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1. SRS SRT SBRT Dr.SK TOSLIM HOSSAIN 2nd YR PGT DEPARTMENT OF RADIATION ONCOLOGY MEDICAL COLLEGE & HOSPITAL, KOLKATA

2. Stereotactic :- Stereotactic RadioSurgery (SRS) & Stereotactic Radiotherapy (SRT) Stereotactic radiosurgery (SRS) and stereotactic radiotherapy(SRT) are techniques to administer precisely directed,high dose irradiation that tightly conforms to an intracranial target to create a desired radiobiologic response while minimising dose to surrounding normal tissue , using stereotactic apparatus and narrow multiple beams delivered through non-coplanar isocentric arcs. Stereotactic refers to using a precise 3 -dimensional mapping technique to guide a procedure. INTRODUCTION

3. Contd …… The term SRS is used mainly for single fraction radiation therapy. But may be use for 2-5 sessions ( also called as FSR – Farctionated Stereotactic Radiosurgery ) For multiple fractions, ( ≥ 6 ) the same procedure is called as SRT SRS delivered by GAMMA KNIFE, modified LINAC , Cyberknife , Tomotherapy , Proton beam system.

4. Dose conformity :- in SRS dose conformity done by Accuracy of beam delivery:- Done by stereotactic apparatus Using appropriate circular beams to fit the lesion Optimising the arc angles & weights Using single or multiple isocenters or dynamically shaping the field during arc rotations with mini or micro MLCs Patient immobilization Imagining Target localization with OAR immobilization during treatment setup Quality assurance before & after Mechanical accuracy:- 0.2 ± 0.1 mm. Although commonly accepted is ± 1mm

5. KEY REQUIREMENTS for optimal stereotactic irradiation REQUIREMENT RATIONALE Small Target Volume Reducing the volume of target tissue irradiated to high doses improves tolerance. Sharply Defined Target Allows treatment with little or no margin of surrounding normal tissue. Avoids unintentional under dosing of the target (marginal miss). Accurate Radiation Delivery No margin of normal tissue needed for setup errors. Reduced chance of under-dosing the target. High Conformality Reduces treatment volume to match the target volume. Sensitive structures Excluded from target Dose limiting structures (e.g. spinal cord) should be defined and excluded from the target volume to limit the risk of radiation injury

6. SRS TECHNIQUES There are three types of radiation used in SRS & SRT Heavily charged particles Cobalt 60 gamma rays Mega voltage x rays Most commonly used :- x-ray produced by Linac , called as X-ray knife

7. X-RAY KNIFE Multiple noncoplanar arcs Circular or dynamically shaped beams Converging on to machine isocenter , matched with target image stereotactically Components of X-ray knife:- Stereotactic frames Isocentric accuracy Stereotactic accuracy Beam collimation

8. Stereotactic frames Attached with patient’s skull as well as to the couch Two systems :- Pedestal mounted frame Couch mounted frame

9. Leksell

10. CIVCO FRAMELESS SYSTEM TruPoint + Arch

11. isocenteric accuracy Alignment of stereotactic frame coordinates with linac isocenter is essential Mechanical as well as Radiation’s isocentre should remain within radius of 1mm AAPM Reports 54 & 142 . Stereotactic Accuracy BRW frame use a verification devices : phantom base Identical coordinates

12. Beam collimation SRS or SRT used for treatment small lesions requiring much smaller fields than conventional RT Here , geometric penumbra must be small as much possible. Tertiary collimation system used for the same . SRS fields can be shaped with MLCs .

13. GAMMA KNIFE Gamma knife delivers simultaneously irradiation with large number of isocentric gamma ray beams Cobalt 60 sources placed in hemispheric orientation, beams collimated to focus on a single point . Sources are contained in heavy shielded central body with shielded entrance door. PERFEXION Gamma KNIFE

14. Contd … Gamma beams delivered by 192 Co-60 sources , arranged on cylindrical configurations in five rings . Beams collimated by single 12cm thick tungsten collimator ring array, subdivided into 8 moveable sectors , each holding 24 sources . Collimator sizes :- 4mm, 8mm, 16mm diameter Patient setup by patient positioning system ( PPs ) Gamma angles :- 70 degree ( chin up) , 90 degree( chin horizontal), & 110 degrees(chin down)

15. Gamma Knife Vs Xray Knife No significant clinical difference Gamma knife is limited to small lesion’s because of its field size limitation, but several isocentres in same target to expand or shape dose distribution For treating multiple isocenters or targets, Gamma knife is preferred because of simplicity to setup Xray knife is more economic , can be used in SRS , SRT, IMRT and CRT.

16. Dose Calculation algorithm in SRS SRT Approximate spherical geometry of human head and homogeneity of tissue density simplify the demands of dose calculation algorithm 2mm grid spacing produces a dose uncertainty of 1% to 2% compared to 3% to 4% uncertainty with 4mm grid spacing CT and MRI for planning preferred in between 3mm to 10mm slice. 1-3 mm slice used if critical structures are closely situated

17. INDICATION S 1. Functional a.Trigeminal neuralgi a , b. Unilateral tremo r 2. Benign tumours : a .) schwannoma . b) pituitary adenoma, c) meningioma,etc . 3. Vascular a.Arteriovenous malformations , b. Cavernous hemangioma 4. Primary malignant brain tumours 5. Brain mets

18. 2 years post treatment ( meningioma )

19. Pitutary adenoma( pre treatment and 54 months post treatment)

20. AVM pre treatment and 2 year post treatment

21. Extracranial Radiosurgery Treating small localized tumors extracranially Techniques are frameless Tumor localized through image guidance such as EXACTRAC and CYBERKNIFE Utilisation of x-ray imaging of bony anatomy and implanted fiducial markers to localise the target & track its motion Sites :- Spine , lungs, liver , pancreas , kidney, prostate.

22. CYBERKNIFE

23. SBRT

24. Stereotactic Body Radiation Therapy Defn :- SBRT refers to stereotactically guided delivery of highly conformal radiation to a defined target volume in 6 or more fractions, typically using noninvasive positioning techniques, although they are often used within 2 to 5 fractions as well. Sites :- Spine Lung Liver Pancreas Kidney Prostate

25. SIMULATION Three components. Sufficient patient immobilization Management/ control of tumor motion 3-D anatomic image data for treatment

26. Immobilization Stereotactic “body frames” characteristic of ideal body frames Light weight( < 10kg) Low density material Use of vacuum cushion to conform and immobilise patient body Localization apparatus attached to the body frame or the couch top to provide reference coordinates of external fiducials May include abdominal compression devices Induce shallow breathing and thus minimising respiratory motion. Manual compression paddle Pneumatic compression belt

27. Stereotactic body frame developed by Blomgren and Lax – Karolinska hospital

28. Tumor motion management Passive :- involves tumor motion in the delineation of target volumes. 4DCT Maximum intensity projection(MIP) Internal target volume (ITV) Position of abdominal surface Respiratory airflow Position of diaphragm

29. Active motion management Abdominal compression devices :– simple, do not need very active patient education Breath hold techniques : patient compliance Contd .. Abdominal compression devices

30. 3-D ANATOMIC IMAGE DATA Clear visualisation of patient anatomy in treatment position Choice of particular imaging modality depends on the tissue characteristics ( CT are gold standard ) Slice thickness: ≤ 3mm.

31. TREATMENT PLANNING CONTOURING DOSE CALCULATIONS DOSE PRESCRIPTION DOSE REPORTING CONTOURING ICRU 83 report Many cases CTV kept same as GTV Larger dose gradient within PTV → rapid dose fallof f outside the PTV → sparing normal tissue Lower energy beam(E<6MV) preferred to reduce beam penumbra AAPM TG101 recommends use of isotropic grid spacing ≤ 2mm . B. DOSE CALCULATIONS

32. C. Dose prescription:- D. DOSE REPORTING :- Ablative doses , effectively larger than conventional fractionation Isodose prescription :- 80% -90 % Margin kept small as much possible to spare normal tissue

33. QUALIFIED PERSONNEL: 1. Board Certified Radiation Oncologist 2. Qualified Medical Physicist 3. Licensed Radiation Therapist 4. Other support staff as indicated Ongoing Machine QUALITY ASSURANCE Program Quality control of Treatment Accessories Quality control of Planning & Treatment Images Quality control of TPS Simulation & treatment systems based on systematic and random errors based on actual measurement of organ motion & setup uncertainty ASTRO-ACR guidelines for SBRT commissioning & QA.

34. Indications for SBRT A. LUNG – inoperable early stage ca lung [ NSCLC STAGE I : LRR = 8.4% when BED> 100Gy. Local control rate of 95% for peripheral lesions vs 46% for central lesions. ( Onishi et al, 2007 ) Dose prescriptions : 12 Gy x 4#, 20 Gy x 3#, 10 Gy x 5#. ] b) Lung mets :- Up to 2 lesions are simultaneously treated in most of the cases. Outcome compared with surgical metastatectomy .

35. B. SPINE :- a) Vertebral mets b) Malignant epidural spinal cord compression c) Benign spinal tumors :- indications are unresectable , C/I for Sx , C. PROSTATE – Dose of 35 Gy /5 fractions for primary treatment of low risk prostate cancer or 50 Gy in 5 fractions as dose escalation. Most important challenge is accurate positioning and correction of inter-fraction motion. D. LIVER :- a) Hepatocellular carcinoma b) Liver mets E. CA PANCREAS

36. SUMMARY SRS & SBRT techniques have become a dominant way of managing a large number of benign & malignant tumors . Safety & effectiveness continue to improve along with technical improvements in radiation targeting & delivery. careful attention to be given for patient selection & safe implementation.

37. THANK YOU