Dosimetric evaluation of static and helical tomotherapy and conventional field-in-field tangential techniques in radiotherapy for breast cancer

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Dosimetric evaluation of static and helical tomotherapy and conventional field-in-field tangential techniques in radiotherapy for breast cancer

 

Author: Chan, Man Ting Jocelyn
Title: Dosimetric evaluation of static and helical tomotherapy and conventional field-in-field tangential techniques in radiotherapy for breast cancer
Degree: M.Sc.
Year: 2012
Subject: Breast -- Cancer -- Radiotherapy.
Radiotherapy.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Health Technology and Informatics
Pages: xii, 77 p. : col. ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2520219
URI: http://theses.lib.polyu.edu.hk/handle/200/6561
Abstract: Introduction: There is wide variation of practices on breast cancer radiotherapy and it is uncertain how much benefit could be offered to the patients when intensity modulated radiotherapy (IMRT) technique is used. Innovation of static tomotherapy technique, also named as TomoDirect, has been receiving increasing attention in the treatment of breast cancer. This study compared and evaluated conventional field-in-field (FIF) tangential technique, TomoDirect and helical tomotherapy (HT) in terms of target dose homogeneity, conformity and degree of organs-at-risk (OARs) sparing. The results provided useful reference to recommend optimal treatment strategy for patients, including the consideration of left or right side breast cancer and with or without SCF lymph nodes involvement. Methods: Total of 30 breast cancer patients with supraclavicular fossa (SCF) lymph nodes involvement were recruited and planned by FIF, TomoDirect and HT. They were divided equally (n=15) in two arms of left and right side group. Conventional field arrangement of SCF field and tangential opposing fields were employed for FIF planning with subfields using multileaf collimator (MLCs) for shielding hotspots and heart (for left breast cancer patients). TomoDirect used three anteior-oblique fields for the SCF target and seven fields for the chest wall target. With the same prescription, target coverage, dose homogeneity and conformity were evaluated. Degree of OARs sparing was assessed by means of maximum dose, mean dose and various dose-volumes parameters. Volume of 3mm skin structure (in the treatment field) receiving over 42Gy was used to estimate skin dose toxicity. Beam-on-time of the three techniques were recorded and compared to evaluate treatment delivery efficiency.
Results: The present dosimetric comparison proved that advanced IMRT techniques of tomotherapy had definite target dosimetric advantages over FIF technique. HT generally increased low dose volumes compared with the other two techniques. This study showed that only TomoDirect achieved high degree of OARs sparing with good target dose dosimetry. However, there was a significant volume of high dose outside the SCF target and the dose distribution was unlikely to be satisfactory in TomoDirect. TomoDirect also resulted in higher contralateral breast dose when chest target lied across patients' midline or on patients with highly concave chest wall. The volume of 3mm skin structure receiving over 42Gy in TomoDirect plans was over 70% in both breast cancer groups, which was highest among the three techniques (p<0.01). Due to the use of greater modulation factor to bring down the higher target dose, TomoDirect required 30% longer treatment delivery time than FIF and HT (p<0.01). The presence of cardiac shield on the left-sided breast further deteriorated the target coverage as compared to right-sided breast using the same FIF technique (p<0.01). Conclusion: Since FIF technique was simple and achieved reasonable dosimetric results, it is recommended for treating right breast cancer. Because of the highly conformal and homogenous target dose, HT is recommended for breast cancer patients with SCF lymph nodes involvement and patients with chest wall target crossed midline and/or with concave chest wall. Both tomotherapy techniques were more favourable for left breast cancer as good target dosimetry was maintained. The advantages of TomoDirect might outweigh its inferior treatment delivery efficiency and provide an alternative treatment strategy only for patients require maximum sparing of OARs.

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