Stereotactic Body Radiation Therapy: Is It Ready For

Primetime?Joseph Herman MD, MScJoseph Herman MD, MSc

Department of Radiation Department of Radiation OncologyOncology

SBRT Overview

• Stereotactic body radiation therapy (SBRT) uses sophisticated technology to deliver a focused ablative dose to tumors.

• Tumors include lung, liver, spine, pancreas, kidney, and prostate.

• Prospective trials have demonstrated efficacy and acceptable acute and subacute toxicities

• Late toxicity requires further careful assessment

Radiation Delivery

• Conventional (3-5 beams)– 3-D conformal radiation therapy– Intensity modulated radiation therapy (IMRT)

• Linac based radiation• Tomotherapy

• Stereotactic Radiation Therapy (10-12 beams) – Gamma Knife– Linac based (isocenter)– Cyberknife (non-isocenter)

• Proton Therapy (one beam repeated)

Radiation: Fractionation

• Standard fractionation: – 1.8-2.0 Gy a day, 5 days a week for 25-30

treatments

• Conventional hypofractionation:– 3-5 Gy a day, 5 days a week for 10-15

treatments

• Stereotactic radiotherapy:– 15-25 Gy a day, 1-3 days a week for 1-5

treatments

Liver

Planning Target Volume

Target VolumesTreatment Planning

Gross Tumor Volume

Planning Target Volume

Target Volumes

Pre-radiation 6 months post-radiation

Radiographic Response

Survival as a Function of Dose

Dawson et. al., J Clin. Onc. 18:2210, 2000; Ben-Josef et al 2006

Time (years)

IMRT Plan to Deliver High Doseto Potential Resection Margin

Vineberg and Ten Haken, 2004

Eliminating Organ Motion and Set-up Error

• In the past we expanded the region of treatment to include breathing motion

• This increases the volume of normal structures treated and limits total dose to the tumor

• Set-up error– Daily or 4-D CT scan or radiographs– Lasers

• Monitoring and controlling breathing– Limit breathing (body cast or compression device)

– Radio-opaque markers implanted in liver (margin)– Active breathing control device to stop breathing in fixed

phase of respiratory cycle– Follow breathing motion (vest and fiducials)

Image Alignment: AP RadiographsImage Alignment: AP Radiographs

Reference Image Treatment Image

Hepatic microcoil

Body Frame

Active Breathing Control

Mouthpiece and filter

Flow sensor

Valve (air bladder)

Dawson et al Int. J. Radiat. Oncol. Biol. Phys., 51:1410, 2001

Breath Hold at Normal Exhale

Pressure

Volume

Flow

Valve closed, Breath held

Valve open

Synchrony™

camera

Treatment couch

Linearaccelerator

Manipulator

Imagedetectors

X-ray sources

Targeting System

Robotic Delivery System

CyberknifeCyberknife

Patient Setup• No rigid fixation required• Intracranial cases: Thermoplastic mask• Extracranial cases

– Spine: no fiducials or markers needed– Soft-tissue lesions: Gold seed markers– Moving lesions: Synchrony vest

Photo courtesy of Naples Community Hospital

CyberKnife® ConformalityNon-Coplanar Beam Delivery

– Automatically minimizes entrance/exit beam interactions– No patient or linac re-positioning required

SRSAxial View

GTV60%

50%

Koong et al. Stanford; IJROBP 2004

SRSCoronal

ViewGTV60%

50%

Koong et al. Stanford; IJROBP 2004

SRS Toxicity

• Radiobiology: – Tumor vs. Normal Tissue

• Normal Tissue Toxicity– Lung: pneumonitis and fibrosis– Pancreas: duodenum and stomach– Spine lesions: cord– Prostate: rectum and bladder– Liver: normal liver (radiation induced liver

disease-RILD)

Results of a phase I dose-escalation study using single-fraction stereotactic radiotherapy

for lung tumors.Le et al. 2006 (Stanford)

• 32 patients with metastatic or unresectable lung cancer• Dose escalation using Cyberknife• 1-year freedom from local progression was 91% for

dose >20 Gy• RT-related complications were noted for doses greater

than 25 Gy– 4 cases of pneumonitis, one pleural effusion, and

three possible treatment-related deaths • Lower doses in patients previously irradiated or tumor

volumes >50 cc

SRS: Questions

• Long term toxicity to normal structures– Depend on prognosis

• Movement between imaging and delivery of radiation

• Overall Efficacy: Response and QOL• Cost and efficiency• Patient selection• Prospective clinical trials (RTOG)• Radiobiology of large fraction sizes

Small Animal IrradiationSmall Animal Irradiation

Thank You

• Jeff Geschwind

• John Wong

• Laura Dawson

• Bob Timmerman

• Ted Lawrence

• Ted DeWeese