Is weekly port filming adequate for verifying patient position in modern radiation therapy?

Richard K Valicenti, Jeff M. Michalski, Walter R. Bosch, Russell Gerber, Mary V. Graham, Abel Cheng, James A. Purdy, Carlos A. Perez

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

Purpose: The objective of this study is to use daily electronic portal imaging to evaluate weekly port filming in detecting patient set-up position. Methods and Materials: A computer-based portal alignment method was used to quantify the field displacements on 191 digitized weekly port films and 848 daily electronic portal images in 21 radiation therapy patients. An electronic portal image data set as a control for actual daily treatment position was used to evaluate weekly port films with respect to same-day field displacement, rate of field placement error detection, and prediction of subsequent daily field displacements. Results: The field displacements measured on a port film frequently deviated from the corresponding field displacements on the electronic portal image obtained in the same treatment set-up. A linear regression analysis showed that the curves fitted to the same-day field displacements had slopes that differed significantly from unity (p < 0.001). Overall, the respective frequencies of field placement error, beyond clinical tolerance limits of 5, 7, and 10 mm (corresponding to head and neck, thoracic, and pelvic sites) for port filming and electronic portal imaging were 11% and 14% (p = 0.4) in the X-direction (lateral or anteroposterior) and 24% and 13% (p = .0001) in the Y-direction (caphalad-caudad). When the data were broken down by anatomical region, this discrepancy was found to be mainly due to the differences in the thorax, and head and neck image data sets. For thoracic fields, error in Y-shifts was 28% by port filming, but only 9% by portal imaging (p = 0.01). In the head and neck region, 18% of the port films exceeded tolerance, whereas only 6% of the electronic portal images did (p = 0.0001). Field displacements on the treatment set-ups between the acquisition of port films were not predicted by those films. Conclusion: There are discrepancies between the field displacements and field placement errors detected by weekly port films and daily electronic portal images. This study suggests that improved methods of treatment verification may be necessary in modern radiation therapy.

Original languageEnglish (US)
Pages (from-to)431-438
Number of pages8
JournalInternational Journal of Radiation Oncology, Biology, Physics
Volume30
Issue number2
DOIs
StatePublished - Sep 30 1994
Externally publishedYes

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radiation therapy
Radiotherapy
Neck
Thorax
Head
electronics
Therapeutics
Linear Models
Regression Analysis
thorax
regression analysis
unity
acquisition
alignment
slopes
Direction compound
Datasets
shift
curves
predictions

Keywords

  • Field placement error
  • Port filming
  • Portal imaging
  • Radiotherapy

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation

Cite this

Is weekly port filming adequate for verifying patient position in modern radiation therapy? / Valicenti, Richard K; Michalski, Jeff M.; Bosch, Walter R.; Gerber, Russell; Graham, Mary V.; Cheng, Abel; Purdy, James A.; Perez, Carlos A.

In: International Journal of Radiation Oncology, Biology, Physics, Vol. 30, No. 2, 30.09.1994, p. 431-438.

Research output: Contribution to journalArticle

Valicenti, Richard K ; Michalski, Jeff M. ; Bosch, Walter R. ; Gerber, Russell ; Graham, Mary V. ; Cheng, Abel ; Purdy, James A. ; Perez, Carlos A. / Is weekly port filming adequate for verifying patient position in modern radiation therapy?. In: International Journal of Radiation Oncology, Biology, Physics. 1994 ; Vol. 30, No. 2. pp. 431-438.
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