A Review of Analytical Models of Stray Radiation Exposures From Photon- And Proton-Beam Radiotherapies

Abstract

External-beam radiation therapy is safe, effective and widely used to treat cancer. With 5-year cancer survival for adults above 70%, increasingly research is focusing on quantifying and reducing treatment-related morbidity. Reducing exposures to healthy tissues is one strategy, which can be accomplished with advanced-technology radiotherapies, such as intensity-modulated photon therapy and proton therapy. Both of these modalities provide good conformation of the therapeutic dose to the tumor volume, but they also deliver stray radiation to the whole body that increases the risk of radiogenic second cancers. To minimize these risks, one needs to create and compare candidate treatment plans that explicitly take into account these risks. Currently, clinical practice does not include routine calculation of stray radiation exposure and, consequently, the assessment of corresponding risks is difficult. In this article, we review recent progress toward stray dose algorithms that are suitable for large-scale clinical use. In particular, we emphasize the current state of physics-based dose algorithms for intensity-modulated photon radiotherapy and proton therapy.

Proton therapy for adults with mediastinal lymphomas: the International Lymphoma Radiation Oncology Group guidelines

“…Specifically, stray radiation exposure is typically underestimated beyond a few centimeters outside the treatment field, precluding routine risk projections based on radiation exposure. 42 Similarly, their risk-modeling capabilities are limited, if they are present at all. 43,44…”

Method to quickly and accurately calculate absorbed dose from therapeutic and stray photon exposures throughout the entire body in individual patients

“…Despite strong evidence of the importance of stray radiation to patient outcomes, commercial treatment planning systems (TPSs) significantly underestimate the total absorbed dose outside of the therapeutic treatment field . Figure shows a representative example of this underestimation.…”

“…This has led to the emergence of numerous alternative methods for quantifying out‐of‐field doses from photon radiotherapy including measurements, Monte Carlo simulations, and analytical models . Of these, measurements are considered the gold standard in terms of accuracy.…”

Normal tissue damage: its importance, history and challenges for the future

“…77,78 New models and algorithms for such calculations are being developed. [79][80][81] Importantly, the prospective adoption of such capabilities at only a few major cancer centers would dramatically accelerate collection of the high-quality dosimetry data that is needed to improve current radiation risk models.…”

“…Prior to the early 2010's, one could reasonably argue that the lack of this capability was justified by a combination of factors: modeling radiation exposures was difficult; stray exposures are deemed clinically insignificant; and the uncertainties in predicted outcomes are excessive. However, since that time, the ability to routinely assess exposures has become eminently more feasible for advanced technology radiotherapies, 80 including proton-and photon-beam treatments and, indeed, has been implemented in non-clinical treatment planning systems. Although the uncertainties in predicting risks of a late effect for an individual patient remain relatively large, especially when the exposure includes neutrons, several studies now have shown that these uncertainties are manageable for comparing risks to the same patient from multiple candidate treatments.…”