- Email: [email protected]
The “Air-Bag System”: A Novel Abdominal Compression Device Collaborated with RPM System
I. J. Radiation Oncology d Biology d Physics
S892
Volume 81, Number 2, Supplement, 2011
Median HDR and LDR Equivalent Doses for ABS Reference Points ABS Point A B P Bladder Rectum
Median HDR Dose (Gy)
HDR Range (Gy)
LDR Equivalent (Gy)
LDR Range (Gy)
27.83 6.93 5.63 18.39 12.80
24.28 - 30.09 4.77 - 12.36 3.63 - 9.48 6.21 - 30.72 7.4 - 19.74
43.70 7.54 5.96 46.88 26.53
36.15 - 48.83 4.94 - 15.1 3.67 - 10.87 9.49 - 109.42 12.01 - 52.31
Author Disclosure: H. Hsu: None. T. Duckworth: None. P. Schiff: None.
3428
Investigation of the Compounding Effect of MLC Positioning Uncertainty and Gantry Angular Acceleration in VMAT Delivery
Y. Song, Q. Zhang, C. Burman, C. Obcemea, B. Mueller, B. Mychalczak Memorial Sloan-Kettering Cancer Center, Sleepy Hollow, NY Purpose/Objective(s): We have successfully developed an aperture-based VMAT planning system to address the inherent deficiencies of IMRT. The significance is that this is the first non-commercial VMAT, developed by a single academic institution, fully tested, and clinically implemented in the Trilogy RapidArc mode. Contrast to IMRT, where intensity modulation is achieved solely through leaf motion, our VMAT creates intensity modulation through MLC aperture, dose rate, and gantry angular speed modulations. The intentional suppression of intensity modulation levels to minimize required MU is compensated for by using a full arc and gantry angular speed modulation. Consequently, the frequent changes in gantry angular speed required to deliver a given angular dose rate lead to a rapidly alternating gantry angular acceleration. As the temporal dose rate (MU/min) is a constant between two consecutive control points, excessive gantry acceleration could potentially become a source of dosimetric error. In addition, unlike IMRT delivery, where a beam-hold-off can be triggered if a leaf fails to reach the target position in given time, RapidArc does not have this function as the MLC motion is constrained by the gantry motion. To ensure a smooth delivery, RapidArc uses a large MLC positioning uncertainty (5 mm). Thus, the compounding effect of the two could result in a big dosimetric error. Our objective is to develop procedures to estimate the order of resulting dosimetric error. Materials/Methods: To estimate the dosimetric error caused by MLC positioning uncertainty, we edited the control point sequence file of a deliverable VMAT plan using a Gaussian function, so that the mean MLC positioning uncertainty was 1, 2, 3, 4, and 5 mm, respectively. The dose and MU of the edited plan were re-calculated. For each mean value, five plans were generated. The edited plans were delivered without gantry angular speed modulation and measured with a MapCHECK. To investigate the dosimetric error caused by gantry angular acceleration, unedited VMAT plans were delivered six times with six different maximum temporal dose rates: 600, 500, 400, 300, 200, and 100 MU/min, respectively. The dose was measured with a MapCHECK in MapPHAN. Results: The dosimetric errors caused by MLC positioning uncertainty without gantry angular speed modulation were about 0.2, 0.5, 1.2, 1.8, and 2.1% for 1, 2, 3, 4, and 5 mm positioning uncertainties. The dosimetric errors caused by gantry angular acceleration were -2.2, -1.5, -0.97, -0.37, and -0.19% at CAX for dose rates of 100, 200, 300, 400, and 500 MU/min, compared with 600 MU/min. Conclusions: The compounding effect of MLC positioning uncertainty and gantry angular speed acceleration is significant and should be taken into account in treatment planning and delivery. Author Disclosure: Y. Song: None. Q. Zhang: None. C. Burman: None. C. Obcemea: None. B. Mueller: None. B. Mychalczak: None.
3429
The ‘‘Air-Bag System’’: A Novel Abdominal Compression Device Collaborated with RPM System
R. Oh, N. Masai, H. Shiomi, T. Inoue Miyakojima IGRT Clinic, Osaka, Japan Purpose/Objective(s): We developed a novel abdominal compression device which monitors the patient’s body volume change as an external respiration signal collaborated with the Real-Time Position Management System (RPM, Varian Medical System, Palo Alto, CA). Materials/Methods: The ‘‘Air-Bag System’’ consists of a non-elastic air bag connected with an elastic air bag. A non-elastic air bag is placed between the patient’s abdomen and the stereotactic fixation frame. Air can be injected into this system to give pressure on the patient’s abdomen. A current meter located between two bags measures the air flow back and forth between these bags. This air flow data are processed by personal computer and translated into swinging decoy markers displayed on the computer screen so that an infrared camera of RPM system can capture the marker instead of an infrared reflective marker. The impedance model was adopted for describing the behavior of the air flow in this system. The phase gap between the respiratory motion and the monitoring signal is defined as q = arctan (X/R). Where R is the resistive part, and X is the reactive part of the impedance. The resistive part represents the viscous forces at the air/wall interface. The reactive part, which is a respiratory frequency dependent parameter, represents the ability of air to store the kinetic energy as potential energy since air is a compressible medium. An elastic air bag also stores potential energy by inflation and deflation. Both values of R and X were obtained experimentally and the theoretical equation was evaluated with the clinical data of 25 patients. 4D-CT data of 93 patients (49 lung cancer patients and 44
Proceedings of the 53rd Annual ASTRO Meeting
S893
liver cancer patients) were acquired by the RPM system with the ‘‘Air-Bag System’’ in order to observe the motion of the diaphragm while free breathing. Results: Both values of R and X were obtained by least squares method with strong correlations (R; r2 = 0.965, X; r2 = 0.973). The theoretical equation was given by q = arctan(X/R) = arctan((25.178f-1/0.604f)/23.780). Where f is the respiratory frequency. Comparing the 25 clinical data to the theoretical equation, the phase gaps were resulted in good correlations on each respiratory frequency. Diaphragm motion was reduced to 7.1 ± 3.8mm (1.2 - 23.5mm) in the superior to inferior direction with 4D-CT data of 93 patients. Conclusions: The novel abdominal compression device which presses on the patient’s abdomen with the air bag reduces the movement of diaphragm without loading additional stress on the patient. This device can also be used for respiratory monitoring which monitors the patient’s body volume change as an external respiration signal. The phase gap between the respiratory motion and the monitoring signal was negligibly small under average respiratory frequency. Author Disclosure: R. Oh: None. N. Masai: None. H. Shiomi: None. T. Inoue: None.
3430
Targeted Hippocampal Irradiation in a Small Rodent Using IMRS and RapidArc SRS: Preliminary Data
D. E. Roa, M. Acharya, O. Bosch, L. Christie, M. Hamamura, M. Lan, C. Limoli University of California Irvine, Orange, CA Purpose/Objective(s): To use a rodent model to develop and optimize the procedures for the precise irradiation of the hippocampal region with minimum radiation dose to the remainder of the brain. For this purpose, IMRS and RapidArc VMAT SRS were used to irradiate one and two hippocampi, respectively, of athymic nude (ATN) rats. Prescribed dose was verified using Mapcheck while irradiated and spared brain region(s) were confirmed through brain cell staining postmortem. Materials/Methods: Seven ATN rats, 6 - 8 weeks old underwent human-like radiation treatment planning followed by imageguided SRS. MRI and CT axial images 0.8-mm thickness of the rat’s skull were acquired and transferred to ECLIPSE treatment planning software to aid in contouring the brain, right and left hippocampi. A 6-field non-coplanar IMRS plan was generated to target the left hippocampus to a dose of 10 Gy while a coplanar two-arc RapidArc SRS plan targeted both hippocampi also to 10 Gy. Treatment was delivered using a 6 MV photon beam from a Varian Trilogy Linac equipped with on-board imaging (OBI). Prior to treatment, the dose was verified through a QA plan generated from the treatment plan and delivered to a Mapcheck detector array imbedded in a virtual water phantom. Orthogonal x-ray images taken with the OBI and co-registered to DRR images from the planning CT were used to precisely adjust the rat’s treatment position. One month post-irradiation, rats were euthanized and 30-micron thick brain sections were evaluated using an immunocytochemical technique to verify the radiation effects in the targeted and non-targeted regions. Results: Table 1 presents dosimetric results for one and two hippocampi irradiation using IMRS and RapidArc SRS, respectively. Percent differences between calculated and measured dose using Mapcheck for one hippocampus and two hippocampi were 5.0% and 2.0%, respectively. Cell staining performed in the single hippocampus irradiation cases revealed a significant reduction in cell population in the ipsilateral hippocampus while populations comparable to those in a non-irradiated subject were observed in the contralateral hippocampal region. Conclusions: Present results demonstrate that precise irradiation of small volumes within a rat’s brain can be achieved with human-like image-guided IMRS and RapidArc SRS treatments. Postmortem clinical analysis of the rat brain provides evidence of high-precision targeted radiation damage and dose sparing. Table 1 One Hippocampus (n = 2)
Left Hippocampus Right Hippocampus Brain w/ Hippocampi Brain w/o Hippocampi
Two Hippocampi (n = 5)
Min (Gy)
Max (Gy)
Mean (Gy)
Min (Gy)
Max (Gy)
Mean (Gy)
7.0 0.1 0.1 0.1
13.6 2.8 13.6 8.5
11.7 0.7 2.6 1.9
9.4 9.7 0.6 0.6
10.7 10.9 11.0 8.0
10.2 10.4 4.4 3.2
Author Disclosure: D.E. Roa: None. M. Acharya: None. O. Bosch: None. L. Christie: None. M. Hamamura: None. M. Lan: None. C. Limoli: None.
3431
Feasibility of TBI with Simultaneous Red Marrow Boost (rTMI)
J. A. Penagaricano, E. G. Moros, P. M. Corry, V. Ratanatharathorn University of Arkansas for Medical Sciences, Little Rock, AR Purpose/Objective(s): TBI continues to be an integral part of preparatory regimes prior to allogeneic stem cell transplantation. A prospective randomized study of 12 Gy at 2 Gy per fraction in 6 days compared to 15.75 Gy at 2.25 Gy per fraction in 7 days showed a decreased probability of relapse in the latter regime in AML adult patients in first remission. However, there was no
S892
Volume 81, Number 2, Supplement, 2011
Median HDR and LDR Equivalent Doses for ABS Reference Points ABS Point A B P Bladder Rectum
Median HDR Dose (Gy)
HDR Range (Gy)
LDR Equivalent (Gy)
LDR Range (Gy)
27.83 6.93 5.63 18.39 12.80
24.28 - 30.09 4.77 - 12.36 3.63 - 9.48 6.21 - 30.72 7.4 - 19.74
43.70 7.54 5.96 46.88 26.53
36.15 - 48.83 4.94 - 15.1 3.67 - 10.87 9.49 - 109.42 12.01 - 52.31
Author Disclosure: H. Hsu: None. T. Duckworth: None. P. Schiff: None.
3428
Investigation of the Compounding Effect of MLC Positioning Uncertainty and Gantry Angular Acceleration in VMAT Delivery
Y. Song, Q. Zhang, C. Burman, C. Obcemea, B. Mueller, B. Mychalczak Memorial Sloan-Kettering Cancer Center, Sleepy Hollow, NY Purpose/Objective(s): We have successfully developed an aperture-based VMAT planning system to address the inherent deficiencies of IMRT. The significance is that this is the first non-commercial VMAT, developed by a single academic institution, fully tested, and clinically implemented in the Trilogy RapidArc mode. Contrast to IMRT, where intensity modulation is achieved solely through leaf motion, our VMAT creates intensity modulation through MLC aperture, dose rate, and gantry angular speed modulations. The intentional suppression of intensity modulation levels to minimize required MU is compensated for by using a full arc and gantry angular speed modulation. Consequently, the frequent changes in gantry angular speed required to deliver a given angular dose rate lead to a rapidly alternating gantry angular acceleration. As the temporal dose rate (MU/min) is a constant between two consecutive control points, excessive gantry acceleration could potentially become a source of dosimetric error. In addition, unlike IMRT delivery, where a beam-hold-off can be triggered if a leaf fails to reach the target position in given time, RapidArc does not have this function as the MLC motion is constrained by the gantry motion. To ensure a smooth delivery, RapidArc uses a large MLC positioning uncertainty (5 mm). Thus, the compounding effect of the two could result in a big dosimetric error. Our objective is to develop procedures to estimate the order of resulting dosimetric error. Materials/Methods: To estimate the dosimetric error caused by MLC positioning uncertainty, we edited the control point sequence file of a deliverable VMAT plan using a Gaussian function, so that the mean MLC positioning uncertainty was 1, 2, 3, 4, and 5 mm, respectively. The dose and MU of the edited plan were re-calculated. For each mean value, five plans were generated. The edited plans were delivered without gantry angular speed modulation and measured with a MapCHECK. To investigate the dosimetric error caused by gantry angular acceleration, unedited VMAT plans were delivered six times with six different maximum temporal dose rates: 600, 500, 400, 300, 200, and 100 MU/min, respectively. The dose was measured with a MapCHECK in MapPHAN. Results: The dosimetric errors caused by MLC positioning uncertainty without gantry angular speed modulation were about 0.2, 0.5, 1.2, 1.8, and 2.1% for 1, 2, 3, 4, and 5 mm positioning uncertainties. The dosimetric errors caused by gantry angular acceleration were -2.2, -1.5, -0.97, -0.37, and -0.19% at CAX for dose rates of 100, 200, 300, 400, and 500 MU/min, compared with 600 MU/min. Conclusions: The compounding effect of MLC positioning uncertainty and gantry angular speed acceleration is significant and should be taken into account in treatment planning and delivery. Author Disclosure: Y. Song: None. Q. Zhang: None. C. Burman: None. C. Obcemea: None. B. Mueller: None. B. Mychalczak: None.
3429
The ‘‘Air-Bag System’’: A Novel Abdominal Compression Device Collaborated with RPM System
R. Oh, N. Masai, H. Shiomi, T. Inoue Miyakojima IGRT Clinic, Osaka, Japan Purpose/Objective(s): We developed a novel abdominal compression device which monitors the patient’s body volume change as an external respiration signal collaborated with the Real-Time Position Management System (RPM, Varian Medical System, Palo Alto, CA). Materials/Methods: The ‘‘Air-Bag System’’ consists of a non-elastic air bag connected with an elastic air bag. A non-elastic air bag is placed between the patient’s abdomen and the stereotactic fixation frame. Air can be injected into this system to give pressure on the patient’s abdomen. A current meter located between two bags measures the air flow back and forth between these bags. This air flow data are processed by personal computer and translated into swinging decoy markers displayed on the computer screen so that an infrared camera of RPM system can capture the marker instead of an infrared reflective marker. The impedance model was adopted for describing the behavior of the air flow in this system. The phase gap between the respiratory motion and the monitoring signal is defined as q = arctan (X/R). Where R is the resistive part, and X is the reactive part of the impedance. The resistive part represents the viscous forces at the air/wall interface. The reactive part, which is a respiratory frequency dependent parameter, represents the ability of air to store the kinetic energy as potential energy since air is a compressible medium. An elastic air bag also stores potential energy by inflation and deflation. Both values of R and X were obtained experimentally and the theoretical equation was evaluated with the clinical data of 25 patients. 4D-CT data of 93 patients (49 lung cancer patients and 44
Proceedings of the 53rd Annual ASTRO Meeting
S893
liver cancer patients) were acquired by the RPM system with the ‘‘Air-Bag System’’ in order to observe the motion of the diaphragm while free breathing. Results: Both values of R and X were obtained by least squares method with strong correlations (R; r2 = 0.965, X; r2 = 0.973). The theoretical equation was given by q = arctan(X/R) = arctan((25.178f-1/0.604f)/23.780). Where f is the respiratory frequency. Comparing the 25 clinical data to the theoretical equation, the phase gaps were resulted in good correlations on each respiratory frequency. Diaphragm motion was reduced to 7.1 ± 3.8mm (1.2 - 23.5mm) in the superior to inferior direction with 4D-CT data of 93 patients. Conclusions: The novel abdominal compression device which presses on the patient’s abdomen with the air bag reduces the movement of diaphragm without loading additional stress on the patient. This device can also be used for respiratory monitoring which monitors the patient’s body volume change as an external respiration signal. The phase gap between the respiratory motion and the monitoring signal was negligibly small under average respiratory frequency. Author Disclosure: R. Oh: None. N. Masai: None. H. Shiomi: None. T. Inoue: None.
3430
Targeted Hippocampal Irradiation in a Small Rodent Using IMRS and RapidArc SRS: Preliminary Data
D. E. Roa, M. Acharya, O. Bosch, L. Christie, M. Hamamura, M. Lan, C. Limoli University of California Irvine, Orange, CA Purpose/Objective(s): To use a rodent model to develop and optimize the procedures for the precise irradiation of the hippocampal region with minimum radiation dose to the remainder of the brain. For this purpose, IMRS and RapidArc VMAT SRS were used to irradiate one and two hippocampi, respectively, of athymic nude (ATN) rats. Prescribed dose was verified using Mapcheck while irradiated and spared brain region(s) were confirmed through brain cell staining postmortem. Materials/Methods: Seven ATN rats, 6 - 8 weeks old underwent human-like radiation treatment planning followed by imageguided SRS. MRI and CT axial images 0.8-mm thickness of the rat’s skull were acquired and transferred to ECLIPSE treatment planning software to aid in contouring the brain, right and left hippocampi. A 6-field non-coplanar IMRS plan was generated to target the left hippocampus to a dose of 10 Gy while a coplanar two-arc RapidArc SRS plan targeted both hippocampi also to 10 Gy. Treatment was delivered using a 6 MV photon beam from a Varian Trilogy Linac equipped with on-board imaging (OBI). Prior to treatment, the dose was verified through a QA plan generated from the treatment plan and delivered to a Mapcheck detector array imbedded in a virtual water phantom. Orthogonal x-ray images taken with the OBI and co-registered to DRR images from the planning CT were used to precisely adjust the rat’s treatment position. One month post-irradiation, rats were euthanized and 30-micron thick brain sections were evaluated using an immunocytochemical technique to verify the radiation effects in the targeted and non-targeted regions. Results: Table 1 presents dosimetric results for one and two hippocampi irradiation using IMRS and RapidArc SRS, respectively. Percent differences between calculated and measured dose using Mapcheck for one hippocampus and two hippocampi were 5.0% and 2.0%, respectively. Cell staining performed in the single hippocampus irradiation cases revealed a significant reduction in cell population in the ipsilateral hippocampus while populations comparable to those in a non-irradiated subject were observed in the contralateral hippocampal region. Conclusions: Present results demonstrate that precise irradiation of small volumes within a rat’s brain can be achieved with human-like image-guided IMRS and RapidArc SRS treatments. Postmortem clinical analysis of the rat brain provides evidence of high-precision targeted radiation damage and dose sparing. Table 1 One Hippocampus (n = 2)
Left Hippocampus Right Hippocampus Brain w/ Hippocampi Brain w/o Hippocampi
Two Hippocampi (n = 5)
Min (Gy)
Max (Gy)
Mean (Gy)
Min (Gy)
Max (Gy)
Mean (Gy)
7.0 0.1 0.1 0.1
13.6 2.8 13.6 8.5
11.7 0.7 2.6 1.9
9.4 9.7 0.6 0.6
10.7 10.9 11.0 8.0
10.2 10.4 4.4 3.2
Author Disclosure: D.E. Roa: None. M. Acharya: None. O. Bosch: None. L. Christie: None. M. Hamamura: None. M. Lan: None. C. Limoli: None.
3431
Feasibility of TBI with Simultaneous Red Marrow Boost (rTMI)
J. A. Penagaricano, E. G. Moros, P. M. Corry, V. Ratanatharathorn University of Arkansas for Medical Sciences, Little Rock, AR Purpose/Objective(s): TBI continues to be an integral part of preparatory regimes prior to allogeneic stem cell transplantation. A prospective randomized study of 12 Gy at 2 Gy per fraction in 6 days compared to 15.75 Gy at 2.25 Gy per fraction in 7 days showed a decreased probability of relapse in the latter regime in AML adult patients in first remission. However, there was no