Imrt In Cervix Cancer

IMRT in Cervix Cancer

Tomas Kron, PhDPeter MacCallum Cancer Centre

AUSTRALIA

Preface

Despite the “availability of IMRT” in approximately 30% of radiotherapy centres in the western world, IMRT is rarely used for treatment of cervix cancer.

Objectives of the lecture

Discuss the need for imaging in the assessment of target volumes in external beam RT of cervix cancer

Introduce the concept of inverse treatment planning in IMRT

Discuss pro- and cons of IMRT Compare IMRT and brachytherapy dose

distributions for cervix radiotherapy

Some anatomy

…is it constant?

From Huh, SJ et al Radiother. Oncol. 71 (2004) 732 MRI T2 weighted images of the same patient 4 weeks and 35Gy apart

Conventional treatment

Mutic S et al IJROBP 55 (2003) 28

Region 2: 45Gy (para-aortic LN)

Region 1: 45Gy + 5.4Gy EBT+ brachytherapy boost

Role of imaging for target definition

Patterns of Care Study 1988/89 in US – Ling et al IJROBP 1996:

• “Fairly uniform approach”

• CT scans 11%

• MRI none

• Target volume outline 14%

• Small bowel outline <1%From ICRU report 38 based onG Fletcher’s work

The impact of patient positioning on the adequate coverage of the uterus in the primary irradiation of cervical carcinoma: a prospective analysis using magnetic resonance imaging. Weiss E et al Radiother. Oncol. 63 (2002) 83

Results: Standard portals [ie 4 field box] did not completely cover the uterus in supine position in 7/21 (33%), in prone position with belly board in 7/21 (33%) and without belly board in 5/21 (24%). Insufficient uterine coverage was found only in the anteroposterior direction. The mean distance (± standard deviation) between the field borders of the lateral portals and the uterus was in supine position anteriorly 3.4 cm (±2.2 cm) and posteriorly 1.8 cm (±1.3 cm), in prone position with belly board anteriorly 2.2 cm (±2.7 cm) and posteriorly 2.6 cm (±1.6 cm), prone without belly board anteriorly 3.3 cm (±2.4 cm) and posteriorly 1.9 cm (±1.1 cm). The difference was statistically significant between supine and prone position with belly board and between prone position with and without belly board. Repeated MRI controls during therapy showed no significant changes compared to the MRIs at the beginning of therapy. Conclusions: The use of standard radiation fields results in a high percentage of geographical misfits. Three-dimensional treatment planning is a prerequisite for adequate uterus coverage.

… what has changed in 10 years?

Patterns of Care Study 1996-99 in US – Eifel et al IJROBP 2004:

• 1/3 stage IIIA - IVA

• CT most common

• 92.4% radical patients had brachytherapy

• 1999: 63% had concurrent chemotherapy

• Small centres (less than about 4 cervix patients per year) tend to provide worse treatment (<80Gy pt A, >70d total treatment time)

Role of imaging for target definition

CT:

• Treatment planning

• Nodal assessment

MRI:

• Extra cervical spread

• Design of lateral portals

PET:

• Lymph node involvement

US/TRUSMutic S et al IJROBP 55 (2003) 28

What can IMRT do ?

Reduction of dose to normal structures - ‘conformal avoidance’

Deliver multiple dose levels at one time

• simultaneous in-field boost

• mimicking brachytherapy distributions

Radiotherapy treatment planning

Patient information

Planning

Treatment unit data

Treatment plan

Treatment

Forward planning:• select parameters• calculate dose• check if it is ok

Inverse planning:• define what is ok• tell the computer• iterative optimization

Inverse planning process

CT scan - 3D, large volume, small slices Outlining of ALL (!) relevant structures (targets

and critical organs) DICOM transfer of CT data sets and

structures to planning system Definition of dose constraints Computer optimization Verification

Eg Tomotherapy planning station interface

Everything of interest MUST be outlined…The system does not care about anything else.

Need for customisation?

Courtesy A Fyles

…scope for customisation

Collage courtesyS Van Dyk,K Narayan

IMRT beneficial

What are the target outlines?

IMRT difficult, if not impossible

Prior to Txt After chemoradiation (40Gy)

K Narayan and Quinn 2003

Prescription panel

Three ways to guide the optimisation: 1. Precedence, 2. Importance, 3. Dose penalty

Inverse treatment planning

Many automatic optimisation algorithms are in use

• gradient based

• iterative least square minimisation

• simulated annealing Do not necessarily find the best

solution (local minima!) Can only be as good as the

specified constraints Very computer and time consuming

Tomotherapy 30processor

Planning as part of a network

Planning com puter

Diagnostic tools:CT scanner

M RI scannerPET, SPECT

OutlinesFilms

Computerisedbeam data

acquisition sytem

Record and verify

Treatm ent devicesM LC, dynam ic wedge

arcs, IM RT

Printer, p lotter

Storage deviceTape, disk

Compensator andBlock cutter

Patientinformation

system

Keyboard

Screen

Issues: reliability, compatibility, security

What can IMRT do ?





Lujan et al IJROBP 57 (2003) 516

What can IMRT do ?





Mutic et al IJROBP 55 (2003) 28

IMRT to mimic Brachytherapy

HDR brachy

7 field IMRT

HDR brachy 7 field IMRT

Schefter et al. Med Dosim 27 (2002) 177

The first issue of a new journal (Elsevier):

Brachytherapy 1 (2002) 191

Point/Counterpoint: Can IMRT replace brachytherapy in the management of cervical cancer?

• K Alektiar (New York): Brachy-therapy

• A Mundt, J Roeske (Chicago): IMRT

K Alektiar:

Brachytherapy is more suitable:

• Can give 80-90Gy to point A safely (even higher to cervix point)

• Target volume difficult to define for EBRT (parametrium particularly)

• Organ motion likely to be larger than in prostate

Inter-fraction Organ Motion

7 July 03 21 July 03

14 July 03 5 Aug 03Courtesy

A Fyles

Some comments

Nucletron

Optimisation of HDR applicators and stepping source pattern will further improve

Experience is very important in brachytherapy

Must consider overall treatment time when using external beam and brachytherapy combination

Dose distributions from four different HDR source movements

as determined using film

A Mundt and J Roeske:

“IMRT is a revolution in the treatment of cancer”

Role of IMRT in cervix cancer

For pelvic treatment sparing of normal structures (bone marrow, intestines)

Potentially replace brachytherapy (80Gy possible with 0.5cm margin) - alternatively applicator based IMRT (Low et al 2002)

Simultaneous integrated boost

Lujan 2003

“...IMRT may one day rival and perhaps replace brachytherapy...” Mundt and Roeske 2002

What can IMRT do ?





Ahmed et al IJROBP

60 (2004) 550

Unlikely

Considering IMRT

And also:

• Leakage

• Integral dose, dose dumping

• Treatment time

• Dose rate

• Resources required for set-up, maintenance and QA

Human errors in data transfer during the preparationand delivery of radiation treatment affecting the finalresult: "garbage in, garbage out"Leunens, G; Verstraete, J; Van den Bogaert, W; Van Dam, J; Dutreix, A; van der Schueren, EDepartment of Radiotherapy, University Hospital, St. Rafaël, Leuven, Belgium

AbstractDue to the large number of steps and the number of persons involved in the preparation of a radiationtreatment, the transfer of information from one step to the next is a very critical point. Errors due toinadequate transfer of information will be reflected in every next step and can seriously affect the finalresult of the treatment. We studied the frequency and the sources of the transfer errors. A total number of464 new treatments has been checked over a period of 9 months (January to October 1990). Erroneous datatransfer has been detected in 139/24,128 (less than 1%) of the transferred parameters; they affected 26%(119/464) of the checked treatments. Twenty-five of these deviations could have led to large geographicalmiss or important over- or underdosage (much more than 5%) of the organs in the irradiated volume, thusincreasing the complications or decreasing the tumour control probability, if not corrected. Such majordeviations, only occurring in 0.1% of the transferred parameters, affected 5% (25/464) of the newtreatments. The sources of these large deviations were nearly always human mistakes, whereas aconsiderable number of the smaller deviations were, in fact, consciously taken decisions to deviate from theintended treatment. Nearly half of the major deviations were introduced during input of the data in thecheck-and-confirm system, demonstrating that a system aimed to prevent accidental errors, can lead to aconsiderable number of systematic errors if used as an uncontrolled set-up system. The results of this studyshow that human mistakes can seriously affect the outcome of patient treatments.(ABSTRACTTRUNCATED AT 250 WORDS) [Journal Article; In English; Netherlands]

Green Journal 1992: > 50 occasions of data transferfrom one point to another for each patient!

Two final comments...

Positioning of the patient is important

Imaging is not all ‘high cost’

Adli et al IJROBP 57 (2003) 230

Small bowel dose with ‘limited arc’ technique

Role of Ultrasound likely to increase

Summary (personal opinion)

Cervix cancer radiotherapy is likely to include brachytherapy in years to come

Promising imaging techniques because of soft tissue contrast are MRI and US

IMRT is likely to play a role in• optimising ‘conventional part’ of external

beam delivery

• allow for simultaneous boost of involved lymph nodes

Any questions?

Thank you

Acknowledgements:

• A Fyles

• K Narayan

• S Van Dyk

Health & Medicine

Imrt In Cervix Cancer