CORRECTED - Sensors, a smart dose of medicine for cancer treatment

The INVORAD project developed two systems: one for real-time radiation monitoring for patient dosimetry in Intensity Modulated Radiotherapy (IMRT); the other for intracavitary in vivo patient dosimetry.

Typically, radiotherapy patients receive 25-30 daily fractions of approximately 2 Gray (Gy) each. Using IMRT, it is possible to increase the dose to the tumour to about 80 Gy whilst still preserving the healthy tissue. This allows the tumour to be killed very effectively but enormous care must be taken to ensure that this high dose is delivered correctly.

Because of the complexity of IMRT it is difficult to verify that the correct dose distribution has been delivered to the patient. Unlike conventional therapy machines, IMRT machines need to be told how and when to move the multi-leaf collimators that can allow or stop the radiation reaching the patient. Calculating and performing these complex movements is a difficult task that must be quality assured. The final step is to monitor, in real-time as the leaves move, the radiation dose actually being delivered to the patent.

INVORAD developed an integrated detector system that can do just that: it is based on an arrangement of p-Si semiconductor diodes that are used as radiation sensors. "These diodes have several features - such as miniature size, excellent response to the radiation involved in radiotherapy, compatibility with microprocessors and low cost, that makes them suitable for the intended application," says Aleksandar Jaksic, INVORAD project coordinator at Ireland’s Tyndall National Institute in Cork.

The sensor system is based on 1069 semiconductor diodes arranged in two orthogonal planes that monitor the radiation dose.

"Our system allows us to monitor radiation with a spatial resolution of less than 1mm, and the diodes can accurately measure small amounts of radiation. We can therefore measure the radiation dose with high accuracy and high precision," says Jaksic.

A read-out unit, based on microprocessor technology, is used to communicate with and retrieve data from, the sensor arrays. A PC and dedicated software provide system control and connectivity to other parts of the radiotherapy process such as record and verify systems.

An important component is a solid plastic cylinder about 20 cm in diameter and in which the detector boards are placed. The treatment is first delivered to this cylinder as if it were the patient. If the 'phantom' treatment matches computerised treatment planning system predictions, then the patient is given treatment. If not, the differences are investigated.

Some types of MOSFETs – called RADFETs can also be used as sensitive radiation detectors. A second system, used for checking the dose by monitoring it inside the patient has been developed using RADFET technology. Ten RADFETs are mounted on a thin flexible array and placed inside a medical catheter. The catheter array can then be placed inside the human body through existing cavities. In this way, we can measure the dose to such areas as the inner wall of the oesophagus during treatment for different head and neck cancers. Specialised PC driven hardware reads the array and writes the output to a simple spreadsheet. We're about to test the catheter device in clinical trials with our partner, Clatterbridge Centre for Oncology, UK.
"The diode system is the most commercially viable, having a much larger potential customer base and demand. Beta versions are being made ready for testing throughout Europe. The first beta test version should be delivered to Clatterbridge late this year," says Jaksic.

"Like any commercial project, work continues on the INVORAD project to further develop and improve the different subsystems and meet ever changing demands," says Jaksic. "However, unlike most projects, the result of this project will go straight to market and our commercial partner, ScandiDos in Uppsala, Sweden, is a start-up who is manufacturing and marketing the device".

Jaksic is particularly pleased because the new sensor systems will improve treatment verification for a large number of cancer patients.

The prevailing opinion is that IMRT improves treatment outcomes. Crucially, IMRT allows the possibility of dose escalation to the tumour with reduced risk of damage to healthy tissue. It thus allows the possibility of a more efficacious treatment with improved quality of life for the patient. "This is the goal of radiotherapy treatment and our devices will help in the delivery of this and other advanced treatments," says Jaksic.