HDR Gives Reliable Delivery of Dose to the Target
Both external beam radiation and permanent seed treatment doses can differ substantially from the planned dose. In the case of external beam it is extremely difficult to get a human body into an exact position with millimeter precision on a treatment table for eight to nine weeks even with the highly touted Calypso system of image guidance. In the case of permanent seeds there can be anatomic changes or migration of seeds during the months it takes the permanents seeds to emit the dose. In contrast, HDR establishes and maintains the anatomic relationships to the target and the adjacent normal tissues throughout treatment because the treatment catheters go wherever the prostate goes. This in conjunction with the short treatment course permits accurate pre-treatment plan representations and reliable treatment delivery.
HDR Controls Dose to Normal Tissue
The urethra, bladder and rectum are within and adjacent to the prostate target. With both external beam and permanent seeds it is very difficult to “mould” the treatment around these sensitive structures. On the other hand with HDR we have a scaffold of treatment catheters and have an unlimited number of treatment positions and intensities to shape the treatment field. In a typical implant we have seventeen catheters and typically there are ten to fifteen treatment points within each catheter so there are over two hundred treatment points within a target roughly the size of a walnut so you can see the accuracy of the method.
HDR Has a Scientific (Radiobiology) Advantage
Prostate cancer unlike some other cancers can have a slower growth rate which can be closer to normal tissue than the more virulent cancers. Research has shown that larger doses of radiation over a shorter period of time as delivered by HDR may be radiobiologically superior to the protracted low doses over a long time that external beam or permanent seeds delivers.22-27
HDR is Intensity Modulated Treatment
With HDR, modulating the intensity of the treatment dose comes from adjusting the time the source stays at each position within the catheter matrix. It does not have the daily patient set up and prostate motion problems associated with external beam intensity modulated treatment (IMRT). Finally, the intensity is modulated at the target not as it enters the body. It is the functional equivalent of having an infinite range of dose intensity at every possible source position.
HDR Dose Calculation is Prospective
Permanent seed treatment doses are determined retrospectively because seeds are first inserted and then the dose is calculated. This is either done attempting to follow a pre operative plan or during the actual implant procedure. In contrast, with HDR the implant catheters and treatment positions are known from 3D imaging and the dose can be adjusted in advance of the source delivery. The final treatment plan is completed and approved by the physician before rather than during or after the source is administered.
HDR Can Treat Cancer that Extends Beyond the Prostate
If permanent seeds are placed at the border of the prostate (prostate capsule) or in the adjacent seminal vesicles there could be migration of the source out of position or into other tissues or into the seminal fluid. In contrast the HDR catheter matrix provides both general stability and the ability to place catheters at or beyond the prostate capsule and into the seminal vesicles without the possibility of source loss or migration.
HDR Can Treat Large Volume Prostates
Unlike permanent seeds which are implanted using parallel needle systems fixed to the operating table, HDR treatment can treat relatively large prostates due to the fexibility of the catheter matrix system. The bony anatomy (pubic arch) is also less limiting because the the catheters can be splayed out past the bony arch.
HDR Radiation Safety Is Excellent
Unlike permanent seeds complicated seed accounting measures are not needed. There is no seed loss or environmental exposure. Radiation exposure to other people does not occur. The HDR source is reuseable so there is no need for the logistics of source inventory or acquisition.
HDR Has Short Period of Acute Symptoms
All forms of radiation treatment to the pelvis cause transient acute inflammation of the pelvic structures and temporary irritation of bowel and bladder function. The duration of these symptoms depends on the volume of tissue irradiated and the time taken to deliver the radiation and the total dose of radiation. HDR limits volume, time and dose of radiation to normal structure so that the symptoms are of relatively short duration. The acute bowel symptoms are resolved in a couple of weeks and the urinary habits are generally back to baseline in about four weeks.
HDR Has Low Long Term Rectal and Urinary Side Effects
Long term side effects of prostate irradiation are related to the total dose and volume of tissue irradiated. HDR gives a gradient of rapid dose falloff to limit the dose to the surrounding normal structures. In our experience if HDR is given without external beam the long term rectal side effects were less than 1%.21 Long term urinary side effects occur in less than 10% of cases and depend on underlying symptomatic benign disease and prior urinary surgeries.4 Conservative measures such as medication and avoidance of urinary surgery after HDR are important for limiting longterm complications. The rates of urinary incontinence for patients who do not have surgical intervention are less than1%.