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CT simulation as a pretreatment quality assurance tool for elliptical MammoSite® balloons
Oral Presentations / Brachytherapy 8 (2009) 105e180
depths (d). Scatter increased as d increased, with dose reductions 1 cm outside the lateral field edge of 50% and 90% at d 5 3 cm and d 5 0 cm, respectively. Non-optimized dose uniformity on the skin was approximately 15%. Using optimized dwell weightings, in-field dose uniformity on the skin improved by about 5%, with greater improvements observed for the largest applicator. Optimized dwell weightings did not affect planar dose uniformity within 1% for dO 3 cm. Ion chamber measurements of depth dose were in good agreement with Monte Carlo results (see Table). Maximum, minimum, and average differences to Monte Carlo results were within 2% for all three applicators. The largest disparities were located at d˜8 cm, and were attributed to scattering environment differences where higher measured results were likely due to increased backscatter from the table supporting the PS. Film depth-dose measurements were also in good agreement (see Table) with Monte Carlo results. Maximum, minimum, and average differences to Monte Carlo results over the 0-8 cm range of comparison were also within 2%. For measured results relative to Monte Carlo results, agreement disparity increased linearly (0.01%/cm). This was attributed to decreased film signal at depth, possible mislocation of the film relative to the applicator centralaxis (estimated positional accuracy within 0.3 cm), possible mislocation of the film as a function of depth (estimated positional accuracy within 0.15 cm) near the film edge/surface, and signal aberration at the film edge/ surface where 100% was defined. Ion chamber measured increases in dose at d 5 8 cm were attributed to differences in the larger scattering environment of the film setup. Dose profiles for a fixed depth determined using film were within 3% of Monte Carlo PS results inside the field for all depths studied, with larger variations observed outside the field in the
135
area of lowest dose. The average differences of film to Monte Carlo results at d 5 3 cm over the -6 cm to + 6 cm lateral range of dose profile comparison were approximately 1% for all three D-shaped applicators. Conclusions: Characterization of D-applicator dose distributions using multiple dosimetry techniques demonstrated agreement typically within 3%.
PO2 CT simulation as a pretreatment quality assurance tool for elliptical MammoSiteÒ balloons Laura Doyle, Amy Harrison, Ying Xiao, Yan Yu, Rani Anne, Haisong Liu Radiation Oncology, Thomas Jefferson University Hospital, Philadelphia, PA. Purpose: To outline a streamlined approach for pre-treatment daily quality assurance of the elliptical MammoSiteÒ balloon and highlight some of the potential uncertainties associated with this applicator. Methods and Materials: Two patients were implanted with the 4 cm x 6 cm elliptical MammoSiteÒ balloon. Each patient received a planning CT scan and 10 subsequent pre-treatment CT scans with seed markers in place, in lieu of time consuming simulation films. The scans were evaluated on our standard 3D treatment planning system, (CMS FocalSim) as follows: The angle of the external beam centered on the elliptical balloon and perpendicular to the catheter was determined on the pre-treatment CT and verified for each fraction, and orthogonal DRRs
136
Abstracts / Brachytherapy 8 (2009) 105e180 This process has helped to identify potential errors and implement corrective actions.
PO3 A comparative clinical study and dosimetry planning experience with the new ConturaÔ multi-lumen versus MammoSiteÒ singlelumen high-dose-rate balloon breast applicators under the RTOG 0413 protocol Serban Morcovescu, M.S.,1 Jeffrey D. Morton, M.D.,2 1Medical Physics, AROS LLC, Colleyville, TX; 2Radiation Oncology, Texas Oncology Denton, Denton, TX.
were generated. From these images, the long axis, short axis, and center position were determined prior to each treatment. Nucletron’s Oncentra Brachy Planning system can be used to confirm and quantify a variation of significant magnitude. This software allows for the rapid and accurate placement of the central lumen along an orthogonal axis using interactive three dimensional views. Once the catheter is defined along an axis, a definitive measurement of the variation can be accurately assessed. This analysis can be done using a limited CT scan with a reconstructed view of the balloon volume. Results: The catheter in the elliptical balloon can be subject to a significant shift relative to the balloon. The distal tip of the catheter can protrude past the distal edge of the balloon, or retract into the balloon cavity, shifting as much as 6 mm. If this variation is not accounted for by altering the dwell positions, PTV coverage can decrease by up to 17%. With our model of producing a DRR perpendicular to the long axis of the balloon with marker seeds in place, the center position of the balloon is easily and accurately located and the catheter position is verified. The source position simulator is used to verify adequate clearance of the source to the distal most dwell position prior to treatment with a new or adjusted dwell position. The average time to complete this QA procedure is about 5 minutes. Conclusions: The elliptical MammoSiteÒ balloon is a more challenging applicator than the traditional spherical balloon. Thorough quality assurance must be performed on a daily basis and can potentially be more time consuming, but with 3D virtual simulation using standard treatment planning software the process can be both quick and effective.
Purpose: In January 2008, SenoRX, Inc. clinically launched its product, the new ConturaÔ MLB applicator, believed to be a better solution for certain cases unfit for PBI (partial breast irradiation) using a similar device, the MammoSiteÒ (Hologic) single-lumen balloon, due to either minimal balloon-to-skin distance, balloon symmetry or tissue-balloon conformance. Our purpose is to present our own clinical experience with both applicators, in a comparative study meant to highlight the relevant advantages of one device over the other, in view of the RTOG 0413 protocol. Methods and Materials: This investigation was conducted on a BrachyVisionÔ 3D (Varian Medical Systems, Inc., Palo Alto, CA) TPS and considered ten (10) cases elected to be treated with the ConturaÔ balloon. CT simulation was done with a Toshiba CT scanner (GE Healthcare, USA) and treatment delivery was performed using a VariSource HDR Afterloader (Varian). The treatment plans were designed following the RTOG 0413 planning guidelines. All five (5) available channels were used when creating plans with the ConturaÔ balloon. Single and multiple dwell position surrogate plans were then designed for each of the ten cases, using only the centered lumen of the ConturaÔ balloon, in order to mimic the use of a MammoSiteÒConturaÔ (MMc) applicator. For each patient, the outcome of the three plans were then compared and analyzed both from a dosimetrical perspective and from the treatment delivery hands-on experience perspective as well. 3D treatment planning and DVH analysis was employed in order to evaluate geometric and dosimetric parameters. Results: The intrinsic design of the ConturaÔ MLB applicator corroborated with an automated plan optimization process that considered the use of all its five (5) channels, contributed to a generally better dosimetrical characterization of the target volumes, when trying to limit the Maximum Skin Dose (MSD) to less then 145% of the Prescription Dose (PD). Coverage Indexes for both PTV and PTV_EVAL structures, as defined in the RTOG 0413 protocol, were evaluated. With ConturaÔ, the PTV Coverage Index e CI1 is better by an additional 1.5e3.5% compared to the MMc balloon. An increase of V150 and V200 values were recorded for ConturaÔ compared with MMc, in the range of 1.0-2.0 cc (V150) and 0.1-1.0 cc (V200), while mantaining acceptable limits for both. The most common limiting factor for the use of interstitial PBI is the MSD. While improving the coverage of both PTV and PTV_EVAL with the ConturaÔ, the MSD was reduced by 8.012.0% of PD compared to the MMc. Close and thorough monitoring of the balloon positioning during the treatment course is also essential, as rotation of the balloon may occur. Conclusions: The symmetry of the balloon no longer plays a crucial role with the ConturaÔ balloon, since adequate shaping of the dose cloud can be achieved by diferential loading of off-centered cathethers. Better conformity can also be achieved with the ConturaÔ balloon due to availability of a suction/vacuum chanel that allows immediate action at the time of the initial CT simulation, when air or/and seroma trapped around the balloon can be removed. The better dosimetrical outcome that the ConturaÔ MLB applicator potentially offers comes with a price though: it involves a more time-consuming planning process and more extensive quality assurance program, that includes prior to each fraction balloon position monitoring and adjustments, incision site retaping and rebandaging. Overall, compared to the simulated MammoSiteÒ-ConturaÔ balloon, better target coverage was possible with the new ConturaÔ MLB applicator while being able to reduce the MSD values and to achieve better conformity.
depths (d). Scatter increased as d increased, with dose reductions 1 cm outside the lateral field edge of 50% and 90% at d 5 3 cm and d 5 0 cm, respectively. Non-optimized dose uniformity on the skin was approximately 15%. Using optimized dwell weightings, in-field dose uniformity on the skin improved by about 5%, with greater improvements observed for the largest applicator. Optimized dwell weightings did not affect planar dose uniformity within 1% for dO 3 cm. Ion chamber measurements of depth dose were in good agreement with Monte Carlo results (see Table). Maximum, minimum, and average differences to Monte Carlo results were within 2% for all three applicators. The largest disparities were located at d˜8 cm, and were attributed to scattering environment differences where higher measured results were likely due to increased backscatter from the table supporting the PS. Film depth-dose measurements were also in good agreement (see Table) with Monte Carlo results. Maximum, minimum, and average differences to Monte Carlo results over the 0-8 cm range of comparison were also within 2%. For measured results relative to Monte Carlo results, agreement disparity increased linearly (0.01%/cm). This was attributed to decreased film signal at depth, possible mislocation of the film relative to the applicator centralaxis (estimated positional accuracy within 0.3 cm), possible mislocation of the film as a function of depth (estimated positional accuracy within 0.15 cm) near the film edge/surface, and signal aberration at the film edge/ surface where 100% was defined. Ion chamber measured increases in dose at d 5 8 cm were attributed to differences in the larger scattering environment of the film setup. Dose profiles for a fixed depth determined using film were within 3% of Monte Carlo PS results inside the field for all depths studied, with larger variations observed outside the field in the
135
area of lowest dose. The average differences of film to Monte Carlo results at d 5 3 cm over the -6 cm to + 6 cm lateral range of dose profile comparison were approximately 1% for all three D-shaped applicators. Conclusions: Characterization of D-applicator dose distributions using multiple dosimetry techniques demonstrated agreement typically within 3%.
PO2 CT simulation as a pretreatment quality assurance tool for elliptical MammoSiteÒ balloons Laura Doyle, Amy Harrison, Ying Xiao, Yan Yu, Rani Anne, Haisong Liu Radiation Oncology, Thomas Jefferson University Hospital, Philadelphia, PA. Purpose: To outline a streamlined approach for pre-treatment daily quality assurance of the elliptical MammoSiteÒ balloon and highlight some of the potential uncertainties associated with this applicator. Methods and Materials: Two patients were implanted with the 4 cm x 6 cm elliptical MammoSiteÒ balloon. Each patient received a planning CT scan and 10 subsequent pre-treatment CT scans with seed markers in place, in lieu of time consuming simulation films. The scans were evaluated on our standard 3D treatment planning system, (CMS FocalSim) as follows: The angle of the external beam centered on the elliptical balloon and perpendicular to the catheter was determined on the pre-treatment CT and verified for each fraction, and orthogonal DRRs
136
Abstracts / Brachytherapy 8 (2009) 105e180 This process has helped to identify potential errors and implement corrective actions.
PO3 A comparative clinical study and dosimetry planning experience with the new ConturaÔ multi-lumen versus MammoSiteÒ singlelumen high-dose-rate balloon breast applicators under the RTOG 0413 protocol Serban Morcovescu, M.S.,1 Jeffrey D. Morton, M.D.,2 1Medical Physics, AROS LLC, Colleyville, TX; 2Radiation Oncology, Texas Oncology Denton, Denton, TX.
were generated. From these images, the long axis, short axis, and center position were determined prior to each treatment. Nucletron’s Oncentra Brachy Planning system can be used to confirm and quantify a variation of significant magnitude. This software allows for the rapid and accurate placement of the central lumen along an orthogonal axis using interactive three dimensional views. Once the catheter is defined along an axis, a definitive measurement of the variation can be accurately assessed. This analysis can be done using a limited CT scan with a reconstructed view of the balloon volume. Results: The catheter in the elliptical balloon can be subject to a significant shift relative to the balloon. The distal tip of the catheter can protrude past the distal edge of the balloon, or retract into the balloon cavity, shifting as much as 6 mm. If this variation is not accounted for by altering the dwell positions, PTV coverage can decrease by up to 17%. With our model of producing a DRR perpendicular to the long axis of the balloon with marker seeds in place, the center position of the balloon is easily and accurately located and the catheter position is verified. The source position simulator is used to verify adequate clearance of the source to the distal most dwell position prior to treatment with a new or adjusted dwell position. The average time to complete this QA procedure is about 5 minutes. Conclusions: The elliptical MammoSiteÒ balloon is a more challenging applicator than the traditional spherical balloon. Thorough quality assurance must be performed on a daily basis and can potentially be more time consuming, but with 3D virtual simulation using standard treatment planning software the process can be both quick and effective.
Purpose: In January 2008, SenoRX, Inc. clinically launched its product, the new ConturaÔ MLB applicator, believed to be a better solution for certain cases unfit for PBI (partial breast irradiation) using a similar device, the MammoSiteÒ (Hologic) single-lumen balloon, due to either minimal balloon-to-skin distance, balloon symmetry or tissue-balloon conformance. Our purpose is to present our own clinical experience with both applicators, in a comparative study meant to highlight the relevant advantages of one device over the other, in view of the RTOG 0413 protocol. Methods and Materials: This investigation was conducted on a BrachyVisionÔ 3D (Varian Medical Systems, Inc., Palo Alto, CA) TPS and considered ten (10) cases elected to be treated with the ConturaÔ balloon. CT simulation was done with a Toshiba CT scanner (GE Healthcare, USA) and treatment delivery was performed using a VariSource HDR Afterloader (Varian). The treatment plans were designed following the RTOG 0413 planning guidelines. All five (5) available channels were used when creating plans with the ConturaÔ balloon. Single and multiple dwell position surrogate plans were then designed for each of the ten cases, using only the centered lumen of the ConturaÔ balloon, in order to mimic the use of a MammoSiteÒConturaÔ (MMc) applicator. For each patient, the outcome of the three plans were then compared and analyzed both from a dosimetrical perspective and from the treatment delivery hands-on experience perspective as well. 3D treatment planning and DVH analysis was employed in order to evaluate geometric and dosimetric parameters. Results: The intrinsic design of the ConturaÔ MLB applicator corroborated with an automated plan optimization process that considered the use of all its five (5) channels, contributed to a generally better dosimetrical characterization of the target volumes, when trying to limit the Maximum Skin Dose (MSD) to less then 145% of the Prescription Dose (PD). Coverage Indexes for both PTV and PTV_EVAL structures, as defined in the RTOG 0413 protocol, were evaluated. With ConturaÔ, the PTV Coverage Index e CI1 is better by an additional 1.5e3.5% compared to the MMc balloon. An increase of V150 and V200 values were recorded for ConturaÔ compared with MMc, in the range of 1.0-2.0 cc (V150) and 0.1-1.0 cc (V200), while mantaining acceptable limits for both. The most common limiting factor for the use of interstitial PBI is the MSD. While improving the coverage of both PTV and PTV_EVAL with the ConturaÔ, the MSD was reduced by 8.012.0% of PD compared to the MMc. Close and thorough monitoring of the balloon positioning during the treatment course is also essential, as rotation of the balloon may occur. Conclusions: The symmetry of the balloon no longer plays a crucial role with the ConturaÔ balloon, since adequate shaping of the dose cloud can be achieved by diferential loading of off-centered cathethers. Better conformity can also be achieved with the ConturaÔ balloon due to availability of a suction/vacuum chanel that allows immediate action at the time of the initial CT simulation, when air or/and seroma trapped around the balloon can be removed. The better dosimetrical outcome that the ConturaÔ MLB applicator potentially offers comes with a price though: it involves a more time-consuming planning process and more extensive quality assurance program, that includes prior to each fraction balloon position monitoring and adjustments, incision site retaping and rebandaging. Overall, compared to the simulated MammoSiteÒ-ConturaÔ balloon, better target coverage was possible with the new ConturaÔ MLB applicator while being able to reduce the MSD values and to achieve better conformity.