treatment planning is performed with respect to source‐guide catheter(s) inserted along the biliary canal under fluoroscopic guidance. The prescription hull refers to a volume at a distance of 0.5–1.0 cm from catheter(s). Because of the irregular shape of the source guides, manual contouring of the prescription hull is time consuming and subject to errors. We describe, and illustrate with actual treatment plans, an automatic algorithm to outline the planning volume. Methods and Materials: The contouring of a single catheter can be considered as the trajectory generated by a moving ball. The path of the ball forms a guide curve, which is given by the digitized‐coordinates of the source‐guide catheter. Given a radius r that defines the thickness of the PTV, our volume‐definition algorithm applies curve fitting via Ferguson spline interpolation, followed by circle generation and sphere generation. For multiple catheters, the algorithm is more complex, requiring curve fitting, warping, slicing, and linking to obtain the resulting tumor shape. Results: For the biliary intraluminal case, the algorithm takes only seconds to generate a 3D‐planning volume. Applying it to complex hypothetical cases reveals that it handles irregular tumor volumes and shapes well, and returns a 3D‐planning volume within 1 CPU‐minute. Conclusion: The automatic volume‐definition algorithm works reliably and quickly, and results in plans that are demonstratively superior to those obtained by manual planning. Furthermore, the planning volume is a necessary input to computer‐based plan optimization. The volume‐definition algorithm improves the treatment dosimetric conformity, a factor that may contribute to improved clinical outcome.
SU‐FF‐T‐53: Comparative Dosimetry of the Xoft Axxent Electronic Brachytherapy Skin Applicator at 50 KVp with Film, Chamber, and Diode in Various Backscatter Media
Authors: Holt R , Rusch T
Published: April 2010

Purpose: The Xoft Axxent Electronic Brachytherapy Skin Applicator and miniature x‐ray source delivers superficial dose to shallow depths using 50 kVp x‐rays over small target areas (⩽ 20 cm2). The Xoft Skin Applicator is a 25 mm SSD cone (1.0–5.0 cm diameter) with an embedded flattening filter which acts to both filter the low energy x‐rays from the beam and to mitigate the radial inverse squares peak on a flat surface. Method and Materials: The relative depth and profile dose characteristics of the 35 mm diameter cone were measured in water and solid water using film (Kodak EDR2, GAFChromic EBT), ionization chambers (A16, RK, Marcus) and stereotactic diode (SFD). Correction factors for diode backscatter response and solid water density are derived by comparison. Beam profile metrics for penumbral transition width (PTW), field width, flatness and asymmetry were computed. A virtual SSD was computed using in‐air diode measurements. The beam energy is defined using a TG‐61 HVL approach at 25 cm distance. Results: The first and second HVL for this system are 1.4 mm and 2.5 mm. A VSSD of 22 mm was computed, differing from the nominal 25 mm SSD. PTWs, ranging from 0.4 to 5.0 mm, correlated with chamber size. Field widths from 38.8 to 42.0 mm correlated with chamber size; 38.2 mm width is expected at 2 mm depth. Flatness ranged from 2.0 to 9.6%, and asymmetry ranged from +/− 0.9 to 6.2%. A linear depth correction can be made solid water density of 1.13, while a non‐linear depth dependant diode backscatter correction is required. Conclusion: The Xoft skin applicator provides depth doses similar to other 50kVp superficial systems. The dose profiles are similar to short SSD applicators. These comparisons provide the clinical physicist with options for measuring energy and beam characteristics. Research Sponsored by Xoft, Inc.
SU‐FF‐T‐56: A Simple Method for Dose Fusion From Multi‐Modality Treatment: Brachytherapy to External Beam Therapy
Authors: Ko S , Cao M , Slessinger E , Johnstone P , Das I
Published: April 2010

Purpose: In case of suboptimal dose to 90% volume (D90) obtained from post‐implant dosimetry study after prostate brachytherapy, it is difficult to determine what needs to be done next. If additional external beam radiation were needed, then there is no standard operating procedure for boost treatment. In order to avoid treating prostate regions that received adequate or very high dose from radioactive seeds, we need to transfer the dose matrix information from seed implant software to external beam treatment software as accurate as possible. Therefore, we have explored the feasibility of such task that is accomplished by using commonly used Variseed® and Eclipse® programs with proper interface. Method and Materials: Four weeks after prostate seed implant, CT scans were performed on the whole pelvis of patients using our standard protocol for prostate planning. The acquired CT datasets were reconstructed using different sizes of field of view (FOV). The images with limited FOV focusing on prostate were imported into Variseed® for post‐operation implant evaluation, while images with full FOV were imported in Eclipse® treatment planning system (TPS) for future boost planning. Results: Dose matrix resulted from the post‐op evaluation was exported from Variseed® in standard DICOM format and imported into Eclipse TPS. The brachytherapy dose matrix was registered with the patient images with full FOV in Eclipse TPS. Targets for dose boost were defined based on the isodose curves from brachytherapy. An external photon beam plan was then generated to delivery dose to compensate for selected underdosed cold regions. Conclusion: Accurate external beam radiation treatment planning utilizing cold‐spot treating IMRT technique can be accomplished using our planning protocols. The proposed technique can be utilized to safely deliver additional external radiation dose using IMRT technique after suboptimal brachytherapy procedure.
SU‐FF‐T‐60: SPECT‐Guided Radiation Therapy Planning for Yttrium‐90 Microspheres Therapy
Authors: Goddu S , Rangaraj D , Yang D , Apte A , Low D , Parikh P , Myerson R
Published: April 2010

Purpose: 90Y based microspheres are used for unresectable liver metastases by selectively transporting the radioactive spheres to the metastases via hepatic‐arteries. This is due to the fact that liver tumors receive most of their blood supply from the hepatic‐arteries, while the normal liver receives the blood through the portal‐vein. The microspheres prescription is based on the body surface area and several studies attempted dose‐calculations using MIRD formalism assuming activity distribution is uniform in tumors and liver. In reality, microsphere distribution is not uniform because the radioactivity selectively administered through the hepatic‐artery. In the absence of commercial radiation treatment planning systems for microsphere therapy, it becomes difficult to determine the radiation dose distribution and the dose volume histograms to determine the target coverage and dose‐volume tolerance of normal liver. In this work we have outlined a method based on intensity volume histogram (IVH) determined from 99mTc‐macroaggregated albumin (MAA) SPECT scan. Methods: Both volumetric SPECT/CT scans and contrast‐enhanced CT scan were acquired for the patient. Liver is contoured on both the SPECT/CT and the contrast CT. Tumor is contoured only on the contrast CT. Both scans were then registered in CERR (Computational Environment for Radiotherapy Research). Intensity values of SPECT scan are converted to dose distribution based on their relative intensity values and the assumption that the microspheres would have the same intensity distribution as the MAA scan. Result: DVH is derived from the converted dose distribution and the contoured structures. Administrable activity is adjusted based on the normal liver DVH with an ultimate goal of keeping 800–1000cc of normal liver below 30 Gy. This methodology is also helpful in determining the activity to be delivered incase of retreatment taking into account the previously administered dose to the normal liver. Conclusion: Using DVH of the normal liver administrable activity can be determined
SU‐FF‐T‐63: Comparison of Optimized Interstitial HDR Brachytherapy Plans Using Adaptive Simulated Annealing Algorithm and Physical, Biological and Hybrid Cost Functions
Authors: Yao R , Templeton A , Chu J , Liao Y , Turian J
Published: April 2010

Purpose: Comparing the optimized interstitial High Dose Rate (HDR) Brachytherapy plans based on physical, biological and hybrid cost functions. Method and Materials: Using an Adaptive Simulated Annealing (ASA) algorithm we have developed a method to optimize dwell times for HDR brachytherapy treatment planning. Three cost functions are used: (1) a function based on doses to PTV; (2) a logistic function based on generalized Equivalent Uniform Dose (gEUD) of PTV and organs‐at‐risk (OAR), and (3) a hybrid function, which includes physical dose‐based objectives of PTV and gEUD‐based objectives of PTV and OAR. We applied these functions to three gynecological cancer cases. Optimizations are run up to 75000 iterations. The prescription dose is normalized to the isodose volume covering 95% of the PTV. Plans are evaluated by DVH, isodose distributions, gEUD, tumor control probability (TCP), normal tissue complication probability (NTCP), homogeneity index (HI), and overdose index (OI) of the target and OARs. Results: The optimized results of three cases based on the three cost functions are summarized. The physical model produces best target dose uniformity and lowest target maximum dose. However, the doses to OARs are also the highest. The gEUD model is able to increase gEUD to the target, reduce gEUD to the OARs, but produce less uniform dose and larger hot spots in the target. By choosing proper penalty factors, the hybrid model can produce balanced plans to achieve high gEUD to the target, low gEUD to the OARs and smaller hot spots on target. Conclusion: We are able to optimize the dwell times of interstitial HDR brachytherapy using an ASA algorithm. The optimization results can be controlled by choosing different cost functions and penalty factors depending on clinical needs of patients.
SU‐FF‐T‐77: Measurement of the Average Seed Strength in a Mick Cartridge
Authors: Plenkovich D
Published: April 2010

Purpose: Develop an efficient method for the measurement of the average strength of brachytherapy seeds according to the 2008 recommendations of the AAPM Low Energy Brachytherapy Source Calibration Working Group. Method and Materials: The reentrant well ionization chamber is calibrated, at ADCL, for a single radioactive seed in a single‐seed holder. When the seeds, loaded in Mick cartridges, are received from the manufacturer, it is necessary, only one time, to open only one cartridge. The strength of each seed in this cartridge is measured in the reentrant well chamber using the single‐source holder and the ADCL calibration factor. As the seeds are removed from the Mick cartridge, one by one, the well chamber measurement is taken of the Mick cartridge, with the remaining seeds, in the Mick cartridge holder. Since the strength of each seed has been measured, the total strength of these remaining seeds in the Mick cartridge can be calculated. Results: Calibration coefficients have been determined for a Mick cartridge containing any number from 1 to 15 125I or 103Pd seeds. Using these coefficients the average strength of the seeds in the cartridge, with any number of seeds, can be determined with one single measurement in the reentrant well chamber. After the initial process, used to calculate the calibration coefficients, there is no more need to remove any seed from any cartridge. Typically, one‐minute measurements of the electric charge generated in the reentrant well chamber are used for each Mick cartridge. Conclusion: A time‐saving method for measurement of the average activity of 125I and 103Pd seeds has been developed. Only a one‐minute measurement of the electric charge generated in a reentrant well chamber is needed to calculate the average strength of the radioactive seeds in the Mick cartridge loaded with any number from 1 to 15 seeds.
SU‐FF‐T‐80: Hybrid Image Guided Radiation Therapy for Hypofractionated Prostate IMRT: Feasibility Study
Authors: Thongphiew D , Zhu X , Wu Q , Wu Q , Yin F
Published: April 2010

Purpose: In prostate IGRT employing hypofractionation, two methods are commonly used: patient re‐positioning and re‐planning. We propose a hybrid IGRT technique in this study. The dosimetric benefits and efficiency improvement of the technique is quantitatively evaluated by comparing with the two conventional techniques. Method and Materials: Five prostate patients were studied, each had 1 planning CT and 11 daily CBCTs. The structure‐of‐interest (SOIs) including CTV (prostate and seminal vesicles), bladder, and rectum were contoured on CT and CBCTs. Initial IMRT plans were generated on Eclipse. Three IGRT techniques (“re‐positioning”, “re‐plan”, and “hybrid”) were applied on each CBCT. “Re‐positioning” utilizes target soft‐tissue matching for patient position correction. “Re‐plan” re‐aligns the patient then reoptimizes the original plan using daily SOIs. “Hybrid” first finds the best‐fit plan from plan‐library for the daily CBCT. If no suitable plan found, “re‐plan” is performed and new plan is added to library. The daily and cumulative doses were calculated and compared for all three techniques. Results: (1) Cumulative dose: For CTV and bladder, the difference among the three IGRT techniques are <1% and <5% at all dose levels. “Re‐positioning” slightly underdoses the CTV. For rectum, the differences between “re‐plan” and “hybrid” are <2% at all dose levels. The Dmean/D30 doses to the rectum of the “re‐positioning” are 5%/10% higher than those of “re‐plan”. (2) Daily dose: The average(min‐max) D30 dose for “re‐positioning” and “hybrid” are [rectum: 84%(67%–94%) and 70%(51%–78%)] and [bladder: 57%(42%–75%) and 59%(46%–70%)]. (3) “Hybrid” required the re‐optimization to be performed 6, 4, 1, 2, and 3 times for patient 1 to 5, respectively. Conclusion: Hybrid‐IGRT retains the target coverage and critical structure sparing of the “re‐plan”, yet it reduces the workload of the re‐optimization by >70% and therefore is a viable option for hypofractionated prostate IGRT. Conflict of Interest: Research sponsored by Varian Medical Systems.
SU‐FF‐T‐93: Assessment of Dose Conformality and the Effects of Inter‐ and Intra‐Fraction Motion On the Dose Distribution Intensity Modulated Proton Radiotherapy for Locally Advanced Prostate Cancer: A Treatment Planning Study
Authors: Qamhiyeh S , Stuschke M , Geismar D , Kaiser A , Abu‐Jawad J , Farr J
Published: April 2010

Purpose: Locally advanced prostate cancers show a strong dose‐response relation. Intensity modulated proton therapy (IMPT). Small spot size proton pencil beam scanning, has the potential of excellent dose conformality to the target volumes with good normal tissue sparing. However, the effect of patient and organ motion on the dose distribution is more evident in highly conformal dose distributions. Here the target volume coverage and dose to the risk organs were assessed using repeated CT scans. Methods and Materials: A planning CT and 2 low dose CTs were obtained during the planning session at 5 min and 10 min in order to estimate intra‐fraction motion. In addition, another planning CT was taken at a later stage of the radiotherapy. Furthermore, three radio‐opaque fiducial markers were implanted into the prostate at least one week prior taking the planning CT to verify the position of the prostate. The conformality and robustness of the dose distributions resulting from two beam field arrangements were investigated. The plans were verified on the repeat low dose CTs to investigate the intra‐fractional motion and on the second planning CT for the inter‐fractional motion. Results: good coverage of the PTVs and CTVs and good dose homogeneity for all beam arrangements was found despite the recorded intra‐fractional motion. Less changes in the mean and maximum doses to the bladder and rectum were registered when slightly oblique field arrangement was used (85° and 275°). The PTV coverage deteriorated due to inter‐fractional motion resulting in cold and hot spots, depending on the motion pattern. However, the angulations of the fields by mere 5° resulted in robust plans. Conclusion: The parallel opposed lateral field arrangement resulted in undesirable sensitivity to motion in comparison to opposed fields slightly oblique by 5 degrees.