High spatial and high contrast resolution images are important for accurate post-implant dosimetry in prostate low-dose-rate (LDR) brachytherapy. Compared to CT, MRI offers excellent soft tissue contrast and exquisite depiction of prostate subglandular and surrounding anatomy. However, MRI is limited in its signal-to-noise ratio (SNR) (and therefore spatial resolution) and inability to directly visualize the radioactive seeds. Using a combination of a positive MRI contrast marker technology [1], an endorectal coil (ERC), and an optimized imaging protocol, we recently demonstrated that it is possible to identify both the anatomy and the radioactive seeds (via positive MRI contrast markers) with MR images from a single acquisition [2]. In this work, we present our initial experience of acquiring prostate brachytherapy post-implant MR images without an ERC and compare the images to those acquired with an ERC in the same patients. Imaging without an ERC obviously incurs an SNR loss but has several potential advantages including increased clinical throughput, better patient tolerance, and lower cost.

This white paper recommends the standardization (content and presentation order) of several "key components" of the radiation therapy prescription to facilitate accurate communication between radiation therapy care providers. The rationale, other similar efforts, and detailed considerations are described. In brief, the Task Force recommends that the prescription's "elements" include: treatment site, method of delivery, dose per fraction, total number of fractions, total dose (eg, right breast, tangent photons, 267 cGy * 16 = 4272 cGy). A similar formalism is recommended for brachytherapy (eg, cervix, Ir-192 brachytherapy, 600cGy * 5 = 3000 cGy) and other modalities. The white paper also considers future directions for other items such as the simulation order, treatment planning objectives, prescription point or volume, treatment schedule, localization imaging, laboratory monitoring, concurrent chemotherapy, patient instructions for treatment, etc. The intent of this white paper is to facilitate accurate communication among providers to support safe practice as well as to guide vendors in product development that is consistent with this standard prescription.

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.

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.

Purpose: To investigate the dosimetric impact of the heterogeneity dose calculation Acuros (Transpire Inc., Gig Harbor, WA), a grid-based Boltzmann equation solver (GBBS), for brachytherapy in a cohort of cervical cancer patients.Methods and Materials: The impact of heterogeneities was retrospectively assessed in treatment plans for 26 patients who had previously received Ir-192 intracavitary brachytherapy for cervical cancer with computed tomography (CT)/magnetic resonance-compatible tandems and unshielded colpostats. The GBBS models sources, patient boundaries, applicators, and tissue heterogeneities. Multiple GBBS calculations were performed with and without solid model applicator, with and without overriding the patient contour to 1 g/cm(3) muscle, and with and without overriding contrast materials to muscle or 2.25 g/cm(3) bone. Impact of source and boundary modeling, applicator, tissue heterogeneities, and sensitivity of CT-to-material mapping of contrast were derived from the multiple calculations. American Association of Physicists in Medicine Task Group 43 (TG-43) guidelines and the GBBS were compared for the following clinical dosimetric parameters: Manchester points A and B, International Commission on Radiation Units and Measurements (ICRU) report 38 rectal and bladder points, three and nine o'clock, and (D2cm3) to the bladder, rectum, and sigmoid.Results: Points A and B, D-2 cm(3) bladder, ICRU bladder, and three and nine o'clock were within 5% of TG-43 for all GBBS calculations. The source and boundary and applicator account for most of the differences between the GBBS and TG-43 guidelines. The D-2cm3 rectum (n = 3), D-2cm3 sigmoid (n = 1), and ICRU rectum (n = 6) had differences of >5% from TG-43 for the worst case incorrect mapping of contrast to bone. Clinical dosimetric parameters were within 5% of TG-43 when rectal and balloon contrast were mapped to bone and radiopaque packing was not overridden.Conclusions: The GBBS has minimal impact on clinical parameters for this cohort of patients with unshielded applicators. The incorrect mapping of rectal and balloon contrast does not have a significant impact on clinical parameters. Rectal parameters may be sensitive to the mapping of radiopaque packing. (C) 2012 Elsevier Inc.

The purpose of this study was to compare the dose distribution of Iridium-192 ((192)Ir) pulsed-dose-rate (PDR) brachytherapy to that of Cesium-137 ((137)Cs) low-dose-rate (LDR) brachytherapy around mini-ovoids and an intrauterine tandem. Ten patient treatment plans were selected from our clinical database, all of which used mini-ovoids and an intrauterine tandem. A commercial treatment planning system using AAPM TG43 formalism was used to calculate the dose in water for both the (137)Cs and (192)Ir sources. For equivalent system loadings, we compared the dose distributions in relevant clinical planes, points A and B, and to the ICRU bladder and rectal reference points. The mean PDR doses to points A and B were 3% +/- 1% and 6% +/- 1% higher than the LDR doses, respectively. For the rectum point, the PDR dose was 4% +/- 3% lower than the LDR dose, mainly because of the (192)Ir PDR source anisotropy. For the bladder point, the PDR dose was 1% +/- 4% higher than the LDR dose. We conclude that the PDR and LDR dose distributions are equivalent for intracavitary brachytherapy with a tandem and mini-ovoids. These findings will aid in the transfer from the current practice of LDR intracavitary brachytherapy to PDR for the treatment of gynecologic cancers.