Medical Professionals Version - National Cancer Centre Singapore
Medical Professionals Version - National Cancer Centre Singapore
Medical Professionals Version - National Cancer Centre Singapore
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PAGE C2<br />
Under The Microscope<br />
SALUBRIS<br />
July / August 2009<br />
ADVANCES IN RADIOTHERAPY<br />
IN THE MANAGEMENT OF<br />
EARLY PROSTATE CANCER<br />
Continued from page C1.<br />
IMAGE GUIDED RADIOTHERAPY<br />
The prostate is a very mobile organ. Its position varies from day to day depending<br />
on the contents in the rectum and bladder. In the past, the uncertainty of the<br />
prostate’s position was dealt with by using larger treatment volumes. But this<br />
would mean a greater volume of normal tissue being irradiated. However, if the<br />
position of the prostate can be determined before each treatment, then smaller<br />
margins can be applied in the treatment volume. Methods of prostate localisation<br />
include ultrasound and the use of fiducial markers implanted within the prostate.<br />
In the latter method, images taken using the treatment machine’s on-board<br />
imaging device are compared with the images obtained during treatment planning.<br />
If the prostate is found to have shifted, then adjustments are made to align the<br />
radiation beam with the organ. This procedure is critical to IMRT as it helps ensure<br />
that the high-dose volume is accurately delivered to the prostate while the smaller<br />
margins required helps reduce the side-effects even when high doses are given.<br />
The most accurate method currently available is Dynamic Targeting Image Guided<br />
Radiotherapy where treatment machines are equipped with an on-board CT<br />
facility which is used to do scans of patients each day before treatment.<br />
These scanned images are the most accurate representation of the shape and<br />
position of a patient’s tumour or involved organ at the time of treatment.<br />
Adjustments based on these images help maximise the dose to the targeted organ<br />
while minimising the damage to the surrounding normal tissues.<br />
Gold fiducial markers have been used in the treatment of prostate cancer here<br />
since 2004 and NCCS installed its first dynamic targeting IGRT machine in 2007.<br />
HORMONES<br />
Prostate cancer is generally a hormone-responsive disease and there is much<br />
experience in the use of hormones in the treatment of advanced or metastatic<br />
disease. There is now also evidence to show that in selected patients the addition<br />
of androgen suppression therapy to radiotherapy improves disease-free survival<br />
and possibly even overall survival.<br />
BRACHYTHERAPY<br />
Brachytherapy is a method of radiation where radioactive seeds are implanted<br />
into the prostate to effect treatment from within. In the past, its use was limited by<br />
the inability to properly implant these radioactive sources into the prostate. With<br />
improvement in technology, we now have good imaging equipment to plan as well<br />
as monitor the placement of the seeds and modern devices which facilitates very<br />
good implantation transperineally with the use of needles.<br />
The advantage of this method of treatment is that much higher radiation doses can<br />
be concentrated in the prostate while sparing the surrounding tissue.<br />
THE FUTURE – CHARGED<br />
PARTICLE IRRADIATION?<br />
Charged particles such as protons<br />
or carbon ions can be focused<br />
even much more highly compared<br />
to photons and have the potential<br />
for even greater relative sparing<br />
of the surrounding normal tissues.<br />
Their biological effectiveness is also<br />
higher than the usual x-rays used in<br />
radiotherapy.<br />
This makes dose escalation to even<br />
higher doses feasible with even<br />
lesser morbidity to surrounding<br />
normal tissues. They, however,<br />
require very expensive facilities<br />
and are available in only very<br />
few research centres around the<br />
world. With the accumulation of<br />
experience from these centres and<br />
hopefully with technology becoming<br />
more affordable with time, it is<br />
hoped that such treatment would<br />
become more widely available for<br />
the treatment of prostate as well as<br />
other cancers in the future.