Benefit of adaptive CT-based treatment planning in high-dose-rate endorectal brachytherapy for rectal cancer

PurposeIn this planning study, we investigated the dosimetric benefit of repeat CT-based treatment planning at each fraction vs. the use of a single CT-based treatment plan for all fractions for high-dose-rate endorectal brachytherapy (HDREBT) for rectal cancer.Methods and MaterialsWe included 11 patients that received a CT scan with applicator in situ for all three fractions. The treatment plan of the first fraction was projected on the repeat CT scans to simulate the use of a single treatment plan. In addition, replanning was performed on the repeat CT scans, and these were compared to the corresponding projected treatment plans.ResultsRepeat CT-based treatment planning resulted on average in a 21% higher (p = 0.01) conformity index compared to single CT-based treatment planning. Projecting the initial treatment plan to the repeat CT scans of fraction two and three, 12/22 fractions reached a CTV D98 of 85% of the prescribed dose of 7 Gy, which increased to 14/22 using replanning. For the remaining fractions, median CTV D98 was 4.2 Gy, and an intervention would be necessary to correct applicator balloon setup or to remove remaining air and/or feces between the CTV and the applicator.ConclusionsUsing a single CT-based treatment plan for all fractions may result in a suboptimal treatment at later fractions. Therefore, repeat CT imaging should be the minimal standard practice in HDREBT for rectal cancer to determine whether an intervention would be necessary. Replanning based on repeat CT imaging resulted in more conformal treatment plans and is therefore recommended.     

Long-term outcomes with high-dose-rate brachytherapy for the management of base of tongue cancer

PurposeTo report the long-term results of a prospective, nonrandomized clinical trial using high-dose-rate (HDR) brachytherapy (BT) for the management of base of the tongue (BOT) tumors.Methods and MaterialsBetween January 1992 and June 2011, 60 patients (mean age, 57 years; range, 36–78 years) with T1–T4 and N0-3 carcinoma of BOT were treated. Fifty-six patients (93%) had advanced (Stage III-IV) disease. HDR BT boost (mean dose, 17 Gy; range, 12–30 Gy) was delivered after 50–70 Gy (mean 62 Gy) locoregional external beam irradiation. Seventeen patients (28%) received radiochemotherapy (RCT) with cisplatin.ResultsThe 5-year actuarial rate of local tumor control, locoregional tumor control, overall survival (OS), and cancer-specific survival (CSS) was 57%, 50%, 47%, and 61%, respectively. OS was significantly better in patients (n = 17) receiving RCT (69% vs. 39%; p = 0.005). Delayed soft-tissue ulceration occurred in seven patients (12%). Only one patient (<2%) developed osteoradionecrosis. In univariate analysis, the tumor size (T1–T2–T3 vs. T4) was found to have a significant effect on CSS (p = 0.043), whereas the nodal status (N0 vs. N+) affected locoregional tumor control (p = 0.042), OS (p = 0.002), and CSS (p = 0.015). Low histologic grade (1–2) was associated with better CSS (p = 0.020), whereas RCT significantly improved OS (p = 0.012).ConclusionsExternal beam irradiation combined with interstitial HDR BT boost results in good local tumor control with an acceptable rate of late side effects in patients with BOT carcinoma. RCT improves OS. Our results are similar to those reported with traditional low-dose-rate BT implants.     

Improved rectal dosimetry with the use of SpaceOAR during high-dose-rate brachytherapy

PurposeHydrogel spacers have been suggested to limit rectal radiation dose with improvements in clinical outcomes in patients undergoing external beam radiation treatment for prostate cancer. No studies to date have assessed the utility and dosimetric effect of SpaceOAR (Augmenix, Inc, Waltham, MA), the only Food and Drug Administration–approved hydrogel rectal spacer, for high-dose-rate (HDR) brachytherapy.MethodsEighteen consecutive patients scheduled for HDR brachytherapy in the treatment of prostate cancer underwent transperineal ultrasound-guided placement of 10 cc of SpaceOAR hydrogel following catheter implantation. Treatment plans were generated using an inverse planning simulated annealing algorithm. Rectal dosimetry for these 18 patients was compared with the 36 preceding patients treated with HDR brachytherapy without SpaceOAR.ResultsFifty-four plans were analyzed. There was no difference in age, pretreatment prostate-specific antigen, Gleason score, clinical stage, prostate volume, or contoured rectal volume between those who received SpaceOAR and those who did not. Patients who received SpaceOAR hydrogel had significantly lower dose to the rectum as measured by percent of contoured organ at risk (median, V₈₀ < 0.005% vs. 0.010%, p = 0.003; V₇₅ < 0.005% vs. 0.14%, p < 0.0005; V₇₀ 0.09% vs. 0.88%, p < 0.0005; V₆₀ = 1.16% vs. 3.08%, p < 0.0005); similar results were seen for rectal volume in cubic centimeters. One patient who received SpaceOAR developed a perineal abscess 1 month after treatment.ConclusionsTransperineal insertion of SpaceOAR hydrogel at the time of HDR brachytherapy is feasible and decreases rectal radiation dose. Further investigation is needed to assess the clinical impact of this dosimetric improvement and potential toxicity reduction.     

Three-dimensional image-guided combined intracavitary and interstitial high-dose-rate brachytherapy in cervical cancer: A systematic review

PurposeTo evaluate the local control and toxicities of three-dimensional image-guided combined intracavitary and interstitial (IC/IS) high-dose-rate brachytherapy (BT) in cervical cancer through a systematic review.Methods and MaterialsA systematic review of relevant studies was performed through the PubMed, Web of Science, and Cochrane Library databases through May 10, 2020. Articles reporting on IC/IS technology, volumetric doses to high-risk clinical target volume (HR-CTV) and organs at risk (OARs), tumor control and/or treatment-related side effects were identified. The key information, including the type of applicator, implantation technology, characteristics of implantation, volumetric doses, tumor control, and/or treatment-related side effects, was extracted. A probit model analysis between HR-CTV D90 and tumor local control was performed.ResultsTwelve studies encompassing 520 patients were included in the probit model between HR-CTV D90 and the local control rate. The probit model showed a significant relationship between the HR-CTV D90 value and the local control probability, p = 0.003. The prescribed dose of 85 Gy_EQD2,10 would in theory warrant an 87.4% (95% confidence interval 82.5%–90.5%) local control rate.ConclusionIC/IS BT is an appropriate method to achieve a high therapeutic ratio for tumors with large volumes or poor responses after external irradiation in cervical cancer. The probit model showed that the dose escalation of HR-CTV D90 was helpful to improve the local tumor control rate.     

Workflow and efficiency in MRI-based high-dose-rate brachytherapy for cervical cancer in a high-volume brachytherapy center

PurposeWe report the clinical workflow and time required for MRI-based image-guided brachytherapy (MR-IGBT) of cervical cancer patients in a high-volume brachytherapy center with 10 years of experiences to provide a practical guideline for implementing MR-IGBT into clinical use.Methods and MaterialsWe recorded the time and workflow of each procedure step within the 40 consecutive ring and tandem applicator fractions of MR-IGBT by our multidisciplinary team. We divided the entire procedure into four sections based on where the procedure was performed: (1) applicator insertion under sedation, (2) MR imaging, (3) planning, and (4) treatment delivery. In addition, we compared the current procedure time to the initial procedure time when first implementing MR-IGBT in 2007–2008 via a retrospective review.ResultsMean total procedure time was 149.3 min (SD 17.9, ranges 112–178). The multidisciplinary team included an anesthesia team, radiologist, radiation oncologist, nurses, radiation therapists, MRI technicians, dosimetrists, and physicists. The mean procedure time and ranges for each section (min) were as follows: (1) 56.2 (28.0–103.0), (2) 31.0 (19.0–70.0), (3) 44.3 (21.0–104.0), and (4) 17.8 (9.0–34.0). Under current setting, the combined mean procedure time for MR imaging and planning was 63.2 min. In comparison, the same procedure took 137.7 min in 2007–2008 period, which was significantly longer than the current workflow (p < 0.001).ConclusionsA skilled and dedicated multidisciplinary team is required for an efficient clinical workflow and delivery of MR-IGBT. Over the years, we have improved efficiency with clinical experience and continuous efforts in staff education.     

High dose rate (HDR) brachytherapy technique: For carcinoma of uterine cervix using nucletron applicators

This study describes our existing treatment method for high dose rate (HDR) brachytherapy of carcinoma of uterine cervix using Nucletron applicators. Based on our clinical experience with low dose rate (LDR) brachytherapy since 1986, we deliver 40–45Gy by external and 30Gy by internal radiation therapy. The change in regimen using HDR brachytherapy is that internal radiation dose is given in 5 total of 100 treatments done at our center using ring-tandem (R-T) and ovoid-tandem (O-T) applicator combinations. Since O-T applicator has more flexibility of using desired tandem length and reduced rectum and bladder dose due to internal shielding inside the ovoids, we have made the transition from R-T to O-T combination of applicator. The dose volume histogram of the isodose curve indicates that there is an increase in isodose volume with the O-T applicator by as much as 1.5 times as compared to R-T applicator. In majority of the treatments, rectum and bladder doses are less than 70% of target dose, however in very few treatments, the bladder dose has increased to more than the target dose, in which case, the applicators were reseated and added more packing or reduced the dose per fraction, for better tolerance of late responding normal tissues. All our dose calculations are checked with an independent calculation method and agreement was obtained with in 5–7% discrepancy. From 1991 to January 1995, we have treated over 20 patients and there has been no report of any rectal or bladder complications, while better local control has been reported.     

Automated applicator digitization for high-dose-rate cervix brachytherapy using image thresholding and density-based clustering

PurposeThe purpose of the study was to develop and evaluate an automated digitization algorithm for high-dose-rate cervix brachytherapy, with the goal of reducing the duration of treatment planning, staff resources, variability, and potential for human error.MethodsAn automated digitization algorithm was developed and retrospectively evaluated using treatment planning data from 10 patients with cervix cancer who were treated with a titanium tandem and ovoids applicator set. Applicators were segmented, without human interaction, by thresholding CT images to isolate high-density voxels and assigning the voxels to applicator and nonapplicator structures using HDBSCAN, a density-based linkage clustering algorithm. The applicator contours were determined from the centroid of the clustered voxels on each image slice and written to a treatment plan file. Automated contours were evaluated against manual digitization using distance and dosimetric metrics.ResultsA close agreement between automatic and manual digitization was observed. The mean magnitude of contour disagreement for 10 patients equaled 0.3 mm. Hausdorff distances were ≤1.0 mm. The applicator tip coordinates had submillimeter agreement. The median and mean dose volume histogram parameter differences were less than or equal to 1% for high-risk clinical target volume D₉₀, high-risk clinical target volume D₉₅, bladder D_2cc, rectum D_2cc, large bowel D_2cc, and small bowel D_2cc. The average execution time for the automated algorithm was less than 30 s.ConclusionThe digitization of titanium tandem and ovoids applicators for high-dose-rate brachytherapy treatment planning can be automated using straightforward thresholding and clustering algorithms. The adoption of automated digitization is expected to improve the consistency of treatment plans and reduce the duration of treatment planning.     

Long-term results of multicatheter interstitial high-dose-rate brachytherapy for accelerated partial-breast irradiation

Purpose

The purpose of this study was to report the long-term results of women treated in one center with accelerated partial-breast irradiation (APBI) with interstitial high-dose-rate (HDR) brachytherapy.

Comparison of clinical outcomes achieved with image-guided adaptive brachytherapy for cervix cancer using CT or transabdominal ultrasound

PurposeThis study aimed to evaluate retrospectively the treatment results when using various image-guided adaptive brachytherapy treatments for cervical cancer treated by radical radiotherapy.Methods and MaterialsFrom 2014 to 2017, 188 patients with cervical carcinoma were treated by whole pelvic radiotherapy plus four fractions of image-guided brachytherapy. Eight patients were excluded because of missing data. Consequently, 180 patients were analyzed. Of 180 patients, 92 were treated by CT-based brachytherapy (CT-BT), and transabdominal ultrasound–based brachytherapy (TAUS-BT) was used to treat another group. The treatment results and toxicity outcomes were evaluated by comparing the image-guidance techniques.ResultsThe mean follow-up time was 32 months (interquartile range 29.5–42 months). The mean age was 57 years (interquartile range from 50 to 65 years). In the CT-BT group, the mean cumulative doses to high-risk clinical target volume, bladder, rectum, and sigmoid were 87.2 Gy, 84.0 Gy, 68.8 Gy, and 69.8 Gy, respectively. In the TAUS-BT group, the mean cumulative doses to the cervix reference, bladder, and rectum points were 84.0 Gy, 65.5 Gy, and 74.0 Gy, respectively. There were no differences in the 2-year local control rate (p = 0.88) and disease-free survival rate (p = 0.34) in both groups. No difference in gastrointestinal and genitourinary toxicity was observed in both groups, but there was higher vaginal toxicity in the TAUS-BT group compared with the CT-BT group (p = 0.03).ConclusionsNo difference in treatment results was observed between CT-based and TAUS-based approaches. However, TAUS-BT had higher vaginal toxicity in our retrospective analysis.     

Volume-based pulsed-dose-rate brachytherapy boosting concurrent chemoradiation as a definitive treatment modality in cervical cancer

PurposeTo report the treatment outcomes and treatment-induced adverse events (AEs) of concomitant chemoradiotherapy boosted with pulsed-dose-rate brachytherapy using volume-based two-dimensional planning in patients with cervical cancer.Patients and MethodsAfter obtaining the institutional review board approval, patients with FIGO Stages IB to IIIB cervical cancer, treated from January 2006 to December 2008 consecutively, were included. Volume-based planning was used and entailed defining an envelope around the tumor on a two-dimensional image and prescribing the dose to this envelope and reporting the dose of the isodose of 60 Gy. Patients and tumor characteristics, dosimetric parameters, AEs and treatment outcomes, local control rate, distant metastases rate, progression-free survival, and overall survival are reported.ResultsThe study included 95 patients; the median age is 50 years. The median tumor size is 50 cc (range, 25–78 cc). Median brachytherapy dose delivered to the envelope is 20 Gy (range, 15–35 Gy), and median volume encompassed by 60 Gy isodose curve is 137 cc (range, 26–365 cc). The 3-year overall survival, progression-free survival, local control rate, and distant metastases rate were 83.8%, 72.4%, 84.8%, and 15.4%, respectively. Gastrointestinal and genitourinary Grade 3 and 4 acute AEs were reported in 11.6% and 3.3% and chronic Grade 3 and 4 AEs were reported in 3.2% and 4.2% of all patients, respectively.ConclusionsChemoradiotherapy followed by pulsed-dose-rate brachytherapy boost is effective and tolerable treatment modality for locally confined cervical cancer.     

Complications and side effects of high-dose-rate prostate brachytherapy

PurposeTo describe technical challenges and complications encountered during and after high-dose-rate prostate brachytherapy (HDR-BT) and review management of these complications.Methods and MaterialsThe authors performed a systematic review of the literature on toxicities encountered after prostate HDR-BT +/− external beam radiotherapy. A total of 397 studies were identified, of which 64 were included. A focused review of literature regarding the management of acute and late toxicities also performed.ResultsMost acute toxicities include grade 0–2 genitourinary and gastrointestinal toxicity. Overall, Grade 3+ Common Terminology Criteria for Adverse Events toxicity after HDR-BT was low [genitourinary: 0–1%; gastrointestinal 0–3%]. Rates of fistula formation were <1%, and radiation cystitis/proctitis were <14% and more commonly reported in cohorts treated with HDR-BT boost and external beam radiotherapy.ConclusionsHDR-BT both as monotherapy or combined with external beam radiotherapy for prostate cancer is well tolerated. Serious complications are rare.     

Improving dose delivery by adding interstitial catheters to fixed geometry applicators in high-dose-rate brachytherapy for cervical cancer

PurposeImage-guided brachytherapy (IGBT) is an essential component of the treatment of locally advanced cervical cancer. Interstitial (IS) catheters are being increasingly used for bulkier tumors. We have retrospectively assessed the dosimetric impact of IS catheters.Methods and MaterialsAll patients who received IGBT for cervical cancer between August 2014 and February 2017 were identified. Clinical and dosimetric data were collected. Patients were grouped into the intracavitary (IC) cohort or the IC and IS implant (IC/IS) cohort. Ten patients who had been treated with IS catheters (IC/IS plan) had their brachytherapy replanned without IS catheters (IC plan). The total D₉₀% received by the high-risk clinical target volume (CTV_HR) and the D₂cm³ (minimum dose received by the most irradiated 2 cm³) to the bladder, bowel, sigmoid, and rectum were compared.ResultsForty-two patients received IGBT in this period. Seventy-four percent of patients were treated with IS catheters. Sixty-one percent of patients in the IC/IS cohort had CTV_HR volumes ≥30 cm³ at Fraction 1 compared to 18% in the IC cohort (p = 0.014). There was no difference in cumulative D₉₀% to CTV_HR between the IC/IS cohort and the IC cohort. The replanned brachytherapy showed that the cumulative CTV_HR D₉₀% was on average 5.8 Gy higher when IS catheters were used (mean CTV_HR D₉₀% 86.1 compared to 80.3 Gy, p < 0.001). The D₂cm³ to the organs at risk was not significantly increased.ConclusionsIS catheters allow the dose to the CTV_HR to be escalated significantly without increasing the dose to the bladder, bowel, sigmoid, and rectum in patients with bulky tumors.     

Optimization for high-dose-rate brachytherapy of cervical cancer with adaptive simulated annealing and gradient descent

PurposeTo validate an in-house optimization program that uses adaptive simulated annealing (ASA) and gradient descent (GD) algorithms and investigate features of physical dose and generalized equivalent uniform dose (gEUD)–based objective functions in high-dose-rate (HDR) brachytherapy for cervical cancer.MethodsEight Syed/Neblett template-based cervical cancer HDR interstitial brachytherapy cases were used for this study. Brachytherapy treatment plans were first generated using inverse planning simulated annealing (IPSA). Using the same dwell positions designated in IPSA, plans were then optimized with both physical dose and gEUD-based objective functions, using both ASA and GD algorithms. Comparisons were made between plans both qualitatively and based on dose–volume parameters, evaluating each optimization method and objective function. A hybrid objective function was also designed and implemented in the in-house program.ResultsThe ASA plans are higher on bladder V_75% and D_2cc (p = 0.034) and lower on rectum V_75% and D_2cc (p = 0.034) than the IPSA plans. The ASA and GD plans are not significantly different. The gEUD-based plans have higher homogeneity index (p = 0.034), lower overdose index (p = 0.005), and lower rectum gEUD and normal tissue complication probability (p = 0.005) than the physical dose-based plans. The hybrid function can produce a plan with dosimetric parameters between the physical dose-based and gEUD-based plans. The optimized plans with the same objective value and dose–volume histogram could have different dose distributions.ConclusionsOur optimization program based on ASA and GD algorithms is flexible on objective functions, optimization parameters, and can generate optimized plans comparable with IPSA.     

Addressing the burden of cervical cancer through IAEA global brachytherapy initiatives

PurposeBrachytherapy (BT) is an essential component of definitive therapy for locally advanced cervical cancer. Despite the advantages of the dose distribution with BT in cervical cancer, there is paucity of specific skills required for good-quality BT applications. Furthermore, replacing BT with other modern external beam techniques as a boost can lead to suboptimal results in cervix cancer.Methods and MaterialsReview of available IAEA resources, research and cooperation programs available from the IAEA was completed. These opportunities can be used to address challenges in Brachytherapy.The International Atomic Energy Agency (IAEA) provides support for BT through various means that includes education and training, both long term, short term and continuing medical education of professionals, providing expert visits to support implementation, development of curricula for professionals, e-learning through the human health campus, contouring workshops, 2D to 3D BT training, and virtual tumor boards. In addition, the IAEA provides support for implementing quality assurance in radiotherapy to its member states and provides guidelines for comprehensive audits in radiation therapy (QUATRO), and produces safety standards and training in radiation safety. In addition, mapping BT resources, making the case for investment and support for setting up BT services and radiotherapy centers are also available. The IAEA Dosimetry Laboratory provides calibration services to Secondary Standards Dosimetry Laboratories for well chambers used to confirm the reference air kerma rate of Co60 and Ir192 high-dose-rate BT sources, as well as for Cs137 low-dose-rate sources.Furthermore, the IAEA supports research and development in radiotherapy (and BT) through coordinated research activities that include controlled randomized clinical trials, Patterns of Care studies among others. Partnerships with professional organizations and funding bodies, as well as through the United Nations Joint Global Programme on Cervical Cancer Prevention and Control support radiotherapy activities, including BT in countries worldwide.ConclusionThe IAEA supports brachytherapy implementation, training and research and provides resources to professionals in the area.     

Implant time and process efficiency for CT-guided high-dose-rate brachytherapy for cervical cancer

PurposeThis investigation details the time and teamwork required for CT-guided tandem and ring high-dose-rate brachytherapy.Methods and MaterialsFrom 2010 to 2012, 217 consecutive implantations were identified on 52 patients. We gathered key workflow times: preoperative, applicator insertion, CT image, treatment planning, treatment, patient recovery, and total time in clinic. Linear fixed-effects models were used, and key workflow times were the outcome variables and factors including age, body mass index, stage, outside referral, number of implant per patient, number of implants per day, and year of implantation were examined as fixed effects.ResultsOf the 52 patients, 62% of the patients were Fédération Internationale de Gynécologie et d'Obstétrique Stage 2B, 88% were treated with concurrent chemotherapy, and 23% were treated at an outside facility and referred for the procedure. The mean times (minutes) for each step were as follows: preoperative evaluation, 93; insertion, 23; imaging, 45; treatment planning, 137; treatment, removal, and recovery, 115; total clinic time, 401. For the insertion time, the greater implant number per patient was significantly associated with a decreased total insertion time, with and without adjusting for other covariates, p = 0.002 and p = 0.0005, respectively. Treatment planning time was expedited with increasing number of implant per patient and comparing treatment times in 2012 with those in 2010, p = 0.01 and p < 0.0001, respectively.ConclusionsGynecologic brachytherapy requires a skillfully coordinated and efficient team approach. Identifying critical components and the time required for each step in the process is needed to improve the safety and efficiency of brachytherapy. Continuous efforts should be made to enhance the optimal treatment delivery in high-dose-rate gynecologic brachytherapy.     

Early toxicity and health-related quality of life results of high-dose-rate brachytherapy as monotherapy for low and intermediate-risk prostate cancer

PurposeTo determine the acute toxicity and effect on health-related quality of life of a two-fraction regimen of high-dose-rate (HDR) prostate brachytherapy.Methods and materialsPatients with low- or intermediate-risk prostate cancer were treated with HDR brachytherapy as monotherapy in two implants of 13.5 Gy spaced 7–14 days apart. Patients completed International Prostate Symptom Score (IPSS) and Expanded Prostate Index Composite (EPIC) questionnaires at 1, 3, 6, 9, 12, 16, 20, and 24 months after brachytherapy. Proportion of patients in each IPSS category (mild = 0–7, moderate = 8–18, severe = 19+) was evaluated at each of the intervals above. Paired t tests with baseline values were done for IPSS and EPIC scores.ResultsThirty patients were accrued to the study. Median prostate-specific antigen was 8,7 (range 4.1–17.5). T stages were T1c = 65%, T2a = 21%, and T2b = 14%. Twenty-seven percent of patients had a Gleason score of 6 and 73% had a Gleason score of 7. IPSS categories at baseline, 1, 3, 6, 12, and 24 months were mild (81%, 43%, 58%, 62%, 76%, 64%), moderate (19%, 32%, 29%, 30%, 20%, 29%), and severe (0%, 25%, 13%, 7%, 4%, 6%), respectively. There was a significant decrease in EPIC sexual summary scores at 1, 3, 6, and 12 months of 0 points (p < 0.001), 17 points (p = 0.01), 18 points (p = 0.02), and 17 points (p = 0.01), respectively.ConclusionsThis is the first report of this cohort of patients treated with two-fraction HDR monotherapy. This regimen shows rates of toxicity and health-related quality of life that appear acceptable as compared to other treatment modalities. These results are also comparable with other reports with similar treatment regimens.     

A novel method for accurate needle-tip identification in trans-rectal ultrasound-based high-dose-rate prostate brachytherapy

Purpose

In real-time trans-rectal ultrasound (TRUS)-based high-dose-rate prostate brachytherapy, the accurate identification of needle-tip position is critical for treatment planning and delivery. Currently, needle-tip identification on ultrasound images can be subject to large uncertainty and errors because of ultrasound image quality and imaging artifacts. To address this problem, we developed a method based on physical measurements with simple and practical implementation to improve the accuracy and robustness of needle-tip identification.

Methods and Materials

Our method uses measurements of the residual needle length and an off-line pre-established coordinate transformation factor, to calculate the needle-tip position on the TRUS images. The transformation factor was established through a one-time systematic set of measurements of the probe and template holder positions, applicable to all patients. To compare the accuracy and robustness of the proposed method and the conventional method (ultrasound detection), based on the gold-standard X-ray fluoroscopy, extensive measurements were conducted in water and gel phantoms.

Results

In water phantom, our method showed an average tip-detection accuracy of 0.7 mm compared with 1.6 mm of the conventional method. In gel phantom (more realistic and tissue-like), our method maintained its level of accuracy while the uncertainty of the conventional method was 3.4 mm on average with maximum values of over 10 mm because of imaging artifacts.

Conclusions

A novel method based on simple physical measurements was developed to accurately detect the needle-tip position for TRUS-based high-dose-rate prostate brachytherapy. The method demonstrated much improved accuracy and robustness over the conventional method.