External beam radiotherapy equipment has been in existence and used to treat cancer patients since the middle of the 20th century. Although many features have been added to the treatment machines, mainly linear accelerators, the basic geometry of the machine has not changed. A gantry containing the radiation source rotates about the horizontal axis around the patient on a couch and the machine can only be used in a special concrete and lead bunker that shields the operator and hospital staff from the direct and scattered radiation. The patient comes in daily for up to 8 weeks for fractionated treatment, and is inside this bunker during the treatments. The operator sets up the patient and leaves the bunker so as not to receive any dose of radiation. The patient not only receives the prescribed dose to the target, but also leakage and scattered radiation that is present in the treatment room when the beam is turned on. The governing principle of the use of radiation for medical procedures is to deliver As Low As Reasonable Achievable dose to the patient (ALARA). The basis for our project is to integrate the bunker into the design of the machine. The integrated shielding will minimize the unwanted dose to the patient and also shield the operator. This concept brings many clinical and financial benefits when compared to current equipment and its use. For the first time ever, the patient will remain “outside” of the bunker and receive a much lower whole body dose. The operator can remain in the same room with the patient during the procedure instead of watching the patient on a closed circuit camera.
For our first application, we have chosen to focus on breast cancer. Breast cancer is the leading cancer in women and it is also accounts for nearly one quarter of all patients undergoing external beam radiotherapy. The breast is an ideal anatomy to pursue in the design of this device. Breast cancer treatment using existing linear accelerators has not progressed significantly in decades. The main reason for this is the incorrect rotational axis of the linear accelerator. The basis for most modern treatment techniques requires the use of multiple beams to focus the dose on the target and avoid the exposure to healthy organs. The breast is still mainly treated with 2 opposing tangential beams, with the lung, heart and skin receiving elevated doses, which can lead to long term complications. The patient is exposed to leakage and scattered radiation which can lead to secondary radiation induced cancer later in life.
The other possibility with an integrated shielding machine is mobile operation. It has been studied and published that some women, especially the ones located in remote areas, would opt for a radical mastectomy versus radiation purely for the convenience factor. Some women simply cannot afford to leave their jobs and families and relocate to a city offering radiotherapy and then spend 6 – 8 weeks receiving treatment. By offering mobile units, as already done with many imaging modalities such as CT and MRI scanners, we can bring breast radiotherapy to remote locations that currently do not have such facilities. |
