Seminar article
What is the best way to radiate the prostate in 2016?

https://doi.org/10.1016/j.urolonc.2016.06.002Get rights and content

Highlights

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    Intensity-modulated radiation therapy with image guidance is considered standard of care for definitive prostate cancer radiation therapy.

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    Brachytherapy is used as monotherapy for lower-risk patients whereas its combination with external beam radiation therapy is used for higher-risk patients.

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    Proton therapy has been shown to be safe and effective for the treatment of prostate cancer, but additional studies would be required to determine whether it leads to improvement in clinical outcomes compared to intensity-modulated radiation therapy.

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    Hypofractionated radiation therapy delivers larger daily radiation dose, reducing the overall treatment time and possibly cost, and it has been shown to be noninferior to conventional fractionation.

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    Stereotactic body radiation therapy is an extreme form of hypofractionation, delivering treatment in a total of 3 to 5 sessions, with growing evidence for its use in low- to intermediate-risk prostate cancer patients.

Abstract

Prostate cancer treatment with definitive radiation therapy (RT) has evolved dramatically in the past 2 decades. From the initial 2-dimensional planning using X-rays, advances in technology led to 3-dimensional conformal RT, which used computerized tomography-based planning. This has allowed delivery of higher doses of radiation to the prostate while reducing dose to the surrounding organs, resulting in improved cancer control. Today, intensity-modulated RT (IMRT) is considered standard, where radiation beams of different shapes and intensities can be delivered from a wide range of angles, thus further decreasing doses to normal organs and likely reducing treatment-related toxicity. In addition, image guidance ascertains the location of the prostate before daily treatment delivery.

Brachytherapy is the placement of radioactive seeds directly in the prostate, and has a long track record as a monotherapy for low-risk prostate cancer patients with excellent long-term cancer control and quality of life outcomes. Recent studies including several randomized trials support the use of brachytherapy in combination with external beam RT for higher-risk patients.

RT for prostate cancer continues to evolve. Proton therapy has a theoretical advantage over photons as it deposits most of the dose at a prescribed depth with a rapid dose fall-off thereafter; therefore it reduces some doses delivered to the bladder and rectum. Prospective studies have shown the safety and efficacy of proton therapy for prostate cancer, but whether it leads to improved patient outcomes compared to IMRT is unknown.

Hypofractionated RT delivers a larger dose of daily radiation compared to conventional IMRT, and thus reduces the overall treatment time and possibly cost. An extreme form of hypofractionation is stereotactic body radiation therapy where highly precise radiation is used and treatment is completed in a total of 4 to 5 sessions. These techniques take advantage of the biological characteristic of prostate cancer, which is more sensitive to larger radiation doses per fraction, and therefore could be more effective than conventional IMRT. Multiple randomized trials have demonstrated noninferiority of moderately hypofractionated RT compared to conventional fractionation. There is also a growing body of data demonstrating the safety and efficacy of stereotactic body radiation therapy for low- and intermediate-risk prostate cancer.

Section snippets

Introduction: Historical perspective

Radiation therapy (RT) has a long track record as a curative treatment modality for localized prostate cancer. Overall, 2 large randomized trials compared androgen deprivation therapy (ADT) vs. ADT plus RT for patients with high-risk/locally advanced prostate cancer, and both showed that RT improves overall survival by an absolute difference of 8% to 10% [1], [2]. Radiation delivered in the form of X-rays or protons causes DNA damage, which is preferentially repaired in the normal tissue

Current standards

In addition to the decreased rates of toxicities, the use of more conformal radiation treatment techniques also enabled safer delivery of higher doses of radiation to the prostate. At least 5 randomized trials have compared traditional radiation doses (64–70 Gy) to dose-escalated RT (74–80 Gy) [11], [12], [13], [14], [15], and all consistently demonstrated improved disease-free survival with escalated doses, and this has become current standard of care (Table 1). By 2011, 90% of patients in the

Brachytherapy

Brachytherapy involves inserting radioactive sources directly into the prostate, and has been used for the treatment of prostate cancer since the 1920s. Low dose rate brachytherapy consists of placing permanent seed implants (either Iodine-125 or Pallidium-103) in the prostate, whereas high dose rate brachytherapy entails temporary insertion of high energy radioactive isotope such as Iridium-192. The direct delivery of radioactive sources into the prostate significantly reduces radiation doses

Proton therapy

Proton therapy uses a different radiation particle (protons) than X-ray (photon radiation). A heavy, charged particle such as a proton deposits most of its dose at a prescribed depth in the body with a rapid dose fall-off beyond this point; this phenomenon is called the “Bragg peak.” This means that proton therapy can reduce radiation dose delivered to tissues beyond the target compared to photon radiation. Although proton and photon particles are deemed to be similarly effective in prostate

Conclusion

Definitive RT for prostate cancer has evolved dramatically in the past 2 decades. Once treated with a few fields based on the patient׳s bony anatomy on X-ray, prostate cancer patients now receive higher doses of radiation using IMRT with image guidance. The “best” way to deliver radiation for prostate cancer continues to evolve through clinical studies including many randomized trials. For low-risk prostate cancer patients, active surveillance is the recommended disease management strategy in

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