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Radiation is a potent genotoxic agent that induces clonogenic cell death through apoptosis and terminal senescence.
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Increasing radiation dose is associated with improved biochemical outcomes, and is facilitated by improvements in image guidance and better target delineation.
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Neoadjuvant or adjuvant androgen deprivation improves biochemical and survival outcomes in intermediate-risk and high-risk patients, but the benefits must be measured against potential toxicity.
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Prostate cancer may respond to
Contemporary Issues in Radiotherapy for Clinically Localized Prostate Cancer
Section snippets
Key points
Principles of radiation therapy
Therapeutic radiation can be delivered with multiple techniques. For most patients, this involves external beam radiotherapy (EBRT) using a linear accelerator to deliver high-energy photons. Alternatively, brachytherapy uses temporary high-dose-rate (HDR) or permanent low-dose-rate (LDR) radioactive sources to deliver the prescribed dose to the target.
Ionizing radiation is a potent genotoxic agent that predominately interacts with biological matter by inducing double-stranded deoxyribonucleic
Risk Stratification
There is significant heterogeneity in the biological behavior observed in prostate cancer. The risk of biochemical failure after local therapy has been explored in detail. Increasing stage at presentation, prostate specific antigen (PSA) level, and grade of tumor all predict for PSA recurrence after therapy with curative intent.10, 11
The National Comprehensive Cancer Network (NCCN) risk stratification (Table 1)11 can be used to stratify patients by risk of biochemical failure after curative
Prostate and Seminal Vesicles
The extent of radiation fields is based on understanding the natural history and potential routes of spread. The multifocal nature of prostate cancer38 has typically suggested that a uniform radiation dose to the whole prostate is required. Tumors may also breach the capsule of the prostate and be found in the periprostatic fat, or involve the adjacent seminal vesicles. The risk of extraprostatic extension and seminal vesicle invasion (SVI) increases significantly in higher-risk groups, as
IMRT
IMRT is based on 2 principles: (1) dynamically changing the open area of each field during each fraction and (2) computer software to divide the planning CT into spatial units (voxels) and then determine the optimal solution to deliver the dose to each voxel for a given beam arrangement. This differs from conventional radiotherapy because target dose characteristics and normal tissue tolerances are specified before plan construction (inverse planning). IMRT prescriptions are highly proscriptive
Brachytherapy
Brachytherapy (short distance therapy) involves the temporary or permanent implantation of radioactive sources to deliver tumoricidal radiation doses within the proposed target volume. Radioactive material exists as an unstable isotope of a base element. The decay of these isotopes into inert substances produces secondary particles and photons. These secondary particles are identical to those emitted by linear accelerators, with 2 chief advantages of being lower in energy and being created
Postprostatectomy radiotherapy
Planned postprostatectomy radiotherapy (PPRT) after prostatectomy is a controversial issue in uro-oncology. Although radical prostatectomy (RP) provides excellent local control for organ-confined disease, when the tumor extends beyond the prostatic capsule, the risk of local relapse is between 10% and 50%.119, 120, 121, 122, 123 This population of patients may benefit from further local therapy to secure long-term disease control. However, patient selection is likely to play an important role
Second malignancy risks from radiotherapy
There is a risk of second primary malignancy after radiation; patients who have had prostate cancer are most likely to get these lesions in the rectum and bladder.141, 142 Estimates suggests that when compared with surgical therapy, prostate radiotherapy increases the relative risk of developing a second solid tumor by approximately 6% (equating to a risk increase of around 1 in 300 compared with surgery) in a study by Brenner and colleagues.142 However, the relative risk seems to increase with
Anatomic and Molecular Imaging
Imaging is likely to have a significant effect on the way radiotherapy is delivered to the prostate in the future. Multiparametric MRI, which adds capabilities such as diffusion maps, dynamic contrast sequences, and spectroscopy,144, 145 can often identify a dominant intraprostatic tumor lesion (DIL), which are regions that often correlate with sites of postradiation treatment failure.146, 147 The usefulness of boosting the DIL is being tested in a randomized trial (FLAME/NCT01168479).148
Summary
Our understanding of the radiation biology of prostate cancer continues to improve. It is well accepted that higher radiation doses are beneficial in prostate cancer, but the strength of the interaction between higher doses of radiation and androgen deprivation is still a compelling question. Newer approaches exploiting the proposed fraction size sensitivity of prostate cancer may lead to a reduction in treatment duration with equivalent toxicity in selected patients. Technological advances
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Dosimetric comparison of intensity-modulated radiotherapy and volumetric-modulated are radiotherapy in patients with prostate cancer: A meta-analysis
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Disclosure: Nothing to disclose.