Radiation Therapy for Cancer

Radiation Therapy for Cancer

INTRODUCTION

Radiation therapy (RT) plays an important and evolving role as definitive and adjuvant therapy for gynecologic malignancies. Based upon evidence-based treatment guidelines, epidemiologic analysis suggests that radiation therapy is indicated for 60 percent of cervical cancer patients, 45 percent of endometrial cancer patients, 35 percent of vulvar cancer patients, 100 percent of vaginal cancer patients, and 5 percent of patients with ovarian cancer (Dalaney et al, 2004).External beam RT (EBRT) and brachytherapy are used individually and in tandem according to cancer site and extent of disease. Advances in treatment planning and delivery of external beam radiation therapy (EBRT), including three-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), and image-guided radiation therapy, provide the technology to precisely plan, target, and deliver radiation therapy with the goal of optimizing the radiation dose to the target while sparing normal tissue. Brachytherapy, with the development of high dose rate (HDR) systems and remote afterloaders, also allows for the precise delivery of high-dose radiation to the target tissue with sparing of the surrounding normal tissue, in a safe and efficient manner. The integration of concurrent chemotherapy is also improving treatment outcomes

Discussion

Cervical cancer

Treatment of cervical cancer depends upon stage of disease and can be approached with surgery often followed by adjuvant RT or definitive RT with or without concurrent chemotherapy.

Adjuvant RT

Adjuvant radiotherapy (RT), usually with concurrent cisplatin-based chemotherapy, offers benefit to patients with high-risk pathologic factors; these include >1/3 cervical stromal invasion, tumor diameter =4 cm, lymph node involvement, lymphovascular space invasion, evidence of microscopic parametrial extension, or a positive resection margin (Rotman, 2006; Sedius, 1999, Peters, 2000).

Adjuvant EBRT targets the at-risk tissues in the pelvis to eradicate potential occult sites of disease. Traditionally, treatment has been delivered using a four-field technique, which employs equally weighted anteroposterior-posteroanterior (AP-PA) and opposed lateral beams. With conventional 2DXRT, radiation field borders and design were described relative to skeletal anatomy. With the use of three-dimensional imaging, 3DCRT plans should be designed to adequately cover soft tissue regions at risk, including nearby parametrial and vaginal tissue and the pelvic lymph nodes. It is important to take into account variations in patient anatomy and postsurgical changes.

It is necessary to adequately cover all locoregionally draining lymphatics, which include obturator, internal iliac, presacral, external iliac, and common iliac lymph nodes through their coalescence at the inferior vena cava, which roughly corresponds to a superior field border at the L4-L5 disk space. Inferiorly, the field edge should extend 3 to 4 cm below the lowest extent of disease or to the bottom of the obturator foramen. The lateral margin should be set 1.5 to 2 cm lateral to the pelvic brim and is designed to give a margin on the pelvic vessels and lymphatics (figure 1).

The recommended dose is 45 to 50.4 Gy given in standard 1.8 to 2 Gy fractions over five to six weeks. If there is any gross residual disease or positive nodes, the dose should be boosted to 54 to 60 Gy, as permitted ...