May 28 – 30, 2015, Montréal, Québec

Breast Tomotherapy

by Camille Pacherand Manon Simard

Disclosure Statement: No Conflict of Interest

May 28 – 30, 2015, Montréal, Québec

I do not have an affiliation, financial or otherwise, with a pharmaceutical company, medical device or communications organization.

I have no conflicts of interest to disclose ( i.e. no industry funding received or other commercial relationships).

I have no financial relationship or advisory role with pharmaceutical or device-making companies, or CME provider.

I will be discussing the results of ____ (“off-label” use), which is currently classified by Health Canada as investigational for the intended use.

I will not discuss or describe in my presentation at the meeting the investigational or unlabeled ("off-label") use of a medical device, product, or pharmaceutical that is classified by Health Canada as investigational for the intended use.

May 28 – 30, 2015, Montréal, Québec

Disclosure Statement: With a Conflict of Interest

I have/had an affiliation, financial or otherwise, with a pharmaceutical company, medical device or communications organization, which could include:

Examples:•having received a grant(s) or an honorarium from a commercial organization.•holding a patent for a product referred to in the CME/CPD program or that is marketed by a commercial organization.•holding investments in a pharmaceutical organization, medical devices company or communications firm.•currently participating in or have participated in a clinical trial within the past two years.

I intend to make therapeutic recommendations for medications that have not received regulatory approval (i.e. "off-label" use of medication).

Introduction 1st part:

Historical overview Machine components How it works

2nd part: Treatment plan creation Examples

Breast Tomotherapy

1st partPhysics

by: Camille Pacher

1993Thomas R. Mackie

2002 First patients treated, UWI

2003Introduced into the clinic

2010~ 280 TomoTherapy units worldwide

2015:> 500

Historical overview

About Origin

Tomo = slice, section (Gk) Therapy = treatment

Conceived specifically for IMRT treatments

IMRT = Intensity Modulated Radiation

Therapy homogeneity D tumor

Limit dose to organs at risk (OARs) Parameter optimisation dosimetry planning

Under the hood Linac

Primary

collimator

Ion chamber

Jaws

MLC

Detector

Shielding

MonitorChambers

Figure reprinted with Accuray®’s permission

Under the hood – for real!

Geometry SAD = 85 cm bore = 85 cm

Real isocenter (1)

Virtual isocenter (2)

D(1-2): 70 cm

0o

90o

180o

270o

Figure reprinted with Accuray®’s permission

Why a “virtual” isocenter? No laser in the bore!

No way of knowing where the radiation isocenter is, therefore:

Introduce a virtual isocenter Fixed point outside the bore Known distance from the real

isocenter Used as a reference

Lasers

Green Fixed Intersect at virtual

isocenter Not used clinically Used for quality

assurance testing

Red Movable Overlap green lasers at

start up Position is specific to each

patient’s treatment plan Serve as a reference point

for patient positioning

Lasers: disposition

Quality control check: red laser motion wrt green lasers

Linac – linear accelerator

Treatment Imaging

Incidentelectrons

6 MeV 3.5 MeV

Target 1.5 mm tungsten

Photons produced

6 MV 3.5 MV

No flatening filter!

Ion Chambers

Device used to measure radiation

Continuous measurement Dose rate monitoring

Connected to a safety trigger If measurement is either too

high or too low, radiation is interrupted

Jaws ~15 cm thick Control field widths 3 field widths (FW) available:

1, 2.5 or 5 cm Dimension at isocentre

x y

z

View from couch

x

y

z

TG148. Figure reproduced with the AAPM’s permission

Multi-Leaf Collimator (MLC)

MLC: 64 leaves Binary; Pneumatic system Thickness: 10 cm, Width: 2-3 mm Maximum field length 40 cm

x y

z

View from couch

x

y

z

Detector Conventional

CT detector array

640 channels in total

Only the 520 central channels are used

FOV = 40 cm

Figure reprinted with Accuray®’s permission

Shielding Up to 23 cm of tungsten

Around the primary collimator Protection from scattered radiation

12.7 cm of lead “beam stop” Reduction in vault shielding

Figures reprinted with Accuray®’s permission

Distinctive features (1)The beam: Fan-shaped Photons only 6 MV only available energy Constant dose rate

Time-based (v. MU-based) Treatment is stopped after a

given amount of time has elapsed

Figure reprinted with Accuray®’s permission

Distinctive features (2) Daily MVCT – 1 to 3 cGy Gantry rotates constantly Couch is in motion

Helical treatmentdelivery

Consequences onplanning

Planning parameters FW selection: 1, 2.5 or 5 cm

in FW treatment time Ex: treat 10 cm area

FW = 5 cm, covered with 2 gantry rotations FW = 1 cm, covered with 10 gantry rotations

Pitch

Modulation factor

Pitch Distance d

traveled by the couch during one gantry rotation

Divided by the field width W

Influences: Gantry rotation

speed Couch speed

d

W

Effect of the pitch Pitch > 1

Pitch = 1

Pitch < 1

d > W

d = W

d < W

dW

Patient =

Patient =

Patient =

dd

Projections and beamlets

Projection = 1 MLC configuration

Fixed number of projections per rotation: 51

One projection = 7o arc

Beamlets = beam associated with one leaf

Max 64 beamlets per projection

~7o

~7o

Modulation factor (MF)

Longest time (t) during which a leaf is open

Divided by the average open time (tave) of

all other leaves (0) Impacts the gantry’s rotation speed For a complex treatment (requiring a lot of MLC

motion for instance), it is best to choose a high MF

Leaf open time histogram Nb of leaves (% normalised) vs open time (ms)

Limiting factors

Equipment’s physical constraints:

1. Gantry speed Minimum: 360o/60 sec Maximum: 360o/10 sec

2. Couch speed 0.0125-40 mm/sec

3. Max treatable length 160 cm

Alternate treatment modeTomoDirect Discreet angles Table moves between irradiations Pitch defined slightly differently:

Distance traveled by the couch between gantry angles

Wrap up Tomotherapy =

unique Build Operation

Combined factors: FW, pitch, modulation

factor …

influence: Treatment duration Resulting dosimetry

Breast Tomotherapy 2nd partDosimetry

by: Manon Simard

Breast+nodes

Treatment plan steps constraints block

Examples

A. Treatment plan creation Steps:

Contouring Region of interest (ROI) Plan settings Beam angles (tomo direct) Optimization Fractionation

1. Contouring

Targets, margins, OARs,done on Pinnacle

Send to Tomo

Add contours if necessary

(ex: avoidance structure in 3D)

Tomo Contouring

2. Region of Interest (ROI) Targets are

separated from the other structures

Choose which region of interest will be used for optimization

Overlap of structures taken into account

Overlap Explanation: 3 structures that do not overlap, the

system distinguishes each structure.

However, if there is an overlap, the machine sees them in the order you have choosen, 1 being the one in front and 3 the one in back

Overlap In the example below, the overlap

priorities (o.p.) have been set as follows:

1: circle 1: triangle

2: triangle 2: rectangle3: rectangle 3: circle

Then the overlap priority is important.

Examples Here is an example, where the o.p. is not

important because all 3 organs are distinct.

However, Here is an example, where the o.p.

is important.

3. Plan Settings Set the patient position

based on: green lasers (vitual isocenter) Tomo limitations

the PTV must be inside the field of view of 40cm

maximum lateral movement of 1.5cm

3. Plan Settings (continued)

Red lasers (positionning

lasers) are placed on markers The offset between green and

red lasers has to be less than 18cm along the Y axis.

3. Plan Settings (continued)

Determine system settings delivery mode:

direct or helical plan mode

IMRT or 3DCRT field width

1.05cm (brain, head/neck) 2.5cm 5cm (long structure)

pitch 0.287 0.430

4. Beam angles (TomoDirect)

TomoDirect is another way to treat breasts without nodes,

2 fields with flash Treatment time longer than

breast case on Pinnacle ex: 6 min for dose of 50Gy-25tx

Can associate fields to specific structures

Breast + nodes all cases of breast with lymph nodes are

treated by Tomotherapy®. the advantage is that there is no field junction. PTVbreast= CTVbreast + 7-10mm (but 3mminternal,

5mmpost ) PTVnodes=CTVnodes+5mm (but 3mm where OARs lung,

thyroide..) Prescribed dose

Breast+nodes: 50Gy 25tx (2Gy/tx) 45Gy 20tx (2.25 Gy/tx)

Internal mammary nodes: 45Gy

Breast + nodes targets objectives See table

the organs at risk (OARs) constraints depend on which lymph nodes are treated. supraclavicular (sc) supraclavicular (sc)+ axillary (ax) supraclavicular+axillary+internal mammary

nodes (im)

See table

Control the low doses by use of avoidance structures block limit

ObjectivesDose objectives for target volumes CTVs/PTVs

CTV/PTV breast CTV/PTV nodes

protocol minor deviation

protocol minor deviation

CTVevalPTVeval

V95 ≤99%V95 ≤95%

≤95-99%≤90-95%

V95 ≤95%V90 ≤95%

≤90-95%≤90-95%

PTVeval, V107%

≤10% ≤20% ≤10% ≤20%

PTVeval, V110%

≤1% ≤5% ≤1% ≤5%

Dose constraints for OARsbreast/chest wall +

supraclavicularsbreast/chest wall+

axillary-supraclavicularsbreast/chest wall

+axillary-supraclavicular+im

protocol minor deviation

protocol minor deviation

protocol minor deviation

controlateral breast

V5 ≤ 1%V2.5 ≤3%

V5 ≤ 3%V2.5 ≤5%

V5 ≤ 1%V2.5 ≤3%

V5 ≤ 3%V2.5 ≤5%

V5 ≤ 5%V2.5 ≤10%

V5 ≤ 10%V2.5 ≤15%

ipsilaterallung

V20 ≤ 25%V5 ≤45%

V20 ≤ 30%V5 ≤50%

V20 ≤ 30%V5 ≤50%

V20 ≤ 35%V5 ≤60%

V20 ≤ 30%V5 ≤50%

V20 ≤ 35%V5 ≤60%

Controlateral lung

V5 ≤ 3%V2.5 ≤5%

V5 ≤ 5%V2.5 ≤10%

V5 ≤ 3%V2.5 ≤5%

V5 ≤ 5%V2.5 ≤10%

V20 ≤ 3%V5 ≤10%

V20 ≤ 5%V5 ≤15%

heart if left breast

V40 ≤ 1%V30 ≤5%

V15 ≤10%

V40 ≤ 3%V30 ≤10%V15 ≤15%

V40 ≤ 1%V30 ≤5%

V15 ≤10%

V40 ≤ 3%V30 ≤10%V15 ≤15%

V40 ≤ 3%V30 ≤10%V15 ≤15%

V40 ≤ 5%V30 ≤15%V15 ≤20%

heart if right breast

V5 ≤ 1%V2.5 ≤5%

V5 ≤ 5%V2.5 ≤10%

V5 ≤ 1%V2.5 ≤5%

V5 ≤ 5%V2.5 ≤10%

V40 ≤ 1%V30 ≤5%

V15 ≤10%

V40 ≤ 3%V30 ≤10%V15 ≤15%

thyroide/larynx/œsophagus (neck)

V40 ≤ 5%V15 ≤30%

V40 ≤ 10%V15 ≤50%

V40 ≤ 5%V15 ≤30%

V40 ≤ 10%V15 ≤50%

V40 ≤ 5%V15 ≤30%

V40 ≤ 10%V15 ≤50%

spinal cord PRV

≤ 15Gy ≤ 25Gy ≤ 15Gy ≤ 25Gy ≤ 15Gy ≤ 25Gy

Block A Tomo plan is like a

puzzle: to control and to direct the radiation one needs structures everywhere.

As soon as we remove a piece, the radiation goes through it.

Block For each structure,

we have to choose among 3 states:

Unblocked accept entering and exiting dose

Directional accept exiting dose

only Complete

no entering nor exiting dose is accepted

If directional

If complete

Block (continued)

The structures that we usually use are:

Breast block (complete)

Nodes block (directionnal)

Arm block (directionnal)

lim internal, external, ant, post, arm

The block must be extended outside the body, where necessary.

Breast block

Nodes block

Arm block

Lim ext

Lim int

Lim ant

Lim post

Lim arm

Block (continued)

Here are the structures that we use only if necessary:

im block (directionnal) chin block (directionnal) Missing body block

(directionnal)

im block

Breast block

missing body block

5. Optimization

Prescription Give constraint to each structure used

for the optimization Choose the modulation factor

Between 1 to 3 (1 less precise but faster treatment,

3 more precise but slower

treatment)

5. Optimization (continued)

5. Optimize and have fun! (continued)

In order to obtain a good treatment plan, good coverage of the targets acceptable hot spot doses to the organs at risk are within

tolerance treatment time is not too long (13-15

min)

6. Fractionation

final dose calculation: time, dose, distribution, gantry period (sec/tour)

signed by doctor produce plan report

Examplesof

treatmentplans

.

Regular cases Breast+axsc

no junction good coverage no high dose in

external treatment time 12-

15min lung

V5Gy<30% V20Gy<20%

Regular cases (continued)

Chest wall+axsc Breast+axsc+im

Regular cases (continued)

Breast+sc palliative

Less common cases

Pacemaker blocked completely dose to

pacemaker=1.1Gy nodes well covered

pacemaker

pacemaker

Less common cases (continued)

Bilateral breasts complete block Doses to OARs respect constraints for cases where

one breast is treated

Treatment time: 12 min 42sec (2 breasts+ nodes)

heart, lung, spinal cord,targets…..all OKHot spot 106%

Double breast

Less common cases (continued)

Marfan Syndrome pay attention to the

heart the dose received by

the heart has been limited,

V5Gy = 3%, V10Gy = 0.8% coverage OK other OARs OK

Less commoncases (continued)

morphology pectus excavatum

breast block=complete int block=directionnal OARs OK with constraints

lung V5Gy=44% V20Gy=24% heart V15Gy=12% V30Gy=3.4% V40Gy=0.4%

Disadvantages

When the optimization is started, and that you want to go back to work on previous tab, you have to cancel your optimization, make the modification, and restart.

Tomo doesn’t share plan from a machine to another one, must be manually copied and transfered.

Low dose

Advantages

copy plan dose accumulation from different

plans has to be on the same scan

conformity avoidance structure excellent coverage

Conclusion Understanding of the workings of

Tomotherapy

Dosimetry offers Excellent target coverage Relatively low hotspots Beware of low doses

TomoEdge is in our future

Thank you for your attention!

QUESTIONS…