The Dosimetric Effects of Ignoring Small Non-bone High-density Regions Using the 5-Bulk-density Method for Photon Dose Calculation
AI Saito, JG Li, C Liu, KR Olivier, D Kahler, K Karasawa, JF Dempsey
Hong Kong J Radiol 2014;17:16-22
DOI: 10.12809/hkjr1413180
Objective: To investigate the effect of the 5-bulk-density dose calculation method without considering small non-bone high-density regions in patients with thoracic cancers.
Methods: A heterogeneity-corrected computed tomography plan and two types of 5-bulk-density treatment plans were generated for patients with lung or oesophageal tumours without any obvious findings of emphysema. In the first 5-bulk-density plan, the bone was contoured using an auto-contouring tool; in the second plan, the bone was contoured manually ignoring small non-bone high-density regions. Treatment plans were made with a commercial treatment-planning system and an adaptive convolution dose-calculation algorithm. The population’s average density was applied, and the heterogeneity-corrected plan was compared with all of the 5-bulk-density regions for each case. Dose-volume histograms and dose-difference distributions were examined for all cases.
Results: A total of 53 patients (57 tumours) were enrolled. Both the auto- and manually contoured plans had average bone and tissue densities of 1.12 g/cm3 and 1.02 g/cm3, respectively. When the manually contoured plan was compared with the heterogeneity-corrected plan, dose-volume histograms of the normal tissue and planning target volume agreed to within 2% of the dose.
Conclusions: For bulk-tissue-density heterogeneous dose calculation, clinically acceptable dosimetric accuracy was achieved for auto-contoured bone cases without considering small non-bone high-density regions. This means that the current method could be applied with magnetic resonance imaging in the treatment planning system for dose calculation where no electron density information exists.
中文摘要
忽略微小的非骨性高密度區運用5倍體積密度法對光子劑量測定的效果
AI Saito, JG Li, C Liu, KR Olivier, D Kahler, K Karasawa, JF Dempsey
目的：探討忽略胸廓內腫瘤患者微小的非骨性高密度區的情況下，5倍體積密度的劑量計算方法的效果。
方法：替沒有任何明顯肺氣腫的肺腫瘤或食管腫瘤患者，制定組織異質性校正的電腦斷層掃描方案和兩種5倍體積密度治療方案。第一種5倍體積密度方案中，用自動工具勾劃出骨輪廓；第二種方案中，忽略微小的非骨性高密度區而人工勾劃出骨輪廓。運用商用治療規劃系統和自適應卷積劑量計算法來制定治療方案。利用人均密度，將每個病例的異質性校正方案與5倍體積密度方法的全部區域作比較；並檢視所有病例的劑量體積直方圖和劑量差異分佈。
結果：總計53名病人（共57個腫瘤）納入研究。自動和人工勾劃輪廓方案的平均骨骼和組織密度分別為1.12 g/cm3和1.02 g/cm3。人工勾劃輪廓方案與異質性校正方案相比，正常組織的劑量體積直方圖和靶區體積的差異均在2%以內。
結論：在異質性組織中運用體積-組織-密度劑量計算法，忽略微小的非骨性高密度區而採用骨輪廓自動勾劃法也能達至臨床可接受的劑量測定精確度。這意味着在治療規劃系統中，可運用該方法以無電子密度信息的磁共振圖像為基礎作劑量測定。