Stereotactic body radiation therapy (SBRT) is a potent noninvasive means of administering high radiation doses to demarcated tumor deposits in extracranial locations. The treatments use image guidance and related advanced treatment delivery technologies for the purpose of escalating the radiation dose to the tumor, while sharply minimizing the radiation doses to surrounding normal tissues. The local tumor control outcomes for SBRT have been higher than any previously published for the radiotherapy of frequently occurring carcinomas. In addition, the pattern, timing and severity of the toxicities have been very different than from those seen with conventional radiotherapy. These issues pose challenges to our understanding of the radiobiological mechanisms and the optimal uses of SBRT. In this review, the clinical characteristics and outcomes of SBRT are presented in the context of their possible underlying mechanisms. While some of these considerations remain theoretical, they may outline at least qualitative understandings of the observed clinical effects, and motivate continuing research into the effects of SBRT that guide its most effective use in the clinic.
Stereotactic body radiation therapy (SBRT) is a potent noninvasive means of administering high-dose radiation to demarcated tumor deposits in extracranial locations. The treatments use image guidance and related treatment delivery technology for the purpose of escalating the radiation dose to the tumor itself with as little radiation dose to the surrounding normal tissue as possible. The local tumor control for SBRT has been higher than anything previously published for radiotherapy in treating typical carcinomas. In addition, the pattern, timing and severity of toxicity have been very different than what was seen with conventional radiotherapy. In this review, the clinical characteristics and outcomes of SBRT are presented in the context of their underlying mechanisms. While much of the material is unproven and speculative, it at least qualitatively searches for understanding as to the biological basis for the observed clinical effects. Hopefully, it will serve as a motivation for more sophisticated biological research into the effects of SBRT.
Purpose: Brachytherapy is frequently used to boost volumes at risk in the treatment of gynecological tumors. Not all the centers have an HDR, or LDR capabilities, however, all have a linear accelerator. We evaluated the possibility of using external beam radiation therapy using Stereotactic Body Radiation Therapy (SBRT) or Intensity Modulated SBRT (IM‐SBRT) approach. Method and Materials: Volumes covered by the HDR prescription were used to define a CTV, with a prescription of 3250 cGy to the CTV over 5 fractions. Planning started with 36 equi‐spaced non‐coplanar beams and beam weight optimization was used to choose the most effective beam orientations. Then, unmodulated beams produced the SBRT plans and by allowing beam modulation IM‐SBRT plans were generated. Both absolute and film dosimetry were performed to ensure accurate deliverability. Results: At least 96% of the CTV was covered by the prescription dose for SBRT and IM‐SBRT plans. Relative to the original HDR plan, bladder dose reduced by 12.8% and 38.5% by SBRT and IM‐SBRT respectively. Rectal dose increased by 49.3% using SBRT and decreased by 5.1% using IM‐SBRT. As expected, The integral dose outside CTV was higher in SBRT and IM‐SBRT approaches. Conclusion: SBRT and IM‐SBRT methods provided similar tumor coverage to HDR. IM‐SBRT reduced dose to bladder and rectal point. In the near future we will be evaluating a novel new device to localize the anatomy on a daily basis so that a precise delivery is possible.
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