Spatiotemporal fractionation schemes for liver stereotactic body radiotherapy

Abstract

Background and Purpose Dose prescription in stereotactic body radiotherapy (SBRT) for liver tumors is often limited by the mean liver dose. We explore the concept of spatiotemporal fractionation as an approach to facilitate further dose escalation in liver SBRT. Materials and Methods Spatiotemporal fractionation schemes aim at partial hypofractionation in the tumor along with near-uniform fractionation in normal tissues. This is achieved by delivering distinct dose distributions in different fractions, which are designed such that each fraction delivers a high single fraction dose to complementary parts of the tumor while creating a similar dose bath in the surrounding noninvolved liver. Thereby, higher biologically effective doses (BED) can be delivered to the tumor without increasing the mean BED in the liver. Planning of such treatments is performed by simultaneously optimizing multiple dose distributions based on their cumulative BED. We study this concept for five liver cancer patients with different tumor geometries. Results Spatiotemporal fractionation presents a method of increasing the ratio of prescribed tumor BED to mean BED in the noninvolved liver by approximately 10–20%, compared to conventional SBRT using identical fractions. Conclusions Spatiotemporal fractionation may reduce the risk of liver toxicity or facilitate dose escalation in liver SBRT in circumstances where the mean dose to the non-involved liver is the prescription-limiting factor.

Fraction‐variant beam orientation optimization for intensity‐modulated proton therapy

“…For the same reason, our FV approach is different from the spatiotemporal modulation proposed by Unkelbach et al [23][24][25] and Gaddy et al 26,27 that introduces a heterogeneous fractional tumor dose to improved overall biologically equivalent dose (BED). By maintaining the same uniform tumor dose throughout the treatment course, our method focuses on the physical dose, is robust to interfractional registration error, and may be more easily accepted by the current clinical practice.…”

Technical Note: A step‐by‐step guide to Temporally Feathered Radiation Therapy planning for head and neck cancer

“…2 When TFRT subplans were generated clinically, not all Other researchers have also examined altering dose distributions over different fractions with the goal of reducing radiation-related side effects. [4][5][6][7] However, the TFRT approach described in this study has two hallmark differences. First, Unkelbach et al examined delivering hypofractionated radiotherapy to parts of the tumor, while maintaining a uniformly fractionated dose to the surrounding organs at risk.…”

Temporally feathered intensity‐modulated radiation therapy: A planning technique to reduce normal tissue toxicity

“…Through the years, researchers in the field of radiation oncology and medical physics have been innovating new ways of widening the therapeutic ratio by either increasing (TCP) or decreasing normal tissue complication probability (NTCP). Recent works have shown the potential of spatiotemporal fractionation schemes delivering distinct radiation dose distributions in different fractions to improve the therapeutic ratio . The goal has been to maximize the mean BED in the tumor and minimize the mean BED in normal tissues by hypofractionating parts of the tumor while delivering approximately identical doses to the surrounding normal tissue.…”