Radiation-induced cancers from modern radiotherapy techniques: intensity-modulated radiotherapy versus proton therapy.
OBJECTIVE
To assess and compare secondary cancer risk resulting from intensity-modulated radiotherapy (IMRT) and proton therapy in patients with prostate and head-and-neck cancer.


METHODS
Intensity-modulated radiotherapy and proton therapy in the scattering mode were planned for 5 prostate cancer patients and 5 head-and-neck cancer patients. The secondary doses during irradiation were measured using ion chamber and CR-39 detectors for IMRT and proton therapy, respectively. Organ-specific radiation-induced cancer risk was estimated by applying organ equivalent dose to dose distributions.


RESULTS
The average secondary doses of proton therapy for prostate cancer patients, measured 20-60 cm from the isocenter, ranged from 0.4 mSv/Gy to 0.1 mSv/Gy. The average secondary doses of IMRT for prostate patients, however, ranged between 3 mSv/Gy and 1 mSv/Gy, approximately one order of magnitude higher than for proton therapy. Although the average secondary doses of IMRT were higher than those of proton therapy for head-and-neck cancers, these differences were not significant. Organ equivalent dose calculations showed that, for prostate cancer patients, the risk of secondary cancers in out-of-field organs, such as the stomach, lungs, and thyroid, was at least 5 times higher for IMRT than for proton therapy, whereas the difference was lower for head-and-neck cancer patients.


CONCLUSIONS
Comparisons of organ-specific organ equivalent dose showed that the estimated secondary cancer risk using scattering mode in proton therapy is either significantly lower than the cases in IMRT treatment or, at least, does not exceed the risk induced by conventional IMRT treatment.
Yoon
Myonggeun
M
Proton Therapy Center, National Cancer Center, Goyang, Korea. mxy131@ncc.re.kr
Ahn
Sung Hwan
SH
Kim
Jinsung
J
Shin
Dong Ho
DH
Park
Sung Yong
SY
Lee
Se Byeong
SB
Shin
Kyung Hwan
KH
Cho
Kwan Ho
KH
D000328:Adult; D000368:Aged; D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D009502:Neutrons; D009928:Organ Specificity; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011522:Protons / Q000009:adverse effects*; D011874:Radiometry / Q000295:instrumentation; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D018570:Risk Assessment; D012542:Scattering, Radiation
D011522:Protons