Trial Information

Prospective Endoscopic Safety Evaluation of Late Rectal Mucosal Injury Following CyberKnife Radiosurgery for Clinically Localized Prostate Cancer

Radiation therapy is a well-established treatment modality for clinically localized prostate
cancer. Current techniques include conventional external beam radiotherapy and intensity
modulated radiation therapy (IMRT). The efficacy of conventional external beam radiation
treatment (60-70 Gy in 2 Gy fractions) using several uniform fields has been documented.
The 10-year disease-free survival rate for patients with disease confined to the prostate in
the pre-PSA era was approximately 50-70%. Analysis of these data suggested that dose
escalation could improve local control in prostate cancer.

On average, men who choose to undergo radiation therapy treatments for prostate cancer will
have to live with the side effects of therapy for many years. Chronic proctitis may occur
after radiotherapy (RT) to the pelvic region. According to a published series, it clinically
occurs after radiation therapy of localized prostate cancer at a frequency of 5-20%. It
occurs months to years after treatment (average 8-12 months) with a large majority within
two years following radiation therapy. Patient characteristics, such as a history of
inflammatory bowel disease or chronic anticoagulation therapy, may increase an individual
patient's risk of clinically significant proctitis. Patients with radiation-induced
proctopathy have described symptoms of rectal pain, diarrhea, urgency, rectal bleeding, and
increased frequency of bowel movements. Endoscopic evaluation shows telangiectasia,
congested mucosa and ulcers. Rectal bleeding occurs from the neovascular telangiectasia
seen in about 60% of patients receiving conventionally fractionated radiation therapy. The
other symptoms probably develop from the decreased rectal compliance associated with rectal
wall fibrosis. These symptoms are, in current reports, most often classified according to
the NCI Common Toxicity Criteria grade for late gastrointestinal side effects. Due to the
proximity of the rectum and bladder to the prostate, using conventional techniques, the
prescription dose is limited to 65-70 Gy. Although attempts were made to protect the
rectum, the incidence of rectal bleeding was unacceptable at doses greater than 70 Gy (20%).

The risk of proctitis and rectal bleeding appeared to be dependent upon both the radiation
dose and the volume of the rectum in the high dose area. Radiation Oncologists' efforts to
optimize the therapeutic ratio for prostate cancer treatment have therefore been directed
toward limiting the high dose volume to the prostate while escalation the dose within that
volume. Intensity modulated radiation therapy (IMRT) is a widely used technology to achieve
this goal. It is accomplished by modulating the radiation beam intensity within each
radiation field in accordance with an optimization algorithm. This has allowed greater
dose-escalation without evident increase in acute complications, although follow-up is too
short to fully assess control and complication rates. Whether IMRT will provide a degree of
conformity that proves to eradicate prostate cancer with a high probability while sparing
local structures is as yet unresolved.

Late Rectal Mucosal Injury Following CyberKnife RadioSurgery for Clinically Localized
Prostate Cancer. The type, extent and incidence of rectal mucosal injury following
CyberKnife radiosurgery are currently unknown. The severity of clinical proctitis following
radiation therapy is commonly documented using the NCI Common toxicity criteria/RTOG/EORTC.
Unfortunately, clinical proctitis has a low sensitivity for detecting rectal mucosal injury.
Endoscopy gives the most accurate estimate of the extent and incidence of rectal mucosal
injury. The Vienna rectoscopy score (VRS) was developed to quantify rectal mucosal changes
following radiation therapy. In this study, endoscopic evaluation of mucosal damage from
CyberKnife treatment will be documented and correlated with gastrointestinal side effects
and treatment planning parameters.