Errors in the planning stage can be serious if they are carried over to treatment delivery.
Random Errors in Planning
Random errors during planning are minimal and due to the limited resolution of CT imaging and contouring tools, as well as by the limit of information supplied from the linear accelerator (down to several decimal points at most).
Systematic Errors in Planning
Systematic errors are more of a concern, and could include:
- Patient identification errors - CTs do not have a photo of the patient and it may be possible to confuse patients, or in the case of a retreatment use the old CT scan to perform planning.
- It is important that patients are well identified on the computer system so that the chance of this occuring is minimised.
- Incorrect entry of beam parameters
- This can lead to errors in calculation of monitor units. It is important that QA of input data is carried out before the TPS becomes operational.
- Incorrect accounting of expansions (CTV/ITV/PTV), leading to underdosing of tumour. Alternatively, incorrect contouring of organs at risk, leading to overdosing of normal tissues
- This can be improved through staff education and training regarding anatomy and ICRU concepts.
Errors in Data Transfer (from TPS to R&V)
This is a special category of errors that is responsible for about 50% of detected errors worldwide.
- Arises from incorrect transfer of data from the TPS to the R&V system, due to:
- Conflict in instructions between TPS and R&V system
- Error in calculations on independent software
- Human error in entering data
These errors can be minimised by having data checked by independent software or performing in vivo dosimetry. In some cases the error may be picked up by an experienced staff member who notices that the monitor units are not appropriate for that treatment type, but with the rapid advancement in technology this is not always possible.
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