Equipment Malfunctions

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Radiation, Electrical, Mechanical Malfunctions


There are three types of errors are classified in the machine. They are Electrical, Mechanical and Radiation malfunctions.  These errors leads to several people died because of under and over exposure.


Errors due to machine malfunctions:

Mechanical Errors:

1. The light field and radiation field congruence is a mandatory. It should be checked periodically.                                                   

2. Source to Surface Distance of Linac’s 100cm and for cobalt-60 80cm, we can check this distance by using the mechanical pointer as well as optical distance indicator (ODI). After a year installation it may show slight variation in reading, so that, it should be cross checked by mechanical pointer.

3. The integrity of the couch interlocks should be checked periodically. Couch movements during the treatment leads to unnecessary exposure to normal tissues or organs.

4. The gantry/collimator accuracy should be checked after each repair to avoid the errors

5. Wedge orientation with the machine should be clarified before changing in the machine.


Electrical Errors:

1. Energy of the radiation beam may change due to software errors in the machines. It leads to a wrong treatment for the patient or even people died in certain some hospitals. It should be checked periodically

2. The failure of the internal ion chambers cause to overexposure of the patient due to miscalculation of the monitor unit.

3. Failure in the software interlocks of the machine leads to variation of energy during each treatment. 

4. Sufficient knowledge of the treatment planning system is require, otherwise it will cause to wrong treatment.

5. Failure of the modes of the beams, instead of choosing the electron mode it has chosen the x-ray mode for treatment because of wrong interpretation of the software module.

6. If, two or three linac’s are present in hospital having one TPS means there is possibility of choosing different machine than planned or patient may get treatment from different machine.


Radiation Errors:

1. The above said two errors would cause the severe radiation potential effect.

2. By delivering the wrong energy than the specified one for the treatment by physicist it leads to over or underdosage of the patient.

3. Radiation treatment induced pacemaker and implantable cardioverter defibrillator malfunction


Till now a lot of radiation errors had been found and some worst accidents are

1. Untested change of procedure for data entry into TPS(Panama, 2000)

2. Incorrect repair of accelerators and communications leads to machine malfunction (Spain-1990)

3. Using the wrong decay curve for co-60 calculation (UK, 1974-76)


References:

1. The Physics of Radiation Therapy 4th edition Faiz. M. khan.

2. ICRP Publication 86 on Radiation accidents

3. Radiotherapy-induced pacemaker and implantable cardioverter defibrillator malfunction.

Tondato F, Ng DW, Srivathsan K, Altemose GT, Halyard MY, Scott LR.

4. www.hpa.org.uk

5. www.bir.org.uk

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