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Radiation Therapy   

전립선암의 방사선치료 종류 소개: 미국 메모리얼 슬론케터링암센터 (뉴욕) 소개

저선량 근접치료법과 고선량 근접치료법의 뛰어난 효과와 안전성

Radiation therapists use high-energy rays delivered by external beam (similar to an x-ray) or brachytherapy (implanted radioactive seeds) to treat prostate cancer. High radiation therapy doses are linked to lower PSA levels and much lower rates of positive biopsies three years after the completion of therapy, and with new techniques radiation therapists can deliver higher doses with fewer side effects.

1) Intensity-Modulated Radiation Therapy (IMRT: 세기조절 방사선 치료법: 외부 방사선치료법)

In 3-D conformal radiation therapy physicians create a 3-D image of the prostate from multiple computed tomography (CT) scans and use this image and moveable leaves similar to the lens on a camera to precisely shape the radiation beam to the contours of the prostate. The beam delivers high doses of radiation specifically to prostate tissues while sparing surrounding organs and reducing the risk of injury to healthy tissues. In 1997, Memorial Sloan-Kettering radiation therapists introduced a sophisticated method of conformal radiotherapy called intensity-modulated radiation therapy (IMRT). With IMRT, radiotherapists calculate variable doses and angles of radiation to target the tumor, further reducing the dosage of radiation to healthy tissues.

In general, these outpatient treatments are given daily, Monday through Friday, for a period of nine to ten weeks. Long-term results are becoming available and indicate that a high rate of success can be achieved with this approach. Side effects include frequent urination and urgency of urination. These effects often are relieved with medications and gradually resolve a few months after treatments have been completed. Late effects are also possible, such as permanent impotence and occasional rectal bleeding, but severe side effects to the rectum and bladder are rare. Patients experiencing side effects meet with Memorial Sloan-Kettering specialists and receive treatment designed to alleviate these problems.

2) Brachytherapy (근접치료법)

Physicians at Memorial Sloan-Kettering also helped develop brachytherapy, in which radioactive seeds implanted into the prostate can deliver high doses of radiation directly to the tumor. In this outpatient procedure, physicians use ultrasound images of the prostate to determine the most effective placement of the seeds, which are permanently implanted in the prostate through thin needles. The seeds are small (about the size of sesame seeds), cause little or no discomfort, and their radioactivity diminishes over time. Brachytherapy can be as effective as surgery in treating men with low-grade, early stage prostate cancer. Possible side effects include impotence, urinary urgency and frequency, and occasional rectal discomfort.

Since 1997, Memorial Sloan-Kettering physicians have integrated a significant refinement to this procedure. In standard brachytherapy, physicians use ultrasound images taken several weeks before the procedure. Once in the operating room, doctors might find swelling in the area or that the prostate's shape or geometry has changed, and determine that the weeks-old images are no longer completely accurate. With a refined approach -- called intraoperative computer-based conformal optimization -- radiation therapists determine optimal seed placement in the operating room using an on-site computer and up-to-the-minute ultrasound images. A sophisticated program developed here can process six to seven million seed-coordinate possibilities and select the placement that will deliver the optimal dose to the prostate and the lowest dose to the rectum and the urethra.

Results with brachytherapy alone have been excellent, particularly for patients whose disease is in the earlier stages. Improvements in technique and enhanced precision have reduced the likelihood of urinary and rectal side effects, but they can still occur, as can late effects such as occasional rectal bleeding. Patients experiencing these effects from the treatment can meet with specialists here to treat the side effects.

For patients with more advanced stages or aggressive disease the combination of a permanent seed implant followed two months later by a five- to six-week course of highly focused, intensity-modulated radiotherapy is another effective means of safely delivering a high dose of radiation to the cancer. Doctors at Memorial Sloan-Kettering have observed high rates of tumor control with this approach as well, and the side effects are comparable to those following brachytherapy or intensity-modulated radiotherapy alone

3) High-Dose-Rate Brachytherapy (고선량 근접치료법)

For patients whose cancer is somewhat more advanced or aggressive, radiotherapists at Memorial Sloan-Kettering use high-dose-rate (HDR) or temporary brachytherapy to deliver weeks' worth of radiation in three to four minutes. In this procedure, radiotherapists send seeds into and out of the prostate on three occasions over the course of a day and a half. The needles that guide the placement of the seeds are left in place during that time. Radiation therapists plan temporary brachytherapy using an intraoperative computer program and always combine it with a five- to six-week course of IMRT. Excellent results have also been observed with this approach.

Researchers here are developing software that will provide instantaneous feedback about brachytherapy seed placement to further enhance and maximize the treatment's precision. Our radiation oncologists are also using the information from magnetic resonance spectroscopy to help intensify the radiation doses to regions of the prostate found to be abnormal.