Sealed sources of Am-241 emit primarily 60 keV photons; produce relative dose distributions in water comparable to those from Cs- 137 or Ra-226 sources; and can produce dose rates up to 100 cG/hr at 1 cm in water. Am-241 gamma rays can be shielded effectively by thin layers of high atomic number materials (HVL in 1/8th of lead) placed on the applicator or inside some body cavities (for example, hypaque in bladder, barium sulphate in rectum). These properties of Am-241 sources open a new approach to optimizing intracavitary irradiation of various cancers by allowing a reduction in dose to and volume of irradiated critical organs or by increasing tumor doses. The relative ease with which highly effective shielding is achievable with Am-241 sources would allow the design and fabrication of partially shielded applicators which can produce asymmetric dose distributions to allow undirectional irradiation of localized lesions and would reduce the radiation exposure to personnel. This proposal seeks to continue an ongoing investigation into physical, biological and clinical aspects of intracavitary irradiation using Am-241 sources. The current first-generation gynecological applicator will be modified to produce a second- generation Am-241 applicator for treatment of primary gynecological cancers. Am-241 sources and clinical applicators for intracavitary irradiation of other disease sites such as rectum, esophagus, etc., will be developed. Dose distributions produced by these applicators will be measured using ionization chambers and thermoluminiscent dosimeters in tissue equivalent phantoms. An existing dose computation model will be extended to include the effects of partial shields on the applicators and source-to-source shielding on the primary and scattered photons using a 3- dimensional scatter-integration model. Relative biological effectiveness (RBE) of Am-241 photons as compared with Ir-192 and I-125 photons will be determined in a rat solid tumor system for dose rates in the range of 10 to 100 cG/hr using tumor cell survival and tumor cure as the endpoint. The potential benefit for brachytherapy provided by partial shielding of a critical organ, for example, part of the circumference of the rectum, will be assessed by studying the early and late radiation response of partially irradiated rodent intestine. Ongoing clinical trials for recurrent gynecological cancers using Am-241 applicators will be continued and clinical studies for intracavitary irradiation of primary gynecological cancers and recurrent cancers of the rectum, esophagus, anus, head and neck, and skin using Am-241 sources will be conducted.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
Project #
Application #
Study Section
Radiation Study Section (RAD)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Yale University
Schools of Medicine
New Haven
United States
Zip Code
Meigooni, A S; Nath, R (1992) A comparison of radial dose functions for 103Pd, 125I, 145Sm, 241Am, 169Yb, 192Ir, and 137Cs brachytherapy sources. Int J Radiat Oncol Biol Phys 22:1125-30
Nath, R; Rockwell, S; King, C R et al. (1992) Development of a shielded 241Am applicator for continuous low dose rate irradiation of rat rectum. Int J Radiat Oncol Biol Phys 23:175-81
Meigooni, A S; Nath, R (1992) Tissue inhomogeneity correction for brachytherapy sources in a heterogeneous phantom with cylindrical symmetry. Med Phys 19:401-7
Muench, P J; Nath, R (1992) Dose distributions produced by shielded applicators using 241Am for intracavitary irradiation of tumors in the vagina. Med Phys 19:1299-306
Morton, J; Nath, R; Meigooni, A S et al. (1991) A simple technique for irradiation of recto-anal cancers with electrons using an internal anal shield. Int J Radiat Oncol Biol Phys 21:1337-41
Williamson, J F; Nath, R (1991) Clinical implementation of AAPM Task Group 32 recommendations on brachytherapy source strength specification. Med Phys 18:439-48
Nath, R; Urdaneta, N; Bolanis, N et al. (1991) A dosimetric analysis of Morris, Fletcher, and Henschke systems for treatment of uterine cervix carcinoma. Int J Radiat Oncol Biol Phys 21:995-1003
Muench, P J; Meigooni, A S; Nath, R et al. (1991) Photon energy dependence of the sensitivity of radiochromic film and comparison with silver halide film and LiF TLDs used for brachytherapy dosimetry. Med Phys 18:769-75
Nath, R; Park, C H; King, C R et al. (1990) A dose computation model for 241Am vaginal applicators including the source-to-source shielding effects. Med Phys 17:833-42
Nath, R; Bongiorni, P; Rossi, P I et al. (1990) Enhanced IUdR radiosensitization by 241Am photons relative to 226Ra and 125I photons at 0.72 Gy/hr. Int J Radiat Oncol Biol Phys 18:1377-85

Showing the most recent 10 out of 17 publications