**Author details**

cal wedge field that arises from the interaction of the beam with the material of the physical

Clinically, this provides an advantage to the nonphysical wedge field [32]. The effect of secondary radiation outside the field is an important consideration for breast cancer treatment. For example, **Figure 4** shows how the low-dose area was expanded to the opposite breast when using physical wedges; such secondary radiation exposure may precipitate the development of another tumor. Warlic et al. reported that the average dose outside of the field with a nonphysical wedge was 2.7–2.8%, whereas the dose was 4.0–4.7% with a physical wedge. The nonphysical wedge is hence a practical advance that improves the dose distribution in patients undergoing breast conservation while simultaneously minimizing the dose to the contralateral breast, thereby reducing potential carcinogenic effects [33].

Nonphysical wedges have significant benefits for both the therapists and patients. Saminathan et al. reported that the number of MUs used to deliver a particular dose using a nonphysical wedge field is less than that used for a physical wedge field [2]. Moreover, Njeh reported that using nonphysical wedges results in significant dose reductions to areas outside of the treatment field [34]. The reduction of MUs can also result in minimizing treatment times; this

**Figure 4.** The dose distributions of radiotherapy in a breast cancer patient using (a) physical wedges or (b) nonphysical

Each of the two wedge types, physical and nonphysical, has several characteristics that produce both advantages and disadvantages under specific conditions. Clinicians should choose between physical and nonphysical wedges with careful consideration to tumor motion, the

effect of secondary radiation, and the performance status of the patient.

wedges. Each line indicates the dose corresponding to each treatment intensity planning.

wedge (such interactions include Compton scattering).

258 Radiotherapy

benefits patients who have worse performance statuses.

**4. Conclusions**

Hiroaki Akasaka\*, Naritoshi Mukumoto, Masao Nakayama, Tianyuan Wang, Ryuichi Yada, Yasuyuki Shimizu, Saki Osuga, Yuki Wakahara and Ryohei Sasaki

\*Address all correspondence to: akasaka@harbor.kobe-u.ac.jp

Division of Radiation Oncology, Kobe University Graduate School of Medicine, Kobe City, Hyogo, Japan
