Determination of monitor unit check tolerances based on a comparison with measurement and treatment planning system data

Aims and background With the introduction of more complex three-dimensional conformal radiotherapy and intensity-modulated radiotherapy techniques in clinical practice, the use of record-and-verify systems is recommended to improve the accuracy of radiotherapy treatments. The aim of the present study was to evaluate, for a commercial record-and-verify system, the efficiency, integration with the treatment planning system, and impact of manual checking of data. The most frequent errors or misses were also evaluated. Materials and methods The development of internal protocols to systematically implement new technologies has been identified as a priority in the departmental quality assurance process. Data electronically fed into the record-and-verify system were compared with those manually recorded in the clinical paper chart over a period of almost 6 years (October 2000 to December 2006). A total of 7768 treated patients was reviewed. The check was performed by using a homemade data base in which the errors are stratified as follows: 1) general section, 2) geometric and dosimetric section, and 3) delivered dose section. Results On a total of 7768 checked patients, one or more mismatches between treatment planning system data and record-and-verify system data or paper chart data were observed for 452 patients (5.8% of total number of inspected patients). The percentage of discrepancies out of the total was: 2.2% in the general section, 3.3% in the dosimetric and geometric section, and 4.2% in the delivered-dose section. Conclusions Although record-and-verify systems assume a crucial role in the accuracy and reproducibility of radiation treatment, their inability to eradicate all the errors requires vigilance on the part of the radiation therapy and physics team.

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Comparison of an in-house developed monitor unit double-check program for 3D conformal radiation therapy and treatment planning system verification

Journal of Radiotherapy in Practice ◽

10.1017/s1460396918000742 ◽

2019 ◽

Vol 18 (03) ◽

pp. 251-261

Author(s):

Noureddine Slassi ◽

Hmad Ouabi ◽

Naïma El Khayati

Keyword(s):

Radiation Therapy ◽

Treatment Planning ◽

Accurate Determination ◽

Planning System ◽

Treatment Planning System ◽

Monitor Unit ◽

Conformal Radiation Therapy ◽

Water Phantom ◽

3D Conformal Radiation Therapy ◽

System Verification

AbstractAimThe treatment planning system (TPS) plays a key role in radiotherapy treatments; it is responsible for the accurate determination of the monitor unit (MU) needed to be delivered to treat a patient with cancer. The main goal of radiotherapy is to sterilise the tumour; however, any imprecise dose delivered could lead to deadly consequences. The TPS has a quality assurance tool, an independent program to double check the MU, evaluate patient plan correctness and search for any potential error.Materials and methodsIn this work, a comparison was carried out between a MU calculated by TPS and an independent in-house-developed monitor unit calculation program (MUCP). The program, written in Cplusplus (C++ Object-Oriented), requires a database of several measured quantities and uses a recently developed physically based method for field equivalence calculation. The ROOT CERN data analysis library has been used to establish fit functions, to extend MUCP use to a variety of photon beams. This study presents a new approach to checking MU correctness calculated by the TPS for a water-like tissue equivalent medium, using our MUCP, as the majority of previous studies on the MU independent checks were based on the Clarkson method. To evaluate each irradiated region, four calculation points corresponding to relative depths under the water phantom were tested for several symmetric, asymmetric, irregular symmetric and asymmetric field cases. A comparison of MU for each radiation fields from readings of the TPS and the MUCP was undertaken.ResultsA satisfactory agreement has been obtained and within the required standards (3%). Additional experimental measurements of dose deposited in a water phantom showed a deviation of <1·6%.FindingsThe MUCP is a useful tool for basic and complex MU verification for 3D conformal radiation therapy plans.

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