Manzoor Hussain | PubMed Health

PubMed2006

Evaluation of TG-43 recommended 2D-anisotropy function for elongated brachytherapy sources.

The original and updated protocols recommended by Task Group 43 from the American Association of Physicists in Medicine (i.e., TG-43 and TG-43U1, respectively), have been introduced to unify brachytherapy source dosimetry around the world. Both of these protocols are based on experiences with sources less than 1.0 cm in length. TG-43U1 recommends that for 103Pd sources, 2D anisotropy function F(r, theta), should be tabulated at a minimum for radial distances of 0.5, 1.0, 2.0, 3.0, and 5.0 cm. Anisotropy functions defined in these protocols are only valid when the point of calculation does not fall on the active length of the source. However, for elongated brachytherapy sources (active length >1 cm), some of the calculation points with r < 1/2 active length and small theta may fall on the source itself and there is no clear recommendation to handle this situation. In addition, the linear interpolation technique recommended by TG-43U1 is found to be valid for seed types of sources as the difference between F(r, theta) for two consecutive radii is <10%. However, in the present investigations it has been found that values of F(r, 5 degrees) for a 5 cm long RadioCoil 103Pd source at radial distances of 2.5, 3.0, and 4.0 cm were 2.95, 1.74, and 1.19, respectively, with differences up to about a factor of 3. Therefore, the validity of the linear interpolation technique for an elongated brachytherapy source with such a large variation in F(r, theta) needs to be investigated. In this project, application of the TG-43U1 formalism for dose calculation around an elongated RadioCoil 103Pd brachytherapy source has been investigated. In addition, the linear interpolation techniques as described in TG-43U1 for seed type sources have been evaluated for a 5.0 cm long RadioCoil 103Pd brachytherapy source. Application of a polynomial fit to F(r, theta) has also been investigated as an alternate approach to the linear interpolation technique. The results of these investigations indicate that the TG-43U1 formalism can be extended for elongated brachytherapy sources, if the two-dimensional (2D) anisotropy function is tabulated at a minimum for radial distances of 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 cm, L/2, and L/2 +/- 0.2 cm. Moreover, with the addition of recommended radial distances for 2D anisotropy functions, the linear interpolation technique more closely replicates Monte Carlo simulated data than a polynomial fit.

Algorithms↗

PubMed2003

Renal transplantation in developing countries.

Healthcare in developing countries less funded than developed nations (0.8 to 4% vs. 10 to 15%, respectively), and must contend against approximately 1/3 of the population living below the poverty line ($1US/day), poor literacy (58% males/29% females), and less access to potable water and basic sanitation. Cultural and societal constraints combine with these economic obstacles to translate into poor transplantation activity. Donor shortage is a universal problem. Paid donation comprises 50% of all transplants in Pakistan. Post-transplant infections are a major problem in developing countries, with 15% developing tuberculosis, 30% cytomegalovirus, and nearly 50% bacterial infections. The solutions to these problems may seem simplistic: alleviate poverty, educate the general population, and expand the transplant programs in public sector hospitals where commerce is less likely to play a major role. The SIUT model of funding in a community-government partnership has increased the number of transplantations and patient and organ survival substantially. Over the last 15 years, it has operated by complete financial transparency, public audit and accountability. The scheme has proven effective and currently 110 transplants/year are performed, with free after care and immunosuppressive drugs. Confidence has been built in the community, with strong donations of money, equipment and medicines. We believe this model could be sustained in other developing nations.

Developing Countries↗