鼻咽癌患者接受強度調控放射治療誘發第二個癌症之風險評估

Estimated the Risk of Secondary Malignancy in Nasopharyngeal Cancer Patients Treated by Intensity Modulated Radiotherapy (IMRT)

10.6316/TRO/200714(3)197

劉明祥(Ming-Hsiang Liou)；梁雲(Stephen Wan Leung)；張寶樹(Pao-Shu Chang)；吳定國(Din-Kao Wu)；連熙隆(Shi-Long Lian)

強度調控放射治療 ； 致死癌病機率 ； 熱發光劑量計 ； 風險 ； Intensity Modulated Radiotherapy IMRT ； Fatal cancer probability ； Thermoluminescent dosimeters TLDs ； Risk

放射治療與腫瘤學

14卷3期（2007 / 09 / 01）

197 - 205

繁體中文

目的：利用輻射劑量計來測量評估當鼻咽癌病患被執行強度調控放射治療(IMRT)時，病患本身各部位的器官可能接受較高的散射劑量，是否有誘發另一個癌症之可能性及致死癌病機率。 材料與方法：首先須對醫用直線加速器所產生的6 MV高能X光射束的能量及劑量輸出做校正，將1MU的劑量輸出校正成1 cGy的吸收劑量。建立熱發光劑量計(TLD-100H)的準確度及劑量響應靈敏度，其誤差須小於3%。將TLD-100H置入Rando人形假體中，按照實際治療情況照射，測量各部位的平均吸收劑量，參酌ICRP60號報告，求得個別組織或器官的致死癌病機率與總體損害的危險度。 結果：整個放射治療療程40個分次(fraction)共72 Gy的總劑量中，眼睛水晶體接受到4.03Gy，對誘發白內障可能有較高的風險，而心臟及腎臟分別是0.86及0.19 Gy，遠低於它們所能接受的耐受劑量(tolerance dose)。根據ICRP60號報告內容換算，肺部及食道可能有1~7%的致死癌病機率，視其靠近治療照野位置而定，而其他器官的致死癌病機率約略為0.04~0.1%。 結論：誘發癌症的危險度很低(0.75%)，但是對於治療部位附近的組織其危險度還是偏高的(7%)，可以針對治療照野靠近危急或耐受劑量較低的器官，或者是總監控單位(MU)比較高的每個病人，尤其是可治癒(curable)的年輕病患，在其接受整個療程裡做此測量評估的工作，以做為變更治療計畫或設計特殊屏蔽物之依據。

Purposes: The radiation dosimeters are used to measure the nasopharyngeal cancer (NPC) patients who are treated by the IMRT technique. The organs doses from scatter radiation are measured, and then the risk is evaluated. For stochastic effect, we estimate the risk for these patients to increase the chance of secondary malignancy and other possible late biological effects. Materials and Methods: First of all, we calibrated the energy and output factor for 6 MV x-ray from a linear accelerator (Elekta Precise-Sli). One monitor unit (MU) output was calibrated as 1 cGy. The accuracy and sensitivity of TLD-100H dosimeters were also measured. TLD-100H dosimeters within 3% accuracy were applied in the study. TLD-100H dosimeters were placed in different anatomical positions of the Rando phantom, then the Rando phantom was irradiated the head and neck area as NPC treatment by IMRT technique. The data of different organs doses were obtained separately for each of IMRT irradiation. The tissue fatal cancer probability and total risk were estimated following the ICRP Publication No.60. Results: Total radiation dose in the IMRT treatment course was 72 Gy in 40 fractions. Len received 4.03 Gy, which had relatively risks to induce cataract. Heart received 0.86 and kidney received 0.19 Gy, which were far less than their maximal tolerance dose. According to the data calculation from ICRP Publication No.60 the lung and esophagus have about 1~7% fatal cancer probability, which depended on the distance of the position from radiation fields. The fatal cancer probability rate for others organs were 0.04~0.1%. Conclusion: The overall risks for inducing fatal cancer is about 0.75%, and the risks for the adjacent tissues to the radiation fields are about 7%. However, a long term evaluation for young cancer patients with curable attempt is feasible.