Dadkhah Hossein, Kim Yusung, Wu Xiaodong, Flynn Ryan T
Department of Biomedical Engineering, University of Iowa, 1402 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242.
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
Med Phys. 2015 Nov;42(11):6579-88. doi: 10.1118/1.4933244.
To present a novel brachytherapy technique, called multihelix rotating shield brachytherapy (H-RSBT), for the precise angular and linear positioning of a partial shield in a curved applicator. H-RSBT mechanically enables the dose delivery using only linear translational motion of the radiation source/shield combination. The previously proposed approach of serial rotating shield brachytherapy (S-RSBT), in which the partial shield is rotated to several angular positions at each source dwell position [W. Yang et al., "Rotating-shield brachytherapy for cervical cancer," Phys. Med. Biol. 58, 3931-3941 (2013)], is mechanically challenging to implement in a curved applicator, and H-RSBT is proposed as a feasible solution.
A Henschke-type applicator, designed for an electronic brachytherapy source (Xoft Axxent™) and a 0.5 mm thick tungsten partial shield with 180° or 45° azimuthal emission angles and 116° asymmetric zenith angle, is proposed. The interior wall of the applicator contains six evenly spaced helical keyways that rigidly define the emission direction of the partial radiation shield as a function of depth in the applicator. The shield contains three uniformly distributed protruding keys on its exterior wall and is attached to the source such that it rotates freely, thus longitudinal translational motion of the source is transferred to rotational motion of the shield. S-RSBT and H-RSBT treatment plans with 180° and 45° azimuthal emission angles were generated for five cervical cancer patients with a diverse range of high-risk target volume (HR-CTV) shapes and applicator positions. For each patient, the total number of emission angles was held nearly constant for S-RSBT and H-RSBT by using dwell positions separated by 5 and 1.7 mm, respectively, and emission directions separated by 22.5° and 60°, respectively. Treatment delivery time and tumor coverage (D90 of HR-CTV) were the two metrics used as the basis for evaluation and comparison. For all the generated treatment plans, the D90 of the HR-CTV in units of equivalent dose in 2 Gy fractions (EQD2) was escalated until the D2cc (minimum dose to hottest 2 cm3) tolerance of either the bladder (90 Gy3), rectum (75 Gy3), or sigmoid colon (75 Gy3) was reached.
Treatment time changed for H-RSBT versus S-RSBT by -7.62% to 1.17% with an average change of -2.8%, thus H-RSBT treatments times tended to be shorter than for S-RSBT. The HR-CTV D90 also changed by -2.7% to 2.38% with an average of -0.65%.
H-RSBT is a mechanically feasible delivery technique for use in the curved applicators needed for cervical cancer brachytherapy. S-RSBT and H-RSBT were clinically equivalent for all patients considered, with the H-RSBT technique tending to require less time for delivery.
介绍一种新型近距离放射治疗技术，称为多螺旋旋转屏蔽近距离放射治疗（H-RSBT），用于在弯曲施源器中精确进行部分屏蔽的角度和线性定位。H-RSBT仅通过辐射源/屏蔽组合的线性平移运动就能实现剂量输送。先前提出的串行旋转屏蔽近距离放射治疗（S-RSBT）方法，即在每个源驻留位置将部分屏蔽旋转到几个角度位置[W. Yang等人，“宫颈癌的旋转屏蔽近距离放射治疗”，《物理医学与生物学》58，3931 - 3941（2013）]，在弯曲施源器中实施具有机械挑战性，因此提出H-RSBT作为一种可行的解决方案。
提出一种Henschke型施源器，专为电子近距离放射治疗源（Xoft Axxent™）和厚度为0.5毫米的钨部分屏蔽设计，其方位发射角为180°或45°，天顶角为116°不对称。施源器的内壁包含六个均匀间隔的螺旋键槽，这些键槽根据施源器内的深度严格定义部分辐射屏蔽的发射方向。屏蔽在其外壁上有三个均匀分布的突出键，并与源相连，使其能够自由旋转，从而源的纵向平移运动传递到屏蔽的旋转运动。针对五名具有不同高危靶区体积（HR-CTV）形状和施源器位置的宫颈癌患者，生成了具有180°和45°方位发射角的S-RSBT和H-RSBT治疗计划。对于每位患者，通过分别使用间隔5毫米和1.7毫米的驻留位置以及分别间隔22.5°和60°的发射方向，使S-RSBT和H-RSBT的发射角总数几乎保持恒定。治疗输送时间和肿瘤覆盖率（HR-CTV的D90）是用作评估和比较基础的两个指标。对于所有生成的治疗计划，将HR-CTV的D90以2 Gy分次等效剂量（EQD2）为单位逐步增加，直到达到膀胱（90 Gy3）、直肠（75 Gy3）或乙状结肠（75 Gy3）的D2cc（最热2 cm3的最小剂量）耐受值。
H-RSBT与S-RSBT相比，治疗时间变化为-7.62%至1.17%，平均变化为-2.8%，因此H-RSBT治疗时间往往比S-RSBT短。HR-CTV D90也变化了-2.7%至2.38%，平均为-0.65%。
H-RSBT是一种机械可行的输送技术，可用于宫颈癌近距离放射治疗所需的弯曲施源器。对于所有考虑的患者，S-RSBT和H-RSBT在临床上等效，且H-RSBT技术往往需要更少的输送时间。
