SBRT&StereoscopicIGRT_2012 [Compatibility Mode]

IGRT and SBRT Programs with 

Siemens Accelerators and ExacTrac 

ExacTrac 

Stereoscopic XX-ray 

XX-ray 

ray System 

System 

Dimitris Mihailidis Mihailidis, , Ph.D. 

Charleston Radiation Therapy, Charleston, West Virginia 

QUESTION: 

Can Stereoscopic x-Ray IG Technology convert a 

conventional Siemens (Primus or Oncor) linac into 

a “precision” IG - SBRT delivery machine ? 

Description of the Systems 

BrainLab ExacTrac System: 

Two X-ray tubes. 

Two amorphous silicon detectors (20x20 cm 2 ). 

Infrared Polaris system. 

Touch screen and arm. 

512x512 Matrix 

X-Ray phantom. 

ISO phantom. 

Rando pelvis phantom. 

Reference star or markers. 

Linear Accelerators with features 

specifically suitable for SBRT 

* Slide courtesy of Brian Kavanagh / University of Colorado 

Introduction and Purpose 

Implement Image Guidance (IG) on a 

Siemens Linac (Primus or Oncor). 

Necessary components to include for IG 

upgrade. 

Compatibility of components to provide an 

IG solution. 

Transition to an SBRT program. 

Siemens PRIMUS with ExacTrac System 

In-room monitor 

Infrared camera 

Imaging 

panels 

X-ray tube 

1

Siemens linac preparation 

Gantry rotation – radiation isocenter 

X-Jaws 1.02 mm 

Y-Jaws 0.06 mm 

TG-142 requirements for IMRT & SBRT: 

Mechanical and radiation isocenter verification: 

Gantry rotation (

Scan direction 

MLC picket fence test for Siemens 

center-to-center 

2 cm 

The Technology at CRTC for SBRT 

• Siemens Primus and Oncor Linacs. 

Scan direction 

• Philips large bore CT simulator (4D-CT capability). 

• Philips Pinnacle 3 Treatment Planning System. 

• BrainLab ExacTrac 6D-Stereoscopic X-ray Image 

Guidance System. 

Planning System Commissioning 

Philips Pinnacle Pinnacle3 v8.0m with with DMPO in in 

step step-and and-shoot shoot mode. 

Have strong 

and 

frequent engineering support ! 

Move on with SBRT 

Utilize more accurate patient immobilization 

devices. 

Utilized 4D-CT simulation for appropriate sites 

(e.g., lung, liver, etc), ITV approach. 

Utilized highly conformal multi-beam treatment 

planning and intensity modulation. 

Utilized image guidance for patient daily setup. 

Utilized on-line patient surveillance and setup 

correction during treatment. 

Utilized 5 and 10 mm MLC width for delivery. 

Small field size measurements 

Model fit to the data 

BEAM MODEL 

3

DMPO 

1.00 

0.90 

0.80 

0.70 

0.60 

0.50 

Small field size measurements 

OUTPUT FACTORS 

0.1cc Scanning IC 

Diode Perp. (norm to 5x5) 

Microchamber 

XV Film 

Small fields-MLC shaped 

Pinnacle Hi Res 

Pinnacle Lo Res 

0.40 

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 

Direct irect Machine achine Parameter arameter Optimization ptimization 

• DMPO produces final segments at the end of the 

optimization process. NO conversion is required. 

Automatically converts the ODM to MLC control 

points. 

• The MLC leaf positions and the weights of the 

segments are optimized at once (equivalent to DAO). 

• The time to prepare a plan is substantially reduced in 

DMPO. 

• You can filter the final control points according to 

area and monitor units. 

Dosimetric Comparison of MLC systems 

Linac MLC system MLC width 

Siemens Primus (X-jaws) Optifocus double-focused (divergent) - 58 leaves 10 mm 

Siemens Oncor (X-jaws) Double-focused (divergent)- 82 leaves 10 mm 

Siemens Artiste (X-jaws) 160MLC (rounded) - 160 leaves 5 mm 

Varian Trilogy (tertiary) Millennium (rounded) - 120 leaves 5 mm 

Elekta Synergy-S BM Beam Modulator (rounded) - 80 leaves 4 mm 

Elekta Synergy Elekta MLC (rounded) - 80 leaves 10 mm 

Novalis TX (tertiary) HD micro-MLC – 120 leaves 2.5 mm 

Detectors for small field measurements 

How important is the MLC system in 

multi multi-beam beam SBRT treatment planning? 

Method of comparison 

“RING”: A special ring-structure around the TV, 1 cm expansion of 

the TV – to evaluate the sparing of normal structures adjacent to TV. 

________________________________________________________________ 

CONFORMITY INDEX: 

TV = target volume 

PIV = prescription isodose volume 

PVTV = is the TV included in PIV 

Paddick, J. Neurosurg. (Suppl. 3) 93:219-222, 2000 

CI = ( PIV / PVTV ) / ( PVTV / TV ) 

CI = 1, perfect conformity 

Nakamura JL, et al., Int. J. Radiat. Oncol. Biol. 

Phys. 51, 1313-1319 (2001). 

The IL was chosen according to the criteria: 

(1) being the greatest IL that covers 95% of TV while 

(2) delivering ≥95% of the prescription dose to 99% of the TV. 

4

CI 

Comparison: Conformity Index 

2.5 

2 

1.5 

1 

0.5 

0 

Conformity Index (CI) 

4.64 (Lung-3D) 4.64(Lung-IM) 7.63(Brain-IM) 9.85(Lung-3D) 25.78(Spine-IM) 

Target Volume (cc) 

3D-CRT vs. Intensity Modulation 

Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660 

Oncor (10mm) 

Artiste (5mm) 

Varian (5mm) 

NovalisTX (2.5mm) 

Synergy (10mm) 

SynergyBM (4mm) 

Comparison: MLC systems 


LUNG: 3D CRT 

Oncor: 10 mm Novalis TX: 2.5 mm 

4500 cGy 

3600 cGy 

Conclusions of comparisons 

4275 cGy 

Our study is the first to include the majority of today’s MLC 

systems in a comprehensive way and has shown no apparent 

indication that smaller MLCs can lead to optimal plans, if 

multi-field techniques (IMRT or 3D) are utilized in SBRT. 

However, we believe that small tumor volumes would benefit 

from small MLC widths and single fraction SRS, instead. 

Tanyi, JA, Radiation Oncology 4:22 (2009) 

5mm Varian 

2.5mm Novalis TX 


Comparisons: 3D conformal vs. Intensity Modulation 

V olum e (% ) 

120 

100 

80 

60 

40 

20 

0 

Peri-tunoral Ring Volume 

4.64 cc Lung target 

50%(IM) 80%(IM) 90%(IM) 50%(3D) 80%(3D) 90%(3D) 

Isodose line 

Oncor (10mm) 

Artiste (5mm) 

Varian (5mm) 

NovalisTX (2.5mm) 

Synergy (10mm) 

SynergyBM (4mm) 


Comparison: Lung IMRT- IMRT all MLC systems 

10mm 

5mm 2.5mm 

10mm 5mm 

4mm 


SBRT – LUNG 

NO – GATING! 

WHY ? 

100% Rx 

90% Rx 

80% Rx 

50% Rx 

5

Patient Immobilization 

With arms over the head. 

Flat lung board with T-bar holder for the arms. 

Vacuum Bag 

Maximum Intensity Projection (MIP) 

CT data is acquired using a Bellows or RPM 

device that records a breathing wave. 

Maximum intensity values are assigned to pixels 

at locations where a tumor moves to over time. 

Are a derived dataset of images that show a 

“composite” of the tumor volume over the time 

period that the CT data was acquired. 

4D CT Simulation for LUNG SBRT 

CT Scanning procedure for moving target 

One free breathing scan – 3 mm slices, entire chest. 

One shorter, time-correlated scan – 3 mm slices, to 

include the tumor area. 

Breathing Waveform is acquired along with CT data 

using a Bellows or RPM device. 

The CT data acquired in one breath can be binned into 

10 equally spaced intervals along the waveform and 

reconstructed. 

The 10 intervals are called Phases. 

Moving Target virtual simulation - Fusion 

GTV 

MIP dataset 

Volume propagation from MIP dataset 

to 

free breathing dataset 

ITV 

Free Breathing 

dataset 

6

Treatment planning 

DMPO - optimization 

SBRT - LUNG 

Patient setup verification 

prior to treatment 

IMAGE GUIDANCE 

Multiple non-coplanar beams 

PTV=ITV + 5mm margin 

www.charlestonradiation.com 

WE HAVE NOTICED: 

2-3 segments allow for 

dose compensation due 

to lack of resolution of 

the 10mm leaf width. 

Mihailidis, et al., AAPM 

2009, Med. Phys. 36, 

(2009) 2660 

Allow for low low-level level Intensity Modulation 

Treatment Isocenter 

DVH results 

Step-and-shoot mode: 

• 2-3 segments per beam. 

• 50Gy in 5 fxs. 

• Optimization objectives 

-heart 

-ribs 

-normal tissues 

Mihailidis, et al., AAPM 

2009, Med. Phys. 36, 

(2009) 2660 

Ipsilateral lung 

ExacTrac setup for lung SBRT 

Virtual isocenter for IG 

ITV 

PTV 50Gy 


ET reconstructed views 

7

ET x-ray 

DRR 

Before Fusion - misalignment 

After fusion – shifts to be implemented 

Match of x-ray and DRR 

SHIFTS 

Patient setup and immobilization 

ExacTrac IR markers 


Excluded from fusion area 

Fusion preparation 

SBRT - Brain 

Fusion MRI – TP CT 

TP CT MRI 

Vargo J, Plants B, Welch C, Mihailidis D, et al., ASTRO 2010, IJROBP 78 (No. 3 Suppl), S279 (2010) 

8

SBRT brain positioning and planning 

Multiple non-coplanar beams 


DRR 

x-ray 

DRR 

SBRT - BRAIN 

Patient setup verification 

prior to treatment 

IMAGE GUIDANCE 

Fusion 

x-ray AFTER 

SHIFTS 

BEFORE 


Prescription: 

40 Gy in 5 fxs 

788 MU 

Sample isodose and DVH 

PTV 


Patient setup with IR markers 

from TPS 

IR marker 

Continuous IG 

objectives 


Allow for live patient survaillance with the IR 

camera and markers. 

Perform a second IG verification between 

treatment fields (residual shifts). 

Compare reference orthogonal treatment ports 

with orthogonal DRRs. 

Keep rotations to less than 3° if possible, 

otherwise…improvise. 

Wood Shims 


9

6D-IGRT accuracy: Infrared vs. stereoscopic x-ray 

Conclusions 

ExacTrac Stereoscopic x-Ray IG system, in 

combination with other technologies, provides 

accurate IG that allows the implementation of an 

SBRT program, 

IF 

additional precautions are taken. 

6D-corrections and residual setup errors 

Comply with published recommendations: 

10

THANK YOU ! 

NRAO Green Bank Observatory, West Virginia 

http://www.gb.nrao.edu/ 

11

SBRT&StereoscopicIGRT_2012 [Compatibility Mode]

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