Extracranial stereotactic body radiotherapy. Review of main SBRT features and indications in primary tumors

Abstract

Aim: Review of main SBRT features and indications in primary tumors.

Background: Stereotactic body radiotherapy has been developed in the last few years. SBRT allows the hypofractionated treatment of extra cranial tumors, using either a single or limited number of dose fractions, and resulting in the delivery of a high biological effective dose with low toxicity.

Material and methods: SBRT REQUIRES A HIGH LEVEL OF ACCURACY FOR ALL PHASES OF THE TREATMENT PROCESS: effective patient immobilization, precise target localization, highly conformed dosimetry and image guided systems for treatment verification. The implementation of SBRT in routine requires a careful considering of organ motion. Gating and tracking are effective ways to do so, and less invasive technologies "fiducials free" have been developed. Due to the hypofractionated scheme, the physician must pay attention to new dosimetric constraints in organ at risk and new radiobiological models are needed to assess the optimal fractionation and dose schemes.

Results: Currently, SBRT is safe and effective to treat primary tumors, which are otherwise untreatable with conventional radiotherapy or surgery. SBRT has quickly developed because of its excellent results in terms of tolerance and its high locoregional control rates. SBRT indications in primary tumors, such as lung primary tumors, have become a standard of care for inoperable patients. SBRT seems to be effective in many others indications in curative or palliative intent such as liver primary tumors, and novel indications and strategies are currently emerging in prostate cancer, head and neck tumor recurrences or pelvis reirradiations.

Conclusion: Currently, SBRT is mainly used when there is no other therapeutic alternative for the patient. This is due to the lack of randomized trials in these settings. However, the results shown in retrospective studies let us hope to impose SBRT as a new standard of care for many patients in the next few years.

Keywords: Early stage NCSLC; Head and neck recurrences; Hepatocellular carcinoma; Organ motion; Requirements; SBRT.

Fig. 1

SBRT treatment for early stage peripheral NSCL cancer. Highly conformed dosimetry with multiple beams. Dose prescribed: 60 Gy in 3 fractions of 20 Gy.

Fig. 2

Organ motion compensating technique example: Novalis® Exactrac Adaptive Gating SBRT for lung and liver lesions. Monitoring organ tumor motion and irradiation within a selected area of the respiratory cycle with Exactrac image guide system localization of the internal marker.

Fig. 3

Follow up with radiological evaluation of response after SBRT treatment for Hepatocellullar carcinoma. Reduction of arterial contrast enhancement is included in the new RECIST criteria of response for HCC.