*Cervical Cancer DOI: http://dx.doi.org/10.5772/intechopen.110131*

as directed by involved nodal distribution). Patients with below one-third vaginal involvement should also have bilateral groins covered. There have been published international consensus guidelines for target volume contouring [34]. The multiinstitutional cooperative group phase III NRG-GY006 clinical trial contouring recommendations derived by Nancy lee and colleagues are presented in **Table 5** [35].

For patients with primary cervical cancer who are not candidates for surgery, brachytherapy is a key component of the ultimate treatment plan that they will follow. In this case, either an intracavitary or an interstitial approach will do the trick. GEC-ESTRO recommendations are available for volume-based brachytherapy contouring, and they recommend utilizing CT or MRI to delineate treatment targets [36]. A highrisk MRI-based CTV is defined as the whole cervix in addition to any parametrial or vaginal extension (gray zones). CT-based CTV (high-risk): all central tissue at the level of ring or ovoids, superiorly to internal os, then 1 cm "cone" along tandem above


#### **Table 5.**

*Target delineation for cervical cancer (per NRG-GY006 protocol).*

cervix; laterally, include any parametrial extension (gray/white) or clinical vaginal involvement. CT-based CTV (low-risk): all central tissue at the level of ring or ovoids, superiorly to internal os. There are two-point definitions for point-based dosage in brachytherapy: ICRU 38 and 2011 ABS point. Point A is located at the point where the tandem meets the line that connects the peaks of the ovoids or the ring; it is situated 2 cms above and 2 cms to the side of the tandem (point B 5 cm lateral to the tandem). The bladder point is the posterior position of the midfoley balloon after it has been inflated with 7 ml of fluid. The rectal point is located 5 mm posterior to the vaginal wall at the lower intrauterine source. The surface of ovoids or cylinders that make up the vaginal cavity.

In patients with an intact cervix, the original tumor and susceptible regional lymphatics are routinely treated with 45 Gy of definitive EBRT (40–50 Gy). The dose of EBRT would be proportional to the nodal status as assessed by surgery or imaging. The primary cervical tumor is then boosted employing brachytherapy with an additional 30–40 Gy using image guidance (preferred) or to point A (in low dose-rate [LDR] equivalent dose), for a total point A dose of 80 Gy for small-volume cervical tumors or 85 Gy for larger-volume cervical tumors. For highly tiny tumors (clinically inoperable IA1 or IA2), 75–80 Gy EQD2 D90 dosages may be explored. Grossly affected, unresected lymph nodes may be boosted with an additional 10–15 Gy of highly conformal EBRT. When employing imaging guidance for EBRT, care must be made to exclude or severely restrict the amount of normal tissue inside the high-dose zones (**Tables 6**–**8**).

The presence of one or more pathologic risk factors following a prior hysterectomy may justify the use of adjuvant RT. The following should be covered at a minimum: the top 3–4 cms of the vaginal cuff, the parametria, and surrounding nodal regions (such as the external and internal iliac, obturator, and presacral nodes). The radiation field's superior edge should be increased accordingly for confirmed nodal metastases. In general, 45–50 Gy in conventional fractionation is advised for IMRT. Four grossly


#### **Table 6.**

*GYN tissue tolerances.*


#### **Table 7.**

*Post-hysterectomy dose constraints.*


#### **Table 8.**

*Brachytherapy for cervical cancer dose constraints.*

affected, unresected lymph nodes may be considered for boosting with an extra 10– 20 Gy of highly conformal EBRT.

In exceptional cases, patients whose anatomy or tumor geometry makes intracavitary brachytherapy impossible may be effectively treated with an interstitial approach; however, such interstitial brachytherapy should be accomplished only by individuals and institutions with the required knowledge and training, and early referral for prompt use of own knowledge and experience is essential. In certain posthysterectomy patients (particularly those with positive or near vaginal mucosal surgical margins), vaginal cylinder brachytherapy may be utilized as an adjunct to external beam radiation treatment (EBRT). Typically, the prescription is applied to the vaginal surface or 5 mm below it. Typical fractionation strategies include 5.5 Gy 2 fractions at 5 mm or 6 Gy 3 fractions at the vaginal surface.

SBRT is the most certain technique among all EBRT modalities in terms of its ability to simulate a brachytherapy dose distribution with a steep dose gradient and, as a result, achieve the same treatment outcomes as ICB, at least theoretically. Although being under investigation and recommended by few retrospective reviews, SBRT is not regarded as a reasonable alternative to brachytherapy for routine use.
