An assessment of respiratory motion to establish patient selection criteria for respiratory gated radiotherapy

Whitaker, M 2011, An assessment of respiratory motion to establish patient selection criteria for respiratory gated radiotherapy, Masters by Research, Applied Sciences, RMIT University.

Document type: Thesis
Collection: Theses

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Title An assessment of respiratory motion to establish patient selection criteria for respiratory gated radiotherapy
Author(s) Whitaker, M
Year 2011
Abstract Radiation therapy is one of the main modalities used to treat cancers of the lung, liver and breast. Respiratory motion during treatment can shift the position of the tumour out of the fixed radiation beam, resulting in underdosing of the tumour and accidental overdosing of normal tissue. Many strategies for respiratory motion management have been developed, such as delineation of an internal target volume to capture the range of tumour movement; adaptive radiotherapy which tracks the tumour motion by following implanted markers; and respiratory gated radiotherapy, where the radiation beam is turned on and off when the tumour moves into and out of a known position respectively.

Not all patients are suitable candidates for gated treatment. Many lung cancer sufferers are unable to sustain their breathing in a reproducible pattern intra- and inter-fraction. A method of pre-selecting those patients suitable for respiratory gated radiotherapy treatment would minimise patient discomfort during treatment and avoid the inefficient use of time and resources.

The aim of this research was to investigate parameters that could quantitatively describe the reproducibility of breathing motion, and to determine if one or more of these parameters could be used as selection criteria to actively assist the clinician in the decision to proceed to 4DCT simulation for treatment planning, and gated treatment.

A software tool was developed to analyse the breathing tracks acquired with a customised spirometer and RPM. A total of 50 breathing tracks of 60 s duration or greater were obtained from 3 volunteers and 9 patients. These tracks were evaluated for intra- and inter-fraction variations.

Five parameters were identified for analysis: mean cyclic baseline (mean value between the maximum inhale and exhale), amplitude, frequency and asymmetry; a relative duty cycle was also calculated as a substitute for the true duty cycle at treatment.

The results show that inter-fraction variation is generally larger than intra-fraction variation. In general, the volunteers exhibited better intra- and inter-fraction reproducibility than the patients. The variation in amplitude for both volunteers and patients indicate that amplitude-based gating regimens should be assessed on an individual basis. The frequency, baseline and asymmetry parameters may be used as indicators of suitability for phase-based gating.

The parameters investigated are useful measures that may assist the clinician in patient selection for respiratory gated radiotherapy when used in conjunction with the requirements, limitations and preferences of the radiotherapy centre and patient.
Degree Masters by Research
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Respiratory gated radiotherapy
intra- and inter-fraction reproducibility
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Created: Thu, 13 Sep 2012, 14:05:46 EST by Brett Fenton
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