- Email: [email protected]
Initial Experience With VMAT Plan and Delivery Verification Using a DICOM-RT Framework and Linac Delivery Log Files
S886
International Journal of Radiation Oncology Biology Physics
described by the quantity called dynamical leaf gap (DLG). In some commercial TPS, the DLG and TR are the dosimetric parameters for the MLC that the user is required to choose with the goal of matching the planned and measured doses. The value of DLG is often measured by extrapolating size of fields formed by synchronized MLC leaves, either static or dynamic, to the size at which the measured dose equals the MLC leakage. Here, synchronized means that the neighboring MLC leaves have the same extension. In this situation, the tongue and groove (T&G) effect would be minimal. Practical IMRT/ VMAT fields, however, are formed by non-synchronized MLC leaves and the T&G plays an important role in dosimetry. In order to reflect the T&G effect in practical plans, we designed test plans to include a wide range of T&G effect. The delivered dose was compared with the calculated in the TPS where different combinations of the values of TR and DLG were used, from which the optimal combination was determined. Typical head-and-neck and prostate plans were investigated to determine the preferred range of leave gaps and T&G on which the optimization was focused. More than 20 original plans were reoptimized with new the TR and DLG values. The plan quality (DVHs, monitor units etc.) was checked. The delivered dose from test plans was measured with ion chambers and the individual QA was performed by a diode-array detector. Results: For typical plans delivered by 3 different MLC systems (HD120, millennium 120, and 160 MLC) integrated in 5 linacs, the optimal combination of TR and DLG (in mm) were (1.3%, 1.9), (1.6%, 2.3), (1.6%, 2.3) and (0.26%, 0.3). The values of TR were from the direct measure and found un-necessary to be adjusted. The QA pass rate (3%/3mm/10% in Gammatest for step-and-shoot technique DTA-test for sliding window technique was much improved, especially for those plans that had failed under the previous settings. All plans with optimal combinations were passed. The plan quality was similar, and was found even to have improved in some plans. Conclusions: Our test plans reflect the T&G effect and the resulted optimal value of DLG can be used to improve the match of delivered and planned doses. It is recommended that the T&G effect should be included in the measurement of DLG. Author Disclosure: W. Yao: None. J. Farr: None.
14.0%, and 19.1 22.1%, respectively. For about 2/3 of patients, the correlation can be seen between the LC-heart distance and the changes of the mean dose, V5, and V25 of heart (p<0.02). No clear correlation was observed between the LC-heart distance and the maximum dose change. Conclusions: The interfractional variation in cardiac doses for WBI in supine position with left-sided breast cancers can be substantial, mainly due to the interfractional shifts of the heart positions. The LC-heart distance is a critical parameter that can be used to assess the variation in cardiac dose. This dose variation should be considered in analyzing the relationship between cardiac dose and toxicities. . Author Disclosure: X. Chen: None. W. Huang: None. A. Currey: None. J.F. Wilson: None. X.A. Li: None.
3718 Interfractional Variation of Cardiac Dose During Whole-Breast Irradiation X. Chen, W. Huang, A. Currey, J.F. Wilson, and X.A. Li; Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): To quantitatively evaluate the interfractional variations of heart and its impact on cardiac dose during whole breast irradiation (WBI) with patients positioned in supine, and determine a parameter to estimate the risk of the dose variation. Materials/Methods: Analysis was performed on daily CTs acquired using an in-room CT during daily IGRT for 12 left-sided breast cancer patients, who were treated with whole breast irradiation in supine position. For each fraction CT, the lumpectomy cavity (LC), breast, heart, left ventricle, and lung, were generated by populating the contours in the planning CT using a commercial auto-segmentation tool with manually editing if necessary. The heart volume and the distance between centers of mass of the lumpectomy and heart (LC-heart distance) were calculated to measure the interfractional variations of heart position. The dose distribution actually received by the patient at a fraction was reconstructed by applying the original plan to the fraction CT considering the repositioning shifts performed during IGRT based on soft-tissue alignment of LC. Dose volume parameters, including the target coverage, mean dose, maximum dose, V5 and V25 of heart, were calculated from the daily dose distributions and were compared with those in the original plan. The correlation between these parameters was analyzed using Spearman rank correlation tests. Results: The interfractional variation in heart volume was small (1.5 3.9%), indicating the respiration and cardiac motions were small. The mean value of the LC-heart distance was 2.3 0.7 cm, but it can be as high as 6 cm. The V95 of the treated breast was reduced by 2.3% on average from the original plan to the daily dose distributions. Compared to the values in the original plans, the mean dose, maximum dose, V5, and V25 of the heart in the daily dose distributions were varied by 12.0 14.6%, 1.8 4.0%, 12.5
3719 A Technique to Quantify and Reduce Backscatter Due to Metallic Dental Restoration in Head and Neck Radiation Therapy K.T. Erickson and J. Rahimian; Kaiser Permanente Southern California, Los Angeles, CA Purpose/Objective(s): The presence of high-Z metallic dental restorations is known to result in increased mucositis during head and neck radiation therapy. Backscatter results in “hot spots” which are often under-recognized in modern treatment planning and evaluation systems. Despite the use of custom dental stents worn during radiation therapy treatment at our institution, severe mucositis is particularly noted adjacent to high-Z metal restorations such as gold crowns and dental implants. We seek to quantify the perturbation of the incident beam and identify a simple method to reduce backscatter related to the presence of dental metal restorations. Materials/Methods: Three high-Z metallic samples were used for our experiments: gold 1.25mm in thickness, silver 2.25mm in thickness and Lipowitz metal (Lipowitz metal: 50% bismuth, 26.7% lead, 13.3% tin, and 10% cadmium by weight) 3mm in thickness. Film was placed on the under and top surface of the metallic samples, and 5 monitor units were delivered from the LINAC with an open field (6 x 12cm) using 6MV photons, each at a SSD of 100cm. The films were developed and digitized using a high-resolution scanner and the Optical Density (OD) was obtained using medical image processing software. Initial values for transmission and backscatter through the metallic sample were calculated using the background from the surrounding open field for comparison. We then employed one of 3 materials (1cm wax, 1cm bolus, and 0.5cm wax) over the metallic samples, and repeated the experiment, calculating the change in backscatter and transmission. Results: Calculated backscatter for the metallic samples were as follows: 22% for gold, 17% for silver, and 24% for Lipowitz metal. The calculated transmission was 95.2% through gold, 94.1% for silver and 94.1% for Lipowitz metal. With the employment of 1 cm of wax, the backscatter was reduced to 2.6%, 4.6%, and 4.1% for gold, silver, and Lipowitz respectively. Application of 1cm bolus material resulted in a similar effect. As expected, transmission remained relatively stable at 94% for both 1cm wax and 1cm bolus. Application of 5mm of wax also showed significant reduction in backscatter to 5.4%, 4.3%, and 4.3% for gold, silver, and Lipowitz respectively. Conclusions: Our technique quantifies backscatter resulting from the presence of high-Z metals, which can be significantly mitigated with the simple application of at least 5mm of wax. We recommend that dental restorations be recognized during the treatment planning process. The use of materials such as dental wax warrants further study as a method to reduce severe radiation mucositis. Author Disclosure: K.T. Erickson: None. J. Rahimian: None.
3720 Initial Experience With VMAT Plan and Delivery Verification Using a DICOM-RT Framework and Linac Delivery Log Files R.R. Reynolds, A. Pompos, X. Gu, S.B. Jiang, and S. Stojadinovic; University of Texas Southwestern Medical Center, Dallas, TX Purpose/Objective(s): A commercial independent verification system utilizing a DICOM-RT framework was used to compare calculated and
Volume 90 Number 1S Supplement 2014 delivered volumetric modulated arc therapy (VMAT) dose distributions in patients’ geometries based on linac treatment log files. Materials/Methods: The independent verification system utilizes measured Linacs’ commissioning data to generate institution specific beam models for evaluating planned and delivered dose distributions. Two VMAT representations consisting of 30 prostate plans and 30 head and neck SmartArc plans were used in this study. For every VMAT plan, DICOM-RT files which included CT images, contoured structure sets, RT plan, and RT dose, were exported to the verification system. This data was used to recalculate patients’ planning CT dose distributions using a collapsed cone convolutionsuperposition algorithm. Moreover, the acquired Linac log files were used to compute patients’ delivered dose distributions based on the actual treatment delivery parameters. The agreement between computed and delivered dose distributions was evaluated utilizing a three dimensional (3D) gamma analysis with 3% global dose difference and 3 mm isodose point distance criteria. Additionally, dosimetric comparisons were also made by comparing dose-volume histogram changes for targets and organs at risk. Results: Excellent 3D gamma agreements were observed for all VMAT plans. On average, for computed and delivered prostate VMAT and headand-neck VMAT plans the gamma passing rates were (99.0%1.4%) and (96.8%1.8%), respectively. The average difference between calculated and delivered primary target prescription dose percent coverage was (-0.09% 2.52%) for the prostate and (-2.71%4.62%) for the head and neck cases. Similarly, the planning target mean dose differences were (1.38%0.96%) for prostate and (1.17%0.72%) for head and neck plans. For the prostate plans, the calculated and delivered variations of V2cc, i.e., the max dose for a 2 cm3 volume, for bladder and rectum were (1.32%1.26%) and (0.65% 1.44%), respectively. For the head and neck plans, the computed and delivered spinal cord dose differences were (3.26%1.68%). Conclusions: Clinical quality assurance practice based on Linac treatment log files for verification of delivered 3D dose distributions in the patients’ geometries represents a paradigm shift from dose measurements in a phantom. This approach offers independent verification of VMAT dose distributions encompassing treatment planning beam modeling differences as well as the Linac uncertainties during treatment delivery of the plan. Author Disclosure: R.R. Reynolds: A. Employee; UT Southwestern Medical Center. A. Pompos: A. Employee; UT Southwestern Medical Center. X. Gu: A. Employee; UT Southwestern Medical Center. S.B. Jiang: A. Employee; UT Southwestern Medical Center. S. Stojadinovic: A. Employee; UT Southwestern Medical Center.
3721 Delivered Target and Organ Dose Estimation Using Deformable Image Registration on Cone Beam Computed Tomography (CBCT) Scans for Head and Neck Radiation Therapy C. Liu, A. Kumarasiri, D. Pradhan, R. Yechieli, M. Shah, I. Chetty, F. Siddiqui, and J. Kim; HFHS, Detroit, MI Purpose/Objective(s): Deformable image registration (DIR) enables calculation of actual delivered dose to targets and nearby organs. The aim of this study was to estimate delivered doses using a DIR algorithm and compare them with the corresponding plan doses for the H&N radiation therapy. Materials/Methods: Five H&N patients were retrospectively selected, where the PTVs were small enough to be entirely encompassed within the CBCT image. The PTV margins were 5 mm from the corresponding CTV volumes. The dose of the day was calculated on each daily CBCT image. Dose was then warped and accumulated on the planning CT image using a parameter-optimized, B-spline DIR algorithm (Elastix, elastix.isi.uu.nl). For each patient, DVH’s of the cumulative total doses were calculated and compared to those of the original plan. The CBCT-bound limitations of small field of views (FOV) and HU value uncertainties were overcome by using deformably-registered CT images in place of daily CBCT images. The accuracy of estimated total dose was compared against a commercially available b-spline algorithm. Results: The dosimetric deviations between cumulative and planned doses for the targets and normal organs are presented in Table 1. The target coverage degradations (DVrx) were -3.00.8% for PTV and 0.61.2% for
Poster Viewing Abstracts S887 CTV. The min. and max. dose deviations (DDmin and DDmax) were greater for the PTV’s, as expected. Among the normal organs, the parotid glands had the largest dose increases with mean deviations (DDmean) of 6.410.6%, due to their proximity to the target volumes. The mandible and spinal cord dose changes were relatively small with respective mean dose deviations of 0.03.6% and 1.00.9%. From visual inspection, it was noticeable that the large dosimetric deviations were seemingly from daily patient setup uncertainties; especially those with uncorrected table roll and pitch angles. Differences between the parameter-optimized and commercial B-spline algorithms were small (0.51.2%). Conclusions: Initial results indicate that, given the large dose discrepancies (up to 6.5%) observed for normal organs, such as the parotid glands, cumulative dose assessment may be beneficial toward adapting the treatment plan during the course of RT. Dose differences are likely to increase with reduced planning margins. Results of this study will be used to design a prospective clinical protocol to evaluate the efficacy of ART for H&N radiation therapy. Author Disclosure: C. Liu: None. A. Kumarasiri: None. D. Pradhan: None. R. Yechieli: None. M. Shah: None. I. Chetty: E. Research Grant; Varian Medical Systems, Palo Alto CA, Philips HealthCare (Best, Netherlands). F. Siddiqui: None. J. Kim: None. Scientific Abstract 3721; Table Percent deviations of the estimated delivered doses from the plan doses (meanstd).
PTV CTV Parotid gland Mandible Spinal cord
DDmin (%)
DDmax(%)
DDmean(%)
DVrx(%)
-4.08.5 -0.90.8 -
2.42.3 1.92.5 2.96.0 0.11.5 3.42.6
0.61.4 0.91.5 6.410.6 0.03.6 1.00.9
-3.10.8 0.61.2 -
3722 Evaluation of Fast Adaptive Planning Method Using Deformable Image Registration and GPU Based RTP for Lung Cancer Patients With Concurrent Chemoradiation Therapy J. Woo, J. Kim, J. Baek, M. Kim, S. Kim, S. Lee, and J. Cho; Yonsei University Health System, Seoul, Korea, Republic of Korea Purpose/Objective(s): We always delineated internal target volume (ITV) observing tumor movement by 4-dimensional computed tomography (4D CT) in lung tumor. However, when we saw the mass outside ITV during verified bone matching using megavoltage CT (MVCT) in 1st treatment. This study evaluated the fast adaptive planning method using commercially deformable image registration (DIR) tool and graphic processing unit (GPU) based radiation treatment planning system from MVCT images. Materials/Methods: From November 2013 to January 2014 we selected lung cancer patients who have irregular breathing pattern with concurrent chemoradiation therapy. Treatment dose was 48 Gy per total in 4 fractions using 3d helical tomotherapy. We got planning CT images and 4D images through 4D CT. We delineated gross tumor volume (GTV) included a gross tumor and ITV included a gross tumor through 4D CT. In addition, planning target volume (PTV) included a 3 to 5 mm safety margin around ITV. Every treatment was verified MVCT because mass can detected by MVCT. If we saw the mass outside ITV during verified MVCT in each treatment. We would perform respiration education as simulation and re_MVCT. Although we have performed re_MVCT, we saw the mass outside the ITV and we would select resimulation and replanning. Most of patients delayed 1st treatment times. If patients have treated chemotherapy before radiation therapy, we could select replanning using MVCT. We sent the MVCT images to Mim_vista for replanning. In addition, we added redelineated GTV and ITV for comparing MVCT and planning 4D CT on Mim_vista. First we evaluated replanning time using GPU based RTP and DIR program. Second we checked dosimetric parameters such as mean lung dose (MLD) and V5, V10, V20.
International Journal of Radiation Oncology Biology Physics
described by the quantity called dynamical leaf gap (DLG). In some commercial TPS, the DLG and TR are the dosimetric parameters for the MLC that the user is required to choose with the goal of matching the planned and measured doses. The value of DLG is often measured by extrapolating size of fields formed by synchronized MLC leaves, either static or dynamic, to the size at which the measured dose equals the MLC leakage. Here, synchronized means that the neighboring MLC leaves have the same extension. In this situation, the tongue and groove (T&G) effect would be minimal. Practical IMRT/ VMAT fields, however, are formed by non-synchronized MLC leaves and the T&G plays an important role in dosimetry. In order to reflect the T&G effect in practical plans, we designed test plans to include a wide range of T&G effect. The delivered dose was compared with the calculated in the TPS where different combinations of the values of TR and DLG were used, from which the optimal combination was determined. Typical head-and-neck and prostate plans were investigated to determine the preferred range of leave gaps and T&G on which the optimization was focused. More than 20 original plans were reoptimized with new the TR and DLG values. The plan quality (DVHs, monitor units etc.) was checked. The delivered dose from test plans was measured with ion chambers and the individual QA was performed by a diode-array detector. Results: For typical plans delivered by 3 different MLC systems (HD120, millennium 120, and 160 MLC) integrated in 5 linacs, the optimal combination of TR and DLG (in mm) were (1.3%, 1.9), (1.6%, 2.3), (1.6%, 2.3) and (0.26%, 0.3). The values of TR were from the direct measure and found un-necessary to be adjusted. The QA pass rate (3%/3mm/10% in Gammatest for step-and-shoot technique DTA-test for sliding window technique was much improved, especially for those plans that had failed under the previous settings. All plans with optimal combinations were passed. The plan quality was similar, and was found even to have improved in some plans. Conclusions: Our test plans reflect the T&G effect and the resulted optimal value of DLG can be used to improve the match of delivered and planned doses. It is recommended that the T&G effect should be included in the measurement of DLG. Author Disclosure: W. Yao: None. J. Farr: None.
14.0%, and 19.1 22.1%, respectively. For about 2/3 of patients, the correlation can be seen between the LC-heart distance and the changes of the mean dose, V5, and V25 of heart (p<0.02). No clear correlation was observed between the LC-heart distance and the maximum dose change. Conclusions: The interfractional variation in cardiac doses for WBI in supine position with left-sided breast cancers can be substantial, mainly due to the interfractional shifts of the heart positions. The LC-heart distance is a critical parameter that can be used to assess the variation in cardiac dose. This dose variation should be considered in analyzing the relationship between cardiac dose and toxicities. . Author Disclosure: X. Chen: None. W. Huang: None. A. Currey: None. J.F. Wilson: None. X.A. Li: None.
3718 Interfractional Variation of Cardiac Dose During Whole-Breast Irradiation X. Chen, W. Huang, A. Currey, J.F. Wilson, and X.A. Li; Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): To quantitatively evaluate the interfractional variations of heart and its impact on cardiac dose during whole breast irradiation (WBI) with patients positioned in supine, and determine a parameter to estimate the risk of the dose variation. Materials/Methods: Analysis was performed on daily CTs acquired using an in-room CT during daily IGRT for 12 left-sided breast cancer patients, who were treated with whole breast irradiation in supine position. For each fraction CT, the lumpectomy cavity (LC), breast, heart, left ventricle, and lung, were generated by populating the contours in the planning CT using a commercial auto-segmentation tool with manually editing if necessary. The heart volume and the distance between centers of mass of the lumpectomy and heart (LC-heart distance) were calculated to measure the interfractional variations of heart position. The dose distribution actually received by the patient at a fraction was reconstructed by applying the original plan to the fraction CT considering the repositioning shifts performed during IGRT based on soft-tissue alignment of LC. Dose volume parameters, including the target coverage, mean dose, maximum dose, V5 and V25 of heart, were calculated from the daily dose distributions and were compared with those in the original plan. The correlation between these parameters was analyzed using Spearman rank correlation tests. Results: The interfractional variation in heart volume was small (1.5 3.9%), indicating the respiration and cardiac motions were small. The mean value of the LC-heart distance was 2.3 0.7 cm, but it can be as high as 6 cm. The V95 of the treated breast was reduced by 2.3% on average from the original plan to the daily dose distributions. Compared to the values in the original plans, the mean dose, maximum dose, V5, and V25 of the heart in the daily dose distributions were varied by 12.0 14.6%, 1.8 4.0%, 12.5
3719 A Technique to Quantify and Reduce Backscatter Due to Metallic Dental Restoration in Head and Neck Radiation Therapy K.T. Erickson and J. Rahimian; Kaiser Permanente Southern California, Los Angeles, CA Purpose/Objective(s): The presence of high-Z metallic dental restorations is known to result in increased mucositis during head and neck radiation therapy. Backscatter results in “hot spots” which are often under-recognized in modern treatment planning and evaluation systems. Despite the use of custom dental stents worn during radiation therapy treatment at our institution, severe mucositis is particularly noted adjacent to high-Z metal restorations such as gold crowns and dental implants. We seek to quantify the perturbation of the incident beam and identify a simple method to reduce backscatter related to the presence of dental metal restorations. Materials/Methods: Three high-Z metallic samples were used for our experiments: gold 1.25mm in thickness, silver 2.25mm in thickness and Lipowitz metal (Lipowitz metal: 50% bismuth, 26.7% lead, 13.3% tin, and 10% cadmium by weight) 3mm in thickness. Film was placed on the under and top surface of the metallic samples, and 5 monitor units were delivered from the LINAC with an open field (6 x 12cm) using 6MV photons, each at a SSD of 100cm. The films were developed and digitized using a high-resolution scanner and the Optical Density (OD) was obtained using medical image processing software. Initial values for transmission and backscatter through the metallic sample were calculated using the background from the surrounding open field for comparison. We then employed one of 3 materials (1cm wax, 1cm bolus, and 0.5cm wax) over the metallic samples, and repeated the experiment, calculating the change in backscatter and transmission. Results: Calculated backscatter for the metallic samples were as follows: 22% for gold, 17% for silver, and 24% for Lipowitz metal. The calculated transmission was 95.2% through gold, 94.1% for silver and 94.1% for Lipowitz metal. With the employment of 1 cm of wax, the backscatter was reduced to 2.6%, 4.6%, and 4.1% for gold, silver, and Lipowitz respectively. Application of 1cm bolus material resulted in a similar effect. As expected, transmission remained relatively stable at 94% for both 1cm wax and 1cm bolus. Application of 5mm of wax also showed significant reduction in backscatter to 5.4%, 4.3%, and 4.3% for gold, silver, and Lipowitz respectively. Conclusions: Our technique quantifies backscatter resulting from the presence of high-Z metals, which can be significantly mitigated with the simple application of at least 5mm of wax. We recommend that dental restorations be recognized during the treatment planning process. The use of materials such as dental wax warrants further study as a method to reduce severe radiation mucositis. Author Disclosure: K.T. Erickson: None. J. Rahimian: None.
3720 Initial Experience With VMAT Plan and Delivery Verification Using a DICOM-RT Framework and Linac Delivery Log Files R.R. Reynolds, A. Pompos, X. Gu, S.B. Jiang, and S. Stojadinovic; University of Texas Southwestern Medical Center, Dallas, TX Purpose/Objective(s): A commercial independent verification system utilizing a DICOM-RT framework was used to compare calculated and
Volume 90 Number 1S Supplement 2014 delivered volumetric modulated arc therapy (VMAT) dose distributions in patients’ geometries based on linac treatment log files. Materials/Methods: The independent verification system utilizes measured Linacs’ commissioning data to generate institution specific beam models for evaluating planned and delivered dose distributions. Two VMAT representations consisting of 30 prostate plans and 30 head and neck SmartArc plans were used in this study. For every VMAT plan, DICOM-RT files which included CT images, contoured structure sets, RT plan, and RT dose, were exported to the verification system. This data was used to recalculate patients’ planning CT dose distributions using a collapsed cone convolutionsuperposition algorithm. Moreover, the acquired Linac log files were used to compute patients’ delivered dose distributions based on the actual treatment delivery parameters. The agreement between computed and delivered dose distributions was evaluated utilizing a three dimensional (3D) gamma analysis with 3% global dose difference and 3 mm isodose point distance criteria. Additionally, dosimetric comparisons were also made by comparing dose-volume histogram changes for targets and organs at risk. Results: Excellent 3D gamma agreements were observed for all VMAT plans. On average, for computed and delivered prostate VMAT and headand-neck VMAT plans the gamma passing rates were (99.0%1.4%) and (96.8%1.8%), respectively. The average difference between calculated and delivered primary target prescription dose percent coverage was (-0.09% 2.52%) for the prostate and (-2.71%4.62%) for the head and neck cases. Similarly, the planning target mean dose differences were (1.38%0.96%) for prostate and (1.17%0.72%) for head and neck plans. For the prostate plans, the calculated and delivered variations of V2cc, i.e., the max dose for a 2 cm3 volume, for bladder and rectum were (1.32%1.26%) and (0.65% 1.44%), respectively. For the head and neck plans, the computed and delivered spinal cord dose differences were (3.26%1.68%). Conclusions: Clinical quality assurance practice based on Linac treatment log files for verification of delivered 3D dose distributions in the patients’ geometries represents a paradigm shift from dose measurements in a phantom. This approach offers independent verification of VMAT dose distributions encompassing treatment planning beam modeling differences as well as the Linac uncertainties during treatment delivery of the plan. Author Disclosure: R.R. Reynolds: A. Employee; UT Southwestern Medical Center. A. Pompos: A. Employee; UT Southwestern Medical Center. X. Gu: A. Employee; UT Southwestern Medical Center. S.B. Jiang: A. Employee; UT Southwestern Medical Center. S. Stojadinovic: A. Employee; UT Southwestern Medical Center.
3721 Delivered Target and Organ Dose Estimation Using Deformable Image Registration on Cone Beam Computed Tomography (CBCT) Scans for Head and Neck Radiation Therapy C. Liu, A. Kumarasiri, D. Pradhan, R. Yechieli, M. Shah, I. Chetty, F. Siddiqui, and J. Kim; HFHS, Detroit, MI Purpose/Objective(s): Deformable image registration (DIR) enables calculation of actual delivered dose to targets and nearby organs. The aim of this study was to estimate delivered doses using a DIR algorithm and compare them with the corresponding plan doses for the H&N radiation therapy. Materials/Methods: Five H&N patients were retrospectively selected, where the PTVs were small enough to be entirely encompassed within the CBCT image. The PTV margins were 5 mm from the corresponding CTV volumes. The dose of the day was calculated on each daily CBCT image. Dose was then warped and accumulated on the planning CT image using a parameter-optimized, B-spline DIR algorithm (Elastix, elastix.isi.uu.nl). For each patient, DVH’s of the cumulative total doses were calculated and compared to those of the original plan. The CBCT-bound limitations of small field of views (FOV) and HU value uncertainties were overcome by using deformably-registered CT images in place of daily CBCT images. The accuracy of estimated total dose was compared against a commercially available b-spline algorithm. Results: The dosimetric deviations between cumulative and planned doses for the targets and normal organs are presented in Table 1. The target coverage degradations (DVrx) were -3.00.8% for PTV and 0.61.2% for
Poster Viewing Abstracts S887 CTV. The min. and max. dose deviations (DDmin and DDmax) were greater for the PTV’s, as expected. Among the normal organs, the parotid glands had the largest dose increases with mean deviations (DDmean) of 6.410.6%, due to their proximity to the target volumes. The mandible and spinal cord dose changes were relatively small with respective mean dose deviations of 0.03.6% and 1.00.9%. From visual inspection, it was noticeable that the large dosimetric deviations were seemingly from daily patient setup uncertainties; especially those with uncorrected table roll and pitch angles. Differences between the parameter-optimized and commercial B-spline algorithms were small (0.51.2%). Conclusions: Initial results indicate that, given the large dose discrepancies (up to 6.5%) observed for normal organs, such as the parotid glands, cumulative dose assessment may be beneficial toward adapting the treatment plan during the course of RT. Dose differences are likely to increase with reduced planning margins. Results of this study will be used to design a prospective clinical protocol to evaluate the efficacy of ART for H&N radiation therapy. Author Disclosure: C. Liu: None. A. Kumarasiri: None. D. Pradhan: None. R. Yechieli: None. M. Shah: None. I. Chetty: E. Research Grant; Varian Medical Systems, Palo Alto CA, Philips HealthCare (Best, Netherlands). F. Siddiqui: None. J. Kim: None. Scientific Abstract 3721; Table Percent deviations of the estimated delivered doses from the plan doses (meanstd).
PTV CTV Parotid gland Mandible Spinal cord
DDmin (%)
DDmax(%)
DDmean(%)
DVrx(%)
-4.08.5 -0.90.8 -
2.42.3 1.92.5 2.96.0 0.11.5 3.42.6
0.61.4 0.91.5 6.410.6 0.03.6 1.00.9
-3.10.8 0.61.2 -
3722 Evaluation of Fast Adaptive Planning Method Using Deformable Image Registration and GPU Based RTP for Lung Cancer Patients With Concurrent Chemoradiation Therapy J. Woo, J. Kim, J. Baek, M. Kim, S. Kim, S. Lee, and J. Cho; Yonsei University Health System, Seoul, Korea, Republic of Korea Purpose/Objective(s): We always delineated internal target volume (ITV) observing tumor movement by 4-dimensional computed tomography (4D CT) in lung tumor. However, when we saw the mass outside ITV during verified bone matching using megavoltage CT (MVCT) in 1st treatment. This study evaluated the fast adaptive planning method using commercially deformable image registration (DIR) tool and graphic processing unit (GPU) based radiation treatment planning system from MVCT images. Materials/Methods: From November 2013 to January 2014 we selected lung cancer patients who have irregular breathing pattern with concurrent chemoradiation therapy. Treatment dose was 48 Gy per total in 4 fractions using 3d helical tomotherapy. We got planning CT images and 4D images through 4D CT. We delineated gross tumor volume (GTV) included a gross tumor and ITV included a gross tumor through 4D CT. In addition, planning target volume (PTV) included a 3 to 5 mm safety margin around ITV. Every treatment was verified MVCT because mass can detected by MVCT. If we saw the mass outside ITV during verified MVCT in each treatment. We would perform respiration education as simulation and re_MVCT. Although we have performed re_MVCT, we saw the mass outside the ITV and we would select resimulation and replanning. Most of patients delayed 1st treatment times. If patients have treated chemotherapy before radiation therapy, we could select replanning using MVCT. We sent the MVCT images to Mim_vista for replanning. In addition, we added redelineated GTV and ITV for comparing MVCT and planning 4D CT on Mim_vista. First we evaluated replanning time using GPU based RTP and DIR program. Second we checked dosimetric parameters such as mean lung dose (MLD) and V5, V10, V20.