Brachytherapy Treatment

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Treatment Planning

Treatment planning is the determination of where each of the 100 or so seeds used should be implanted in the prostate for maximum cure rates, minimum complication rates, and conformal dose distribution. Most treatment planning is done one or two weeks before the implant with an older and inaccurate technique called “pre-planning”. Modern high speed computers now allow the plan to be created in the operating room in one or two minutes at the time of the implant with a technique called “computerized intraoperative treatment planning”.

The old pre-plan method involves the collection of the ultrasound pictures one week prior to implant. These images are used to create a treatment plan by a physicist. This plan is brought to the operating room and used to treat the patient. Unfortunately, the ultrasound probe position and patient position cannot be exactly duplicated due to normal, daily anatomical shifts. Additionally, the prostate volume can increase up to 40% under anesthesia which makes the old pre-plan method inaccurate. The inaccuracies found in the pre-plan method can lead to hot and/or cold spots in the gland and incorrect prostate volume estimates which can result in radiation damage complications or recurrence of the cancer.

Additionally the old pre-plan method does not permit the use of advanced techniques such as Prostascint /MRI image fusion, dynamic dosimetry or nerve sparing brachytherapy since the pre-plan cannot be altered or modified. In distinction, intraoperative treatment planning allows complete customization of the plan at the time of anesthesia so the prostate and patient position do not change in the few minutes that elapses between the plan creation and the start of the implant.

Dr. Doggett’s research has shown that intraoperative treatment planning decreases the rectal dose by 33% and decreases the urethral dose by 12% compared to the old pre-plan method. Equally important, the radiation coverage of the prostate is increased 11% by the use of intraoperative treatment planning. (CLICK HERE FOR DR DOGGETT’S INTERNATIONAL PRESENTATION). The American Brachytherapy Society has published a report co-authored by Dr. Doggett that concluded “Intraoperative treatment planning addresses many of the limitations of current permanent prostate brachytherapy and has some advantages over the pre-planned technique”.

Dynamic dosimetry is an advanced software and hardware dependent proprietary technique that allows the determination of the seed position in 3D immediately after it has been placed in the prostate. After a seed is placed, its position as seen on a sideways (sagittal) ultrasound image is recorded in 3D by the computer. The computer automatically changes the isodose curves to reflect any deviation of seed position. As the implant proceeds, dynamic dosimetry allows the detection of hot spots and cold spots as they are forming, and re-calculates how the next row of seeds should be placed in order to minimize these hot and cold spots. Dynamic dosimetry enables the final implanted seed positions to be optimized and quantifies seed position deviation so corrections can be made intraoperatively. Dynamic dosimetry is not possible with the old pre-plan method.

Prostascint imaging combined with MRI scanning is a new technological advance in the diagnosis and treatment of prostate cancer. New state of the art software combines the anatomic clarity of an MRI picture with the ability of the Prostascint test to immunologically detect deposits of PSMA bearing cells.

The Prostascint/MRI fusion images are useful in the preoperative evaluation of newly diagnosed cases of prostate cancer as well as for guiding the intraoperative planning of a radioisotope seed implant.

Recent studies have shown the surprising finding of intra-abdominal lymph node metastasis in 20% of newly diagnosed prostate cancer patients. This does not appear related to PSA or Gleason score and emphasizes the heterogeneous nature of prostate cancer. This finding of intra-abdominal lymph node metastasis can indicate the need for systemic treatment such as hormone therapy.

Finally, the fusion images allow customization of the intraoperative treatment planning for brachytherapy. This permits increasing radiation doses to areas of higher cancer cell burden. Prostascint/MRI evidence of extra capsular extension or seminal vesicle involvement allows increase of radiation doses at these sites.

Dr. Doggett is an early adopter of a new technology called “systems pathology”. Patients’ existing pathology specimens are examined at a highly specialized laboratory with a computer utilizing pattern recognition technology and machine intelligence. Multiple different stains for specific molecular cancer markers, such as the androgen receptor, are evaluated and ranked according to computer specified parameters. This information is compared against a library of prostate cancer specimens from over 1000 patients who have been followed for over eight years. This comparison allows Dr. Doggett to more accurately determine which patients are at higher risk of cancer spread outside of the prostate and will benefit from additional therapy such as external beam radiation, chemotherapy and hormone therapy. The comparison also permits elimination of additional therapy such as external beam radiation, chemotherapy and hormone therapy in patients that the comparison shows are at low risk of cancer spread outside of the prostate.

History and Development of Brachytherapy

Dating back to 1901, shortly after the discovery of radioactivity, Pierre Curie of France first suggested the use of radioactive isotopes to treat cancer. Around the same time Alexander Graham Bell made a similar suggestion in America which began the interest in refining the science within the medical community. Two early pioneers of brachytherapy, Henri-Alexandre Danlos of the Curie Institute in France and Robert Abbe of St. Luke’s Memorial Hospital in New York tested the idea of shrinking tumors through exposure to radioactive materials. These early developments provided interest into the effects of radiation.

In the 1970’s several medical centers used brachytherapy to treat prostate cancer. Radioactive sources were placed using an open surgical technique using a hand-placed method whereby the the surgeon would use a finger placed in the rectum to identify the approximate location of the tumor and place the radioactive material accordingly. Long-term follow up of these early cases often provided less than satisfactory results and cancer control could not always be predicted. It is now well understood that these outcomes were the result of 1) technical inability to accurately or precisely place seeds, 2) lack of adequate means by which to estimate the volume of the prostate and develop an effective dose.

During the late 80’s and early 90’s the invention of transrectal ultrasound emerged allowing for improved the evaluation of the prostate. This advancement directly addressed the need for improved volume estimates of the prostate gland. Combined with the developments of template guidance, or precise needle placement of radioactive sources, Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) these technical improvements addressed the issues of the early years and advanced brachytherapy as a viable treatment for prostate cancer.

 

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