The 'cause' of all conditions and sickness lies in the psychological and the spiritual realms. This is because the human, like any other animal is an information system, or a complex of information systems. And organs, and cells respond to these 'bits' of information.
While some may say that some conditions are caused on the 'material' plane, the body's response must involve all information systems available. And these systems must respond accordingly. But a complication arises; one's psychology and spiritual condition may negate healing.
Also in this case, we must realize that radiotherapy damages the cells, strains your organs, and all these activities will tend to lower blood circulation.
Add the fact that the back plays a crucial role in walking. A weakened back means difficulty in walking.
Healing, and healthy living shouldn't be, and isn't so difficult to find for humans.
Especially this problem shouldn't make you panic, or make you increase your costs unduly.