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Use of respiratory gating and tomosynthesis reconstruction in cone beam CT-based brachytherapy treatment planning
Abstracts / Brachytherapy 6 (2007) 77e118 Value Layer (HVL) and Tenth Value Layer (TVL) have been derived. Also an analytical expression for the calculation of lead and concrete barrier thicknesses necessitated by any combination of distance, dose limit, and occupancy and facility workload is presented. The potential effect of attenuation within the patient to radiation shielding calculations is also evaluated. Results: From the transmission curves HVL and TVL for both lead and concrete were obtained for each radionuclide. HVL for concrete are: 65 mm (Ir-192), 32 mm (Yb-169), 20 mm (Ce-144), 20 mm (Tm-170), 20 mm (W-181), 14 mm (Ga-153) and 8 mm (Sm-154). HVL for lead are: 2.8 mm (Ir-192), 0.25 mm (Yb-169), 0.13 mm (Ce-144), 0.17 mm (Tm170), 0.14 mm (W-181), 0.08 mm (Ga-153) and 0.06 mm (Sm-154). Furthermore, the attenuation by the patient in a typical gynaecologycal application vary between 0.5 (Ir-92) and 0.2 (Sm-154) depending upon the radionuclide. Conclusions: The radionuclides studied are of potential use in brachytherapy. The broad beam transmission curves have been obtained using Monte Carlo methods and HVL and TVL values have been deduced from these curves. The reduction of HVL values for these new radionuclides compared to those for Ir-192 are significant.
PO-28 An independent dosimetry calculation of intracavitary brachytherapy plans utilizing the ring applicator Albert M. Sabbas, Ph.D., Fridon Kulidzhanov, Ph.D., Samuel Trichter, M.Sc. Radiation Oncology, New York Presbyterian Hospital/Cornell Campus, New York, NY. Purpose: To independently check the dosimetry calculations of brachytherapy plans that utilize the ring intracavitary applicator to treat carcinoma of the cervix. Methods and Materials: Gynecological cases with carcinoma of the cervix are now routinely treated with high dose rate brachytherapy. We have been using the two channel CT-compatible ring applicator towards this purpose. The ring applicator comes in a variety of tandem lengths (2, 4, 6 cm) and ring angles (30, 45, and 60 degrees) to accommodate individual anatomies. The ring circumference is 10 cm allowing for 20 dwell positions, at 0.5 cm spacing, to completely surround the cervical os. This feature provides more flexibility in tailoring the dose distributions compared with the three channel tandem and ovoids applicators. As is the case with all computer-generated plans, the calculations have to be independently checked prior to treating the patient. A 5% agreement between the independent check and the output of the HDR planning system is considered satisfactory. Our independent check computes the dose to point A which is the usual prescription point for these intracavitary applications. For a given ring angle relative to the patient’s axis, the corresponding tandem is always perpendicular to the plane of the ring. We use this feature to reconstruct two orthogonal planes that are used to measure distances from point A to the center of each dwell position. One plane, containing the tandem and point A, is used to record distances from point A to each dwell position along the tandem. The other plane coincides with the plane of the ring and is used to measure the distance from each dwell position along the ring and the point A’s projection on this plane. The total distance to each of the ring dwell positions is then computed knowing the perpendicular distance of point A to the plane of the ring, normally around 2 cm. These distances, along with the dwell times and the source activity are then input into a spreadsheet which yields the dose to point A. Results: The independent dosimetry calculation is carried out prior to each brachytherapy application. The results of these calculations have been within the 5% tolerance level with the majority falling within 3% from the output of the brachytherapy planning system. Conclusions: We have found that this spreadsheet-based independent dosimetry calculation is easy to implement due to the fixed geometry of the ring relative to the tandem and the ability of the brachytherapy planning system to reconstruct any orientation plane.
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PO-29 Use of respiratory gating and tomosynthesis reconstruction in cone beam CT-based brachytherapy treatment planning Amir G. Sadeghi, Ph.D.1,2 Dave Murry1,2 Bradley R. Prestidge, M.D.1,2 Larry L. Partain3 Hassan Mostafavi3 1Radiation Oncology, Texas Cancer Clinic, San Antonio, TX; 2Radiological Sciences, University of Texas Health Science Center, San Antonio, TX; 3Research and Development, Varian Medical Systems, Inc., Palo Alto, CA. Purpose: We present our initial results from the use of respiratory gating during cone beam CT and digital tomosynthesis (DST) reconstruction in order to increase the image quality for cone beam CT-based brachytherapy treatment planning. Methods and Materials: Several prostate and breast patients as well as CIRS pelvic and chest phantom were scanned using Varian Acuity CBCT scanner consists of a conventional X-ray tube and flat panel imager with a maximum filed of view of 25 25 cm and 512 512 pixel resolution. The scans were acquired with and without Varian respiratory gating RPM system. To acquire a 3D volume, the gantry is rotated 360 degree for a full scan using 125 KvP, 80 MA and 25 ms. The digital tomosynthesis reconstruction used image sequences acquired over a limited gantry movement. The scans form the patients and phantoms were also compared between Cone BeamCT and conventional CT. Varian’s BrachyVision treatment planning was used in both sets of images for dose calculation, image resolution, Houndsfields numbers and patient’s anatomy and contouring. Results: The images form CBCTwith motion correction created a substantial artifact throughout the entire scan for all the patients and phantoms. The motion artifact was significantly decreased when respiratory gating was applied or the images were reconstructed using tomosynthesis. Conclusions: Slow moving gantry and patient motion during CBCT acquisition contributed to more artifact overall compare to regular conventional CT however Respiratory gating and tomosynthesis reconstruction during CBCT image acquisition has improved image. Varian Medical Systems, Inc. provides support for one graduate student working on this research. PO-30 Modifications in the TG-43U1 formalisms for accurate dose calculation around elongated brachytherapy sources Shahid B. Awan, Ph.D.1,2 Kai Dou, Ph.D.1,2 Sharifeh A. Dini, M.S.1,2 Ali S. Meigooni, Ph.D.1,2 Manzoor Hussain, Ph.D.1,2 1Radiation Medicine, University of Kentucky, Lexington, KY; 2Physics, University of the Punjab, Lahore, Pakistan. Purpose: Recently, RadioCoilÔ Pd-103 brachytherapy sources have been introduced for interstitial prostate implants to eliminate the problems such as seed migration, embolization, clumping and bunching associated with seed type sources. However, this innovative design could not be benefited for clinical application due to several limitations. These limitations include pitfalls of TG-43 parameterization, inability of NIST source calibration, and shortcomings of treatment planning systems. At our institution we provided recommendations as an intermediate solution for two problems. However, the problems of treatment planning systems remained a challenge for the dose calculation with elongated sources. One of the problems associated with treatment planning system is an improper application of 2D anisotropy function for elongated sources. In our previous publication we demonstrated that the dose calculation around an elongated source can be performed by using a series of 1 cm linear source segments (LSS). However, discrepancies of up to 15% have been observed with LSS model, outside of the active length, which were attributed to the 2D anisotropy function F(r,q). Methods and Materials: In this project, the TG-43 protocol has been modified to facilitate the dosimetric evaluation of elongated sources. These evaluations were performed by experimental and theoretical determination of the TG-43U1 recommended parameters of 1.0 cm and 5.0 cm long RadioCoilÔ Pd-103 source in cylindrical coordinate system (CCS) and polar coordinate system (PCS). In addition, dose profiles along the transverse and longitudinal direction of a 5 cm long source have been
PO-28 An independent dosimetry calculation of intracavitary brachytherapy plans utilizing the ring applicator Albert M. Sabbas, Ph.D., Fridon Kulidzhanov, Ph.D., Samuel Trichter, M.Sc. Radiation Oncology, New York Presbyterian Hospital/Cornell Campus, New York, NY. Purpose: To independently check the dosimetry calculations of brachytherapy plans that utilize the ring intracavitary applicator to treat carcinoma of the cervix. Methods and Materials: Gynecological cases with carcinoma of the cervix are now routinely treated with high dose rate brachytherapy. We have been using the two channel CT-compatible ring applicator towards this purpose. The ring applicator comes in a variety of tandem lengths (2, 4, 6 cm) and ring angles (30, 45, and 60 degrees) to accommodate individual anatomies. The ring circumference is 10 cm allowing for 20 dwell positions, at 0.5 cm spacing, to completely surround the cervical os. This feature provides more flexibility in tailoring the dose distributions compared with the three channel tandem and ovoids applicators. As is the case with all computer-generated plans, the calculations have to be independently checked prior to treating the patient. A 5% agreement between the independent check and the output of the HDR planning system is considered satisfactory. Our independent check computes the dose to point A which is the usual prescription point for these intracavitary applications. For a given ring angle relative to the patient’s axis, the corresponding tandem is always perpendicular to the plane of the ring. We use this feature to reconstruct two orthogonal planes that are used to measure distances from point A to the center of each dwell position. One plane, containing the tandem and point A, is used to record distances from point A to each dwell position along the tandem. The other plane coincides with the plane of the ring and is used to measure the distance from each dwell position along the ring and the point A’s projection on this plane. The total distance to each of the ring dwell positions is then computed knowing the perpendicular distance of point A to the plane of the ring, normally around 2 cm. These distances, along with the dwell times and the source activity are then input into a spreadsheet which yields the dose to point A. Results: The independent dosimetry calculation is carried out prior to each brachytherapy application. The results of these calculations have been within the 5% tolerance level with the majority falling within 3% from the output of the brachytherapy planning system. Conclusions: We have found that this spreadsheet-based independent dosimetry calculation is easy to implement due to the fixed geometry of the ring relative to the tandem and the ability of the brachytherapy planning system to reconstruct any orientation plane.
109
PO-29 Use of respiratory gating and tomosynthesis reconstruction in cone beam CT-based brachytherapy treatment planning Amir G. Sadeghi, Ph.D.1,2 Dave Murry1,2 Bradley R. Prestidge, M.D.1,2 Larry L. Partain3 Hassan Mostafavi3 1Radiation Oncology, Texas Cancer Clinic, San Antonio, TX; 2Radiological Sciences, University of Texas Health Science Center, San Antonio, TX; 3Research and Development, Varian Medical Systems, Inc., Palo Alto, CA. Purpose: We present our initial results from the use of respiratory gating during cone beam CT and digital tomosynthesis (DST) reconstruction in order to increase the image quality for cone beam CT-based brachytherapy treatment planning. Methods and Materials: Several prostate and breast patients as well as CIRS pelvic and chest phantom were scanned using Varian Acuity CBCT scanner consists of a conventional X-ray tube and flat panel imager with a maximum filed of view of 25 25 cm and 512 512 pixel resolution. The scans were acquired with and without Varian respiratory gating RPM system. To acquire a 3D volume, the gantry is rotated 360 degree for a full scan using 125 KvP, 80 MA and 25 ms. The digital tomosynthesis reconstruction used image sequences acquired over a limited gantry movement. The scans form the patients and phantoms were also compared between Cone BeamCT and conventional CT. Varian’s BrachyVision treatment planning was used in both sets of images for dose calculation, image resolution, Houndsfields numbers and patient’s anatomy and contouring. Results: The images form CBCTwith motion correction created a substantial artifact throughout the entire scan for all the patients and phantoms. The motion artifact was significantly decreased when respiratory gating was applied or the images were reconstructed using tomosynthesis. Conclusions: Slow moving gantry and patient motion during CBCT acquisition contributed to more artifact overall compare to regular conventional CT however Respiratory gating and tomosynthesis reconstruction during CBCT image acquisition has improved image. Varian Medical Systems, Inc. provides support for one graduate student working on this research. PO-30 Modifications in the TG-43U1 formalisms for accurate dose calculation around elongated brachytherapy sources Shahid B. Awan, Ph.D.1,2 Kai Dou, Ph.D.1,2 Sharifeh A. Dini, M.S.1,2 Ali S. Meigooni, Ph.D.1,2 Manzoor Hussain, Ph.D.1,2 1Radiation Medicine, University of Kentucky, Lexington, KY; 2Physics, University of the Punjab, Lahore, Pakistan. Purpose: Recently, RadioCoilÔ Pd-103 brachytherapy sources have been introduced for interstitial prostate implants to eliminate the problems such as seed migration, embolization, clumping and bunching associated with seed type sources. However, this innovative design could not be benefited for clinical application due to several limitations. These limitations include pitfalls of TG-43 parameterization, inability of NIST source calibration, and shortcomings of treatment planning systems. At our institution we provided recommendations as an intermediate solution for two problems. However, the problems of treatment planning systems remained a challenge for the dose calculation with elongated sources. One of the problems associated with treatment planning system is an improper application of 2D anisotropy function for elongated sources. In our previous publication we demonstrated that the dose calculation around an elongated source can be performed by using a series of 1 cm linear source segments (LSS). However, discrepancies of up to 15% have been observed with LSS model, outside of the active length, which were attributed to the 2D anisotropy function F(r,q). Methods and Materials: In this project, the TG-43 protocol has been modified to facilitate the dosimetric evaluation of elongated sources. These evaluations were performed by experimental and theoretical determination of the TG-43U1 recommended parameters of 1.0 cm and 5.0 cm long RadioCoilÔ Pd-103 source in cylindrical coordinate system (CCS) and polar coordinate system (PCS). In addition, dose profiles along the transverse and longitudinal direction of a 5 cm long source have been