比較一般射束及高強度射束之周邊低劑量於立體定位消融性放射治療和旋弧調控放射治療

Comparison of Peripheral Low Dose with or without Flattening Filter in SABR and VMAT

陳韋霖(Wei-Lin Chen)

指導教授 ： 張寶樹

高雄醫學大學/健康科學院/醫學影像暨放射科學系碩士在職專班/碩士(2016年)

摘要

目的：探討直線加速器之高強度(flattening filter free, FFF)光子射束特性，並評估高強度光子射束應用於目前主流放射治療技術如旋弧調控放射治療(volumetric modulated arc therapy, VMAT)及立體定位消融性放射治療(stereotactic ablative radiotherapy, SABR)時，對周邊低劑量(peripheral low dose)的影響。
材料與方法：在相同的治療計畫品質下，以一般模式和高強度模式之光子射束，分別執行SABR治療第一期非小細胞肺癌及VMAT治療兒童神經膠質瘤，使用光刺激發光劑量計(optically stimulated luminescence dosimetry, OSLD)和擬真人形假體(Rando phantom)，實際度量照野外的正常組織所接受的劑量，並比較其差異。
結果：SABR治療第一期非小細胞肺癌，總處方劑量60 Gy時，使用FFF射束，周邊劑量減少為水晶體27.03%、甲狀腺8.23%、肺尖14.11%、肺部17.40%、食道17.85%、心臟13.00%、下肺部20.09%、乳房21.69%、肝臟25.28%、胃23.62%、腎臟23.99%、升結腸36.71%、降結腸27.11%、卵巢57.71%及膀胱40.52%。VMAT治療兒童神經膠質瘤，總處方劑量54 Gy時，使用FFF射束，周邊劑量減少為甲狀腺22.64%、肺尖27.20%、食道21.33%、心臟22.78%、肺部22.36%、乳房22.35%、肝臟24.25%、腎臟22.54%、腸道31.10%、卵巢46.98%及膀胱45.76%。相較於傳統射束，以FFF模式治療之所有周邊器官平均吸收劑量均較一般射束模式低。
結論：實驗結果顯示相較於傳統射束使用FFF射束可減少周邊劑量，降低由輻射誘發二次癌症之風險。於距照野10 cm後更明顯，平均為47% ( MAX )、32% ( SABR )及28% ( VMAT )。對於預估有較長存活期的癌患病人和兒童病患是需要考慮的。

關鍵字

高強度光子射束 ； 周邊低劑量 ； 立體定位消融放射治療 ； 光刺激發光劑量計

並列摘要

Purpose: To investigate the flattening filter free (FFF) photon beam properties and assessing the impact of peripheral low dose in current mainstream radiotherapy in VMAT and SABR.
Materials and Methods: In the same quality of treatment plans, we compare the convention and FFF beam modes, respectively. The T1 phase non-small cell lung cacer (NSCLC) treatment by stereotactic ablative radiotherapy (SABR) and the pediatric glioma treat by volumetric modulated arc therapy (VMAT), using optically stimulated luminescence dosimetry (OSLD) and anthropomorphic Rando phantom, measurement the out of field dose of normal tissues.
Results: The NSCLC T1 phase treat by SABR FFF beam mode, total prescription dose was 60 Gy, peripheral dose including the lens, thyroid, apex, lung, esophagus, heart, lower lung, breast, liver, stomach, kidney, ascending colon, descending colon, ovarian and bladder show an average reduction was 27.03%, 8.23%, 14.11%, 17.40%, 17.85 %, 13.00%, 20.09%, 21.69%, 25.28%, 23.62%, 23.99%, 36.71%, 27.11%, 57.71% and 40.52% , respectively. The pediatric glioma treat by VMAT FFF beam mode, total prescription dose was 54 Gy, peripheral dose including the thyroid, apex, esophagus, heart, lung, breast, liver, kidney, intestine, ovarian and bladder show an average reduction was 22.64%, 27.20%, 21.33%, 22.78%, 22.36%, 22.35%, 24.25%, 22.54%, 31.10%, 46.98% and 45.76%, respectively. Compared to conventional beam, all the average absorbed dose of surrounding organs was lower when treat by FFF beam mode.
Conclusion: Comparing with flattening filter beam and FFF beam, results showed that FFF beam decrease peripheral dose and reduced the risks of the radiation induced secondary malignancies, more obvious at 10 cm distance from field size edge and average reduces 47% (MAX), 32% (SABR) and 28% (VMAT). It need to be consider in patients with longer survival life after radiation therapy or pediatric patients.

並列關鍵字

FFF beam ； peripheral low dose ； SABR ； OSLD

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