弧形強度調控放射治療低分次治療肺癌病人皮膚劑量之假體研究

Skin Dose for Early Stage Lung Cancer Patients on Simulated Phantoms Using Hypofractionated Therapy Treated with Volumetric Modulated Arc Therapy (VMAT)

蔡維達(Wei-Ta Tsai) ； 李哲暐(Chi-Wei Li) ； 傅筱如(Hsiao-Ju Fu)

《中華放射線技術學雜誌》 40卷4期 (2016/12) Pp. 219-226

摘要

本實驗主要利用假體測量早期肺癌的患者接受低分次放射線治療之皮膚劑量，以及評估當腫瘤接近皮膚表面時如何選取適合的治療計畫。本研究利用假體以及Pinnacle3 planning system version 9.0的SmartArc治療計畫系統製作處方劑量為6 Gy的弧形強度調控放射治療（volumetric modulated arc therapy, VMAT）治療計畫，並模擬腫瘤位於肺部不同位置時製作不同治療計畫並進行輻射變色軟片以及薄片型熱發光劑量計絕對劑量之測量。本實驗之薄片型TLD變異係數在3%以內，計讀值與給予劑量間呈現良好線性關係，輻射變色軟片校正區線上每個點之變異係數在1%以內，薄片型TLD與EBT2 film的量測值，兩者表面劑量的平均量測值誤差小於5%。當處方劑量為6 Gy時IMRT QA phantom前端、中部、背端腫瘤以及降低表面劑量之背端腫瘤之假體表面輻射變色軟片和薄片型熱發光劑量計量測結果分別為3.06±0.15和3.20±0.08 Gy、3.43±0.06和3.38±0.06 Gy、3.55±0.09和3.57±0.13 Gy以及2.81±0.01和2.69±0.01 Gy。立體定位軀體放射線治療會因為單次的高劑量增強生物效應造成更嚴重的皮膚毒性，把皮膚當成一個危急器官以降低表面劑量的治療計畫是必須的，未來此研究將針對在高劑量情況下的皮膚反應做觀察，減少病人因為低分次治療可能發生更嚴重皮膚反應的機率。

關鍵字

皮膚劑量 ； 薄片型熱發光劑量計 ； 輻射變色軟片

並列摘要

This experiment focused on the measured skin dose for early stage lung cancer patients on simulated phantoms using hypofractionated therapy and also assessed how to select the appropriate treatment planning when tumor was close to the skin surface. This study adopted phantoms and SmartArc (Pinnacle3 planning system version 9.0) treatment planning to produce the prescribed dose of 6 Gy VMAT (volumetric modulated arc therapy) treatment plan and simulated the different treatment plans when lung tumor was located in a different location. The EBT2 film and ultrathin TLD were adopted to measure the absolute dose. In this experiment the variance coefficient of ultrathin TLD is within 3%. The reading values and delivered doses are in a good linear relationship. The points on calibration curve of Gafchromic film are within 1%. The measured mean surface doses between ultrathin TLD or EBT2 film are within 5% deviation. When tumor was located in anterior, middle, back position and back position with decreasing surface dose of prescribed dose of 6 Gy in IMRT QA phantom, the results of the EBT2 film and ultrathin TLD were 3.06±0.15 and 3.20±0.08 Gy, 3.43±0.06 and 3.38±0.06 Gy, 3.55±0.09, and 3.57±0.13 Gy, 2.81±0.01 and 2.69±0.01 Gy, respectively. Stereotactic radiation therapy will cause more severe skin toxicity due to a single high dose inducing the enhancement of biological effects. A treatment planning with taking skin as a critical organ in order to decrease surface dose is necessary. In the future, we will observe the skin reaction in a high dose condition and could reduce the probability of more serious skin reaction due to hypofractionated therapy.

並列關鍵字

skin dose ； ultrathin TLD ； EBT2 film