RADIATION MEDICINE INNOVATIONS FOR THE NEW MILLENIUM: ULTRASOUND-GUIDED TRANSPERINEAL

30 Jan
2010

radiation therapy

The optimal management of clinically localized prostate cancer remains controversial. The technique of ultrasound-guided transperineal radioactive seed implants has rapidly gained popularity in the treatment of early-stage prostate cancer with a five-year disease-specific survival of 90%. This methodology has several potential advantages to external beam radiotherapy or other implantation techniques, such as (1) pre-treatment planning; (2) precision of seed placement; (3) higher total dose to the prostate; (4) the ability to place seeds in the periprostatic region; (5) outpatient treatment; (6) low morbidity; and (7) preliminary PSA progression-free survival rates equal or superior to external beam irradiation and radical prostatectomy. It remains to be seen whether the long-term (15-year) results are as encouraging. RTOG 9805 is a multi-institutional phase II trial that will help clarify the indications and role of this popular treatment option. There has been such an increase in the utilization of these procedures that by the year 2005, it is expected that one-third of all prostate cancer patients with organ confined disease will be treated by brachytherapy only (2000-2001 ACR Standards for Radiation Oncology).

HIGH-DOSE RATE BRACHYTHERAPY

High-dose rate (HDR) brachytherapy has become a popular treatment modality for cervical cancer, endobronchial lung and esophageal lesions, and for prostate cancer. It also has been used as an adjunct after resection of soft tissue sarcomas, or recurrent rectal carcinoma. More recently, it has been utilized for coronary stenosis. The advantages of this technique include the ability to deliver treatment on an out-patient basis, with its associated potential for reduced cost, while elimi­nating radiation exposure to medical personnel. In the case of cervical cancer, one also avoids the inpatient risk of bed-rest induced venostasis and the associated risk of pulmonary embolus, which has been reported with Cesium-137 low-dose rate (LDR) brachytherapy. The history of HDR in the treatment of cervical cancer is well documented  The role of HDR in palliative treatment of bronchial obstruction has been established. Viagra Online Canadian Pharmacy

Unlike recurrences from colon cancer, patients with an isolated local recurrence from rectal cancer should be given the opportunity for aggressive surgical treatment, since approximately 50% of patients with locally recurrent disease have isolated lesions that are amenable to surgical resection.

At the time of surgery, HDR catheters can be positioned, externalized, and secured to the skin with silk ties. Similar doses of radiation as with intra-operative radiotherapy (IORT) can be achieved, because the treatment plan can be fractionated. Since the catheters are remotely after-loaded, treatment of patients in postoperative care units can be delayed until patients are stable. Approximately one-quarter of patients survive more than two years, as compared to six months for those treated with supportive care or chemotherapy only.

Researchers at the University of Southern California examined the combination of external beam irradiation, protracted infusion (PI) chemotherapy plus intraluminal brachytherapy boost in the treatment of esophageal carcinoma. The goal was to assess the effect of this combined modality treatment on improving local and regional control as well as on overall survival. The combined modalities of external beam radiation, continuous infusion chemotherapy, and intraluminal brachytherapy boost appears to have led to prolongation of survival in patients with esophageal carcinoma. However, the toxicity of pain and stricture were significant.

The role of preoperative neoadjuvant chemoradiation and adjuvant high-dose rate brachytherapy in the management of unfavorable soft tissue sarcomas of the extremities was examined at the University of Southern California. The effect of high-dose rate interstitial brachytherapy

(HDR-IBT) on reducing the risk of local recurrence following limb-sparing resection was evaluated with a secondary goal of shortening the overall treatment time. Following an en bloc resection, HDR-IBT was administered after catheters (4.7 Fr. Teflon) were secured in the tumor bed and the distal end was externalized. Radiation doses ranged from 13 to 30 Gy given in twice-daily fractions prescribed to a distance of 5mm to 7.5mm from the center of the radioactive source. HDR-IBT reduced local recurrence of high-risk soft tissue sarcomas of the extremity following en bloc resection.

Adjuvant chemotherapy may play a role in local control, as well as in overall and disease-free survival. This modality is a viable alternative since preoperative radiation therapy only increases wound complications, and in many tumors with negative margins, postoperative high-dose rate brachytherapy will suffice, with catheters placed at the time of surgical resection. buy kamagra tablets

High-dose rate brachytherapy is being investigated in the treatment of prostate cancer as an adjunct to definitive external beam radiation therapy, with excellent results, or as monotherapy, always as a temporary interstitial implant. There appear to be some inherent biological advantages of high-dose rate radiation over low-dose rate irradiation in terms of improved tissue tolerance, but this has yet to be confirmed in prospective randomized trials.

Considerable attention has been given over the last five years, to interstitial brachytherapy as an adjuvant to lumpectomy in breast-conserving therapy. The technique was developed more than 40 years ago by Ulrich Henschke, as boost therapy after external beam radiation using low-dose rate Ir-192 wires. This preceded and was later replaced by the availability of linear accelerators with electron capability that became the standard way to deliver the radiation boost in breast cancer. Renewed interest in breast brachytherapy has led to its increasing use as the only treatment after lumpectomy using an Ir-192 HDR source. It was first employed by Robert Kuske et al. at the Oschner Clinic in New Orleans and led to the

Radiation Therapy Oncology Group (RTOG) Clinical Trial for early stage, along with a separate experience at William Beaumont Hospital (near Detroit, MI) of 50 patients. The RTOG trial closed March 1, 2001, and analysis has not been completed. Kuske et al. had a mean follow-up of 46 months, whereas Vicini et al. had a median follow-up of 36 months. In the Oschner and William Beaumont groups, there have been no recurrences in the target volume. Both clinicians and patients have expressed great interest in this technique, as it may dramatically reduce the treatment time of six to seven weeks, to approximately one week.

Vascular restenosis remains a vexing problem for patients with coronary and other arterial diseases. Percutaneous transluminal coronary angioplasty (PTCA), with or without stent placement, has dramatically improved the outcome in patients with coronary artery disease. Nevertheless, the majority of patients suffer restenosis within six months, and this remains the “Achilles’ heel” of PTCA. Nearly 75% of the 700,000 cases of PTCA require a repeat procedure due to re-occlusion. Anatomic and radiographic studies have suggested that the greatest incidence of neointimal proliferation predisposing to vascular restenosis occurs within the first seven days after angioplasty. erectalis 20

Coronary intravascular brachytherapy, when delivered soon after PTCA, can markedly reduce the incidence of restenosis. Condado et al. reported the first clinical experience in human subjects in a non-randomized trial from Venezuela using an Ir-192 source inserted on a monorail catheter. The procedure was well tolerated, without adverse treatment-related effects, and with significant rate of vascular patency. Subsequently, several trials, including two lead articles in the New England Journal of Medicine, have demonstrated the efficacy of this technique. Reasonable expectations for improved patency of the coronary vessel, reduction in the need for repeat PTCA, and a reduction in cardiac events have been reported. Further refinement of this technique is ongoing and relates to the timing of radiation and mechanism of radiation delivery, radiation source (i.e. alpha or beta particle emitters), as well as criteria for patient selection.

CONCLUSION

Radiation oncology has experienced major technological advances during the past decade. Complications and side effects, recognized and reported by early pioneers in this field, are now significantly reduced. Recent advances have followed a well-established concept that deliverable radiation dose is inversely proportional to the volume treated. As the target (i.e. tumor) definition improves, dose to normal surrounding and critical structures can be markedly reduced, thus improving the therapeutic ratio. This reduction in toxicity may also permit dose escalation with the potential improvement in local control and survival. Technological advances in equipment and techniques have positioned radiation therapy as a major modality in the multidisciplinary management of benign and malignant disease. eriacta tablets

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