Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia.
Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia.
Pract Radiat Oncol. 2013 Oct-Dec;3(4):e131-7. doi: 10.1016/j.prro.2012.12.007. Epub 2013 Feb 11.
The thyroid is not routinely considered an organ at risk in supraclavicular (SC) nodal radiation therapy (RT) for breast cancer. We compared the dosimetric impact of the following 2 RT planning techniques on the thyroid: (1) conventional single anterior field to encompass the SC nodal volume defined clinically; and (2) 3-dimensional conformal radiation therapy (3DCRT) planning to encompass the computed tomography (CT)-contoured SC nodal volume.
The thyroid, SC nodal volumes, and organs at risk were contoured on the planning CT of 20 patients who received 50 Gy in 2-Gy daily fractions to the breast or chest wall, and SC nodes. Comparisons of dosimetric parameters between the techniques were performed: thyroid, mean and maximum dose, V5, V30, and V50 (percentage of thyroid receiving ≥5 Gy, ≥30 Gy, and ≥50 Gy, respectively); SC nodal volume, homogeneity index (HI, percentage volume receiving 95%-107% of prescribed dose); and maximum doses of spinal cord and brachial plexus. Anatomic characteristics that influenced the dose distributions were investigated.
The 3DCRT planning technique significantly increased all thyroid dosimetric measures (mean dose 17.2 Gy vs 26.7 Gy; maximum dose 48.5 Gy vs 51.9 Gy; V5 45.7% vs 64.9%; V30 33.7% vs 48%; and V50 0.6% vs 26.7%; P < .001). It improved HI for the SC nodal volumes (P < .001) but resulted in higher maximum doses to the spinal cord (6.1 Gy vs 30 Gy) and brachial plexus (43.2 Gy vs 51.4 Gy). The thyroid volume and depth of SC nodes did not influence the thyroid dose distribution. The depth of SC nodes impacted on the HI of SC nodal volumes in the conventional technique (P = .004).
The 3DCRT planning improved dosimetric coverage of the SC nodal volume but increased thyroid radiation doses. The potential adverse effects of incidental thyroid irradiation should be considered while improving dosimetric coverage in SC nodal irradiation for breast cancer.
甲状腺通常不被认为是乳腺癌锁骨上（SC）淋巴结放疗（RT）的危险器官。我们比较了以下两种 RT 计划技术对甲状腺的剂量学影响：（1）常规的单前野，以包含临床定义的 SC 淋巴结体积；（2）三维适形放疗（3DCRT）计划，以包含 CT 勾画的 SC 淋巴结体积。
对 20 例接受 50 Gy 分 2 Gy 每日剂量照射乳房或胸壁和 SC 淋巴结的患者的计划 CT 进行了甲状腺、SC 淋巴结体积和危险器官的勾画。比较了两种技术的剂量学参数：甲状腺、平均和最大剂量、V5、V30 和 V50（分别为甲状腺接受≥5 Gy、≥30 Gy 和≥50 Gy 的百分比）；SC 淋巴结体积、均匀性指数（HI，接受 95%-107%处方剂量的百分比体积）；以及脊髓和臂丛的最大剂量。研究了影响剂量分布的解剖特征。
3DCRT 计划技术显著增加了所有甲状腺剂量学指标（平均剂量 17.2 Gy 比 26.7 Gy；最大剂量 48.5 Gy 比 51.9 Gy；V5 45.7%比 64.9%；V30 33.7%比 48%；V50 0.6%比 26.7%；P<0.001）。它提高了 SC 淋巴结体积的 HI（P<0.001），但导致脊髓（6.1 Gy 比 30 Gy）和臂丛（43.2 Gy 比 51.4 Gy）的最大剂量增加。甲状腺体积和 SC 淋巴结的深度不影响甲状腺的剂量分布。SC 淋巴结的深度影响传统技术中 SC 淋巴结体积的 HI（P=0.004）。
3DCRT 计划提高了 SC 淋巴结体积的剂量学覆盖范围，但增加了甲状腺的辐射剂量。在提高乳腺癌 SC 淋巴结照射的剂量学覆盖范围的同时，应考虑意外甲状腺照射的潜在不良影响。
