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Investigation of VMAT Algorithms and Dosimetry
S20
Poster Presentations
Author Disclosure Block: L. Sun: None. D. Joh: None. M. Stangl: None. A. Al-Zaki: None. S. Murty: None. M. Alonso-Basanta: None. G. Kao: None. J. Dorsey: None. A. Tsourkas: None.
146 Investigation of VMAT Algorithms and Dosimetry A. Taqaddas, Student at The Open University, UK, Milton Keynes, United Kingdom Purpose/Objectives: Planning and dosimetry of different VMAT algorithms (SmartArc, Ergo++, Autobeam) is compared with IMRT for Head and Neck Cancer patients. Modeling was performed to rule out the causes of discrepancies between planned and delivered dose. Materials/Methods: Five HNC patients previously treated with IMRT were re‐planned with SmartArc (SA), Ergo++ and Autobeam. Plans were compared with each other and against IMRT and evaluated using DVHs for PTVs and OARs, delivery time, monitor units (MU) and dosimetric accuracy. Modeling of control point (CP) spacing, Leaf‐end Separation and MLC/Aperture shape was performed to rule out causes of discrepancies between planned and delivered doses. Additionally estimated arc delivery times, overall plan generation times and effect of CP spacing and number of arcs on plan generation times were recorded. Results: Single arc SmartArc plans (SA4d) were generally better than IMRT and double arc plans (SA2Arcs) in terms of homogeneity and target coverage. Double arc plans seemed to have a positive role in achieving improved Conformity Index (CI) and better sparing of some Organs at Risk (OARs) compared to Step and Shoot IMRT (ss‐IMRT) and SA4d. Overall Ergo++ plans achieved best CI for both PTVs. Dosimetric validation of all VMAT plans without modeling was found to be lower than ss‐ IMRT. Total MUs required for delivery were on average 19%, 30%, 10.6% and 6.5% lower than ss‐IMRT for SA4d, SA2d (Single arc with 20 Gantry Spacing), SA2Arcs and Autobeam plans respectively. Autobeam was most efficient in terms of actual treatment delivery times whereas Ergo++ plans took longest to deliver. Conclusions: Overall SA single arc plans on average achieved best target coverage and homogeneity for both PTVs. SA2Arc plans showed improved CI and some OARs sparing. Very good dosimetric results were achieved with modeling. Ergo++ plans achieved best CI. Autobeam resulted in fastest treatment delivery times. Author Disclosure Block: A. Taqaddas: J. Funding Other; RMH provided financial support in terms of paying the University fee for the project module. N. Royalty; No royalty for this research; however, this research was mentioned in my physics VMAT book and I get royalty for my book.
147 Radiation Exposure Incurred by Healthcare Providers During Radioactive Seed Localization for Surgical Resection of Nonpalpable Breast Cancers J. Giesbrandt, M. McDonough, Mayo Clinic Florida, Jacksonville, FL Purpose/Objectives: With the widespread implementation of mammographic screening, more breast cancers are being detected before they reach a size which can be detected clinically. Radioguided localization was first described in 1998 by Luini et al as an alternative to wire localization for resection of nonpalpable breast lesions. A few years later, a modified technique involving the use of radio-opaque titanium seeds containing radioactive Iodine-125 was reported. Radioactive seed localization (RSL) has largely replaced wire localization at our institution, as it is associated with fewer complications and has a much lower incidence of positive margins following surgical resection. Materials/Methods: The Instadose dosimeter contains a USB port that allows accumulated radiation exposure to be recorded and reset in a
Practical Radiation Oncology: April-June Supplement 2013 matter of minutes from any computer with internet access. Two separate monitoring devices are used in this study- one worn at the wrist by the radiologist placing the seed and one worn at the wrist by the assisting technologist. Following each seed placement, data from both devices are entered into the system and then recalibrated in preparation for the next procedure. Each technologist and radiologist are also wearing personal ring detectors which will be collected and analyzed at the end of a 6 month time period. This project will not only allow us to determine the amount of radiation incurred during a single procedure, but also allow an estimate of the cumulative dose that could be expected of a full time breast radiologist or technologist. Results: Preliminary data indicate that the level of radiation exposure incurred by both the radiologist and assisting technologist to be negligible, with only two technologists incurring a 1 month cumulative dose greater than the detectible level of our monitoring equipment (1 mrem/0.01 mSv). We will continue to monitor each radioactive seed placement for a total of 6 months, with an estimated study population of 100. This should allow for enough statistical power to confidently exclude any significant radiation exposure to radiologists and technologists involved with placement of radioactive seeds for nonpalpable breast lesions. Conclusions: The titanium seed inserted during RSL contains 0.3 mCi of radioactive iodine-125. A series of 300 RSL procedures approximated the radiation exposure to the residual breast tissue to be 2 cGy, equivalent to a single two-view mammogram. However data looking at the cumulative exposure to medical staff involved with RSL has not been collected to confirm these beliefs. This study aims to confirm that there is not significant radiation exposure to radiologists or assisting mammography technologists involved in radioactive seed placement. Author Disclosure Block: J. Giesbrandt: None. M. McDonough: None.
148 Phase/Amplitude-matched Digital Tomosynthesis (DTS) Imaging for Moving Target Localization L. Ren, Y. Zhang, F. Yin, Duke University, Durham, NC Purpose/Objectives: To develop phase/amplitude-matched DTS imaging techniques for localization of moving targets prior to or during radiation therapy delivery. Materials/Methods: Phase-matched reference DTS (Ref-DTS-4DCTPhase) is reconstructed from digitally reconstructed radiographs (DRRs) of 4D-CT that have the same phases in the breathing cycle as the on-board OBI projections acquired for on-board DTS reconstruction. Amplitudematched reference DTS (Ref-DTS-4DCT-Amp) is reconstructed from DRRs of 4D-CT that correspond to the same amplitudes in the breathing cycle as the OBI projections. Target positioning errors are determined by registering reference DTS with on-board DTS (OBI-DTS). The 4D Digital Extended Cardiac Torso (XCAT) Phantom was used to simulate patient 4DCT, average intensity projection CT (AIP), freebreathing CT (FBCT) and on-board OBI projections using breathing patterns fed into the software. Target positioning errors were simulated by shifting the CT images along three axes by a known amount. An ROI surrounding the tumor was used for registration. The simulated shifts were compared with the registered shifts to evaluate the registration error. The following four scenarios were tested: 1). OBI DTS scan duration (t) = 5/6 breathing cycle (T), breathing amplitude in OBI scan (A_OBI) = amplitude in CT scan (A_CT); 2). t=5/6T, A_OBI = 1.5 x A_CT; 3). t=T, A_OBI = A_CT; 4). t=T, A_OBI = 1.5 x A_CT. Note that T is 5sec in our simulation, which corresponds to a 30° scan angle. Results: In scenario 1, the average vector registration errors for registering Ref-DTS-FBCT, Ref-DTS-AIP and Ref-DTS-4DCT-Phase with OBI-DTS are 6.62mm, 2.55mm, and 1.47mm, respectively. In scenario 2, the corresponding errors are 7.26mm, 2.57mm, and 1.58mm, respectively. In
Poster Presentations
Author Disclosure Block: L. Sun: None. D. Joh: None. M. Stangl: None. A. Al-Zaki: None. S. Murty: None. M. Alonso-Basanta: None. G. Kao: None. J. Dorsey: None. A. Tsourkas: None.
146 Investigation of VMAT Algorithms and Dosimetry A. Taqaddas, Student at The Open University, UK, Milton Keynes, United Kingdom Purpose/Objectives: Planning and dosimetry of different VMAT algorithms (SmartArc, Ergo++, Autobeam) is compared with IMRT for Head and Neck Cancer patients. Modeling was performed to rule out the causes of discrepancies between planned and delivered dose. Materials/Methods: Five HNC patients previously treated with IMRT were re‐planned with SmartArc (SA), Ergo++ and Autobeam. Plans were compared with each other and against IMRT and evaluated using DVHs for PTVs and OARs, delivery time, monitor units (MU) and dosimetric accuracy. Modeling of control point (CP) spacing, Leaf‐end Separation and MLC/Aperture shape was performed to rule out causes of discrepancies between planned and delivered doses. Additionally estimated arc delivery times, overall plan generation times and effect of CP spacing and number of arcs on plan generation times were recorded. Results: Single arc SmartArc plans (SA4d) were generally better than IMRT and double arc plans (SA2Arcs) in terms of homogeneity and target coverage. Double arc plans seemed to have a positive role in achieving improved Conformity Index (CI) and better sparing of some Organs at Risk (OARs) compared to Step and Shoot IMRT (ss‐IMRT) and SA4d. Overall Ergo++ plans achieved best CI for both PTVs. Dosimetric validation of all VMAT plans without modeling was found to be lower than ss‐ IMRT. Total MUs required for delivery were on average 19%, 30%, 10.6% and 6.5% lower than ss‐IMRT for SA4d, SA2d (Single arc with 20 Gantry Spacing), SA2Arcs and Autobeam plans respectively. Autobeam was most efficient in terms of actual treatment delivery times whereas Ergo++ plans took longest to deliver. Conclusions: Overall SA single arc plans on average achieved best target coverage and homogeneity for both PTVs. SA2Arc plans showed improved CI and some OARs sparing. Very good dosimetric results were achieved with modeling. Ergo++ plans achieved best CI. Autobeam resulted in fastest treatment delivery times. Author Disclosure Block: A. Taqaddas: J. Funding Other; RMH provided financial support in terms of paying the University fee for the project module. N. Royalty; No royalty for this research; however, this research was mentioned in my physics VMAT book and I get royalty for my book.
147 Radiation Exposure Incurred by Healthcare Providers During Radioactive Seed Localization for Surgical Resection of Nonpalpable Breast Cancers J. Giesbrandt, M. McDonough, Mayo Clinic Florida, Jacksonville, FL Purpose/Objectives: With the widespread implementation of mammographic screening, more breast cancers are being detected before they reach a size which can be detected clinically. Radioguided localization was first described in 1998 by Luini et al as an alternative to wire localization for resection of nonpalpable breast lesions. A few years later, a modified technique involving the use of radio-opaque titanium seeds containing radioactive Iodine-125 was reported. Radioactive seed localization (RSL) has largely replaced wire localization at our institution, as it is associated with fewer complications and has a much lower incidence of positive margins following surgical resection. Materials/Methods: The Instadose dosimeter contains a USB port that allows accumulated radiation exposure to be recorded and reset in a
Practical Radiation Oncology: April-June Supplement 2013 matter of minutes from any computer with internet access. Two separate monitoring devices are used in this study- one worn at the wrist by the radiologist placing the seed and one worn at the wrist by the assisting technologist. Following each seed placement, data from both devices are entered into the system and then recalibrated in preparation for the next procedure. Each technologist and radiologist are also wearing personal ring detectors which will be collected and analyzed at the end of a 6 month time period. This project will not only allow us to determine the amount of radiation incurred during a single procedure, but also allow an estimate of the cumulative dose that could be expected of a full time breast radiologist or technologist. Results: Preliminary data indicate that the level of radiation exposure incurred by both the radiologist and assisting technologist to be negligible, with only two technologists incurring a 1 month cumulative dose greater than the detectible level of our monitoring equipment (1 mrem/0.01 mSv). We will continue to monitor each radioactive seed placement for a total of 6 months, with an estimated study population of 100. This should allow for enough statistical power to confidently exclude any significant radiation exposure to radiologists and technologists involved with placement of radioactive seeds for nonpalpable breast lesions. Conclusions: The titanium seed inserted during RSL contains 0.3 mCi of radioactive iodine-125. A series of 300 RSL procedures approximated the radiation exposure to the residual breast tissue to be 2 cGy, equivalent to a single two-view mammogram. However data looking at the cumulative exposure to medical staff involved with RSL has not been collected to confirm these beliefs. This study aims to confirm that there is not significant radiation exposure to radiologists or assisting mammography technologists involved in radioactive seed placement. Author Disclosure Block: J. Giesbrandt: None. M. McDonough: None.
148 Phase/Amplitude-matched Digital Tomosynthesis (DTS) Imaging for Moving Target Localization L. Ren, Y. Zhang, F. Yin, Duke University, Durham, NC Purpose/Objectives: To develop phase/amplitude-matched DTS imaging techniques for localization of moving targets prior to or during radiation therapy delivery. Materials/Methods: Phase-matched reference DTS (Ref-DTS-4DCTPhase) is reconstructed from digitally reconstructed radiographs (DRRs) of 4D-CT that have the same phases in the breathing cycle as the on-board OBI projections acquired for on-board DTS reconstruction. Amplitudematched reference DTS (Ref-DTS-4DCT-Amp) is reconstructed from DRRs of 4D-CT that correspond to the same amplitudes in the breathing cycle as the OBI projections. Target positioning errors are determined by registering reference DTS with on-board DTS (OBI-DTS). The 4D Digital Extended Cardiac Torso (XCAT) Phantom was used to simulate patient 4DCT, average intensity projection CT (AIP), freebreathing CT (FBCT) and on-board OBI projections using breathing patterns fed into the software. Target positioning errors were simulated by shifting the CT images along three axes by a known amount. An ROI surrounding the tumor was used for registration. The simulated shifts were compared with the registered shifts to evaluate the registration error. The following four scenarios were tested: 1). OBI DTS scan duration (t) = 5/6 breathing cycle (T), breathing amplitude in OBI scan (A_OBI) = amplitude in CT scan (A_CT); 2). t=5/6T, A_OBI = 1.5 x A_CT; 3). t=T, A_OBI = A_CT; 4). t=T, A_OBI = 1.5 x A_CT. Note that T is 5sec in our simulation, which corresponds to a 30° scan angle. Results: In scenario 1, the average vector registration errors for registering Ref-DTS-FBCT, Ref-DTS-AIP and Ref-DTS-4DCT-Phase with OBI-DTS are 6.62mm, 2.55mm, and 1.47mm, respectively. In scenario 2, the corresponding errors are 7.26mm, 2.57mm, and 1.58mm, respectively. In