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A Tool for Characterizing Randomness and Irregularity in Patient Respiratory Motion
E748
3777 A Tool for Characterizing Randomness and Irregularity in Patient Respiratory Motion S. Zhou, D. Zheng, S. Wang, Q. Fan, X. Wang, and C.A. Enke; University of Nebraska Medical Center, Omaha, NE Purpose/Objective(s): Patient random irregular breathing undermines the fundamental assumption for 4DCT and radiotherapy based on it, either ITV-based or gated treatments. During patient’s 4DCT simulation, Respiratory Gating Signal Waveform (RGSW) is usually collected over a duration much longer than one breathing cycle. Therefore, RGSW may contain valuable information on irregularities in the patient breathing cycles and help to improve imaging and delivery in 4D radiation therapy. In this study, we developed a RGSW based tool for quantitatively accessing the randomness and irregularity level in patient respiratory motion. Materials/Methods: Totally 242 clinical RGSWs obtained with Varian Real-time Position Management (RPM) system were included in this study. For each RGSW, firstly we constructed its unwrapped phase 4(t) using Hilbert transform. Secondly, we computed the phase differences, i.e., 4(t+s)-4(t), between any two points along the waveform with a fixed time interval s. Thirdly, we estimated the standard deviation s of the phase differences. Finally, we calculated volatility (i.e., s ⁄Os) of the RGSW’s phase in the given time interval s. Sixteen intervals (i.e., sZ1s, 2s, 3s, ., 16s) were selected for volatility’s computation to examine if it was stable over different time intervals. The relative standard deviation of the acquired volatility values at all 16 time-intervals was computed for each RGSW. Fittings were performed on the histograms formed by observed volatility over a fixed time interval (e.g., 4s) and the relative standard deviation in its measured values with all 16 intervals from all patient RPM RGSWs. A stochastic random walk phase model was utilized to interpret the results. Results: The unwrapped phase of an ideal periodic RGSW always has zero volatility. For our clinical RGSWs, the volatility is non-zero but reasonably stable over the selected time intervals. The observed volatility at 4s interval from the 242 RGSWs (˛ [0.07, 3.7] (1⁄Os), medianZ0.78 (1⁄Os)) could be approximated by a Gamma distribution G(3.0, 0.3). The population histogram of the relative standard deviation in volatility for the investigated time intervals (˛[2%, 35%], medianZ11.5%) could be fitted with a Gamma distribution G(3.5, 0.04). The stochastic random walk phase model, which yields a fixed volatility value over any given time interval, might serve as a useful tool in explaining our observations on phase volatility in patient’s RGSW. Conclusion: We proposed a new application of patient’s RGSW for measuring the randomness and irregularity in patient respiratory motion. The volatility in RPM RGSW phase has a potential correlation to the eligibility and treatment response of a given patient to a given clinical procedure. Further studies are needed to explore its potential clinical role in patient 4D image acquisition and patient radiotherapy delivery. Author Disclosure: S. Zhou: None. D. Zheng: None. S. Wang: None. Q. Fan: None. X. Wang: None. C.A. Enke: None.
3778 Robust Treatment Planning of Intensity Modulated Proton Therapy for Pelvic Lymph Node Irradiation in High-Risk Prostate Cancer Patients M. Zhu,1 A. Kaiser,2 Y. Kwok,1 M.V. Mishra,2 P.P. Amin,2 S.N. Badiyan,1,2 Z. Vujaskovic,2 and K.M. Langen1; 1University of Maryland School of Medicine, Baltimore, MD, 2University of Maryland Medical Center, Baltimore, MD Purpose/Objective(s): Using intensity modulated proton therapy (IMPT) for pelvic nodes irradiation in high risk prostate cancer patients can achieve better sparing of the normal tissues in the abdomen than photon plans. However, patient anatomic variation, such as increased bowel free air, can create large, sometimes unacceptable uncertainties. This work proposes a method of creating IMPT plans that are robust against dosimetric uncertainty due to anatomic variation.
International Journal of Radiation Oncology Biology Physics Abstract 3778; Table 1 Maximum doses for the treated plans (without RO) and RO plan on the original CT and recalculated on the re-scan CTs Number of Dmax (%) of re-scan CTs
Pt. 1 2 3 4 5
3 4 4 4 5
On Planning CT 104.9 107.3 107.3 105.9 105.3
Treated plan
Dmax(%) of
RO plan
On re-scan CT
On Planning CT
On re-scan CT
105.1 107.4 107.6 108.7 106.7
-
120.1 134.0 123.2 145.2 132.3
105.7 108.9 106.5 107.3 106.0
105.7 109.4 106.6 108.0 106.8
-
107.0 111.2 108.7 110.0 108.0
Materials/Methods: Data from 5 representative patients were used. The originally-treated IMPT plans were created in XX treatment planning system (TPS) without robustness optimization (RO). The plan robustness was evaluated by recalculating the dose with isocenter offset of 5mm combined with a range variation of 3.5%. All the treated plans (without RO) had acceptable robustness per our institutional guidelines. During the treatment, 3-5 re-scan CT images were acquired for each patient and were registered with the planning CT image. Doses were recalculated on the rescan CTs to evaluate the dosimetric variations due to patient anatomy change. In this work, treatment plans with RO were created in YY TPS. In addition to the native planning CT, two copies of the CT images were created. On the first copy, rectum, large bowel, and small bowel are assigned the density of air; and on the second copy, these structures are assigned the density of tissue. All 3 CT images are included in the robustness optimization process, which also includes a 5mm isotropic setup uncertainty and a 3.5% range uncertainty. The RO plans are normalized to the same target coverage as the treated plans, and doses are also recalculated on the re-scan CTs for the RO plans. Results: Table 1 lists the maximum doses (Dmax) of the treated plans (without RO) and the RO plans on the planning CT as well as the Dmax range of those respective plans when recalculated on the 3-5 re-scan CTs. Without RO, the Dmax can be as high as 145.2%, and the hot spot can be in or close to the critical structures, such as the rectum and bowel. With RO, the Dmax are no greater than 111.2% for all 5 patients on all re-scan CTs, and the 105% doses are usually limited to small volumes. Conclusion: Our method of including modified copies of the planning CT images in the RO to simulate the potential bowel filling variations greatly improved the plan robustness as evaluated by the doses recalculated on the re-scan CTs. The improved plan robustness eliminated the need of re-plan due to patient anatomy variation. Author Disclosure: M. Zhu: None. A. Kaiser: None. Y. Kwok: None. M.V. Mishra: Employee; Orthofix. Research Grant; ASTRO, Keep Punching. Advisory Board; Patient Centers Outcomes Research Institute (PCORI). Travel Expenses; Patient Centers Outcomes Research Institute (PCORI). P.P. Amin: None. S.N. Badiyan: None. Z. Vujaskovic: None. K.M. Langen: Editor; IJROBP.
3779 A Preliminary Study of Early Indicators for Cervical Cancer Radiation Therapy Response R. Meerschaert, S.R. Miller II, and L. Zhuang; Wayne State University School of Medicine, Detroit, MI Purpose/Objective(s): To identify indicators for treatment response for cervical cancer radiotherapy based on multi-modality images and patient information collected prior to and during treatment. Materials/Methods: This study included 37 biopsy proven cervical cancer patients (stage IB-IVA) treated from 2011-2015. Treatment included a combination of external beam radiotherapy (EBRT) and 5 fractions of high-dose-rate brachytherapy (BT). A 18F-FDG-PET/CT and a treatment planning CT were acquired for each patient prior to EBRT. The clinical tumor volume (CTV) was propagated from the planning CT to the PET/CT through image fusion. A standardized uptake value (SUV) map was then generated for the CTV from the PET image. Functional metabolic parameters including kurtosis, skewness, standard deviation, mean,
3777 A Tool for Characterizing Randomness and Irregularity in Patient Respiratory Motion S. Zhou, D. Zheng, S. Wang, Q. Fan, X. Wang, and C.A. Enke; University of Nebraska Medical Center, Omaha, NE Purpose/Objective(s): Patient random irregular breathing undermines the fundamental assumption for 4DCT and radiotherapy based on it, either ITV-based or gated treatments. During patient’s 4DCT simulation, Respiratory Gating Signal Waveform (RGSW) is usually collected over a duration much longer than one breathing cycle. Therefore, RGSW may contain valuable information on irregularities in the patient breathing cycles and help to improve imaging and delivery in 4D radiation therapy. In this study, we developed a RGSW based tool for quantitatively accessing the randomness and irregularity level in patient respiratory motion. Materials/Methods: Totally 242 clinical RGSWs obtained with Varian Real-time Position Management (RPM) system were included in this study. For each RGSW, firstly we constructed its unwrapped phase 4(t) using Hilbert transform. Secondly, we computed the phase differences, i.e., 4(t+s)-4(t), between any two points along the waveform with a fixed time interval s. Thirdly, we estimated the standard deviation s of the phase differences. Finally, we calculated volatility (i.e., s ⁄Os) of the RGSW’s phase in the given time interval s. Sixteen intervals (i.e., sZ1s, 2s, 3s, ., 16s) were selected for volatility’s computation to examine if it was stable over different time intervals. The relative standard deviation of the acquired volatility values at all 16 time-intervals was computed for each RGSW. Fittings were performed on the histograms formed by observed volatility over a fixed time interval (e.g., 4s) and the relative standard deviation in its measured values with all 16 intervals from all patient RPM RGSWs. A stochastic random walk phase model was utilized to interpret the results. Results: The unwrapped phase of an ideal periodic RGSW always has zero volatility. For our clinical RGSWs, the volatility is non-zero but reasonably stable over the selected time intervals. The observed volatility at 4s interval from the 242 RGSWs (˛ [0.07, 3.7] (1⁄Os), medianZ0.78 (1⁄Os)) could be approximated by a Gamma distribution G(3.0, 0.3). The population histogram of the relative standard deviation in volatility for the investigated time intervals (˛[2%, 35%], medianZ11.5%) could be fitted with a Gamma distribution G(3.5, 0.04). The stochastic random walk phase model, which yields a fixed volatility value over any given time interval, might serve as a useful tool in explaining our observations on phase volatility in patient’s RGSW. Conclusion: We proposed a new application of patient’s RGSW for measuring the randomness and irregularity in patient respiratory motion. The volatility in RPM RGSW phase has a potential correlation to the eligibility and treatment response of a given patient to a given clinical procedure. Further studies are needed to explore its potential clinical role in patient 4D image acquisition and patient radiotherapy delivery. Author Disclosure: S. Zhou: None. D. Zheng: None. S. Wang: None. Q. Fan: None. X. Wang: None. C.A. Enke: None.
3778 Robust Treatment Planning of Intensity Modulated Proton Therapy for Pelvic Lymph Node Irradiation in High-Risk Prostate Cancer Patients M. Zhu,1 A. Kaiser,2 Y. Kwok,1 M.V. Mishra,2 P.P. Amin,2 S.N. Badiyan,1,2 Z. Vujaskovic,2 and K.M. Langen1; 1University of Maryland School of Medicine, Baltimore, MD, 2University of Maryland Medical Center, Baltimore, MD Purpose/Objective(s): Using intensity modulated proton therapy (IMPT) for pelvic nodes irradiation in high risk prostate cancer patients can achieve better sparing of the normal tissues in the abdomen than photon plans. However, patient anatomic variation, such as increased bowel free air, can create large, sometimes unacceptable uncertainties. This work proposes a method of creating IMPT plans that are robust against dosimetric uncertainty due to anatomic variation.
International Journal of Radiation Oncology Biology Physics Abstract 3778; Table 1 Maximum doses for the treated plans (without RO) and RO plan on the original CT and recalculated on the re-scan CTs Number of Dmax (%) of re-scan CTs
Pt. 1 2 3 4 5
3 4 4 4 5
On Planning CT 104.9 107.3 107.3 105.9 105.3
Treated plan
Dmax(%) of
RO plan
On re-scan CT
On Planning CT
On re-scan CT
105.1 107.4 107.6 108.7 106.7
-
120.1 134.0 123.2 145.2 132.3
105.7 108.9 106.5 107.3 106.0
105.7 109.4 106.6 108.0 106.8
-
107.0 111.2 108.7 110.0 108.0
Materials/Methods: Data from 5 representative patients were used. The originally-treated IMPT plans were created in XX treatment planning system (TPS) without robustness optimization (RO). The plan robustness was evaluated by recalculating the dose with isocenter offset of 5mm combined with a range variation of 3.5%. All the treated plans (without RO) had acceptable robustness per our institutional guidelines. During the treatment, 3-5 re-scan CT images were acquired for each patient and were registered with the planning CT image. Doses were recalculated on the rescan CTs to evaluate the dosimetric variations due to patient anatomy change. In this work, treatment plans with RO were created in YY TPS. In addition to the native planning CT, two copies of the CT images were created. On the first copy, rectum, large bowel, and small bowel are assigned the density of air; and on the second copy, these structures are assigned the density of tissue. All 3 CT images are included in the robustness optimization process, which also includes a 5mm isotropic setup uncertainty and a 3.5% range uncertainty. The RO plans are normalized to the same target coverage as the treated plans, and doses are also recalculated on the re-scan CTs for the RO plans. Results: Table 1 lists the maximum doses (Dmax) of the treated plans (without RO) and the RO plans on the planning CT as well as the Dmax range of those respective plans when recalculated on the 3-5 re-scan CTs. Without RO, the Dmax can be as high as 145.2%, and the hot spot can be in or close to the critical structures, such as the rectum and bowel. With RO, the Dmax are no greater than 111.2% for all 5 patients on all re-scan CTs, and the 105% doses are usually limited to small volumes. Conclusion: Our method of including modified copies of the planning CT images in the RO to simulate the potential bowel filling variations greatly improved the plan robustness as evaluated by the doses recalculated on the re-scan CTs. The improved plan robustness eliminated the need of re-plan due to patient anatomy variation. Author Disclosure: M. Zhu: None. A. Kaiser: None. Y. Kwok: None. M.V. Mishra: Employee; Orthofix. Research Grant; ASTRO, Keep Punching. Advisory Board; Patient Centers Outcomes Research Institute (PCORI). Travel Expenses; Patient Centers Outcomes Research Institute (PCORI). P.P. Amin: None. S.N. Badiyan: None. Z. Vujaskovic: None. K.M. Langen: Editor; IJROBP.
3779 A Preliminary Study of Early Indicators for Cervical Cancer Radiation Therapy Response R. Meerschaert, S.R. Miller II, and L. Zhuang; Wayne State University School of Medicine, Detroit, MI Purpose/Objective(s): To identify indicators for treatment response for cervical cancer radiotherapy based on multi-modality images and patient information collected prior to and during treatment. Materials/Methods: This study included 37 biopsy proven cervical cancer patients (stage IB-IVA) treated from 2011-2015. Treatment included a combination of external beam radiotherapy (EBRT) and 5 fractions of high-dose-rate brachytherapy (BT). A 18F-FDG-PET/CT and a treatment planning CT were acquired for each patient prior to EBRT. The clinical tumor volume (CTV) was propagated from the planning CT to the PET/CT through image fusion. A standardized uptake value (SUV) map was then generated for the CTV from the PET image. Functional metabolic parameters including kurtosis, skewness, standard deviation, mean,