The Impact of Maximum Rectal Distention and Tandem Angle on Rectal Dose Delivered in 3D Planned Gynecologic High Dose–Rate Brachytherapy

Abstract

Objective Computed tomography (CT)-based treatment planning for cervical cancer has allowed investigation into the volumetric radiation dose delivered to the rectum. The goal of intracavitary brachytherapy is to maximize the tumor dose while decreasing the dose to normal tissue like the rectum. We investigated the effects of tandem angle and maximum rectal distention on rectal dose delivered in HDR brachytherapy for locally advanced cervical cancer. Methods and Materials Between July 2007 and January 2010, 97 brachytherapy treatment planning CT scans from the first and last implant of 51 patients with locally advanced cervical cancer were reviewed. The rectum was manually contoured from the ischial tuberosity to the bottom of the sacroiliac joint. The maximum rectal distention was determined by measuring the largest anterior-posterior diameter of the rectum superior to the tandem ring and inferior to the end of the applicator. A volumetric measurement of the maximum and mean rectal dose, dose to 2cc (D2cc), dose to 1cc (D1cc) of the rectum was calculated. The tandem angle and the ICRU rectal point were recorded, and a dose volume histogram was referenced. Results The mean maximum rectal distention was 3.01cm. The mean D1cc, D2cc, mean rectal dose, maximum rectal dose, and ICRU rectal dose were 3.03 Gy, 2.78 Gy, 4.19 cGy, 1.40 cGy, and 2.99 Gy per treatment, respectively. In a multivariate analysis controlling for surface area, tandem angle, and body mass index (BMI), there was a significant increase in D2cc with increasing rectal distention (P=.016). There were no significant findings when observing the effects of tandem angle on D2cc. Conclusion Rectal distention significantly impacts D2cc delivered in HDR brachytherapy. In contrast, tandem angle does not. Concerted efforts to decrease rectal distention should be considered during treatment planning and delivery.

The usefulness of fleet rectal enemas on high-dose-rate intracavitary cervical cancer brachytherapy. A prospective trial

“…Then we started a parallel project with the aim to evaluate the dosimetric value of rectal enemas during modern fractionated therapy in two HDR gynecological brachytherapy settings, the postoperative VCB [ 14 ] and radical brachytherapy for cervical cancer. Previous studies showing a positive correlation between rectal distension and DVH rectal parameters, either in VCB [ 11 , 13 , 16 ] or in radical cervical cancer treatment [ 10 ] are the background for our project. During VCB it has been demonstrated that gas pocket evacuation reduced rectal volume by a third on average, which lead to reductions in DVH parameters [ 13 ].…”

“…In the opposite way, the use of rectal contrast has been linked to a 20% increase statistically on the rectal volume, which also translated to an increase in all DVH parameters analyzed [ 11 ]. A study into cervical cancer at the University of California has shown a significant D 2cc increase of 6.58 Gy for each additional centimeter of distension [ 10 ].…”

“…Nevertheless, the similar doses obtained by both experimental conditions suggest that differences in rectal toxicity would be hard to demonstrate. Other factors that can modify DVH doses, such as the applicator position [ 10 , 25 ], the body mass index [ 26 , 27 ], or the bladder volume [ 28 ] were out of the scope of the study. These factors have not been extensively studied and results are contradictory among the few published reports.…”

“…The long-lasting low-dose-rate (LDR) applications with several hospital rest days avoid rectal discharge for applications lasting longer than two days [ 9 ], and rectal enemas prior to the procedure have been advised [ 10 ]. Rectal evacuation was also recommended for LDR vaginal cuff brachytherapy (VCB) [ 9 ].…”

The clinical impact of removing rectal gas on high‐dose‐rate brachytherapy dose distributions for gynecologic cancers

“…Lim et al. evaluated 97 intracavitary brachytherapy implants for 51 patients with locally advanced cervical cancer and reported the impact of the tandem angle and rectal distension on rectal DVH 13 . The authors reported an increased rectal D2cm 3 of 6.58Gy with each additional centimeter of distention, however the tandem angle did not correlate with rectal dose.…”