Purpose/Objective(s): To compare maximum genitourinary (GU) and gastrointestinal (GI) toxicities within 5 weeks of starting radiation therapy between intensity-modulated radiation therapy (IMRT) and conventional radiation therapy (non-IMRT) in post-hysterectomy patients treated for cervical or endometrial cancer. We also were interested to determine the dose volume histogram (DVH) values that predict grade 2+ toxicities.

Materials/Methods: Post-hysterectomy cervical and endometrial cancer patients treated at our institution were retrospectively analyzed for toxicity. GU and GI toxicities were collected prospectively using CTCAE version 4.0 during weekly on-treatment visits using a centralized database from week 1 to 6 of radiation therapy. DVH parameters were analyzed. Univariate analysis of toxicity, patient characteristics, and DVH parameters was performed using chi-square test and logistic regression.

Results: A total of 105 post-hysterectomy patients with stages I-IIIC2 endometrial (n=83, 79%) or IA-IIA cervical (n=22, 21%) cancer were treated from May 2003-November 2016. Ninety-one patients (87%) had on treatment visit assessments to evaluate (51 with IMRT and 40 with non-IMRT), including 55 patients (30 with IMRT and 25 with non-IMRT) with DVH parameters available. There was no difference between the two groups regarding baseline patient characteristics. Within 5 weeks of treatment, 23.5% patients in IMRT and 40% in non-IMRT had at least one grade 2+ toxicity (p=0.12). Bowel V40 and V45 were lower in the IMRT (median [Q1-Q3] 216cc [145-373]) than non IMRT (570cc [334-668]) cohorts. Among all patients, bowel V25, V30, V40 and V45 were all significantly associated with increased incidences of any grade 2+ toxicity, while bowel V5, V10, V15, V20 and V35 were not (Table 1). The medians (Q1-Q3) of bowel V45 were 199cc (80-457cc) among those had < grade 2 GI toxicity and 527cc (147-829cc) among those had 2+ GI toxicity (p=0.03). Table 1: DVH Parameters and Toxicity

Bowel DVH: Median cc (Q1-Q3cc)	< Grade 2 Toxicity	Grade 2+ Toxicity	P Value
V5	1066 (654-1517)	1200 (826-1615)	0.5
V10	907 (588-1392)	1108 (780-1565)	0.36
V15	814 (537-1160)	1037 (680-1499)	0.2
V20	745 (475-1102)	1004 (508-1393)	0.1
V25	605 (408-897)	905 (395-1270)	0.038
V30	466 (327-727)	788 (258-1075)	0.027
V35	398 (271-615)	681 (214-966)	0.4
V40	289 (177-472)	607 (189-887)	0.009
V45	184 (78 - 388)	527 (155-800)	0.005

Conclusion: The rates of experiencing at least one grade 2 or higher toxicity were lower for patients treated with IMRT than non-IMRT. Bowel V45 was associated with Grade 2+ toxicity. IMRT was associated with a lower bowel V40 and V45 in this group of post hysterectomy patients.