Medical Radiation – Neutrons vs Protons





Type of particle

Neutral, mass=1

Positively charged, mass=1 

Production [high energy]

Nuclear reactions [40-70 MeV protons or deuterons on beryllium]
(66 MeV protons)

Accelerator beams [>150  MeV]
(200 MeV)

Interactions with tissue

Nuclei (mainly hydrogen)


No. of centres

(2 high-energy)

(6 low energy) 

Beam delivery


Vertical, horizontal, mainly isocentric beams. [Fixed, variable, multileaf collimators] 
(Isocentric, variable collimator, multiblade trimmer)

Mainly horizontal, vertical, isocentric beams; passive, active beam spreading. [Fixed, multileaf collimators] 
(Horizontal, fixed collimators)

Major clinical advantage

Biological effect
[large, slow-growing lesions] 

Dose distribution
[lesions close to critical structures] 

No. of patients treated wordwide

40 000 (estimated)




No. of fields

1 – 6
(1 – 8)

1 – 12
(1 – 5)

No. of 

12 – 20


1 – 36

(1 – 5)

* definite cure for most cases 

(Malignant only)
Salivary gland*, paranasal sinus,
head and neck, soft tissue sarcoma*,
uterine sarcoma, prostate * ,
melanoma, bone tumour, breast 

(Benign and malignant) 
Uveal melanoma*, pituitary adenoma * , meningioma*, prostate,
arteriovenous malformation * , cervix, acoustic neuroma*,
paranasal sinus, chondrosarcoma *

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