The evolution of technology in radiotherapy

Intra-Operative Radiation Therapy (IORT) with mobile accelerators is a technique suitable for the control of tumors located in anatomical areas which present technical limitations to surgery because of the presence of healthy tissue surrounding the diseased area, or to safeguard cosmetic aspects. IORT mobile accelerators deliver a single large dose (10-20 Gy) during surgery to the tumor bed and to adjacent regions at higher risk of local recurrence, immediately after tumor removal.

The radiation beam produced by the accelerator is specifically designed to work directly in the operating room. The devices are extremely light and easy to install in order to obtain a correct positioning of the equipment and to direct the radiation beam to fully cover the tumor bed. Crucial aspects are also decided, such as radiation beam energy and the dose rate at which this beam is utilised in order to minimize the time of irradiation on the patient.

Electron beam radiation dose rate is an important issue in order to minimize the time of irradiation to the patient. Innovations brought to a recent Mobile Accelerator consist of the following two features C one practical and the other constructive:

- Compact in size and high mobility that allow the device to be easily placed and moved in and around the operating room, thus avoiding the transfer of the patient from the operating room during surgery to the radiation therapy vault, or the transfer of the patient onto a dedicated operating table.

- The absence of collimators drastically reduces the scattered photon radiation diffused by the radiating head, thus permitting the use of the accelerator in any operating room and minimizing radio-protection requirements.

The more technologically innovative IORT electron system has an auto-focusing radiating structure (patented) and is magnetic lens free, this has permitted a particular construction philosophy which is characterized by an articulated arm (stand alone) that is very light due to the absence of magnetic focusing lenses that would require added lead shielding, therefore allowing anthropomorphic movements that are particularly fast and effective during preparation and treatment.

The homogeneity and dose distribution on the target to be treated are obtained directly by utilising the applicators and the electrons colliding with air molecules inside the applicators.

The energy range produced by these mobile LINACs, varies from 4 to 10 MeV and is deliberately limited to avoid the production of neutrons which, although of low intensity, would result difficult to screen in the operating room. This choice does not affect the capacity to be highly effective on the tumor bed even when the surgical macroscopic residues are evident.

At maximum energy, Isodose 80% reaches in fact a depth of 30 mm. In this case, environmental radiation to be shielded is that generated by the patient who acts as a bremsstrahlung target and converts into X-rays about 0.2% of the incident radiation.

This radiation directed along the beam axis extension can be easily shielded by a mobile horizontal lead (Pb) shield, placed under the operating table utilizing a newly developed electronic positioning system.

Stray radiation generated from the body in other directions is negligible, to the point where the operator may absorb a 1mSv dose at a distance of 4 m., for a 10 Gy dose delivered to the patient, In some cases, additional mobile screens positioned around the operating table during the treatment are utilised, to reduce altogether the X-radiation exposure to the personnel. Treatment speed and benefits: the possibility to irradiate the tumor bed in any operating room during surgery with better effects on the patient, optimizes the work of conventional radiation therapy facilities.

For example, in the case of breast treatments less than two minutes of irradiation in the operating room eliminates the need for five or more weeks of external radiation therapy in a vault and results in less inconvenience to the patient and better management of waiting lists in the ward. Expansion of protocols: the increasing number of patients treated with IORT and accumulated data from literature, stimulate randomized studies paving the way for new application protocols unfeasible in the past due to the difficulties in applying the technique; breast cancer which is now treated systematically with this technique is a clear example.

Characteristics of the electron beam: the possibility to produce a collimated high energy electron beam of a few millimeters of diameter paves the way for innovative applications such as intracavitary IORT, radiation therapy of skin lesions, the reduction of hypertrophic scar tissues and treatment of some optical cancers.

Mobile accelerators are specifically designed to fit the operating room. Totally free from interference on surgical or monitoring equipment, they carry out the entire course of treatment in about 15 minutes, of which about one minute dedicated to irradiation. Their applicators are easy to use and to sterilise. The radiation oncologist and the surgeon usually take no more than 10 minutes to determine the radiation field, choose the appropriate applicator and its dose, place the mobile horizontal shield and/or the mobile vertical shields.

About two minutes are required to prepare the device for the irradiation procedure and less than 20 seconds to release a dose of 10Gy over a 6 cm range. All isodose curves are stored in the computer corresponding to the different choices of irradiation parameters; this option permits the radiation oncologist to readily evaluate the correct dose depth and distribution to use during treatment.