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Intra-operative radiotherapy (IORT)


Introduction

IORT is a special radiotherapeutic technique that delivers in a single session a high radiation dose to a surgically exposed internal organ, tumor or tumor bed. IORT combines two modalities of cancer treatment: surgery and radiotherapy. An IORT team therefore includes a surgeon, radiation oncologist, medical physicist, anesthesiologist and a nurse. IORT is often applied as part of a treatment protocol that incorporates other modalities such as chemotherapy and external beam radiotherapy. QA for IORT treatments is at least as important as that for standard radiotherapy, since IORT treatments are almost always given in a single session, making it essentially impossible to correct a misadministration of dose. A QA programme in IORT consists of basic QA dealing with the IORT equipment, pre-treatment QA dealing with equipment preparation and QA during the IORT procedure.


Important Principles

IORT requires an operating room for the surgical procedure and a treatment room for delivery of radiation. Often these rooms are merged into one, resulting in a specially shielded operating suite in which a dedicated radiation treatment unit is installed permanently. Special applicators are needed to define the target area and to shield tissues outside the target area from radiation. Three different modalities may be used to deliver IORT: orthovoltage x-rays, megavoltage electron beams and high dose rate brachytherapy sources. Most IORT programmes today are based on electron beams produced by linacs, since electron beams provide several advantages over x-rays for IORT. With the development of new technology, mobile linear accelerators have recently become available for IORT, which offer flexibility in treatment location.


Introduction to References

AAPM TG 72 Report complements the work of the previous Task Group 48 on IORT, and provides information concerning room selection, radiation shielding, acceptance, machine commissioning and a QA programme to bring a mobile unit into clinical operation. More information on IORT can be found in J. Van Dyk's Compendium and in the IAEA Handbook.