SU-E-T-143：6和15兆伏光子束在不同源皮距下物理楔形板和虚拟楔形板对表面剂量的影响

SU-E-T-143: Effect of Physical and Virtual Wedges on the Surface Dose at Various SSD for 6 and 15 MV Photon Beam.

作者信息

Yadav Girigesh, Sinha S N, Ashokkumar S, Raman Kothanda, Mishra M, Thiyagarajan Rajesh, Yadav R S

机构信息

Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India.

Department of Physics, D.A.V. (P.G.) College, Kanpur, U.P. India.

出版信息

Med Phys. 2012 Jun;39(6Part11):3736. doi: 10.1118/1.4735201.

DOI:10.1118/1.4735201

PMID:28517136

Abstract

PURPOSE

To study the effect of the virtual wedge and physical wedge filters on the surface and build-up region doses for 6 and 15MV high-energy photon beams for different field sizes and various source to surface distance(SSD).

METHODS

The measurements were made in water equivalent (PMMA) solid phantom in the build-up region at various SSD for various field sizes using virtual and physical wedge filters having different angles. A parallel-plate ion chamber (Markus) was used to measure the percent depth doses at surface and buildup region. Plane parallel ion chamber with fixed plate separation on the surface and buildup region would perturbate the dose measured, to get the proper dose over response correction factor was used.

RESULTS

The percentage depth dose at surface (PDD0) increased as the field size increased for open, virtual, and physical wedged beams. For open, 30 degree physical, and virtual wedged beams, the surface doses were found to be 15.4%, 11.2%, and 15.2% with 6-MV photons and 11.2%, 9.4%, 11.2% with 15-MV photons, respectively, at 10 × 10 cm field size at 100cm SSD.As SSD increases percentage depth dose at surface (PDD0) decreases for open,physical and virtual wedge field.

CONCLUSIONS

Percentage depth dose at surface (PDD0) of virtual wedged beams were similar to those of open beams. PDD0 of physical wedged beams were lower than those of open and virtual wedged beams. Surface doses for both PW and VW increases with field size and small increase in surface dose for both PW and VW fields as wedge angle increases especially for large fields.

摘要

目的

研究虚拟楔形滤过器和物理楔形滤过器对6MV和15MV高能光子束在不同射野大小及不同源皮距（SSD）时表面剂量和建成区剂量的影响。

方法

使用不同角度的虚拟和物理楔形滤过器，在水等效（PMMA）固体模体的建成区，于不同SSD下针对不同射野大小进行测量。采用平行板电离室（ Markus型）测量表面和建成区的百分深度剂量。表面和建成区具有固定极板间距的平行板电离室会干扰测量剂量，因此使用合适的剂量响应校正因子来获取准确剂量。

结果

对于开放野、虚拟楔形野和物理楔形野，表面百分深度剂量（PDD0）随射野大小增加而增加。对于开放野、30度物理楔形野和虚拟楔形野，在100cm SSD下10×10cm射野大小处，6MV光子束的表面剂量分别为15.4%、11.2%和15.2%，15MV光子束的表面剂量分别为11.2%、9.4%、11.2%。随着SSD增加，开放野、物理楔形野和虚拟楔形野的表面百分深度剂量（PDD0）降低。