VERIFICATION PROTOCOL

Our next presentation was regarding the verification protocols.

TREATMENT PLANT

These past few weeks, our schedule has been packed with presentations. A few of it were for Radiotherapy Instrumentation course. Given below are slides from our presentation that states the accuracy of the beam direction using treatment planning in CT-Simulator.

STANDING WAVE

Our lecturer had gave us a task about the travelling waveguide. She distribute the works into 3 groups, and our group had been assigned with the standing waveguide topic. Basically, what we decided to insert in this blog is the summary of the standing waveguide. Here we got some explanations regarding the characteristics of the particular waveguide for you to have a look.

HOW THE ELECTRON TRAVEL TROUGH THE STANDING TRAVELLING WAVEGUIDE???

CYCLOTRON

Recently, we are given task about particle beam therapy in cyclotron.

HISTORY OF CYCLOTRON

In 1932, Ernest O. Lawrence invented cyclotron which is a type of particle accelerator in which charged particle accelerate outwards from the centre along a spiral path.The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field. 

Cyclotrons were the most powerful particle accelerator technology until the 1950s when they were superseded by the synchrotron, and are still used to produce particle beams in physics and nuclear medicine. 

l The largest single-magnet cyclotron was the 4.67 m (184 in) synchrocyclotron ( 1940 & 1946 ) by which could accelerate protons to 730 MeV. 

l The largest cyclotron is the 17.1 m (56 ft) multimagnet TRIUMF accelerator at the University of British Columbia in Vancouver, British Columbia which can produce 500 MeV protons.

THE PRINCIPLE OF OPERATION FOR CYCLOTRON

A cyclotron accelerates a charged particle beam using a high frequency.

Alternating voltage which is applied between two hollow "D"-shaped sheet metal electrodes called "dees" inside a vacuum chamber.

The dees are placed face to face with a narrow gap between them, creating a cylindrical space within them for the particles to move. 

The particles are injected into the center of this space. The dees are located between the poles of a large electromagnet

The magnetic field from dees causes the particles path to bend in a circle due to the Lorentz force perpendicular to their direction of motion.

Magnetic field would travel in a circular path within the dees under the influence of the magnetic field if speed is constant. 

CYBER KNIFE

What is Cyber Knife?

•  A robotic radiosurgery
• A non-invasive method for treatment  of both cancerous and non-cancerous tumor in the body
• The treatment which deliver beam of high radiation dose to tumor with extreme accuracy

Equipment of Cyber Knife

Procedure

• Patient lie on treatment table, robotic arm moves around body delivering high radiation directly to tumor.
• Tumor cells are killed while exposure to surrounding tissue is minimized

Special Feature

• Moves with unlimited mobility- to deliver radiation with accuracy to exact location without touching them
• Has advanced imaging and tracking system- update on tumor location through treatment, compensating patient movement and ensuring radiobeams are locked on tumor 

Advantages

• Non-surgical  treatment option - non-invasive, fewer complications
• Greater flexibility - superior reach and maneuverability
• Unparalled precision - conc. radiation beam
• Superior accuracy - tracks patient movements
• Frameless system - no metal frames and skull pin
• Higher radiation dose - targeted treatment precision

ICRU 50

HISTORY

The ICRU (originally known as the International X-Ray Unit Committee and later as the International Committee for Radiological Units) was conceived at the First International Congress of Radiology (ICR) in London in 1925 and officially came into being at ICR-2 in Stockholm in 1928. The primary objective was to propose a unit for measurement of radiation as applied in medicine. From 1950 the ICRU expanded its role significantly to embrace a wider field. Initially meetings were held every 3 years at ICR congresses (excluding the 13-year period encompassing World War II) with one physicist and one radiologist from each participating country having the right of attendance with the Chairman being nominated by the ICR host country. A permanent Commission was elected in 1953. L S Taylor (USA) served ICRU as a member [1928 – 1934] and then Secretary [1934 – 1953], first permanent Chairman [1953 – 1969] and then Honorary Chairman [1969 until his death in 2004]. Subsequent ICRU Chairmen have been: H O Wyckoff 

(USA) [1969 – 1987]; A Allisy (France) [1987 – 1994]; A Wambersie (Belgium) [1994 – 2006]; and P M DeLuca, Jr (USA) [2006 – 2009]. H-G Menzel (Switzerland) is the current Chairman

ICRU 50 REPORT

· ICRU 50 (1993) - "Prescribing, Recording, and Reporting Photon Beam Therapy"

o   Supercedes and updates Report 29

o   Aim of Therapy: Should be defined as radical, palliative, or non-malignant

     o   Volumes are defined:

§ Gross Tumour Volume (GTV):
Gross palpable or visible/demonstrable extent and location of malignant growth

§ Clinical Target Volume (CTV):
Anatomical concept. Tissue volume that contains a GTV and/or subclinical microscopic malignant disease, which has to be eliminated. This volume has to be treated adequately in order to achieve the aim of therapy: cure or palliation. The CTV is an anatomical-clinical concept, that has to be defined before a choice of treatment modality and technique is made

§ Planning Target Volume (PTV):Geometrical concept. Defined to select appropriate beam sizes and beam arrangements, taking into consideration the net effect of all the possible geometrical variations and inaccuracies in order to ensure that the prescribed dose is actually absorbed in the CTV. Its size and shape depend on the CTV but also on the treatment technique used, to compensate for the effects of organ and patient movement, and inaccuracies in beam and patient setup

§ Treated Volume:
Volume enclosed by an isodose surface (e.g. 95% isodose), selected and specified by radiation oncologist as being appropriate to achieve the purpose of treatment. Ideally, Treated Volume would be identical to PTV, but may also be considerably larger than PTV

§ Irradiated Volume:
Tissue volume which receives a dose that is considered significant in relation to normal tissue tolerance. Dose should be expressed either in absolute values or relative to the specified dose to the PTV

§ Organs at Risk:
Normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose

o   Recommendations for Reporting Dose

§  ICRU Reference Point:

· Dose at the point should be clinically relevant and representative of the dose throughout PTV

· The point should be easy to define in a clear and unambigous way

· The point should be selected where the dose can be accurately determined (physical accuracy)

· The point should be selected in a region where there is no steep dose gradient

·  ICRU Reference point should be located at the center of the PTV and when possible at the intersection of the beam axes

· The dose at the ICRU Reference Point is the ICRU Reference Dose

§ Dose at/near center of PTV, maximum dose to PTV, and minimum dose to PTV should always be reported

§ Maximum Dose:
Highest dose in PTV. A volume is considered clinically meaningful if its minimum diameter exceeds 15 mm; however, if it occurs in a small organ (e.g. the eye, optic nerve, larynx), a dimension smaller than 15 mm has to be considered

§ Minimum Dose:
Lowest dose in PTV. In contrast to Maximum Dose, no volume limit is recommended.

§ Hot Spots:
Volume outside the PTV which receives dose larger than 100% of the specified PTV dose. In general considered significant only if minimum diameter exceeds 15 mm; however, if it occurs in a small organ (e.g. the eye, optic nerve, larynx), a dimension smaller than 15 mm has to be considered

§  Levels of Dose Evaluation for Reporting:

· Basic:
Only dose at ICRU Reference Point and its variation along a central beam axis is available

· Advanced:
Dose distribution can be computed for plane(s)

· Developmental:
Dose distribution can be computed for volume(s)

VIRTUAL SIMULATION

What is virtual simulation

Simulators are medical devices used in the oncology clinics to perform the simulation for external beam radiotherapy treatment. Unlikely for a clinic to obtain a real simulator is a high investmet in terms of money, space and personnel. The alternative here can be Virtual Simulator (VS).

Virtual simulation is a work station, equipped with 

- CT scanner

- Software to perform volume definition/treatment planning dose calculation

- Software to produce DRR (Digital Reconstructed Radiograph)

The target is defined first and then the fields are shaped to conform to the target during 3DCRT treatment planning.

How Virtual Simulation Works

1. Collect patient’s CT data including attached aluminium markers. 

2. Transfer CT data to VS. The physician defines the tumour volume and the organs at risk and she/he will place the necessary fields relative to the tumour volume. 

3. The simulation plan and the CT data are transferred via DICOM (Digital image and Communication in Medicine) server to the TPS for dose calculation and final treatment plan optimization. 

4. Verify patient position on LINAC before irradiation. 

5. Perform treatment on the treatment machine (Linear Accelerator or LINAC).

Advantages of virtual simulation



• has contour facilities such as an outlining system
• has system for interference correction
• has geometric reconstruction in all planes and in 3D
• ability to establish protocols with preset values for different techniques and portals
• has a dynamic representation of the structures and beams in planes and 3D
• has image magnification
• has automatic establishment of margins in 3D
• an automatic determination of the treatment isocentre
• has manipulation in real time
• has graphic print facility for documentation

LIMITATION OF VIRTUAL SIMULATION

• Significantly increased expenditure

The CT-based virtual simulator required high cost due to its specialities. It numbered a great price as the machine is furnished with the treatment capability. The treatment is based on the use of the digital patient data, mainly CT slices, instead of the real patient.

Equipment needed for planning and verification also being recorded as its limitations as the simulation process will become more complicate thus it’s contribute to further demanding. Software and computer hardware also resulting in high costs, as the virtual simulation or 3D simulation works need a special software to develop the simulation efficiently.

• Extensive physics
  The simulation steps basically it was done to precisely identify the area on patient’s body where they will receive radiation. It is a planning session done before the first external beam radiation treatment is given. This charge included the role of radiation oncology team and also a specialised software which required manpower and time.

• Conformal nature
  3D conformal radiation is a radiation therapy technique that sculpts radiation beam to the shape of tumour. This is ideal for tumours that have irregular shapes or that lay close to healthy tissues and organs. Even though it is efficient in simulation but the thing is it was highly susceptible to motion whether voluntary or involuntary. It also aroused by the setup related errors.

Conventional Vs Virtual Simulation

Virtual Simulation have been developed which integrate a CT scanner with features designed for radiation theraphy with an advanced 3D radiation therapy planning computer.The virtual simulation software provides many advanced image manipulation and viewing advantages.These systems allow for all the features of the physical simulators plus additional imaging features which are impossible on a physical simulator.Radiation field placement,and isocenter definition take place this step (without the patient having to be present for this potentially lengthy procedure).The choice of beam directions and beam aperture design (radiation field shape) can be individually optimized by using a Beam’s-Eye-View display.The patient anatomy is displaced so that the viewer’s eye “sees” what the beam sees to maximize target coverage through a beam direction and aperture that minimizes critical structure radiation.

Work concept Conventional :

1. Localized area to be irradiated on the simulator.

2. Collect patient's CT data including attached aluminium markers

3.Transfer CT data to treatment planning system (TPS), where the physician performs the tumour volume definition. In this step the physicist will define the organs at risk, will place the necessary fields to perform the specific treatment technique and she/he will calculate the dose distribution around the tumour area of organs at risk

4. The treatment plan parameters will be verified on the real Simulator

5.Verify patient position on (Linear Accelerator) LINAC before irradiation.

Work concept Virtual :

1. Collect patient's CT data including attached aluminium markers

2. Transfer CT data to VS. The physician defines the tumour volume and the organs at risks and she/he will place the necessary fields relative to the tumour volume

3. The simulation plan and the CT data are transferred via DICOM (Digital Image and Communication in Medicine) server to the TPS for doe calculation and final treatment plan optimization

4. Verify patient position on LINAC before irradiation

5. Perform treatment on the treatment machine (Linear Accelerator or LINAC)