Basics of Anatomy, Planning and Treatment Delivery for Brain Tumors

John H. Suh, M.D.Professor and Chairman, Dept. of Radiation Oncology

Associate Director of the Gamma Knife CenterRose Ella Burkhardt Brain Tumor and Neuro-oncology Center

Taussig Cancer Institute

Conflict of interest

• Abbott Oncology Consultant

• Varian Travel funds

Objectives

• Provide overview of brain anatomy

• Review advances in treatment planning and delivery oncology that have allowed optimization of radiation therapy of brain tumors.

• Discuss methods to direct dose to the tumor while minimizing dose to the normal neural tissues.

• Review advances in stereotactic radiosurgery.

Brain anatomy

Structures that are contoured

• Lenses

• Eyes (retina)

• Optic nerves and chiasm

• Brain stem

• Spinal cord

• Cochlea

• Temporal lobes and hippocampus

• T2/FLAIR and T1 changes for gliomas

Cranial Anatomy

• Brainstem = midbrain + pons + medulla

Midbrain

Pons

Medulla

Cerebral Aqueduct

Chiasm

Foramen Magnum

C1

Cranial Anatomy Motor Strip

Motor Strip“Omega” Sign

Cochlea

Optic Chiasm

• Chiasm is always above the sella

Pituitary

Chiasm

Visual Cortex

fMRI Visually Evoked PotentialsVariability of visual cortex

MR Images courtesy of: Holmes CJ, Hoge R, Collins L, et al. "Enhancement of MR Images Using Registration for Signal Averaging" Journal of Computer Assisted Tomography 22, 324-333 (1998)

Hippocampal 1) Tail 2) Body3) Head

Red: Hippocampus Green: Hippocampal Avoidance Zone

Hippocampal 1) Tail 2) Body3) Head

The hippocampus has three anatomic subdivisions: the head, body, and tail; note that the head is inferior or caudad, the body is superoposterior and the tail is most cephalad (superior) and posterior, and an overall “banana” shape emerges on sagittal images, located in the plane of the lateral ventricle.

RTOG Atlas

Radiation Therapy in 1990s

Dose distribution for WBRT

Linear accelerator

Conventional RadiotherapyConventionalBeam Shaper

Desired Dose

Distribution

Actual Dose Distribution

CT simulator use in radiation oncology

Provides cross sectional anatomical information

1) Target volume delineation

2) Relative geometry of critical structures

3) Beam placement and field shaping

4) Dose distribution calculation and analysis

Beam’s Eye View (BEV)

What are the Best Beam Directions?

Fusion of MRI to CT

Intensity Modulated Radiotherapy (IMRT)

Intensity ModulatorTransmitted

Beamlets

Desired Dose Distribution

Actual Dose Distribution

IMRT using Rotational Arc (Peacock)- 1996

Photo courtesy of Siemens Medical Solutions

3D Multileaf Collimator

Elekta Synergy

RADIATION ONCOLOGY Transition to Image Guided Radiation Therapy

Dose (Gy)

Tu

mo

r co

ntr

ol

(%)

Control

Complications

50

100

Therapeutic Index

0

95002052-0195002052-01

On Board Imager (OBI)–KV/MV-Cone Beam CT

Elekta KV-OBI Varian KV-OBI Siemens MV-OBI

Siemens CTvision

Daily CT Prior to Treatment

Tomotherapy Units

Image guided radiation therapy (IGRT) Novalis Shaped Beam Therapy

Cranial Patient Positioning

ExacTrac CBCT

Glioblastoma of right temporal region

Sequential Planning

Six static IMRT beams were usedwith 3 non-planar beams.

The beam was on for 11 minutes.

Dose Constraints for RTOG 0825

• Lenses 7 Gy

• Retina 50 Gy

• Optic nerves 55 Gy

• Optic chiasm 56 Gy

• Brainstem 60 Gy

63.059.450.445.030.0

Conventional Dose Painting

Simultaneous Integrated Boost Delivery

Four partial arcs are used for the plan.

Estimated beam time was about 4 minutes

Beam arrangement for meningioma

Coronal isodose distribution

RTOG 0933Phase II Trial of Hippocampal Avoidance During Whole Brain Radiotherapy for brain metastases

• Fused planning MRI CT image set• Hippocampal avoidance regions will 3D expansion of hippocampal contours by 5 mm.

Hippocampal sparing

Importance of optimizing image performance to achieve fundamental objectives of radiation therapy

Dawson LA et al. The Oncologist 15:338-349, 2010

“Replace the needle by narrow beams of radiation energy and thereby produce a local destruction of the tissue”

Lars LeksellThe stereotaxic method and radiosurgery of the brainActa Chirurgica Scandinavia Vol 102, Fasc 4, 1952

Stereotactic Radiosurgery

Early days of Stereotactic Radiosurgery

Dose (Gy)

Tu

mo

r co

ntr

ol

(%)

Control

Complications

50

100

Therapeutic Index

0

95002052-0195002052-01

Stereotactic radiosurgery

• Small, well-defined target < 4 cm diameter

• Single fraction

• Steep dose gradient

• Intersection of multiple beams of radiation at isocenter

Clinical uses of stereotactic radiosurgery

• Vascular malformations

• Benign brain tumors

• Malignant brain tumors

• Functional disorders

Model B unit

Plugging helmets to shape dose

Perfexion Gamma Knife

Leksell Gamma Knife PERFEXION

Leksell Gamma Knife®

Treatable volumeLeksell Gamma Knife C

Collimator system 8-16-8-16-16-16-16-16

Collimator system 8-16-8-16-8-16-8-16

Treatment plan with composite shots

Discordance caused by loose frame

Artifact caused by dental work

Different radiosurgery units

Novalis Radiosurgery System

Micro Multileaf Collimators (mMLC)

Different linac approaches for brain SRS

Circular Arc

IMRT

Dynamic Conformal ArcConformal Beam

HybridArc

Frameless Cranial Stereotaxy• Upper palate based immobilization

– Good dentition helpful

– Must be able to tolerate the mouthpiece

• Mask based

– More uncertainty

• Relocatable

– Hypofractionation

–Larger lesions

–Near dose sensitive structures

–Post op cavity

–Prior RT

– Image guided

–Skull is an excellent fiducial marker

– Reusable

• Not restricted by physical limitations

Radiation oncology team• Therapists

• Nurses and nurse practitioners

• Dosimetrists

• Medical physicists

• Clinical engineers

• Schedulers

• Secretaries

• Radiation oncologists

Strong teamwork and q/a program helps ensure proper and safe radiation delivery

Conclusions

• Understanding brain anatomy and dose constraints are essential.

• Technical advances in radiation oncology have allowed optimization of radiation delivery for brain tumors.

• Dose painting, dose sculpting, and conformal avoidance for brain tumors can be achieved given the advances in technology, imaging and treatment planning.

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