International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationRole of the Technical Aspects of Hypofractionated Radiation Therapy Treatment of Prostate Cancer: A Review
Introduction
Hypofractionated (HF) radiation therapy of prostate cancer has garnered increasing attention owing to its proposed low α/β value, which is close to 1.5 Gy 1, 2. Hypofractionated treatments increase the therapeutic ratio and ameliorate logistical inconveniences for both patients and their providers 2, 3, 4.
Supporting data have recently been summarized in a systematic review by Tree et al (5). Importantly, extreme (EHF) and moderate (MHF) hypofractionated regimens do not lead to higher toxicity to the nearby rectum and bladder than conventional regimens (2 Gy per fraction) and have the additional benefit of biochemical control.
The effect of geometric uncertainties is known to be one of the major concerns in radiation dose delivery in prostate cancer (6). These uncertainties are mostly due to patient setup errors and extensive motion of the rectum and bladder that is dependent on organ filling. In this regard, an augmented impact of geometric uncertainties is expected when high doses per fractions are adopted. This could occur because in HF treatments, any single targeting error causes a greater biologic impact by consistently underdosing the target organ at greater expense of the organs at risk (OARs) (7).
Several technological innovations have boosted the high-precision localization of the prostate during treatment, allowing the delivery of highly conformed dose fractions to a well-defined target with sharp dose fall-off toward the bladder and rectum (8). However, multiple technical parameters and operational variables can affect the correct localization of the prostate and the reproducibility of the procedures. For this reason, we focused our attention on these features to investigate the potential correlation/association with clinical outcome in prostate cancer patients treated with EHF and MHF schemes.
We performed a search of the available literature on the PubMed database, concentrating on technical and dosimetric aspects such as delivery techniques, immobilization devices, setup position, rectum and bladder preparation, imaging, margins, localization imaging on-line systems, dose prescriptions, dose constraints, and clinical outcome.
Section snippets
Search strategy
An extensive PubMed search was performed on April 31, 2014, including the search terms (((“Prostatic Neoplasms/radiotherapy”[Mesh] AND “Radiosurgery”[Mesh])) OR ((Prostat* AND (hypofraction* OR SBRT OR “stereobody radiotherap*” OR stereotactic OR radiosurger*))) NOT proton* NOT ion* NOT metastases) and using the filters: published in the last 10 years, English. A reference list of 433 articles resulted from the database according to this criterion. The list of articles was screened by 2
Results
In total, 275 reports were retrieved from the initial PubMed search. As a result of the abstracts reading, 236 were excluded because they did not fit exactly with the inclusion criteria. There was no discrepancy between the 2 reviewers.
We reviewed the data from 733 and 3454 patients from 15 EHF 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 and 24 MHF 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47 reports, respectively.
Discussion
The aim of this study was to describe the state of the art on technical strategies used in HF radiation therapy treatments and their potential correlation with clinical outcome. Targeting this goal, a review of published studies on HF regimens in prostate cancer patients treated with EHF and MHF schemes was performed.
We would like to point out that our work may be not a comprehensive and exhaustive analysis of the known literature; neither is it a systematic review, but it can be considered a
Conclusions
Recent clinical data support a low value for α/β ratio as predicted by radiobiological models; hence, large doses per fraction should result in a higher probability of tumor control together with a reduced probability of complications for healthy tissue. Nevertheless, in the evaluation of the cost-effectiveness of the treatment, it is mandatory to also consider the associated morbidity. In this review, we focused on the technical parameters and treatment strategies adopted in the analyzed HF
Acknowledgments
The authors thank Simona Marzi; Raffaella Marconi for the English revision of the manuscript; and the staff of the Library of the National Cancer Institute Regina Elena (Gaetana Cognetti, Fabio D'Orsogna, and Francesca Servoli) for helping in the PubMed search.
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Conflict of interest: none.