Page 1

James S Welsh, MS, MDDepartment of Human OncologyUniversity of Wisconsin, Madison

Novel Clinical Applications of IMRT

HelicalScanning

Helical (Spiral) Tomotherapy

Helical Fan Beam

Ring Gantry

Linac

CT Detector

CT Couch

X-Ray Fan Beam

Binary MLC Leaves

Binary MultileafCollimator

Helical (Spiral) Tomotherapy

X-Ray Beam

Binary MLC LeavesHelical Fan Beam Delivery

UW Helical Tomotherapy Unit

Status June 2003•MVCT scans obtained on 10 lung and 10 prostate cancer patients•9 dogs treated•10 human patients treated

•9 palliative•1 definitive

Advantages of HelicalTomotherapy

• CT component allows real-time imaging of patients to verify set-up and detect variations in positioning

• Relative Simplicity • An optimal means of delivering co-planar therapy• Adaptive Radiotherapy• Conformal Avoidance• Wide range of IMRT applications

MVCT of an Anesthetized Dog with a Sinus Tumor

SinusTumor

ErodedBone

Page 2

MVCT Before Our First Patient Treatment

Target Volume

MVCT of a Lung Cancer Patient #1 at 3 cGySoft Tissue Window Lung Window

LungTumor

MVCT of a Lung Cancer Patient # 2 at 3 cGySoft Tissue Window Lung Window

LungTumor

MVCT of a Prostate

Cancer Patient at 2.5 cGy

Prostate

Advantages of HelicalTomotherapy

• CT component allows real-time imaging of patient to verify set-up and detect variations in positioning

• Relative Simplicity• An optimal means of delivering co-planar therapy• Adaptive Radiotherapy• Conformal Avoidance

Preliminary TomotherapyPlanning

95%90%50%20%

Page 3

Preliminary TomotherapyPlanning

95%90%50%20%

Spinal cord NTDmean

0

5

10

15

20

25

P1 P2 P3 P4 P5 Mean

Patient

3D plans

Tomotherapy

Tomotherapy decreasesmean NTD (spinal cord)

Conformal Avoidance• Wide field XRT is frequently employed to target regional

micrometastatic extension • This regional disease extension is not precisely defined in terms of

anatomic detail• As a consequence, normal critical tissues are frequently irradiated

and yield toxicities• Conformal avoidance can “shield” these structures and improve the

therapeutic index by decreasing these often permanent and debilitating NTCPs– Salivary glands: Xerostomia/Dental hygiene/Osteonecrosis– Oto-acoustic apparatus: Hearing/Balance– Optic/Lacrimal tissues: Vision/Xerophthalmia/Corneal complications

Rationale for Conformal Avoidance Radiotherapy

• The gross tumor volume (GTV) may not be clearly visible • Uncertainty in defining the clinical target volume (CTV)• The planning target volume (PTV) may be uncertain• The target dose is limited by normal sensitive tissue

• Conformal avoidance is the ideal paradigm to treat suspected regional/nodal involvement

Conformal dose-distribution with tomotherapy

Continuum Between Conformal Therapy and Conformal Avoidance

Know wheretumor is and will not harm sensitive tissue

•Don’t really know where tumor is •May miss part of target if overly conformal•…..and still harm sensitive tissue

Page 4

The Mantle

• Successfully used for many decades• A classic example of the need to treat

invisible microscopic regional disease• Generally not easy to duplicate using

conformal therapy• A potential application of conformal

avoidance IMRT• Can reduce dose to Thyroid, Larynx, Heart,

Spinal cord thereby reducing complications• Can reduce dose to breast in young women

(possibly) reducing risk of future breast cancer

Conformal Mantle FieldConformal Avoidance Radiotherapy for A Mantle Equivalent using

Helical Tomotherapy

Mediastinal

R.axila node

L.axila node

RegionalfieldLungs

LarynxSpine

Subtotal/Total Lymphoid Irradiation

• Inverted-Y• Can be effectively duplicated using IMRT via

linac or helical tomotherapy• Significantly less dose to sensitive normal

structures than older techniques is possible

The dose should be Divided by 10

Page 5

Dose Rate Cumulative Dose

ROI slice 27

Mesothelioma

Slice 27 Slice 31 Slice 36

50 %80 %90 %

50 %80 %90 %

50 %80 %90 %

Tomotherapy Mesothelioma Dose Distributions

Partial Breast Irradiation

• Good clinical results have been obtained using HDR brachytherapy

• Recent applications of partial breast irradiation using external beam approaches

• Visualization of target and immobilization of breast will be essential for success of this approach

Limited Field Prone Breast

Limited Field Prone Breast

PTV

Skin

Muscle

GTV

Lt Lung Rt Lung

Page 6

IMRT for complicated tumor volumes

• IMRT can handle complicated tumor volumes using either a conformal therapy or conformal avoidance approach

• High conformality of isodose curves – Lower doses to surrounding normal structures– Higher dose to tumor volume

Skull Irradiation

Lt Eye Chiasm

PTVRt Optic Nerve

Rt Eye

Lumbar Spine Treatment

PTVKidneys Optimize ~5min

Setup ~3min

MVCT ~7min

Contour ~10min

Delivery ~5min

MVCT, Simple Contour, Plan & Treat Palliative Case: 30 Minutes Total

SimpleContour

Page 7

Page 8

Summary

• Conformal avoidance radiotherapy, the complement to conformal radiotherapy, focuses on avoiding dose to normal tissue

• IMRT, especially helical tomotherapy appears particularly well-suited for conformal avoidance

• Many innovative clinical procedures will evolve from conformal avoidance IMRT

Potential Clinical Applications of Conformal Avoidance IMRT

• Improved irradiation of nodal chains using the conformal avoidance strategy

– Improved “Mantle” and “Inverted-Y”– Para-aortic irradiation for GYN, GU and lymphoid

malignancies• Brain-sparing total scalp irradiation

– Scalp-sparing whole brain irradiation

• Pacemaker/defibrillator avoidance• Bone marrow ablation while sparing visceral

organs• Craniospinal Irradiation

Potential Clinical Applications of Conformal Avoidance IMRT

• Accelerated partial breast irradiation• Complicated tumor volumes

– mesothelioma

• Extracranial stereotactic radiotherapy• Widespread metastatic disease?

– Visible disease handled with radiotherapy– Microscopic disease handled by chemotherapy– “Intermediate” disease identified by PET and handled by IMRT