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Chapter 7 Biological Effects of Radiation. 影響生物效應的因子. 輻射種類與能量-輻射品質 (radiation quality) 輻射劑量 (radiation dose) 生物效應種類 DNA 效應 細胞效應 個體效應 確定效應 (deterministic effects) 機率效應 (stochastic effects) 癌症 (cancers) :器官劑量 遺傳效應 (hereditary effects) :生殖腺劑量. Biological Effects (Organism).

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Chapter 7 Biological Effects of Radiation

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    1. Chapter 7 Biological Effects of Radiation

    2. 影響生物效應的因子 • 輻射種類與能量-輻射品質(radiation quality) • 輻射劑量(radiation dose) • 生物效應種類 • DNA效應 • 細胞效應 • 個體效應 • 確定效應(deterministic effects) • 機率效應(stochastic effects) • 癌症 (cancers):器官劑量 • 遺傳效應 (hereditary effects):生殖腺劑量

    3. Biological Effects (Organism) • Animal Studies • Epidemiological Studies • Atomic Bomb Survivors • Medical Exposure • High Background Residents • Occupational Exposure • Dial Painter • Miner • Nuclear Installation

    4. Stochastic and Non-Stochastic Effects • 機率效應(癌病、遺傳效應等) • 效應發生的機率(風險)與劑量呈正比;效應的嚴重程度與劑量無關;沒有低限劑量。 • 非機率效應(皮膚紅斑、白內障等) • 效應的嚴重程度與劑量呈正比;有低限劑量。當劑量小於低限劑量時,效應不會發生;當劑量大於低限劑量時,效應確定發生。

    5. Deterministic Effects (確定效應) 小於低限劑量 效應不會發生 大於低限劑量 效應一定發生 劑量愈高 愈嚴重 • 當劑量小於低限劑量(threshold dose)時效應確定不發生 • 當劑量大於低限劑量時效應確定會發生 • 效應發生後嚴重程度(severity)與劑量呈比例

    6. Linear and Non-threshold (LNT) Hypothesis Characteristics of Stochastic and Non-Stochastic Effects

    7. Threshold Dose (低限劑量)

    8. Radiation-induced Cancer (輻射誘發癌症) • 效應發生的機率與劑量呈正比 1 Sv 2 Sv 3 Sv • 效應的嚴重程度與劑量無關 • 低限劑量可能不存在

    9. Radiation-induced Hereditary Disease (輻射誘發遺傳疾病) • 生殖腺(男:睪丸,女:卵巢)劑量引起之 • 基因突變 • 顯性突變 • 隱性突變 • X突變 • 多因突變 • 染色體變異  所導致之遺傳疾病

    10. Direct Action 分子或組織直接因輻射造成游離而解離 e.g. LD50/30 day dose: 50%在30天內致 死之劑量 4 Gy (for person of gamma ray)

    11. Direct Action • If any form of radiation-x- or y-rays, charged • or uncharged particles-is absorbed in biologic material, there is a possibility that it will interact directly with the critical targets in the cells. • The atoms of the target itself may be ionized or excited, thus initiating the chain of events that leads to a biologic change. This is called direct action of radiation ; • it is the dominant process if radiations with high linear energy transfer (LET), such as neutrons or a-particles, are considered.

    12. Direct Action Alternatively, the radiation may interact with other atoms or molecules in the cell (particularly water) to produce free radicals that are able to diffuse far enough to reach and damage the critical targets. This is called indirect action of radiati0n.

    13. Indirect Action: Free Radicals (自由基) • About two thirds of the biologic damage by x-rays is caused by indirect action.

    14. Radiation Effects---Acute Effects • At doses close to the dose that would belethal to 50% of the population (LD5,), theprincipal symptoms of the prodromalsyndrome are • anorexia, nausea, vomiting,and easy fatigability. • Immediate diarrhea, fever, or hypotensionindicate a supralethal exposure. • The cerebrovascular syndrome results from a total-body exposure to about 100 Gy of x-rays and in humans results in death in 24 to 48 hours. The cause of death may be changes in permeability of small blood vessels in the brain.

    15. Radiation Effects---Acute Effects • The gastrointestinal syndrome results from a total-body exposure to about 10 Gy. Death occurs in about 5 to 10 days in humans because of depopulation of the epithelial lining of the gastrointestinal tract. • The hematopoietic syndrome results fromtotal-body exposure to 2.5 to 5 Gy. The radiation sterilizes some or all of themitotically active precursor cells.Symptomsresult from lack of circulating blood elements3 or more weeks later

    16. Radiation Effects---Acute Effects • The LD50 for humans is 3 to 4 Gy for young adults without medical intervention. It may be less for the very young or the old. • In primates, the LDS0 can be raised by a factor of 2 by appropriate treatment, including careful nursing and antibiotics, and the same may be assumed for humans. • The dose window over which bone-marrow transplants may be useful is narrow, namely, 8 to 10 Gy.

    17. Acute Exposure Effects

    18. Radiation Effects---Delayed Effects • Radiation carcinogenesis is a stochastic effect; that is, the probability of an effect increases with dose, with no dose threshold, but the severity of the effect is not dose related. Hereditary effects are also stochastic. • Latency refers to the time interval between irradiation and the appearance of the malignancy. • The shortest latency is for leukemia, with a peak at 5 to 7 years. For solid tumors, the latency may extend for 60 years or more.

    19. Radiation Effects---Delayed Effects • Regardless of the age at exposure, radiation-induced malignancies tend to appear at the same age as spontaneous malignancies of the same type. Indeed, for solid cancers, the excess risk is apparently more like a lifelong elevation of the natural age-specific cancer risk. • Based on reports of the UNSCEAR and BElR V committees, the ICRP suggests a risk estimate of excess cancer mortality in a working population of per sievert for high doses and high dose rates and per sievert for low doses and low dose rates.

    20. Radiation Track (輻射徑跡):輻射品質 DNA 游離密度小 LET小 電子 a粒子 游離密度大 LET大

    21. Radiation Quality (輻射的質) A輻射 B輻射 吸收劑量: DA DB 相同生物效應 量:吸收劑量(D) 質:相對生物效應(RBE) RBE=D200keV X-ray/Dradiation

    22. RBE(相對生物效應)、LET(直線能量轉移) Q RBE A、B兩輻射,產生相同生物效應之 吸收劑量為DA及DB,則相對生物效應(relative biological effectiveness, RBE)的定義為: RBEA/RBEB=DB/DA

    23. Q(射質因數)、wR(輻射加權因數) ICRP-26 H=QD H=dose equivalent (等效劑量), unit=Sv (西弗) Q=quality factor (射質因數) D=absorbed dose (吸收劑量), unit=Gy (戈雷) ICRP-60 HT,R=wRDT,R HT,R=equivalent dose (T組織R輻射的等價劑量) wR=radiation weighting factor (輻射加權因數) DT,R=absorbed dose (T組織R輻射的吸收劑量)

    24. Dose Equivalent (等效劑量) Equivalent Dose (等值劑量) ICRP 26 ICRP 60

    25. Q與wR的建議值

    26. Equivalent Dose (等價劑量)

    27. Effective Dose (有效劑量)

    28. Comparison Between Tissue Weighting Factors in ICRP-26 and ICRP-60 Tissue (WT,26) Tissue (WT,60) Thyroid (0.05) Oesophagus (0.05) Breast (0.05) Lung (0.12) Stomach (0.12) Liver (0.05) Colon (0.12) Bladder (0.05) Gonads (0.20) Skin (0.01) Bone surface (0.01) Red bone marrow (0.12) Remainder (0.05) Thyroid (0.03) Lung (0.12) Breast (0.15) Gonads (0.25) Bone surface (0.03) Red bone marrow (0.12) Remainder (0.30)

    29. Risk Coefficient (風險係數)

    30. Weighting Risk Coefficient (加權風險係數)

    31. 相對安全與絕對安全 機率大 危險 低限劑量 安全 機率小 確定效應 機率效應

    32. 輻射防護目的 • 防止確定效應之損害發生(絕對安全)。 • 抑低機率效應之發生率,至可接受的低水平(相對安全)。 可 接 受 的 低 水 平 劑量限度

    33. ICRU: International Commission on Radiation Units and Measurements ICRP : International Commission on Radiological Protection