A method to determine an optimal planning target volume margin for intensity modulated radiotherapy of prostate cancer

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A method to determine an optimal planning target volume margin for intensity modulated radiotherapy of prostate cancer

 

Author: Chan, Kwok-ting
Title: A method to determine an optimal planning target volume margin for intensity modulated radiotherapy of prostate cancer
Degree: M.Sc.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Prostate -- Cancer -- Radiotherapy.
Department: Dept. of Health Technology and Informatics
Pages: vi, 67 leaves : ill. ; 31 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2391081
URI: http://theses.lib.polyu.edu.hk/handle/200/5852
Abstract: Purpose/objectives: To investigate the feasibility to establish the extended No-Action-Level offline correction protocol (eNAL) and improve the treatment accuracy of prostate IMRT. With the improved treatment accuracy, a new and optimal PTV margin can be defined for prostate IMRT using CBCT. Materials/Methods: Fifteen subjects diagnosed with localized prostate cancer without distant metastasis were recruited and a total of 120 CBCT scans were conducted on the 15 subjects. The eNAL was firstly applied to reduce the systematic errors and improve the treatment accuracy using CBCT. A Modified eNAL protocol was proposed by the author to determine the systematic error by calculating the mean measured displacements of all available CBCT scans of each subject before correction. The residual systematic errors between eNAL and Modified eNAL protocols were compared using paired t-test (2-tailed). Then a new and optimal PTV margin for IMRT of prostate cancer was defined using the measured errors of the optimal protocol. Results: The gross systematic error and SD (in millimeters) of the population were -4.0 ± 4.0, -0.04 ± 1.5 and 0.2 ± 3.2 for antero-posterior, left-right and supero-inferior directions respectively. The Residual Systematic error and SD (in millimeters) of the population using eNAL protocol were -0.01 ± 1.1, 0.09 ± 0.4 and -0.05 ± 0.8 while that of using the Modified eNAL protocol were 0.5 ± 1.7, 0.5 ± 0.8 and -0.9 ± 1.5 for antero-posterior, left-right and superior-inferior directions respectively. There was significant difference of the residual systematic errors between eNAL and those in the Modified eNAL protocols with p-value 0.044, 0.041 and 0.022 for antero-posterior, left-right and supero-inferior directions respectively. The residual systematic errors of the eNAL protocol were less than those of the Modified eNAL protocol and the correction efficacy was better. The PTV margins calculated by using the gross systematic and random errors were 12.7 mm, 4.8 mm and 10.0 mm for antero-posterior, left-right and supero-inferior directions respectively. The results showed that the current PTV margin was not adequate for posterior direction. The new PTV margin from the eNAL correction protocol were 4.6 mm, 2.1 mm and 4.4 mm for antero-posterior, left-right and supero-inferior directions respectively. The new PTV margin was obviously smaller than and was about half of the PTV margin calculated by using the gross systematic and random errors. Conclusion: The eNAL offline correction protocol could be adopted to improve treatment accuracy of prostate IMRT. The new PTV margin can be greatly reduced by 2.4 mm, 12.9 mm and 10.6 mm for antero-posterior, left-right and supero-inferior directions respectively from the current PTV margin using eNAL protocol.

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