Stereotactic Body Radiation Therapy: Planning and Delivery

Transcription

1 Stereotactic Body Radiation Therapy: Planning and Delivery Yong Yang, Ph.D. Department of Radiation Oncology Stanford University 6 AAPM Therapy Educational Course Stanford Radiation Physics Lei Xing, Ph.D. Ruijiang Li, Ph.D. Ben Fahimian. Ph.D. Anie Hsu, Ph.D. Karl Bush, Ph.D. Amy Yu, Ph.D. Bin Han, Ph.D. Gary Luxton, Ph.D. Dimitre Hristov, Ph.D. Peter Maxim, Ph.D. Lei Wang, Ph.D. Tony Lo, Ph.D. Nataliya Kovalchuk, Ph.D. Thomas Niedermayr, Ph.D. Disclosure I have no conflicts of interest to disclose. Acknowledgement Stanford Radiation Oncology Bill W. Loo, M.D., Ph.D. Albert Koong, M.D., Ph.D. Daniel Chang, M.D. Scott G. Scoltys, M.D. Max Diehn, M.D., Ph.D. Quynh-Thu Le, M.D. Challenges for SBRT How to accurately define target? ---4D imaging How to accurately localize target? ---IGRT How to obtain conformal dose and steep dose gradients? ---DCRT, Inverse Planning, IMRT, VMAT How to reduce irradiated volume of critical organs for a moving target? --- Gating, Tracking Image Courtesy of UPMC Intracranial SRS SBRT

2 SBRT Planning Inhomogeneous dose inside PTV Sharp dose fall-off outside PTV High fractional dose --- High BED Image Guidance Target definition Motion management DCRT or IMRT/VMAT Interplay effect Dose calculation Prescription and Dose constraints Stereotactic Radiosurgery SBRT IMRT/VMAT/D Conformal Delivery AAPM Task Group N. Target Definition Static Target: PTV = CTV+ setup margin Moving Target: ITV = CTVi or CTV_MIP (for Lung) PTV = ITV+ ~5mm setup margin Larger margin for irregular breathing MIP/MinIP only for target definition ITV GTV CTV GTV PTV Target Definition (ICRU 6) Lung example Pancreas example PTV : ITV +~mm margin Motion Management (Delivery) Gating Technique Breath-holding Technique Tracking Technique Static Gating Tracking Non-Gating (motion<=5mm) Respiratory Gating (motion>5mm) Breath-holding technique Tracking technique

3 Relative Dose % DCRT vs. IMRT/VMAT Spine/Prostate/Pancreas/HN IMRT/VMAT Some Lung/Liver DCRT Advantages: Better dose conformity Easy to control/constrain dose to OARs Disadvantages: Higher MU, longer treatment time Interplay effect between target and MLC motion Spine Pancreas Lung: Central Lung: Peripheral Interplay Effect D 4D DVH comparison between static and 4D dose calculation.9 lung D.8 lung 4D.7 CTV D.6 CTV 4D.5 PTV D.4 PTV 4D Relative Volume % IMRT/SBRT: Trilogy SRS MU/Min, GyX4F VMAT/SBRT: TrueBeam 6FFF 4MU/Min, 8GyXF Li, Yang et al, JACMP, Interplay Effect: Gated RapidArc 5mm residual motion Isodose Dose Profile mm residual motion cm D motion, 4.s period %/mm γ map Case 7mm total motion, % -75% gating window with 5mm residual motion Isodose % failed Quasar phantom with real patient data Case Riley, Yang et al, Med. Phys. 4 mm total motion, 5% -75% gating window with 5mm residual motion 9% failed

4 Inhomogeneity Correction PTV Dose difference for targets from PBC and AcurosXB could be more than % PBC should not be used for lung SBRT PBC Acuros XB RPC Thorax Phantom Eclipse PBC Eclipse AAA TomoTherapy CSA S. E. Davidson et al, Med. Phys., 8. Inhomogeneity Correction GTV PTV Fiducial For a small isolated target, even AAA is not accurate enough! Courtesy of Amy Yu, Ph.D. Beam energy Target size Lung density Target location AAA Lung Water Acuros XB Lung.4 gcm Re-Build up LD Lung Air. gcm. gcm 6 MV 4. cm x 4. cm photon beam Bush et al, Med Phys 8, Prescriptions and Dos Constraints AAPM TG Table III ROTG Protocols Lung: 6, 68, 8 and 95 Spine: 6 Liver: 48, These protocols specify detailed requirements for treatment planning: Dose Prescription Target Coverage Dose Constraints 4

5 RTOGs: Lung Gy/f Prescribed 5Gy/5 6Gy/f 6Gy/f vs. Dose f Gy/4f Location Peripheral Peripheral Central Peripheral Allow IMRT? No Yes Yes Yes Inhomogeneity No No Yes Yes Correction? Timmerman s definition of centrality Dose Constraints 8 and 95 Table Stanford: Volume-Adapted SABR Trakul et al, IJROBP, Global dose maximum > % and centered in GTV % of GTV receives % of prescription dose MU optimization Avoid beam entrance through the contralateral lung when possible Conformity : Dose Volume vs. PTV Volume Intermediate Dose Spillage: R 5% and D cm RTOG : Liver Gy in 5 fx Prescription dose based on mean liver dose Cover 95% of PTV Stanford Gy-6Gy in ~5F Mean liver dose<gy 5cc liver <7Gy 7cc liver <Gy 5

6 RTOG 6: Spine Prescription: 6 or 8 Gy in fx Dose constraints: Spine Cord: Dmax (.cc)<4 Gy V<.5cc Esophagus: Dmax (.cc)<6 Gy D(5 cc)<.9 Gy Stanford Prescription: 8 or Gy in fx 4 or 7 Gy in fx Dose constraints: Spine Cord: fx: Dmax <4 Gy, V<.5cc fx: Dmax< Gy, V5<cc Esophagus: fx: Dmax < Gy, V5<cc fx: Dmax < Gy, V<cc Target Localization & Plan Delivery Pre-Treatment Setup (kv/mv, CT/CBCT) Fluoroscopic Verification TrueBeam - Varian Cyberknife - Accuray Plan Delivery & Beam-Level Imaging (kv, Fluoro, Cine MV, kv/mv CBCT) Versa - Elekta Post-Treatment Image & Data Analysis Novalis - Brainlab Pre-Treatment Setup Accuracy Spine ~ mm Lung <5mm Abdomen <5mm Before Treatment First Fraction AAPM Task Group N. After Treatment Second Fraction 6

7 DEVIATIONS [deg] DEVIATIONS [mm] TRANSLATION IN X COORDINATE - LATERAL ROTATION IN X COORDINATE - PITCH DEVIATIONS [deg] DEVIATIONS [mm] - - TRANSLATION IN Y COORDINATE - LONGITUDINAL ROTATION IN Y COORDINATE - ROLL DEVIATIONS [deg] DEVIATIONS [mm] TRANSLATION IN Z COORDINATE - AP ROTATION IN Z COORDINATE - YAW Target Positioning: Spine Positional setup accuracy with CT guided correction assessed by an immediate post-treatment CT 5 cases with 9 isocenter setup E. L. Chang et al, IJROBP, 59, cases Middle(mm): End (mm) X.5±.5.5±.5 Y.5±.5.5±.5 Z.5±.5.5±.5 D.±.6.±.7 Middle( ) End ( ) Yaw.±.4.±. Roll.4±.5.4±.5 Pitch.±.5.4±.5 Gerszten et al, J Neurosurg, V, Target Positioning: Lung Intra-fraction variation (mm) AP.±.7 ML.6±. SI -.±. D.±. A total of 49 patients with 47 tumors underwent 59 fractions of lung SBRT Shah C, et al, PRO, Fluoroscopy Verification Fluoroscopic imaging to verify target motion and gating window: Yellow: in gating window, beamon; Green: out gating window, Beam- Off. Gating window should be adjusted so that fiducials fall within tracking structures when beam is on. Pre-Treatment fluoro for a pancreas SBRT case 7

8 Beam-Level Imaging: kv Imaging Continous/Fluoro kv During treatment Triggered kv image at Beam On Beam-Level kv images for the same pancreatic SBRT case Beam-Level Imaging: Cine MV Imaging Advantage: No dose, free information Beam eye view Disadvantage: MLC blocks image Image quality D tracking if combined with kv imaging Images courtesy of Azcona, Xing Azcona, Li, Xing, et al, Med Phys Post-Tx Data Analysis: Beam-Level kv Triggered Imaging Verification of Intra-fraction geometric accuracy of SABR SABR patients (lung/liver/pancreas) RPM-based gating treatment Geometric error:.8 mm on average;. mm at 95th percentile Li R, Xing L, et al. IJROBP, 8

9 Post-Tx Data Analysis: Beam-Level kv Volumetric Imaging Continuous fluoroscopy during dose delivery In-house program for CBCT reconstruction lung SABR patients Treatment verification Routine clinical use Li R, Xing L et al, IJROBP. Post-Tx Data Analysis: Beam-Level MV Volumetric Imaging Target Beam-Level MV CBCT Planning CT Target Planning CT Dynamic Arc Beam-Level MV CBCT RapidArc Images courtesy of Tianfang Li, Ph.D., UPMC Summary 4D imaging is required for accurate motion management New techniques (Inverse planning, IMRT/VMAT, Gating/Tracking, ) can improve target conformity and critical structure sparing Patients should be positioned with IGRT Beam-level imaging is a necessary step to insure accurate SBRT delivery 9

10 Thank You!