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IORT is

CONTENTS 1. Rationale 2. Methods 3. Clinical Applications 4. IORT in Breast Cancer 5. Tolerability 6. Professional Society for IORT 7. See also 8. References IORT Intraoperative radiation therapy (IORT) is a method where the radiation is applied during an operation. The goal of IORT is to improve local tumor control and survival rates for patients with different types of cancer. Further IORT is an option for patients with recurring cancer that already had traditional radiation therapy and are not suitable for a second radiation treatment. Rationale The rationale for IORT is to deliver a high dose of radiation precisely to the targeted area with minimal exposure of surrounding tissues which are displaced or shielded during the IORT. Conventional radiation techniques such as external beam radiotherapy (EBRT) following surgical removal of the tumor have several drawbacks: The tumor bed where the highest dose should be applied is frequently missed due to the complex localization of the wound cavity even when modern radiotherapy planning is used. Additionally, the usual delay between the surgical removal of the tumor and EBRT may allow a repopulation of the tumor cells. These potentially harmful effects can be avoided by delivering the radiation more precisely to the targeted tissues leading to immediate sterilization of residual tumor cells. Another aspect is that woundfluid has a stimulating effect on tumor cells. IORT was found to inhibit the stimulating effects of wound fluid. Methods IORT can both be performed with electron beams (IOERT) and X-rays. Modern IORT started in shielded operation rooms in which a linear accelerator was used to deliver the radiation. In recent years, miniaturised and mobile-linear accelerators have been developed which deliver a variable range of electron energies (from 3 to 12 MeV), e.g. the Mobetron (Intraop Medical Corporation, USA). A newer concept is Intrabeam, (Carl Zeiss, Germany) a miniature and mobile X-ray source which emits low energy X-ray radiation (max. 50 kV) in isotropic distribution. Due to the higher ionization density caused by soft X-ray radiation in the tissue, the relative biological effectiveness (RBE) of low-energy X-rays on tumor cells is higher when compared to high-energy X-rays or gamma rays which are delivered by linear accelerators. The radiation which is produced by mobile radiation systems has a limited range. For this reason, conventional walls are regarded sufficient to stop the radiation scatter produced in the operating room and no extra measures for radiation protection are necessary. This makes IORT accessible for more hospitals. Clinical Applications IORT was found to be useful and feasible in the multidisciplinary management of many solid tumors but further studies are needed to determine the benefit more precisely. Single-institution experiences have suggested a role of IORT e.g. in brain tumors and cerebral metastases, locally advanced and recurrent rectal cancer, skin cancer, retroperitoneal sarcoma, pancreatic cancer and selected gynaecologic and genitourinary malignancies. For local recurrences, irradiation with IORT is besides brachytherapy the only radiotherapeutic option if repeated EBRT is no longer possible. Generally, the normal tissue tolerance does not allow a second full-dose course of EBRT, even after years. IORT in Breast Cancer The largest experience with IORT and the best evidence for its potentials exists in breast cancer where a substantial number of patients have already been treated, e.g. in the TARGIT trial. In this study, evidence has been established for the efficacy of IORT in administering a boost after lumpectomy. In conventional EBRT, the boost is delivered at the end of a complete course of EBRT. Clinical evidence suggests that boost radiation improves treatment outcome for breast cancer. With IORT the boost can be delivered intraoperatively without any delay and more precisely as compared to conventional EBRT. A multicenter clinical trial has demonstrated that the boost administered with IORT resulted in a lower rate of local recurrence (1.52 %) as compared to an EORTC study which used external boost radiation. Besides TARGIT, other study groups using similar protocols and concepts have also demonstrated the effectiveness and safety of IORT in breast cancer patients. , Tolerability IORT has similar side effects when compared to external beam radiotherapy. In a study which examined acute side effects after boost radiation in patients with breast cancer, treatment was well tolerated with no grade 3/4 acute toxicity. Rare adverse effects following IORT included wound healing problems (2 %), erythema grade I-II (3 %), palpable seroma (6 %) and mastitis (2-4 %). Professional Society for Intraoperative Radiation Therapy In 1998, the International Society of IORT (ISIORT) was formed to foster the scientific and clinical development of IORT. The ISIORT has more than 1000 members worldwide and meets every two years. See also Brachytherapy External beam radiotherapy IOERT Radiation therapy TARGIT trial

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