# Proton therapy

Source: https://onco.cc/technologies/proton-therapy/  
OnCo record `proton-therapy` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Radiation using protons, which stop inside the tumour instead of passing through, so tissue behind it gets no dose.

## Summary

Proton therapy exploits the Bragg peak: protons deposit maximum energy at a depth set by their energy and then stop, so there is no exit dose, and pencil-beam scanning paints the tumour layer by layer. This lowers the integral dose to normal tissue and reduces second cancers in children, which is why it is established for paediatric tumours, skull-base and spine tumours, and re-irradiation. Clinical dose is reported at a constant relative biological effectiveness of 1.1; linear energy transfer, and therefore RBE, rises at the distal edge, so that convention can under- or over-state biological dose to a late-responding organ sitting just beyond the target. Whether that window, plus the tissue's alpha/beta ratio, is large enough to beat modern IMRT in adults is the open question (PARTIQoL, RADCOMP, NRG oesophagus and lung). Range uncertainty and cost remain. Compact single-room systems (Mevion, IBA Proteus One) expand access. The simple version is that protons stop inside the tumour, so tissue behind it is spared.

## Fields

- Kind: Technology
- Status: established
- Last checked: 2026-09-17
- Principle: Bragg peak: protons deposit maximum energy at a depth set by their energy, with no exit dose. Pencil-beam scanning paints the tumour.
- Strengths: No exit dose; lower integral dose; Reduced second cancers in children
- Limitations: Cost; Range uncertainty; Limited randomised evidence in adults; Constant RBE 1.1 is a convention; variable RBE at the distal edge is unverified in the clinic

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Proton_therapy
- Wikipedia: https://en.wikipedia.org/wiki/Proton_therapy
- Paganetti, RBE values for proton beam therapy (IJROBP 2014): https://doi.org/10.1016/j.ijrobp.2014.07.001

## Connected records

- technologies: [Breast cancer after chest radiotherapy in childhood, and the screening that follows](https://onco.cc/technologies/rejuv-paed-breast-after-chest-radiotherapy/), [Carbon-ion synchrotrons and facilities](https://onco.cc/technologies/carbon-ion-synchrotrons/), [Carbon-ion therapy](https://onco.cc/technologies/carbon-ion/), [CT (computed tomography)](https://onco.cc/technologies/ct/), [Dry mouth, teeth and taste after head and neck radiotherapy](https://onco.cc/technologies/dry-mouth-teeth-after-head-neck-radiotherapy/), [Growth and final height after treatment in childhood, and growth hormone](https://onco.cc/technologies/rejuv-paed-growth-and-height/), [Hearing after platinum and cranial radiotherapy in a developing child](https://onco.cc/technologies/rejuv-paed-hearing/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [In vivo dosimetry and patient-specific quality assurance](https://onco.cc/technologies/in-vivo-dosimetry/), [Late deaths after childhood cancer, what causes them, and the proof that gentler treatment worked](https://onco.cc/technologies/rejuv-paed-late-mortality/), [Linac, proton system and brachytherapy machine manufacturing](https://onco.cc/technologies/radiotherapy-equipment-manufacturing/), [Memory, attention and learning after treatment of a childhood cancer](https://onco.cc/technologies/rejuv-paed-neurocognitive/), [Pencil-beam scanning and intensity-modulated proton therapy](https://onco.cc/technologies/intensity-modulated-proton-therapy/), [Proton arc therapy](https://onco.cc/technologies/proton-arc-therapy/), [Proton therapy machines: cyclotrons, synchrotrons and single-room systems](https://onco.cc/technologies/proton-therapy-systems/), [Radiotherapy treatment planning and QA software](https://onco.cc/technologies/treatment-planning-systems/), [Second cancers after childhood cancer: the risk by treatment, and why it is falling](https://onco.cc/technologies/rejuv-paed-second-cancers/), [Teeth, jaws and facial growth after treatment in childhood](https://onco.cc/technologies/rejuv-paed-teeth-and-face/), [The linear-quadratic model and fractionation](https://onco.cc/technologies/linear-quadratic-model/), [The pituitary, puberty and the hypothalamic axis after cranial radiotherapy in childhood](https://onco.cc/technologies/rejuv-paed-pituitary-and-puberty/), [Very-high-energy electron therapy](https://onco.cc/technologies/vhee-radiotherapy/)
- pairings: [Caution: proton therapy vs IMRT](https://onco.cc/pairings/proton-vs-imrt/)
- ideas: [A coordinated FLASH radiotherapy evidence programme with shared dose-rate standards](https://onco.cc/ideas/idea-fund-flash-evidence-programme/), [A national repository of radiotherapy dose plans linked to outcomes](https://onco.cc/ideas/idea-data-radiotherapy-dose-repository/), [Compact FLASH and proton systems at the price of a conventional linac](https://onco.cc/ideas/idea-moon-compact-flash-proton/), [Measure the late effects of the treatments being given now, not the ones given in 1975](https://onco.cc/ideas/lymphoma-ev-late-effects-of-the-treatments-given-now/), [Pooled coverage-with-evidence for proton therapy across all centres](https://onco.cc/ideas/idea-fund-proton-coverage-with-evidence/), [Use LET, RBE and alpha/beta to decide when protons beat IMRT](https://onco.cc/ideas/idea-bio2-let-rbe-ab-selects-protons/)
- fronts: [Radiation Therapy](https://onco.cc/fronts/radiation/)
- companies: [Hitachi (particle therapy)](https://onco.cc/companies/hitachi/), [IBA (Ion Beam Applications)](https://onco.cc/companies/iba/), [Leo Cancer Care](https://onco.cc/companies/leo-cancer-care/), [Mevion Medical Systems](https://onco.cc/companies/mevion/), [P-Cure](https://onco.cc/companies/p-cure/), [ProTom International](https://onco.cc/companies/protom/), [RaySearch Laboratories](https://onco.cc/companies/raysearch/), [Sumitomo Heavy Industries](https://onco.cc/companies/sumitomo-heavy-industries/), [Varian (Siemens Healthineers)](https://onco.cc/companies/varian/)
- terms: [Alpha/beta ratio](https://onco.cc/terms/alpha-beta-ratio/), [Biologically effective dose (BED) and EQD2](https://onco.cc/terms/biologically-effective-dose/), [Bragg peak](https://onco.cc/terms/bragg-peak/), [Choices made at the time of treatment that change the second cancer risk](https://onco.cc/terms/rejuv-second-choices-made-at-treatment/), [IMRT / IGRT / VMAT (modern external beam radiotherapy)](https://onco.cc/terms/imrt-term/), [Late effects of Hodgkin lymphoma treatment, and the follow-up that answers them](https://onco.cc/terms/lymphoma-tx-hodgkin-late-effects/), [Linear energy transfer (LET)](https://onco.cc/terms/linear-energy-transfer/), [Persistent radiation-induced alopecia](https://onco.cc/terms/alopecia-radiotherapy-persistent/), [Radiation pneumonitis and lung fibrosis](https://onco.cc/terms/radiation-pneumonitis/), [Radiotherapy](https://onco.cc/terms/radiotherapy/), [Radiotherapy and second cancers: field, dose and age at exposure](https://onco.cc/terms/rejuv-second-radiotherapy-dose-field-and-age/), [Radiotherapy in lymphoma: involved-site fields, 24 Gy, 4 Gy and total skin electron therapy](https://onco.cc/terms/lymphoma-tx-radiotherapy/), [Relative biological effectiveness (RBE)](https://onco.cc/terms/relative-biological-effectiveness/), [Second cancers after radiotherapy](https://onco.cc/terms/second-cancers-after-radiotherapy/)
- trials: [COG ACNS0331](https://onco.cc/trials/acns0331/), [Comparing Photon Therapy To Proton Therapy To Treat Patients With Lung Cancer](https://onco.cc/trials/nct01993810/), [Hemithoracic irradiation with proton therapy in malignant pleural mesothelioma (UCL)](https://onco.cc/trials/ucl-proton-hemithoracic-mpm/), [PARTIQoL](https://onco.cc/trials/partiqol/), [RADCOMP](https://onco.cc/trials/radcomp/), [SJMB12](https://onco.cc/trials/sjmb12/), [Testing Proton Craniospinal Radiation Therapy Versus the Usual Radiation Therapy for Leptomeningeal Metastasis, RADIATE-LM Trial](https://onco.cc/trials/nct06500481/)
- key papers: [Cardiovascular disease after Hodgkin lymphoma treatment: 40-year disease risk](https://onco.cc/key-papers/paper-van-nimwegen-cardiovascular-disease-after-hodgkin-jama-intern-med-2015/), [Paganetti 2014: proton RBE is not a fixed 1.1](https://onco.cc/key-papers/paper-paganetti-proton-rbe-ijrobp-2014/), [PARTIQoL: phase 3 randomised trial of proton therapy versus IMRT for localised prostate cancer (ASTRO 2024 late-breaking abstract)](https://onco.cc/key-papers/paper-partiqol-astro-2024/), [Second cancer risk up to 40 years after treatment for Hodgkin's lymphoma](https://onco.cc/key-papers/paper-schaapveld-second-cancer-risk-40-years-hodgkin-nejm-2015/)
- cancers: [Adenoid cystic carcinoma](https://onco.cc/cancers/adenoid-cystic-carcinoma/), [Atypical teratoid/rhabdoid tumour (ATRT)](https://onco.cc/cancers/atrt/), [Central nervous system germ cell tumours (germinoma and non-germinomatous)](https://onco.cc/cancers/cns-germ-cell-tumours/), [Cervical cancer](https://onco.cc/cancers/cervical/), [Chondrosarcoma](https://onco.cc/cancers/chondrosarcoma/), [Chordoma](https://onco.cc/cancers/chordoma/), [Craniopharyngioma](https://onco.cc/cancers/craniopharyngioma/), [Dedifferentiated chordoma](https://onco.cc/cancers/dedifferentiated-chordoma/), [Early-stage classical Hodgkin lymphoma (stage I to II)](https://onco.cc/cancers/early-stage-classical-hodgkin-lymphoma/), [Ependymoma](https://onco.cc/cancers/ependymoma/), [Esthesioneuroblastoma (olfactory neuroblastoma)](https://onco.cc/cancers/esthesioneuroblastoma/), [Ewing sarcoma](https://onco.cc/cancers/ewing-sarcoma/), [Germ cell tumours of childhood and adolescence (extracranial and CNS)](https://onco.cc/cancers/paediatric-germ-cell-tumours/), [Glioma & glioblastoma](https://onco.cc/cancers/glioblastoma/), [Group 3 and group 4 medulloblastoma (non-WNT/non-SHH)](https://onco.cc/cancers/medulloblastoma-group-3-4/), [Head and neck squamous cell carcinoma](https://onco.cc/cancers/head-and-neck/), [High-risk neuroblastoma](https://onco.cc/cancers/neuroblastoma-high-risk/), [Hodgkin lymphoma](https://onco.cc/cancers/hodgkin-lymphoma/), [Locally advanced cervical cancer](https://onco.cc/cancers/locally-advanced-cervical-cancer/), [Locoregionally advanced nasopharyngeal carcinoma (stage III to IVA)](https://onco.cc/cancers/locoregionally-advanced-nasopharyngeal-carcinoma/), [Medulloblastoma](https://onco.cc/cancers/medulloblastoma/), [Meningioma](https://onco.cc/cancers/meningioma/), [Mesothelioma](https://onco.cc/cancers/mesothelioma/), [Nasal cavity and paranasal sinus cancers (including esthesioneuroblastoma)](https://onco.cc/cancers/sinonasal/), [Nasopharyngeal carcinoma](https://onco.cc/cancers/nasopharyngeal/), [Neuroblastoma (paediatric)](https://onco.cc/cancers/neuroblastoma/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Osteosarcoma](https://onco.cc/cancers/osteosarcoma/), [Paediatric high-grade glioma (excluding diffuse midline glioma)](https://onco.cc/cancers/paediatric-high-grade-glioma/), [Paediatric low-grade glioma](https://onco.cc/cancers/paediatric-low-grade-glioma/), [Poorly differentiated chordoma (SMARCB1-deficient)](https://onco.cc/cancers/poorly-differentiated-chordoma/), [Primary mediastinal (thymic) large B-cell lymphoma](https://onco.cc/cancers/primary-mediastinal-b-cell-lymphoma/), [Recurrent and metastatic nasopharyngeal carcinoma](https://onco.cc/cancers/recurrent-metastatic-nasopharyngeal-carcinoma/), [Rhabdomyosarcoma](https://onco.cc/cancers/rhabdomyosarcoma/), [Salivary gland cancers](https://onco.cc/cancers/salivary-gland/), [Sarcomas (soft tissue, bone, GIST)](https://onco.cc/cancers/sarcoma/), [SHH-activated medulloblastoma](https://onco.cc/cancers/medulloblastoma-shh/), [Sinonasal undifferentiated carcinoma (SNUC) and SWI/SNF-deficient sinonasal carcinoma](https://onco.cc/cancers/sinonasal-undifferentiated-carcinoma/), [Spinal cord tumours (intramedullary and intradural)](https://onco.cc/cancers/spinal-cord-tumours/), [Thymic carcinoma](https://onco.cc/cancers/thymic-carcinoma/), [Thymoma (WHO types A, AB, B1, B2 and B3)](https://onco.cc/cancers/thymoma/), [Thymoma and thymic carcinoma](https://onco.cc/cancers/thymic-epithelial/), [Unresectable stage III non-small-cell lung cancer](https://onco.cc/cancers/stage-iii-unresectable-nsclc/), [Uveal melanoma](https://onco.cc/cancers/uveal-melanoma/), [WNT-activated medulloblastoma](https://onco.cc/cancers/medulloblastoma-wnt/)
- institutions: [Aarhus University Hospital](https://onco.cc/institutions/aarhus-university-hospital/), [Abramson Cancer Center, University of Pennsylvania](https://onco.cc/institutions/penn-abramson/), [Advanced Centre for Treatment, Research and Education in Cancer](https://onco.cc/institutions/actrec/), [American Society for Radiation Oncology](https://onco.cc/institutions/astro/), [Apollo Hospitals (Apollo Cancer Centres)](https://onco.cc/institutions/apollo-hospitals/), [BC Cancer](https://onco.cc/institutions/bc-cancer/), [Cancer Center Clínica Universidad de Navarra / CIMA](https://onco.cc/institutions/cun-navarra/), [Case Comprehensive Cancer Center](https://onco.cc/institutions/case-ccc/), [Centre Antoine Lacassagne](https://onco.cc/institutions/centre-antoine-lacassagne/), [Centre François Baclesse](https://onco.cc/institutions/centre-francois-baclesse/), [Chang Gung Memorial Hospital](https://onco.cc/institutions/chang-gung-memorial-hospital/), [Charité Universitätsmedizin Berlin](https://onco.cc/institutions/charite/), [Children's Hospital of Philadelphia](https://onco.cc/institutions/chop/), [Cleveland Clinic Abu Dhabi](https://onco.cc/institutions/cleveland-clinic-abu-dhabi/), [Cleveland Clinic Taussig Cancer Institute](https://onco.cc/institutions/cleveland-clinic/), [Comprehensive Cancer Center Vienna, Medical University of Vienna / AKH](https://onco.cc/institutions/ccc-vienna/), [Erasmus MC Cancer Institute](https://onco.cc/institutions/erasmus-mc/), [European Society for Radiotherapy and Oncology](https://onco.cc/institutions/estro/), [Fred Hutchinson Cancer Center](https://onco.cc/institutions/fred-hutch/), [Fudan University Shanghai Cancer Center](https://onco.cc/institutions/fuscc/), [Georgetown Lombardi Comprehensive Cancer Center](https://onco.cc/institutions/georgetown-lombardi/), [Heidelberg University Hospital / NCT / DKFZ](https://onco.cc/institutions/heidelberg-nct/), [Hokkaido University Hospital](https://onco.cc/institutions/hokkaido-university-hospital/), [Huntsman Cancer Institute, University of Utah](https://onco.cc/institutions/huntsman/), [Institut Curie](https://onco.cc/institutions/institut-curie/), [Johns Hopkins Hospital / Sidney Kimmel Comprehensive Cancer Center](https://onco.cc/institutions/johns-hopkins/), [King Faisal Specialist Hospital and Research Centre](https://onco.cc/institutions/kfshrc/), [Leiden University Medical Center](https://onco.cc/institutions/lumc-leiden/), [Maastricht UMC+ Comprehensive Cancer Center](https://onco.cc/institutions/maastricht-umc/), [Maria Skłodowska-Curie National Research Institute of Oncology](https://onco.cc/institutions/nio-warsaw/), [Massachusetts General Hospital Cancer Center](https://onco.cc/institutions/mgh/), [Mayo Clinic](https://onco.cc/institutions/mayo-clinic/), [Mayo Clinic Comprehensive Cancer Center in Arizona](https://onco.cc/institutions/mayo-clinic-arizona/), [Mayo Clinic Comprehensive Cancer Center in Florida](https://onco.cc/institutions/mayo-clinic-florida/), [MD Anderson Cancer Center](https://onco.cc/institutions/md-anderson/), [MUSC Hollings Cancer Center](https://onco.cc/institutions/musc-hollings/), [National Cancer Center Hospital East](https://onco.cc/institutions/ncc-hospital-east/), [National Cancer Center Korea](https://onco.cc/institutions/ncc-korea/), [National Cancer Centre Singapore](https://onco.cc/institutions/nccs/), [National Taiwan University Hospital](https://onco.cc/institutions/ntuh/), [NCT/UCC Dresden, University Hospital Carl Gustav Carus](https://onco.cc/institutions/nct-dresden/), [New York Proton Center](https://onco.cc/institutions/new-york-proton-center/), [O'Neal Comprehensive Cancer Center at UAB](https://onco.cc/institutions/oneal-uab/), [Oslo University Hospital, The Norwegian Radium Hospital](https://onco.cc/institutions/oslo-radium-hospital/), [Princess Máxima Center for Pediatric Oncology](https://onco.cc/institutions/princess-maxima/), [Robert H. Lurie Comprehensive Cancer Center of Northwestern University](https://onco.cc/institutions/northwestern-lurie/), [Royal Adelaide Hospital](https://onco.cc/institutions/royal-adelaide-hospital/), [Ruijin Hospital, Shanghai Jiao Tong University](https://onco.cc/institutions/ruijin-hospital/), [Samsung Medical Center](https://onco.cc/institutions/samsung-medical-center/), [Shandong Cancer Hospital and Institute](https://onco.cc/institutions/shandong-cancer-hospital/), [Shizuoka Cancer Center](https://onco.cc/institutions/shizuoka-cancer-center/), [Siteman Cancer Center, Washington University](https://onco.cc/institutions/wustl-siteman/), [St. Jude Children's Research Hospital](https://onco.cc/institutions/st-jude/), [Sylvester Comprehensive Cancer Center, University of Miami](https://onco.cc/institutions/sylvester-miami/), [The Christie NHS Foundation Trust](https://onco.cc/institutions/the-christie/), [The Clatterbridge Cancer Centre NHS Foundation Trust](https://onco.cc/institutions/clatterbridge/), [The Ohio State University Comprehensive Cancer Center, James Cancer Hospital and Solove Research Institute](https://onco.cc/institutions/osu-james/), [The University of Kansas Cancer Center](https://onco.cc/institutions/ku-cancer-center/), [Union Hospital, Tongji Medical College](https://onco.cc/institutions/union-hospital-wuhan/), [University College London Hospitals / UCL Cancer Institute](https://onco.cc/institutions/uclh/), [University Medical Center Groningen Comprehensive Cancer Center](https://onco.cc/institutions/umcg-groningen/), [University of Florida Health Cancer Center](https://onco.cc/institutions/uf-health-cancer-center/), [University of Maryland Marlene and Stewart Greenebaum Comprehensive Cancer Center](https://onco.cc/institutions/maryland-greenebaum/), [University of Michigan Rogel Cancer Center](https://onco.cc/institutions/michigan-rogel/), [Uppsala University Hospital / Uppsala University](https://onco.cc/institutions/uppsala-akademiska/), [UZ Leuven / Leuven Cancer Institute](https://onco.cc/institutions/uz-leuven/), [West German Cancer Center (WTZ), University Hospital Essen](https://onco.cc/institutions/essen-wtz/), [Winship Cancer Institute of Emory University](https://onco.cc/institutions/emory-winship/), [Zhejiang Cancer Hospital](https://onco.cc/institutions/zhejiang-cancer-hospital/)
- people: [Amar Gajjar](https://onco.cc/people/amar-gajjar/), [Anthony L. Zietman](https://onco.cc/people/anthony-zietman/), [Ashya King](https://onco.cc/people/ashya-king/), [Charles B. Simone II](https://onco.cc/people/charles-simone/), [Goh Cheng Liang](https://onco.cc/people/goh-cheng-liang/), [Jeffrey D. Bradley](https://onco.cc/people/jeffrey-bradley/), [Joan Spencer](https://onco.cc/people/joan-spencer/), [Joe Y. Chang](https://onco.cc/people/joe-chang/), [Jürgen Debus](https://onco.cc/people/juergen-debus/), [Marianne van Rooijen](https://onco.cc/people/marianne-van-rooijen/), [Michael Baumann](https://onco.cc/people/michael-baumann/), [Paul Herijgers](https://onco.cc/people/paul-herijgers/), [Theodore S. Hong](https://onco.cc/people/theodore-hong/), [Thomas J. George](https://onco.cc/people/thomas-george/)
- bottlenecks: [Surgery and radiotherapy cure most, get least](https://onco.cc/bottlenecks/b-surgery-radiation-innovation/)
- roadmaps: [Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH](https://onco.cc/roadmaps/radiation-roadmap/)

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JSON: https://onco.cc/api/v1/entities/proton-therapy.json