X-ray radiation therapy

X-RAY RADIATION THERAPY (XRT) ENHANCEMENT 3.1 General Overview Potential Benefit of Sensitizers... 

The metallotexaphyrins have also been found to be easy to reduce and capable of capturing hydrated electrons in aqueous solution. This has made them of potential interest as X-ray radiation therapy (XRT) enhancement agents. While a discussion of this and other applications of metallotexaphyrins is deferred to Chapter 10 of this book, it is worth mentioning that preliminary results have been obtained that are highly encouraging. This, in turn, is stimulating on-going efforts to prepare additional texaphyrin and texaphyrin-like macrocycles. ... 

Sapphyrins and Vinylogous Porphyrins X-Ray Radiation Therapy Enhancement... 

This problem is further complicated by the fact that attempts to eliminate risk result instead in the often unfortunate displacement of risk (Malasky 1982). For example, some approved (by the US Food and Drug Administration) preservatives currently utilized in the food processing industry to prevent bacteria growth and spoilage are, themselves, a suspected cause of cancer (e.g., sodium nitrates). Likewise, there is a risk trade-off between the known benefits of improved medical diagnosis and treatment which result from the use of radiation (e.g.. X-rays, radiation therapy), against the known risks of human exposure to radiation. Hence, safety is really more of a relative issue in that nothing is completely safe under all circumstances or all conditions. There is always some example in which a relatively safe material or... 

Another potentially curative application of expanded porphyrins is to use them as sensitizers in X-ray tumor therapy (XRT). While so far only proposed in the context of the gadolinium(III) texaphyrin system 10.2, such a use is one that carries within it the possible seeds of enormous societal benefit. This is because it would allow one of the most important of all cancer control strategies, namely radiation therapy, to be made more efficacious. 

Some actinides have medical applications for example, radioactive cali-fornium-252 (Cf) is used in cancer therapy. Better results in killing cancer cells have been achieved using this isotope of californium than by using the more traditional X-ray radiation. 

Hematopoietic suppression with pancytopenia may occur in the first week after completion of therapy. Proctitis, diarrhea, glossitis, cheilitis, and ulcerations of the oral mucosa are common dermatological manifestations include alopecia, as well as erythema, desquamation, and increased inflammation and pigmentation in areas previously or concomitantly subjected to x-ray radiation. Severe injury may occur as a result of local toxic extravasation. 

Long-term follow-up monitors patients for continued disease remission or relapse with careful physical examination of the lymph nodes and sites of prior disease involvement and imaging studies. Patients will have routine chest x-rays and CT scans administered to screen for recurrence of disease. Patients require long-term monitoring for toxicities of their primary treatment, either chemotherapy or radiation therapy. 

Radiation therapy The use of high-energy radiation from x-rays, gamma rays, neutrons, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body in the area near cancer cells (internal radiation therapy, implant radiation, or brachytherapy). Systemic radiation therapy uses a radioactive substance, such as a radiolabeled monodonal antibody, that circulates throughout the body. Also called radiotherapy, [nih]... 

Particles emitted from radioactive isotopes are generally too low in energy to provide the penetration required for conventional treatments of tumors with external radiation beams. Most external beam radiation therapies are performed with high-energy x-rays or electrons produced with compact linear accelerators with accelerating potentials between about 4 and 20 MeV. One notable exception is certain devices designed for stereotactical radiosurgery or radiation therapy of superficial tumors that use cobalt-60 y-rays. The... 

Improvements in the physical selectivity, from orthovoltage x-ray to cobalt-60 and high-energy linear accelerators, combined with more powerful diagnostic tools and radiation delivery methods have continuously improved the results of photon therapy (3-D or inverse planning, conformal- and intensity-modulated radiation therapy, and stereotactic methods). The safety and the reliability of photon therapy are well established. 

An alternative to further improve or optimize the photon techniques is to replace the conventional photon beams with new types of radiation. Indeed, since the beginning of radiation therapy, the radiation oncologists have always been eager to search new types of beams (different from conventional x-rays/photons) in order to improve the efficacy of radiation therapy. In principle, different approaches can be adopted (Table 2). 

Historically, the progress in radiation therapy has been linked mainly to technological developments. The physical selectivity of the irradiations was significantly increased when 200-kV x-rays were progressively replaced by cobalt-60, betatrons, and linear accelerators. As a consequence, the clinical results were dramatically improved. 

Figure 28 Schematic presentation of the relative situation of the different types of radiations used in therapy. Two criteria are considered the physical selectivity and the LET (or radiobiological properties). For the low-LET radiations, the physical selectivity was improved from the historical 200-kV x-rays to cobalt-60 gamma rays and the modern linacs. Even with the linacs today, significant improvement is continuously achieved (IMRT, etc.). Among the low-LET radiation, the proton beams have the best physical characteristics, but one of the issues is the proportion of patients who will benefit from proton irradiation. A similar scale can be drawn for high-LET radiation the heavy-ion beams have a physical selectivity similar to protons. Selection between low- and high-LET radiation is a biological/medical problem it depends on the tumor characteristics, and reliable criteria still need to be established (see text). (From Ref 54.)...

A replication-deficient adenovirus has been used to deliver a gene construct, which contains within its promoter region a radiation-responsive element. Upon irradiation with conventional doses of X rays, this construct initiates transcription of the gene coding for the toxic cytokine, tumor necrosis factor-a (35). The above is an exquisite example of how emerging delivery and gene therapies are fast blurring the distinction between an active and an excipient (Fig. 3D). 

Medical and dental diagnostics X rays - 20 mrem per visit Gastrointestinal X rays = 200 mrem per visit Dental X rays = 10 mrem per visit Radiation therapy (ask your radiologist)... 

Dosimetry of X-Ray and Gamma-Ray Beams for Radiation Therapy in the Energy Range 10 keV to 50 MeV (1981)... 

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