Dosimetric Predictors of Radiation-Induced Vaginal Stenosis After Pelvic Radiation Therapy for Rectal and Anal Cancer.
OBJECTIVE
Although vaginal stenosis (VS) is a recognized toxicity in women who receive pelvic radiation therapy (RT), the relationship between RT dose and the volume and extent of toxicity has not been analyzed. We modeled this relationship to identify predictors of VS.


METHODS
We evaluated 54 women, aged 29 to 78 years, who underwent pelvic RT for rectal or anal cancer during 2008 to 2011 and were enrolled in a prospective study evaluating vaginal dilator use. Maximum dilator size was measured before RT (baseline) and 1 month and 12 months after RT. Dilator use was initiated at 1 month. The difference (D) in dilator size before and after RT was recorded. Those with D ≤-1 were classified as having VS (n=35); those with D ≥0 were classified as having no VS (n=19 at 1 month). Dose-volume parameters were extracted, and the generalized equivalent uniform dose (gEUD) was used to build a predictive model.


RESULTS
The mean vaginal doses were 50.0 Gy and 36.8 Gy for anal and rectal cancer patients, respectively. One month after RT, a gEUD model using a wide range of a values suggests that sparing of vaginal volume to a low dose may be important. When gEUD (a = -1) was <35 Gy and the mean vaginal dose was <43 Gy, severe VS was reduced (P=.02). A 1-year analysis suggests increasingly negative D values with increasing mean dose. However, patients with compliance <40% were more likely to have toxicity.


CONCLUSIONS
Vaginal stenosis is influenced by multiple RT dose-volume characteristics. Mean dose and gEUD constraints together may reduce the risk of severe VS. Patients receiving higher mean vaginal doses should have greater compliance with dilator therapy to minimize risk of toxicity. Further validation with independent datasets is needed.
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
Christina H
CH
Son
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
Ethel
E
Law
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York.
Jung Hun
JH
Oh
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York.
Aditya P
AP
Apte
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
T Jonathan
TJ
Yang
Department of Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, New York.
Elyn
E
Riedel
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
Abraham J
AJ
Wu
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York.
Joseph O
JO
Deasy
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York. Electronic address: goodmank@mskcc.org.
Karyn A
KA
Goodman
D000230:Adenocarcinoma / Q000473:pathology / Q000532:radiotherapy; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001005:Anus Neoplasms / Q000532:radiotherapy; D019540:Area Under Curve; D002294:Carcinoma, Squamous Cell / Q000473:pathology / Q000532:radiotherapy; D003251:Constriction, Pathologic / Q000209:etiology / Q000473:pathology / Q000628:therapy; D004106:Dilatation / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008875:Middle Aged; D058958:Organs at Risk / Q000473:pathology / Q000528:radiation effects; D010388:Pelvis; D011446:Prospective Studies; D011832:Radiation Injuries / Q000473:pathology / Q000628:therapy*; D011879:Radiotherapy Dosage; D012004:Rectal Neoplasms / Q000532:radiotherapy*; D018709:Statistics, Nonparametric; D013997:Time Factors; D014621:Vagina / Q000473:pathology / Q000528:radiation effects*