What should you know about physics of radiotherapy?

Most external radiotherapy uses high-energy photons or particles. A treatment machine directs the beam, while shaping devices adjust its outline. Beams can enter from several angles so the planned dose overlaps at the tumour. Imaging shows the target and nearby organs, and computer calculations estimate how energy will be distributed through the body. Positioning supports, image guidance and checks before delivery help the team reproduce the plan at each visit.

Radiation can damage the genetic material of cells. Tumour cells may be less able to repair that damage than healthy tissue, although normal cells can also be affected. Physics planning therefore balances tumour coverage with protection of organs such as the brain, bowel, breast, skin and spinal cord.

You may have a planning scan and a mould or other support to keep your body in a repeatable position. Tell the team if pain, breathing difficulty or mobility problems make the position hard to hold. Ask whether the plan uses image guidance, how motion is managed and which body areas need protection. Radiotherapy can be used for conditions including basal cell carcinoma, brain tumour, breast cancer, cervical cancer, bowel cancer, womb cancer, glioblastoma and head and neck cancer, with plans tailored to each site.

Tell the radiotherapy team about severe skin reaction, worsening pain, repeated vomiting, difficulty swallowing, new weakness, confusion or breathlessness. Seek emergency help for a seizure, sudden loss of movement, severe breathing difficulty or inability to stay awake. The urgent symptoms depend on the treated body area, so ask for a written contact plan before treatment starts.

What type of radiation is planned, and why? Which organs are near the target? How will movement and positioning be managed? What checks confirm the machine is delivering the intended plan? Which side effects relate to the treated area, and who should I call if they appear?