Dabaja Bouthaina, Salehpour Mohammad R, Rosen Isaac, Tung Sam, Morrison William H, Ang K Kian, Garden Adam S
Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Int J Radiat Oncol Biol Phys. 2005 Nov 15;63(4):1000-5. doi: 10.1016/j.ijrobp.2005.03.069. Epub 2005 Jun 22.
Oropharynx cancers treated with intensity-modulated radiation (IMRT) are often treated with a monoisocentric or half-beam technique (HB). IMRT is delivered to the primary tumor and upper neck alone, while the lower neck is treated with a matching anterior beam. Because IMRT can treat the entire volume or whole field (WF), the primary aim of the study was to test the ability to plan cases using WF-IMRT while obtaining an optimal plan and acceptable dose distribution and also respecting normal critical structures.
Thirteen patients with early-stage oropharynx cancers had treatment plans created with HB-IMRT and WF-IMRT techniques. Plans were deemed acceptable if they met the planning guidelines (as defined or with minor violations) of the Radiation Therapy Oncology Group protocol H0022. Comparisons included coverage to the planning target volume (PTV) of the primary (PTV66) and subclinical disease (PTV54). We also compared the ability of both techniques to respect the tolerance of critical structures.
The volume of PTV66 treated to >110% was less in 9 of the 13 patients in the WF-IMRT plan as compared to the HB-IMRT plan. The calculated mean volume receiving >110% for all patients planned with WF-IMRT was 9.3% (0.8%-25%) compared to 13.7% (2.7%-23.7%) with HB-IMRT (p = 0.09). The PTV54 volume receiving >110% of dose was less in 10 of the 13 patients planned with WF-IMRT compared to HB-IMRT. The mean doses to all critical structures except the larynx were comparable with each plan. The mean dose to the larynx was significantly less (p = 0.001), 18.7 Gy, with HB-IMRT compared to 47 Gy with WF-IMRT.
Regarding target volumes, acceptable plans can be generated with either WF-IMRT or HB-IMRT. WF-IMRT has an advantage if uncertainty at the match line is a concern, whereas HB-IMRT, particularly in cases not involving the base of tongue, can achieve much lower doses to the larynx.
采用调强放疗（IMRT）治疗的口咽癌通常采用单中心或半束技术（HB）进行治疗。IMRT仅用于照射原发肿瘤和上颈部，而下颈部则采用匹配的前向射束进行治疗。由于IMRT可以治疗整个靶区或全野（WF），本研究的主要目的是测试使用WF-IMRT进行病例计划的能力，同时获得优化的计划和可接受的剂量分布，并保护正常关键结构。
13例早期口咽癌患者分别采用HB-IMRT和WF-IMRT技术制定治疗计划。如果计划符合放射治疗肿瘤学组协议H0022的计划指南（定义的或轻微违规的），则认为该计划是可接受的。比较内容包括对原发灶（PTV66）和亚临床病灶（PTV54）计划靶区（PTV）的覆盖情况。我们还比较了两种技术保护关键结构耐受剂量的能力。
与HB-IMRT计划相比，13例患者中有9例采用WF-IMRT计划时，接受大于110%剂量照射的PTV66体积更小。所有采用WF-IMRT计划的患者，计算得出接受大于110%剂量照射的平均体积为9.3%（0.8%-25%），而采用HB-IMRT计划的患者为13.7%（2.7%-23.7%）（p = 0.09）。与HB-IMRT计划相比，13例采用WF-IMRT计划的患者中有10例接受大于110%剂量照射的PTV54体积更小。除喉之外，各计划对所有关键结构的平均剂量相当。与WF-IMRT计划的47 Gy相比，HB-IMRT计划对喉的平均剂量显著更低（p = 0.001），为18.7 Gy。
关于靶区体积，采用WF-IMRT或HB-IMRT均可生成可接受的计划。如果匹配线处的不确定性是一个问题，WF-IMRT具有优势，而HB-IMRT，特别是在不涉及舌根的病例中，可使喉接受的剂量低得多。
