- Email: [email protected]
Maintaining Treatment Position in Brachytherapy Procedures using Digital Tomosynthesis
Abstracts / Brachytherapy 9 (2010) S23eS102 such that the %D90 (relative dose received by 90% of PTV_EVAL) was within 5% for all plans. The %V95 (percent of the target volume receiving 95% of the prescription dose), %V100, %V150, %V200, and %V300 were extracted from the dose volume histograms for each plan. The Dose Homogeneity Index (DHI, defined as DHI 5 [(%V100 - %V150)/%V100]) was calculated for each plan. Results: For all three applicators, the MMeBx plan achieved a superior DHI compared to the eBx or the 192Ir HDR plan, as shown in Table 1. Dose Homogeneity Index (DHI) MODALITY PLAN 192
Iridium ( Ir HDR) Electronic (eBx) Mixed Modality (MMeBx)
MIAMI
SAVI
CONTURAÔ
0.54 0.47 0.61
0.44 0.33 0.50
0.52 0.35 0.53
In the case of the Miami cylinder, the MMeBx plan also achieved a lower Max Dose Bladder (178.0%) compared with both the eBx (260.5%) and the 192Ir HDR (213.3%) plans. With regard to the SAVI, the MMeBx plan also achieved a lower Max Skin Dose (78.6%) relative to eBx (96.2%) and 192Ir HDR (93.6%). The ConturaÔ MMeBx plan achieved a lower Max Dose Skin (101.2%) as well (eBx 105.4%; 192Ir HDR 106.1%). In addition, the MMeBx plan achieved a lower mean dose breast (95.9%) compared with both the eBx (128%) and the 192Ir HDR (96.4%) plans. Conclusions: Mixed modality brachytherapy (MMeBx) provides the physician with additional dose-shaping flexibility that can be tailored to the individual patient’s anatomy and thus can achieve a higher therapeutic ratio.
S61
comparative purposes, the gold standard for this study was a 360-degree cone beam CT (CBCT) reconstruction based on 360 projections. Results: By combining three sweeps; two orthogonally-centered L-arm sweeps (one vertically-centered and one laterally-centered) and one vertically-centered C-arm sweep, the measured volume of the central sphere fell within 1.0% of the measured volume of the sphere in the CBCT-based reconstruction. Central slices in the coronal, sagittal, and axial planes of this reconstruction are shown from left-to-right, respectively, in the bottom right of the figure. Also producing a measured volume within 1.0% of the gold standard is a two-sweep combination consisting of two orthogonally-centered L-arm sweeps (one verticallycentered and one laterally-centered). Conclusions: The presented study shows that multi-arc tomosynthesis reconstructions can be generated with high volumetric image fidelity when compared with CBCT volumes. The feasibility of using this system for acquiring three-dimensional images for purposes such as patient alignment is shown. Better matching between treatment and planning positions will create more reproducible treatments in brachytherapy procedures.
PD12 Maintaining Treatment Position in Brachytherapy Procedures using Digital Tomosynthesis Jacob A. Gersh, Ph.D., David B. Wiant, Ph.D., Michael T. Munley, Ph.D., Mahta M. McKee, M.S., Yuchuan Wei, Ph.D., June D. King, C.M.D., Alan H. Baydush, Ph.D. Radiation Oncology, Wake Forest University School of Medicine, Winston-Salem, NC. Purpose: The integration of three-dimensional imaging into the treatment planning of brachytherapy procedures reinforces the necessity for the actual treatment position to match the planning position. The method introduced herein demonstrates how tomosynthesis (or limited-arc-angle cone beam CT) can be used to provide three-dimensional imaging while the patient remains in the treatment position. This study determines suitable radiographic image-sweep combinations that can be performed in a clinical setting for three-dimensional image reconstruction using tomosynthesis. Materials and Methods: Reconstructions were acquired from projections obtained using the Digital Integrated Brachytherapy Unit, or IBU-D (Nucletron B.V., Veenendaal, The Netherlands). Similar to a C-arm-based fluoroscopic imaging system, this system can acquire digital radiographic images while rotating around a patient. The unique and advantageous aspect of this system is that images can be acquired while the source-anddetector are at canted angles. This is achievable through the suspension of a rotating C-arm by an independently-rotating L-arm. The motion of the C-arm and the L-arm around an anthropomorphic phantom are shown in the figure in the top-left and top-right, respectively. This study used the cylindrical phantom shown as a CT-based volumetric reconstruction in the lower-left of the figure. This water-filled phantom consisted of a central contrast-filled sphere, attached by a wand and surrounded by several water equivalent sphere-and-wands. Using in-house software, 44 three-dimensional image sets were reconstructed, each unique in that they were comprised of varying combinations of L-arm and C-arm image sweeps. Each independent sweep rotates the source-and-imager by a total of 40 degrees. To maintain approximate dose equivalence, all 44 reconstructions were based on a total of 36 projection images. The volume of the central, contrast-filled sphere was used as the fidelity metric and was determined through slice-by-slice contouring. For
PD13 A Method to Check the Design and Specification of Seeds in LowDose-Rate Brachytherapy Michael Doring, Frank-Andre Siebert, Ph.D. Radiotherapy, University Hospital of Schleswig-Holstein, Campus Kiel, Kiel, Germany. Purpose: Using 125I or 103Pd in LDR brachytherapy for prostate implants is a worldwide well-established method. An important factor for the success of the treatment is the exact knowledge of the dose distribution. Each seed type has its own dosimetric characteristics. These can be expressed for example by the TG-43 calculation method that allow for an accurate dose calculation. Due to the different design of the seed models they have an own dosimetric characterization. When using a modern seed treatment planning system the user must rely on that the design of the seeds and the TG-43 data set that is based on this design. It is a consumption that the individual seeds are within the seed types hardware specification. The internal design of six different seed models (Bebig S06, Bebig S17, BrachySeed, IBt, Oncura 6734, Theragenics Modell 200) was investigated and the resulting dimensions can be compared with their specifications. Materials and Methods: To analyze the design of the sources nonradioactive seeds were at first casted in a plastic resin in a cuboid form of about 20 mm x 10 mm x 5 mm size. The casted seeds were manually grinded in longitudinal direction of the seeds until the half of the source was cut. In this way it was possible to visualize the internal design of the seeds over the whole source length. To check that the seed is grinded exactly halfway and consistently over the whole seed length thin marker plates with well known thickness were casted directly beneath the sources. When the grinding procedure reaches the marker this was an indicator that the source was cut halfway. After this process a microscope with an attached digital camera was used to take pictures of the cut seed.
Iridium ( Ir HDR) Electronic (eBx) Mixed Modality (MMeBx)
MIAMI
SAVI
CONTURAÔ
0.54 0.47 0.61
0.44 0.33 0.50
0.52 0.35 0.53
In the case of the Miami cylinder, the MMeBx plan also achieved a lower Max Dose Bladder (178.0%) compared with both the eBx (260.5%) and the 192Ir HDR (213.3%) plans. With regard to the SAVI, the MMeBx plan also achieved a lower Max Skin Dose (78.6%) relative to eBx (96.2%) and 192Ir HDR (93.6%). The ConturaÔ MMeBx plan achieved a lower Max Dose Skin (101.2%) as well (eBx 105.4%; 192Ir HDR 106.1%). In addition, the MMeBx plan achieved a lower mean dose breast (95.9%) compared with both the eBx (128%) and the 192Ir HDR (96.4%) plans. Conclusions: Mixed modality brachytherapy (MMeBx) provides the physician with additional dose-shaping flexibility that can be tailored to the individual patient’s anatomy and thus can achieve a higher therapeutic ratio.
S61
comparative purposes, the gold standard for this study was a 360-degree cone beam CT (CBCT) reconstruction based on 360 projections. Results: By combining three sweeps; two orthogonally-centered L-arm sweeps (one vertically-centered and one laterally-centered) and one vertically-centered C-arm sweep, the measured volume of the central sphere fell within 1.0% of the measured volume of the sphere in the CBCT-based reconstruction. Central slices in the coronal, sagittal, and axial planes of this reconstruction are shown from left-to-right, respectively, in the bottom right of the figure. Also producing a measured volume within 1.0% of the gold standard is a two-sweep combination consisting of two orthogonally-centered L-arm sweeps (one verticallycentered and one laterally-centered). Conclusions: The presented study shows that multi-arc tomosynthesis reconstructions can be generated with high volumetric image fidelity when compared with CBCT volumes. The feasibility of using this system for acquiring three-dimensional images for purposes such as patient alignment is shown. Better matching between treatment and planning positions will create more reproducible treatments in brachytherapy procedures.
PD12 Maintaining Treatment Position in Brachytherapy Procedures using Digital Tomosynthesis Jacob A. Gersh, Ph.D., David B. Wiant, Ph.D., Michael T. Munley, Ph.D., Mahta M. McKee, M.S., Yuchuan Wei, Ph.D., June D. King, C.M.D., Alan H. Baydush, Ph.D. Radiation Oncology, Wake Forest University School of Medicine, Winston-Salem, NC. Purpose: The integration of three-dimensional imaging into the treatment planning of brachytherapy procedures reinforces the necessity for the actual treatment position to match the planning position. The method introduced herein demonstrates how tomosynthesis (or limited-arc-angle cone beam CT) can be used to provide three-dimensional imaging while the patient remains in the treatment position. This study determines suitable radiographic image-sweep combinations that can be performed in a clinical setting for three-dimensional image reconstruction using tomosynthesis. Materials and Methods: Reconstructions were acquired from projections obtained using the Digital Integrated Brachytherapy Unit, or IBU-D (Nucletron B.V., Veenendaal, The Netherlands). Similar to a C-arm-based fluoroscopic imaging system, this system can acquire digital radiographic images while rotating around a patient. The unique and advantageous aspect of this system is that images can be acquired while the source-anddetector are at canted angles. This is achievable through the suspension of a rotating C-arm by an independently-rotating L-arm. The motion of the C-arm and the L-arm around an anthropomorphic phantom are shown in the figure in the top-left and top-right, respectively. This study used the cylindrical phantom shown as a CT-based volumetric reconstruction in the lower-left of the figure. This water-filled phantom consisted of a central contrast-filled sphere, attached by a wand and surrounded by several water equivalent sphere-and-wands. Using in-house software, 44 three-dimensional image sets were reconstructed, each unique in that they were comprised of varying combinations of L-arm and C-arm image sweeps. Each independent sweep rotates the source-and-imager by a total of 40 degrees. To maintain approximate dose equivalence, all 44 reconstructions were based on a total of 36 projection images. The volume of the central, contrast-filled sphere was used as the fidelity metric and was determined through slice-by-slice contouring. For
PD13 A Method to Check the Design and Specification of Seeds in LowDose-Rate Brachytherapy Michael Doring, Frank-Andre Siebert, Ph.D. Radiotherapy, University Hospital of Schleswig-Holstein, Campus Kiel, Kiel, Germany. Purpose: Using 125I or 103Pd in LDR brachytherapy for prostate implants is a worldwide well-established method. An important factor for the success of the treatment is the exact knowledge of the dose distribution. Each seed type has its own dosimetric characteristics. These can be expressed for example by the TG-43 calculation method that allow for an accurate dose calculation. Due to the different design of the seed models they have an own dosimetric characterization. When using a modern seed treatment planning system the user must rely on that the design of the seeds and the TG-43 data set that is based on this design. It is a consumption that the individual seeds are within the seed types hardware specification. The internal design of six different seed models (Bebig S06, Bebig S17, BrachySeed, IBt, Oncura 6734, Theragenics Modell 200) was investigated and the resulting dimensions can be compared with their specifications. Materials and Methods: To analyze the design of the sources nonradioactive seeds were at first casted in a plastic resin in a cuboid form of about 20 mm x 10 mm x 5 mm size. The casted seeds were manually grinded in longitudinal direction of the seeds until the half of the source was cut. In this way it was possible to visualize the internal design of the seeds over the whole source length. To check that the seed is grinded exactly halfway and consistently over the whole seed length thin marker plates with well known thickness were casted directly beneath the sources. When the grinding procedure reaches the marker this was an indicator that the source was cut halfway. After this process a microscope with an attached digital camera was used to take pictures of the cut seed.