Stereotactic Body Radiation Therapy (SBRT)

RadiantCare Radiation Oncology

James F Raymond MD

SBRT: What is it?

• Highly conformal radiation treatment confined to an extracranial target

• Use of multiple radiation beams that converge upon the target isocenter

• Very high dose radiation given in only a few fractions with 2X-3X the biological effect

• Intended to ablate all cells within the target volume

Rationale for SBRT

• Local control is poor after standard radiation treatment for many extra-cranial tumors

• Local control can be improved with dose escalation but there is risk of normal tissue injury due inaccuracies in treatment delivery

• Improvements in the delivery of radiation therapy now permit dose escalation while sparing injury to surrounding normal tissues

Conventional Dose Distribution

SBRT Dose Distribution

Origin from Intracranial Treatment

• Stereotactic radiosurgery was first developed in 1951 by Swedish neurosurgeon

• Single treatment with doses intended to kill all cells within an irradiated volume

• Utilization of an external 3D reference system (stereotactic system) for accurate localization of the target and for directing the radiation therapy

Stereotactic Methods

• Intracranial targets require fixation of the stereotactic frame to the skull bone

• Extracranial applications preclude fixation and the target can move

• Stereotactic body frames help to minimize the internal motion of the target

• CT treatment planning and LINAC “on board” CT imaging help to avoid missing the target

Brain vs Body Setup

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 2.

Geometric Verification• SBRT coordinate system is based on the target

and not on normal anatomy• The stereotactic reference system correlates the

LINAC and the CT scan images to locate the target

• Imaging of the target during treatment delivery permits a direct comparison to the reference image which improves accuracy

Coordinate Systems

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 3.

Verification of Alignment

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 3.

Heterogeneous Dose Distribution

• Radiation resistance of many tumors is likely due to hypoxic core

• SBRT increases the dose to the central parts of the tumor by approximately 50% compared to the periphery of the target

• This is accomplished by using multiple beams converging at the center of the target

SBRT increases the dose within the target

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 4.

SBRT utilizes multiple beams

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 112.

Fractionation

• Single fraction schemes were initially employed based on the experience of intracranial radiosurgery

• A few fractions of very high dose per fraction (hypofractionation) preferred due to toxicity using single fraction schemes

• Few fractions better than many due to emphasis on geometric accuracy and patient comfort

Equipment

• LINAC with multileaf collimator• 3D or IMRT treatment capability• CT for treatment planning• Image Guided Radiation Therapy

– Fiducial markers or CBCT• Internal Organ Motion Control• Stereotactic Body Frame

Modern LINAC

LINAC with CBCT

Stereotactic Body Frame

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 5.

Tumor Types treated at the Karolinska Hospital with SBRT from 1991-2003

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 6.

Summary

• SBRT is a good non-surgical option for eradicating small volume tumors mostly in the lung and liver

• Appropriate patient selection is important

• CT treatment planning is required

• Treatment delivery is complicated and requires state-of-the-art treatment facilities

Case Examples

SBRT for Lung Cancer

Results of SBRT for Early Stage Lung Cancer

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 104.

Results of SBRT for Metastatic Lung Tumors

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 104.

Complications of Lung SBRT

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 105.

Case Example Lung SBRT

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 111.

Case Examples

SBRT for Liver Metastases

Single-institution Reports of SBRT for Liver Metastases

Kavanaugh and Timmerman, Stereotactic Body Radiation Therapy 2005; pg 118.

Case Example of SBRT for Liver Metastases

Follow-up scans after SBRT