Concept and Advantages of Intraoperative Single Dose Radiotherapy (SDRT)
Radiation therapy can be completed with a single-dose application done using the Intra Operative Radiotherapy (IORT) method during surgery. Direct visualization of the tumour bed and ability to space out the normal tissues from the tumor bed allows maximization of the dose to the tumor while minimizing the dose to normal tissues. Once a tumor is removed during an operative procedure, the special applicator in the tool is placed in the tumor area. Following the necessary calculations, high-dose radiation is given only to this area, completing all local treatments and protecting healthy tissue.
In the Single-Dose Radiotherapy (SDRT) application, the IORT portable tool utilizes a linear accelerator in a process that is no different from the same way that traditional radiotherapy does. However, this method is a 5-6 minute procedure used in an operating room using a safe tool that operates in a linear and accelerated manner, only producing electron energy but not requiring too much protection for the personnel present in the same room like a traditional linear accelerator does. Therefore, for delivering single dose radiotherapy, not only the surgical team carrying out the operation is present, a radiation oncology specialist and a medical physicist are also present in the operating room. This way, radiotherapy is delivered by the radiology team and completed at the time of the surgery.
However, although single-dose application has become more globally accepted in recent years, single-dose application may not be suitable for every patient. The decision whether a patient is suited to receive this treatment must be made collectively by the radiation oncologist, the surgeon and the pathologist dealing directly with the patient. The patient’s age, the size of the tumor and other pathological qualities of the tumor play an important role in this decision. Usually, this method is most suitable for early stage disease.
The major advantage with this type of radiotherapy delivery method is that there is no need to wait for the surgical wound to heal to initiate or to plan radiotherapy at a later stage. Further, future hospital visits each day for radiotherapy may be avoided. This way, the total duration of the treatment is also cut down.
In addition, the IORT technology may help in destroying microscopic disease. The tumor bed is typically at high risk for recurrence, and traditional radiation therapy can only be provided after a recovery period after surgery, which leaves microscopic disease in the body longer and can result in tumor recurrence.
Also, IORT technology that provides radiotherapy as a single dose can behave like an added radiation “boost” to an already preoperatively radiated tumor ensuring clearance of cancer cells from the tumor bed. Furthermore, other than protecting healthy tissue, the skin remains protected, which may be damaged using other techniques. The goal is to also protect critical organs within the radiation field, such as the lungs or heart.
In recent years the advances in Linear Accelerator assembly and feasibility of creating non-co-planar arcs and fixation of the prostate movement with a rectal balloon have made it possible to treat prostate cancers with SDRT as an out patient treatment.
Similarly availability of Cyberknife allows SDRT to be delivered for intra-cranial benign tumours e.g. Acoustic Neuroma, Meningioma, Optic Glioma, Pituitary adenoma and vertebral metastases. The results of SDRT in judiciously selected cases are excellent and this is also known as Stereotactic RadioSurgery(SRS).
Thus, IORT has demonstrated its efficacy in a wide variety of intra-abdominal tumours, recurrent colorectal cancers, recurrent gynecological cancers, and soft-tissue tumours. Recently, it has emerged as an attractive treatment option for selected, early-stage breast cancer, owing to the ability to complete the entire course of radiotherapy during surgery.