Intensity Modulated Radiation Therapy

Outline

1. Introduction2. Literature review3. Physical aspect 4. Discussion 5. Conclusion

Introduction•Intensity modulated radiation therapy

(IMRT) is the product of advances in the RT technology.

•Aims to deliver radiation more precisely to the tumor while relatively limiting dose to the surrounding normal tissues.

•The purpose of this presentation is to discuss the new concept of IMRT, its physical aspect, its applications and comparison with other RT methods.

Literature Review• 1950’s the medical linear accelerator was

developed and marketed to treat cancer.• 1980’s the 3D-Conformal Radiotherapy

(3D-CRT) was introduced.• 3D-CRT based on 3D dose planning system.• Conform the shape of the radiation beam to

that of the tumor.• Problem: Cannot conform well to 3D objects

due to the uniformity of beam strength.• 30% of tumors exhibit concave features

difficult conventional Conformal RT.

Literature Review•1960’s IMRT was first conceptualized •1994 the 1st commercial IMRT delivery

unit was introduced.•IMRT An advanced form of 3D-CRT. •Based on linear accelerator(LINAC)

where the radiation intensity could be modulated during the treatment.

•The field is geometrically shaped by MLC’s.

•The intensity is varied pixel-by-pixel within the shaped field.

Figure: differences between

(a) conventional radiotherapy,

(b) conformal radiotherapy (CFRT) without intensity-modulation and

(c) CFRT with intensity modulation (IMRT).

Physical Aspect

IMRT combines two advanced concepts to deliver 3D CRT:

1. Inverse treatment planning with optimization by computer

2. computer-controlled intensity modulation of the radiation beam during treatment

Treatment planning •Based on “Inverse planning”1.Initially, a CT scan is performed on the

affected region.2.A radiation oncologist defines the PTV3.Enters the plan criteria: max dose, mini

dose, desired -limiting dose(for critical

structures) and a dose-volume histogram4.Then, an optimisation program is run to

find the treatment plan which best matches all the input criteria.

Planning

Dose volume histogram

DVH is to summarize 3D dose distributions in a graphical 2D format

Treatment planning • Inverse planning methods are divided into:

A.Analytic methodsB.Iterative methods

Many computer programs use both methods to achieve a beam arrangement.

Analytic methods:

•It a mathematical techniques in which the TV dose distribution depends on the point dose intensity.

Iterative methods:

•It is a manual technique and the beamlets depends on the cost function that is the energy dose for each point in the TV.

Electronically

transmitted

How to modulate intensity?

•By MLC’s

MLC’s•L.A. must be equipped with computer-

controlled MLC’s•MLC’s consists of up to 120 individually

adjusted metal leaves. •The leaves move in & out contouring the

radiation beam to the shape of the tumor & block out unwanted radiation.

MLC modes

A. Multi segmented static fieldsB. Dynamic deliveryC. Intensity modulated arc therapy

Multi segmented static fields•Also called, step-and-shoot or stop-and-shoot1.The patient is treated by multiple fields2. MLC divides each field into a set of

subfields irradiated with uniform beam intensity levels.

3.Delivered in an arrangement one at a time in sequence without operator intervention.

4.The LINAC is turned off while the leaves move to create the next subfield.

Dynamic Delivery

•Shift during delivery

•The radiation is “on” all the time, even when the leaves are moving from one static subfield to the next.

Intensity modulated arc therapy• Similar to step-and-shoot in that each field

(positioned along the arc) is subdivided into subfields.

• However, the MLC moves dynamically to shape each subfield while the gantry is rotating

• Beam is on all the time.

• An alternative to tomotherapy

IMRT plan to treat tumor & avoid critical structures

Image showing TV in red and spinal cord in blue

Map of intensities calculated by inverse planning software for the beam shown on the LT.

Some Application of IMRT

1. Brain Tumors: IMRT can treat• Intracranial tumors (benign &

malignant). • large, irregular, and solitary, or smaller &

multiple Brain lesions.•IMRT limit the dose to surrounding

normal tissues; optic nerve, chiasm, lens, & brainstem.

 Brain IMRT

Some Application of IMRT •2. Head and Neck Cancer: •Many of the technique issues for brain

tumors also apply to head and neck ca.•Limiting dose to the parotid gland to

prevent xerostomia, or permanent dry mouth that occurs with typical head and neck radiotherapy.

Head & neck IMRT

3. Prostate Cancer:• RT has been a mainstay of localized

prostate ca therapy for several decades.

•Higher doses to the prostate and better shielding of the rectum and bladder to minimize morbidity.

Some Application of IMRT

Prostate IMRT

Some Application of IMRT

4. Breast cancer:•IMRT is the better treatment. •Gives more even dose to the breast with

fewer hot spots & less dosing to normal tissues (lung & heart).

•Common SE of radiation, like swelling, breast heaviness and sunburn-like changes, can be reduced with IMRT.

Discussion IMRT & 3D-CRT•Many studies have generated 3D-CRT &

IMRT treatment plans predicted dose distributions within the target & adjacent tissues compared them.

Results: •IMRT doses to the normal organs,• target dose conformity, •hypothesized that IMRT may improve

treatment outcomes

Discussion IMRT & IGRT• Image-guided RT is by far the most advanced

form of RT today.• To see the location of the tumor during the

delivery treatment sessions. • In IGRT, Cone Beam CT is taken just before

the treatment delivery aligned with the previous planning CT image appropriate corrections are made online.

•  IMRT improves the radiation delivery precision

• IGRT improves accuracy• e.g. of IGRT, CYBERKNIFE, TOMOTHERAPY

Conclusion

•Both theoretical and clinical data have shown the benefits of IMRT

•Tumor dose esclation and critical organ sparing would not be a problem

•IMRT holds promise in radiation oncology in the new century

• More clinical data are needed to confirm the potential promise.

A smiling face demonstrating how radiation can be deposited in almost any pattern.

Thank youThank you

References

• http://bjr.birjournals.org/cgi/content/full/76/910/678• http://www.cancernews.com/data/Article/259.asp• http://www.oncolink.org/treatment/article.cfm?

c=5&s=33&id=181• http://www.sinaigrace.org/?id=351• http://www.asco.org/ascov2/Meetings/Abstracts?• &vmview=abst_detail_view&confID=52&abstractID=40388• http://www.oralcancerfoundation.org/facts/pdf/radiation_types.pdf• http://www.fchp.org/providers/medical-management/~/media/

Files/FCHP/• Imported/IMRTBreast.pdf.ashx• http://www.oncolink.org/treatment/article.cfm?

c=5&s=33&id=181• http://www.cancerinfotech.com/igrt.asp• The Physics of Radiation Therapy - 3rd Edition - Faiz M. Khan