[Retrospective analysis of the reproducibility of the daily set-up of the irradiation fields of cancer of the rectum using a megavoltage imaging system].
OBJECTIVE
To evaluate a ionization chamber on-line portal imaging system in routine clinical radiotherapy of rectum cancers.


METHODS
Megavolt portal images were obtained using a fast electronic megavoltage radiotherapy imaging system in 13 cases of pelvic fields. A total of 208 portal images and 13 simulator films were used to determine the values of set-up deviations in the X-Z-directions of a fixed co-ordinate system, and of the rotation fields (R).


RESULTS
Mean standard deviations of the difference between simulation and treatment images were 3.2 mm and 0.9 mm for X and Z, 3.6 mm for the rotation fault. The standard deviations were, respectively, 7.1 mm, 7.1 mm and 1.5 mm. The cumulative frequency distributions revealed that 80% and 95% of the absolute differences were less than 10 mm and 17.5 mm, respectively.


CONCLUSIONS
These results indicate the difficulty of a reproducible daily set-up. A weekly control could be proposed in order to increase the quality of pelvic site treatment. The introduction of masks to improve the set-up is also discussed.
Klinik für Strahlentherapie und Radioonkologie, Universität Göttingen, Allemagne.
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Pradier
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Laurent
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Bouscayrol
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Gaci
A
A
Daban
C F
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Hess
D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012004:Rectal Neoplasms / Q000532:radiotherapy*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013997:Time Factors
Analyse rétrospective de la reproductibilité de la mise en place quotidienne des champs d'irradiation de cancer du rectum par imagerie de contrôle de haute énergie.