Volumetric Modulated Arc Therapy vs 3-Dimensional Conformal Radiotherapy in Head and Neck Cancer: a Comparative Planning and Dosimetry Study

Full Article

SM Lee, CK Lee, KS Yu, KC Ngan

Hong Kong J Radiol 2012;15:149-54

Objective: In this study, we evaluate the advantages of volumetric modulated arc therapy (VMAT) compared to conventional 3-dimensional conformal radiotherapy (3DCRT) with respect to dosimetry, verification, and treatment efficiency.

Methods:Seven patients with locally advanced squamous cell cancer of the head and neck treated by the VMAT and re-planned by 3DCRT techniques were studied retrospectively. The VMAT and 3DCRT plans were evaluated for (i) the homogeneity and conformity of radiation dose to the treatment targets, and (ii) doses to organs at-risk including the spinal cord and parotid glands. The treatment and verification time spent were estimated, so as to compare the efficiency of the VMAT and 3DCRT treatments.

Results:The median of the conformity and inhomogeneity indices of planning target volume 60 (to be covered by 60 Gy) were 1.60 and 6.1, respectively for VMAT, and 2.32 and 14.9, respectively for 3DCRT. The median maximum spinal cord dose of the VMAT plans was 38.9 Gy, compared to 44.5 Gy for the 3DCRT plans. Both parotids of two patients with central tumours could be spared for which the median dose was below 30 Gy. The contralateral parotid of all other patients with unilateral primary tumour could be spared except a patient with a close proximity tumour location. Compared to 3DCRT, the VMAT technique saved 4.25 machine-hours per patient for the full course of radiation treatment.

Conclusions: Compared to 3DCRT plans, VMAT plans produced significantly better target coverage as well as dose conformity. Doses to organs at-risk such as the spinal cord and parotid glands were also reduced. Besides, the delivery of VMAT treatment was more efficient.



頭頸癌的弧形調控放射治療與三維適形放射治療: 治療計劃及放射劑量的比較研究


目的:評估弧形調控放射治療(VMAT)與三維適形放射治療(3DCRT)在放射劑量、驗證時間和 治療效率三方面的比較。

方法:回顧研究七名原位末期鱗狀細胞頭頸癌患者,他們先接受VMAT,再以3DCRT跟進。然後評 估兩種方法在以下兩方面的表現:(1)放射劑量到達目標器官的同質性和一致性;(2)到達高風 險器官如脊髓和腮腺的放射劑量。估計治療及驗證時間,然後比較VMAT和3DCRT的治療效率。

結果:計劃靶區60(即用60 Gy)的一致性指標及非均勻指標的中位數方面,VMAT分別為1.60 和6.1,而3DCRT分別為2.32和14.9。脊髓最大放射劑量的中位數,VMAT為38.9 Gy,3DCRT為 44.5 Gy。兩名有中央腫瘤的患者,其腮腺的受照劑量中位數在30 Gy以下。至於其他有單側原發灶的 病人,除了一名有近距離腫瘤的病人外,對側腮腺的受照劑量下降。與3DCRT比較,VMAT技術在 放射治療整個過程中減低了每位病人4.25機器小時。

結論:與3DCRT比較,VMAT產生明顯更好的覆蓋目標及劑量一致性。到達高風險器官如脊髓和腮 腺的放射劑量亦減少了。此外,VMAT有較高的治療效率。