Leung T W, Wong V Y, Wong C M, Tung S Y, Tsang A, Lowes M, Au M Y, Chan C S, Sze W K, Leung L C, O S K
Department of Clinical Oncology, Tuen Mun Hospital, Tsing, Hong Kong.
Clin Oncol (R Coll Radiol). 1998;10(4):231-6. doi: 10.1016/s0936-6555(98)80006-x.
High dose rate (HDR) interstitial tongue brachytherapy is a new treatment modality. This study describes important technical details required for its successful use. Thirteen patients with carcinoma of the oral tongue were treated solely with interstitial brachytherapy using HDR remote afterloading techniques during the years 1994-1997. The afterloading catheters were positioned by the submandibular approach with the assistance of a template set. Custom-made mandibular lead shields were inserted prior to treatment. Special reusable Tuen Mun Hospital (TMH) lead buttons were made for improved radiation protection. The median dose given was 55 Gy in ten fractions over 6 days. The interfraction interval was 7 hours for the first seven patients treated and was extended to 8 hours for the other six. Shrinking field techniques were employed and the treatment length of the last fraction was reduced by 5 mm. Commencing with the second patient treated with double planar implants, the medial plane was treated with eight fractions while the lateral plane received ten fractions. To reduce further the potential risk of tract seeding, additional coverage to the implantation tracts was given for the last four patients, with the resultant isodose curves resembling a 'comb rake/brush'. The mean and median measured doses on the inner face of the mandibular shields were 113% and 93% of the reference dose respectively (range 77-247). The dose to the corresponding sites on the gingival surface can be reduced by 75% if the 3 mm thick lead shield is placed successfully. With the use of the TMH button, the transmitted dose to the tissue in direct contact can be reduced by one-third. With the 'comb rake/brush' dose distribution, the high dose volume of the single planar implants could be reduced by 44%, compared with the low dose rate technique, if loading to just 5 mm short of the submandibular skin was required. The mean doses for the combination of eight double planar plus two single planar implants, and ten double planar implants, are on average 29% and 37% greater than the reference dose respectively. An 8% reduction in absolute dose in the region between the planes of the catheters would lead to an even greater magnitude of reduction in morbidity to late responding tissue. The prerequisite for the success of HDR interstitial implants is to develop a good technique in positioning the afterloading catheters and protection of the normal tissue. Its importance merits special attention if HDR remote afterloading interstitial tongue brachytherapy is to realize its full potential.
高剂量率（HDR）组织间舌部近距离放射治疗是一种新的治疗方式。本研究描述了其成功应用所需的重要技术细节。1994年至1997年间，13例口腔舌癌患者仅接受了使用HDR遥控后装技术的组织间近距离放射治疗。后装导管通过下颌下途径并借助模板定位。治疗前插入定制的下颌铅屏蔽。特制了可重复使用的屯门医院（TMH）铅按钮以改善辐射防护。给予的中位剂量为55 Gy，分10次，在6天内完成。前7例患者的分次间隔为7小时，后6例延长至8小时。采用缩野技术，最后一次分割的治疗长度减少5 mm。从第二例接受双平面植入的患者开始，内侧平面接受8次分割，外侧平面接受10次分割。为进一步降低种植道播散的潜在风险，对最后4例患者的植入道给予额外覆盖，所得等剂量曲线类似“梳齿/刷子”。下颌屏蔽内表面的平均测量剂量和中位测量剂量分别为参考剂量的113%和93%（范围77 - 247）。如果成功放置3 mm厚的铅屏蔽，牙龈表面相应部位的剂量可降低75%。使用TMH按钮，直接接触组织的透射剂量可降低三分之一。与低剂量率技术相比，如果需要加载至距下颌下皮肤仅5 mm处，采用“梳齿/刷子”剂量分布时，单平面植入的高剂量体积可减少44%。8个双平面加2个单平面植入组合以及10个双平面植入的平均剂量分别比参考剂量平均高29%和37%。导管平面之间区域的绝对剂量降低8%将导致晚期反应组织的发病率降低幅度更大。HDR组织间植入成功的前提是开发一种良好的后装导管定位技术和正常组织保护技术。如果HDR遥控后装组织间舌部近距离放射治疗要充分发挥其潜力，其重要性值得特别关注。
