سبحانك ال علم قالوا ”

علمتنا إنك أنت لنا إال ماالحكيمالعليم “

الرحيم الرحمن الله بسم

OUTLINEPrinciple of Tomotherapy.CT scan similarity.Tomotherapy idea.Serial and Spiral.Clinical Application and Overview.

Tomotherapy Tomotherapy

Tomotherapy is intensity-modulated Tomotherapy is intensity-modulated rotational radiotherapy utilizing a photon rotational radiotherapy utilizing a photon fan beam. fan beam.

Radiation therapy device designed on a Radiation therapy device designed on a CT scanner-based platform.CT scanner-based platform.

Tomotherapy means slice therapy coined Tomotherapy means slice therapy coined to describe IMRT using fan beam. to describe IMRT using fan beam.

Computer TomographyComputer Tomography

CTCT

Pro

spec

tive

Gat

ing

Ret

rosp

ectiv

e G

atin

g

Types of CT ScannerTypes of CT Scanner

Two FlavorTwo Flavor

Medco, a company formed by neurosurgeon Medco, a company formed by neurosurgeon Mark Carol began developing the serial Mark Carol began developing the serial tomotherapy concept. tomotherapy concept.

Their first presentation was in 1992 (Carol et Their first presentation was in 1992 (Carol et al. 1993) and their first patient was treated al. 1993) and their first patient was treated with tomotherapy in 1994with tomotherapy in 1994

BasicBasic PrinciplePrinciple Rotation therapy is relatively insensitive to the energy of Rotation therapy is relatively insensitive to the energy of

the beam (Johns and Cunningham 1983). the beam (Johns and Cunningham 1983). Before megavoltage beams were developed, rotation Before megavoltage beams were developed, rotation

therapy was used to deliver x-radiation deep within the therapy was used to deliver x-radiation deep within the body. body.

The lower exit dose of orthovoltage photon beams The lower exit dose of orthovoltage photon beams approximately compensated for the high entrance dose.approximately compensated for the high entrance dose.

of megavoltage beams, rotational delivery fell into disfavor of megavoltage beams, rotational delivery fell into disfavor because skin-sparingbecause skin-sparing

could be achieved even for single fields of radiation.could be achieved even for single fields of radiation.

IntensityIntensity ModulationModulation

The linac output can be varied. The linac output can be varied. The jaw opening can be changed.The jaw opening can be changed.The gantry speed can be altered.The gantry speed can be altered.The couch speed can be modified. The couch speed can be modified. The leaf states can be changed.The leaf states can be changed.

TomotherapyTomotherapy InformationInformation

The primary collimator and jaws are The primary collimator and jaws are fabricated from an alloy containing 95% fabricated from an alloy containing 95% tungsten.tungsten.

The thickness of the clamshell is about 22 The thickness of the clamshell is about 22 cm, which reduces the leakage for IMRT cm, which reduces the leakage for IMRT with high numbers of monitor units to with high numbers of monitor units to values typical for conventional delivery values typical for conventional delivery with conventional monitor units.with conventional monitor units.

At the axis of rotation, the leaf thickness is At the axis of rotation, the leaf thickness is 0.625 cm and the leaf height is 10 cm of 0.625 cm and the leaf height is 10 cm of 95% tungsten. The leaves have a tongue-95% tungsten. The leaves have a tongue-and-groove design that results in an inter- and-groove design that results in an inter- leaf leakage less than 0.5% of its open leaf leakage less than 0.5% of its open intensity, which makes it the best-shielded intensity, which makes it the best-shielded radiotherapy unit used for IMRT. radiotherapy unit used for IMRT.

can irradiate up to a 160 cm long field.can irradiate up to a 160 cm long field.The Tomotherapy unit has instead a set of The Tomotherapy unit has instead a set of

uniform thickness filters before and after uniform thickness filters before and after the monitor chamber to provide buildup to the monitor chamber to provide buildup to the monitor chamber, to shield the monitor the monitor chamber, to shield the monitor chamber from the jaws, and to remove chamber from the jaws, and to remove extremely low-energy photons.extremely low-energy photons.

The rate of fall-off at a plane through the The rate of fall-off at a plane through the machine axis is about 2.5% to 3% per cm machine axis is about 2.5% to 3% per cm so that by the edge of the field (20 cm so that by the edge of the field (20 cm from the central axis) the output is 40% to from the central axis) the output is 40% to 50% of its value at the center of the beam. 50% of its value at the center of the beam. The intensity variation leaf-to-leaf is about The intensity variation leaf-to-leaf is about 2%,but this small discretization cannot be 2%,but this small discretization cannot be discerned dosimetrically.discerned dosimetrically.

The major advantage of a lack of a field-The major advantage of a lack of a field-flattening filter is the beam quality. The thin flattening filter is the beam quality. The thin set of filters produces far less head scatter set of filters produces far less head scatter than a conventional linac equipped with a than a conventional linac equipped with a field-flattening filter. field-flattening filter.

This also improves the imaging This also improves the imaging characteristics of the beam. The energy characteristics of the beam. The energy spectrum at the center of the field is not spectrum at the center of the field is not significantly harder than the spectrum at significantly harder than the spectrum at the edge of the field. This means that the the edge of the field. This means that the beam is easier to characterize with model- beam is easier to characterize with model- based dose calculation systemsbased dose calculation systems

The helical tomotherapy has a conventional The helical tomotherapy has a conventional xenon ion chamber CT detec- tor system xenon ion chamber CT detec- tor system on board the system that acquires a on board the system that acquires a transmission signal from the linac beam. transmission signal from the linac beam. The parameters of the linac radiofrequency The parameters of the linac radiofrequency system are adjusted for imaging from those system are adjusted for imaging from those for treatment so that the beam has a lower for treatment so that the beam has a lower energy (about 3.5 MV),lower pulse repe- energy (about 3.5 MV),lower pulse repe- tition frequency,and smaller output.tition frequency,and smaller output.

Absence Of Metal Artifacts Metal artifacts Absence Of Metal Artifacts Metal artifacts arise in conventional CT scanners arise in conventional CT scanners because the attenuation of the metal is because the attenuation of the metal is non-linear due to the photoelectric effect. non-linear due to the photoelectric effect. In helical CT, the beam is penetrating In helical CT, the beam is penetrating enough to eliminate metal artifacts arising enough to eliminate metal artifacts arising from hip prostheses and dental filings. from hip prostheses and dental filings.

This means that a verification CT could be This means that a verification CT could be a more reliable CT system for prostate a more reliable CT system for prostate patients with hip replacements and head patients with hip replacements and head and neck patients with cancer of the and neck patients with cancer of the tongue.tongue.

For a typical 30-fraction treat- ment For a typical 30-fraction treat- ment schedule, daily imaging delivers a total schedule, daily imaging delivers a total exposure dose to the imaged volume of exposure dose to the imaged volume of less than 1 Gy.less than 1 Gy.

For a typical 30-fraction treatment For a typical 30-fraction treatment schedule, daily imaging delivers a total schedule, daily imaging delivers a total exposure dose to the imaged volume of exposure dose to the imaged volume of less than 1 Gy.less than 1 Gy.

Nonetheless, MV CT images are far superior Nonetheless, MV CT images are far superior to planar images (either kV or MV) for the to planar images (either kV or MV) for the verification of correct patient setup. verification of correct patient setup. Moreover, helical MV CT imaging is a slow Moreover, helical MV CT imaging is a slow CT imaging technique that allows for the CT imaging technique that allows for the encoding of target motion in the resulting MV encoding of target motion in the resulting MV CT data set (see fig. 10 , 11 ), and therefore CT data set (see fig. 10 , 11 ), and therefore the pretreatment verification of a motion the pretreatment verification of a motion envelope defined from four-dimensional CT. envelope defined from four-dimensional CT.

Tungsten MLC 2cm in width

CRANECRANE

Rock Mackie with the University of Wisconsin Tomotherapy Research Unit

TomotherapyTomotherapy

Hi - ARTHi - ART

Tomos ’Universal’ SignatureTomos ’Universal’ Signature

Tomotherapy And Adaptive Tomotherapy And Adaptive RadiotherapyRadiotherapy

instead of simply delivering the intended instead of simply delivering the intended treatment plan, one would take an exit treatment plan, one would take an exit dose measurement during treatment and dose measurement during treatment and reconstruct the dose distribution that has reconstruct the dose distribution that has been delivered. Using any of a number of been delivered. Using any of a number of metrics, one could then compare this metrics, one could then compare this actually delivered dose dis- tribution with actually delivered dose dis- tribution with the intended one.the intended one.

the pretreatment dose guidance that is the pretreatment dose guidance that is currently possible with tomotherapy. The currently possible with tomotherapy. The overlaid isodose cloud can be used to overlaid isodose cloud can be used to visually verify that the intended targets lie visually verify that the intended targets lie within the high-dose region and that within the high-dose region and that organs at risk lie outside the high-dose organs at risk lie outside the high-dose region.region.

Positioning Verification Positioning Verification

However, placing a slippery polyethylene However, placing a slippery polyethylene sheet with handholds between the couch sheet with handholds between the couch top and mattress can easily effect lateral top and mattress can easily effect lateral movements. The next generation of movements. The next generation of couches on helical tomotherapy units has couches on helical tomotherapy units has lateral adjustments. Tomotherapy comes lateral adjustments. Tomotherapy comes equipped with a set of moveable CT-equipped with a set of moveable CT-simulator lasers so that the modified simulator lasers so that the modified position of the patient can be confirmed. position of the patient can be confirmed.

The process is not accurate unless a CT The process is not accurate unless a CT of the patient at the time of treatment is of the patient at the time of treatment is used. Dose reconstruc- tion has been used. Dose reconstruc- tion has been tested using the UW tomotherapy tested using the UW tomotherapy benchtop unit but not yet implemented on benchtop unit but not yet implemented on the UW clinical unit. the UW clinical unit.

Deformable Registration And Deformable Registration And Autocontouring Autocontouring

Deformable registration algorithms Deformable registration algorithms typically use common features such as typically use common features such as contours or points that are identified contours or points that are identified automatically in both images (Blake and automatically in both images (Blake and Isard 1998). The intervening space Isard 1998). The intervening space between identifiable features is deformed between identifiable features is deformed according to finite element methods using according to finite element methods using established elastic property parameters (established elastic property parameters (

Re-optimization is the modification of Re-optimization is the modification of subsequent treatment fractions on the subsequent treatment fractions on the basis of the dose reconstruction and basis of the dose reconstruction and deformable registration of the regions of deformable registration of the regions of interest and the dose distribution (Wu interest and the dose distribution (Wu 2002)2002)

While it is not possible to remove the While it is not possible to remove the excess dose delivered to a sensitive excess dose delivered to a sensitive structure, it may be possible to take this structure, it may be possible to take this into account in re-optimization so that the into account in re-optimization so that the dose delivered in the whole course of dose delivered in the whole course of therapy might be the same or only therapy might be the same or only marginally higher. marginally higher.

Re-optimization might also be done if it is Re-optimization might also be done if it is decided that the target volume needs to decided that the target volume needs to change part way through the course of change part way through the course of ther- apy. Re-optimization is a research ther- apy. Re-optimization is a research topic and not yet being tested on the UW topic and not yet being tested on the UW clinical unitclinical unit

DisadvantageDisadvantage

Ring gantry are minimal since few patients Ring gantry are minimal since few patients are treated with non-coplanar radiation are treated with non-coplanar radiation fields fields and IMRT diminishes the need for and IMRT diminishes the need for these types of field arrangementsthese types of field arrangements..

Clinical AppliactionClinical Appliaction

Image-Guided Stereotactic Body Image-Guided Stereotactic Body Radiotherapy of Non-Small-Cell Lung Radiotherapy of Non-Small-Cell Lung Cancer.Cancer.

Treatment of Multiple Treatment of Multiple MetastasisMetastasis

Future Future

Needs to be able to calculate the dose Needs to be able to calculate the dose actually delivered during therapy.actually delivered during therapy.

The actually delivered dose can be The actually delivered dose can be calculated from collected exit dose calculated from collected exit dose measurements during treatment using back-measurements during treatment using back-projectionprojection

has to have the ability to reliably track four-has to have the ability to reliably track four-dimensional target motion envelopes since dimensional target motion envelopes since tomotherapy is a fully dynamic therapy tomotherapy is a fully dynamic therapy

reliably contour changes in the target and reliably contour changes in the target and to quantify organ deformation. Target to quantify organ deformation. Target variation and organ deformation can be variation and organ deformation can be handled using deformable image handled using deformable image registration and projecting the contours registration and projecting the contours from the old data set onto the new data set from the old data set onto the new data set using nonlinear transformationusing nonlinear transformation

MRIgRTMRIgRT

Tomotherapy With MRI Tomotherapy With MRI

Against

“There are no non-violent

revolutions…”Malcolm X

WITH!

Highly Arched Chest WallMore than conventional: 3 fieldsConventional: 2 tangential fields

50%50%70%70%90%90%120%120%

IMRTIMRT

Spare Time on the treatment Machine. Single Plan reduce planning work Load. Reduced work on Linac.

Reduces treatment time from 7 to 5 weeks

Herce

ptin

Anthracyclin

Taxanes

Radiotherapy

Cramp?

Better