Kudchadker Rajat J, Hogstrom Kenneth R, Garden Adam S, McNeese Marsha D, Boyd Robert A, Antolak John A
Department of Radiation Physics, M.D. Anderson Cancer Center, University of Texas, Houston, TX 77030, USA.
Int J Radiat Oncol Biol Phys. 2002 Jul 15;53(4):1023-37. doi: 10.1016/s0360-3016(02)02811-0.
Conformal electron beam therapy can be delivered using shaped bolus, which varies the penetration of the electrons across the incident beam so that the 90% isodose surface conforms to the distal surface of the planning target volume (PTV). Previous use of this modality has shown that the irregular proximal surface of the bolus causes the dose heterogeneity in the PTV to increase from 10%, the typical dose spread of a flat-water surface to approximately 20%. The present work evaluates the ability to restore dose homogeneity by varying the incident electron intensity.
Three patients, one each with chest wall, thorax, and head-and-neck cancer, were planned using electron conformal therapy with bolus, with and without intensity modulation. Resulting dose distributions and dose-volume histograms were compared with non-intensity-modulated bolus plans.
In all cases, the DeltaD(90%-10%) for the PTV was reduced; for example, for the head-and-neck case, the DeltaD(90%-10%) for the PTV was reduced from 14.9% to 9.2%. This reduction in dose spread is a direct result of intensity modulation.
The results showed that intensity-modulated electron beams could significantly improve the dose homogeneity in the PTV for patients treated with electron conformal therapy using shaped bolus.
适形电子束治疗可使用成形填充物来实施，该填充物会改变电子在入射束中的穿透情况，从而使90%等剂量面与计划靶区（PTV）的远端面相符。此前使用这种方式的研究表明，填充物不规则的近端表面会使PTV中的剂量不均匀性从平面水表面典型的剂量扩散10%增加到约20%。本研究评估通过改变入射电子强度来恢复剂量均匀性的能力。
对三名患者进行了计划，分别患有胸壁癌、胸段癌和头颈癌，采用有和没有强度调制的带填充物电子适形治疗。将所得剂量分布和剂量体积直方图与非强度调制的填充物计划进行比较。
在所有病例中，PTV的ΔD(90%-10%)均降低；例如，对于头颈病例，PTV的ΔD(90%-10%)从14.9%降至9.2%。剂量扩散的这种降低是强度调制的直接结果。
结果表明，对于使用成形填充物进行电子适形治疗的患者，强度调制电子束可显著改善PTV中的剂量均匀性。
