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Jpn J Radiol. 2015 Jun;33(6):303-10. doi: 10.1007/s11604-015-0418-1. Epub 2015 Apr 16.

Prediction error and required internal margin provided for irregular respiratory movements: a phantom study.

Author information

1
Proton Medical Research Center, University of Tsukuba, 1-1-1, Tennoudai, Tsukuba, 305-8575, Japan, fukumitsun@yahoo.co.jp.

Abstract

PURPOSE:

To estimate the prediction error and required internal margin provided for irregular respiratory movements.

MATERIALS AND METHODS:

Twenty-eight patterns of irregular movement were prepared using a moving phantom. For irregular cycle movement, a cycle of 2.0-5.0 s was inserted into the baseline movement data (3.5-s cycle, 6-mm amplitude) every four cycles. In addition, a cycle of 2.5-4.5 s was further inserted into one of the irregular data points every four cycles to produce more complicated irregularity. For irregular amplitude movement, an amplitude of 3.0-9.0 mm was inserted into the baseline respiratory movement data. In addition, an amplitude of 4.0-8.0 mm was further inserted into one of the irregular data points every four cycles to produce more complicated irregularity. Images of the moving target were acquired using a real-time position management (RPM) and four-dimensional CT (4DCT) system. The displacement from the baseline image and required margin to compensate for irregular movement were calculated.

RESULTS:

Amplitude irregularity tended to lose stable placement and need larger margins to compensate for the reduction of image reproducibility than cycle irregularity. There was a large displacement and required margin when the target moved with more complicated irregular amplitude.

CONCLUSION:

The RPM and 4DCT system has a risk of prediction error, which may result from the complicated amplitude irregularity of respiratory movement.

PMID:
25877673
DOI:
10.1007/s11604-015-0418-1
[Indexed for MEDLINE]

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