目的:在头颈部(H&N)放疗中,临床靶区(CTV)延伸至患者皮肤是很常见的。添加设置不确定性和交付的余量会创建超出患者表面的计划目标体积(PTV)。这可能导致过多的注量被递送到积聚区域并因此递送到皮肤。本研究评估了将CTV扩展到皮肤的反向计划H&N放射治疗时使用的四种不同的计划方法。研究的目的是确定哪种计划方法具有出色的计划质量。
方法:使用四种计划方法对10名具有皮肤轮廓的CTV的H&N癌症患者进行逆向计划。比较的计划方法是:将优化的PTV从皮肤表面裁剪5.0、3.0和0.0mm,以及虚拟推注方法。对于每种规划方法,分析了皮肤表面的注量增加。比较了CTV覆盖率和皮肤剂量。通过在主轴上施加±3.0mm的等中心偏移来评估计划稳健性。
结果:在距皮肤表面0.0mm处裁剪PTV的计划方法会导致积聚区域的通量增加。接受98%处方剂量的CTV平均体积为89.6%±3.4%,91.6%±2.4%,裁剪5.0、3.0和0.0mm时,为93.5%±1.7%,分别,虚拟推注法为93.4%±2.1%。在裁剪5.0mm时,引入计划不确定性对CTV覆盖范围的影响最大。当考虑计划不确定性时,裁剪5.0、3.0mm、并且虚拟推注方法具有在±0.3%内的相同平均皮肤剂量。
结论:这项研究表明,虚拟推注计划方法不会导致患者表面的注量增加,提高了CTV的覆盖率,并且对设置和患者解剖结构的变化最强大。
OBJECTIVE: In radiotherapy of the head and neck (H&N) it is common for the clinical target volume (CTV) to extend to the patient\'s skin. Adding a margin for set-up uncertainty and delivery creates a planning target volume (PTV) that extends beyond the patient surface. This can result in excessive fluence being delivered to the build-up region and therefore the skin. This study evaluates four different planning methods used when inverse-planning H&N radiotherapy treatments with CTV extending to the skin. The aim of the study was to determine which planning method gives superior plan quality.
METHODS: Ten H&N cancer patients with a CTV contoured to the skin were inverse-planned using four planning methods. The planning methods compared were: cropping the optimization PTV back from the skin surface by 5.0, 3.0, and 0.0 mm and a virtual bolus method. For each planning method, the increased fluence at the skin surface was analyzed. The CTV coverage and skin doses were compared. Plan robustness was evaluated by applying an isocenter shift of ±3.0 mm in the major axes.
RESULTS: The planning method cropping the PTV 0.0 mm from the skin surface results in an increased fluence in the build-up region. The average volume of CTV receiving 98% of the prescription dose was 89.6% ± 3.4%, 91.6% ± 2.4%, and 93.5% ± 1.7% when cropped 5.0, 3.0, and 0.0 mm, respectively, and 93.4% ± 2.1% for the virtual bolus method. Introducing plan uncertainty affects CTV coverage the most when cropping 5.0 mm. When plan uncertainties are considered the methods of cropping 5.0, 3.0 mm, and the virtual bolus method have the same average skin dose within ±0.3%.
CONCLUSIONS: This study shows that a virtual bolus planning method results in no increased fluence at the patient\'s surface, improves CTV coverage, and is the most robust to changes in setup and patient anatomy.