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體積調控弧形治療與照野內照野技術運用於全腦放射治療之劑量分佈

THE DOSE DISTRIBUTIONS OF VMAT AND FIELD-IN-FIELD TECHNIQUE USED IN WHOLE BRAIN RADIOTHERAPY

摘要


目的:癌症腦轉移病人在進行全腦放射線治療時,傳統上使用治療時間較短與節省製作治療計劃時間之雙側向照野對照之技術(bilateral field, BF),但簡單且粗糙的治療計劃之劑量均勻度與劑量順形度均不佳,可能增加正常組織的副作用。然而隨著科技進步,治療計劃系統運算速度加快及照野內照野技術治療(field-in-field, FIF)與體積調控弧形治療(volumetric modulated arc therapy, VMAT)等技術的發展,應該重新考慮能增進治療品質之全腦照射技術。材料與方法:針對十位病患分別製作雙側向照野(BF)、照野內照野(FIF)、體積調控弧形治療(VMAT)等治療計劃,所有治療計劃之總醫囑劑量均為30 Gy與12分次,且歸一化至相同的腫瘤包覆度計算出總體最大劑量值、劑量順形度與劑量均勻度。所有器官劑量均歸一至2 Gy單次劑量之生物劑量,並以無母數檢定進行統計分析。結果:BF、FIF與VMAT治療計畫平均的最大劑量百分比(歸一化至醫囑劑量)分別為113.28% ± 1.62%、108.33% ± 1.16%與110.53% ± 0.25%;平均的劑量順形度分別為0.633 ± 0.033、0.664 ± 0.023與0.853 ± 0.011,平均的劑量均勻度分別為0.552 ± 0.166、0.841 ± 0.150與0.284 ± 0.086。VMAT治療計畫有較佳的劑量順形度,所以顯著降低靶區外危及器官劑量,如頸椎、視神經、唾液腺、內耳與後腦杓皮膚;然而較差的劑量均勻度也使得靶區內危及器官劑量(如腦幹、海馬回與視交叉)有些微提高。結論:FIF治療計劃有最低的最大劑量百分比及最佳的劑量均勻度,故FIF治療計劃可完全取代BF治療計劃以增進全腦照射治療品質。VMAT治療計劃有最佳的劑量順形度可降低靶區外危及器官劑量,劑量均勻度稍差。無論FIF或VMAT技術均可作為增進腦轉移病人生活品質的治療選擇。

並列摘要


Purpose: Cancer patients with intracranial metastasis were traditionally treated with bilateral-field (BF) technique for whole brain radiation therapy (WBRT). Planning BF is simple and saves both treatment and planning time. However, the relatively crude method suffers from lack of dose conformity and homogeneity. These two factors may increase the complications of normal tissue and hair loss. However, with current improved techniques, the rapid development of therapeutic planning systems and the development of new treatment technologies such as volume modulated arc therapy (VMAT), and field-in-field (FIF) techniques, the treatment quality of whole brain irradiation should be reconsidered. Materials and Methods: The contours of whole brain PTV and the critical organs of ten patients were determined by one radiation oncologist and checked by another one. Bilateral- fields whole brain treatment plans were created. At the same time, a pair of sub-fields from the BF plans were modified to MLCs to create FIF plans. All BF, FIF and VMAT plans for each patient had a prescribed dose of 30 Gy in 12 fractions. The global maximum dose, dose comformity, and dose homogeneity were calculated to the same level as the tumor coverage. All organ doses were normalized to a single biological equivalent dose of 2 Gy fractions. All data was analyzed with non-parametric statistics. Results: The average maximal doses (normalized to the prescribed dose) of BF, FIF and VMAT plans were 113.28% ± 1.62% (mean ± std), 108.33% ± 1.16% and 110.53% ± 0.25%. The mean conformity of BF, FIF and VMAT plans were 0.633 ± 0.033, 0.664 ± 0.023 and 0.853 ± 0.011. The mean homogeneity of BF, FIF and VMAT plans were 0.552 ± 0.166, 0.841 ± 0.150 and 0.284 ± 0.086. The VMAT regimen had a better dose conformity and therefore significantly reduced organ damage at the critical organs, such as spinal cord, optic nerve, parotid glands, cochleae, and posterior scalp. However, poor dose homogeneity also compromised organ dose endpoints (such as the brainstem, hippocampus and optic chiasm) with slightly elevated doses. Conclusions: The FIF treatment plan has the lowest percentage of maximum dose and the best dose homogeneity, so the FIF treatment plan could completely replace the BF treatment plan to improve the quality of whole-brain irradiation treatment. The better dose conformity for the VMAT treatment plan reduces organ complications outside the target area with somewhat worse homogeneity. Both FIF or VMAT can be used as a treatment option to improve the quality of life of patients with brain metastases.

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