Chuxiong Ding, Ph.D., Cheng-Hui Chang, Ph.D., Joshua Haslam, Ph.D., Robert Timmerman, M.D., Timothy Solberg, Ph.D.

Transcription

1 Dosimetric comparison of SBRT for lung cancer: Cyberknife vs. Linac Chuxiong Ding, Ph.D., Cheng-Hui Chang, Ph.D., Joshua Haslam, Ph.D., Robert Timmerman, M.D., Timothy Solberg, Ph.D. Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX

2 History of Stereotactic Radiosurgery Single large radiation dose. Multiple non-coplanar beams. Accurate targeting. Leksell L, A stereotaxic apparatus for intracerebral surgery, Acta Chir Scand. 99:231, 1949

3 Evolution of Technological l Innovation Lung, Liver, Pancreas, Prostate, Spine

4 Stereotactic Body Radiation Therapy (SBRT) Radiation delivery to a demarcated tumor target using: optimal immobilization motion accounting many small fields accurate targeting g heterogeneous target dose steep dose gradients outside targets ablative intent few large dose treatments

5 Conformal high dose Prescription Dose: 60Gy in 3 fractions Target 60Gy 30Gy 7.5Gy

6 Challenges for lung tumor SBRT Localization treatment Respiratory Motion Inhalation Exhalation MIP Tumor excursion Diaphragm excursion

7 Purpose of Study IGRT technique Immobilization Linac used Collimator Respiration Compensation Treatment planning system etc. Dosimetric Difference

8 Linac Based Lung Cancer SBRT- Tumor Localization SBRT Frame: immobilization, localization. Cone Beam CT

9 Linac Based Lung Cancer SBRT- Respiratory Motion Control Large margin to GTV, Gating, ABC, Abdominal Compression, etc. Breathing Signal Upper Threshold Playba ck Indicat or GTV PTV Lower Threshold Beam On / Off Indicator

10 Cyberknife Lung Cancer SBRT- Tumor Localization Sophisticated image guidance tumor Localization

11 Cyberknife Lung Cancer SBRT- Respiratory Motion Control Internal Fiducial Markers External Optical Markers

12 Clinical SBRT Procedure in UTSW 0% 50% 90% 4DCT MIP for contour Tx Planning QA Dose Delivery CBCT Alignment Patient Setup

13 SBRT Dose prescription in UTSW RTOG 0236 A Phase II Trial of Stereotactic Body Radiation Therapy (SBRT) in the Treatment of Patients with Medically Inoperable Stage I/II Non-Small Cell Lung Cancer Prescription: 60Gy in 3 fractions % isodose line cover at least 95% of PTV. 99% of PTV should receive a minimum of 90% of prescript dose. Parallel Tissue Critical Volume (cc) Critical Volume Dose Max (Gy) Lung (Right & Left) 1000 cc 13.5 Gy Pneumonitis Endpoint ( Grade 3)

14 Target Definition Inhalation Exhalation MIP Tumor excursion Diaphragm excursion PTV3D ITV GTV PTV4D

15 Study Protocol GTV PTV4D Radiation Start Timing Respiratory Cycle 4D CT Study PTV3D ITV 0% 50% 90% ITV, PTV 3D, MIP, and AVG images Synchrony 4D calculation GTV, PTV 4D, 50% phase CT 0% 50% 90% Deformable Registration 50% phase GTV PTV4D

16 Result (1): Dose to Tumor 1 Patient 1 a 0.8 Volume GTV_Cyber PTV4D_Cyber GTV SBRT PTV4D SBRT b Dose (Gy) c Tumor coverage Tumor dose homogeneous Maximum Dose

17 Result (1): Dose to Tumor DHI for GTV Maximum point dose to (D 20 -D 80 )/D prespcription GTV (Gy) Cyberknife Linac Cyberknife Linac Patient Volume 0.8 GTV_Cyber 0.6 PTV4D_Cyber GTV SBRT PTV4D SBRT Dose (Gy) Linac Cyber ± ± ± ±2.37±2

18 Result (1): Dose to Tumor 7~10 beams More Than 100 Beams 1 Patient 1 Volume GTV_Cyber PTV4D_Cyber GTV SBRT PTV4D SBRT Dose (Gy)

19 Result (2): Dose to Lung Institutional Dose Limit for Lung SBRT: 1000cc lung get less than 13.5Gy V20 Dose to 1000cc Lung

20 Result (2): Dose to Lung Minimum Dose to 1000cc Lung Dose (Gy y) Anterior Middle Posterior Patients Cyberknife Linac SBRT vs.

21 Result (2): Dose to Lung Patient V PTV4D V 20 Cyberknife Linac % 1.34% 3.27% % 3.67% 3.11% % 4.31% 4.90% % 16.32% 13.37% % 2.16% 2.59% % 911% 9.11% 6.95% % 2.21% 2.74% % 4.83% 5.67% mean±std 1.5%±1% 5.5%±5% 5.3%±3.6% V20 V 20 = m V PTV 4 D + b r 2 = 0.88 r 2 = 0.84

22 Result (3): Whole body dose Cyberknife: Total MU 25,000 ~ 50,000 Linac: Total MU 10,000 ~ 15,000 Cover PTV Cover 60~80% PTV dimension

23 Result (3): Whole body dose The absolute risk of both modalities are minimal. CyberKnife risk was higher due to the greater number of MU s. CK risk / IMRT risk CK risk / Hypo IMRT risk Bellon M, Followill D, Ibbott G, et al. Risk of Secondary Fatal Malignancies From Cyberknife Radiosurgery. Med Phys 2008:35: (A joint Study by UTSW and RPC, MD Anderson)

24 Some Practical Consideration Cyberknife Linac Treatment Planning Inverse Planning. No beam come through posterior of patient Beam can come through posterior of patient Beam angle limited by table and gantry collision Tumor Localization Few X-Ray images CBCT Required Respiratory Control Need Fiducial (Synchrony) Non Fiducial tracking (X- sight Lung tracking). Larger target area Abdominal compression Dose Delivery Robert moving time Less MU More oemu Adjust treatment e t couch angle

25 Conclusion No difference in dose coverage. Cyberknife is heterogeneous dose to GTV. All lung dose within constrains. No difference to lung in high dose region. Lung dose depends on tumor location in low dose region.

26 Thank you!