- Email: [email protected]
Dosimetric Comparison of Intensity Modulated Radiosurgery and Helical Tomotherapy for Multiple Intracranial Metastases
Proceedings of the 50th Annual ASTRO Meeting symmetry with a median distance of 1.20cm from the PTV border in all directions. The other regions had the following Results: [A/ P]temp1.03, [S/I]temp1.09, [R/L]temp1.16; [A/P]frontal1.34, [S/I]frontal1.02, [R/L]frontal1.21; [A/P]BS1.33, [S/I]BS0.75, [R/L]BS1.12; [A/P]mid1.09, [S/I]mid0.99, [R/L]mid2.20. The conformality indices CI’s and the 3-D measurements did not correlate to the PTV volume. Conclusions: IMRT has been proven to increase conformality compared to 3D-CRT for intracranial lesions. We have attempted to define IMRT conformality benchmarks for dosimetric evaluation. The asymmetry of the 30 Gy isodose level within each region suggests that other factors affecting the isodose distributions should be investigated. Author Disclosure: M.B. Palmer, None; B. Banwo, None; R. Georges, None; K. Jones, None; T. Lewis, None; W. Du, None; A. Mahajan, None.
2819
Image Guided, Motion-free Patient Body Setup using 3D Volumetric Image Registration of Classified Stable Bony Landmarks
G. Li, H. Ning, A. Brown, D. Citrin, H. Xie, J. Chang, B. Arora, J. Capala, K. Camphausen, R. W. Miller Radiation Oncology Branch, National Cancer Institute/NIH, Bethesda, MD Purpose/Objective(s): Different motions and motion artifacts residing in planning and setup CT images show altered and distorted patient anatomies, which undermine the reliability of rigid image registration and introduce hidden uncertainties in image-guided radiation therapy (IGRT). A motion-free approach is pursued to improve the IGRT patient setup. Materials/Methods: The 3D volumetric image registration (3DVIR) utilizes classified, motion-less bony landmarks for rigid image registration. Image classification is performed by controlling voxel transparency using an opacity lookup table based on image histogram in real-time. Both visual and quantitative measures of color homogeneity distributed on the volumetric landmarks are used as registration criteria. Mutual information (MI) based registration is used for comparison. For respiratory motion characterization, four sets of 4D-CT images with 10 phases under normal respiration are studied. For IGRT patient setup, daily Tomotherapy MVCT images are aligned with the planning kVCT image. Two patients’ daily MVCT and planning kVCT images are used for IGRT setup for treatment of lesions in or near the spine. Results: Using the 4D-CT images, stable bony landmarks in the averaged respiratory cycle have been identified. The native alignment of the 3D bony structures in different respiratory phases shows that the spine, clavicle, scapula and upper sternum are motionfree under normal respiration, with an uncertainty of\± 0.2 mm, while the ribs and lower sternum may have .2 mm displacement. MI-based rigid image registration, however, produces an overall 1-2 mm shift from the native alignment. Using these stable bony landmarks, registrations of the MVCT and kVCT images, free from respiratory, cardiac and digestive motions, have been achieved. The MVCT and kVCT carry distinctive motions and motion artifacts, as they are acquired in different time frames. The kVCT (scans at 1 second per rotation, or 1 SPR) represents an anatomy in an arbitrary breathing stage and contains image distortion artifacts (imaging anatomies at different respiratory phases); while the MVCT (scans at 10 SPR) has image blurring artifacts (averaged over respiratory cycles). This 3DVIR approach does not use moving anatomies for alignment, eliminating the motion/ deformation uncertainties, and therefore is superior to any rigid image registration that does. This result indicates that the use of stable bony landmarks should provide improved accuracy and reproducibility for IGRT patient setup. These improvements can be critical in stereotactic body radiation therapy (SBRT). Conclusions: This image-guided, motion-free approach eliminates the interference of moving soft tissues and ribs, providing accurate and reproducible IGRT patient setup. Author Disclosure: G. Li, None; H. Ning, None; A. Brown, None; D. Citrin, None; H. Xie, None; J. Chang, None; B. Arora, None; J. Capala, None; K. Camphausen, None; R.W. Miller, None.
2820
Dosimetric Comparison of Intensity Modulated Radiosurgery and Helical Tomotherapy for Multiple Intracranial Metastases
L. VanderSpek1, G. Bauman1, J. Wang2, S. Yartsev1, K. T. Murphy2 1 London Regional Cancer Program, University of Western Ontario, London, ON, Canada, 2Moores Cancer Center, University of California, San Diego, La Jolla, CA
Purpose/Objective(s): The treatment of multiple brain metastases with multi-isocenter stereotactic techniques is time consuming and does not allow the optimization of dose delivery considering the contribution from all lesions treated. Single fraction, singleisocenter, intensity-modulated radiosurgery (IMRS) and helical tomotherapy (HT) are techniques that could address these limitations through the simultaneous optimized planning and treatment of multiple lesions. We compared the treatment of 3-6 intracranial metastases using these two techniques. Materials/Methods: Dose plans for 10 patients with 3-6 brain metastases treated at UCSD with IMRS were re-planned with HT. Comparisons were based on the V100%, conformity index, conformation number, maximum dose to prescription dose ratio (MDPD), maximum doses to organs at risk, integral dose to normal brain, and treatment time. Results: The sliding-window IMRS plans (Varian Trilogy linear accelerator with 120 leaf multi-leaf collimator) consisted of single-isocenter, single fraction plans using noncoplanar fields and frameless optical guidance. The mean number of lesions was 5 and the mean PTV volume was 22 cm3. The dose consisted of 16 Gy (3 patients), 18 Gy (3 patients), and 20 Gy (4 patients). The HT plans utilized a field width of 2.5 cm, mean pitch of 0.2, and a mean actual modulation factor of 2.4. The mean V100% was 90.0 (IMRS) and 95.4 (HT) (p = 0.04), and the mean conformation number was 0.6 (IMRS) and 0.7 (HT) (NS). The mean conformity index was 1.4 and the mean MDPD was 1.1 for both. The mean maximum doses (Gy) to organs at risk for IMRS and HT, respectively, were as follows: brainstem (11.9, 12.7) (NS), chiasm (4.2, 5.2) (p = 0.05), Lt eye (0.5, 2.6) (p\0.001), Rt eye (0.5, 2.5) (p\ 0.001), Lt optic nerve (2.0, 3.4) (p = 0.01), and Rt optic nerve (2.1, 2.8) (NS). For brain, the integral dose (Gy-kg) was 5.1 and 6.8 (p \ 0.001) and mean dose (Gy) was 4.0 and 5.4 (p \ 0.001) for IMRS and HT, respectively. The total mean treatment times were 23 minutes (IMRS) and 41 minutes (HT).
S535
I. J. Radiation Oncology d Biology d Physics
S536
Volume 72, Number 1, Supplement, 2008
Conclusions: Conformity and homogeneity of target coverage were equivalent for IMRS and HT and sparing of organs at risk was clinically acceptable for both. The overall integral dose to normal brain was lower with IMRS as was overall treatment time. Additional comparisons with traditional radiosurgery (Gamma Knife) are in process. Author Disclosure: L. VanderSpek, None; G. Bauman, None; J. Wang, None; S. Yartsev, None; K.T. Murphy, Varian Medical Systems, D. Speakers Bureau/Honoraria.
2821
Simultaneous Integrated Boost with Helical Tomotherapy can be Delivered with no Significant Increase in Dose to Surrounding Normal Tissue for Primary Brain Tumors
J. M. Baisden, N. Dunlap, K. Sheng, J. M. Larner University of Virginia Hospital, Charlottesville, VA Purpose/Objective(s): A standard approach for the delivery of fractionated radiation to primary brain tumors uses a sequential boost IMRT technique (SEQ). Combining these into a single delivery plan with a simultaneous integrated boost (SIB) using IMRT allows for improved normal tissue sparing and equal target coverage. The purpose of this study was to determine whether Helical Tomotherapy (HT) could deliver an SIB plan without a clinically significant increase in dose to the normal brain, compared to the initial SEQ plan for primary brain tumors. Materials/Methods: Twenty-two treatment plans were evaluated. Hypothetical cylindrical planning target volumes (PTV) were created which corresponded to peritumoral edema with diameters of 8 cm, 7 cm, 6 cm and 5 cm. Within each PTV, a minimum of 4 boost volumes (PTVboost) was created that corresponded to contrast-enhancement, ranging from 7.5 cm to 3 cm in diameter. The SIB plans were prescribed 60 Gy/25 fractions to the PTVboost and 50 Gy/25 fractions to the PTV. SEQ plans were prescribed 50 Gy/25 fractions to the PTV followed by and additional 10 Gy/5 fractions to the PTVboost. Normal tissue sparing was evaluated by comparing the mean dose to the brain (subtracting the PTV and PTVboost) and integral dose (ID) between the SIB plan and the first 50 Gy of the SEQ plan. Validation was performed by analyzing 5 patients previously treated at our institution with an IMRT SEQ delivery. SIB plans were created using nearly identical constraints on normal tissue. The mean brain dose and ID were compared between the SIB plans and the previously delivered SEQ plans. Results: Target coverage and normal tissue constraints were maintained with the SIB technique. The increase in mean brain dose with the SIB technique was a linear function of the ratio of the PTVboost to the PTV (R2 = 0.831). A PTVboost volume of 25%, 50%, or 75% of the initial PTV corresponded to an approximate 1%, 3%, or 5% increase, respectively, in the mean brain dose compared to the first 50 Gy of the SEQ plan. A similar relationship was seen with integral dose (R2 = 0.810). Subsequent validation in patients treated at our institution corroborated our findings. SIB delivery with a PTVboost volume less than 50% of the PTV volume showed an increase in the mean brain dose of 1.2-2.3% compared to initial portion of the SEQ treatment. Conclusions: For the treatment of primary brain tumors the SIB technique results in a clinically insignificant increase in normal tissue dose, compared to the first portion of the SEQ technique. Thus, dose escalation may be feasible which could achieve substantially higher central tumor doses with acceptable increases in mean brain dose and ID. Author Disclosure: J.M. Baisden, None; N. Dunlap, None; K. Sheng, None; J.M. Larner, None.
2822
Approximated Returning-to-origin Probability Diffusion Imaging for Better Observation of Radiation Treatment Response of High-grade Glioma
A. C. Chu1, J. Knisely1, R. Fulbright2, R. T. Constable2, R. Nath1 1
Yale New Haven Hospital, New Haven, CT, 2Yale University, New Haven, CT
Purpose/Objective(s): This study is to provide a novel high diffusion weighting imaging technique for better observation for highgrade glioma treatment responses. Background: Since the late 90s, the sensitive detection to cancer treatment responses by using apparent diffusion coefficient (ADC) derived either from diffused magnetic resonance spectroscopy or images had been recognized by animal and human studies. However the low signal-to-noise ratio (SNR) in diffused NMR signal and the problems eddy-current and motion artifacts as results of utilizing high gradient pulses in this technique impair its imaging quality, not to mention attempting to use even higher diffusion weighting imaging to reveal more information that lower diffusion weighting technique cannot reach. For example, in some highgrade glioma studies, the slower water diffusion (requiring higher diffusion weighting) usually appeared in more confined areas like white matter tracts and higher cellularity (i.e., palisading cells), which could be critical for evolution glioma treatment responses. Currently the popular high-diffusion analysis using bi-exponential model to resolve slow/fast diffusion compartments presents even more challenges on analyzing its resulted images due to the uncertainties aggregated from fitting algorithm. In this study we used an alternative methodology, the returning-to-origin probability (a special case of q-space analysis) to analyze highly diffused data because q-space theory is based on much more solid theory foundation than bi-exponential model. Materials/Methods: Only 9 diffusion encoded points (in q-space) within 12-minute scan time were sampled (b-values from 1000 4000 sec mm-2). The approximated returning-to-origin probability (ARTOP) is also has the tensor properties like ADC used in conventional diffusion tensor imaging (DTI). To fulfill a tensor requirement, 6-direction diffusion gradient pulses were uniformly sampled over 3 dimensions. The smoothing over 9-point diffusion encoded data for each voxel was made, then was transformed from q-space to spatial space. A glioblastoma (GBM) patient’s data is presented. Results: (1) ARTOP results highlighted slow diffusion in white matter and parts of GBM location. (2) The diffusing displacement at half-value of ARTOP clearly presented higher diffusivity with brighter scale similar to conventional ADC map. (3) The SNR of ARTOP is obviously better than the conventional ADC mapping under the same conditions (with 2 averages). (4) The FA derived from ARTOP has similar results as conventional one. (5) The ARTOP has a superior imaging quality compared to the results of biexponential model from the same set of data. Conclusions: Its better results provide great potential for treatment responses. Author Disclosure: A.C. Chu, None; J. Knisely, None; R. Fulbright, None; R.T. Constable, None; R. Nath, None.
2819
Image Guided, Motion-free Patient Body Setup using 3D Volumetric Image Registration of Classified Stable Bony Landmarks
G. Li, H. Ning, A. Brown, D. Citrin, H. Xie, J. Chang, B. Arora, J. Capala, K. Camphausen, R. W. Miller Radiation Oncology Branch, National Cancer Institute/NIH, Bethesda, MD Purpose/Objective(s): Different motions and motion artifacts residing in planning and setup CT images show altered and distorted patient anatomies, which undermine the reliability of rigid image registration and introduce hidden uncertainties in image-guided radiation therapy (IGRT). A motion-free approach is pursued to improve the IGRT patient setup. Materials/Methods: The 3D volumetric image registration (3DVIR) utilizes classified, motion-less bony landmarks for rigid image registration. Image classification is performed by controlling voxel transparency using an opacity lookup table based on image histogram in real-time. Both visual and quantitative measures of color homogeneity distributed on the volumetric landmarks are used as registration criteria. Mutual information (MI) based registration is used for comparison. For respiratory motion characterization, four sets of 4D-CT images with 10 phases under normal respiration are studied. For IGRT patient setup, daily Tomotherapy MVCT images are aligned with the planning kVCT image. Two patients’ daily MVCT and planning kVCT images are used for IGRT setup for treatment of lesions in or near the spine. Results: Using the 4D-CT images, stable bony landmarks in the averaged respiratory cycle have been identified. The native alignment of the 3D bony structures in different respiratory phases shows that the spine, clavicle, scapula and upper sternum are motionfree under normal respiration, with an uncertainty of\± 0.2 mm, while the ribs and lower sternum may have .2 mm displacement. MI-based rigid image registration, however, produces an overall 1-2 mm shift from the native alignment. Using these stable bony landmarks, registrations of the MVCT and kVCT images, free from respiratory, cardiac and digestive motions, have been achieved. The MVCT and kVCT carry distinctive motions and motion artifacts, as they are acquired in different time frames. The kVCT (scans at 1 second per rotation, or 1 SPR) represents an anatomy in an arbitrary breathing stage and contains image distortion artifacts (imaging anatomies at different respiratory phases); while the MVCT (scans at 10 SPR) has image blurring artifacts (averaged over respiratory cycles). This 3DVIR approach does not use moving anatomies for alignment, eliminating the motion/ deformation uncertainties, and therefore is superior to any rigid image registration that does. This result indicates that the use of stable bony landmarks should provide improved accuracy and reproducibility for IGRT patient setup. These improvements can be critical in stereotactic body radiation therapy (SBRT). Conclusions: This image-guided, motion-free approach eliminates the interference of moving soft tissues and ribs, providing accurate and reproducible IGRT patient setup. Author Disclosure: G. Li, None; H. Ning, None; A. Brown, None; D. Citrin, None; H. Xie, None; J. Chang, None; B. Arora, None; J. Capala, None; K. Camphausen, None; R.W. Miller, None.
2820
Dosimetric Comparison of Intensity Modulated Radiosurgery and Helical Tomotherapy for Multiple Intracranial Metastases
L. VanderSpek1, G. Bauman1, J. Wang2, S. Yartsev1, K. T. Murphy2 1 London Regional Cancer Program, University of Western Ontario, London, ON, Canada, 2Moores Cancer Center, University of California, San Diego, La Jolla, CA
Purpose/Objective(s): The treatment of multiple brain metastases with multi-isocenter stereotactic techniques is time consuming and does not allow the optimization of dose delivery considering the contribution from all lesions treated. Single fraction, singleisocenter, intensity-modulated radiosurgery (IMRS) and helical tomotherapy (HT) are techniques that could address these limitations through the simultaneous optimized planning and treatment of multiple lesions. We compared the treatment of 3-6 intracranial metastases using these two techniques. Materials/Methods: Dose plans for 10 patients with 3-6 brain metastases treated at UCSD with IMRS were re-planned with HT. Comparisons were based on the V100%, conformity index, conformation number, maximum dose to prescription dose ratio (MDPD), maximum doses to organs at risk, integral dose to normal brain, and treatment time. Results: The sliding-window IMRS plans (Varian Trilogy linear accelerator with 120 leaf multi-leaf collimator) consisted of single-isocenter, single fraction plans using noncoplanar fields and frameless optical guidance. The mean number of lesions was 5 and the mean PTV volume was 22 cm3. The dose consisted of 16 Gy (3 patients), 18 Gy (3 patients), and 20 Gy (4 patients). The HT plans utilized a field width of 2.5 cm, mean pitch of 0.2, and a mean actual modulation factor of 2.4. The mean V100% was 90.0 (IMRS) and 95.4 (HT) (p = 0.04), and the mean conformation number was 0.6 (IMRS) and 0.7 (HT) (NS). The mean conformity index was 1.4 and the mean MDPD was 1.1 for both. The mean maximum doses (Gy) to organs at risk for IMRS and HT, respectively, were as follows: brainstem (11.9, 12.7) (NS), chiasm (4.2, 5.2) (p = 0.05), Lt eye (0.5, 2.6) (p\0.001), Rt eye (0.5, 2.5) (p\ 0.001), Lt optic nerve (2.0, 3.4) (p = 0.01), and Rt optic nerve (2.1, 2.8) (NS). For brain, the integral dose (Gy-kg) was 5.1 and 6.8 (p \ 0.001) and mean dose (Gy) was 4.0 and 5.4 (p \ 0.001) for IMRS and HT, respectively. The total mean treatment times were 23 minutes (IMRS) and 41 minutes (HT).
S535
I. J. Radiation Oncology d Biology d Physics
S536
Volume 72, Number 1, Supplement, 2008
Conclusions: Conformity and homogeneity of target coverage were equivalent for IMRS and HT and sparing of organs at risk was clinically acceptable for both. The overall integral dose to normal brain was lower with IMRS as was overall treatment time. Additional comparisons with traditional radiosurgery (Gamma Knife) are in process. Author Disclosure: L. VanderSpek, None; G. Bauman, None; J. Wang, None; S. Yartsev, None; K.T. Murphy, Varian Medical Systems, D. Speakers Bureau/Honoraria.
2821
Simultaneous Integrated Boost with Helical Tomotherapy can be Delivered with no Significant Increase in Dose to Surrounding Normal Tissue for Primary Brain Tumors
J. M. Baisden, N. Dunlap, K. Sheng, J. M. Larner University of Virginia Hospital, Charlottesville, VA Purpose/Objective(s): A standard approach for the delivery of fractionated radiation to primary brain tumors uses a sequential boost IMRT technique (SEQ). Combining these into a single delivery plan with a simultaneous integrated boost (SIB) using IMRT allows for improved normal tissue sparing and equal target coverage. The purpose of this study was to determine whether Helical Tomotherapy (HT) could deliver an SIB plan without a clinically significant increase in dose to the normal brain, compared to the initial SEQ plan for primary brain tumors. Materials/Methods: Twenty-two treatment plans were evaluated. Hypothetical cylindrical planning target volumes (PTV) were created which corresponded to peritumoral edema with diameters of 8 cm, 7 cm, 6 cm and 5 cm. Within each PTV, a minimum of 4 boost volumes (PTVboost) was created that corresponded to contrast-enhancement, ranging from 7.5 cm to 3 cm in diameter. The SIB plans were prescribed 60 Gy/25 fractions to the PTVboost and 50 Gy/25 fractions to the PTV. SEQ plans were prescribed 50 Gy/25 fractions to the PTV followed by and additional 10 Gy/5 fractions to the PTVboost. Normal tissue sparing was evaluated by comparing the mean dose to the brain (subtracting the PTV and PTVboost) and integral dose (ID) between the SIB plan and the first 50 Gy of the SEQ plan. Validation was performed by analyzing 5 patients previously treated at our institution with an IMRT SEQ delivery. SIB plans were created using nearly identical constraints on normal tissue. The mean brain dose and ID were compared between the SIB plans and the previously delivered SEQ plans. Results: Target coverage and normal tissue constraints were maintained with the SIB technique. The increase in mean brain dose with the SIB technique was a linear function of the ratio of the PTVboost to the PTV (R2 = 0.831). A PTVboost volume of 25%, 50%, or 75% of the initial PTV corresponded to an approximate 1%, 3%, or 5% increase, respectively, in the mean brain dose compared to the first 50 Gy of the SEQ plan. A similar relationship was seen with integral dose (R2 = 0.810). Subsequent validation in patients treated at our institution corroborated our findings. SIB delivery with a PTVboost volume less than 50% of the PTV volume showed an increase in the mean brain dose of 1.2-2.3% compared to initial portion of the SEQ treatment. Conclusions: For the treatment of primary brain tumors the SIB technique results in a clinically insignificant increase in normal tissue dose, compared to the first portion of the SEQ technique. Thus, dose escalation may be feasible which could achieve substantially higher central tumor doses with acceptable increases in mean brain dose and ID. Author Disclosure: J.M. Baisden, None; N. Dunlap, None; K. Sheng, None; J.M. Larner, None.
2822
Approximated Returning-to-origin Probability Diffusion Imaging for Better Observation of Radiation Treatment Response of High-grade Glioma
A. C. Chu1, J. Knisely1, R. Fulbright2, R. T. Constable2, R. Nath1 1
Yale New Haven Hospital, New Haven, CT, 2Yale University, New Haven, CT
Purpose/Objective(s): This study is to provide a novel high diffusion weighting imaging technique for better observation for highgrade glioma treatment responses. Background: Since the late 90s, the sensitive detection to cancer treatment responses by using apparent diffusion coefficient (ADC) derived either from diffused magnetic resonance spectroscopy or images had been recognized by animal and human studies. However the low signal-to-noise ratio (SNR) in diffused NMR signal and the problems eddy-current and motion artifacts as results of utilizing high gradient pulses in this technique impair its imaging quality, not to mention attempting to use even higher diffusion weighting imaging to reveal more information that lower diffusion weighting technique cannot reach. For example, in some highgrade glioma studies, the slower water diffusion (requiring higher diffusion weighting) usually appeared in more confined areas like white matter tracts and higher cellularity (i.e., palisading cells), which could be critical for evolution glioma treatment responses. Currently the popular high-diffusion analysis using bi-exponential model to resolve slow/fast diffusion compartments presents even more challenges on analyzing its resulted images due to the uncertainties aggregated from fitting algorithm. In this study we used an alternative methodology, the returning-to-origin probability (a special case of q-space analysis) to analyze highly diffused data because q-space theory is based on much more solid theory foundation than bi-exponential model. Materials/Methods: Only 9 diffusion encoded points (in q-space) within 12-minute scan time were sampled (b-values from 1000 4000 sec mm-2). The approximated returning-to-origin probability (ARTOP) is also has the tensor properties like ADC used in conventional diffusion tensor imaging (DTI). To fulfill a tensor requirement, 6-direction diffusion gradient pulses were uniformly sampled over 3 dimensions. The smoothing over 9-point diffusion encoded data for each voxel was made, then was transformed from q-space to spatial space. A glioblastoma (GBM) patient’s data is presented. Results: (1) ARTOP results highlighted slow diffusion in white matter and parts of GBM location. (2) The diffusing displacement at half-value of ARTOP clearly presented higher diffusivity with brighter scale similar to conventional ADC map. (3) The SNR of ARTOP is obviously better than the conventional ADC mapping under the same conditions (with 2 averages). (4) The FA derived from ARTOP has similar results as conventional one. (5) The ARTOP has a superior imaging quality compared to the results of biexponential model from the same set of data. Conclusions: Its better results provide great potential for treatment responses. Author Disclosure: A.C. Chu, None; J. Knisely, None; R. Fulbright, None; R.T. Constable, None; R. Nath, None.