**6. Reported treatment results**

*5.2.4. Dose prescription and optimization*

*5.2.4.2. Combined intracavitary/interstitial BT*

**5.3. Limitations of CT‐based planning**

The basic treatment plan prescribed to point A according to Japanese guidelines is first created for every implant. The point A dose is 6.0 Gy. Then, graphical optimization is performed

Similar to intracavitary BT, a basic plan prescribed to point A (6.0 Gy) is first created. Next, optimization of the intracavitary applicator is performed to reduce the doses to the OAR. Then, the interstitial needles are activated to increase the target coverage. Additional optimi-

In performing CT-based planning, the most important limitation is inaccurate delineation of the HR‐CTV. CT‐based delineation is often very different from MRI‐based delineation (**Figure 5**). The HR‐CTV D90 may be significantly affected by the difference in imaging modality at BT (MRI or CT). Hegazy et al. reported that CT-based HR-CTV contouring based on FIGO stage led to a large overestimation of the width and volume. They concluded that if only CT was available, a minimum two-third of the uterine height might be a good surrogate for the height of the HR-CTV [13]. Clinical gynecologic examination and acquisition of MR

**Figure 5.** Comparison of CT-based and MRI-based delineation of HRCTV. CT-based delineation is quite large compared

images just before the start of BT can help to improve the accuracy of delineation.

to achieve the treatment aim for both the HR-CTV and the OAR.

zation is usually performed to achieve the treatment aim.

*5.2.4.1. Intracavitary BT*

98 Radiotherapy

to MRI-based delineation.

There are an increasing number of published reports regarding treatment results of IGABT for cervical cancer as shown in **Table 4** [8–12, 14–17]. In 2011, Pötter et al. retrospectively analyzed 156 patients with FIGO stage IB to IVA cervical cancer treated by IGABT at Medical University of Vienna [8]. A combined IC/IS approach was used in 44% of the patients with residual disease at the time of BT. They reported the three-year overall survival (OS) rates for stage IB, IIB, and IIIB disease were 74, 79, and 45%, respectively. They also reported that three-year local control (LC) rates for stage IB, IIB, and IIIB disease were 100, 96, and 86%, respectively. These results indicate that IGABT can achieve excellent LC rates even in cases of unfavorable advanced disease, such as stage IIIB disease, by using interstitial needles.

In a recent large multicenter study called RetroEMBRACE, Sturdza et al. analyzed 731 patients [17]. They reported that three-year overall survival rates for stage IB, IIB, and IIIB patients


Notes: IGABT: image-guided adaptive brachytherapy, HR-CTV: high risk clinical target volume, LC: local control, CSS: cancer specific survival, OS: overall survival.

**Table 4.** Reported treatment results of IGABT for cervical cancer.

were 88, 78, and 56%, respectively. They also reported that three-year LC rates were 98, 93, and 79%, respectively. These results indicate that IGABT is an indispensable treatment tool to achieve excellent LC rates. Lindegaard et al. compared the treatment results of MRI-guided IGABT to X-ray-based BT [14]. Both OS and cancer‐specific survival (CSS) rates were significantly better in the patient group treated with MRI‐guided IGABT.

The mean total HR-CTVs in these reports ranged from 80.3 to 93 Gy in EQD2. All of the total HR-CTV D90s were more than 80 Gy. In our experience with IGABT for 50 cervical cancer patients, the mean total HR-CTV D90 was 77.0 Gy, lower than that at the representative centers. This difference was caused by the CS technique. According to other reports from Japan, although treatment outcomes were excellent, HR-CTV D90s were less than 70 Gy [18, 19]. These results are also lower than our findings. The studies used CT‐based planning, which also accounted for the large difference when combined with CS technique. It is likely that a larger HR‐CTV delineated using CT and a lower WPI dose combined with CS technique resulted in a significantly lower D90. MRI-based planning without CS technique might achieve HR-CTV D90 comparable to that in foreign institutions. More institutions in Japan should perform MRI-based planning because it may become the global standard. Use of CS technique should also be discussed.

In summary, the use of IGABT can help achieve excellent LC even in advanced stage cervical cancer with the help of interstitial needles. Survival results with IGABT showed superiority to those achieved with traditional X‐ray‐based BT. HR‐CTV D90 can be easily affected by imaging modality and variability of EBRT dosing. However, 45 Gy of WPI and MRI-based treatment planning aiming for a total HR-CTV D90 from 80 to 85 Gy should be considered the most appropriate treatment regimen.
