Reducing the side effects of external beam radiotherapy in prostate cancer: role of imaging techniques

Prostate cancer is the most common male cancer with an annual incidence of 36,000 cases in the UK [301]. Management of these patients includes surveillance and radical treatment with either surgery or radiotherapy. Active surveillance of prostate cancer is a possible management strategy for men with low-risk disease, avoiding treatment-related morbidity but requiring a robust follow-up strategy, which may include imaging to assess disease progression. Other radical treatment options include radiotherapy and surgery. Radiotherapy is the most commonly given curative option in the UK, with around 10,000 men treated with external beam radiotherapy annually [1]. Radical radiotherapy is delivered with the intention of delivering a sufficient dose of radiation to provide tumor control while minimizing dose to the neighboring normal tissues (dose-limiting). External beam radiotherapy is an established treatment for localized prostate cancer and has survival and biochemical control rates similar to that seen with surgery and in selected cases, brachytherapy [2]. There is increasing evidence to suggest its benefit in locally advanced disease [3]. A number of randomized controlled trials have demonstrated biochemical disease control (measured by prostate-specific antigen [PSA]) when using escalated doses of radiation [4–8] but late morbidity is increased in the groups of patients receiving higher doses. Prostate cancer can be indolent and have a long natural history; therefore it is essential to keep treatment-related morbidity to a minimum. In the post-PSA era, more men are being treated for prostate cancer and at an increasingly younger age. Consequently, late sequelae and survivorship issues are important. Recent advances in radiation technology such as intensity-modulated radiotherapy (IMRT) enable complex 3D dose distributions and steep dose gradients to be delivered. This allows further dose escalation to the target along with the potential of sparing dosage to nearby organs at risk (OARs), thereby increasing the therapeutic ratio. Advances in imaging technologies have potential for more precise staging and delineation of disease in prostate cancer. Image-guided radiotherapy (IGRT) is becoming widespread and more sophisticated techniques are now available to improve verification of target position prior to treatment. This raises the possibility of a reduction in planning safety margins around targets with the further potential to decrease dose to the OARs. At present the full potential of these recent advances is limited by: