[en] This paper reports on the unified evaluation of the relative biologic effectiveness (RBE) of low dose rates of Cf-252 neutrons based on the available experimental data. The RBE of Cf-252 neutrons compared with that of reference radiation (radium) has been defined as the ratio of the dose rates of reference radiation and Cf-252 neutrons that produce the same biologic effect in the same exposure time. Direct experimental evaluation of RBEs defined as above is practically impossible. Cf-252 emits neutrons (∼66%) and photons (∼34%); therefore, the biologic effect of Cf-252 and reference radiation may be described by the following formula: the biologic effect of neutrons (T,D_n) plus the biologic effect of californium photons (T,Dγ) equals the biologic effect of reference photons (T,D_ref). The contribution of Cf-252 photons may be estimated based on the time-dose-factor (TDF) concept proposed by Orton or the LQ model for low-dose radiation presented recently by Dutriex

[en] Using the Monte Carlo method, the distribution of estimators of number degrees of freedom for the chi²-distribution with ν = 1, ν = 2, derived from the poor sample (n = 5;8;12) was received. The distribution of estimators of correlation coefficients, for poor samples of uncorrelated pairs of numbers drawn at random from the population governed by chi²-distribution with ν = 1, was received in the same way. Both the above mentioned problems have essential significance in neutron spectroscopy, when nuclear characters are obtained basing, as a rule, on the poor experimental data of neutron resonance widths. It was shown, that estimators derived from the poor samples can seriously differ from the expected values of characters, and in this connection certain caution in drawing conclusions and in evaluation in accurancy of derived character is required. (author)

[en] The use of brachytherapy in the treatment of soft tissue sarcoma (STS) has been well established. Recently, reports have detailed utilization of new technologies and dose rate strategies (i.e. high dose rate) in the treatment of these tumors. We report our initial experience with Cf-252 in the treatment of these tumors. Between 8/95 and 1/96, seven patients with histologically confirmed STS were treated with curative intent radiation which included part (n=5) or all of the radiations delivered with Cf-252. There were five high grade and two low grade tumors. All patients with high grade STS received chemotherapy, one low grade STS received chemotherapy prior to irradiation. Therapy with Cf-252 consisted of 100 neutron cGy given twice daily to a total dose of 700-900 neutron cGy. External beam irradiation delivered between 4500 - 5400 cGy. Follow up has ranged from one to five months. There has been no local, regional, or distant relapse in any patient. One patient had moist desquamation, which resolved with conservative management, one patient had grade three mucositis (RTOG criteria). This preliminary experience with the neutron emitting Cf-252 has demonstrated excellent tolerance and patient compliance with no unexpected acute or subacute complications. Although follow up was too short to make definitive statements regarding its efficacy, the early data is promising. We will discuss the reasons for dose selection and RBE data, as well as future strategies

[en] Dosimetric measurements are the only way to calibrate radioactive sources. Dose distribution around sources have also been determined experimentally, but in recent years, dramatic technological developments have made computer simulations an attractive method for dose distribution studies. Monte Carlo simulations are especially useful if the radiation field has several components with different biological properties. The dose in the vicinity of ²⁵²Cf source has five components: primary fast neutron, primary photon, secondary 2.2 MeV photon from the H(n,γ) reaction, protons from the ¹⁴N(n,p) reaction, and products of the boron neutron capture reaction if the tumor is augmented by ¹⁰B. The RBE values for these components are different, and their independent determination is essential for ²⁵²Cf brachytherapy. We used MCNP, neutron-photon transport code to calculate all five components of the total dose. The ²⁵²Cf medical source is 2.3 cm long and has diameter 2.8 mm. To construct along-away tables, we divided the volume into cells using concentric cylinders with the source length and planes perpendicular to the source. The computer simulated both neutron and photon histories using cross sections provided by the code library. The neutron/photon energy spectrum and kerma values for particular components were made based on the most recent data available. Results of neutron/photon flux and dose rates were obtained for all cells. Based on these data, along-away tables were constructed for all components of the total dose which will be entered into the treatment planning computer and used for total dose calculations with the appropriate RBE multipliers. Similar calculations may also be done for ²⁵²Cf source of any design

[en] A program has been initiated at the Oak Ridge National Laboratory (ORNL) to develop small, high strength ²⁵²Cf brachytherapy sources. Twenty years ago; several medical source designs were developed at the Savannah River Laboratory. The active core of these designs contained sintered Cf₂O₃-Pd material with a ²⁵²Cf content less than 1% by weight and diameter of 0.4 mm. The strength of these sources ranged from 1 μg to 1 mg of ²⁵²Cf. Only one of these designs, afterloading tubes of strength 30 μg, have been used clinically at the Wayne State University Neutron Therapy Program. The new design began with melted Cf₂O₃-Pd, then the pellet was cooled and rolled out into 1.1 mm diameter wire, followed by swaging down to <0.4 mm. Practical cermet loadings of more than 3% by weight of ²⁵²Cf have already been achieved. The new Cf seed will have the following dimensions: length 6 mm, diameter 0.8 mm, active length 4 mm, active diameter 4 mm, wall thickness 0.17 mm. Initially we anticipate strength of the source to reach 200 μg. Fabrication of prototype is expected in early 1996, after which, licensing efforts will begin. The next step is development of an alternative method of source fabrication based on the electro-deposition onto a wire in cylindrical electrode geometry. The goals of this project are seed activities as high as 1 mg. Such a source would require remote-afterloading. The described above sources will be calibrated at ORNL, and again at the user's site using the two-chamber method. The dose distribution around the source will be obtained using Monte Carlo simulations

[en] In 1995, the American Association of Physicists in Medicine Task Group 43 (AAPM TG-43) published a protocol obsoleting all mixed-field radiation dosimetry for Cf-252. Recommendations for a new brachytherapy dosimetry formalism made by this Task Group favor quantification of source strength in terms of air kerma rather than apparent Curies or other radiation units. Additionally, representation of this dosimetry data in terms of radial dose functions, anisotropy functions, geometric factors, and dose rate constants are in an angular and radial (spherical) coordinate system as recommended, rather than the along-away dosimetry data (Cartesian coordinate system) currently available. This paper presents the initial results of calculated neutron dosimetry in a water phantom for a Cf-252 applicator tube (AT) type medical source soon available from Oak Ridge National Laboratory (ORNL)

[en] This work describes the current status of the US low dose rate (LDR) Cf-252 brachytherapy program. The efforts undertaken towards development of a high dose rate (HDR) remotely after loaded Cf-252 source, which can accommodate 1 mg or greater Cf-252, are also described. This HDR effort is a collaboration between Oak Ridge National Laboratory (ORNL), commercial remote after loader manufactures, the Gershenson Radiation Oncology Center (ROC), and Wayne State University. To achieve this goal, several advances in isotope chemistry and source preparation at ORNL must be achieved to yield a specific material source loading of greater than or equal 1 mg Cf-252 per mm3. Development work with both radioactive and non-radioactive stand-ins for Cf-252 have indicated the feasibility of fabricating such sources. As a result, the decreased catheter diameter and computer controlled source placement will permit additional sites (e.g. brain, breast, prostate, lung, parotid, etc.) to be treated effectively with Cf-252 sources. Additional work at the Radiochemical Engineering and Development Center (REDC) remains in source fabrication, after loader modification, and safe design. The current LDR Cf-252 Treatment Suite at the ROC is shielded and licensed to hold up to 1 mg of Cf-252. This was designed to maintain cumulative personnel exposure, both external to the room and in direct isotope handling, at less than 20 microSv/hr. However, cumulative exposure may be greatly decreased if a Cf-252 HDR unit is employed which would eliminate direct isotope handling and decrease treatment times from tilde 3 hours to an expected range of 3 to 15 minutes. Such a Cf-252 HDR source will also demonstrate improved dose distributions over current LDR treatments due to the ability to step the point-like source throughout the target volume and weight the dwell time accordingly

[en] The Gershenson Radiation Oncology Center of Wayne State University (WSU), Detroit, Michigan, is using ²⁵²Cf medical sources for neutron brachytherapy. These sources are based on a 20-year-old design containing ≤ 30 microg ²⁵²Cf in the form of a cermet wire of Cf₂O₃ in a palladium matrix. The Radiochemical Engineering Development Center (REDC) of Oak Ridge National Laboratory has been asked to develop tiny high-activity ²⁵²Cf neutron sources for use with remote afterloading equipment to reduce treatment times and dose to clinical personnel and to expedite treatment of brain and other tumors. To date, the REDC has demonstrated that ²⁵²Cf loadings can be greatly increased in cermet wires much smaller than before. Equipment designed for hot cell fabrication of these wires is being tested. A parallel program is under way to relicense the existing source design for fabrication at the REDC

[en] Using Monte Carlo methods, neutron dosimetry for ²⁵²Cf Applicator Tube (AT) type medical sources available from Oak Ridge National Laboratory (ORNL) has for the first time been determined in terms of TG-43 formalism. This approach, as compared to previous open-quotes along-awayclose quotes formalisms, demonstrates the relative angular independence of dose rate data, when the geometry factor has been removed. As the ORNL-made ²⁵²Cf AT type sources are considerably physically larger than most clinical sources used today, the radial dose function increases for radii less than 3.0 mm due to breakdown of the line source model. A comparison of the ²⁵²Cf neutron radial dose function with those for other medical sources revealed similarities with that from ¹³⁷Cs. Differences with respect to previous ²⁵²Cf AT source neutron dosimetry data generally increased at increasing distances. This was attributed to differences in the various ²⁵²Cf AT source models and phantom compositions. The current status of ²⁵²Cf medical source fabrication and calibration procedures at ORNL is presented. copyright 1999 American Association of Physicists in Medicine