Honing in On HDR

By Daniel G. Petereit, MD
(Originally printed in November 2001 issue of Advance for Imaging and Oncology Administrators. This is the second of a two-part series. Part 1 detailed using HDR brachytherapy for treating cervical cancer.)

The most common female malignancy of the reproductive tract with nearly 36,000 cases annually, endometrial cancer still boasts a lower mortality rate than cervical or ovarian cancer, since most patients present with early stage disease. While surgery remains the treatment of choice, a small percentage of patients are inoperable because of severe medical problems or morbid obesity. For these patients, radiation is the only potentially curable option. The use of high-dose-rate (HDR) brachytherapy, with its shorter treatment duration, offers a chance for cure and improved quality of life.

Standard surgical therapy consists of an extrafascial hysterectomy, bilateral salpingo-oophorectomy, peritoneal washings, and an assessment of the draining lympthatics.¹ In addition, adjuvant pelvic radiotherapy is often administered in the presence of known risk factors for recurrence such as deep myometrial invasion and/or high-grade lesions.

Vaginal Cuff Brachytherapy

Thoroughly staged patients with uterine-confined endometrial cancer usually exhibited a pattern of failure predominately at the vaginal apex, according to two recent randomized studies.^2-3

For these patients, vaginal cuff brachytherapy (VCB) is a cost-effective, low-morbidity alternative to external beam radiotherapy that treats the site of greatest risk for recurrence. Because pelvic radiotherapy can potentially induce significant bowel complications (1 percent to 11 percent),^2-3 VCB is offered for both low- and intermediate-risk endometrial patients. Having significantly fewer toxicities and affording nearly the same protection against recurrences, VCB is also supported by several recent reports for treating higher-risk state I patients who previously would have received whole pelvic radiotherapy.

Intended to treat occult vaginal disease following a hysterectomy, vaginal brachytherapy involves treating the vaginal mucosa with low-dose-rate (LDR) brachytherapy – which, unfortunately, hospitalizes, immobilizes and bed-confines a patient for 50 to 60 hours, due to the low activity of the radiation sources (<200 rads/hour). Because of the attendant cost, potential morbidity and modest therapeutic gains for low-risk-endometrial patients, LDR vaginal brachytherapy is generally restricted to patients with higher risk for vaginal recurrences.

HDR Brachytherapy

Ovoids and cylinders are used as vaginal applicators in HDR brachytherapy. Figure 1 illustrates the gynecologic applicators used to treat the vaginal apex. At Rapid City Regional Cancer Center, patients are lightly sedated and receive a 10- to 15-minute ovoid treatment in a dedicated brachytherapy suite. The treatment schedule consists of two fractions of 16.2 Gy delivered to the vaginal surface, which delivers an LDR equivalent of 60 Gy at 100 rads/h. Each insertion is separated by one week.

Since the dose is prescribed to the vaginal surface and the dwell time positions depend only on ovoid diameter and iridium source strength, a simple computerized program can eliminate the need for individual treatment planning. Typically, the dwell time positions have been calculated by the time insertion has been completed. An AP and lateral film assess the insertion and packing, and are retained for documentation purposes. Alternatively, cylinders can treat the upper third of the vagina. Conscious sedation isn't required when using cylinders, since packing is omitted.

Petereit et al. reported the University of Wisconsin Experience using vaginal cuff brachytherapy for 191 patients with uterine-confined endometrial cancer.⁴ The patients, treated with only two insertions using the technique described above, had four-year survival, relapse-free survival and vaginal-control rates of 95 percent, 98 percent and 100 percent, respectively. Although one patient experienced a significant complication; none experienced moderate or severe vaginal fibrosis or shortening.

In a recent fractionation schedule analysis for endometrial patient receiving only HDR brachytherapy, findings show that several schedules appear effective in reducing the risk for isolated vaginal cuff recurrence with minimal complication rates.⁵ The University of Wisconsin Experience, using only two HDR brachytherapy insertions, is the most convenient fractionation schedule reported. The most common fractionation schedule is 7 Gy over three treatments prescribed at 5 mm, using vaginal cylinders to treat the upper third to half of the vagina.

While treating cervical cancer patients with HDR brachytherapy remains controversial, its use as adjuvant treatment for endometrial cancer patients is widely accepted. In fact, using LDR brachytherapy makes little sense, unless an institution doesn't have access to HDR.

Inoperable Endometrial Cancer

For a small percentage of inoperable endometrial patients, primary radiotherapy is the only curative option, with five-year survival rates ranging from 25 percent to 75 percent. Most publications describe LDR – not HDR – brachytherapy. Nguyen and Petereit described the University of Wisconsin Experience for 36 patients with medically inoperable Stage I endometrial cancer treated with HDR brachytherapy alone.⁵ Surgery was precluded because of obesity and/or poor cardiopulmonary reserve. Patients received five weekly HDR outpatient brachytherapy applications while under intravenous conscious sedation. No external beam radiation was administered.

The three-year survival, disease-free survival and uterine-control rates were 65 percent, 85 percent and 88 percent, respectively. The pelvic control rate was 85 percent, with one patient failing in the lower vagina. No pelvic lymph node recurrences were reported. Figure 2 illustrates the applicator and close prescription points used for inoperable endometrial cancer.

While primary surgery will continue to be the standard of care for endometrial carcinoma for the foreseeable future, HDR brachytherapy treatment has demonstrated that it can play a prominent role in treating medically and technically inoperable patients.

References

1. Petereit, D.G. (2000). Complete surgical staging in endometrial cancer provides prognostic information only. Seminars in Radiation Oncology; 10, 8-14.
2. Roberts, J.A., Burnetto, V.L., Keys, H.M., et al. (1998). A phase III randomized study of surgery vs. surgery plus adjunctive radiation therapy in intermediate-risk endometrial. Gynecologic Oncology; 68, 135.
3. Creutzberg, C.L., van Putten, W.L., Koper P.C., et al. (2000). Treatment morbidity in patients with endometrial cancer: results from a multicenter randomized trial. Lancet; 355, 1404-11.
4. Petereit, D.G., Tannehill, S.P., Grosen, E.A., et al. (1999). Outpatient vaginal cuff brachytherapy for endometrial cancer. International Journal of Gynecologic Cancer; 9, 456-62.
5. Pearcey, R.G., Petereit, D.G. (2000). Post-operative high-dose-rate brachytherapy in patients with low to intermediate risk endometrial cancer: evidence for a favorable therapeutic ratio. Radiotherapy and Oncology; 56, 17-22.

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