目的：強度調控放射治療計畫通常包含兩大部分：初始治療計畫，治療範圍涵蓋臨床上可能受腫瘤侵犯之臨床標靶體積(Clinical Target Volume，CTV)及週邊可能具危險性的淋巴區域；局部增強治療計畫，針對腫瘤體積做局部的劑量補強。本篇研究以不同劑量限制組合來評估局部增強治療計畫的優劣，以及對整體治療計劃的影響，限制方式分為對初始計畫有依存性及無依存性兩種。材料與方法：本篇研究選取了六位頭頸部癌症的病人，治療計畫系統為Pinnacle Version 7.4 (Philips Medical Systems，Madison，WI)。兩種劑量限制的治療計畫皆以相同初始治療計畫為基礎，藉由不同劑量參數來評估和分析治療計劃的優劣。治療計畫之劑量輸出監測單位(monitor unit，MU)亦包含在評估的範圍內。結果：結果顯示，初始治療計畫的優劣對局部增強治療計畫之劑量曲線分布有顯著的影響。就依存性劑量限制方式而言，為達到整體劑量分布的均勻度，在局部增強治療計畫中會產生極不均勻的劑量分布及MU過高的情形；在無依存性劑量限制方式中，局部增強治療計畫不但具有良好的劑量分布，總劑量也只有些微的增加。綜觀其結果，無依存性劑量限制方式是較適合用於局部增強治療計畫。結論與討論：根據兩種劑量限制方式比較其結果，由於無依存性劑量限制方式可以達到完整的腫瘤包覆，關鍵器官亦不會接受到過多的劑量，對於生物效應及治療效果都能有完整的評估。因此，建議使用無依存性劑量限制方式來製作局部增強治療計畫，並且審慎的設定關鍵器官的劑量限制，而其整體治療計畫就可以達到預期的治療效果，關鍵器官亦不會超出耐受劑量。

Purpose: IMRT treatment planning generally includes two parts: initial comprehensive IMRT (C-IMRT) plan to cover the CTV and risky nodal regions and the Cone Down (CD) IMRT plan for gross tumor boost. We try to evaluate the impact of the 2 CD constrain sets, dependent and independent constrain sets in relation to the initial plan on the final composite isodose distribution. Materials and Methods: A total of six IMRT plans with head and neck cancer were performed with the Philip Pinnacle3 Planning System. Two different constrain sets of CD IMRT plan had been done with the same C-IMRT plan for each patient. Isodose distributions, dose-volume histograms (DVHs), and the various dosimetric parameters were generated and calculated for each plans. Comparison was made to evaluate the differences of DVHs and composite isodose distributions of 2 CD constrain sets both superimposed on the initial C-IMRT planning. We also compared the monitor unit (MU) in two CD constrain sets plans. Result: Our finding showed that the initial IMRT plan has a great impact on CD IMRT plan. Dependent constrain sets in CD IMRT plan could be negatively influenced by the initial IMRT plan with unacceptable surplus of MUs due to the non-uniform intensity map summarization. The independent constrain sets may not generate an acceptable composite dose distribution since summation of the two acceptable individual intensity maps may not create an optimum composite intensity to meet the final dose criteria. However, taken all consideration together, the independent constrain sets could be adequate for CD IMRT plan. Conclusion and Discussion: According to the aforementioned planning comparisons, it is perfered to implement the CD IMRT plan without summating the initial IMRT plan. CD IMRT paln with independent constrain sets was prefered over dependent constrain sets because of consistent minimum tumor coverage in the cone down phase, similar tumor coverage, equal critial organ sparing and bioradiological evaluation. The dose constrains defined in the initial IMRT plan has a great effect on the critical organ dose. Analysis of the composite IMRT plan is indispensable.