Dogan Nesrin, Glasgow Glenn P
Loyola University Chicago Medical Center, Department of Radiation Oncology, Maywood, Illinois 60153, USA.
Med Phys. 2003 Dec;30(12):3091-6. doi: 10.1118/1.1625116.
This study investigates the surface dose and build-up region dosimetry for oblique IMRT beams. The dependence of surface and build-up region doses of 0 degrees (perpendicular incidence) and 75 degrees (oblique incidence) IMRT fields on field size was measured and compared with open field dosimetry. Measurements were performed using a parallel-plate chamber and KODAK EDR2 films in a polystyrene phantom for a 6 cm x 6 cm and a 12 cm x 12 cm, 6 MV photon beam at depths of 0 mm (surface) through dmax. Data were normalized to the dmax value of each field. Four intensity modulated delivery patterns were created and delivered using step-and-shoot IMRT: (1) six static 1 cm x 6 cm strips (IMRTstrip), (2) 12 static 1 cm x 12 cm strips (IMRTstrip), (3) intensity modulated beam patterns created by using the inverse planning optimization software (IMRTopt) for 6 cm x 6 cm, and (4) IMRTopt for 12 cm x 12 cm field sizes. The percent depth doses (PDDs) of 0 degrees, 6 cm x 6 cm IMRTstrip beam at the surface and 5 mm were lower by 8.8% and 1.6%, respectively, compared to the open field. The PDDs of 75 degrees, 6 cm x 6 cm IMRTstrip beam at the surface and 5 mm were lower by 6.7% and 2.4%, respectively, compared to the open field. This study showed that IMRT itself is not contributing to greater skin doses.
本研究调查了斜向调强放疗（IMRT）射束的表面剂量和剂量建成区剂量学。测量了0度（垂直入射）和75度（斜入射）IMRT射野的表面和剂量建成区剂量随射野大小的变化，并与开放野剂量学进行了比较。在聚苯乙烯模体中，使用平行板电离室和柯达EDR2胶片，对6厘米×6厘米和12厘米×12厘米、6兆伏光子束在从0毫米（表面）到剂量最大值（dmax）深度范围内进行测量。数据以每个射野的dmax值进行归一化。使用静态调强放疗创建并输出了四种调强放疗模式：（1）六个静态1厘米×6厘米条带（IMRTstrip），（2）12个静态1厘米×12厘米条带（IMRTstrip），（3）使用逆向计划优化软件创建的6厘米×6厘米调强射束模式（IMRTopt），以及（4）12厘米×12厘米射野大小的IMRTopt。与开放野相比，0度、6厘米×6厘米IMRTstrip射束在表面和5毫米深度处的百分深度剂量（PDD）分别降低了8.8%和1.6%。与开放野相比，75度、6厘米×6厘米IMRTstrip射束在表面和5毫米深度处的PDD分别降低了6.7%和2.4%。本研究表明，调强放疗本身并不会导致更高的皮肤剂量。
