Neoadjuvant radiation therapy for the management of myoepithelial carcinoma of the upper extremity.

Myoepithelial tumors of the soft tissue are a rare tumor displaying myoepithelial elements and lacking obvious ductal differentiation. The rarity of these precludes any evidence-based consensus regarding optimal management. Nevertheless, the current approach to these lesions begins with amputation or complete excision. The efficacy of neoadjuvant or adjuvant radiation therapy or chemotherapy has not been established. Here, we present the first report to the authors' knowledge of neoadjuvant radiation therapy for the treatment of this rare soft tissue neoplasm and review the management and outcomes of published cases of myoepithelial carcinoma. A patient with a soft tissue myoepithelial carcinoma that declined both amputation and chemotherapy was treated with neoadjuvant radiation therapy and wide surgical excision followed by a brachytherapy boost to the resected tumor bed. Neoadjuvant radiation therapy resulted in an excellent response with extensive treatment-related changes consisting predominantly of fibrosis, hyalinization and hemorrhage and only 10% residual viable myoepithelial carcinoma present in the surgical specimen.

Correlation of total reference air-kerma (TRAK) to prescription isodose surface volume in vaginal cylinder high-dose-rate brachytherapy.

PURPOSE: The purpose of this technical note was to investigate correlation of total reference air-kerma (TRAK) with volume enclosed by the prescription isodose surface in vaginal cylinder high-dose-rate (HDR) brachytherapy. MATERIAL AND METHODS: Treatment plans of 175 gynecological cancer patients treated at our institution with iridium-192 (192Ir) HDR brachytherapy using a single-channel vaginal cylinder applicator were retrospectively reviewed. Applicator size in diameter ranged from 20 mm to 40 mm. Treatment length ranged from 30 mm to 90 mm (median, 50 mm). Brachytherapy fractional dose was 5 Gy (DoseRef) prescribed to 5 mm distance from cylinder surface. Parameters TRAK (cGy), source activity during treatment (Ci), total treatment time (s), and prescription isodose surface volume ISVRef (cm3) were recorded from individual treatment plans. In each case, vaginal tissue volume (VVT) enclosed by prescription isodose was calculated by subtracting cylinder volume enclosed by the prescription isodose from ISVRef. RESULTS: Total reference air-kerma correlated with the total volume enclosed by the prescription isodose via ISVRef = 4768 × (TRAK/DoseRef)1.47. TRAK related linearly to the volume of vaginal tissue enclosed by the prescription dose via VVT = ((138.3 × TRAK) - 8.2). Secondarily, TRAK related to the treatment time through time (s) = 882 (s/cGy) × TRAK (cGy), where 882 is (1/air-kerma strength) for 10 Ci apparent activity of 192Ir source. CONCLUSIONS: The correlation of TRAK to the vaginal tissue volume encompassed by the prescription dose surface yields a useful predictive equation. The TRAK treatment time relationship enables quick verification of planned treatment time by knowing TRAK in any HDR brachytherapy application.

Hybrid tandem and ovoids brachytherapy in locally advanced cervical cancer: impact of dose and tumor volume metrics on outcomes.

PURPOSE: To report the impact of dose and tumor volume metrics at brachytherapy on outcomes for locally advanced cervical cancer treated with tandem and ovoids intracavitary/interstitial brachytherapy. MATERIAL AND METHODS: FIGO stage IB1-IIIB locally advanced cervical cancer treated with intracavitary/interstitial brachytherapy via a tandem and ovoids hybrid applicator were analyzed. Median high-risk clinical target volume (HR-CTV), rate of tumor volume reduction, EQD2 D90, organ at risk doses, and outcomes were recorded. Univariable and multivariable Cox regression was applied for survival analysis, and logistic regression was used for toxicity analysis. RESULTS: Seventy-one patients were identified. Median follow-up was 24.9 months, with a 2-year local control of 83.6%, loco-regional control of 72.0%, and overall survival of 88.6%. Median HR-CTV D90 was 87.4 Gy (IQR = 85.7-90.2). Median HR-CTV D90 > 90 Gy10 showed a trend toward improved local control (LC) (p = 0.19). Median HR-CTV was 37.9 cm3, and median V100 was 86.5%. A median HR-CTV of ≥ 40 cm3 demonstrated worse loco-regional control (LRC) (p = 0.018) and progression-free survival (p = 0.021). Two-year LC and LRC for stage IIB patients with a median HR-CTV < 40 cm3 were significantly improved as compared to ≥ 40 cm3 at 100% and 71.8%, respectively (p = 0.019) and 100% and 56.5%, respectively (p = 0.001). However, this trend was not statistically significant for stage IIIB patients. Higher percent per day reduction in HR-CTV during brachytherapy showed improved LRC (p = 0.045). Four percent of patients experienced acute grade 3 genitourinary toxicity, 1% late grade 3 genitourinary and 1% late grade 3 gastrointestinal toxicity. CONCLUSIONS: Tandem and ovoids intracavitary/interstitial brachytherapy provides satisfactory outcomes with modest toxicity. Higher HR-CTV D90 coverage demonstrated a trend toward improved tumor control. Tumor volume based on median HR-CTV ≥ 40 cm3 at brachytherapy was prognostic for poor outcomes, even within initial FIGO stage groups warranting caution.

Optimal timing of radiotherapy in high risk prostate cancer: Do missed days matter?

INTRODUCTION: High-risk prostate cancer is associated with poorer overall survival (OS) and biochemical control compared to more favorable risk groups. External beam radiation therapy (EBRT) is widely used; however, outcomes data are limited with respect to time elapsed between diagnosis and initiation of EBRT. METHODS: The National Cancer Database was queried from 2004 to 2015 for patients diagnosed with high-risk adenocarcinoma of the prostate who received androgen deprivation therapy (ADT) and definitive EBRT. Logistic regression was utilized to determine covariates associated with missing EBRT treatments. OS was analyzed using multivariate cox proportional hazards models and propensity score matching. RESULTS: 9,610 patients met inclusion criteria with median follow-up of 40.6 months and median age of 72 years. Median PSA was 8.7 and median EBRT dose was 78 Gy. ADT was initiated at a median of 36 days and EBRT at a median of 63 days post-diagnosis. Median number of prolonged treatment days was 2.2. Black race (OR: 1.40; p < 0.01), treatment at a community clinic (OR: 1.32; p < 0.01), and living in an urban/densely populated area were associated with prolonged treatment. Time elapsed between ADT and EBRT > 74 days (HR: 1.20; p = 0.01) and prolonged treatment>3 days of EBRT (HR: 1.26; p = 0.005) were associated with an increased hazard of death. The 5-year OS was 79.6% and 82.9% for patients with prolonged treatment of 3 days or more of EBRT and those missing 3 days or less, respectively (p = 0.0006). CONCLUSION: In this hypothesis-generating study, prolonged treatment delays and missing three or more EBRT treatments was associated with poorer OS in patients with high-risk adenocarcinoma of the prostate.

A skin dose prediction model based on in vivo dosimetry and ultrasound skin bridge measurements during intraoperative breast radiation therapy.

PURPOSE: Using in vivo measurements from optically stimulated luminescence dosimeters (OSLDs) to develop and validate a prediction model for estimating the skin dose received by patients undergoing breast intraoperative radiation therapy (IORT). METHODS AND MATERIALS: IORT was performed using INTRABEAM-600 with spherical applicators placed in the lumpectomy cavity. Ultrasound skin bridge measurements were used to determine the applicator-to-skin distance, with OSLDs placed to measure the skin surface dose at the corresponding points. The OSLD response was calibrated for the 50 kVp INTRABEAM-600 output. Models were fit to describe the dose fall-off with increasing applicator-to-skin distance and the best fitting model was chosen for estimating skin dose. RESULTS: Twenty four patients with 25 lumpectomy cavities were included, and the average skin dose recorded was 1.18 Gy ± 0.88 Gy, ranging from 0.17 Gy to 4.77 Gy, with an average applicator-to-skin distance of 19.9 mm ± 5.1 mm. An exponential-plateau model was found to best describe the dose fall-off with a root-mean-square error of 0.73. This model was then validated prospectively using skin dose measurements from five consecutive patients. Validation measurements were well within the 95% prediction limits of the model, with a root-mean-square error of 0.52, showing that the prediction model accurately estimates skin dose using ultrasound skin bridge measurements. CONCLUSIONS: This prediction model constitutes a useful tool for estimating the skin dose received during breast lumpectomy IORT. The model and accompanying 95% confidence intervals can be used to establish a minimum allowable skin bridge distance, effectively limiting the maximum allowable skin dose.

Interstitial Surgical Cavity Sizing Applicators for the Treatment of the Breast Lumpectomy Cavity with Intraoperative Radiation Therapy.

Surgical cavity sizing applicators were developed for utilization prior to intraoperative radiation therapy (IORT) of the breast lumpectomy cavity with the Zeiss INTRABEAM (Carl Zeiss Meditec AG, Jena, Germany) device. The use of these applicators minimizes the number of sterilizations of the treatment applicator, which is currently limited to 100 sterilizations per applicator. This maximizes the number of patients who can be treated with each applicator, resulting in cost savings for the treating institution.

Continuous Activity Monitoring During Concurrent Chemoradiotherapy.

PURPOSE: To perform a prospective trial testing the feasibility and utility of acquiring activity data as a measure of health status during concurrent chemoradiotherapy. METHODS AND MATERIALS: Ambulatory patients who were planned for treatment with concurrent chemoradiotherapy with curative intent for cancers of the head and neck, lung, or gastrointestinal tract were provided with activity monitors before treatment initiation. Patients were asked to wear the devices continuously throughout the radiation therapy course. Step count data were downloaded weekly during radiation therapy and 2 and 4 weeks after radiation therapy completion. The primary objective was to demonstrate feasibility, defined as collection of step counts for 80% of the days during study subjects' radiation therapy courses. Secondary objectives included establishing step count as a dynamic predictor of unplanned hospitalization risk. RESULTS: Thirty-eight enrolled patients were treated with concurrent chemoradiotherapy. Primary diagnoses included head and neck cancer (n=11), lung cancer (n=13), and a variety of gastrointestinal cancers (n=14). Step data were collected for 1524 of 1613 days (94%) during patients' radiation therapy courses. Fourteen patients were hospitalized during radiation therapy or within 4 weeks of radiation therapy completion. Cox regression modeling demonstrated a significant association between recent step counts (3-day average) and hospitalization risk, with a 38% reduction in the risk of hospitalization for every 1000 steps taken each day (hazard ratio 0.62, 95% confidence interval 0.46-0.83, P=.002). Inferior quality of life scores and impaired performance status were not associated with increased hospitalization risk. CONCLUSION: Continuous activity monitoring during concurrent chemoradiotherapy is feasible and well-tolerated. Step counts may serve as powerful, objective, and dynamic indicators of hospitalization risk.

Dosimetric Evaluation of a Flexible Dual Balloon-Constructed Applicator in Treating Anorectal Cancer.

BACKGROUND AND PURPOSE: To assess the dosimetric flexibility of a dual balloon brachytherapy applicator developed for the treatment of anorectal lesions. MATERIALS AND METHODS: Different amounts of water were infused into the inner and outer balloon separately to study the asymmetrical distribution of the catheter, the radial distance of the active source channel to the inner surface of the global target volume , the space between the active source channels, and their dosimetric impact to target tissues and uninvolved rectum. RESULTS: Increasing inner balloon volume directly increased both the space between the active source channels and the radial distance of the active source channel to the inner surface of the global target volume. The space between the active source channels and the percentage of global target volume received 150% or more of the prescribed dose to target had a strong inverse correlation (-0.881/P = .007, -0.976/P = .001, respectively) with the radial distance of the active source channel to the inner surface of the global target volume. Conformity index, dose to 2 cm3 of rectum, and total reference air kerma were strongly correlated with the radial distance of the active source channel to the inner surface of the global target volume, with values of 0.952 (P = .001), 0.833 (P = .015), and 0.922 (P = .002), respectively. Percentage of global target volume received 150% or more of the prescribed dose was significantly correlated with the space between the active source channels (0.81/P = .022), and conformity index was strongly inversely correlated with the space between the active source channels (-0.833/P = .015). CONCLUSION: The dual balloon-constructed Anorectal Applicator offers a flexible way to adjust the distances of the active source positions to the target in relation to uninvolved rectal wall. This flexibility simplifies planning which results in a highly conformal dose distribution to the target lesion while minimizing dose to normal rectal tissue.

Model assessment of individual tumor control rate and adverse effects in comparing locally advanced cervical cancer treatment using intracavitary with and without interstitial brachytherapy.

PURPOSE: This study assessed the modeled probability of tumor control and organ at risk toxicities in locally advanced cervical cancer in patients treated by external beam radiation plus brachytherapy using intracavitary combined with interstitial brachytherapy (IC/IS) vs. intracavitary brachytherapy (IC) alone. MATERIAL AND METHODS: Twenty cervical cancer patients with a mean HR-CTV volume of 47.4 cm3 and a mean width of 54 mm were planned with both IC/IS and IC brachytherapy alone. A probit model was utilized to model 3-year (3-yr) local control rate (LC), 3-yr cancer specific survival rate (CSS), and the adverse effect (AE) of the organ at risk by using a modeled data set from multiple institutions. Modeling results were used to estimate the LC, CSS, and AE of the treatments in this study. RESULTS: Using the IC/IS technique, an EQD2 increase of 12.3 Gy to D90 (from 76.1 Gy to 88.3 Gy) of HR-CTV is expected to increase 3-yr LC and 3-yr CSS by 12.5%, and 11.0%, respectively. Comparing IC/IS to IC alone, the expected G2+ AE were 7.7% vs. 7.9% for the bladder, and 5.9% vs. 6.8% for the rectum. CONCLUSIONS: The IC/IS technique improved dose coverage to the HR-CTV without significantly increasing dose to 2 cm3 of the organ at risk (OAR) surrounding it. With different regimens of EBRT combined with BT, IC/IS can be used to increase the probability of LC and CSS, or decrease the risk of AE.

Do changes in interfraction organ at risk volume and cylinder insertion geometry impact delivered dose in high-dose-rate vaginal cuff brachytherapy?

PURPOSE: Within a multifraction high-dose-rate vaginal cuff brachytherapy course, we determined if individual variations in organ at risk (OAR) volume and cylinder insertion geometry (CIG) impacted dose and whether planned minus fractional (P - F) differences led to a discrepancy between planned dose and delivered dose. METHODS AND MATERIALS: We analyzed vaginal cuff brachytherapy applications from consecutive patients treated with three fractions of 5 Gy after each undergoing a planning CT and three repeat fractional CTs (fCTs). Rectal and bladder D2ccs and volumes were recorded in addition to the x (in relationship to midplane) and y (in relationship to the table) angles of CIG. Paired t-tests and multiple regression analyses were performed. RESULTS: Twenty-seven patients were identified. In comparing the planning CT vs. mean fCT rectal volumes, bladder volumes, x angles, and y angles, only bladder volume was significantly different (planned volume higher, t = 2.433, p = 0.017). The cumulative mean planned OAR D2cc vs. delivered D2cc was only significantly different for the bladder (planned dose lower, t = -2.025, p = 0.053). Regression analysis revealed planned rectal D2cc (p < 0.0003) and a positive (posterior) y insertion angle (p = 0.015) to significantly impact delivered rectal D2cc. Additionally, P - F rectal volume (p = 0.037) was significant in determining rectal delivered dose. CONCLUSIONS: A more posterior y angle of insertion was found to increase rectal D2cc leading us to believe that angling the vaginal cylinder anteriorly may reduce rectal dose without significantly increasing bladder dose. Although attention should be paid to OAR volume and CIG to minimize OAR dose, the clinical significance of P - F changes remains yet to be shown.

Bone marrow-derived stromal cell therapy in cirrhosis: clinical evidence, cellular mechanisms, and implications for the treatment of hepatocellular carcinoma.

Current treatment options for hepatocellular carcinoma (HCC) are often limited by the presence of underlying liver disease. In patients with liver cirrhosis, surgery, chemotherapy, and radiation therapy all carry a high risk of hepatic complications, ranging from ascites to fulminant liver failure. For patients receiving radiation therapy, cirrhosis dramatically reduces the already limited radiation tolerance of the liver and represents the most important clinical risk factor for the development of radiation-induced liver disease. Although improvements in conformal radiation delivery techniques have improved our ability to safely irradiate confined areas of the liver to increasingly higher doses with excellent local disease control, patients with moderate-to-severe liver cirrhosis continue to face a shortage of treatment options for HCC. In recent years, evidence has emerged supporting the use of bone marrow-derived stromal cells (BMSCs) as a promising treatment for liver cirrhosis, with several clinical studies demonstrating sustained improvement in clinical parameters of liver function after autologous BMSC infusion. Three predominant populations of BMSCs, namely hematopoietic stem cells, mesenchymal stem cells, and endothelial progenitor cells, seem to have therapeutic potential in liver injury and cirrhosis. Preclinical studies of BMSC transplantation have identified a range of mechanisms through which these cells mediate their therapeutic effects, including hepatocyte transdifferentiation and fusion, paracrine stimulation of hepatocyte proliferation, inhibition of activated hepatic stellate cells, enhancement of fibrolytic matrix metalloproteinase activity, and neovascularization of regenerating liver. By bolstering liver function in patients with underlying Child's B or C cirrhosis, autologous BMSC infusion holds great promise as a therapy to improve the safety, efficacy, and utility of surgery, chemotherapy, and hepatic radiation therapy in the treatment of HCC.

Contouring and constraining bowel on a full-bladder computed tomography scan may not reflect treatment bowel position and dose certainty in gynecologic external beam radiation therapy.

PURPOSE: To evaluate, in a gynecologic cancer setting, changes in bowel position, dose-volume parameters, and biological indices that arise between full-bladder (FB) and empty-bladder (EB) treatment situations; and to evaluate, using cone beam computed tomography (CT), the validity of FB treatment presumption. METHODS AND MATERIALS: Seventeen gynecologic cancer patients were retrospectively analyzed. Empty-bladder and FB CTs were obtained. Full-bladder CTs were used for planning and dose optimization. Patients were given FB instructions for treatment. For the study purpose, bowel was contoured on the EB CTs for all patients. Bowel position and volume changes between FB and EB states were determined. Full-bladder plans were applied on EB CTs for determining bowel dose-volume changes in EB state. Biological indices (generalized equivalent uniform dose and normal tissue complication probability) were calculated and compared between FB and EB. Weekly cone beam CT data were available in 6 patients to assess bladder volume at treatment. RESULTS: Average (±SD) planned bladder volume was 299.7 ± 68.5 cm(3). Median bowel shift in the craniocaudal direction between FB and EB was 12.5 mm (range, 3-30 mm), and corresponding increase in exposed bowel volume was 151.3 cm(3) (range, 74.3-251.4 cm(3)). Absolute bowel volumes receiving 45 Gy were higher for EB compared with FB (mean 328.0 ± 174.8 vs 176.0 ± 87.5 cm(3); P=.0038). Bowel normal tissue complication probability increased 1.5× to 23.5× when FB planned treatments were applied in the EB state. For the study, the mean percentage value of relative bladder volume at treatment was 32%. CONCLUSIONS: Full-bladder planning does not necessarily translate into FB treatments, with a patient tendency toward EB. Given the uncertainty in daily control over bladder volume for treatment, we strongly recommend a "planning-at-risk volume bowel" (PRV_Bowel) concept to account for bowel motion between FB and EB that can be tailored for the individual patient.

Day to day treatment variations of accelerated partial breast brachytherapy using a multi-lumen balloon.

PURPOSE: To evaluate the variations of multi-lumen balloon (MLB)-based brachytherapy from simulation day to treatment day and their dosimetric impacts during accelerated partial breast irradiation (APBI). MATERIAL AND METHODS: A total of 42 CT images scanned from seven patients were evaluated with regards to daily variation due to of: 1) internal uncertainty: size and shape of balloon, seroma volume; 2) geometrical uncertainty-random: length of each catheter was measured for each fraction (total 70); 3) geometrical uncertainty-systematic: virtual systematic errors were tested by offsetting dwell positions. The original plans (as group A) had a mean value of 96.8% on V95 of the PTV_Eval. Plans were rerun (as group B) such that the mean value of the V95 was relaxed to 90.4%. By applying the reference plan to each daily CT image, variations of target coverage under different sources of error were evaluated. RESULTS: Shape and size of the balloon had means of < 1 mm decreased in diameter and < 0.4 cm(3) decreased in volume; the mean seroma volume increased by 0.2 cm(3). This internal variation has a mean of < 1% difference for both V90 and V95. The geometrical uncertainty made a mean deviation of 2.7 mm per root of sum of square. It caused the degradations of V90 and V95 by mean values of 1.0% and 1.2%, respectively. A systematic error of 3 mm and 4 mm would degrade both of V90 and V95 by 4% and 6%, respectively. The degradations on target coverage of the plans in group A were statistically the same as those in group B. CONCLUSIONS: Overall, APBI treatments with MLB based brachytherapy are precise from day to day. However, minor variation due to daily treatment uncertainties can still degrade tumor bed coverage to an unacceptable coverage when V95 of the original plan is close to 90%.

Feasibility study and optimum loading pattern of a multi-ring inflatable intravaginal applicator.

PURPOSE: A cylinder applicator is the standard treatment device for intravaginal brachytherapy. However, they are limited in their ability to simultaneously spare the organs at risk (OAR), and reduce the hot spot in the vaginal mucosa, while achieving adequate dose conformality. This study aims to compare the dosimetric characteristics of single and multi-channel cylinders, and utilizes volume point dose optimizations to investigate the feasibility and optimum loading method for a multi-ring inflatable intravaginal applicator. MATERIAL AND METHODS: STUDIES WERE DESIGNED TO: (1) test the feasibility of multi-ring applicators, (2) compare dose distributions between different multi-channel applicators and loading patterns, (3) test non-uniform prescription depths around the multi-ring cylinder. RESULTS: Compared to a cylinder with a single central channel, a cylinder with 6 lumina arranged around the periphery, providing the lumina had adequate distance to the cylinder surface, could reduce dose beyond the prescription depth. However, when the number of outer lumina increased from 6 to 12, no further dose reduction could be achieved and the high dose volume close to the surface of the cylinder increased. Moreover, an additional ring, with lumina further away from the surface, provided increased dose shaping capabilities, allowing for individualized dose distributions. CONCLUSIONS: Dose could be reduced to normal tissue and the inner mucosa, and better conformity was seen to unique anatomical shapes. A modified peripheral loading pattern provided the optimum dose distribution, yielding good conformity, dose sparing at adjacent organs, and dose reduction in the high dose region of the vaginal mucosa.

Progressive transition from pre-planned to intraoperative optimizing seed implant: post implementation analysis.

PURPOSE: To perform a dosimetric comparison between a pre-planned technique and a pre-plan based intraoperative technique in prostate cancer patients treated with I-125 permanent seed implantation. MATERIAL AND METHODS: Thirty patients were treated with I-125 permanent seed implantation using TRUS guidance. The first 15 of these patients (Arm A) were treated with a pre-planned technique using ultrasound images acquired prior to seed implantation. To evaluate the reproducibility of the prostate volume, ultrasound images were also acquired during the procedure in the operating room (OR). A surface registration was applied to determine the 6D offset between different image sets in arm A. The remaining 15 patients (Arm B) were planned by putting the pre-plan on the intraoperative ultrasound image and then re-optimizing the seed locations with minimal changes to the pre-plan needle locations. Post implant dosimetric analyses included comparisons of V(100)(prostate), D(90)(prostate) and V(100)(rectum). RESULTS: In Arm A, the 6D offsets between the two image sets were θ(x)=-1.4±4.3; θ(y)=-1.7±2.6; θ(z)=-0.5±2.6; X=0.5±1.8 mm; Y=-1.3±-3.5 mm; Z=-1.6±2.2 mm. These differences alone degraded V(100) by 6.4% and D(90) by 9.3% in the pre-plan, respectively. Comparing Arm A with Arm B, the pre-plan based intraoperative optimization of seed locations used in the plans for patients in Arm B improved the V(100) and D(90) in their post-implant studies by 4.0% and 5.7%, respectively. This was achieved without significantly increasing the rectal dose (V(100)(rectum)). CONCLUSIONS: We have progressively moved prostate seed implantation from a pre-planned technique to a pre-plan based intraoperative technique. In addition to reserving the advantage of cost-effective seed ordering and efficient OR implantation, our intraoperative technique demonstrates increased accuracy and precision compared to the pre-planned technique.

Timing of postseed imaging influences rectal dose-volume parameters for cesium-131 prostate seed implants.

PURPOSE: To study the influence of timing of postseed implant imaging on rectal dose-volume parameters for cesium-131 ((131)Cs) seed prostate implants. METHODS AND MATERIALS: Fifteen patients were treated in our institution with combination (131)Cs brachytherapy followed by pelvic external beam radiation therapy for intermediate to high-risk prostate cancers. For all patients, CT scans were scheduled at 7 days (CT(7)) and again at 2 months for external beam radiation therapy simulation purpose (CT(60)) postseed implantation. Comprehensive postseed implant dosimetry was performed for both CT(7) and CT(60) scans. In each case, dose-volume histogram parameters, rectal separation (the distance between the center of posterior most seed and most anterior rectal wall), and posterior row activity (the total activity implanted within 2-4mm anterior to the posterior wall of the prostate) data were collected. The absolute rectal volumes receiving 100% and 110% prescription dose were also collected. RESULTS: Rectal dose correlated strongly with rectal separation (p<0.001). The mean change in rectal separation between CT(7) and CT(60) scans was 1.1 (±1.7) mm, and the corresponding change in 0.1-cc rectal dose was 18 (±26.5) Gy. Posterior row activity did not correlate with rectal dose (p=0.51). The mean volume of rectum that receives between 100% and 110% of the prescription dose (RV(100) and RV(110)) increased twofold, between CT(7) and CT(60) evaluations (0.03 [±0.06] cc vs. 0.07 (±0.05) cc, respectively, p=0.06). CONCLUSIONS: Our study has demonstrated that rectal doses after (131)Cs seed implants are influenced by the timing of postseed imaging. This may be a consequence of prostatic and periprostatic edema resolution.