Author: Chiu, George
Title: To evaluate the differences between the prone technique and supine technique using tomotherapy in treating breast cancer
Advisors: Wu, Vincent (FHSS)
Degree: DHSc
Year: 2015
Subject: Breast -- Cancer -- Radiotherapy
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Health and Social Sciences
Pages: xix, 192 pages : color illustrations
Language: English
Abstract: Background: The value of breast cancer treated in prone position using tomotherapy has only been evaluated by dosimetric studies. Although treating breast patients in prone position can minimize dose to the lungs as the gravity can pull the treatment site further away from the ribs, the heart will get closer to the treatment site and may receive a higher dose. Tomotherapy has its advantage to deliver a more conformal dose to the target, but with the expenses of higher integral dose. Combining prone technique and tomotherapy together may be new initiative and it is worth to study whether this could be the optimal approach in treating breast cancer. Aims & Objectives: With regards to breast cancer patients, this study evaluated 1) setup accuracy, 2) accuracy of actual treatment dose as compared with the planned dose and 3) skin toxicity between supine and prone position. Method: Forty early breast cancer patients were recruited. Thirty were treated in supine position and 10 were treated in prone position. The primary endpoint was the rate of acute radiation skin reaction. Three sets of data were collected and analyzed: 1) Comparison of setup accuracy: The systematic and random errors of all directional discrepancies in the supine and prone position were compared. 2) Comparison of actual treatment dose to planned dose: The means of total actual dose and planned dose of targets and normal structures, the mean percentage difference between total actual dose and planned dose of each structure and homogeneity index of clinical target volume (CTV) and planning target volume (PTV) were compared. 3) Comparison of acute radiation skin reaction (ARSR): The score for each patient using acute radiation morbidity scoring criteria was analyzed according to the 6th, 11th, 16th and 21st treatment day by means of Chi-square test.
Results: 1) Comparison of setup accuracy: Results showed that the prone position had larger set up deviation than that of the supine position, and the differences in random error for lateral, longitudinal, vertical and roll directions were significant (p < 0.05). Result for systematic errors was also highly significant except in vertical direction (p = 0.0570). 2) For comparison of planned dose/ actual dose of supine versus prone position: V20Gy of ipsilateral lung was significant in all comparisons (p < 0.05) and values of prone were lower than that of supine. D98% of PTV was significant only in planned dose comparison of supine versus prone position and value of prone was higher than that of supine. For comparison of mean percentage difference between supine and prone position: Only D2% of CTV & PTV and D98% of PTV were statistically significant. The value of prone was smaller than that of supine in D2% of CTV and D2% of PTV, where it was opposite for D98% of PTV. For comparison of actual dose versus planned dose in supine/ prone position: D2%, D95% & D98% of CTV, D2%, D95% & D98% of PTV and Dmean of contralateral breast were statistically significant (p < 0.05) for all supine, left-sided supine and right-sided supine position, and the actual dose delivered to the target was lower than expected. For prone position, only D95% & D98% of PTV were statistically significant (p < 0.05) and the actual dose delivered to the target was lower than expected. For left-sided prone position, D98% of CTV and D95% & D98% of PTV were statistically significant (p < 0.05) and the actual dose delivered to the target was lower than expected. Homogeneity index of CTV and PTV was significant in all supine, left-sided supine, all prone and left-side prone position. Homogeneity index of PTV in right-sided supine position was also significant. 3) Comparison of skin reaction: Only Grade 2 or below acute radiation skin reaction (ARSR) was found for both supine and prone position. In 21st treatment, 60 % of patients in supine position suffered from Grade 1 and 2 acute skin reactions whereas only 30 % of patients in prone position suffered from Grade 1 of acute skin reaction. No patient in the prone position suffered from Grade 2 or above acute radiation skin reaction. By means of chi-square test, the difference between supine and prone position only significant at 21st treatment (p < 0.05). Hence prone position would give a better acute radiation skin reaction than that in supine position. Conclusion: Supine position was found to have the smallest systematic and random errors. Prone position was found to be a good choice for left-sided breast for its better dose sparing of lungs and heart without scarifying much in CTV and PTV homogeneity. Prone position was more favorable in lowering ARSR (i.e. primary endpoint). If daily image verification is used, prone position is recommended to treat left-sided breast. Supine position is recommended for treating right-sided breast.
Rights: All rights reserved
Access: restricted access

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