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Revolutionizing Cancer Treatment with High Dose
Rate Brachytherapy

By Jim Hslang, MD

Brachytherapy is radiotherapy whereby a radioactive source is placed inside or next to the area requiring treatment. Brachy is from a Greek word for "short", so brachytherapy is hence short distance therapy. Sources are inserted either into tissue such as the prostate, into cavities such as for breast, cervical, endometrial or nasopharynx cancers, or into lumens such as for lung or esophageal cancers.

Brachytherapy allows the treatment of cancers with either permanent or temporary implants precisely placed in tumors so that radiation dose lines can conform to the size and shape of the target while at the same time limiting dose and side effects to surrounding normal structures.

High Dose Rate (HDR) brachytherapy is an exciting new treatment regimen with significant advantages over low dose rate (LDR) brachytherapy. HDR applicators in the form of catheters are placed in the target volume and a high dose rate source such as iridium-192 at the end of a wire, travels along these catheters via the control of an automated computer while the patient is treated in a room. The source dwells in a predetermined position and time; it moves along the length of the catheters in this pattern in order to build up the planned dose distribution. This “remote afterloading” technique allows healthcare providers to be outside the shielded brachytherapy suite during treatment, and thus markedly decreases staff exposure to radiation. Patients also enjoy the benefit of a quick outpatient treatment compared to overnight stays as an inpatient, previously required with LDR.

Partial breast irradiation HDR with the Mammosite system shows much promise as patients can complete treatments in 5 days, compared to a typical 6 weeks. Patients would receive 10 fractions of 340cGy each for 5 treatment days using a twice a day fractionation scheme. An initial study reported a total ipsilateral breast failure rate of 0.9 percent with very low “elsewhere” failures. And women out greater than 3 years experienced 100 percent good/excellent cosmetic results. Similarly, a large single institution study here in San Antonio reported an “in breast” failure rate of 0.8 percent, with “excellent” and “good/fair” cosmesis rates of 78 percent and 16 percent respectively with limited followup.

Patients selected for this treatment modality should have similar characteristics to patients deemed eligible for the national phase III randomized study: National Surgical Adjuvant Breast and Bowel Project (NSABP) Protocol B-39 or Radiation Therapy Oncology Group (RTOG) 0413. This trial compares whole breast irradiation versus partial breast irradiation for women with stage 0, I or II breast cancer. Eligibility criteria includes patients age 18 and older, invasive adenocarcinoma or DCIS, tumor size <=3cm, negative microscopic surgical margins of excision based on NSABP definition, lymph node negative or 1-3 nodes positive.

Prostate HDR brachytherapy is another new and revolutionizing treatment regimen. While permanent seed
brachytherapy with the LDR technique has already gained popularity, appearing to replace radical prostatectomy for early stage prostate cancer, the HDR modality offers another equally effective alternative. HDR has enabled dose escalation in prostate cancer using pelvic external beam radiotherapy combined with HDR boost treatments in intermediate and high risk patients. A prospective but nonrandomized study showed a 5-year biochemical failure rate of 14 percent, cause specific survival of 100 percent, and overall survival of 97.8 percent. Data on HDR as monotherapy in low risk patients when compared to LDR brachytherapy were recently shown to have similar clinical outcomes with low and acceptable acute and chronic toxicities.

Jim Hsiang, MD is a Board Certified Radiation Oncologist at the Texas Cancer Clinic and an investigator participating in the National Cancer Institute sponsored Radiation Therapy Oncology Group cooperative group studies. Dr. Hsiang has a BS degree from UCLA, MD degree from UC Davis and an MBA from the University of Pittsburgh.