immobilization in radiotherapy

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IMMOBILIZATION IMMOBILIZATION IN IN RADIOTHERAPY RADIOTHERAPY Leo Prabhu Leo Prabhu RTT RTT

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Immobilization in RT

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IMMOBILIZATION IMMOBILIZATION IN IN

RADIOTHERAPYRADIOTHERAPY

Leo Leo PrabhuPrabhu

RTTRTT

Role of immobilizationRole of immobilization

• Patient positioning and immobilization are Patient positioning and immobilization are said to be the most crucial parts of radiation said to be the most crucial parts of radiation therapy treatment.therapy treatment.

• For accurate delivery of a prescribed radiation For accurate delivery of a prescribed radiation dose to a target volume,while sparing dose to a target volume,while sparing sourrounding normal and critical tissues.sourrounding normal and critical tissues.

• Without proper immobilization,the patient is Without proper immobilization,the patient is at risk for improper treatment and unwanted at risk for improper treatment and unwanted side effectsside effects

• Immobilization such as Immobilization such as molds,casts,headrests,and other devices are molds,casts,headrests,and other devices are constructed to reduce setup error and patient constructed to reduce setup error and patient movement during treatment.movement during treatment.

ContdContd....

• Although the primary goal of immobilization Although the primary goal of immobilization system is to limit patient motion and reduce system is to limit patient motion and reduce the probability of major positioning errors, the probability of major positioning errors, there are other benefits as well..there are other benefits as well..

• A well constructed immobilizing system can A well constructed immobilizing system can reduce the time for daily patient set up.reduce the time for daily patient set up.

• It can make the patient feel more secure It can make the patient feel more secure and less apprehensive.and less apprehensive.

• It can reduce the reliance on patient co-It can reduce the reliance on patient co-operation and alertness, and it can help to operation and alertness, and it can help to stabilize the relationship between external stabilize the relationship between external skin marks and internal structures.skin marks and internal structures.

Desirable characteristics of Desirable characteristics of immobilization devicesimmobilization devices

• Ease of use.Ease of use.

• Ease of making the device.Ease of making the device.

• Comfort for the patient.Comfort for the patient.

• Minimal space requirement for storage.Minimal space requirement for storage.

• Resistance to bending and streching.Resistance to bending and streching.

• Minimal perturbation of the beam so as not Minimal perturbation of the beam so as not to produce artefacts in image acquisition.to produce artefacts in image acquisition.

HEAD,NECK AND BRAIN HEAD,NECK AND BRAIN IMMOBILIZATIONIMMOBILIZATION

• Initial construction and selection of proper Initial construction and selection of proper immobilization for head and neck cancer is one immobilization for head and neck cancer is one of the most important parts of ensuring proper of the most important parts of ensuring proper treatment of the patient.treatment of the patient.

• In the past,patients for head&neck cancers In the past,patients for head&neck cancers were taped to the table across their forehead.a were taped to the table across their forehead.a bite block was occasionally used in order to tilt bite block was occasionally used in order to tilt the neck in a reproducible manner.the neck in a reproducible manner.

• Current methods for head&neck and brain Current methods for head&neck and brain tumours include a variety of masks,molds and tumours include a variety of masks,molds and frame systems.In some instances,shoulder frame systems.In some instances,shoulder straps are used to pull the shoulders out of the straps are used to pull the shoulders out of the treatment field for the neck. treatment field for the neck.

Contd..Contd..

• The most common The most common immobilization device immobilization device used to treat used to treat head&neck cancers is head&neck cancers is an aquaplast.an aquaplast.

• This device is made This device is made from a rigid plastic that from a rigid plastic that becomes pliable when becomes pliable when placed in warm water.placed in warm water.

• When it is wet ,it is When it is wet ,it is placed over the patients placed over the patients body and conforms to body and conforms to the contour of the the contour of the treatment area.treatment area.

contd…contd…• Advantages: Aquaplast provide great Advantages: Aquaplast provide great

reproducibility in daily reproducibility in daily

treatments,lightweight and easy to usetreatments,lightweight and easy to use..• Additionally modifications can be made to Additionally modifications can be made to

the mask if the patient experiences swelling the mask if the patient experiences swelling or weight loss during the treatment. or weight loss during the treatment.

• Disadvantages: windows cut cannot be Disadvantages: windows cut cannot be reused.reused.

when old becomes brittle and too soft when when old becomes brittle and too soft when activated. activated.

ContdContd……

• Base plate: the plate Base plate: the plate onto which the head onto which the head immobilization immobilization systems are secured systems are secured is usually referred to is usually referred to as a base plate.as a base plate.

• Its material should be Its material should be strong ,yet it should strong ,yet it should minimally attenuate minimally attenuate the radiation beam.the radiation beam.

• Most base plates are Most base plates are acrylic and recently acrylic and recently carbon fiber base carbon fiber base plates are hugely plates are hugely devolpeddevolped

Contd..Contd..• Indexing bar: the two pin Indexing bar: the two pin

indexing bar is designed indexing bar is designed for reproducible for reproducible positioning and stable positioning and stable fixation of base plates on fixation of base plates on the treatment couch.the treatment couch.

• The indexing bar can be The indexing bar can be placed at the desired placed at the desired indexing indents of the indexing indents of the couch and it can be locked couch and it can be locked down by rotating the down by rotating the levers.levers.

• The base plates then can The base plates then can be positioned over the be positioned over the pins of the two pin pins of the two pin indexing bar.indexing bar.

Contd..Contd..• Shoulder retraction: in patients with short Shoulder retraction: in patients with short

neck or in patients where opp lateral fields neck or in patients where opp lateral fields are used to treat the neck, the shoulders are used to treat the neck, the shoulders need to be retracted caudally to avoid need to be retracted caudally to avoid entrance and exit doses.entrance and exit doses.

• An elastic strap ,equipped with handles and An elastic strap ,equipped with handles and attached to each side of the treatment attached to each side of the treatment couch,can be used for the patient to pull on.couch,can be used for the patient to pull on.

IMMOBILIZATION IN BRAIN IMMOBILIZATION IN BRAIN TUMORSTUMORS

• Immobilization becomes more complex for Immobilization becomes more complex for radiosurgery or gamma knife radiosurgery or gamma knife procedures,because the requirements for procedures,because the requirements for positional and numerical accuracy in dose positional and numerical accuracy in dose delivery are ±1mm and 5% respectively.delivery are ±1mm and 5% respectively.

• Hence highly precised and accurate Hence highly precised and accurate reproducibility is needed.reproducibility is needed.

• Two types of fixation systems are used in Two types of fixation systems are used in radiosurgeryradiosurgery

1)GTC frame for fractionated therapy 1)GTC frame for fractionated therapy 2)BRW system for single fraction 2)BRW system for single fraction

radiosurgery.radiosurgery.

Contd..Contd..• 1)GTC relocatable head 1)GTC relocatable head

ring is a non invasive ring is a non invasive device that can be device that can be repeatedly fixed to the repeatedly fixed to the patient’s head in patient’s head in precisely the same precisely the same position.position.

• It has an impression It has an impression taken of the patients taken of the patients upper dentition and the upper dentition and the mold is then mounted to mold is then mounted to the head ring.the head ring.

• An impression is also An impression is also taken of the occiput to taken of the occiput to conform to the shape of conform to the shape of the patient’s head.the patient’s head.

ContContd..d..• A biasing strap holds A biasing strap holds

these two components these two components firmly in place,so that firmly in place,so that precise repositioning can precise repositioning can be achieved in each be achieved in each treatment sessiontreatment session

• The depth helmet The depth helmet provides quality provides quality assurance.it allows to assurance.it allows to conform the positional conform the positional accuracy.accuracy.

• A depth probe with mm A depth probe with mm scale can be passed in to scale can be passed in to the guide tubes on the the guide tubes on the helmet,so that the helmet,so that the distance from the hole to distance from the hole to the patient’s head can be the patient’s head can be measured to mm measured to mm accuracy.accuracy.

ContContd..d..

• 2)In single fraction radiosurgery,invasive 2)In single fraction radiosurgery,invasive procedure is followed,the patient is fitted procedure is followed,the patient is fitted with a BRW system and then bolted to the with a BRW system and then bolted to the treatment table.Bolts are fitted and screwed treatment table.Bolts are fitted and screwed into the patients skull to minimize any into the patients skull to minimize any movement during treatment.movement during treatment.

THORAX AND BREAST THORAX AND BREAST IMMOBILIZATIONIMMOBILIZATION

• There are two common There are two common immobilization systems immobilization systems used when treating used when treating tumors in chest cavity.tumors in chest cavity.

• 1)VACLOK:these are 1)VACLOK:these are custom,beanbag type custom,beanbag type pillows that are placed pillows that are placed around the patients around the patients upper body.upper body.

• The air is then The air is then vaccumed out of the bag vaccumed out of the bag for a custom fit and for a custom fit and sealed in order to retain sealed in order to retain its shape.its shape.

• vacloks are vacloks are radiotranslucent.,almost radiotranslucent.,almost air equivalent. they are air equivalent. they are washable and reusable.washable and reusable.

ContdContd....

• 2)BREAST BOARD: is 2)BREAST BOARD: is used specifically for the used specifically for the treatment of breast treatment of breast cancer.cancer.

• It has several adjustable It has several adjustable features to allow for the features to allow for the manipulation of patients manipulation of patients arms,wrists,head and arms,wrists,head and shoulders.shoulders.

• Breast boards are Breast boards are generally constructed of generally constructed of carbon fiber,allowing carbon fiber,allowing the device to be the device to be lightweight and durable.lightweight and durable.

ContdContd....

• Carbon fiber boards have lower attenuation Carbon fiber boards have lower attenuation levels,which permit maximum beam levels,which permit maximum beam penetration.penetration.

• The breast can also be immobilized using a The breast can also be immobilized using a thermoplastic breast support system,the thermoplastic breast support system,the aquaplast mold is taken of the breast to aid aquaplast mold is taken of the breast to aid in placement when lying supine on a breast in placement when lying supine on a breast board.board.

• Vacloks can also be used to improve patient Vacloks can also be used to improve patient set-ups for the breast field.this type of set-ups for the breast field.this type of treatment can involve the simultaneous use treatment can involve the simultaneous use of the vaclok system with breast board.of the vaclok system with breast board.

PELVIC IMMOBILIZATIONPELVIC IMMOBILIZATION

• There are two different crucial aspects in There are two different crucial aspects in the immobilization of pelvic region.the immobilization of pelvic region.

1)to properly maintain patients outer 1)to properly maintain patients outer contour during treatment..with respect to contour during treatment..with respect to isocentre.isocentre.

2)other is related to variation of internal 2)other is related to variation of internal structures during daily treatments.structures during daily treatments.

• Immobilization systems such as Immobilization systems such as vacloks,belly boards,and the hip-fix(using vacloks,belly boards,and the hip-fix(using aquaplast) system are commonly used aquaplast) system are commonly used during treatments of pelvic regionduring treatments of pelvic region

Contd..Contd..• Most of the pelvic Most of the pelvic

malignancies are treated malignancies are treated with partial body casts.with partial body casts.

• A mask from the A mask from the patient’s mid thorax to patient’s mid thorax to upper thighs is made by upper thighs is made by streching warm, pliable streching warm, pliable thermoplast over the thermoplast over the patient and then patient and then securing that mask to securing that mask to the pelvic board by a the pelvic board by a locking system.locking system.

• Windows on either sides Windows on either sides can be cut on the mask, can be cut on the mask, so that skin tattoos are so that skin tattoos are visible and can be used visible and can be used for alignment.for alignment.

Contd..Contd..

• A vaclok can also be A vaclok can also be used for used for immobilization in immobilization in pelvic treatments.pelvic treatments.

• It should extend from It should extend from the lower thoracic the lower thoracic area to the mid thigh.area to the mid thigh.

• Vacloks are popular Vacloks are popular choice for hip and choice for hip and pelvic positioning due pelvic positioning due to patient comfort to patient comfort and set up and set up reproducibility. reproducibility.

Contd.Contd...

• Advantages: easy to use, Advantages: easy to use,

very little time to prepare,very little time to prepare,

comfortable for the patient, comfortable for the patient,

and can be reused.and can be reused.• Disadvantages: contour and shape may Disadvantages: contour and shape may

change with change with handling and handling and use. use.

expensive.expensive.

Contd..Contd..• Belly boards are used Belly boards are used

when the patient is when the patient is treated prone.treated prone.

• Belly boards allow the Belly boards allow the small bowel to drop small bowel to drop below the lateral field to below the lateral field to avoid severe side effects avoid severe side effects of irradiation.of irradiation.

• Use of the belly board Use of the belly board significantly decreases significantly decreases the average volume of the average volume of small bowel that would small bowel that would otherwise be within the otherwise be within the lateral field during lateral field during standard box technique standard box technique treatment. treatment.

IMPROVED IMMOBILIZATION TECHNIQUES

SMALLER TREATMENTVOLUMEHIGHER CONTROLLED DOSESHIGHLY PRECISED TREATMENT

HIGHER CURE RATE