- Email: [email protected]
PO-0830: A new method for dose reconstruction untilizing PET-CT in patients treated with radioembolization
S72
ESTRO 33, 2014 sites. For H&N CBCT scans acquired with M20/F1 the departmental CTderived treatment planning curve gives good dosimetric agreement although presently this is based on phantom data only. Further work will investigate the accuracy of dose calculation on patient CBCT scans when using M20/F1, and will investigate an atlas based method for generating planning structures in order to generate dose-volume-histograms for plan comparison during adaptive radiotherapy investigation.
Conclusions: Our dosimetric study demonstrated that the use of FFF beams in IMRT will slightly increase the absorbed dose in the build-up region, but these differences become extremely small at the surface. Regarding calculation accuracy, important deviations between measured and calculated doses were found for both the 10MV FF and FFF beams. PO-0829 Calculating dose distributions in cone beam CT for head and neck adaptive radiotherapy G. Ntentas1, C. Thomas1, T. Greener1 1 Guys and St Thomas NHS Foundation Trust, Medical physics, London, United Kingdom Purpose/Objective: To recalculate radiotherapy treatment plans for head and neck (H&N) patients onto cone-beam CT (CBCT) data (Elekta XVI), evaluate the dosimetric difference using gamma analysis and explore a method to be applied in clinical practice. Materials and Methods: 6 patients were retrospectively selected who received a repeat replanning CT during their course of IMRT treatment. Using the patient’s replan CT data and the patient’s first CBCT image once starting their replan treatment a mutual information (M-I) technique was used to generate a H&N specific Hounsfield unit to electron density (HU-ED) calibration curve for CBCT acquisitions acquired using S20 collimator and F0 filter (S20/F0). Nine-field IMRT treatment plans were recalculated onto CBCT in the Monaco® treatment planning system by assigning two alternative HU-ED curves (M-I curve from 6 patients and the treatment planning curve derived from conventional CT scanner). Resulting dose distributions were compared with original treatment plan using 2D gamma analysis (3%/3mm). To increase the accuracy of dose distribution comparison, an anthropomorphic H&N phantom was developed. The head of Rando® phantom was used whilst its neck was replaced by 5 inserts of known ED. The 5 inserts covered a range of ED representative of neck anatomy. CBCT scans were acquired for S20/F0 and M20/F1. Results: Dose was not recalculated for 2 of the patients as they had unilateral treatment volumes and full anatomy had not been imaged on CBCT. For the remaining patient cases anatomical changes were evident even in the short time period between rescan CT and CBCT (range 4 to 10 days). However, for slices where image registration was good and there was no change in patient contour, gamma analysis gave pass rates of 96 ± 2% (Figure 1) when using the M-I calibration curve. For slices where anatomical changes were significant, pass rates were poorer at 83 ± 8% (Figure 1). Results were poorer when using treatment planning curve, 72 ± 10%. For the S20/F0 phantom scans pass rates were 97 ± 2% when using M-I curve. Dose calculated on the M20/F1 phantom scan gave pass rates of 98 ± 2% when using the treatment planning curve and poorer results when using the M-I curve: 85 ± 6%.
PO-0830 A new method for dose reconstruction untilizing PET-CT in patients treated with radioembolization E. Fourkal1, I. Veltchev1, J. Meyer1, M. Johson1, M. Doss2, J. Yu2 1 Fox Chase Cancer Center, Radiation Oncology, Philadelphia PA, USA 2 Fox Chase Cancer Center, Nuclear Medicine, Philadelphia PA, USA Purpose/Objective: The development of radioembolization with SIRSpheres represents a significant advance in the treatment of patients with metastatic disease to the liver. This technique has evolved to use a formula for dose calculation that relies on body surface area as the main determinant of dose. However, what is prescribed is not dose, but rather activity. It has been traditionally thought that the tracer 90Y is a pure electron emitter. However, the decay of 90Y has also a minor branch to the first excited state of 90Zr, constrained to follow e- e+creation, which happens in 34 out of a million decays. While the emission is rare, it can be observed using the PET scanner. Therefore the main objective of this work is to develop a new method of 3D dose reconstruction based on the PET imaging of SIR-Spheres. Materials and Methods: Using Fluka Monte Carlo code, the voxel dose kernel was calculated for 90Y source of size equal to that of the PET scanner voxel size chosen during the reconstruction process. Subsequently, the convolution of the VDK with measured PET data was performed to recover the absorbed dose. The absolute dose calibration was done by taking a ratio between the measured positron activity and the known activity due to electrons. Results: Four patients underwent treatment with SIR-Spheres for liver metastases from colorectal cancer and 2 patients were treated with Therasphere for hepatocellular cancer. A total of 11 target tumors were contoured on post-treatment PET-CT scans for dosimetric evaluation. Mean prescription activity was 1.51 GBq (range: 0.58 to 3.29 GBq). The resulting mean maximum measured dose to targets was 167 Gy (range: 71 to 311Gy). Mean minimum dose to 70% of target (D70) was 54 Gy (range: 29 to 83 Gy). Mean minimum dose to 90% of target (D90) was 36 Gy (range: 13 to 58 Gy). The mean volume of liver receiving at least 30 Gy (V30) was 856 cc (range: 257 to1199 cc). The mean maximum dose to 1cc of the right kidney was 42 Gy (range: 28to 60 Gy). The mean maximum dose for Therasphere and SIR-spheres was 266 Gy versus 111 Gy. The mean D70 for Therasphere and SIR-Spheres was 79 Gy versus 40 Gy. The mean D90 for Therasphere versus SIR-Spheres was 48 and 28 Gy. Conclusions: The proposed method offers significant improvement in characterization of the dose deposited by SIR-Spheres with the hope that this may enable to answer some of the clinical questions concerning the influence of the dose on the response rate, progression-free or overall survival.
POSTER: PHYSICS TRACK: TREATMENT PLANNING AND PLAN COMPARISONS PO-0831 A feasibility multicenter SBRT planning study on prostate cancer over 17 centers C. Marino1, M. Esposito2, L. Strigari3, D. Fedele4, C. Fiandra5, M.R. Malisan6, E. Bonanno7, C. Carbonini8, M.R. Nardiello9, P. Mancosu10 1 Humanitas C.C.O., Radiotherapy, Catania, Italy 2 Azienda Sanitaria Firenze, Radiotherapy, Firenze, Italy 3 Instituto Regina Elena IFO, Radiotherapy, Roma, Italy 4 Casa di Cura San Rossore, Radiotherapy, Pisa, Italy 5 A.O. Città della Salute e della Scienza, Radiotherapy, Torino, Italy 6 A.O.U. S.Maria della Misericordia, Radiotherapy, Udine, Italy 7 A.O. Cannizzaro, Radiotherapy, Catania, Italy 8 A.O. Ospedale Niguarda Ca' Granda, Radiotherapy, Milano, Italy 9 UPMC San Pietro FBF, Radiotherapy, Roma, Italy 10 IRCCS Istituto Clinico Humanitas, Radiotherapy, Milano, Italy
Conclusions: The patient-derived M-I HU-ED curve can be used to accurately calculate dose on CBCT scans acquired with S20/F0 for H&N
Purpose/Objective: The implementation of multicenter clinical studies assumes planning standardization as a prerequisite. The Italian Association of Medical Physics (AIFM), has created a working group
ESTRO 33, 2014 sites. For H&N CBCT scans acquired with M20/F1 the departmental CTderived treatment planning curve gives good dosimetric agreement although presently this is based on phantom data only. Further work will investigate the accuracy of dose calculation on patient CBCT scans when using M20/F1, and will investigate an atlas based method for generating planning structures in order to generate dose-volume-histograms for plan comparison during adaptive radiotherapy investigation.
Conclusions: Our dosimetric study demonstrated that the use of FFF beams in IMRT will slightly increase the absorbed dose in the build-up region, but these differences become extremely small at the surface. Regarding calculation accuracy, important deviations between measured and calculated doses were found for both the 10MV FF and FFF beams. PO-0829 Calculating dose distributions in cone beam CT for head and neck adaptive radiotherapy G. Ntentas1, C. Thomas1, T. Greener1 1 Guys and St Thomas NHS Foundation Trust, Medical physics, London, United Kingdom Purpose/Objective: To recalculate radiotherapy treatment plans for head and neck (H&N) patients onto cone-beam CT (CBCT) data (Elekta XVI), evaluate the dosimetric difference using gamma analysis and explore a method to be applied in clinical practice. Materials and Methods: 6 patients were retrospectively selected who received a repeat replanning CT during their course of IMRT treatment. Using the patient’s replan CT data and the patient’s first CBCT image once starting their replan treatment a mutual information (M-I) technique was used to generate a H&N specific Hounsfield unit to electron density (HU-ED) calibration curve for CBCT acquisitions acquired using S20 collimator and F0 filter (S20/F0). Nine-field IMRT treatment plans were recalculated onto CBCT in the Monaco® treatment planning system by assigning two alternative HU-ED curves (M-I curve from 6 patients and the treatment planning curve derived from conventional CT scanner). Resulting dose distributions were compared with original treatment plan using 2D gamma analysis (3%/3mm). To increase the accuracy of dose distribution comparison, an anthropomorphic H&N phantom was developed. The head of Rando® phantom was used whilst its neck was replaced by 5 inserts of known ED. The 5 inserts covered a range of ED representative of neck anatomy. CBCT scans were acquired for S20/F0 and M20/F1. Results: Dose was not recalculated for 2 of the patients as they had unilateral treatment volumes and full anatomy had not been imaged on CBCT. For the remaining patient cases anatomical changes were evident even in the short time period between rescan CT and CBCT (range 4 to 10 days). However, for slices where image registration was good and there was no change in patient contour, gamma analysis gave pass rates of 96 ± 2% (Figure 1) when using the M-I calibration curve. For slices where anatomical changes were significant, pass rates were poorer at 83 ± 8% (Figure 1). Results were poorer when using treatment planning curve, 72 ± 10%. For the S20/F0 phantom scans pass rates were 97 ± 2% when using M-I curve. Dose calculated on the M20/F1 phantom scan gave pass rates of 98 ± 2% when using the treatment planning curve and poorer results when using the M-I curve: 85 ± 6%.
PO-0830 A new method for dose reconstruction untilizing PET-CT in patients treated with radioembolization E. Fourkal1, I. Veltchev1, J. Meyer1, M. Johson1, M. Doss2, J. Yu2 1 Fox Chase Cancer Center, Radiation Oncology, Philadelphia PA, USA 2 Fox Chase Cancer Center, Nuclear Medicine, Philadelphia PA, USA Purpose/Objective: The development of radioembolization with SIRSpheres represents a significant advance in the treatment of patients with metastatic disease to the liver. This technique has evolved to use a formula for dose calculation that relies on body surface area as the main determinant of dose. However, what is prescribed is not dose, but rather activity. It has been traditionally thought that the tracer 90Y is a pure electron emitter. However, the decay of 90Y has also a minor branch to the first excited state of 90Zr, constrained to follow e- e+creation, which happens in 34 out of a million decays. While the emission is rare, it can be observed using the PET scanner. Therefore the main objective of this work is to develop a new method of 3D dose reconstruction based on the PET imaging of SIR-Spheres. Materials and Methods: Using Fluka Monte Carlo code, the voxel dose kernel was calculated for 90Y source of size equal to that of the PET scanner voxel size chosen during the reconstruction process. Subsequently, the convolution of the VDK with measured PET data was performed to recover the absorbed dose. The absolute dose calibration was done by taking a ratio between the measured positron activity and the known activity due to electrons. Results: Four patients underwent treatment with SIR-Spheres for liver metastases from colorectal cancer and 2 patients were treated with Therasphere for hepatocellular cancer. A total of 11 target tumors were contoured on post-treatment PET-CT scans for dosimetric evaluation. Mean prescription activity was 1.51 GBq (range: 0.58 to 3.29 GBq). The resulting mean maximum measured dose to targets was 167 Gy (range: 71 to 311Gy). Mean minimum dose to 70% of target (D70) was 54 Gy (range: 29 to 83 Gy). Mean minimum dose to 90% of target (D90) was 36 Gy (range: 13 to 58 Gy). The mean volume of liver receiving at least 30 Gy (V30) was 856 cc (range: 257 to1199 cc). The mean maximum dose to 1cc of the right kidney was 42 Gy (range: 28to 60 Gy). The mean maximum dose for Therasphere and SIR-spheres was 266 Gy versus 111 Gy. The mean D70 for Therasphere and SIR-Spheres was 79 Gy versus 40 Gy. The mean D90 for Therasphere versus SIR-Spheres was 48 and 28 Gy. Conclusions: The proposed method offers significant improvement in characterization of the dose deposited by SIR-Spheres with the hope that this may enable to answer some of the clinical questions concerning the influence of the dose on the response rate, progression-free or overall survival.
POSTER: PHYSICS TRACK: TREATMENT PLANNING AND PLAN COMPARISONS PO-0831 A feasibility multicenter SBRT planning study on prostate cancer over 17 centers C. Marino1, M. Esposito2, L. Strigari3, D. Fedele4, C. Fiandra5, M.R. Malisan6, E. Bonanno7, C. Carbonini8, M.R. Nardiello9, P. Mancosu10 1 Humanitas C.C.O., Radiotherapy, Catania, Italy 2 Azienda Sanitaria Firenze, Radiotherapy, Firenze, Italy 3 Instituto Regina Elena IFO, Radiotherapy, Roma, Italy 4 Casa di Cura San Rossore, Radiotherapy, Pisa, Italy 5 A.O. Città della Salute e della Scienza, Radiotherapy, Torino, Italy 6 A.O.U. S.Maria della Misericordia, Radiotherapy, Udine, Italy 7 A.O. Cannizzaro, Radiotherapy, Catania, Italy 8 A.O. Ospedale Niguarda Ca' Granda, Radiotherapy, Milano, Italy 9 UPMC San Pietro FBF, Radiotherapy, Roma, Italy 10 IRCCS Istituto Clinico Humanitas, Radiotherapy, Milano, Italy
Conclusions: The patient-derived M-I HU-ED curve can be used to accurately calculate dose on CBCT scans acquired with S20/F0 for H&N
Purpose/Objective: The implementation of multicenter clinical studies assumes planning standardization as a prerequisite. The Italian Association of Medical Physics (AIFM), has created a working group