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Improving Accuracy of Delivery for Volumetric Modulated Arc Therapy Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy by Maximizing Gantry Speed
International Journal of Radiation Oncology Biology Physics
E604 Abstract 3482; Table 1. Original
HI_PGTV HI_PTV CI_PGTV CI_PTV D50%_UB D50%_FH Dm_UB Dm_FH
All
S.
P.
0.040.01 0.250.01 1.020.06 1.010.03 33.982.98 15.713.28 34.112.81 16.332.69
0.040.01 0.250.01 1.020.06 1.010.02 34.132.74 18.872.63 34.272.93 19.252.36
0.040.01 0.250.01 1.020.06 1.010.03 33.903.16 14.142.30 34.032.83 14.871.30
KB PS.
vs. P.
0.64 0.37 0.88 0.33 0.85 <0.01 0.91 <0.01
objectives that were manually defined for VMAT optimizer. Because the model does not estimate target DVHs, fixed objectives were incorporated to VMAT-optimizer to facilitate automated planning. KB-IMRT also increased Dmax(DZ2.79%, P<0.01) due to higher Monitor Units (DZ49.88%, P<0.01) and missing steps of hot spot control by specific manual optimizing or fluence map editing. Impact of setups was negligible, except some suboptimal field geometries induced higher S. FH dose to both original and KB-IMRT, yet the model reduced them largely for both setups. Conclusion: KB-model trained on a technique and an orientation can be used for another, which improved organ sparing and consistency (smaller standard deviations). Yet the target-objectives for VMAT-optimizer should be readapted to IMRT planning, followed by manual hot spot processing. Author Disclosure: Y. Zhang: Research Grant; National Natural Science Foundation of China, Beijing Municipal Administration of Hospitals’ Youth Programme. H. Wu: Research Grant; Special Fund for Quality Scientific Research in the Public Welfare. Chief Physicist; Beijing Cancer Hospital. F. Jiang: None. H. Yue: None. J. Deng: None.
3483 Improving Accuracy of Delivery for Volumetric Modulated Arc Therapy Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy by Maximizing Gantry Speed A. Odom,1,2 T.R. Denton,1,2 L. Shields,2,3 J. Howe,1,2 D. Dellamonica,1,2 M. Gagai,1,2 C. Bond,1,2 C. Dedich,1,2 and A.C. Spalding2,3; 1Associates in Medical Physics, Lanham, MD, 2The Norton Cancer Institute Radiation Center, Louisville, KY, 3The Brain Tumor Center, Norton Healthcare, Louisville, KY Purpose/Objective(s): Volumetric modulated arc therapy (VMAT) planning utilizes modulation of dose rate, gantry speed and multi-leaf collimator (MLC) motion. The large moment of inertia of the gantry creates significant mechanical considerations when modulating gantry motion. We tested the hypothesis that gantry speed modulation could result in reduced accuracy of delivery of VMAT plans due to limitations in gantry motion control. Materials/Methods: The VMAT optimizer delivers the planned MU by keeping either the gantry speed or the dose rate at maximum and modulating the other. When there is a sufficient total arc length to keep the gantry moving at maximum speed and deliver the MU, the dose rate is modulated. When the dose rate becomes saturated, the gantry is modulated to accommodate the requisite MU per control point. Gantry speed modulation was identified by VG Z R/D*Q, where VG is the average gantry speed, R is the max dose rate (MU/s), D is the total plan MU, and Q is the total plan arc length (o). When the prescribed dose, and thus the number of MU, is large, as in SRS and SBRT, the total plan arc length required for maximum gantry speed is greatly increased. Accuracy of delivery was examined for all patients (nZ82) treated on our primary SRS/SBRT linear accelerator during the study period, including a variety of diagnoses and fractionation schemes. Each plan was delivered on a cylindrical diode array. Dose delivered to the diode array was calculated with the same algorithm used for the clinical patient plan. QA was considered passing if 95% of diode measurements passed gamma criteria of 3% /1.5 mm.
All
Supine
Prone
PS. vs. P.
0.050.01 0.260.01 1.020.05 1.180.05 25.091.32 13.731.43 26.251.22 14.621.10
0.050.01 0.250.01 1.010.06 1.190.07 25.120.84 14.671.80 26.190.97 15.411.07
0.050.01 0.260.02 1.020.05 1.180.05 25.071.53 13.260.94 26.271.36 14.230.91
0.65 0.22 0.50 0.65 0.93 0.01 0.95 0.01
POriginal
vs. KB
0.01 <0.01 0.67 <0.01 <0.01 <0.01 <0.01 <0.01
Results: True probability of plan failure was assumed to be demonstrated in the sample without gantry speed modulation, VG6.0 o/s, (nZ39, 3 failures). The one-tail P value for the sample with V
3484 Ultrasound-Based Real-Time Tracking During Abdominal Stereotactic Body Radiation Therapy: Ultrasound Probe Does Not Influence Plan Quality Significantly J. Boda-Heggemann,1 C. Weiss,2 L. Vogel,1 K. Siebenlist,1 D.S.K. Sihono,1 H. Wertz,1 A. Jahnke,1 A.O. Simeonova-Chergou,1 M. Ehmann,1 F. Wenz,1 and F. Lohr3; 1Department of Radiation Oncology, Universita¨tsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany, 2Abteilung fuer Medizinische Statistik, Biomathematik und Informationsverarbeitung, Universita¨tsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany, 3Department of Radiation Oncology, Modena, Modena, Italy Purpose/Objective(s): Online tracking of target or surrogate structures ensure precise delivery and reduction of intrafractional repositioning errors during liver/upper abdominal SBRT. Ultrasound-based tracking provides a non-invasive, markerless possibility for real-time, soft-tissue based 3D surveillance. Ultrasound probes, however, should not be placed into the primary beam due to sensitivity of electronical components to ionizing radiation and undesired distortion of the treatment beam. SBRT plans should therefore ideally spare the probe. We compared VMAT plans with ultrasound probe (partial rotation VMAT arc with spared angle, sp-VMAT) versus a full-arc VMAT (full VMAT without ultrasound probe) to quantify the loss of plan quality. We tested a setup also with an additional noncoplanar arc (noncopl-VMAT and noncopl dMLC with spared angle) to assess if this can compensate for probe sparing. Materials/Methods: Six patients with 7 liver lesions were treated with image-guided SBRT in DIBH (deep inspiratory breath hold) with daily cone-beam CT with additional real-time ultrasound-based tracking with an experimental system. Plans (sp-VMAT, full-VMAT, noncopl-VMAT and noncopl dMLC) were calculated and compared regarding the following parameters: minimal, maximal, mean, median doses to PTV,
E604 Abstract 3482; Table 1. Original
HI_PGTV HI_PTV CI_PGTV CI_PTV D50%_UB D50%_FH Dm_UB Dm_FH
All
S.
P.
0.040.01 0.250.01 1.020.06 1.010.03 33.982.98 15.713.28 34.112.81 16.332.69
0.040.01 0.250.01 1.020.06 1.010.02 34.132.74 18.872.63 34.272.93 19.252.36
0.040.01 0.250.01 1.020.06 1.010.03 33.903.16 14.142.30 34.032.83 14.871.30
KB PS.
vs. P.
0.64 0.37 0.88 0.33 0.85 <0.01 0.91 <0.01
objectives that were manually defined for VMAT optimizer. Because the model does not estimate target DVHs, fixed objectives were incorporated to VMAT-optimizer to facilitate automated planning. KB-IMRT also increased Dmax(DZ2.79%, P<0.01) due to higher Monitor Units (DZ49.88%, P<0.01) and missing steps of hot spot control by specific manual optimizing or fluence map editing. Impact of setups was negligible, except some suboptimal field geometries induced higher S. FH dose to both original and KB-IMRT, yet the model reduced them largely for both setups. Conclusion: KB-model trained on a technique and an orientation can be used for another, which improved organ sparing and consistency (smaller standard deviations). Yet the target-objectives for VMAT-optimizer should be readapted to IMRT planning, followed by manual hot spot processing. Author Disclosure: Y. Zhang: Research Grant; National Natural Science Foundation of China, Beijing Municipal Administration of Hospitals’ Youth Programme. H. Wu: Research Grant; Special Fund for Quality Scientific Research in the Public Welfare. Chief Physicist; Beijing Cancer Hospital. F. Jiang: None. H. Yue: None. J. Deng: None.
3483 Improving Accuracy of Delivery for Volumetric Modulated Arc Therapy Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy by Maximizing Gantry Speed A. Odom,1,2 T.R. Denton,1,2 L. Shields,2,3 J. Howe,1,2 D. Dellamonica,1,2 M. Gagai,1,2 C. Bond,1,2 C. Dedich,1,2 and A.C. Spalding2,3; 1Associates in Medical Physics, Lanham, MD, 2The Norton Cancer Institute Radiation Center, Louisville, KY, 3The Brain Tumor Center, Norton Healthcare, Louisville, KY Purpose/Objective(s): Volumetric modulated arc therapy (VMAT) planning utilizes modulation of dose rate, gantry speed and multi-leaf collimator (MLC) motion. The large moment of inertia of the gantry creates significant mechanical considerations when modulating gantry motion. We tested the hypothesis that gantry speed modulation could result in reduced accuracy of delivery of VMAT plans due to limitations in gantry motion control. Materials/Methods: The VMAT optimizer delivers the planned MU by keeping either the gantry speed or the dose rate at maximum and modulating the other. When there is a sufficient total arc length to keep the gantry moving at maximum speed and deliver the MU, the dose rate is modulated. When the dose rate becomes saturated, the gantry is modulated to accommodate the requisite MU per control point. Gantry speed modulation was identified by VG Z R/D*Q, where VG is the average gantry speed, R is the max dose rate (MU/s), D is the total plan MU, and Q is the total plan arc length (o). When the prescribed dose, and thus the number of MU, is large, as in SRS and SBRT, the total plan arc length required for maximum gantry speed is greatly increased. Accuracy of delivery was examined for all patients (nZ82) treated on our primary SRS/SBRT linear accelerator during the study period, including a variety of diagnoses and fractionation schemes. Each plan was delivered on a cylindrical diode array. Dose delivered to the diode array was calculated with the same algorithm used for the clinical patient plan. QA was considered passing if 95% of diode measurements passed gamma criteria of 3% /1.5 mm.
All
Supine
Prone
PS. vs. P.
0.050.01 0.260.01 1.020.05 1.180.05 25.091.32 13.731.43 26.251.22 14.621.10
0.050.01 0.250.01 1.010.06 1.190.07 25.120.84 14.671.80 26.190.97 15.411.07
0.050.01 0.260.02 1.020.05 1.180.05 25.071.53 13.260.94 26.271.36 14.230.91
0.65 0.22 0.50 0.65 0.93 0.01 0.95 0.01
POriginal
vs. KB
0.01 <0.01 0.67 <0.01 <0.01 <0.01 <0.01 <0.01
Results: True probability of plan failure was assumed to be demonstrated in the sample without gantry speed modulation, VG6.0 o/s, (nZ39, 3 failures). The one-tail P value for the sample with V
3484 Ultrasound-Based Real-Time Tracking During Abdominal Stereotactic Body Radiation Therapy: Ultrasound Probe Does Not Influence Plan Quality Significantly J. Boda-Heggemann,1 C. Weiss,2 L. Vogel,1 K. Siebenlist,1 D.S.K. Sihono,1 H. Wertz,1 A. Jahnke,1 A.O. Simeonova-Chergou,1 M. Ehmann,1 F. Wenz,1 and F. Lohr3; 1Department of Radiation Oncology, Universita¨tsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany, 2Abteilung fuer Medizinische Statistik, Biomathematik und Informationsverarbeitung, Universita¨tsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany, 3Department of Radiation Oncology, Modena, Modena, Italy Purpose/Objective(s): Online tracking of target or surrogate structures ensure precise delivery and reduction of intrafractional repositioning errors during liver/upper abdominal SBRT. Ultrasound-based tracking provides a non-invasive, markerless possibility for real-time, soft-tissue based 3D surveillance. Ultrasound probes, however, should not be placed into the primary beam due to sensitivity of electronical components to ionizing radiation and undesired distortion of the treatment beam. SBRT plans should therefore ideally spare the probe. We compared VMAT plans with ultrasound probe (partial rotation VMAT arc with spared angle, sp-VMAT) versus a full-arc VMAT (full VMAT without ultrasound probe) to quantify the loss of plan quality. We tested a setup also with an additional noncoplanar arc (noncopl-VMAT and noncopl dMLC with spared angle) to assess if this can compensate for probe sparing. Materials/Methods: Six patients with 7 liver lesions were treated with image-guided SBRT in DIBH (deep inspiratory breath hold) with daily cone-beam CT with additional real-time ultrasound-based tracking with an experimental system. Plans (sp-VMAT, full-VMAT, noncopl-VMAT and noncopl dMLC) were calculated and compared regarding the following parameters: minimal, maximal, mean, median doses to PTV,