Dosimetric comparison between cone-based Linac radiosurgery system and helical Tomotherapy-based radiosurgery system for intra-cranial lesions

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Dosimetric comparison between cone-based Linac radiosurgery system and helical Tomotherapy-based radiosurgery system for intra-cranial lesions

 

Author: Yip, Ho-yin
Title: Dosimetric comparison between cone-based Linac radiosurgery system and helical Tomotherapy-based radiosurgery system for intra-cranial lesions
Degree: M.Sc.
Year: 2011
Subject: Hong Kong Polytechnic University -- Dissertations
Radiation dosimetry
Department: Dept. of Health Technology and Informatics
Pages: 93 leaves : ill. (some col.) ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2412267
URI: http://theses.lib.polyu.edu.hk/handle/200/5964
Abstract: Purpose: The aim of the research was to differentiate the characteristics of dosimetry between cone-based Linac radiosurgery system and Tomo-based radiosurgery system. Hence, the guidelines of selection of radiosurgery system, based on the research result, could be set-up. Methodology: Twenty-seven (n=27) patients treated with cone-based Linac radiosurgery system in Hong Kong Sanatorium & Hospital from 2005 to 2009 were re-planned for Tomotherapy-based radiosurgery system. The mean of average overall conformity index (CIoverall), that of average homogeneity index (HIoverall) and that of average gradient score index (GSIoverall) of both systems were calculated for statistical analysis of dosimetric performances between the two radiosurgery systems. Wilcoxon matched-pairs test was used to compare the dosimetric performances between two radiosurgery systems in terms of target dose conformity, target dose homogeneity and dose fall-off. The cases with single target (n=12), i.e. single PTV and treated with single isocenter in cone-based Linac radiosurgery system, and that with single irregular target (n=6), i.e. single irregular PTV and treated with multiple isocenters in cone-based Linac radiosurgery system, were analyzed separately. Furthermore, Pearson correlation was used to analyze the relationships between number of targets of dosimetric evaluation indices and those between the total volume of Planning Target Volume (PTV) and dosimetric evaluation indices. Finally, the relationships between volume of PTV and dosimetric evaluation indices were analyzed separately for the cases with single target.
Results: There was no significant difference between cone-based Linac radiosurgery system and Tomo-based radiosurgery system in terms of target dose conformity (p-value:0.4309). Tomo-based radiosurgery system performed better in target dose homogeneity (p-value:0.009) while cone-based radiosurgery system performed better in dose fall-off (p-value:0.0001). For those with single target, there was no significant different between the two systems in terms of target dose conformity (p-value: 0.8501) and target dose homogeneity (p-value: 0.0522) while cone-based Linac radiosurgery system was better in dose fall-off (p-value: 0.0303). For those with single irregular target, there was no significant different between two systems, in terms of target dose conformity (p-value:0.1536) and dose fall-off (p-value:0.3125) but Tomo-based radiosurgery system performed better in terms of dose homogeneity (p-value:0.0313). There were very weak relationships between the number of targets and dosimetric indices and weak relationships between the total PTV volume and dosimetric indices. For the cases with single target, moderate relationship between PTV volume and dosimetric indices was observed also. Conclusion: First, Tomo-based radiosurgery system should be the first line treatment for all brain diseases with multiple targets because of shorter treatment time. Second, cone-based Linac radiosurgery system should be the treatment of choice for single and relatively small regular target because of the rapid dose fall-off and reasonable treatment time. Third, Tomo-based radiosurgery system should be the treatment of choice for the disease with irregular target, i.e. pituitary adenoma, trigeminal neuroma etc, because of homogeneous dose within target and shorter treatment time. Finally, if any one of the targets is close to OAR, e.g. brainstem, less than 3mm, cone-based radiosurgery system would be the only treatment of choice in order to reduce dose to OARs.

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