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Breath-Hold Intensity Modulated Proton Therapy (BH-IMPT) for Lung SBRT: Feasibility Study
S142
International Journal of Radiation Oncology Biology Physics
tumors with DE 4 mm. Pearson correlation was performed to associate clinical factors with DE. Continuous variables were analyzed with an independent samples t-test and categorical variables with chi-square. Results: Eight hundred forty-four 4D-CBCT’s were analyzed (495 CRT, 349 HRT). DE was largest in the SI direction overall, with mean (SD) of 0.5 ( 3) mm (-25 - 17). Mean DE (mm) in the SI direction was larger in HRT as compared to CRT, with smaller SD (1.1 ( 2.3) v 0.03 ( 3.3), p < 0.001). A similar trend was noted in the AP direction, and no difference was seen in the LR direction. Eleven percent of the 844 4D-CBCT’s had DE > 4 mm (38% HRT, 62% CRT). For treatments with DE > 4 mm, overall mean target dose reduction was largest in the SI direction, -7.4 4.2%. The following factors were significantly correlated with DE: age, weight, tumor location, performance status (KPS), smoking history, pre-RT O2 use, and planning 4D-CT excursion. Tumor size and right v left lung did not correlate. Tumors with 4 mm DE in any direction were found in younger patients with higher weight and KPS, male gender, and lower lobe (LL) location (Table 1). Conclusions: The largest degree of DE is seen in the SI direction for both CRT and HRT, causing > 5% target dose reduction in 11% of daily RT deliveries. Target margins designed based only on pre-treatment 4D-CT without considering clinical variables could under compensate for target motion during treatment. Large DE seems predictable, and seen more in young patients with higher baseline weight, KPS, male gender, and LL tumors. Online 4D-CBCT provides a means to monitor excursion and adapt RT, and further analysis to optimize timing is underway.
spot size of 3 mm. The delivery time of each field was estimated based on the four scanning parameters combinations. The average spot delivery time was scaled up by a factor of 6 to represent high dose delivery. Based on the delivery time and PTV lengths of the 20 BH-IMPT plans, we extended this study for another 30 patients to evaluate the PTV lengths and the percentage of patients that can be treated with BH-IMPT. Results: The PTV lengths along the beam path range from 2.0 to 6.8 cm for the BH-IMPT plans. On average, each field contains 9.5 1.8 scanning layers and 230 18 scanning spots. As shown in Table 1, the layer switching time dominates the delivery time of the entire field. The estimated delivery time per field is 14.3 2.4 s (9.9-19.3 s), 16.7 2.7 s (11.1-21.5 s), 29.6 4.8 s (19.7-38.7 s), and 86.4 14.9 s (55.7-114.7 s) for the 1 s/5 ms, 1.2 s/5 ms, 2.0 s/10 ms, and 8 s/10 ms systems, respectively. The retrospective analysis shows an average PTV length of 4.3 1.3 cm (1.8-7.2 cm) for a total of 50 lung SBRT patients. With 15 second BH as selection criteria for BH-IMPT, the 1 s/5 ms and 1.2 s/5 ms systems would be feasible to treat 74% and 32% of lung SBRT cases, respectively while the 2 s/10 ms and 8 s/10 ms systems were not feasible. Conclusions: Improvements of the energy switching time makes the BHIMPT lung SBRT feasible for the fast pencil beam scanning systems. For the majority of cases, the BH-IMPT fields can be delivered within one breath hold. For the remaining cases, it may be required to divide each fraction into several sub-deliveries such that each sub-delivery could be treated within one breath hold.
Oral Scientific Abstract 311; Table Analysis of Mean Excursion or < 4 mm in Any Direction (For All Patients, CRT and HRT)
DE < 4 mm Variable
(n Z 747)
DE 4 mm (n Z 97)
p-value
Mean Age Mean Baseline Weight (kg) Mean Original Excursion LR (mm) Mean Original Excursion SI (mm) Mean Original Excursion AP (mm) Mean Charlson Comorbidity Index Total Score Mean Karnofsky Performance Status Male Gender Lower Lobe Tumor Location
73 75.5
69 88.8
< 0.001 < 0.001
1.4
1.5
0.16
1.8
2.1
0.09
4.1
9.9
2.7
3.3
87
92
411 (55%) 231 (31%)
69 (71%) 77 (79%)
Oral Scientific Abstract 312;Table Scanning Parameter Combinations 1.0 1.2 2.0 8.0
s/5 ms s/5 ms s/10 ms s/10 ms
Layer Switching Time (s) 9.0 11.4 19.0 75.8
1.8 2.2 3.6 14.4
Spot Delivery Time (s) 5.3 5.3 10.6 10.6
1.5 1.5 3.0 3.0
Author Disclosure: M. Lin: None. L. Jolinta: None. S.J. Feigenberg: None. M.P. Mehta: None. W.D. D’Souza: None. K.M. Langen: None.
< 0.001 0.03
313
0.001
Evaluation of a Template-Based Algorithm for Markerless Lung Tumor Tracking on Single Energy and Dual Energy kV Images A.M. Block, R. Patel, J. Panfil, J. Breunig, M. Surucu, M.M. Harkenrider, and J.C. Roeske; Loyola University Medical Center, Maywood, IL
0.003 < 0.001
Author Disclosure: M.S. Jawad: None. S.M. Vance: None. I.S. Grills: None. H. Ye: None. S.K. Prausa: None. J. Wloch: None. D. Yan: None.
312 Breath-Hold Intensity Modulated Proton Therapy (BH-IMPT) for Lung SBRT: Feasibility Study M. Lin,1 L. Jolinta,1 S.J. Feigenberg,1 M.P. Mehta,1 W.D. DSouza,2 and K.M. Langen1; 1University of Maryland School of Medicine, Baltimore, MD, 2University of Maryland, Baltimore, MD Purpose/Objective(s): Respiratory motion can compromise the delivery quality of the intensity modulated proton therapy (IMPT) plans. Several new pencil beam scanning systems feature a fast switching between scanning layers. This may enable delivering each IMPT field within one breath hold (BH). This work aims to investigate the feasibility of BH-IMPT for four energy switching time/average spot delivery time (assuming a dose delivery of 2 Gy) combinations: 1 s/5 ms, 1.2 s/5 ms, 2.0 s/10 ms, and 8 s/10 ms. Materials/Methods: Twenty consecutive patients treated with photon SBRT who underwent 4D CT scan were selected (GTV 0.65 - 46 cm3) for this study. BH IMPT plans were generated based on patients T50 phase CT. PTVs were defined as the GTV with a 6 mm isotropic expansion accounting for subclinical disease and setup error. Range uncertainties were considered in the beam design. The prescribed dose was 48 Gy in 4 fractions. Each BH-IMPT plan was composed of 2-3 fields with a scanning
Purpose/Objective(s): Dual-energy (DE) subtraction takes advantage of the higher differential attenuation of bone as a function of energy relative to soft tissue to produce tissue-selective composite images. In the thorax, planar DE imaging can improve tumor visualization by removing obscuring bony anatomy. Previously, our group demonstrated that DE thoracic imaging enhances tumor localization in lung cancer patients receiving kV-based image guided radiation therapy (IGRT). The purpose of the present study is to evaluate a template-based matching algorithm on single energy (SE) and DE radiographs for markerless-motion tracking of lung tumors. Materials/Methods: A total of 59 images from 12 patients with Stage IAIIIA lung cancer treated with stereotactic body radiation therapy (SBRT) (n Z 9) or 3D conformal radiation therapy (n Z 3) were considered. At the time of treatment, patients had gated end-expiration SE radiographs obtained at 60 and 120 kVp at a variety of gantry angles (28 anterior, 31 oblique). Using these radiographs, weighted logarithmic subtraction was performed to remove bones (ribs) to create soft-tissue enhanced DE images. Separately, the gross tumor volume (GTV) was contoured on respiratory-gated CT simulation scans at end-expiration. A template-based matching algorithm was then used to localize individual GTVs on both SE and DE radiographs. Two physicians independently identified the “ground truth” locations of the GTVs, which were defined by manual placement of each template on each image set. The GTV centroid coordinates obtained from the template matching software on both SE and DE images were subsequently compared with the “ground truth” coordinates.
International Journal of Radiation Oncology Biology Physics
tumors with DE 4 mm. Pearson correlation was performed to associate clinical factors with DE. Continuous variables were analyzed with an independent samples t-test and categorical variables with chi-square. Results: Eight hundred forty-four 4D-CBCT’s were analyzed (495 CRT, 349 HRT). DE was largest in the SI direction overall, with mean (SD) of 0.5 ( 3) mm (-25 - 17). Mean DE (mm) in the SI direction was larger in HRT as compared to CRT, with smaller SD (1.1 ( 2.3) v 0.03 ( 3.3), p < 0.001). A similar trend was noted in the AP direction, and no difference was seen in the LR direction. Eleven percent of the 844 4D-CBCT’s had DE > 4 mm (38% HRT, 62% CRT). For treatments with DE > 4 mm, overall mean target dose reduction was largest in the SI direction, -7.4 4.2%. The following factors were significantly correlated with DE: age, weight, tumor location, performance status (KPS), smoking history, pre-RT O2 use, and planning 4D-CT excursion. Tumor size and right v left lung did not correlate. Tumors with 4 mm DE in any direction were found in younger patients with higher weight and KPS, male gender, and lower lobe (LL) location (Table 1). Conclusions: The largest degree of DE is seen in the SI direction for both CRT and HRT, causing > 5% target dose reduction in 11% of daily RT deliveries. Target margins designed based only on pre-treatment 4D-CT without considering clinical variables could under compensate for target motion during treatment. Large DE seems predictable, and seen more in young patients with higher baseline weight, KPS, male gender, and LL tumors. Online 4D-CBCT provides a means to monitor excursion and adapt RT, and further analysis to optimize timing is underway.
spot size of 3 mm. The delivery time of each field was estimated based on the four scanning parameters combinations. The average spot delivery time was scaled up by a factor of 6 to represent high dose delivery. Based on the delivery time and PTV lengths of the 20 BH-IMPT plans, we extended this study for another 30 patients to evaluate the PTV lengths and the percentage of patients that can be treated with BH-IMPT. Results: The PTV lengths along the beam path range from 2.0 to 6.8 cm for the BH-IMPT plans. On average, each field contains 9.5 1.8 scanning layers and 230 18 scanning spots. As shown in Table 1, the layer switching time dominates the delivery time of the entire field. The estimated delivery time per field is 14.3 2.4 s (9.9-19.3 s), 16.7 2.7 s (11.1-21.5 s), 29.6 4.8 s (19.7-38.7 s), and 86.4 14.9 s (55.7-114.7 s) for the 1 s/5 ms, 1.2 s/5 ms, 2.0 s/10 ms, and 8 s/10 ms systems, respectively. The retrospective analysis shows an average PTV length of 4.3 1.3 cm (1.8-7.2 cm) for a total of 50 lung SBRT patients. With 15 second BH as selection criteria for BH-IMPT, the 1 s/5 ms and 1.2 s/5 ms systems would be feasible to treat 74% and 32% of lung SBRT cases, respectively while the 2 s/10 ms and 8 s/10 ms systems were not feasible. Conclusions: Improvements of the energy switching time makes the BHIMPT lung SBRT feasible for the fast pencil beam scanning systems. For the majority of cases, the BH-IMPT fields can be delivered within one breath hold. For the remaining cases, it may be required to divide each fraction into several sub-deliveries such that each sub-delivery could be treated within one breath hold.
Oral Scientific Abstract 311; Table Analysis of Mean Excursion or < 4 mm in Any Direction (For All Patients, CRT and HRT)
DE < 4 mm Variable
(n Z 747)
DE 4 mm (n Z 97)
p-value
Mean Age Mean Baseline Weight (kg) Mean Original Excursion LR (mm) Mean Original Excursion SI (mm) Mean Original Excursion AP (mm) Mean Charlson Comorbidity Index Total Score Mean Karnofsky Performance Status Male Gender Lower Lobe Tumor Location
73 75.5
69 88.8
< 0.001 < 0.001
1.4
1.5
0.16
1.8
2.1
0.09
4.1
9.9
2.7
3.3
87
92
411 (55%) 231 (31%)
69 (71%) 77 (79%)
Oral Scientific Abstract 312;Table Scanning Parameter Combinations 1.0 1.2 2.0 8.0
s/5 ms s/5 ms s/10 ms s/10 ms
Layer Switching Time (s) 9.0 11.4 19.0 75.8
1.8 2.2 3.6 14.4
Spot Delivery Time (s) 5.3 5.3 10.6 10.6
1.5 1.5 3.0 3.0
Author Disclosure: M. Lin: None. L. Jolinta: None. S.J. Feigenberg: None. M.P. Mehta: None. W.D. D’Souza: None. K.M. Langen: None.
< 0.001 0.03
313
0.001
Evaluation of a Template-Based Algorithm for Markerless Lung Tumor Tracking on Single Energy and Dual Energy kV Images A.M. Block, R. Patel, J. Panfil, J. Breunig, M. Surucu, M.M. Harkenrider, and J.C. Roeske; Loyola University Medical Center, Maywood, IL
0.003 < 0.001
Author Disclosure: M.S. Jawad: None. S.M. Vance: None. I.S. Grills: None. H. Ye: None. S.K. Prausa: None. J. Wloch: None. D. Yan: None.
312 Breath-Hold Intensity Modulated Proton Therapy (BH-IMPT) for Lung SBRT: Feasibility Study M. Lin,1 L. Jolinta,1 S.J. Feigenberg,1 M.P. Mehta,1 W.D. DSouza,2 and K.M. Langen1; 1University of Maryland School of Medicine, Baltimore, MD, 2University of Maryland, Baltimore, MD Purpose/Objective(s): Respiratory motion can compromise the delivery quality of the intensity modulated proton therapy (IMPT) plans. Several new pencil beam scanning systems feature a fast switching between scanning layers. This may enable delivering each IMPT field within one breath hold (BH). This work aims to investigate the feasibility of BH-IMPT for four energy switching time/average spot delivery time (assuming a dose delivery of 2 Gy) combinations: 1 s/5 ms, 1.2 s/5 ms, 2.0 s/10 ms, and 8 s/10 ms. Materials/Methods: Twenty consecutive patients treated with photon SBRT who underwent 4D CT scan were selected (GTV 0.65 - 46 cm3) for this study. BH IMPT plans were generated based on patients T50 phase CT. PTVs were defined as the GTV with a 6 mm isotropic expansion accounting for subclinical disease and setup error. Range uncertainties were considered in the beam design. The prescribed dose was 48 Gy in 4 fractions. Each BH-IMPT plan was composed of 2-3 fields with a scanning
Purpose/Objective(s): Dual-energy (DE) subtraction takes advantage of the higher differential attenuation of bone as a function of energy relative to soft tissue to produce tissue-selective composite images. In the thorax, planar DE imaging can improve tumor visualization by removing obscuring bony anatomy. Previously, our group demonstrated that DE thoracic imaging enhances tumor localization in lung cancer patients receiving kV-based image guided radiation therapy (IGRT). The purpose of the present study is to evaluate a template-based matching algorithm on single energy (SE) and DE radiographs for markerless-motion tracking of lung tumors. Materials/Methods: A total of 59 images from 12 patients with Stage IAIIIA lung cancer treated with stereotactic body radiation therapy (SBRT) (n Z 9) or 3D conformal radiation therapy (n Z 3) were considered. At the time of treatment, patients had gated end-expiration SE radiographs obtained at 60 and 120 kVp at a variety of gantry angles (28 anterior, 31 oblique). Using these radiographs, weighted logarithmic subtraction was performed to remove bones (ribs) to create soft-tissue enhanced DE images. Separately, the gross tumor volume (GTV) was contoured on respiratory-gated CT simulation scans at end-expiration. A template-based matching algorithm was then used to localize individual GTVs on both SE and DE radiographs. Two physicians independently identified the “ground truth” locations of the GTVs, which were defined by manual placement of each template on each image set. The GTV centroid coordinates obtained from the template matching software on both SE and DE images were subsequently compared with the “ground truth” coordinates.