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Target and Organ at Risk DefinitionDose Prescription and Reporting
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Stereotactic radiation therapy (SRT) is a technique whereby the spatial coordinates of the target are accurately defined, allowing a high dose to be delivered to a small target in a single or a few fraction(s) by combining the contribution of multiple small beams (see Chapter 40). The small size of the fields (typically less than 3 cm diameter) raises specific issues, because the dose falls off very rapidly from the centre to the periphery, most of the target being in practice always in the penumbra region (see Section 5.8.2). In the absence of a plateau, it is impossible to define a satisfactory ICRU reference point, and from the very beginning of this technique, the common practice was to prescribe the dose to a reference (or coverage) isodose expressed as a percentage of the dose at the centre of the target.* Despite the objections formulated previously (see Section 31.4.2 and Figure 31.3), this is still commonly done, based on the arguments that it is acceptable for such a technique to have a large difference between the centre and periphery and that it allows steeper dose fall-off around the target.
Basics of Radiation and Radiotherapy
Published in Prakash Srinivasan Timiri Shanmugam, Understanding Cancer Therapies, 2018
Prakash Srinivasan Timiri Shanmugam, Pramila Bakthavachalam
Stereotactic radiation therapy is an external beam radiation therapy technique that is utilized to irradiate small tumors or lesions. The treated lesions are preferably small, the patient is carefully set up in the dedicated system, and a multileaf collimator with small leaf width is usually used. The resulting dose distributions are exceptionally conformal, but the treatment setup procedure is time consuming. The use of fewer fractions is thus both a possibility and a practical necessity. Stereotactic radiation therapy was initially used to treat intracranial tumors and nonmalignant, malfunctioning vascular bundles.
Surgical management of pituitary adenomas
Published in Philip E. Harris, Pierre-Marc G. Bouloux, Endocrinology in Clinical Practice, 2014
Garni Barkhoudarian, Edward R. Laws
Stereotactic radiosurgery (SRS) or stereotactic radiation therapy is an occasionally useful adjunct to treat persistent or recurrent acromegaly. A recent prospective study demonstrated normalization of IGF-I and GH levels in 23% and 37% of patients, respectively.67 Similar results have been reported in retrospective series.68,69 The average time to normalization of GH occurred at 1.4 years after stereotactic radiosurgery (SRS). Conventional radiation therapy has a higher incidence of complications (optic nerve, pituitary function) and a slower rate to normalization (7 years). Because of the effectiveness of medical therapy, fewer patients with acromegaly are being referred for radiotherapy or radiosurgery.
Brain metastases and treatment: multiplying cognitive toxicities
Published in Expert Review of Anticancer Therapy, 2019
Elise F. Nassif, Alexandre Arsène-Henry, Youlia M. Kirova
Stereotactic radiation therapy and SRS allow delivery of high radiation doses to the tumour and their efficacy is established [69]. SRS and stereotactic radiation therapy indications in clinical practice are expanding. The major toxicity appears to be dose-dependent radionecrosis, which can be symptomatic and difficult to differentiate from tumour progression. Both treatments have been reviewed elsewhere in meta-analyses [56,69]. To sum up, SRS added to WBRT allows better local control. Survival with SRS alone is comparable to WBRT in selected young patients with oligo-metastatic disease. Intra-cranial disease control is better when WBRT is added to SRS. However, inconsistency in cognitive evaluation does not allow definitive conclusions on omission of WBRT, though strongly suggested.
Intraorbital extraocular metastasis of breast cancer 11 years after mastectomy – case report and review of the literature
Published in Journal of Obstetrics and Gynaecology, 2019
Adam Kluska, Anna Papis-Ubych, Jacek Fijuth, Karolina Loga, Michal Spych, Leszek Gottwald
The management of patients with a cancer that has metastasised to the orbit often requires a multidisciplinary approach. The possible modalities for use in this group of patients include surgery, radiotherapy, chemotherapy (capecitabine, taxanes, anthracyclines), intraocular bevacizumab, a hormonal therapy in the patients with hormone-sensitive tumours or a combination thereof. The main treatment option is radiotherapy with reported 60–90% improvement in the presenting symptoms. A stereotactic radiation therapy (SRT; 12–20 Gy in 1 fraction or 30 Gy in 10 fractions) has a shorter treatment course compared with an external-beam radiotherapy (EBRT; 20–40 Gy delivered over 1–2 weeks), thus contributing to a better quality of life (Vlachostergios et al. 2009; Soobrah et al. 2015; Pierson et al. 2016). Palliative care is aimed at the improvement of life quality and the conservation of sight (Shields et al. 2001; Ahmad and Esmaeli 2007; Soobrah et al. 2015). The mean survival time for these patients varies from a few months to three years after their diagnosis (Shields et al. 2001; Kuchel and Bowling 2006; Pierson et al. 2016).
Tumor regression and immunity in combination therapy with anti-CEA chimeric antigen receptor T cells and anti-CEA-IL2 immunocytokine
Published in OncoImmunology, 2021
Seung E. Cha, Maciej Kujawski, Paul J. Yazaki, Christine Brown, John E. Shively
Tumor antigens such as CEA that are expressed in normal colon are poorly immunogenic but can be retargeted by the use of chimeric antigen receptors (CARs) expressed on T cells since they are derived from monoclonal antibodies that were produced by immunization of mice with a human antigen.27–30 Similarly, endogenous T cells do not target CEA, but CAR T cells break tolerance by using CARs derived from monoclonal antibodies and bypass the requirement for antigen presentation in the context of MHC.31 In a pre-clinical study, Chmielewski et al. showed that anti-CEA CAR T cells reduced the size of orthotopic CEA-positive pancreatic tumors in immunocompetent CEA transgenic (CEATg) mice without inducing tissue damage to CEA-positive organs such as the normal colon, despite the infiltration of anti-CEA CAR T cells.32 In clinical studies, Katz et al. showed that anti-CEA CAR T cell therapy did not induce therapy-related grade 4 or 5 adverse events in patients with CEA-positive liver metastases.33 Nonetheless, CAR T therapy alone for solid tumors is relatively ineffective and requires additional support. In an attempt to improve tumor responses, combination therapy of anti-CEA CAR T cell therapy plus systemic IL2 was attempted but had IL2-related toxicity preventing further treatment. The issue of systemic IL2 toxicity33 can be reduced by genetic fusion of tumor antigen-specific antibodies to form immunocytokines (ICKs). We have previously shown that the ICK, humanized anti-CEA antibody (M5A) fused to IL2, was effective against orthotopic CEA transfected breast carcinoma E0771 tumors in a CEATg mouse model.34 Furthermore, combination of ICK with fractionated stereotactic radiation therapy (SRT) eradicated tumors and established tumor immunity. These studies prompted us to combine two antigen-targeted therapies, namely anti-CEA CAR T cells plus ICK therapy to determine their therapeutic efficacy.