A dosimetric evaluation of conventional and conformal radiotherapy for oesophageal cancer

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A dosimetric evaluation of conventional and conformal radiotherapy for oesophageal cancer

 

Author: Kwok, Po-ming
Title: A dosimetric evaluation of conventional and conformal radiotherapy for oesophageal cancer
Degree: M.Sc.
Year: 2000
Subject: Esophagus -- Cancer -- Radiotherapy
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Optometry and Radiography
Pages: xii, 79 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1541813
URI: http://theses.lib.polyu.edu.hk/handle/200/4286
Abstract: For a long time, oesophageal tumours have been treated by the conventional two-dimensional radiotherapy (2DRT). However, the 2DRT calculation algorithm has inherent deficiencies and the accuracy of target volume localisation is limited. With the advancement of technologies, three-dimensional conformal radiotherapy (3DCRT) is now feasible to be implemented in the clinical situations. As more resources and facilities are needed to implement 3DCRT, if it is not superior in the aspect of dosimetry, then the rationale for it being used to treat the oesophageal cancer instead of 2DRT is questionable. Thirteen patients with oesophageal cancer were accrued retrospectively to the study to carry out dosimetric evaluation between the treatment approach of conventional two-dimensional radiotherapy and three-dimensional conformal radiotherapy, using different sizes of planning target volume, so as to determine which treatment provides better overall dose distribution. The relationship between the size of the planning target volume and the radiation doses received by the organs at risk is also assessed. A two-phase 2DRT plan was retrospectively created for each of the thirteen patients to carry out dosimetric comparison with a two-phase 3DCRT plan, which the patient was actually treated with. For 3DCRT plans, three PTV were outlined in each patient by adding 1cm, 1.5cm and 2cm margins to the CTV. For 2DRT plans, three 2D target volumes of size 4cm, 5cm and 6cm diameter circles were outlined. Then 3DCRT and 2DRT computer planning with these PTV and 2D target volumes were carried out, with standardised plan optimisation criteria, for further dosimetric comparison. The effectiveness of each treatment plan was assessed using dose volume histograms. On average, the dose delivered to 90% of the PTV in 3DCRT plan was 30.0% higher than that in 2DRT plan; however, dose to the lung was similar in both treatment approaches. Also, in 3DCRT plan, the mean spinal cord dose and mean heart dose were 16.7% and 10.3% less respectively. Based on the dose received by OARs, it is possible to escalate the phase II prescribed dose from 30Gy to as much as 42.8Gy. For the PTV of 2cm margin added, the percentage volume of lung that received dose greater than 20Gy throughout the treatment was found to be as high as 33.0%. The mean dose received by 90% of the PTV achieved 96.0% of the prescribed dose in 2DRT plans produced with 2D target volume of 6cm circle size. Furthermore, there was significant (p=0.01 to 0.05) correlation between the dose received by the organs at risk and the margin added to the CTV and the size of 2D target volume, with the Pearson correlation coefficient ranged from 0.2876 to 0.6590. In conclusion, the data collected demonstrate that 3DCRT plans have promising dosimetric advantages over 2DRT plans for treating oesophageal cancer. Moreover, escalation of phase II prescribed dose to 38Gy is suggested (i.e. total dose of 68Gy) in 3DCRT plans. Finally, the recommended PTV margin is 1.5cm in the 3DCRT plans and the size of 2D target volume is recommended to be 6cm diameter circle if conventional 2DRT plans are being adopted.

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