Beckham Wayne A, Popescu Carmen C, Patenaude Veronica V, Wai Elaine S, Olivotto Ivo A
Radiation Therapy Program of the British Columbia Cancer Agency, Vancouver Island Centre, Victoria, British Columbia, Canada.
Int J Radiat Oncol Biol Phys. 2007 Nov 1;69(3):918-24. doi: 10.1016/j.ijrobp.2007.06.060.
When treatment intent is to include breast and internal mammary lymph nodes (IMNs) in the clinical target volume (CTV), a significant volume of the heart may receive radiation, which may result in late morbidity. The value of conformal intensity-modulated radiation therapy (IMRT) to avoid heart dose was studied.
Breast, IMNs, and normal tissues were contoured for 30 consecutive patients previously treated with RT after lumpectomy for left-sided breast cancer. Eleven-beam, conformal, inverse-planned IMRT plans were developed and compared with best standard plans. Conformity Index (CI), Homogeneity Index (HI), and doses to normal tissues were compared.
Intensity-modulated RT significantly improved (two-sided paired t test) HI (0.95 vs. 0.74), CI (0.91 vs. 0.48), volume of the heart receiving more than 30 Gy (V30-heart) (1.7% vs. 12.5%), and volume of lung receiving more than 20-Gy (V20-left lung) (17.1% vs. 26.6%), all p < 0.001. The mean Healthy Tissue Volume (HTV = CT set - PTV) dose was similar between IMRT and best standard plans (6.0 and 6.9 Gy, respectively), but IMRT increased the volume of normal tissues receiving low-dose RT: V5-right lung (13.7% vs. 2.0%), V5-right breast (29.2% vs. 7.9%), and V5-HTV (31.7% vs. 23.6%), all p < 0.001. IMRT plans were generated in less than 60 min and treatment delivered in approximately 20 min, suggesting that this technique is clinically applicable.
IMRT significantly improved conformity and homogeneity for plans when the breast + IMNs were in the CTV. Heart and lung volume receiving high doses were decreased, but more healthy tissue received low doses. A simple algorithm based on amount of heart included in the standard plan showed limited ability to predict the benefit from IMRT.
当治疗目的是将乳腺及内乳淋巴结（IMN）纳入临床靶区（CTV）时，心脏的很大一部分可能会受到辐射，这可能导致晚期并发症。本研究旨在探讨调强适形放射治疗（IMRT）在避免心脏受量方面的价值。
对30例左侧乳腺癌保乳术后接受放疗的患者的乳腺、IMN及正常组织进行轮廓勾画。制定了11野适形逆向计划IMRT方案，并与最佳标准方案进行比较。比较了适形指数（CI）、均匀性指数（HI）及正常组织受量。
调强放疗显著改善了（双侧配对t检验）HI（0.95对0.74）、CI（0.91对0.48）、接受超过30 Gy照射的心脏体积（V30-心脏）（1.7%对12.5%）以及接受超过20 Gy照射的左肺体积（V20-左肺）（17.1%对26.6%），所有p<0.001。IMRT与最佳标准方案的平均健康组织体积（HTV = CT设定值 - PTV）受量相似（分别为6.0和6.9 Gy），但IMRT增加了接受低剂量放疗的正常组织体积：V5-右肺（13.7%对2.0%）、V5-右乳腺（29.2%对7.9%）以及V5-HTV（31.7%对23.6%），所有p<0.001。IMRT计划在不到60分钟内生成，治疗在约20分钟内完成，表明该技术具有临床应用价值。
当乳腺+IMN在CTV中时，IMRT显著改善了计划的适形性和均匀性。接受高剂量照射的心脏和肺体积减少，但更多的健康组织接受了低剂量照射。基于标准方案中心脏包含量的简单算法预测IMRT获益的能力有限。
