Dosimetric and toxicity comparison between Syed-Neblett and Fletcher-Suit-Delclos Tandem and Ovoid applicators in high dose rate cervix cancer brachytherapy.

PURPOSE: To compare patient and tumor characteristics, dosimetry, and toxicities between interstitial Syed-Neblett and intracavitary Fletcher-Suit-Delclos Tandem and Ovoid (T&O) applicators in high dose rate (HDR) cervical cancer brachytherapy. METHODS: A retrospective analysis was performed for cervical cancer patients treated with 3D-based HDR brachytherapy from 2011 to 2023 at a single institution. Dosimetric parameters for high-risk clinical target volume and organs at risk were obtained. Toxicities were evaluated using the Common Terminology Criteria for Adverse Events version 5.0. RESULTS: A total of 115 and 58 patients underwent Syed and T&O brachytherapy, respectively. Patients treated with Syed brachytherapy were more likely to have larger tumors and FIGO stage III or IV disease. The median D2cc values to the bladder, small bowel, and sigmoid colon were significantly lower for Syed brachytherapy. Patients treated with Syed brachytherapy were significantly more likely to be free of acute gastrointestinal (44% vs. 21%, p = 0.003), genitourinary (58% vs. 36%, p = 0.01), and vaginal toxicities (60% vs. 33%, p = 0.001) within 6 months following treatment compared to patients treated with T&O applicators. In contrast, Syed brachytherapy patients were more likely to experience late gastrointestinal (68% vs. 49%, p = 0.082), genitourinary (51% vs. 35%, p = 0.196), and vaginal toxicities (70% vs. 57%, p = 0.264). CONCLUSIONS: Syed-Neblett and T&O applicators are suitable for HDR brachytherapy for cervical cancer in distinct patient populations. Acute toxicities are more prevalent with T&O applicators, while patients treated with Syed-Neblett applicators are more likely to develop late toxicities.

Surface mould brachytherapy in oral and oropharyngeal cancers.

INTRODUCTION: There are insufficient data on surface mold brachytherapy (SMB) in treating oral cancers. We reviewed our institutional experience to investigate the efficacy and toxicity of this treatment modality. MATERIAL AND METHODS: We retrospectively reviewed all the patients treated between 1989 and 2018 with high-dose-rate iridium-192 SMB for oral and oropharyngeal squamous cell carcinomas at our institution. Surface mold brachytherapy was delivered via an acrylic surface mold with 1-5 inserted catheters spaced 1 cm apart fabricated by our dental oncologist. The Kaplan-Meier product estimator was used to assess local control (LC), locoregional control (LRC), distant metastasis-free survival (DMFS), and overall survival (OS). Cox proportional hazards regression analysis was used to assess the relationship of various variables and patient outcomes. RESULTS: Eighteen patients met the inclusion criteria and were evaluated. Indications for treatment were primary tumor (n = 13), local recurrence (2), locoregional recurrence (1), and oligometastatic disease (1). Ten patients received SMB alone and 8 received external beam radiotherapy with an SMB boost. The acute toxicity outcomes were as follows: no toxicity (n = 1), grade 1 (7), grade 2 (9), and grade 3 (1). Late effects were rare, only occurring in 3 patients. The one- and two-year LC were 81% and 68%, LRC 77% and 64%, DMFS 81% and 81%, and OS 77% and 46%. CONCLUSIONS: Surface mold brachytherapy is a viable modality as either primary or boost treatment for superficial oral cancers. In our patients, this treatment method has a low toxicity profile and resulted in reasonable LC.

Squamous Cell and Adenoid Cystic Carcinoma Collision Tumor of the Soft Palate Treated with Surface Mold Brachytherapy.

Simultaneous primary cancers are rare in the oropharynx. This report describes the first reported case of a collision tumor of squamous cell and adenoid cystic carcinoma in the soft palate. The patient was immunosuppressed with a history of liver transplantation, smoking and heavy alcohol drinking. He was treated with wide local excision followed by adjuvant radiotherapy with surface acrylic mold brachytherapy. This technique was used instead of external beam radiotherapy in order to minimize toxicity. The patient tolerated the treatment well and with the only acute grade two mucositis at the soft palate and minimal late toxicity. There is no evidence of disease recurrence and the patient continues to maintain excellent quality of speech and swallowing 14 months after treatment completion.

Investigation of a source model for a new electronic brachytherapy tandem by film measurement.

PURPOSE: To investigate the accuracy of a vendor-supplied source model for a new Xoft Axxent 0-degree titanium tandem by film measurement. METHODS: We measured the anisotropy factors at varying distances and angles from the tandem in water using radiochromic film (Gafchromic EBT3) and an Epson Perfection v750 desktop flatbed scanner (US Epson, Long Beach, CA). A 0-degree tandem was placed vertically in a water phantom. Four pieces of film, each at varying depths, were positioned orthogonal to the longitudinal axis of the tandem for azimuthal anisotropy measurements. Polar anisotropy measurements were taken with the film aligned parallel to the tandem. An absolute dose calibration for the film was verified with a PTW 34013 Soft X-Ray Chamber. The film measurements were analyzed using different color channels. The measured polar anisotropy for varying source positions was compared to the vendor's data. Azimuthal anisotropy was measured as a function of the radius and angle, and normalized to the mean value over all angles at the specified radius. RESULTS: The azimuthal anisotropy of the tandem and source was found to be consistent for different positions along the tandem's longitudinal axis and at varying distances from the tandem. Absolute dose using a calibrated parallel plate chamber showed agreement to within 2% of expected TPS values. The custom tandem, which has a thicker tip than the wall, was attenuating the 50 kV photons more than expected, at the angles where the photons had more wall material to traverse. This discrepancy was verified at different distances from the tandem and with different measurement techniques. As distance increased, anisotropy values had better agreement. CONCLUSIONS: We quantified the agreement between the measured and provided anisotropy factors for a new Xoft Axxent 0-degree titanium tandem. Radiochromic film response at low kV energy was also investigated. Our results showed that vendor-supplied TG-43 values were appropriate for clinical use at majority of the angles. A rigorous quality assurance method for new electronic brachytherapy sources and applicators, along with complete knowledge of all dosimetric measuring tools, should be implemented for all parts of the verification and commissioning process.

Computed tomography-planned interstitial brachytherapy for locally advanced gynecologic cancer: Outcomes and dosimetric predictors of urinary toxicity.

PURPOSE: To identify dosimetric predictors of outcome and toxicity in patients receiving CT-planned interstitial brachytherapy (ISBT) for gynecologic cancers. METHODS AND MATERIALS: Patients who received ISBT between 2009 and 2014 were reviewed. Demographic, disease specific, treatment, and toxicity data were collected. Logistic regression was used to model toxicity. A least absolute shrinkage and selection operator penalty was used to identify relevant predictors. Receiver operating characteristic curves were used to analyze the relation between dosimetric factors and urinary toxicity. RESULTS: Seventy-three patients received ISBT (21 at time of cancer recurrence and 52 at the first presentation). Thirty-six patients had cervical cancer, 16 had vaginal cancer, 13 had uterine cancer, and 8 had vulvar cancer. ISBT was performed using both high-dose-rate and low-dose-rate 192Ir sources (27 low dose rate and 46 high dose rate). With a median followup of 12 months, Grade 3 vaginal, urinary, and rectal toxicity occurred in 17.8%, 15.1%, and 6.8% of patients, respectively. No patients experienced Grade 4 or 5 toxicity. Dose to 0.1cc of urethra predicted for development of Grade 3 urinary toxicity (area under the curve of 0.81; 95% confidence interval: 0.66, 0.96). A 10% probability of a Grade 3 urinary toxicity associated with a dose of 23.1 equivalent dose in 2 Gy fractions (95% confidence interval: 9.51, 36.27 equivalent dose in 2 Gy fractions). CONCLUSIONS: ISBT is a safe treatment for gynecologic malignancies. The dose to 0.1cc significantly predicts for severe urinary toxicity. Our data suggests that dose to a small urethral volume may be the most significant predictor of urinary toxicity in patients receiving ISBT for gynecologic cancer.

Simultaneous integrated boost using stereotactic radiosurgery for resected brain metastases: rationale, dosimetric parameters, and preliminary clinical outcomes.

BACKGROUND: Radiosurgery has been shown to reduce the rates of local recurrence in the postoperative bed after the resection of brain metastases, but the ideal radiation dose has not been well defined. OBJECTIVE: To present dosimetric parameters and preliminary clinical outcomes for patients undergoing postoperative stereotactic radiosurgery (SRS) with simultaneous integrated boost (SIB) for brain metastases. METHODS AND MATERIALS: 3 patients underwent surgery for a dominant metastatic focus and had residual or recurrent disease in the resection cavity. Our technique delivered a low dose to the resection cavity with an SIB dose to the gross tumor. Clinical target volume (CTV) was the magnetic resonance (MR)-defined resection cavity. Gross tumor volume (GTV) was the MR-defined residual disease. No additional margin was added to either the resection cavity or the residual disease area. Doses ranged from 14-15 Gy for CTV and 17-18 Gy for GTV prescribed to the 71%-78% isodose line. A traditional postoperative radiosurgery plan was constructed for each patient, and dosimetric values were compared using the paired t-test. RESULTS: 3 patients were treated at our institution using SRS with SIB. No patient experienced local recurrence. 2 patients developed distant brain failure (mean, 3.5 months). No grade 3 or greater toxicities were observed. The volume of brain receiving 12 Gy was significantly reduced using SIB compared with traditional postoperative SRS (𝑃 = .04). There were no differences in the maximum dose delivered to the tumor (𝑃 = .15) and cavity (𝑃 = .13). The average mean cavity dose was 16.20 Gy using the SIB plan, compared with 19.71 Gy using the traditional plan (𝑃 = .05). CONCLUSIONS: In patients with either recurrent or residual disease following surgical resection, SRS using SIB is technically feasible and safe.

Computed tomography planned interstitial brachytherapy for recurrent gynecologic cancer.

PURPOSE: To report outcomes and identify predictors of toxicity in patients undergoing reirradiation with interstitial brachytherapy (ISBT) for recurrent cancers of the female reproductive tract. METHODS AND MATERIALS: Twenty-one patients received ISBT performed using (192)Ir sources (10 low dose rate and 11 high dose rate) at our institution between 2009 and 2013. Demographic, disease specific, treatment, toxicity, and outcome data were collected. Kaplan-Meier and proportional hazard models were used to estimate survival and logistic regression to model toxicity. A least absolute shrinkage and selection operator penalty was used to identify relevant predictors of outcome and toxicity. RESULTS: Eleven patients had uterine cancer, 7 patients had cervical cancer, and 3 patients had vulvar cancer. One-year actuarial freedom from local-regional failure, progression-free survival (PFS), and overall survival were 71.5%, 66.0%, and 82.2%, respectively. Tumor size was a significant predictor of worse PFS and overall survival (1 cm increase in tumor size = hazard ratio [HR], 1.61; 95% confidence interval [CI]: 1.16, 2.62 for PFS; HR, 2.02; 95% CI: 1.21, 3.38). Grade 3 or higher vaginal, urinary, and rectal toxicity occurred in 28.5%, 9.5%, and 19% of patients, respectively. Urethra D0.1cc predicted for grade 2 or higher urinary toxicity (one equivalent dose in 2 Gy fraction increase = HR, 1.156; 95% CI: 1.001, 1.335). CONCLUSIONS: Reirradiation with ISBT is both safe and effective. In patients with recurrent cancer, urethra D0.1cc predicts for increased urinary toxicity. Increased tumor size is a negative prognostic factor in patients receiving ISBT for cancer recurrence.

Negative effect of seroma on breast balloon brachytherapy dosimetry.

PURPOSE: Balloon brachytherapy is commonly used to deliver Accelerated Partial Breast Irradiation (APBI). Seroma interference is a relatively common phenomenon during APBI. The negative effect of seroma accumulation on the planning target volume evaluation (PTV_Eval) coverage is not well understood. METHODS AND MATERIALS: This is a dosimetric replanning study on 10 patients with evidence of seroma collection at time of initial computed tomographic simulation around the catheter. Total dose was 34 Gy given at 3.4 Gy twice a day over 5 treatment days. A total of 20 plans were generated, 10 plans without accounting for and 10 after subtracting the seroma. We then compared the changes seen in PTV_Eval between plans as a factor of the seroma volume. RESULTS: Median age was 62 years (51-83). Histology was invasive in 7/10 cases and in situ in 3/10. Median balloon to skin distance was 8.5 mm (3-14). Median balloon volume was 39 cc (30-104). Median seroma volume was 3.34 cc (1.13-13.71). For every 1 cc of accumulated seroma the percentage of PTV_Eval coverage by the 90% isodose line (V90) was found to decrease by 2.45% (P < .0001; confidence interval [CI], 1.87-3.03) and coverage by the 100% isodose line (V100) was decreased by 1.11% (P < .0001; CI, 0.81-1.41). Fifty percent (5/10) of previously acceptable plans with seroma not accounted for failed to meet the V90 ≥90% requirement after subtracting the seroma. CONCLUSIONS: Accumulation of seroma was associated with a considerable negative impact on PTV_Eval dosimetry with a greater impact on V90 compared with the V100. Clinicians must be careful in detecting and accounting for such accumulation in treatment plans to prevent underdosing of the at risk target breast tissue.

Acute toxicity and early cosmetic outcome in patients treated with multilumen balloon brachytherapy with skin spacing ≤ 7.0 millimeters.

PURPOSE: To review institutional experience treating patients who underwent breast conserving surgery and adjuvant accelerated partial breast irradiation with multilumen balloon brachytherapy (MLB) with close skin spacing (≤7 mm). MATERIAL AND METHODS: Since July 2009, 26 patients with skin spacing ≤ 7.0 mm were treated with breast-conserving therapy and adjuvant MLB brachytherapy. Patients were treated with either the Contura or MammoSite ML catheter to a total dose of 34 Gy in 10 fractions. Patients were assessed for acute toxicity at the completion of treatment and 1-month post treatment. Cosmesis and late toxicity were assessed at three-month intervals thereafter. RESULTS: The median age of the patients was 56 years and median follow-up was 9 months. Sixteen patients had skin spacing of 5.0-7.0 mm, 10 with < 5.0 mm (median 5.8). The median percentage of the target (PTV_EVAL) receiving ≥ 95% of the prescription dose was 95.6%. The median volume of PTV_EVAL receiving ≥ 200% of the prescription dose was 6.1 cc. The maximum skin dose was 118.2% (median). The most commonly observed acute toxicity was grade 1-2 dermatitis (65.4%). The rate of post-treatment seroma and infection was 38.5% and 3.8%, respectively. Excellent/good cosmetic outcomes seen at the time of last follow-up was 92.3%. CONCLUSIONS: MLB brachytherapy is safe and feasible in patients with close skin spacing, with acute toxicity and early cosmesis similar to other published series. These devices may broaden the application of balloon brachytherapy in patients previously excluded from this treatment based on anatomy.

Impact of interfraction seroma collection on breast brachytherapy dosimetry - a mathematical model.

PURPOSE: Balloon brachytherapy is a widely accepted modality for delivery of accelerated partial breast irradiation (APBI). Our hypothesis was that inter-fraction seroma collection around the balloon surface would have an adverse effect on dosimetry of the target. MATERIAL AND METHODS: This is a dosimetric re-planning study using two volumetric models (30 cc and 45 cc) in a Contura(®) multi-lumen balloon (MLB) catheter. In a previously treated patient, two customized baseline plans were generated using multiple channels of the Contura(®) catheter prescribed to the Planning Target Volume Evaluation (PTV_Eval). Symmetric expansions of 1.0 mm (0-9 mm) increments around the balloon surface were performed to simulate a "Virtual Seroma" (VS) accumulation for both balloon volumes and plans were obtained for each expansion using Eclipse Brachyvision™. An analysis of these plans was then performed to evaluate the effect of seroma accumulation on dosimetric parameters of V100 and V90. RESULTS: 20 plans were generated and analyzed (10 plans for each balloon volume), representing VS of 6.0-66.0 cc. There was a commensurate decrease in the dose delivered to the PTV_Eval V100 and V90 (as defined by the original treatment plan) with increasing VS accumulation leading to a sub-optimal coverage of the PTV_Eval. For 30 cc MLB catheter, V100 decreased by 1.4% and V90 decreased by 0.9% for every 1 cc of VS. For 45cc MLB catheter, V100 decreased by 1.3% and V90 decreased by 1.15% for every 1.0 cc accumulation of VS. CONCLUSIONS: Balloon catheter-tissue adherence ensures daily dose delivery to the planned PTV_Eval. Accumulation of seroma, hematoma or air between HDR fractions can significantly impact PTV_Eval dosimetry. Vacuum-port aspiration prior to delivery of each fraction, if available, should be considered to minimize the risk of geographic under dosing.

Interfraction accumulation of seroma during accelerated partial breast irradiation: preliminary results of a prospective study.

PURPOSE: To quantify and characterize the process of seroma accumulation during accelerated partial breast irradiation using multicatheter balloon brachytherapy. MATERIALS AND METHODS: Twenty-two patients were treated using the Contura Multilumen brachytherapy catheter to a dose of 34Gy in 10 fractions over 5 treatment days. Serial aspirations of the vacuum port of the catheter were performed at the time of CT simulation and before each treatment. Volume and characteristics of fluid drawn were recorded. Univariate analysis was performed to evaluate various factors predictive of seroma formation. RESULTS: Median patient age was 59.5 years, body mass index was 31, and volume of surgical specimen was 62.4cm(3). Median time from breast conservation surgery to placement of Contura catheter was 18.5 days. Pericatheter seroma, typically scant with a median volume of 0.75mL, was noted in 91% of patients at CT simulation. A total of 203 aspirations were performed with a median-aspirated seroma volume of 4.05mL. There was no significant correlation between the volume of seroma and histology (invasive vs. in situ), quadrant of location, body mass index, reexcision or reoperation, days from breast conservation surgery to balloon placement, or the volume of specimen removed. Radiation treatment factors, including balloon volume, balloon to skin distance, and planning target volume evaluation, also did not correlate with aspirated seroma. CONCLUSIONS: Interfraction seroma accumulation has a variable pattern of development with no discernible predictors of occurrence. Routine pretreatment aspirations via vacuum port may potentially improve dosimetric reproducibility for a minority of patients.

Evaluation of the dose distribution for prostate implants using various 125I and 103Pd sources.

Recently, several different models of 125I and 103Pd brachytherapy sources have been introduced in order to meet the increasing demand for prostate seed implants. These sources have different internal structures; hence, their TG-43 dosimetric parameters are not the same. In this study, the effects of the dosimetric differences among the sources on their clinical applications were evaluated. The quantitative and qualitative evaluations were performed by comparisons of dose distributions and dose volume histograms of prostate implants calculated for various designs of 125I and 103Pd sources. These comparisons were made for an identical implant scheme with the same number of seeds for each source. The results were compared with the Amersham model 6711 seed for 125I and the Theragenics model 200 seed for 103Pd using the same implant scheme.

Monte Carlo dosimetric characterization of the IsoAid ADVANTAGE 103Pd brachytherapy source.

For roughly 25 years, 125I and 103Pd sources have been used in the treatment of various malignant diseases such as prostate cancer. Various new sources have been marketed and produced to meet the demand for new sources to use in treatment. Recently, IsoAID LLC created the ADVANTAGE 103Pd source. Various dosimetric parameters must be determined to facilitate treatment planning using this source. Theoretical determination of dosimetric characteristics, dose rate constant, radial dose function, and anisotropy function for this new source followed the American Association of Physicists in Medicine (AAPM) Task Group 43U1 recommendations. Theoretical calculations were performed in liquid water using the PTRAN Monte Carlo code version 7.44. The radial dose function of the new source was calculated in liquid water at distances up to 10.0 cm, and the anisotropy function, at distances ranging from 0.5 cm to 7.0 cm. The anisotropy factors and anisotropy constant were derived from the anisotropy function. The results in water indicate that the dose rate constant is 0.709 +/- 0.014 cGy x h-1 x U-1 and that the anisotropy constant is 0.880 +/- 0.040. The dosimetric characteristics of this new source compare favorably with those of other commercially available 103Pd sources.

Evaluation of the veridose QC phantom.

Daily, monthly, and annual quality control (QC) of linear accelerators are part of the major tasks of the medical physicist to verify that patients are receiving proper radiation treatment. The control tests consist of the measurement of beam output, verification of the beam energy, and determination of the beam flatness and symmetry in a linear accelerator. A new device, referred to as QC phantom, was designed and fabricated for the QC of linear accelerators. This device is accompanied by software generating the reports of all measured data, keeping track of day-to-day data, and plotting the results. The accuracy, reproducibility, and linearity of the QC phantom were evaluated in this project. Also, the user friendliness of this device for morning warmup of linear accelerators was tested.

Experimental and theoretical determination of dosimetric characteristics of IsoAid ADVANTAGE 125I brachytherapy source.

125I brachytherapy sources are being used for interstitial implants in tumor sites such as the prostate. Recently, the ADVANTAGE 125I, Model IAI-125, source became commercially available for interstitial brachytherapy treatment. Dosimetric characteristics (dose rate constant, radial dose function, and anisotropy function) of this source were experimentally and theoretically determined, following the AAPM Task Group 43 recommendations. Derivation of the dose rate constant was based on recent NIST WAFAC calibration performed in accordance with their 1999 standard. Measurements were performed in Solid Water phantom using LiF thermoluminescent dosimeters. The theoretical calculations were performed in both Solid Water and water using the PTRAN Monte Carlo code. The results indicated that a dose rate constant of the new source in water was 0.98 +/- 0.03 cGy h(-1) U(-1). The radial dose function of the new source was measured in Solid Water and calculated both in water and Solid Water at distances up to 10.0 cm. The anisotropy function, F(r, theta), of the new source was measured and calculated in Solid Water at distances of 2 cm, 3 cm, 5 cm, and 7 cm and also was calculated in water at distances ranging from 1 cm to 7 cm from the source. From the anisotropy function, the anisotropy factors and anisotropy constant were derived. The anisotropy constant of the ADVANTAGE 125I source in water was found to be 0.97 +/- 0.03. The dosimetric characteristics of this new source compared favorably with those from the Amersham Health Model 6711 source. Complete dosimetric parameters of the new source are presented in this paper.

A Monte Carlo evaluation of the dosimetric characteristics of the Best Model 2301 125I brachytherapy source.

Recently a new design of a 125I brachytherapy source was introduced for interstitial seed implants, particularly for prostate seed implants. This new source is the Best Model 2301 brachytherapy source. Due to the differences in source design and manufacturing process from one new source to the next, their dosimetric parameters should be determined according to the AAPM TG-43 guidelines. As per AAPM recommendation (Med. Phys. 25 (12) (1998) 2269), it is required to perform the seed dosimetry using at least one experimental study and one Monte Carlo simulation, preferably done by two separate investigators. Other investigators have experimentally determined the dosimetric parameters of this new source. In this project, the Monte Carlo simulated dosimetric parameters of the Best Model 2301 125I source have been provided. The results of this evaluation indicate the value of dose rate constant of 1.01 +/- 3% cGyh-1U-1 in liquid water, which is in good agreement with 1.02 +/- 8% cGyh-1U-1 reported by Nath and Yue, 2002. The anisotropy constant was found to be 0.98 in liquid water.

Experimental determination of the TG-43 dosimetric characteristics of EchoSeed model 6733 I25I brachytherapy source.

Recently an improved design of a 125I brachytherapy source has been introduced for interstitial seed implants, particularly for prostate seed implants. This design improves the in situ ultrasound visualization of the source compared to the conventional seed. In this project, the TG-43 recommended dosimetric characteristics of the new brachytherapy source have been experimentally determined in Solid Water phantom material. The measured dosimetric characteristics of the new source have been compared with data reported in the literature for other source designs. The measured dose rate constant, A, in Solid Water was multiplied by 1.05 to extract the dose rate constant in water. The dose rate constant of the new source in water was found to be 0.99 +/- 8% cGy h(-1) U(-1). The radial dose function was measured at distances between 0.5 and 10 cm using LiF TLDs in Solid Water phantom. The anisotropy function, F(r, theta), was measured at distances of 2, 3, 5, and 7 cm.

Determination of the dosimetric characteristics of InterSource125 iodine brachytherapy source.

The TG-43 recommended dosimetric characteristics of a new 125I brachytherapy source have been experimentally and theoretically determined. The measurements were performed in Solid Water using LiF TLDs. The calculations were performed using Monte Carlo simulations in Solid Water and water. The measured data were compared with calculated values as well as the reported data in literature for other source designs. The dose rate constant this source in water was 1.01 +/- 3% cGy h(-1) U(-1) and the anisotropy constant was 0.956.

Evaluation of the veridose in vivo dosimetry system.

Recently, a new design of an in vivo diode dosimetry system, VeriDose diodes, has been introduced by Nuclear Associates to verify the radiation dose delivery to patients treated with either photon or electron beams. The goal of this study is to evaluate the linearity, accuracy, reproducibility, energy dependence, and orientation dependence of this system. These investigations were performed in Solid Water phantom material for both photon and electron beams. The results of the diode dosimetry were compared with the data measured simultaneously using a calibrated ion chamber. Also, for verification of the reproducibility of the results, the investigations were repeated on different days. The results indicated less than a 4% deviation between the diode and ion chamber measured dose for both photon and electron beams. Also, the responses of the photon and electron diodes were linear for doses greater than 2 cGy and 10 cGy, respectively. The response of the photon diode is insensitive (less than 5%) except when the beam is tangent to the skin or beam entering from the tail (wire) end of the diode. However, the electron diode is angular independent between 20 degrees and 90 degrees relative to the patient's skin.

A Monte Carlo evaluation of the dosimetric characteristics of the EchoSeed Model 6733 (125)I brachytherapy source.

PURPOSE: Recently a new design of a (125)I brachytherapy source was introduced for interstitial seed implants, particularly for prostate seed implants. This new source is the EchoSeed Model 6733 (125)I brachytherapy source. Due to the differences in source design and manufacturing process from one new source to the next, their dosimetric parameters should be determined according to the American Association of Physicists in Medicine (AAPM) TG-43 guidelines. METHODS AND MATERIALS: As per AAPM recommendation, it is required to perform at least one experimental study and one Monte Carlo simulation, preferably done by two independent investigators. Other investigators have experimentally determined the dosimetric parameters of this new source. In this project, the Monte Carlo simulated dosimetric parameters of the EchoSeed Model 6733 source have been provided. RESULTS: The results of this evaluation indicate the value of the dose rate constant of 0.97 +/- 3% cGyh(-1)U(-1) in liquid water, which is in good agreement with the measured value of 0.99 +/- 8% cGyh(-1)U(-1) reported by Meigooni et al. The anisotropy constant of the EchoSeed (125)I brachytherapy source was found to be 0.960 in liquid water. CONCLUSIONS: The Monte Carlo Simulated TG-43 dosimetric parameters of the EchoSeed were determined and the results were compared with the published measured data.