What process does the radiation oncologist follow when preparing to treat a new patient?
Radiation therapy is a very technical treatment and takes a great deal of work by the radiation oncologist, the dosimetrist and the radiation physicist to create a radiation plan which would deliver the required dose of radiation to the cancer while minimizing radiation dose to the surrounding normal and critical organs. To create such a fine balance, sophisticated technology and treatment planning software are utilized.
Traditional radiation therapy used plain X-ray films to map the target area and radiation fields. This was a two-dimensional technique and the exact dose of radiation to critical organs was not determined carefully. Three-dimensional conformal radiation therapy uses CT scans to carefully define each and every critical organ at risk of receiving radiation as well as the tumor itself.
Over the past decade or so a more sophisticated form of three-dimensional conformal radiation therapy called IMRT (Intensity Modulated Radiation Therapy) has evolved. This technique utilizes reverse planning. That is instead of learning how much of radiation the critical organs would receive should we deliver a certain dose of radiation to a tumor, we can set limits on how much of radiation these organs can tolerate in advance.
Nowadays we also have the capability of fusing MRI and PET images with our CT scan images to enhance the quality of our contours and mapping of the target areas. By doing so we can be more precise in focusing radiation on the areas requiring radiation.
So in general before starting radiation treatments a planning session or simulation is required. During this session immobilization devices are used prior to obtaining CAT scan of the area which requires radiation. Once the images are obtained, a radiation oncologist would define i.e. contour the target area as well as adjacent critical organs. Radiation oncologist would set limits on how much of radiation these organs can safely receive and also prescribes the required dose of radiation to the tumor.
Using sophisticated treatment planning software, the dosimetrist would generate one or more plan for the radiation treatment. Radiation oncologist would review the plans and chooses the plan which has optimized the dose of radiation to the target and adjacent organs.
Once the optimal plan is chosen, the physicist would review the plan for quality assurance and subsequently approved by radiation oncologist.
Prior to delivering the very first fraction of radiation, patient would undergo another simulation consisting of obtaining films on the radiation table (AKA Port Films). Radiation oncologist would review these films to make sure that everything is aligned with what has been planned. Once the radiation oncologist approves these films, the actual treatments can begin.
Patients are anxious to begin radiation immediately but as you can appreciate, a considerable amount of time and work is spent in preparation for radiation. Our moto as radiation oncolgoists: safety first!