Intensity Modulated Breast Radiotherapy

In an effort to improve dose inhomogeneity in breast cancer treatment, intensity modulated radiotherapy has become a more popular option. Unlike most other sites where computer assistance is needed to perform IMRT with 7 or 9 fields, breast radiotherapy IMRT is often forward planned using tangential beams.

Rationale

Some patients, particularly those with larger breasts, are unable to achieve dose homogeneity that conforms with ICRU guidelines with 3D conformal radiotherapy using wedged opposed tangents. Some techniques, such as using higher energy photons (10-18 MV) can improve dose distribution in larger breasts but dose to surface may be compromised if the higher energy makes up more than 20% of the dose from a tangent. Other possible techniques include using a half beam block in special circumstances.
Intensity modulation avoids the use of these techniques by using 2 or more beam apertures to improve dose conformality. Randomised evidence suggests that forward planned IMRT can improve dose distribution and early follow up

Technique

The first aperture treats the entire breast volume, usually without a wedge. Dose distribution is calculated and then the second aperture is adjusted to block areas of high dose and deliver dose to low dose regions. This process is repeated until an even dose distribution is created.


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