How many times of heavy ion radiotherapy need to be repositioned can not be specified, it needs to be decided according to the shrinking speed of the lesion, the change of body size and the size of single dose. 1. Reduction speed of lesions: with the continuous radiotherapy, the irradiated tumor cells gradually decrease, and the scope of lesions will be reduced accordingly. It is necessary to reformulate the radiotherapy plan and determine the target area of radiotherapy according to the changes of the lesion, which is also called real-time radiotherapy. 2. Changes in body shape: Radiation may damage both tumor cells and normal cells during radiotherapy, so some of them will lose weight and change body shape rapidly during the treatment. With the change of body shape, the scope of the originally determined lesion will also change, in which case it is necessary to reposition the lesion. 3. The size of the single dose: If the single radiotherapy dose reaches a large dose, it must be precisely added to the lesion to avoid damage to normal tissues caused by the rays, and in this case the lesion needs to be repositioned. This should be done under the guidance of a specialist.