BACKGROUND:Local tumor control (LC), overall survival (OS), symptom palliation, and late toxicity for patients with locally recurrent anorectal cancer treated with a computed tomography (CT)-guided interstitial brachytherapy implant were examined.METHODS:The medical records of 20 consecutive patients who had received interstitial brachytherapy for locally recurrent anorectal cancer from 2000 through 2012 were reviewed. Seventeen patients (85 %) had rectal cancer and three had anal cancer [median follow-up time for living patients, 23 months (range 13-132)]. Brachytherapy was used most commonly at the second pelvic recurrence (n = 13, 65 %). The implant dose was prescribed to 80 Gy to a 1-cm margin or 120 Gy to 100 % of the gross tumor volume. Endpoints were OS, LC, toxicity, and symptom palliation rate, all calculated from the time of implant.RESULTS:The actuarial 1-year rates of LC and OS were 80 and 95 %, respectively. At presentation, 17 patients (85 %) had symptoms related to the treated tumor which were palliated in 13 patients (76 %) at a median time of 3 months (range 1-6); palliation was permanent for seven patients (54 %), and the other six patients lost palliation after a median 8 months (range 5-17). One patient experienced a grade 3 late complication requiring a stent for hydronephrosis; five had grade 2 toxicity, and four had grade 1 toxicity.CONCLUSIONS:CT-guided interstitial brachytherapy for locally recurrent anorectal tumors produced durable tumor control and long-term survival, with effective palliation and minimal long-term morbidity.

Accurate assessment of normal tissue doses is critical in 3D image-based brachytherapy. The purpose of this study was to determine if normal tissue motion in the time interval between imaging and treatment impacts the dose to critical organs. Fourteen patients enrolled from December 2012 to August 2013 on a prospective study evaluating image-based brachytherapy for cervical cancer with available 3D image reconstruction in all cardinal planes were included in this analysis. Each patient underwent a non-contrast pelvic CT and MRI following placement of the applicator and prior to initiation of pulsed-dose rate brachytherapy. The average time elapsed between CT and MRI was 87 minutes (range 43-151 minutes). The external contours of the normal organs at risk (OARs), including bladder, rectum, and sigmoid, were delineated on both image sets in Oncentra brachytherapy planning system. The minimum dose delivered to the most irradiated 2 cm3 (D2cc) and 1 cm3 (D1cc) for all OARs was recorded on each image set. The D2cc volume for each OAR was then converted to a 3D structure. The hottest point within the D2cc volume was plotted on a DICOM coordinate system, with the origin of the coordinate system designated as the intersection between the tandem and the top of the ovoids or cylinder. The distance formula was used to calculate each point's change in position between image sets. Nine patients were treated with a tandem and ovoid applicator and five patients were treated with a tandem and cylinders. The average difference in D2cc bladder between the two scans was 2.4 Gy (range 0.1-6 Gy); the difference in D1cc bladder was 2.8 Gy (range 0.09-8.0 Gy). The average displacement of the hottest point within the bladder D2cc volume was 8.3 mm (range 1.2-20.0 mm). For the rectum and sigmoid, the average difference in D2cc dose was 1.8 Gy (range 0.4-7.4 Gy) and 1.0 Gy (range 0.5-3.5 Gy), while the average difference in D1cc dose was 2.1 Gy (range 0.3-8.5 Gy) and 1.1 Gy (0.07-4.2 Gy), respectively. The average displacement was 11.7 mm (range 2.9-56.4 mm) for the rectum and 11.2 mm (range 2.3-28.1 mm) for the sigmoid. For the sigmoid and bladder, there was no evidence that imaging modality impacted the OAR contour, since higher doses were equally likely to be observed on the CT or MRI image set. However, the rectal D2cc and D1cc were significantly higher on CT images as compared to MRI, suggesting that the use of different imaging modalities at each time point may limit accurate assessment of the effects of organ motion on rectal dose in this study. Internal organ motion impacts the dose and volume of critical structures treated during brachytherapy. Efforts to limit organ motion and reduce the time between imaging and treatment will improve accurate assessment of normal tissues doses.

Current commercially available MRI compatible tandem and ovoid sets used for cervical cancer brachytherapy do not have ovoid shields, which reduce the dose to the bladder and rectum. Shields have been omitted from CT and MRI compatible applicators due to artifact on CT and lack of MRI compatibility. We designed a novel MRI compatible applicator with movable shields called the Fletcher CT/MR Shielded Applicator and performed a dosimetric comparison to determine the impact of the shields on dose to critical structures. Twelve patients undergoing definitive radiation therapy on a prospective protocol at The University of Texas MD Anderson Cancer Center for stage >/= IB2 cervical cancer were treated with external beam radiation therapy followed by intracavitary pulsed dose rate brachytherapy (ICBT) with the Fletcher CT/MR Shielded Applicator for one of two insertions. Each patient had a pelvic CT and MRI with the applicator in place. The applicator was then reconstructed on the MRI. The bladder, rectum, and sigmoid were contoured for all twelve patients and a high-risk clinical target volume (HR-CTV) was contoured for two of the patients. A film based treatment plan was created for each patient and then optimized based on CT and/or MRI at the discretion of the treating physician. The following DVH parameters were analyzed; D2cc, 1cc, 0.1cc to bladder, rectum, and sigmoid as well D90 for the HR-CTV. A paired t-test was than used to compare the above DVH parameters with and without the shields modeled in the reconstructed applicator. Six patients (50%) were stage IB2, three (25%) stage IIA, and three (25%) stage IIB. For bladder the mean D2cc was reduced by 1.4% (1576 to 1555 cGy, p=0.0003), D1cc by 1.2% (1761 to 1739 cGy, p = 0.0003) and D0.1cc by 0.6% (2218 cGy to 2205 cGy, p = 0.0191) with the shield in place. For rectum the mean D2cc was reduced by 6.2% (818 to 767 cGy, p = <0.0001), D1cc by 6.5% (892 to 834 cGy, p = <0.0001) and D0.1cc by 7.9% (1049 to 966 cGy, p = 0.0068) with the shield in place. There was not a significant reduction in the dose to sigmoid. For the two patients with HR-CTVs the mean D90 without and with the shield was 2183 cGy and 2176 cGy, respectively. The Fletcher CT/MR shielded applicator significantly reduces the dose to the bladder and rectum with the largest and most significant reductions in the rectum. With only two patients with a HR-CTV delineated there appears to be minimal effect on dose to tumor although a larger number of patients will be required to confirm this.