Noyes W R, Peters N E, Thomadsen B R, Fowler J F, Buchler D A, Stitt J A, Kinsella T J
Department of Human Oncology, University of Wisconsin Medical School, Madison.
Int J Radiat Oncol Biol Phys. 1995 Jan 1;31(1):79-86. doi: 10.1016/0360-3016(94)00401-6.
Different treatment techniques are used in high dose rate (HDR) remote afterloading intracavitary brachytherapy for uterine cervical cancer. We have investigated the differences between "optimized" and "nonoptimized" therapy using both a tandem and ring (T/R) applicator, and a tandem and ovoids (T/O), applicator.
HDR afterloading brachytherapy using the Madison System for Stage IB cervical cancer was simulated for 10 different patients using both a T/R applicator and a T/O applicator. A treatment course consists of external beam irradiation and five insertions of HDR afterloading brachytherapy. Full dosimetry calculations were performed at the initial insertion for both applicators and used as a reference for the following four insertions of the appropriate applicator. Forty dosimetry calculations were performed to determine the dose delivered to Point M (similar to Point A), Point E (obturator lymph nodes), vaginal surface, bladder, and rectum. "Optimized" doses were specified to Point M and to the vaginal surface. "Nonoptimized" doses were specified to Point M only. Using the linear-quadratic equation, calculations have been performed to convert the delivered dose using HDR to the biologically equivalent doses at the conventional low dose rate (LDR) at 0.60 Gy/h.
Major differences between "optimized" and "nonoptimized" LDR equivalent doses were found at the vaginal surface, bladder, and rectum. Overdoses at the vaginal surface, bladder, and rectum were calculated to be 208%, nil, and 42%, respectively, for the T/R applicator with "nonoptimization." However, for the T/O applicator, the overdoses were smaller, being nil, 32%, and 27%, respectively, with "nonoptimization."
Doses given in high dose rate intracavitary brachytherapy border on tissue tolerance. "Optimization" of either applicator decreases the risk of a dose that may have potential for complications. Optimization of a tandem and ovoids best ensures that the doses are not diminished at the treatment sites, and that the potential for overdose is reduced.
高剂量率（HDR）远程后装腔内近距离放射治疗宫颈癌采用不同的治疗技术。我们使用串联和环形（T/R）施源器以及串联和卵圆形（T/O）施源器，研究了“优化”治疗与“非优化”治疗之间的差异。
使用麦迪逊系统对10例IB期宫颈癌患者进行HDR后装近距离放射治疗模拟，分别使用T/R施源器和T/O施源器。一个疗程包括外照射和五次HDR后装近距离放射治疗插入。对两种施源器在初次插入时进行了完整的剂量学计算，并将其用作后续四次相应施源器插入的参考。进行了40次剂量学计算，以确定输送到M点（类似于A点）、E点（闭孔淋巴结）、阴道表面、膀胱和直肠的剂量。向M点和阴道表面指定“优化”剂量。仅向M点指定“非优化”剂量。使用线性二次方程，进行计算以将使用HDR输送的剂量转换为传统低剂量率（LDR）0.60 Gy/h时的生物等效剂量。
在阴道表面、膀胱和直肠处发现“优化”和“非优化”LDR等效剂量之间存在主要差异。对于“非优化”的T/R施源器，阴道表面、膀胱和直肠的过量剂量分别计算为208%、无过量和42%。然而，对于T/O施源器，“非优化”时过量剂量较小，分别为无过量、32%和27%。
高剂量率腔内近距离放射治疗给予的剂量接近组织耐受极限。两种施源器的“优化”均降低了可能引发并发症的剂量风险。串联和卵圆形施源器的优化最能确保治疗部位的剂量不减少，并降低过量照射的可能性。
