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Commissioning of a Prostate Model Created Using Knowledge-Based Planning as a Tool to Guide the Planning Process
S870
International Journal of Radiation Oncology Biology Physics
Materials/Methods: Nine patients with biopsy proven H&N tumors were enrolled on an IRB approved imaging protocol. Each patient was treated to 70 Gy in 33-35 fractions with concurrent chemotherapy when indicated. Daily pre-treatment imaging was performed with cone beam CT (CBCT), kV paired orthogonal x-ray and 6d stereoscopic x-ray imaging systems. The daily couch shifts were computed from offline matches and the vertical and lateral shifts were compared using linear regression with correlation being assessed using Pearson’s correlation coefficient (R). Bland-Altman analysis was also performed to assess for trends in the correlations. Results: The best mean shift correlation was observed between stereoscopic x-ray and orthogonal x-ray imaging (vertical R Z 0.67, lateral R Z 0.72) and orthogonal x-ray and CBCT (vertical R Z 0.66, lateral R Z 0.76). The CBCT and stereoscopic x-ray vertical shifts exhibited the worst correlation (vertical R Z 0.48, lateral R Z 0.71). For most patients, the vertical shifts had worse correlation than the lateral shifts. Overall, it was observed that the stereoscopic x-ray shifts were smaller than the CBCT or orthogonal x-ray shifts. We also observed that the shift correlations appeared to be worse in the earliest enrolled patients compared to the more recently enrolled patients. Initial inspection revealed that time on the table between imaging was much shorter for more recent patients as the imaging workflow efficiency was improved. Conclusions: This preliminary analysis revealed that the largest differences in shift information occur between stereoscopic x-ray and CBCT imaging. We generally found that shifts from stereoscopic imaging were smaller than CBCT or orthogonal x-ray, which could be explained by the additional rotational corrections inherent to the stereoscopic system. To date, there is no “gold standard” in terms of on-board imaging and our results confirm that not all imaging systems produce equal shifts when used on the same patient. In addition, our findings reinforce the need for efficient treatment workflows to minimize the risk of patient movement between imaging and treatment. Author Disclosure: N. Serrano: None. J. Evans: None. D. Asher: None. M.E. Schutzer: None. M. Fatyga: None. W. Sleeman: None. N. Dogan: None. S. Song: None.
accurate (-4% to 4%) and is likely to be due to the planning technique (Maximum dose objective) and the steep dose fall-off exhibited by the DVHs of these structures. The estimated DVHs were used to guide the optimization process without any user interaction (allowing 2% normalization) and yielded clinically acceptable plans 43% of the time. Additional runs were only necessary in three patients as a result of the inability of the plans to meet the clinical goals for the OARs. The reminder of the plans, that required additional runs; did so, due to the inability to meet the clinical goals of the target. Further planning was conducted to achieve acceptable target goals and had little effect on the DVHs of the OARs obtained after the user-free run (The DVHs agreed 94% of the time within 2% at the clinically relevant goals). Conclusions: The created Prostate Model is able to estimate the DVH of the OARs within 4%. This accuracy improves at large Bladder and Rectum doses and can be used to guide the planning process to yield clinically acceptable plans. Further investigation would be required to adjust the optimization objectives for automatic planning. Author Disclosure: J.E. Alpuche Aviles: G. Consultant; This work was partly supported by Varian Medical Systems. The author is a clinical evaluators for Varian Medical Systems. D. Sasaki: G. Consultant; This work was partly supported by Varian Medical Systems. The author is a clinical evaluator for Varian Medical Systems. K. Sutherland: G. Consultant; This work was partly supported by Varian Medical Systems. The author is a clinical evaluator for Varian Medical Systems.
3677 Commissioning of a Prostate Model Created Using KnowledgeBased Planning as a Tool to Guide the Planning Process J.E. Alpuche Aviles, D. Sasaki, and K. Sutherland; Cancercare Manitoba, Winnipeg, MB, Canada Purpose/Objective(s): The purpose of this study was twofold: (I) To quantify the accuracy of Dose Volume Histograms (DVHs) that can be estimated using Knowledge Based Planning (KBP) for Organs at Risk (OARs) of the Prostate. (II) To evaluate if the obtained accuracy can yield clinically acceptable Prostate plans. Materials/Methods: A Prostate Model was created using a commercial implementation of KBP. KBP is able to estimate DVHs of OARs prior to the planning process based on the DVHs obtained from previous plans. The Model was created using treatment plans of the Intact Prostate and Post-Op cases. The Model was also trained to include different prescription doses: 20 Gy and 66 Gy (For Post-op cases) while 32 Gy and 78 Gy (for cases of the Intact Prostate). The Model was created to include the Bladder, Rectum and the Femoral Heads. All plans were created using 6 MV and Volumetrically Modulated Arc Therapy. The volumes of the estimated DVHs were compared against those of the clinical DVHs of 40 independent (from the patients used to create the Model) validation patients. The difference between DVHs was quantified at 50%, 85% and 99% of the maximum dose received by the organ. Finally, the estimates were used to guide the planning process of the validation set of patients. Results: The generated Model is able to estimate Bladder DVHs within 1% on average. A similar accuracy can be achieved for large Rectum doses (more than 85% of the Rectum maximum dose). This is not the case in the intermediate Rectum doses where the estimates were, on average, 4% larger than the clinical DVH. The estimates of the Femoral Heads are less
3678 Prostate Deformation From Rectal Balloon and Dosimetric Effects in Prostate Brachytherapy J. Lian, Y. Shao, R.C. Chen, D. Shen, and A.Z. Wang; University of North Carolina at Chapel Hill, Chapel Hill, NC Purpose/Objective(s): Prostate brachytherapy is an important curative treatment for patients with localized prostate cancer. In brachytherapy, rectal balloon is generally needed to adjust for unfavorable prostate position for seed placement. However, rectal balloon causes prostate deformation, which is not accounted for in dosimetric planning. Therefore, it is possible that brachytherapy dosimetry deviates significantly from initial plan when prostate returns to its non-deformed state (after procedure). The goal of this study is to assess the effect of prostate deformation on brachytherapy dosimetry, and to develop a novel algorithm that can account for this deformation during brachytherapy planning. Materials/Methods: We prospectively collected ultrasound images of prostate pre- and post- rectal balloon inflation from 5 consecutive patients undergoing I-125 brachytherapy. We developed a learning-based deformable image registration method for correlating the voxels between the deformed and non-deformed images. Based on the cylinder coordinate systems, we learned the coordinate transformation parameters between the manual segmentations of both deformed and non-deformed prostates of each patient in training set, and averaged them as the initialization (r0,q0,z0) of coordinate transformation. With the nearest-neighbor interpolation, we searched the best transformation (r,q,z) between both cylinder coordinate system to maximum the mutual information of deformed and non-deformed images, using the transformed manual segmentation of non-deformed prostate as mask. With the best coordinate transformation, the correspondence of points (voxels) in both cylinder coordinate systems was established. Using this method, we then mapped the implanted seeds from the deformed prostate into non-deformed prostate. Brachytherapy dosimetry of non-deformed prostate was calculated using VariSeed software and compared to dosimetry from deformed prostate. Results: The accuracy of image registration is 87.5% as quantified by Dice Index. The prostate coverage V100% dropped from 96.50.5% of prostate-deformed plan to 91.92.6% (p Z 0.04) of non-deformed plan. The rectum V100% decreased from 0.440.26 cc to 0.100.18 cc (p Z 0.04). The dosimetry of the urethra showed mild change but not significant: V150% changed from 0.050.10 cc to 0.140.15 cc (p Z 0.3) and D1%
International Journal of Radiation Oncology Biology Physics
Materials/Methods: Nine patients with biopsy proven H&N tumors were enrolled on an IRB approved imaging protocol. Each patient was treated to 70 Gy in 33-35 fractions with concurrent chemotherapy when indicated. Daily pre-treatment imaging was performed with cone beam CT (CBCT), kV paired orthogonal x-ray and 6d stereoscopic x-ray imaging systems. The daily couch shifts were computed from offline matches and the vertical and lateral shifts were compared using linear regression with correlation being assessed using Pearson’s correlation coefficient (R). Bland-Altman analysis was also performed to assess for trends in the correlations. Results: The best mean shift correlation was observed between stereoscopic x-ray and orthogonal x-ray imaging (vertical R Z 0.67, lateral R Z 0.72) and orthogonal x-ray and CBCT (vertical R Z 0.66, lateral R Z 0.76). The CBCT and stereoscopic x-ray vertical shifts exhibited the worst correlation (vertical R Z 0.48, lateral R Z 0.71). For most patients, the vertical shifts had worse correlation than the lateral shifts. Overall, it was observed that the stereoscopic x-ray shifts were smaller than the CBCT or orthogonal x-ray shifts. We also observed that the shift correlations appeared to be worse in the earliest enrolled patients compared to the more recently enrolled patients. Initial inspection revealed that time on the table between imaging was much shorter for more recent patients as the imaging workflow efficiency was improved. Conclusions: This preliminary analysis revealed that the largest differences in shift information occur between stereoscopic x-ray and CBCT imaging. We generally found that shifts from stereoscopic imaging were smaller than CBCT or orthogonal x-ray, which could be explained by the additional rotational corrections inherent to the stereoscopic system. To date, there is no “gold standard” in terms of on-board imaging and our results confirm that not all imaging systems produce equal shifts when used on the same patient. In addition, our findings reinforce the need for efficient treatment workflows to minimize the risk of patient movement between imaging and treatment. Author Disclosure: N. Serrano: None. J. Evans: None. D. Asher: None. M.E. Schutzer: None. M. Fatyga: None. W. Sleeman: None. N. Dogan: None. S. Song: None.
accurate (-4% to 4%) and is likely to be due to the planning technique (Maximum dose objective) and the steep dose fall-off exhibited by the DVHs of these structures. The estimated DVHs were used to guide the optimization process without any user interaction (allowing 2% normalization) and yielded clinically acceptable plans 43% of the time. Additional runs were only necessary in three patients as a result of the inability of the plans to meet the clinical goals for the OARs. The reminder of the plans, that required additional runs; did so, due to the inability to meet the clinical goals of the target. Further planning was conducted to achieve acceptable target goals and had little effect on the DVHs of the OARs obtained after the user-free run (The DVHs agreed 94% of the time within 2% at the clinically relevant goals). Conclusions: The created Prostate Model is able to estimate the DVH of the OARs within 4%. This accuracy improves at large Bladder and Rectum doses and can be used to guide the planning process to yield clinically acceptable plans. Further investigation would be required to adjust the optimization objectives for automatic planning. Author Disclosure: J.E. Alpuche Aviles: G. Consultant; This work was partly supported by Varian Medical Systems. The author is a clinical evaluators for Varian Medical Systems. D. Sasaki: G. Consultant; This work was partly supported by Varian Medical Systems. The author is a clinical evaluator for Varian Medical Systems. K. Sutherland: G. Consultant; This work was partly supported by Varian Medical Systems. The author is a clinical evaluator for Varian Medical Systems.
3677 Commissioning of a Prostate Model Created Using KnowledgeBased Planning as a Tool to Guide the Planning Process J.E. Alpuche Aviles, D. Sasaki, and K. Sutherland; Cancercare Manitoba, Winnipeg, MB, Canada Purpose/Objective(s): The purpose of this study was twofold: (I) To quantify the accuracy of Dose Volume Histograms (DVHs) that can be estimated using Knowledge Based Planning (KBP) for Organs at Risk (OARs) of the Prostate. (II) To evaluate if the obtained accuracy can yield clinically acceptable Prostate plans. Materials/Methods: A Prostate Model was created using a commercial implementation of KBP. KBP is able to estimate DVHs of OARs prior to the planning process based on the DVHs obtained from previous plans. The Model was created using treatment plans of the Intact Prostate and Post-Op cases. The Model was also trained to include different prescription doses: 20 Gy and 66 Gy (For Post-op cases) while 32 Gy and 78 Gy (for cases of the Intact Prostate). The Model was created to include the Bladder, Rectum and the Femoral Heads. All plans were created using 6 MV and Volumetrically Modulated Arc Therapy. The volumes of the estimated DVHs were compared against those of the clinical DVHs of 40 independent (from the patients used to create the Model) validation patients. The difference between DVHs was quantified at 50%, 85% and 99% of the maximum dose received by the organ. Finally, the estimates were used to guide the planning process of the validation set of patients. Results: The generated Model is able to estimate Bladder DVHs within 1% on average. A similar accuracy can be achieved for large Rectum doses (more than 85% of the Rectum maximum dose). This is not the case in the intermediate Rectum doses where the estimates were, on average, 4% larger than the clinical DVH. The estimates of the Femoral Heads are less
3678 Prostate Deformation From Rectal Balloon and Dosimetric Effects in Prostate Brachytherapy J. Lian, Y. Shao, R.C. Chen, D. Shen, and A.Z. Wang; University of North Carolina at Chapel Hill, Chapel Hill, NC Purpose/Objective(s): Prostate brachytherapy is an important curative treatment for patients with localized prostate cancer. In brachytherapy, rectal balloon is generally needed to adjust for unfavorable prostate position for seed placement. However, rectal balloon causes prostate deformation, which is not accounted for in dosimetric planning. Therefore, it is possible that brachytherapy dosimetry deviates significantly from initial plan when prostate returns to its non-deformed state (after procedure). The goal of this study is to assess the effect of prostate deformation on brachytherapy dosimetry, and to develop a novel algorithm that can account for this deformation during brachytherapy planning. Materials/Methods: We prospectively collected ultrasound images of prostate pre- and post- rectal balloon inflation from 5 consecutive patients undergoing I-125 brachytherapy. We developed a learning-based deformable image registration method for correlating the voxels between the deformed and non-deformed images. Based on the cylinder coordinate systems, we learned the coordinate transformation parameters between the manual segmentations of both deformed and non-deformed prostates of each patient in training set, and averaged them as the initialization (r0,q0,z0) of coordinate transformation. With the nearest-neighbor interpolation, we searched the best transformation (r,q,z) between both cylinder coordinate system to maximum the mutual information of deformed and non-deformed images, using the transformed manual segmentation of non-deformed prostate as mask. With the best coordinate transformation, the correspondence of points (voxels) in both cylinder coordinate systems was established. Using this method, we then mapped the implanted seeds from the deformed prostate into non-deformed prostate. Brachytherapy dosimetry of non-deformed prostate was calculated using VariSeed software and compared to dosimetry from deformed prostate. Results: The accuracy of image registration is 87.5% as quantified by Dice Index. The prostate coverage V100% dropped from 96.50.5% of prostate-deformed plan to 91.92.6% (p Z 0.04) of non-deformed plan. The rectum V100% decreased from 0.440.26 cc to 0.100.18 cc (p Z 0.04). The dosimetry of the urethra showed mild change but not significant: V150% changed from 0.050.10 cc to 0.140.15 cc (p Z 0.3) and D1%