Question

State the limitations of radiation method

Answer 1

in my opinion the main limitation of radiotherapy is caused by the fact, that we are treating patients. Irradiation devices are feasible for very precise and accurate treatment in submillimeter range. Furthermore, imaging can be performed with very high resolution in most modalities. And also treatment planning incl. dosimetry and dose calculation can be done with few percent uncertainty.

Now lets look at the patient with its anatomy and physiology. Stable, reproducible positioning is hard to achieve because of the deformable soft tissue. And you will have movement of the patient during the treatment because of breathing, swallowing, heart beat, etc. and the simple fact that it is difficult to lie still for several minutes. Besides these intrafractional changes, you will find interfractional alteration, such as filling of hollow organs (bladder, bowel, nasal area, oral cavity, stomach,...) or volume changes of soft tissue due to tumour shrinkage, patient weight loss or inflamation (swelling, fluid accumulation). Last but not least: delineation / contouring of the target volume is really hard even though you have lots of imaging modalities showing you different information (anatomy, physiology,...) that could be relevant or not. You can handle a lot of these problems using a combination of different systems and technology, but remaining uncertainty will be in the millimeter range (ok, maybe submillimeter for cranial radiosurgery).

Answer 2

Two could be identified: The inverse problem assume that the cross-section of the patient and its radiation absorption characteristics are known, which has not been fully resolved in the literature. The problem is centered in a computationally focus, although an complete analytic or mathematical representation is not available.