And some more Protons vs. Photons

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A review of the impact of photon and proton external beam

radiotherapy treatment modalities on the dose distribution in field

and out-of-field; implications for the long-term morbidity of cancer

survivors.

Palm A, Johansson KA.

Department of Therapeutic Radiation Physics, Medical Physics and

Biomedical Engineering, Sahlgrenska University Hospital, Göteborg,

Sweden. asa.palm@...

The use of untraditional treatment modalities for external beam

radiotherapy such as intensity modulated radiation therapy (IMRT)

and proton beam therapy is increasing. This review focuses on the

changes in the dose distribution and the impact on radiation related

risks for long-term cancer survivors. We compare conventional

radiotherapy, IMRT, and proton beam therapy based on published

treatment planning studies as well as published measurements and

Monte Carlo simulations of out-of-field dose distributions. Physical

dose parameters describing the dose distribution in the target

volume, the conformity index, the dose distribution in organs at

risk, and the dose distribution in non-target tissue, respectively,

are extracted from the treatment planning studies. Measured out-of-

field dose distributions are presented as the dose equivalent as a

function of distance from the treatment field. Data in the

literature clearly shows that, compared with conventional

radiotherapy, IMRT improves the dose distribution in the target

volume, which may increase the probability of tumor control. IMRT

also seems to increase the out-of-field dose distribution, as well

as the irradiated non-target volume, although the data is not

consistent, leading to a potentially increased risk of radiation

induced secondary malignancies, while decreasing the dose to normal

tissues close to the target volume, reducing the normal tissue

complication probability. Protons show no or only minor advantage on

the dose distribution in the target volume and the conformity index

compared to IMRT. However, the data consistently shows that proton

beam therapy substantially decreases the OAR average dose compared

to the other two techniques. It is also clear that protons provide

an improved dose distribution in non-target tissues compared to

conventional radiotherapy and IMRT. IMRT and proton beam therapy may

significantly improve tumor control for cancer patients and quality

of life for long-term cancer survivors.