Clinical diagnosis
Case 261
【Discussion】
Tolerance dose (TD) after radiation therapy is expressed to be TD5/5 and TD50/5 that imply that late adverse effect occurs in 5% in 5 years and 50% in 5 years, respectively. Tolerance dose also differs dependent upon radiation field in organ (1-4). Then, it is documented that tolerance dose is discriminated to be 1/3rd, 2/3rd and 3/3rd that indicates one third of organ is irradiated, two thirds and three thirds. Further, tolerance dose differs in number of fractions to total doses. Standard radiation is 2 gray (Gy)/per fraction to total doses (1-4).
Based on tolerant doses, radiation treatment is planned to reach less than tolerant doses to normal tissue such as irradiation of central nervous system is less than 40Gy (tolerant dose is brain and spinal cord is approximately 50Gy). Lung is less than 20Gy, Liver is less than 35 Gy, kidney is less than 20Gy, parotid gland is less than 30Gy, mandibular bone is less than 60Gy (although tolerant dose of mandibular dose is greater than 70Gy).
In our case, our patient received radiation treatment of total dose of 60 Gy, 2 Gy/fraction, 30 fractions for hypopharyngeal cancer whose size is approximately 3 cm. It induced complete response after radiation treatment.
However, there years later, late adverse effect of bilateral mandibular bone, bone necrosis occurred. He got separation of mandibular bone and plate insertion. Infection to plate and osteomyelitis recurred and scheduled to the second separation of mandibular bone and re-insertion of new plates in our hospital. Our patient got radiation doses of less than 60 Gy but experienced late adverse effect of bone necrosis and osteomyelitis. He has suffered from diabetes mellitus for about 25 years and might be susceptible to infection.
Radiation treatment prevailed to treat cancer. A half of patients with neoplasms receive radiation treatment that induces better prognosis. There are two hypotheses of radiation effect. Radiation treatment is based on deterministic effect but not on stochastic effect. Stochastic effect implies there is no threshold on radiation affect but its affects increase linear as radiation doses increase. Meanwhile, deterministic effect is based on the existence of threshold. As long as not exceeding threshold, radiation affects – adverse effects – rarely occur. When radiation treatment irrespective IMRT, beam therapy or three-dimensional radiation treatment is given to patients, radiation beams are planned to concentrate in target, namely tumor and avoid radiation beams to normal organ as little as possible. Even if the target radiation doses increase as ideally as possible, low dose to normal tissue is unavoidable. It is very rare to happen radiation-induced tumor at present. That is rationale to supply radiation treatment to patients with neoplasm.
However, the rare adverse effect occurred in our case that does not imply the contradict of the rationale. The threshold of mandibular bone can be less than 60 Gy, in case of having diabetes mellitus.
【Summary】
We presented a seventy four-year-old male for myelitis of right maxillary bone after radiation therapy for 60Gy for hypopharyngeal cancer whose size was 3 cm in diameter. It induced complete response but three years after, late adverse effects of mandibular osteo-necrosis appeared. He underwent surgical separation of mandibular bone and plate insertion. He had suffered from diabetes mellitus and was given insulin injection for 25 years. His oral condition was not clean and had repeatedly osteomyelitis and infected plate inducing reseparation of mandibular bone and reinsertion of oral plate. It is borne in mind that tolerance dose, TD 5/5 implies adverse effect occurring in 5% in 5 years and tolerance dose of mandibular bone is over 60Gy, indicating our case is included in 5% causing adverse effects. Radiation treatment is conducted based on deterministic effect that indicate that as long as not exceeding threshold, radiation affects – adverse effects – do not occur. However, the rare adverse effect occurred in our case. The threshold of mandibular bone can be less than 60 Gy, in case of having diabetes mellitus.
【References】
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2022.3.22