(Radiology. 1999;212:155-158.)
© RSNA, 1999
Localization of the Apex of the Vagina: Implications for Radiation Therapy Planning1
Choong R. Kim, MD,
Beverly A. Eaton, RT(T) and
Kenneth R. Stevens, Jr, MD
1 From the Department of Radiation Oncology, St John Medical Center, 1614 E Kessler Blvd, Longview, WA 98632 (C.R.K., B.A.E.), and the Department of Radiation Oncology, School of Medicine, Oregon Health Sciences University, Portland, Ore (K.R.S.). From the 1996 RSNA scientific assembly. Received October 7, 1997; revision requested December 16; final revision received August 28, 1998;
accepted December 15. Address reprint requests to C.R.K.
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Abstract
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PURPOSE: To evaluate (a) the displacement of the vaginal apex by a rod during radiation therapy simulation for gynecologic malignancy and (b) apical localization with implanted radiopaque markers.
MATERIALS AND METHODS: Metallic markers were implanted in the cervix or vaginal cuff in nine patients with cervical or endometrial carcinoma who underwent irradiation. In all but one patient, radiographs were obtained with and then without the vaginal rod. Displacement of the markers relative to bone landmarks was measured. The total displacement was the square root of the sum of the squares of displacement in each axial direction.
RESULTS: All patients showed displacement of the cervical markers by the vaginal rod (mean total displacement, 1.9 cm; range, 0.6–3.6 cm). The greatest displacement was cephalic (mean, 1.5 cm; range, 0.5–2.4 cm). Anteroposterior displacement occurred in all patients but was not as predictable as cephalic displacement. Displacement was anterior in five of the eight patients, posterior in three patients, and lateral in four patients.
CONCLUSION: Displacement of the vaginal apex and/or cervix with placement of the vaginal rod during simulation was marked in all patients. Use of implanted cervical markers to localize the vaginal apex or the cervix during simulation is more accurate than use of a vaginal rod.
Index terms: Therapeutic radiology, 854.1269 • Treatment planning, 854.1269 • Uterine neoplasms, therapeutic radiology, 854.1269, 854.32
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Introduction
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Radiation treatment is widely used as either the primary or a postoperative adjuvant therapy for cervical or endometrial carcinoma. Irradiation options for gynecologic malignancy often involve external-beam radiation therapy of the whole pelvis, with an additional dose to the cervix, apex of the vagina, or vaginal cuff. The boost dose to this area can be delivered by using either a vaginal intracavitary implant or small fields of external-beam irradiation.
The external boost irradiation generally consists of a four-field box technique or bilateral arc rotation with the isocenter at the vaginal apex. Fields are small to avoid an excessive dose to the rectum and bladder. Simulation procedures usually involve placement of a rigid vaginal rod into the vagina to radiographically determine the location of the vaginal cuff or cervix at the tip of the vaginal rod. The isocenter is then set at the tip of the vaginal rod. However, the vagina is flexible and expandable, and the apex or the cervix can easily be displaced by the vaginal rod. This may result in a misapplication of irradiation and an underdosing to the apex of the vagina.
We performed this study to measure and evaluate the displacement of the vaginal apex due to placement of the vaginal rod and to evaluate the implantation of metallic markers in the vaginal apex or cervix for localizing the vaginal apex.
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MATERIALS AND METHODS
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From April 1993 through February 1996, nine patients with cervical or endometrial carcinoma who underwent radiation treatment and implantation of cervical markers were evaluated. All patients were informed of the risks of the procedure and consented to the placement of the cervical markers. The median age was 56 years (age range, 30–73 years). The patient characteristics are shown in Table 1.
All patients received external-beam irradiation of the whole pelvis (4,500 cGy), which included parametrial and pelvic lymph nodes. Three of the seven patients with cervical cancer received radiation treatment as the primary therapy, with an additional dose administered by using cesium 137 in a Fletcher-Suit applicator. Three patients underwent total abdominal hysterectomy and received postoperative adjuvant external-beam radiation therapy, with an additional dose administered to the vaginal cuff by using 5 x 5-cm fields. One patient with locally advanced cervical carcinoma received palliative radiation treatment for uncontrolled bleeding.
One of the two patients with the endometrial carcinoma received postoperative adjuvant therapy, which included placement of an intracavitary vaginal implant with 137Cs sources by using the vaginal applicator. The other patient with endometrial carcinoma received radiation therapy for recurrence.
All patients had gold markers (Anderson Marker; Best Industries, Springfield, Va) implanted in either the cervix or the vaginal cuff after 4,500-cGy external-beam irradiation of the whole pelvis. Markers were placed at the 5- and 11-o'clock positions. Orthogonal radiographs (Cascade Simulator; Cascade X-ray, Yakima, Wash; with barium [Liquid Polibar Plus, E-Z-Em, Westbury, NY] in the rectum [30–50 mL]) were obtained with and then without the vaginal rod, except in patient 3, in whom a lateral image was not obtained. The location of the markers was referenced to the top of the symphysis pubis and the most anterior tip of S1. The displacement of the markers was measured in the cephalocaudal, anteroposterior, and lateral directions by using simulation radiographs. The total displacement was determined by using the Pythagorean theorem (by determining the square root of the sum of the squares of displacement in each direction).
Computed tomography (CT; CT HiSpeed Advantage, GE Medical Systems, Milwaukee, Wis) was performed with the vaginal rod and then without the vaginal rod in patient 2, who had cervical carcinoma.
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RESULTS
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All patients showed displacement of the cervical markers by the vaginal rod (Table 2). The mean total displacement was 1.9 cm (range, 0.6–3.6 cm). The most substantial displacement was in the cephalic direction. The mean cephalic shift was 1.5 cm (range, 0.5–2.4 cm). Due to the pressure to keep the rod in place, the length of the vagina increased when the vaginal rod was placed. Figure 1 shows the displacement of the cervical marker in the cephalic direction.
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Figure 1a. Anteroposterior radiographs obtained during simulation (a) without and (b) with the vaginal rod in place. In b, the cervical markers (arrows in a and b) with the rod in place show the cephalic displacement. The tip of the vaginal rod (arrowhead) is more cephalic than the markers.
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Figure 1b. Anteroposterior radiographs obtained during simulation (a) without and (b) with the vaginal rod in place. In b, the cervical markers (arrows in a and b) with the rod in place show the cephalic displacement. The tip of the vaginal rod (arrowhead) is more cephalic than the markers.
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The tip of the vaginal rod was more cephalic than the implanted cervical markers in three patients (Table 3, Fig 1). Their ages were 30, 36, and 44 years. They all had cervical carcinoma, and radiation treatment was the primary treatment. The tip of the vaginal rod was 1–2 cm more cephalic than the original location of the cervical markers. This finding was confirmed with CT in patient 2. The tip of the vaginal rod was 2 cm more cephalic, as shown in Figure 2.
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Figure 2. CT scan of the pelvis with the vaginal rod in place. The location of the implanted marker (arrow) is noted in relation to the vaginal rod (arrowhead). The tip of the vaginal rod was 2 cm cephalic to the markers on another image (not shown).
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The anterior and posterior displacements of the marker were also noted in all patients (Table 2), but these were not as predictable as cephalic displacement. Five of the eight patients evaluated showed a mean anterior displacement of the implanted markers of 0.8 cm (range, 0.5–1.4 cm). Three patients showed posterior displacement of markers of 0.6, 1.0, and 2.5 cm. The tip of the vaginal rod was 0.5 and 2.0 cm more anterior to the implanted markers in patients 1 and 2, respectively. The tip of the vaginal rod was 2.0 cm more posterior to the markers in patient 4.
Lateral displacement of the implanted markers was not as marked. Only four of the nine patients showed lateral displacement. Two patients showed a shift to the right (0.2 and 1.0 cm), and two patients showed a shift to the left (0.4 and 1.0 cm).
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DISCUSSION
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Localization of the apex of the vagina during simulation may involve the placement of a vaginal rod. The rod is usually a rigid straight applicator with radiopaque measurement markers. The apex of the vagina is assumed to be at the tip of the rod, and the isocenter is usually set on it during simulation. However, the displacement of the vaginal apex due to the rod during simulation is not recognized.
The vagina is expandable, with great potential to change its length and diameter. Placement of the vaginal rod causes displacement of the vaginal apex.
The tip of the vaginal rod, when it is placed in the vaginal vault during simulation, does not necessarily indicate the location of the cervix. The cervix or vaginal cuff can shift up to 3.6 cm. When the vaginal rod is removed, the apex of the vagina reverts back to its normal position, and the apex of the vagina may be missed with a small field. This becomes clinically important when external irradiation is used to boost a small area in the apex of the vagina.
The change in the location of the apex of the vagina or cervix was previously noted with gynecologic brachytherapy that involves placement of rigid implants. Grigsby et al (1) reported on 40 patients who underwent irradiation and received two intracavitary implants with a Fletcher-Suit tandem and ovoids; these patients had displacement of the reference points between the first Fletcher-Suit implantation and the second implantation. The displacement of the individual reference points ranged from 0 to 2.6 cm. Grigsby et al postulated the change in the anatomy was due to tumor shrinkage and fibrosis. They did not mention the possibility of geometric variation due to the pressure from the vaginal packing and the Fletcher-Suit tandem and ovoids placed during the implantation procedure. Kim et al (2) reported that posterior vaginal packing was responsible for 20% of geographic variation between multiple high-dose-rate applications of brachytherapy for cervical carcinoma.
The shift of other soft and expandable tissues from the position of the body has been reported. Smoron et al (3) observed that the esophagus is not fixed and can shift up to 6 cm anteriorly or posteriorly with a change from supination to pronation. Corn et al (4) reported that the esophagus can shift anteriorly up to 4.2 cm with a change from supination to pronation.
The displacement of a semifixed soft-tissue organ such as the prostate to expansion or contraction of the lumen of the rectum and bladder during simulation in patients with prostate cancer has been reported. Ten Haken et al (5) reported the displacement of the prostate gland was a mean of 0.5 cm (range, 0–2 cm) in 31 of 50 consecutive patients, with the bladder and the rectum naturally filled or emptied. These differences were noted between CT-based treatment plans and simulation radiographs obtained during simulation. Pickett et al (6) demonstrated anterior movement of the prostate on the CT scan when the rectum was filled with barium solution compared with the position when the rectum was empty. The full rectum displaced the prostate anteriorly and superiorly. Beard et al (7) reported that distention of the rectum can change the position of the prostate and the seminal vesicles up to 1.5 to 2.2 cm. The direction of displacement of the prostate or the seminal vesicles could not be predicted in their studies.
Findings of our study demonstrate that the vaginal rod causes displacement of the vaginal apex during the simulation performed to establish the locations of small boost irradiation fields. This may result in a misapplication of irradiation in the treatment due to substantial displacement of the vaginal apex during the simulation. Implanted cervical or vaginal markers are more accurate for localizing the cervix or the apex of the vagina during simulation.
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Footnotes
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Author contributions: Guarantors of integrity of entire study, C.R.K., K.R.S.; study concepts, C.R.K.; study design, C.R.K., B.A.E.; definition of intellectual content, C.R.K., K.R.S.; literature research, C.R.K.; clinical studies, C.R.K., B.A.E.; data acquisition, C.R.K., B.A.E.; data analysis, C.R.K.; manuscript preparation, C.R.K., B.A.E.; manuscript editing, B.A.E., K.R.S.; manuscript review, K.R.S.
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References
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-
Grigsby PW, Georgiou A, Williamson JF, Perez CA. Anatomic variation of gynecologic brachytherapy prescription points. Int J Radiat Oncol Biol Phys 1993; 27:725-729.[Medline]
-
Kim RY, Meyer JT, Plott WE, et al. Major geometric variations between multiple high-dose-rate applications of brachytherapy in cancer of the cervix: frequency and type of variation. Radiology 1995; 195:419-422.[Abstract/Free Full Text]
-
Smoron GL, O'Brien CA, Sullivan CA. Tumor localization and treatment technique for cancer of the esophagus. Radiology 1974; 111:735-736.[Medline]
-
Corn BW, Coia LR, Chu JCH, Hwang CC, Stafford PM, Hanks GE. Significance of prone position in planning treatment for esophagus cancer. Int J Radiat Oncol Biol Phys 1991; 21:1303-1309.[Medline]
-
Ten Haken RK, Forman JD, Heimberger DK, et al. Treatment planning issues related to prostate movement in response to differential filling of the rectum and bladder. Int J Radiat Oncol Biol Phys 1991; 20:1317-1324.[Medline]
-
Pickett B, Roach M, III, Verhey L, et al. The value of nonuniform margins for six-field conformal irradiation of localized cancer. Int J Radiat Oncol Biol Phys 1995; 32:211-218.[Medline]
-
Beard CJ, Kijewski P, Bussiere M, et al. Analysis of prostate and seminal vesicle motion: implication for treatment planning. Int J Radiat Oncol Biol Phys 1996; 34:451-458.[Medline]
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Abstract
Introduction
