Experience of brachytherapy using I-125 seed permanent implants for localized prostate cancer

PURPOSE: We report here our experience of brachytherapy using I-125 seeds for localized prostate cancer in 100 patients. MATERIALS AND METHODS: We carried out brachytherapy with I-125 seed permanent implants in 100 patients with localized prostate cancer between September 2003 and October 2004. Preplanning dosimetry was done using transrectal ultrasonic images obtained three or four weeks prior to treatment. Using transrectal ultrasound, we inserted I-125 seeds in the prostate through needles according to the preplanning diagram. We then examined the results on prostate CT performed one month later. RESULTS: It was necessary to describe transrectal ultrasonic image such as preplanning. There were several cases in which the source arrangement of the schedule was corrected immediately before the operation. In the examination after one month, the numerical value at the start of treatment initially was not satisfactory, but we eventually obtained a result that could to be evaluated. CONCLUSION: We carried out permanent implant brachytherapy for localized prostate cancer using I-125 seeds and reported our experience.     

Procedures for radioactive I-125 seed implants

Typical safety procedures and guidelines for the use of radioactive I-125 seed implant are presented. Topics covered include: Physical properties, management and planning of I-125, source logging, source transportation, source accounting during and after implant, room monitoring, recording, dosimetry films, nursing procedures, discharge of patient. These guidelines have been found to be of practical value for personnel involved with the implant to ensure compliance with the regulations, but are not necessarily the only procedures that could be utilized.     

Loading technique comparison in permanent 125I prostate implants

Treatment of prostate cancer utilizing iodine 125 (¹²⁵I) interstitial seed implants has become an accepted and widely used modality. Numerous variations in ¹²⁵I seed implant loading distribution techniques have developed as a result of the preferences of individual institutions implementing the modality. No particular universal standard is currently used for ¹²⁵I seed implants. A major concern with ¹²⁵I seed implants is coverage of the prostate with the desired dose and the minimization of dose to the urethra. A variation of seed distribution per individual anatomy is desirable. Historically, brachytherapy relied on dosimetry systems, such as the Paris, Quimby, and Manchester systems to achieve the desired dose distribution. Use of various peripherally loaded ¹²⁵I seed implant distributions to accommodate anatomic variations within the same institution prompted the interest of how the results compare to the Manchester system.     

The effect of the radial function on I-125 seeds used for permanent prostate implantation.

The purpose of this study was to evaluate the integrity of eight commercially-available low-activity Iodine-125 (125I) seeds for their radial function g(r) and its effect on the dose delivered to the adjacent critical structures when used in permanent prostate implants (PPI). Ten previously treated patients were retrospectively used in this comparison. The Amersham Health Oncura seed was used to peripherally design an isodose distribution with urethral and anterior rectal wall sparing. Plan criteria included minimum coverage of 144 Gy to the planning target volume (PTV), < or = 70% dose to 150% of the PTV volume (V150-PTV), and the quantity of needles < or = 70% of the size of the PTV, in cc. Upon completion of the Oncura plan, the seed type was changed and the activity was adjusted until the V100-PTV for each of the other 7 seed types matched the V100-PTV defined by the Oncura seed. Computed tomography (CT)-based postimplant dosimetry was used to determine the dose to 40% (D40) of the bulb of the penis (in Gy). Dose-volume histograms (DVH) were used to evaluate the differences to V100 (in %) and D40 (in Gy) of the anterior rectal wall and bulb of the penis, and V100 (in %) of the urethra. The data was tabulated. Radioactive 125I sources included in this study were 125I Source 2301 (Best); I-Plant (MedTech), IoGold (Mentor), Oncura (Amersham Health), ProstaSeed (UroCor), SelectSeed (Nucletron), SourceTech (Bard), and Symmetra (UroMed). The sizes of the PTV for the 10 patients ranged from 18.82 cc to 48.99 cc. The Oncura seed was used as the reference seed and all other seed types were normalized to it for data comparison. It was determined that the dose rate constant (Delta) and anisotropy factor (phi) contribute to the activity needed to achieve comparable V100-PTV doses, but a strong dependence on the radial function g(r) was found to effect the doses to the critical structures studied. Values of g(r) at 4 cm were calculated and the IoGold and SourceTech seeds were determined to have the highest g(r) values, with ProstaSeed and SelectSeed having the lowest values. 125I Source 2301 and IoGold required less activity per seed to achieve the same dose to the V100-PTV due to the higher dose rate and anisotrophy constants (Delta.phi). The seed types with silver were less penetrating and resulted in the production of characteristic x-rays that modified the energy spectrum and influenced the radial function. The seeds requiring the lowest activity showed the highest dose to the anterior rectal wall, a posterior adjacent structure; the urethra, an interior structure; and the bulb, an inferior structure. This study was designed to investigate the integrity of eight different commercially-available seed types, and their dependence on the g(r) in seed choice. It was determined that the dose rate constant and anisotropy factor determine the activity needed for implantation but a strong dependence on the radial function was found to effect the doses to the adjacent structures.     

Deflections in computed dose distribution of I-125 seed implant due to angularly averaged approximation

Dose rate distribution of commercially available I-125 seeds is strongly anisotropic due to self absorption. Effects of this anisotropy to dose distribution of linear, planar and volume implants are studied. Results suggest that this anisotropy should be taken into account especially when one is considering dose distribution near the seeds. Angularly averaged distribution of single seed is found to cause serious deflections to isodoses of the implant in high dose region. To use true anisotropic dose rate distribution one must be able to evaluate angular orientation of seeds in the implant. A method is presented to compute this orientation also when seeds are poorly visible in radiographs.     

Quality assurance of I-125 seed permanent implant therapy using a self-color developing reflection-type dosimetry sheet film

PURPOSE: We evaluated a self-color developing sheet-type film for the detection of dead seeds in I-125 permanent implant therapy for prostate cancer. MATERIALS AND METHODS: As a preliminary study, we irradiated X-rays to a self-developing reflection-type sheet film and created a relational curve between absorbed dose and film density. I-125 seeds were placed on a film and the approximate absorbed dose of I-125 was calculated from the relational curve of X-rays. A cartridge in which a dead seed was loaded among 10 I-125 seeds was placed on the film and the detectability of the dead seed was evaluated. RESULTS: Using the relational curve of X-rays, it was possible to measure the approximate absorbed dose of I-125 seeds and to easily detect a dead seed at a glance. Using sterilized film, it was possible to detect a dead seed. CONCLUSION: The self-developing film method is feasible for the detection of a dead seed in a cartridge without re-sterilization of seeds.     

The technique of stereotactic I125 brachytherapy (permanent implants) of brain tumors in Vienna

Methods of stereotactic target localisation are used in brachytherapy of brain tumors for many years. Since 1987 eight patients with inoperable astrocytomas grade I to III were treated at the Neurosurgical Clinic and Clinic for Radiotherapy of the University Vienna by permanent stereotactic I125-seed implantation. For that purpose a newly developed applicator was used. Preliminary results confine the low risk of operation, but the follow-up time is too short for evaluation of the treatment success. Principal problems of brain brachytherapy are discussed in the light of international data. In general, I125 brachytherapy is a useful and well tolerated way of treatment of low grade astrocytomas, the risk is low, which is especially important for children and old patients.     

A versatile physical phantom design and construction for I-125 dose measurements and dose-to-medium determination

PURPOSEIn this paper we present a phantom designed to provide conditions to generate set of “true” independent reference data as requested by TG-186, and mitigating the scarcity of experimental studies on brachytherapy validation. It was used to perform accurate experimental measurements of dose of ¹²⁵I brachytherapy seeds using LiF dosimeters, with the objective of experimentally validating Monte Carlo (MC) calculations with model-based dose calculation algorithm (MBDCA). In addition, this work intends to evaluate a methodology to convert the experimental values from LiF into dose in the medium.METHODS AND MATERIALSThe proposed PMMA physical phantom features cavities to insert a LiF dosimeter and a ¹²⁵I seed, adjusted in different configurations with variable thickness. Monte Carlo calculations performed with MCNP6.2 code were used to score the absorbed dose in the LiF and the dose conversion parameters. A sensitivity analysis was done to verify the source of possible uncertainties and quantify their impact on the results.RESULTSThe proposed phantom and experimental procedure developed in this work provided precise dose data within 5.68% uncertainty (k = 1). The achieved precision made it possible to convert the LiF responses into absorbed dose to medium and to validate the dose conversion factor methodology.CONCLUSIONSThe proposed phantom is simple both in design and as in its composition, thus achieving the demanded precision in dose evaluations due to its easy reproducibility of experimental setup. The results derived from the phantom measurements support the dose conversion methodology. The phantom and the experimental procedure developed here can be applied for other materials and radiation sources.     

Radiation protection and dosimetry issues for patients with prostate cancer after I-125 low-dose-rate brachytherapy permanent implant

PurposeThe aim of this work was to analyze the exposure rates measured in the proximity of patients who underwent prostate low-dose-rate brachytherapy with I-125 implant. Effective doses to relatives and to population were computed to estimate the time to reach radioprotection dose constraints.Methods and MaterialsMeasurements were obtained from 180 patients, whereas the body mass index was calculated and reported for 77 patients. The day after the implant, $\dot{K}$ measurements were conducted at various skin distances and positions and converted to effective doses. A theoretical model was developed to estimate effective doses from total implanted activity. The latter was approximated with a 10-mL vial inside the patient.ResultsThe $\dot{K}$ measurements showed a low correlation with the total implanted activity, albeit an increasing trend of $\dot{K}$ was observed on increasing the activity. A stronger correlation was found between body mass index and $\dot{K}$ measurements.The effective dose to population is in general lower than dose constraints as well as the effective doses to relatives, with the exception of children and pregnant women, who command special precautions. We report differences between the experimental model– and theoretical model–based dose evaluation together with their comparison with previous studies found in literature.ConclusionsBased on the $\dot{K}$ measurements and the results of the present analysis, it is possible to provide the patient with radiation safety instructions specifically tailored to his relatives’ habits and working environment.     

On the biological efficiency of I-123 and I-125 decay on the molecular level

Purpose: To evaluate DNA damage of Auger emitters by numerical modelling at the molecular level.

Material and methods: Energy emission spectra of I-123 and I-125 were used as input data for a computer code that simulates the complete transport of electrons and photons from the physical stage up to the primary chemical stage at 10^?7 s. The simulation was performed in a complex environment of liquid water, DNA structures and scavengers. Electron and photon interactions with the DNA molecules were carefully managed. Simulations were carried out with both I-123 and I-125 bound to a pBR322 plasmid or free in its vicinity.

Results: The distributions of direct and indirect single strand breaks (SSB) and double strand breaks (DSB) as a function of the kinetic energy of the emitted Auger electrons show that damage is caused primarily by electrons with energies lower than 800 eV, while higher energy electrons are mainly involved in indirect effects. The yields per unit energy emitted strengthen this fact. When compared to experimental values, the calculated yields of linearization (LE) and relaxation (RE) events show good agreement as well as does the ratio LE/RE for each radionuclide and the ratio I-125/I-123 in the case of LE.     

Choroidal melanoma: I-125 plaque therapy

An iodine-125 eye plaque was used to treat 58 patients with choroidal melanoma. Patients were followed up for a mean of 48.7 months. Fifty patients had medium-sized lesions (height between 3.1 and 8.0 mm and base diameter less than 16.0 mm), and six patients had large lesions. There were 24 lesions less than 3.0 mm from the optic nerve. The average radiation dose to the apex of the tumor was 8,468 cGy (dose rate, 71 cGy per hour). Initial local disease control was achieved in 50 patients (86.2%). One patient with local treatment failure received another plaque treatment, which controlled disease, so the total disease control rate was 87.9%. Only eight patients died of their disease. Complications were similar to those with other treatment methods, but none of the patients in this study developed optic nerve atrophy.     

Preliminary study of correction of original metal artifacts due to I-125 seeds in postimplant dosimetry for prostate permanent implant brachytherapy

Purpose

We investigated a subtraction-based reprojection approach to reduce CT metal artifacts due to I-125 seeds and evaluated the clinical implications in postimplant dosimetry for prostate permanent implant brachytherapy.

Materials and Methods

The raw projection data were used to reduce metal artifacts due to I-125 seeds. CT images of the metal parts only were separated from the original CT images by setting the threshold for pixel value to that of the I-125 seeds. Using these images, sinograms of CT images with and without seeds were obtained by inverse Radon transform (iRT), and the sinogram of the metal image was subtracted from that of the original image. Finally, the image was reconstructed using the sinogram by Radon transform (RT). This technique was applied to a prostate phantom and to a patient undergoing prostate permanent implant brachytherapy.

Results

Metal artifacts from I-125 seeds were reduced in both the phantom and patient studies. This technique decreased the density of the inner region of seeds but enhanced the density of the seed edge, thereby facilitating the identification of seed number, orientation, and location.

Conclusion

This method reduces metal artifacts from I-125 seeds, and has potential for decreasing the time required for and improving the accuracy of postimplant dosimetry.     

125I粒子永久性组织间植入治疗颈部转移性恶性肿瘤10例

目的 探讨125I粒子永久性组织间植入治疗颈部转移性恶性肿瘤的临床效果。 方法 在B超引导下将125I粒子植入10例恶性肿瘤切除术后颈部淋巴结转移11处病灶肿瘤组织内,治疗1个月后观察疼痛缓解情况和瘤灶大小等变化并定期随访。 结果 接受125I治疗的10例患者,随访6~14个月,均无不良反应发生。125I粒子植入1个月后,肿瘤病灶疼痛症状完全缓解2处,部分缓解9处;肿瘤病灶体积部分缓解10处,1处无改变。 结论 125I粒子永久性组织间植入治疗颈部转移性恶性肿瘤是一种安全、微创、疗效好的方法。     

A computer program for I-125 seed implant

A computer program, written in FORTRAN, for I-125 permanent interstitial implants has been developed. After implantation, isocentric radiographs are taken using radiotherapy simulator (Siemens) in order to obtain two X-ray images of seeds on the same film. Honeywell DPS8 computer and Hewlett-Packard 7221A plotter are used for the dose calculation. The program calculates the dose distribution at the plane desired using 100 X 100 matrix.     

Monte Carlo single-cell dosimetry of I-131, I-125 and I-123 for targeted radioimmunotherapy of B-cell lymphoma

Abstract

Purpose: To study the dosimetric characteristics of a non-internalizing and an internalizing monoclonal antibody (MAb) labeled with ¹³¹I, ¹²⁵I or ¹²³I, which targets a typical lymphoma B-cell. Materials and methods: Using our hybrid Monte Carlo (MC) code which combines detailed- and condensed-history electron track simulation we carry out transport calculations of Auger and beta electrons for different intracellular distributions of radioactivity. Results: Assuming permanent retention of the MAb in cells, ¹²⁵I gave the highest absorbed dose and ¹²³I the highest absorbed dose rate. Under the more realistic scenario of biologic excretion from the cells, ¹²³I resulted in the highest absorbed dose and absorbed dose rate. Conclusion: The present dosimetric analysis shows that biological half-life, subcellular localization, and the proper account of low-energy electrons is critical in assessing the energy deposition inside the targeted cells from the three iodide radioisotopes examined. From a dosimetric point of view and under the present approximations ¹²³I might be superior to the other two radioiodides in the treatment of microscopic disease in B-cell lymphoma patients.