IGRT in Lung

CancerDr Santam Chakraborty

Assistant Professor

Radiation Oncology

IGRT

Image Guided Radiotherapy

Describes a chain rather than a single process

“Exclusive” of the delivery process

Typically “onboard” guidance utilized

Leads to action that improves / verifies accuracy

T. Gupta, C. A. Narayan, Image-guided radiation therapy: Physician’s perspectives. J. Med. Phys. 37, 174–

182 (2012).

Why IGRT

S. S. Korreman, Image-guided radiotherapy and motion management in lung cancer. Br. J. Radiol. 88,

20150100 (2015).

Why IGRT ...

J.-J. Sonke, J. Lebesque, M. van Herk, Variability of four-dimensional computed tomography patient models. Int. J. Radiat. Oncol.

Biol. Phys. 70, 590–598 (2008).

Target Volume Changes due to Imaging

S. S. Korreman, Image-guided radiotherapy and motion management in lung cancer. Br. J. Radiol. 88,

20150100 (2015).

FDG PET CT in Target Volume Delineation

Y. Zheng et al., FDG-PET/CT imaging for tumor staging

and definition of tumor volumes in radiation treatment

planning in non-small cell lung cancer. Oncol. Lett. 7,

1015–1020 (2014).

● 35% have change in stage

assignment

● Fused CT / PET result in target

volume changes in 60%

● Reduced variability seen in

GTV delineation between

observers.

IGRT Technology & Imaging

Image Guided RT

Ionizing Radiation Based Other Technologies

Planar Imaging Volumetric Imaging

KV Fluoro / X ray

MV Fluoro / X ray

KV CT

MV CT

Electromagnetic Tracking

Optical Surface Tracking

Ultrasound Tracking

MRI based Tracking

IGRT Image Technologies

Technology Energy Type Accuracy Comments

EPID MV 2D 1-2 mm Surrogate imaging of soft tissue

KV Xray KV 2D 1-2 mm Better resolution w.r.t. EPID

CBCT KV 3D < 1mm Volumetric “slow” scan.

MVCT MV 3D < 1mm Can be useful for adaptive radiotherapy

Stereoscopic Xray KV 2D < 1mm Useful in tumor tracking. Oblique angles.

USG - 3D 3 mm Main utility in prostate cancers

Surface - 2D 1 mm Surface based optical tracking and localization

Transponders - 2D - Independent system for tumor tracking

IGRT Issues in Lung Cancer

1. Lung tumors are difficult to see with megavoltage imaging.

1. Significant movement of the tumor in all 3 directions in addition to “hysteresis”

1. Significant changes in the course of treatment

1. Lung motion is independent of bony motion

Difficulty in

Visualization

EPID based matching

Difficulty in

Visualization

Changes in

Volume

K. R. Britton et al., Assessment of Gross Tumor Volume Regression and Motion Changes

During Radiotherapy for Non–Small-Cell Lung Cancer as Measured by Four-

Dimensional Computed Tomography. International Journal of Radiation

Oncology*Biology*Physics. 68, 1036–1046 (2007).

Changes in

Volume

L. A. Dawson, M. B. Sharpe, Image-guided radiotherapy: rationale, benefits, and limitations.

Lancet Oncol. 7, 848–858 (2006).

Changes in

Volume

Ways to implement IGRT

IGRT Protocols

Offline Online

Q : Which one can correct for random errors?

➢ Large step

reduction

➢ Limited workload

➢ Mean error

correction

➢ Allows larger dose

through smaller

margins

➢ Daily error

correction

Basic points prior to Imaging

1. Reproducible comfortable positioning with immobilization

2. Tattoos help but skin marks mobile over bone (~ 5 mm)

3. Laser alignment is must

4. Rigid couchtop with indexed immobilization

5. Assume setup is incorrect unless proven otherwise

Bone Matching vs Soft Tissue Matching

M. Guckenberger, Image-guided Radiotherapy Based on Kilovoltage Cone-beam Computed Tomography — A Review of Technology and

Clinical Outcome. European Oncology & Haematology. 07, 121 (2011).

Good CBCT Match

Slide Image

courtesy Dr J P

Aggarwal

(TMH)

What to match on CBCT

4D-CBCT

https://www.aapm.org/meetings

/06ss/documents/SonkeConeBe

am.pdf

Systematic vs Random Error

Systematic error : Reproducible, consistent errors, occurring in the same

direction and of similar magnitude.

It affects the dose distribution by producing a “miss”

Defined as the AVERAGE of a set of displacement.

Random error: Varies in direction and magnitude in each fraction.

It affects the dose distribution by producing a “blur”

Defined as the STANDARD DEVIATION of a set of displacements

Example Systematic & Random Error

https://docs.google.com/spreadsheets/d/1_w1dJzakVPJeMqFFRr5PZs4MVmKrN4lFPIMr0tRHZWA/edit?usp=sharing

NAL correction

workflow

Example of a NAL protocol

Levels of IGRT implementation

0 1 2

RT Planning

Done more

accurately

(e.g. contrast /

PET CT /

4DCT)

3 4

Surrogate

based

matching

using bony

anatomy

Matching

based on

target

anatomy

(implanted

markers /

volumetric)

Adjustment /

correction for

intrafraction

motion

Adaptive

Radiotherapy

National Cancer Action Team, “National Radiotherapy Implementation Group Report IGRT Final Guidance for Implementation and Use”

(NHS, 2012), (available at link).

IGRT Lung Recommendation

Level 0 CT with contrast

PET CT for accurate target delineation

4DCT for accurate capture of motion

For all patients

Level 1 Planar imaging with matching to reliable bony surrogate

± volumetric imaging weekly (tumor morphology / volume changes)*

Pancoast tumors

3DCRT

Level 2 Imaging with offline matching and NAL pathway with target volume

matching (volumetric / fiducial)

± volumetric imaging weekly (tumor morphology / volume changes)*

All other lung tumors

3DCRT

Level 2 Imaging with daily online correction with target volume matching

(volumetric / fiducial)

Complex IMRT /

Boost or reduced

margins

Level 3 Intrafraction motion monitoring SABR

National Cancer Action Team, “National Radiotherapy Implementation Group Report IGRT Final Guidance for Implementation and Use”

(NHS, 2012), (available at link).

Imaging Dose & consequences

Modality Effective Dose (mSv) Daily IGRT (30#)

Diagnostic Chest CT 6.4 -

EPID AP 3.6 246

EPID Lat 4.6

KV CBCT 24.6 738

KV XVI (Elekta) 8.1 243

Estimated life-time probability of 2nd malignancy : 1.2% - 3.7%

M. J. Murphy et al., The management of imaging dose during image-guided radiotherapy: Report of the AAPM Task

Group 75. Med. Phys. 34, 4041–4063 (2007).

Conclusions

● Image guided radiotherapy is an integral part of any conformal radiotherapy

program for lung cancer

● IGRT allows safer radiotherapy in terms of OAR dose reduction.

● IGRT however needs specialized equipment and expertise

● A team effort is needed for commissioning and implementation

● Physics and Technologists need to be a part of the team !!