A Patient's Guide to
Managing Hormone-Refractory Prostate Cancer
Chapter 12. Radiation
Therapy and When to Use it
Radiation to individual bone or soft tissue lesions
Radiation therapy is one of
the primary treatments for prostate cancer. In the case of hormone
refractory prostate cancer the use of radiotherapy is mostly palliative. Radiotherapy may be beneficial for reducing or eliminating pain or,
in some circumstances, reducing or eliminating a tumor. At this stage of
prostate cancer, the disease is systemic and not localized and treating a
lesion in bone or soft tissue is proper and often used to improve the
quality of life of the patient.
Radiation therapy can be used for controlling
individual bone lesions, reducing pain in 80% of patients and also reducing
the risk of fracture. Treatment of one bone metastasis has little risk, but
as more and more bone metastases are treated using radiation, the greater
the toxicity to bone marrow. This is usually a limiting factor for those
hrpc patients treated primarily with radiotherapy.
The treatment of painful lesions in bone or soft
tissues involves several methods of delivering radiation to those areas. The
forms of radiation are the same as in the primary treatment of PCa,
including IMRT, 3DCRT and RT. A newer modality called Tomotherapy is said to
be more targeted and precise delivery in the treatment of individual
lesions. Because of the more precise nature of this therapy, a higher dose
can be delivered to the target without collateral damage.
Tomotherapy is IMRT with helical/spiral computed
tomography scanning delivery. The small beams of radiation are delivered
from every point on a spiral. Tomotherapy, or "slice therapy," gets its name
from tomography, or cross-sectional imaging.
In a small trial, 22 spinal lesions were treated (De
Salles, et al., 2004). Treatment was planned using IMRT fields in 15 cases,
dynamic arcs in five, and conformal beams in two. Researchers stated that
shaped beam and IMRS/IMRT may delay neurological deterioration, improving
quality of life. They noted the lack of complication suggests that higher
doses can be delivered to improve the control rate in patients with
metastases.
Radiopharmaceutical treatment (infused radioisotopes)
If a patient has multiple lesions, the type of
radiation mentioned above is impractical, if not practically impossible. In
such patients, radiopharmaceuticals are used to treat the lesions
systemically. The two FDA approved and most commonly used radioisotopes are
Strontium-89 and Samarium-153. These radiopharmaceuticals are
preferentially taken up when infused intravenously and deliver beta or gamma
irradiation in sites where there is new bone formation. The exact mechanism
of action of pain relief is not known, although PSA declines reported after
treatment in some studies suggest there is some direct effect on the cells
(cell kill). This form of therapy can be used effectively more than once as
long as the production of blood cells is not impacted. This type of
radiation has been used in combination with chemotherapy to reduce bone
pain.
A newer modality of
radiotherapy is being developed by the use of radiochemicals complexed with
a humanized monoclonal antibody which has targeted affinity for prostate
specific membrane antigen (PSMA). Indium-111, Yttrium-90 and Lutetium-177
are some of the materials under investigation and in clinical trials.
Radioimmunotherapy is therefore a potential new avenue to treat hrpc. At one
time, Millennium Pharmaceuticals was
developing the Yttrium-90 combination, but they do not currently list
anything with a radioactive component on their website (www.mlnm.com
). There is a trial using Lutetium-177 being started at MSKCC in NYC.
For a more detailed information on the use of
radiotherapy to treat hrpc patients please visit the
radiation pages in the main website.
A good website
for information about radiation therapy can be found at the RT Answers
Website, which is a product of ASTRO
(American
Society for Therapeutic Radiology and Oncology)
http://www.rtanswers.org/index.htm. Included are a glossary,
cancer specific information, side effects and more.
Continue to Chapter 13
Ralph Valle & Howard Hansen 10/6/05
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