[10] To treat tumors at greater depth, one needs a beam with higher energy, typically given in MeV (mega electron volts).

FLASH radiotherapy is a technique under development for photon and proton treatments, using very high dose rates (necessitating large beam currents).

[16][17][18][19] The first suggestion that energetic protons could be an effective treatment was made by Robert R. Wilson in a paper published in 1946[20] while he was involved in the design of the Harvard Cyclotron Laboratory (HCL).

[21] The first treatments were performed with particle accelerators built for physics research, notably Berkeley Radiation Laboratory in 1954 and at Uppsala in Sweden in 1957.

Later, the Northeast Proton Therapy Center at Massachusetts General Hospital was brought online, and the HCL treatment program was transferred to it in 2001 and 2002.

This conformal delivery is achieved by shaping the dose through magnetic scanning of thin beamlets of protons without needing apertures and compensators.

This type of scanning delivery provides greater flexibility and control, letting the proton dose conform more precisely to the shape of the tumor.

IMPT is to proton therapy what IMRT is to conventional photon therapy—treatment that more closely conforms to the tumor while avoiding surrounding structures.

A study led by Memorial Sloan Kettering Cancer Center suggests that IMPT can improve local control when compared to passive scattering for patients with nasal cavity and paranasal sinus malignancies.

Physicians use protons to treat conditions in two broad categories: Two prominent examples are pediatric neoplasms (such as medulloblastoma) and prostate cancer.

[39] Position verification and correction must ensure that the radiation spares sensitive tissue like the optic nerve to preserve the patient's vision.

[53] One recent study showed that proton therapy has low toxicity to nearby healthy tissues and similar rates of disease control compared with conventional radiation.

Unfortunately, treatment-related toxicities caused by chemotherapy agents and radiation exposure to healthy tissues are major concerns for lymphoma survivors.

Some published studies found a reduction in long term rectal and genito-urinary damage when treating with protons rather than photons (meaning X-ray or gamma ray therapy).

[60][61] The relatively small improvement found may be the result of inconsistent patient set-up and internal organ movement during treatment, which offsets most of the advantage of increased precision.

[68] A growing amount of data shows that proton therapy has great potential to increase therapeutic tolerance for patients with GI malignancy.

Proton therapy will play a decisive role for ongoing intensified combined modality treatments for GI cancers.

[76] Research shows the feasibility of using proton therapy with acceptable side effects, even in patients who have had multiple prior courses of photon radiation.

A phase III randomized controlled trial of proton beam therapy versus radiofrequency ablation (RFA) for recurrent hepatocellular carcinoma organized by the National Cancer Center in Korea showed better 2-year local progression-free survival for the proton arm and concluded that proton beam therapy (PBT) is "not inferior to RFA in terms of local progression-free survival and safety, denoting that either RFA or PBT can be applied to recurrent small HCC patients".

[70] A phase IIB randomized controlled trial of proton beam therapy versus IMRT for locally advanced esophageal cancer organized by University of Texas MD Anderson Cancer Center concluded that proton beam therapy reduced the risk and severity of adverse events compared with IMRT while maintaining similar progression free survival.

One recently introduced method, 'model-based selection', uses comparative treatment plans for IMRT and IMPT in combination with normal tissue complication probability (NTCP) models to identify patients who may benefit most from proton therapy.

A tumor with a sizable thickness is covered by the IMRT spread out Bragg peak (SOBP) shown as the red lined distribution in the figure.

One study estimates that passively scattered proton fields have a slightly higher entrance dose at the skin (≈75%) compared to therapeutic megavoltage (MeV) photon beams (≈60%).

In proton therapy, skin exposure at the entrance point is higher, but tissues on the opposite side of the body to the tumor get no radiation.

Spot scanning can adjust the width of the SOBP on a spot-by-spot basis, which reduces the volume of normal (healthy) tissue inside the high dose region.

[117] Amitabh Chandra, a health economist at Harvard University, said, "Proton-beam therapy is like the Death Star of American medical technology...

Several industrial teams are working on development of comparatively small accelerator systems to deliver the proton therapy to patients.

The building will house the Australian Bragg Centre for Proton Therapy & Research, a A$500+ million addition to the largest health and biomedical precinct in the Southern Hemisphere, Adelaide's BioMed City.

The report also mentions that "Proton therapy for cancer treatment has arrived in Israel and the Middle East with a clinical trial underway that sees Hadassah Medical Center partnering with P-Cure, an Israeli company that has developed a unique system designed to fit into existing hospital settings".

[217] In October 2021, the Amancio Ortega Foundation arranged with the Spanish government and several autonomous communities to donate 280 million euros to install ten proton accelerators in the public health system.