Department of Therapeutic Radiology, Yale University, New Haven, CT 06510-3221, USA.
Int J Radiat Oncol Biol Phys. 2012 Jan 1;82(1):e39-47. doi: 10.1016/j.ijrobp.2011.01.071. Epub 2011 Apr 12.
To investigate testicular doses contributed by kilovoltage cone-beam computed tomography (kVCBCT) during image-guided radiotherapy (IGRT) of prostate cancer.
An EGS4 Monte Carlo code was used to calculate three-dimensional dose distributions from kVCBCT on 3 prostate cancer patients. Absorbed doses to various organs were compared between intensity-modulated radiotherapy (IMRT) treatments and kVCBCT scans. The impact of CBCT scanning mode, kilovoltage peak energy (kVp), and CBCT field span on dose deposition to testes and other organs was investigated.
In comparison with one 10-MV IMRT treatment, a 125-kV half-fan CBCT scan delivered 3.4, 3.8, 4.1, and 5.7 cGy to the prostate, rectum, bladder, and femoral heads, respectively, accounting for 1.7%, 3.2%, 3.2%, and 8.4% of megavoltage photon dose contributions. However, the testes received 2.9 cGy from the same CBCT scan, a threefold increase as compared with 0.7 cGy received during IMRT. With the same kVp, full-fan mode deposited much less dose to organs than half-fan mode, ranging from 9% less for prostate to 69% less for testes, except for rectum, where full-fan mode delivered 34% more dose. As photon beam energy increased from 60 to 125 kV, kVCBCT-contributed doses increased exponentially for all organs, irrespective of scanning mode. Reducing CBCT field span from 30 to 10 cm in the superior-inferior direction cut testicular doses from 5.7 to 0.2 cGy in half-fan mode and from 1.5 to 0.1 cGy in full-fan mode.
Compared with IMRT, kVCBCT-contributed doses to the prostate, rectum, bladder, and femoral heads are clinically insignificant, whereas dose to the testes is threefold more. Full-fan CBCT usually deposits much less dose to organs (except for rectum) than half-fan mode in prostate patients. Kilovoltage CBCT-contributed doses increase exponentially with photon beam energy. Reducing CBCT field significantly cuts doses to testes and other organs.
研究千伏锥形束计算机断层扫描（kVCBCT）在前列腺癌图像引导放疗（IGRT）中对睾丸剂量的贡献。
使用 EGS4 蒙特卡罗代码计算了 3 例前列腺癌患者的 kVCBCT 的三维剂量分布。比较了调强放疗（IMRT）治疗与 kVCBCT 扫描之间各器官的吸收剂量。研究了 CBCT 扫描模式、千伏峰能量（kVp）和 CBCT 视野跨度对睾丸和其他器官剂量沉积的影响。
与单次 10-MV IMRT 治疗相比，125-kV 半扇区 CBCT 扫描分别向前列腺、直肠、膀胱和股骨头输送 3.4、3.8、4.1 和 5.7 cGy，占兆伏光子剂量贡献的 1.7%、3.2%、3.2%和 8.4%。然而，同一 CBCT 扫描使睾丸接受 2.9 cGy，比 IMRT 期间接受的 0.7 cGy 增加了三倍。在相同的 kVp 下，全扇区模式向器官沉积的剂量比半扇区模式少得多，从前列腺的 9%减少到睾丸的 69%，直肠除外，全扇区模式的剂量增加了 34%。随着光子束能量从 60 增加到 125 kV，所有器官的 kVCBCT 贡献剂量呈指数增长，与扫描模式无关。在上-下方向将 CBCT 视野跨度从 30 cm 减少到 10 cm，将半扇区模式的睾丸剂量从 5.7 cGy 降低到 0.2 cGy，将全扇区模式的睾丸剂量从 1.5 cGy 降低到 0.1 cGy。
与 IMRT 相比，kVCBCT 对前列腺、直肠、膀胱和股骨头的贡献剂量在临床上无足轻重，而对睾丸的剂量则增加了三倍。在前列腺癌患者中，全扇区 CBCT 通常向器官沉积的剂量比半扇区模式少得多（直肠除外）。千伏 CBCT 贡献剂量随光子束能量呈指数增长。显著减少 CBCT 视野可显著降低睾丸和其他器官的剂量。
