Optimizing ovarian dose sparing for young cervical cancer patients after oophoropexy: a dosimetric and radiobiological comparison of three radiotherapy techniques (IMPT, TOMO, and VMAT).

PURPOSE: To systematically compare the dosimetric performance and model-based radiobiological estimates of intensity-modulated proton therapy (IMPT), helical tomotherapy (TOMO), and volumetric modulated arc therapy (VMAT) for ovarian dose sparing in young cervical cancer patients after oophoropexy.

METHODS: Ten premenopausal cervical cancer patients who received postoperative pelvic radiotherapy following bilateral ovarian transposition were retrospectively enrolled. Three treatment plans (IMPT, TOMO, and VMAT) were designed for each patient with a uniform prescription of 45 Gy in 25 fractions. IMPT plans incorporated robust optimization accounting for setup uncertainty (5 mm) and range uncertainty (3.5%). Dosimetric parameters evaluated included target coverage ([Formula: see text]), homogeneity index (HI), ovarian mean dose ([Formula: see text]) and maximum dose ([Formula: see text]), and dose-volume metrics for organs at risk (OARs: rectum, bladder, small intestine, sigmoid, femoral heads). Radiobiological analyses included equivalent uniform dose (EUD), normal tissue complication probability (NTCP), and excess absolute risk (EAR) estimation for secondary malignancies using Schneider's mechanistic model.

RESULTS: All three techniques achieved clinically acceptable target coverage. IMPT showed superior dose homogeneity and the most favorable planned ovarian dose-sparing profile, reducing ovarian [Formula: see text] by approximately 95% compared with photon-based techniques (0.11-0.35 Gy vs. 4.44-5.24 Gy, [Formula: see text]) and substantially lowering low-dose exposure ([Formula: see text] cc vs. 2.86-7.68 cc, [Formula: see text]). Both IMPT and TOMO achieved significantly lower [Formula: see text] to the rectum, bladder, and small intestine than VMAT ([Formula: see text]). IMPT also reduced small intestine [Formula: see text], mean bladder dose, and integral dose to normal tissue compared with both photon techniques ([Formula: see text]). Model-based NTCP analysis showed that IMPT yielded lower estimated complication probabilities for the small intestine, rectum, and bladder compared with TOMO and VMAT ([Formula: see text]), while femoral head estimates were comparable between IMPT and VMAT and lower than TOMO. EAR modeling suggested organ-specific and endpoint-dependent differences across pelvic OARs. VMAT had the shortest beam-on time (2.20 ± 0.05 min vs. TOMO 8.18 ± 0.99 min, [Formula: see text]).

CONCLUSION: IMPT achieved the lowest ovarian radiation exposure and the most favorable overall dosimetric profile for ovarian dose sparing after ovarian transposition. TOMO provided competitive sparing for several high-dose pelvic OAR endpoints, whereas VMAT offered the shortest photon beam-on time. Overall, IMPT appears to be the most favorable dosimetric option for ovarian dose sparing when available, while VMAT and TOMO remain reasonable alternatives depending on clinical priorities and resource availability. These findings should be interpreted as dosimetric and model-based advantages rather than direct evidence of improved ovarian endocrine function or reduced clinical toxicity.