Quality Assurance in Immobilization & Patient Positioning for Radiation Therapy

Quality Assurance in Immobilization AND Patient Positioning for Radiation TherapyRAJIV GANDHI CANCER INSTITUTE & RESEARCH CENTRE- DELHI Akhil Chaudhary , Vishvendra Gaur , R.S.Bedi , S. Mitra , S.N.Sinha ,G.S.Wadhawan ,

The clinical aim of radiotherapyTo maximize the therapeutic index by:Delivering lethal doses of radiation to cancerous cells (so increasing chances of survival) ,whileSparing normal tissue (so reducing side-effects and increasing quality of life)This is achieved by precisely shaping and directing the radiation beams based on information from medical images.

What is patient positioning?a reproducible localization of the patient with the use of a device onto which a patient lays a specific part of their anatomy

designed to guide the patient into the original simulation position for radiation beam administration.

What is patient immobilization?A reproducible localization of the patient with a device into which the patient is locked, to aid in the restriction of anatomical movementWhy use positioning and immobilization devices?Increase target accuracyEasy to useQuick to setupComfortable for patientDurable enough to withstand an entire course of treatment

History of patient positioningsand bags

Tape

bite block

plaster casts

home-made devices

Current methods for positioning and immobilization

Thermoplastic mask of the headTreatment chairPositioning aids Head restBelly boardsPelvic boardsExtremities

AIO Indexed Immobilization

Exact reproducibility of the patients position in imaging and therapy.High level of patient comfort.Precise immobilization of all body regions.Reduction of patient set-up time.Reduction of risk of random and systematic errors.

Considerations for selecting a deviceCostValue for money.ConvenienceIf its not convenient it will just gather dust on the shelf.AccuracyThe identical position must be reproduced day to day.

Considerations for selecting a deviceSpeedMinimal time should be required to get the device ready for patient use.Compatibilitydevices should be constructed of radio-translucent materials to avoid image artifact or anatomical obstructionsAttenuationBeam integrity must be maintained.

Considerations for selecting a deviceDurabilityDevices must be able to withstand repeated use.Positioning aids:Silvermanshoulder retractorsbite bockfoam wedgeincline boardprone pillow

Benefits of positioning aidswork with positioning devices to increase stability, comfort and reproducibility.

LIMITATIONS OF POSITIONING AIDS:During immobilization, patients still have freedom of movement.

Ten systemsskeletal systemcirculatory systemdigestive systemrespiratory systemurinary systemreproductive systemnervous systemmuscular systemendocrine systemintegumentary system

Verbal statements to immobilize patients:Please do not move.Dont wiggle, now.Lay heavy, become as one with the table.Be placid, man.

Patient positioning, fixation and reproducibility of setup

Whether you are doing conventional radiotherapy, 3D conformal or IMRT treatments accurate, reproducible positioning and rigid fixation are important factors for precise dose delivery to the treatment portals.Thermoplastic shells offers a reliable method for accurate positioning and immobilization.There are three essential components required for making these shells:(i) Base plate: made up of acrylic material or carbon fibre. Available for head and neck cases, chest, pelvic regions. (ii) Neck supports: foam type poly urethane material or silver man standard supports. (iii) Thermoplastic masks.

Abdomen / Pelvis positioning and fixation

Position the patient (prone or supine) onto the board. Do an initial visual check to make sure the patient is centered as accurately as possible on the board, adjust patient if needed. Once positioning is ok marked the patient to the lateral and midline. These marks will now serve as daily repositioning marks in the treatment room. Avoid compressing the skin as much as possible.To avoid shrinkage cool the casts completely, make sure the heat is out of cast before removing from the patient.Use laser to align the patient, ensuring identical repositioning from simulation.

Benefits of thermoplastic masksEconomical

Disposable

can re-use PVC frame (with re-loadable systems)

markers can be placed on the mask rather than the patient.

reproducible positioning is achieved.

Challenges of the hip and pelvis region

cylindrical shape of this anatomical regionrotation of the body axiscast fabrication is technique sensitive choosing supine or prone positioningLIMITATIONS OF THERMOPLASTIC IMMOBILIZATIONthermoplastic sheets are expensivetechnique sensitive application requires hands-on training by vendormust have a large water bath.

ErrorsLocalization Error:results from the failure to appreciate the full extent of the disease or to design adequate treatment fieldsImmobilization Error:occurs as a result of displacement of the treatment fields relative to the intended treatment volume.

Integrated positioning and immobilizationcombining several positioning or immobilization devices to adequately position a patient.

VAC-LOK

A complete vacuum is drawn through the quick-release valve, cushion becomes a rigid and comfortable mold, offering accurate reproducibility throughout the course of simulation and treatment. Made up of Nylon-urethane material, can be cleaned and reused.

VAC-LOKBenefits of VAC-LOK

Limitations of VAC-LOK

cost-effectivere-usablequick to set upfull range of sizeslongevity is dependent on care and use.vacuum or wall suction is requiredstorage space is requiredmay puncture or develop leakscan not cut-away into the cushion.

LasersLaser lines reference the radiation beam parameters to the patients anatomy. Repositioning the patient from simulation room to the treatment.For the daily setup in the treatment room.

Indexed immobilizationThe ability to provide a method of indexing, and locking down, a positioning device to multiple points along the top of a treatment, simulator or CT tabletop.

Features of indexed immobilizationclose tolerance repositioningimproved target accuracyincreased patient through-putquick and accurate patient set-upreliable repeatabilitymaximized clinical efficiency

Benefits of indexed immobilizationsame spatial reference between simulation and treatmentsame spatial reference between treatmentsstandardization of the spatial relationship for all couches and treatment tables in the department, including CT couchesimproved target accuracyreduced patient set-up time resulting in increased patient through-put.

Quality Assurance Achievement

comfortable to minimize movementreproducible for the treatment planPortal Identification.CONSISTENCY:Consistency in patient positioning and immobilization from treatment planning to simulation, and from simulation to treatment must be maintained.

ACUITY( simulation)

RESULTs prescription of target dose

physical dosimetry of the beam

planning of individual treatment

precision of daily dose delivery

PATIENT FLOW CHART IN RTImmobilization setup CT Simulation/Imaging Target Organ Delineation Specify Objective Function Optimization Leaf Sequence Generation Dose Distribution Calculation Plan Evaluation Plan Implementation MLC Controller EPID portal Treatment.

Whats in the future for positioning and immobilization?CT scanner:more immobilization devices and increased target accuracy.more upgrades3D treatment planning systems will increase the need for accurate patient positioning and immobilization.more centers utilizing:Conformal and/or fractionated radiotherapy.Stereotactic Radiosurgery(SRS).Intensity Modulated Radiation Therapy.

RADIATION ONCOLOGY Conformal beam shaping

Limitations of positioning methods

cONCLUSIONCurrently most IMRT/3D-CRT/stereotactic radiotherapy, approaches have increased the time and efforts required by radiation oncologists ,medical physicist , dosimetrist and radiation therapy technologist In precise delivery of radiation dose . Actually in radiation therapy execution in hands of radiotherapy technologists resulting Safety of normal organsProper coverage of target volumePrecise delivery of doseDecreased toxicity in grade and sizeImproved overall survival and quality of life

CONT.Immobilization improves : the reproducibility of patient positioning during conventional/Conformal/IMRT Radiation therapy.Purpose : to determine the magnitude of patient positioning errors and to assess the impact of immobilization on these errors.The record of 22 patients , in our department whose immobilization was prepared in open environment (Mould room) were compared with rigid immobilization prepared in closed environment (simulator room) and it was observed there is 2 to 5 mm shift in open Vs closed environment setup.

CONT. Portal films of patients: treated at both facilities were subsequently review and deviation each portal from the simulation film was determined.Simulation-to-Treatment variability & Treatment-to-Treatment variability: was 2-5mm along the patient treated with open vs closed immobilization.

CONT.The use of immobilization devices significantly reduces errors in patient positioning , potentially permitting the use of smaller treatment volumes.Immobilization should be a component of conformal radiation therapy programs for cervix carcinoma to achieve the integrity of treatment plan.

MethodAccuracy Limit

laser alignmentusing skin marks2.0 2.5mm

radiographic alignment using anatomy1.0 2.0mm

radiographic alignment using point markers