A study to determine the optimal gating phase for treatments of lung tumours under the influence of breathing using biological indices

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A study to determine the optimal gating phase for treatments of lung tumours under the influence of breathing using biological indices

 

Author: Chan, Chun-lun Alan
Title: A study to determine the optimal gating phase for treatments of lung tumours under the influence of breathing using biological indices
Degree: M.Sc.
Year: 2008
Subject: Hong Kong Polytechnic University -- Dissertations.
Lungs -- Cancer -- Treatment.
Lungs -- Cancer -- Radiotherapy.
Radiotherapy.
Department: Dept. of Health Technology and Informatics
Pages: ix, 66 p. : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2174241
URI: http://theses.lib.polyu.edu.hk/handle/200/1233
Abstract: Purpose; The low survival rate of inoperable non-small cell lung cancer (NSCLC) patients by radiation therapy (RT) may be improved by the advanced techniques of gated dose delivery with intensity modulated radiation therapy (IMRT). During gated treatment, end-expiration (EE) phase of respiratory is more stable whereas end-inspiration (El) spares more normal lung tissue. This study compared the relative plan quality of using El and EE in gated IMRT for delivering the dose package to the planning target volume (PTV) and sparing normal lung tissue and organ at risk (OAR). Besides, the correlations between PTV size / PTV movement magnitude with plan quality were also investigated. Methods and materials: Sixteen NSCLC patients treated by IMRT and planned by four dimensional computer tomography (4DCT) were recruited. A 9-equi-spaced coplanar IMRT plan for a prescription dose of 60 Gy per each respiratory phase was prepared. Heart, spinal cord, lungs and PTV were outlined. Normal tissue complication probability (NTCP) of OARs and tumour control probability (TCP) of PTV were used for plan evaluation with priority. Results: With regards to the influence of gating phase on biological indices, the means of NTCP for all OARs in El were equal to or slightly lower than those in EE, whereas the mean TCP in EE was slightly higher than that in El, with no significant difference (p > 0.05). For the effects of PTV size, the means of all NTCPs and TCP in the large PTV size group (> 100 cm3) were larger than those in the group of PTV size < 100 cm3. The differences were mildly significant (0.064 for heart, 0.070 for PTV). The means of NTCPs were less and TCP were higher for the group of PTV movement magnitude < 9.29 mm. Conclusions: Based on the results of this study, it was difficult to decide the gating phase solely by the biological indices. In addition, the consideration of some practical issue benefits such as PTV movement stability and patient comfort were taken into account for determining the ultimate gating phase. El was recommended for patients who can perform breath hold whereas EE was recommended for those cannot. There was a mild correlation of the PTV size with the heart NTCP. However, its impact on TCP was not anticipated, which might be due to the limitation of the TCP calculation model. Increase in PTV movement magnitude would deteriorate the TCP and NTCP values.

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