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performed for the 34 prostate patients only. All patients received daily pretreatment MVCT scans, which were registered automatically with planning kilovoltage CT scans by bony landmarks. Registered images were used to obtain translational and rotational setup corrections in all patients, and internal organ motion corrections were determined manually by comparing soft tissue positions in prostate patients only. MVCT scans in weeks 1 and 4 of treatments were used for analysis of rotational variations in prostate and H&N patients, and for translational variations in H&N patients, while MVCT scans in all treatment fractions (weeks 1 through 8) were used to analyze both translational variations and internal organ motion corrections in prostate patients. Results: In prostate patients, mean and standard deviations for setup variations were 3.17.3 mm in the lateral direction, -0.84.9 mm in the SI direction, -0.26.4 in the AP direction, -0.60°1.42° in pitch, 0.66°1.22° in roll, and -0.33°0.83° in yaw. In H&N patients, mean and standard deviations for setup variations were 4.264.84 mm in the lateral direction, 1.433.54 mm in the SI direction, 0.314.26 mm in the AP direction, -0.24°1.19° in pitch, -0.12°1.53° in roll, and 0.25°1.42° in yaw. Mean and standard deviations of internal organ motion corrections in prostate patients were -0.10.8 mm, -0.10.7 mm, and 0.01.9 mm in the lateral, SI, and AP directions, respectively. Less than 10% of the MVCT scans for prostate patients received manual corrections in the SI direction. Prostate motion variation did not change significantly during the course of treatment. No significant difference in rotational variations was observed between weeks 1 and 4 of treatment. H&N patients had significantly smaller pitch variation, but significantly larger yaw variation, than prostate patients. Conclusions: The helical tomotherapy MVCT system provides an effective way for patient setup corrections and internal organ motion corrections. Yet it has some limitations in internal organ motion corrections in the SI direction based on soft tissue delineation. In prostate patients, translational setup variations due to bony landmark positions were more significant than internal organ motion. Rotational variations for prostate and H&N patients were statistically significant, small in magnitude, and did not vary considerably during the course of radiotherapy. The data are relevant to image-guided radiotherapy treatment planning and couch design for correcting rotational setup variations. Author Disclosure: C. Han, TomoTherapy Inc., B. Research Grant; A. Kaiser, TomoTherapy Inc., B. Research Grant; T.E. Schultheiss, None; J.Y.C. Wong, None; D.D. Smith, None; A. Liu, None; N.L. Vora, None; R.D. Pezner, None; Y. Chen, None; E. Radany, None. 2742 Evaluation of Adequate Margin Size for Prostate IMRT by Cone-Beam CT Interfraction Imaging B. F. Koontz, S. Yoo, S. Kim, S. Das, M. Anscher, F. Yin Duke University Medical Center, Durham, NC Purpose/Objective(s): Intensity-modulated radiotherapy (IMRT) is now commonly utilized to treat prostate cancer. While the improved penumbra of intensity-modulated fields allows for tighter margins and reduced dose to normal tissues, the margins used in generating a planning treatment volume (PTV) to ensure adequate coverage of the clinical target volume (CTV) must also take into account patient set-up uncertainty and organ motion. There must be a limit to how small margins can be set to ensure adequate coverage of the CTV. Using cone-beam CT (CBCT) imaging over the course of treatment we can measure the interfraction variation in target position and evaluate coverage of the initial plan. We hypothesize that with this technique, we can determine the minimum adequate margin needed for target coverage throughout the treatment course. Materials/Methods: Patients undergoing IMRT treatment for intact prostate cancer at DUMC underwent serial CBCTs during treatment. For each patient, contours of the prostate and seminal vesicles (SV) were made for the first five CBCTs. Each CBCT was aligned with the planning CT using bone structure matching. Composite prostate and SV volumes were generated by combining these volumes from each CBCT. IMRT plans using different margin width were designed (PTV05 5mm around prostate SV, PTV10 10mm, PTV15 15mm, PTV10_5 10mm with 5mm posteriorly, and PTV15_10 15mm with 10mm posteriorly). Each IMRT plan was optimized to have coverage of 95% of its PTV. Verification plans were created based on the first CBCT with the composite prostate and SV contours. Each verification plan was then evaluated by the percentage of prescription dose given to 95% of the composite target volumes (V95). Results: 23 patients have completed the protocol, and preliminary results are discussed below. Reviewing the prostate contours, there was some interfraction motion primarily along the anterior-posterior direction. The composite prostate volume was 152 /- 19% the average volume of the individual prostate CBCT contours. In 40% of patients, 5mm margin around the prostate SV provided excellent coverage of the composite prostate volume (VPTV05 V95 100% prescription dose). In the remaining patients, the VPTV10_5 plan gave sufficient coverage: 95–101% prescription dose. There was substantially more motion of the SV than of the prostate in all patients, resulting in a significantly larger composite SV volume: 245 /- 94% the mean individual SV CBCT contours. The patients with the least amount of SV motion (composite volume 177 /- 7% mean individual SV CBCT contours) had adequate coverage of the composite SV volume by either the VPTV05 or VPTV10_5 plans. Two patients had extensive anterior-posterior SV motion due to changes in bowel gas. One required 15_10mm margin and the other only reached a V95 89% prescription dose using the largest margin size, 15mm in all directions. Conclusions: There is substantial variation of interfraction prostate and SV motion between patients. Rather than develop a minimum adequate margin generalizable to all patients, it is necessary to establish a new method for determining a patient-specific margin size. CBCT is particularly useful in investigating SV interfraction motion. Poor SV coverage in actual treatment plans may contribute to clinical failure of treatment. Future work will include designing a strategy for adaptive planning and evaluating normal tissue coverage. Author Disclosure: B.F. Koontz, None; S. Yoo, None; S. Kim, None; S. Das, None; M. Anscher, None; F. Yin, None. S623 Proceedings of the 48th Annual ASTRO Meeting
Transcript of 2742
performed for the 34 prostate patients only. All patients received daily pretreatment MVCT scans, which were registeredautomatically with planning kilovoltage CT scans by bony landmarks. Registered images were used to obtain translational androtational setup corrections in all patients, and internal organ motion corrections were determined manually by comparing softtissue positions in prostate patients only. MVCT scans in weeks 1 and 4 of treatments were used for analysis of rotationalvariations in prostate and H&N patients, and for translational variations in H&N patients, while MVCT scans in all treatmentfractions (weeks 1 through 8) were used to analyze both translational variations and internal organ motion corrections in prostatepatients.
Results: In prostate patients, mean and standard deviations for setup variations were 3.1�7.3 mm in the lateral direction,-0.8�4.9 mm in the SI direction, -0.2�6.4 in the AP direction, -0.60°�1.42° in pitch, 0.66°�1.22° in roll, and-0.33°�0.83° in yaw. In H&N patients, mean and standard deviations for setup variations were 4.26�4.84 mm in thelateral direction, 1.43�3.54 mm in the SI direction, 0.31�4.26 mm in the AP direction, -0.24°�1.19° in pitch,-0.12°�1.53° in roll, and 0.25°�1.42° in yaw. Mean and standard deviations of internal organ motion corrections inprostate patients were -0.1�0.8 mm, -0.1�0.7 mm, and 0.0�1.9 mm in the lateral, SI, and AP directions, respectively.Less than 10% of the MVCT scans for prostate patients received manual corrections in the SI direction. Prostate motionvariation did not change significantly during the course of treatment. No significant difference in rotational variations wasobserved between weeks 1 and 4 of treatment. H&N patients had significantly smaller pitch variation, but significantlylarger yaw variation, than prostate patients.
Conclusions: The helical tomotherapy MVCT system provides an effective way for patient setup corrections and internal organmotion corrections. Yet it has some limitations in internal organ motion corrections in the SI direction based on soft tissuedelineation. In prostate patients, translational setup variations due to bony landmark positions were more significant thaninternal organ motion. Rotational variations for prostate and H&N patients were statistically significant, small in magnitude, anddid not vary considerably during the course of radiotherapy. The data are relevant to image-guided radiotherapy treatmentplanning and couch design for correcting rotational setup variations.
Author Disclosure: C. Han, TomoTherapy Inc., B. Research Grant; A. Kaiser, TomoTherapy Inc., B. Research Grant; T.E.Schultheiss, None; J.Y.C. Wong, None; D.D. Smith, None; A. Liu, None; N.L. Vora, None; R.D. Pezner, None; Y. Chen, None;E. Radany, None.
2742 Evaluation of Adequate Margin Size for Prostate IMRT by Cone-Beam CT Interfraction Imaging
B. F. Koontz, S. Yoo, S. Kim, S. Das, M. Anscher, F. Yin
Duke University Medical Center, Durham, NC
Purpose/Objective(s): Intensity-modulated radiotherapy (IMRT) is now commonly utilized to treat prostate cancer. While theimproved penumbra of intensity-modulated fields allows for tighter margins and reduced dose to normal tissues, the marginsused in generating a planning treatment volume (PTV) to ensure adequate coverage of the clinical target volume (CTV) mustalso take into account patient set-up uncertainty and organ motion. There must be a limit to how small margins can be set toensure adequate coverage of the CTV. Using cone-beam CT (CBCT) imaging over the course of treatment we can measure theinterfraction variation in target position and evaluate coverage of the initial plan. We hypothesize that with this technique, wecan determine the minimum adequate margin needed for target coverage throughout the treatment course.
Materials/Methods: Patients undergoing IMRT treatment for intact prostate cancer at DUMC underwent serial CBCTs duringtreatment. For each patient, contours of the prostate and seminal vesicles (SV) were made for the first five CBCTs. Each CBCTwas aligned with the planning CT using bone structure matching. Composite prostate and SV volumes were generated bycombining these volumes from each CBCT. IMRT plans using different margin width were designed (PTV05 � 5mm aroundprostate � SV, PTV10 � 10mm, PTV15 � 15mm, PTV10_5 � 10mm with 5mm posteriorly, and PTV15_10 � 15mm with10mm posteriorly). Each IMRT plan was optimized to have coverage of 95% of its PTV. Verification plans were created basedon the first CBCT with the composite prostate and SV contours. Each verification plan was then evaluated by the percentageof prescription dose given to 95% of the composite target volumes (V95).
Results: 23 patients have completed the protocol, and preliminary results are discussed below. Reviewing the prostatecontours, there was some interfraction motion primarily along the anterior-posterior direction. The composite prostatevolume was 152 �/- 19% the average volume of the individual prostate CBCT contours. In 40% of patients, 5mm marginaround the prostate � SV provided excellent coverage of the composite prostate volume (VPTV05 V95 � 100%prescription dose). In the remaining patients, the VPTV10_5 plan gave sufficient coverage: 95–101% prescription dose.There was substantially more motion of the SV than of the prostate in all patients, resulting in a significantly largercomposite SV volume: 245 �/- 94% the mean individual SV CBCT contours. The patients with the least amount of SVmotion (composite volume 177 �/- 7% mean individual SV CBCT contours) had adequate coverage of the composite SVvolume by either the VPTV05 or VPTV10_5 plans. Two patients had extensive anterior-posterior SV motion due tochanges in bowel gas. One required 15_10mm margin and the other only reached a V95 � 89% prescription dose usingthe largest margin size, 15mm in all directions.
Conclusions: There is substantial variation of interfraction prostate and SV motion between patients. Rather than develop aminimum adequate margin generalizable to all patients, it is necessary to establish a new method for determining apatient-specific margin size. CBCT is particularly useful in investigating SV interfraction motion. Poor SV coverage in actualtreatment plans may contribute to clinical failure of treatment. Future work will include designing a strategy for adaptiveplanning and evaluating normal tissue coverage.
Author Disclosure: B.F. Koontz, None; S. Yoo, None; S. Kim, None; S. Das, None; M. Anscher, None; F. Yin, None.
S623Proceedings of the 48th Annual ASTRO Meeting
