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臥躺式全身照射放射治療劑量補償技術探討
Compensating Technique Dosimetry of the Total Body Irradiation in Supine Position
摘要
全身光子照射治療，體內劑量的均勻性和敏感器官劑量的控制是最重要的兩個部份，而體內劑量的均勻性容易受到體表輪廓不平整和組織密度非均勻性影響。本文目的是藉由組織補償物—米的全身性補償，以克服體表輪廓的不平整，及組織缺陷的影響，改善躺式側面全身照射放射治療內劑量的差異，並設法降低肺部組織劑量。 使用西門子PRIMUS3008直線加速器，15MV光子，照野40×40 cm²，機頭旋轉90度，與治療距離處相距(SSD) 415公分。針對百分深度劑量、米與壓克力的等效深度、側剖面圖與輸出因子四項物理特性分析，進而校正熱發光劑量計(TLD)，並置放於擬人假體中評估未加米補償時之側面與正面照射，以米補償後側面照射，以及另外以0.5與1.5公分的鉛合金擋塊遮擋肺部劑量之米補償側面照射三方面。最後再以TLD實測劑量與理論計算值及三度空間治療計畫系統結果相比較。 實驗結果顯示米相當適合當作組織補償物，且可藉由米補償而改善體內劑量的差異性。此外加入0.5公分鉛合金的肺部遮擋，更可使中平面各點劑量與指定點劑量差異控制在10%以內。且TLD量測結果與三度空間治療計畫結果相吻合。
並列摘要
During total body irradiation therapy, the dose uniform in total body and the dose control of some important organ are very important. The dose uniform in body can be easily affected by the convex of contour. The aim of the article is to overcome the convex of contour by adding the rice as tissue compensator to improve the uniform in body, and try to decrease the dose of lung by adding the shielding of lead. The accelerator was a SIEMENS PRIMUS3008 giving a 15 MV photon beam. With the beam horizontal, a therapy unit that projects a 40×40cm² field at 100cm will project a diagonal field 234×234cm² at the source-skin distance (SSD) 415cm. Physical measurements consisted of central axis depth doses, effective depths of rice and acrylic, beam profile and output calibrations. We placed the thermoluminescent dosimeters (TLDs) at mid-plane of Rando phantom and irradiated at different conditions. These included bilateral and anterior/posterior irradiation without rice tissue compensator, bilateral irradiation with rice compensator only, and with rice compensator and lung shielding both. At last, we used the 3D treatment planning system to calculate the dose distribution and compared with the results of TLD. We found that it could improve the dose uniform in body by adding the rice as tissue compensator. Besides, we may control dose of mid-plane different from the precision dose within 10%. Again, from the calculating results of planning system, these were good fit to the measurements of TLD.
延伸閱讀
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