On-line measurement of field placement errors in external beam radiotherapy

W. C. Lam, M. Partowmah, D. J. Lee, M. D. Wharam

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


An on-line electronic portal imaging system was used in a quantitative measurement of field placement errors in external beam radiotherapy. Data from 30 patients, giving a total of 150 portals with 66% in the thoracic region and 34% in the abdominal region, were analysed. Displacements from the prescription delineated by physicians were measured. The displacements included errors due to block malposition, field malposition, field malrotation and patient malposition, and these were classified in two categories of displacements, those associated with the portal boundary and those with anatomic structures. Except for one rotational error, only translational errors were found. Displacements greater than 1 cm amounted to 17% with respect to the portal boundary and between 10% and 46% with respect to anatomic landmarks within the portal. From the results of the study, a margin of 1 cm around the tumour is barely sufficient if a 5% accuracy in dose delivery is desired.

Original languageEnglish (US)
Pages (from-to)361-367
Number of pages7
JournalBritish Journal of Radiology
Issue number712
StatePublished - 1987
Externally publishedYes

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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