{"entity":{"id":"intensity-modulated-proton-therapy","kind":"technology","name":"Pencil-beam scanning and intensity-modulated proton therapy","aka":[],"tldr":"Modern proton machines paint the tumour spot by spot with a magnetically steered pencil beam, so the dose can be shaped in three dimensions and the proton's stop-point is put to full use.","summary":"Early proton therapy used passive scattering with brass apertures and compensators for each field. Pencil-beam scanning, in routine use since the late 2000s, steers a narrow proton beam across the target layer by layer and varies its energy to set the depth, allowing intensity-modulated proton therapy that optimises all fields together. Almost all new centres use scanning only; it underpins proton arc therapy and proton FLASH research, and reduces neutron dose to the patient. Range uncertainty and sensitivity to anatomy changes remain the technique's weak points.","status":"established","asOf":"2026-09-16","links":[{"label":"Wikipedia","url":"https://en.wikipedia.org/wiki/Proton_therapy"}],"tags":["radiation-wave1"],"related":[],"cancers":["childhood-cancers","head-and-neck","brain-tumours"],"sections":["radiation"],"technologies":["proton-therapy","proton-arc-therapy","flash-rt"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"notes":[],"principle":"A scanned monoenergetic proton beam deposits most of its energy at a controllable depth (the Bragg peak); layering spots of different energies fills the target with dose and stops beyond it.","strengths":["No exit dose beyond the target","Full 3D dose shaping","Lower neutron dose than passive scattering"],"limitations":["Range uncertainty of a few millimetres","Sensitive to motion and anatomy change","High capital and running cost"],"since":2008},"route":"/technologies/intensity-modulated-proton-therapy/","neighbours":{"cancer":[{"id":"brain-tumours","kind":"cancer","name":"Brain and spinal cord tumours (all types)","route":"/cancers/brain-tumours/"},{"id":"childhood-cancers","kind":"cancer","name":"Childhood cancers (all types)","route":"/cancers/childhood-cancers/"},{"id":"head-and-neck","kind":"cancer","name":"Head and neck squamous cell carcinoma","route":"/cancers/head-and-neck/"}],"section":[{"id":"radiation","kind":"section","name":"Radiation Therapy","route":"/fronts/radiation/"}],"technology":[{"id":"flash-rt","kind":"technology","name":"FLASH radiotherapy","route":"/technologies/flash-rt/"},{"id":"proton-arc-therapy","kind":"technology","name":"Proton arc therapy","route":"/technologies/proton-arc-therapy/"},{"id":"proton-therapy","kind":"technology","name":"Proton therapy","route":"/technologies/proton-therapy/"}]}}