Effect of intensity-modulated pelvic radiotherapy on second cancer risk in the postoperative treatment of endometrial and cervical cancer.
OBJECTIVE
To estimate and compare intensity-modulated radiotherapy (IMRT) with three-dimensional conformal radiotherapy (3DCRT) in terms of second cancer risk (SCR) for postoperative treatment of endometrial and cervical cancer.


METHODS
To estimate SCR, the organ equivalent dose concept with a linear-exponential, a plateau, and a linear dose-response model was applied to dose distributions, calculated in a planning computed tomography scan of a 68-year-old woman. Three plans were computed: four-field 18-MV 3DCRT and nine-field IMRT with 6- and 18-MV photons. SCR was estimated as a function of target dose (50.4 Gy/28 fractions) in organs of interest according to the International Commission on Radiological Protection.


RESULTS
Cumulative SCR relative to 3DCRT was +6% (3% for a plateau model, -4% for a linear model) for 6-MV IMRT and +26% (25%, 4%) for the 18-MV IMRT plan. For an organ within the primary beam, SCR was +12% (0%, -12%) for 6-MV and +5% (-2%, -7%) for 18-MV IMRT. 18-MV IMRT increased SCR 6-7 times for organs away from the primary beam relative to 3DCRT and 6-MV IMRT. Skin SCR increased by 22-37% for 6-MV and 50-69% for 18-MV IMRT inasmuch as a larger volume of skin was exposed.


CONCLUSIONS
Cancer risk after IMRT for cervical and endometrial cancer is dependent on treatment energy. 6-MV pelvic IMRT represents a safe alternative with respect to SCR relative to 3DCRT, independently of the dose-response model. 18-MV IMRT produces second neutrons that modestly increase the SCR.
Alfred Hospital and Monash University, Melbourne, Australia. daniel.zwahlen@gmx.ch
Daniel R
DR
Zwahlen
Jeremy D
JD
Ruben
Phillip
P
Jones
Frank
F
Gagliardi
Jeremy L
JL
Millar
Uwe
U
Schneider
D000368:Aged; D004307:Dose-Response Relationship, Radiation; D016889:Endometrial Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D007044:Hysterectomy; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D016609:Neoplasms, Second Primary / Q000209:etiology*; D010052:Ovariectomy; D010388:Pelvis; D020266:Radiotherapy, Conformal / Q000009:adverse effects; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D018570:Risk Assessment; D012878:Skin Neoplasms / Q000209:etiology; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy* / Q000601:surgery