Radiobiology of stereotactic body radiation therapy (SBRT)

Abstract

a b s t r a c tRecent advances in the technology of radiotherapy have enabled the development of new therapeutic modalities that deliver radiation with very high accuracy, reduced margins and high dose conformation, allowing the reduction of healthy tissue irradiated and therefore minimizing the risk of toxicity. The next step was to increase the total tumor dose using conventional fractionation (which remains the best way to relatively radioprotect healthy tissues when large volumes are treated) or to use new fractionation schemes with greater biological effectiveness. Based on the experience gained in radiosurgery, the latter way was chosen for small and well-defined tumors in the body. Stereotactic body radiotherapy delivers high doses of radiation to small and well-defined targets in an extreme hypofractionated (and accelerated) scheme with a very high biological effectiveness obtaining very good initial clinical results in terms of local tumor control and acceptable rate of late complications.In fact, we realize a posteriori that it was not feasible to administer such biologically equivalent dose in a conventional fractionation because the treatment could last several months.So far, these new therapeutic modalities have been developed due to technologic advances in image guidance and treatment delivery but without a solid biological basis. It is the role of traditional radiobiology (and molecular radiobiology) to explain the effects of high doses of ionizing radiation on tumor and normal tissues. Only through a better understanding of how high doses of ionizing radiation act, clinicians will know exactly what we do, allowing us in the future to refine our treatments. This article attempts to describe through simple and understandable concepts the known aspects of the biological action of high doses of radiation on tumor and normal tissues, but it is clear that we need much more basic research to better understand the biology of high doses of radiation.

The Special Medical Physics Consult Process for Reirradiation Patients

“…Although there is some concern that the linear-quadratic model fails to accurately predict cell kill at higher doses per fraction,23, 24 it remains one of the most frequently used and accepted forms of dose summation 25 . The calculated biological dose may be sensitive to the chosen α/β ratio, and using a single value for a biological dose limit does not always realize practical results when adding together multiple hypofractionated plans or a combination of multiple different fractionations.…”

Stereotactic radiosurgery versus stereotactic radiotherapy in the management of intracranial meningiomas: a systematic review and meta-analysis

“…In fact, fractionation allows SRT to deliver a higher radiation dose, even to complex-shaped tumors, with high precision and accuracy, and minimize the unwanted dose to the adjacent healthy tissues. 24 This hypothesis is strengthen by the fact that, with respect to SRS, tumor control was better achieved by FSRT (OR 0.46, 95% CI 0.26-0.80, p = 0.006) than by hFSRT (OR 0.81, 95% CI 0.21-3.17, p = 0.76).…”

Stereotactic Body Radiotherapy Immunological Planning – Road to Abscopal Effect by Design

“…Although the onset of accelerated repopulation is not explicitly known for a particular type of cancer in the temporal timeline, one to two weeks of treatment with fractionated SBRT may be advantageous in reducing the acceleration in repopulation. This phenomenon particularly holds good for rapidly proliferating cells and may contribute to the improvement of local control [11] in aggressive disease. The delayed acceleration can happen in slow responding tumors like prostate cancer, as late as 69 days, depending on the stage.…”