Japanese Journal of Clinical Oncology 30:180-184 (2000)
© 2000 Foundation for Promotion of Cancer Research
Reduction of Late Complications After Irregularly Shaped Four-Field Whole Pelvic Radiotherapy Using Computed Tomographic Simulation Compared with Parallel–Opposed Whole Pelvic Radiotherapy
Division of Radiation Oncology, Department of Radiology, Hokkaido University School of Medicine, Sapporo, Japan
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Background: Tumor control and late complication rates of irregularly shaped four-field whole pelvic radiotherapy using CT simulation were compared with those of whole pelvic radiotherapy using parallel–opposed fields in a non-randomized study.
Methods: From 1986 to 1996, 74 patients who underwent surgery for clinical stage I, II or III squamous or adenosquamous cell carcinoma of the uterine cervix were treated with postoperative radiotherapy consisting of 50 Gy in 25 fractions in 6 weeks. Thirty-four patients were treated with an irregularly shaped four-field technique following computed tomography (CT) simulation using beam’s eye view and three-dimensional treatment planning and lead blocks. Forty patients received the conventional two-field technique, with CT simulation in 13 patients and X-ray simulation in 27 patients. There was no significant difference in patients’ characteristics between the two groups.
Results: There was no statistical difference in survival, relapse-free survival or pelvic control rate between the two-field and irregularly shaped four-field groups with a mean follow-up period of 60 months. The actual 5-year pelvic control rate was 94% for the two-field technique and 100% for the irregularly shaped four-field technique. The incidence of grade II–III bowel complications in the irregularly shaped technique group (2.9%, 1/34) was significantly lower than that in the two-field technique group (17.5%, 7/40) (p < 0.05). The actual 5-year complication rates of grade II leg edema were 28.6 and 3.1% for the two-field technique and irregularly shaped four-field technique groups, respectively (p = 0.0123).
Conclusions: Irregularly shaped four-field post-operative pelvic radiotherapy using CT simulation appears to be as effective as parallel–opposed whole pelvic radiotherapy with a lower incidence of bowel complication and chronic leg edema.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Post-operative whole pelvic radiotherapy has been widely used for the treatment of uterine cervical cancer when metastatic pelvic lymph nodes, microscopic positive margins or deep stromal invasion are found after a hysterectomy (1,2). However, post-operative radiotherapy is often associated with increased morbidity, especially when a bilateral pelvic lymphadenectomy is performed (3). Late complications include those of combined surgery and irradiation in the abdomen and pelvis, such as small bowel obstruction and leg edema.
The treatment is often performed on anterior–posterior parallel–opposed fields (1–6). Four-field radiotherapy consisting of an anterior, a posterior and two lateral portals has sometimes been utilized to reduce the complications resulting from two-field whole pelvic irradiation (7–9). Recently, based on bone references on X-ray simulation, the lateral fields of the four-field technique were shown to fail to encompass the planning target volume in a significant number of patients (10). One possible solution to this problem is that images of internal organs could be used for the determination of target volume.
We have used three-dimensionally (3D) reconstructed computed tomographic (CT) images of whole pelvic organs and beam’s eye view in the treatment planning of post-operative irregularly shaped four-field pelvic radiotherapy to reduce the uncertainty of the determination of the target volume. In this study, tumor control and late complication rates were investigated and compared with the historical records of post-operative control patients who were irradiated with the two-field technique with X-ray simulation.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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From 1986 to 1996, 74 patients who underwent surgery for clinical stage I, II or III squamous or adenosquamous cell carcinoma of uterine cervix were treated with postoperative radiotherapy. The patients’ characteristics are summarized in Table 1. Seventy-four patients received radical hysterectomy and two received simple hysterectomy before radiotherapy. At least one of the following factors was present for each patient: inadequate surgical margins, positive pelvic lymph nodes, histological deep cervical stromal invasion. All patients were treated with external pelvic irradiation. External radiotherapy was started 3–6 weeks after surgical treatment. X-radiation of 10 MV was used for all patients; 50 Gy in 25 fractions was given in 6 weeks.
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Beginning in 1988, irregularly shaped four-field pelvic irradiation with CT simulation has been applied as a way of reducing the radiation dose to the small bowel and anterior abdominal wall (11). Thirty-four patients received irregularly shaped four-field pelvic irradiation consisting of the anterior, posterior and two lateral opposed fields using CT simulation. Forty patients received anterior–posterior parallel–opposed whole pelvic radiotherapy and these patients were investigated as the control group. Treatment for 13 of the 40 patients was planned using a CT simulator and treatment for the other 27 patients was planned using a conventional X-ray simulator. The decision to use the two-field technique was according to the physician’s preference rather than some rigid criteria.
Since a multi-leaf collimator was not available during the study period, conventional lead blocks were used to make appropriate fields. In the X-ray simulation, the upper border was the intervertebral space between L4 and L5 and the lower margin was at the bottom of the obturator foramen. The lateral border was 1.5 cm lateral to the internal lateral rim of the bony pelvis and sacrum–iliac joint. In CT simulation, target volume was determined slice by slice for CT scan images of 1 cm slice thickness and 1 cm table shift. The upper border was defined to include the aortic bifurcation. The lateral border was defined to include the iliac artery and veins so that the relationship between the lead blocks and the bony structure was patient dependent. The lower border was determined by inclusion of the vaginal cuff. The clinical target volume included the anterior surface of the sacral bone and the external iliac and common iliac arteries and veins. The small bowel, anterior abdominal wall and anus were blocked by the beam’s eye view using digitally reconstructed radiography. The planning target volume margin was 1 cm for the clinical target volume. Dose distribution was calculated three-dimensionally using THERAC (NEC, Japan) or FOCUS (CMS, USA). As verification procedures, portal film was taken and compared with the simulation film in the X-ray simulation or the digitally reconstructed radiography in the CT simulation. Representative dose distribution for the two techniques are shown in Fig. 1.
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Survival and relapse-free survival were calculated using the Kaplan–Meier method and compared using a generalized Wilcoxon test. Late complications were graded as grade I, II, III and IV for no requirement for medication, requirement for medical treatment, requirement for surgical treatment and death due to complications, respectively. The Kaplan–Meier method and chi-squared test were used for the comparison of late complications. The mean follow-up period was 108 months for the two-field technique and 55 months for the four-field technique. The patients in this study gave informed consent to the work.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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There was no statistical difference in survival, relapse-free survival and pelvic control rate between the two-field and irregularly shaped four-field groups. Actual 5-year survival rates for the two-field and irregularly shaped four-field technique were 100 and 92%, respectively. Actual 5-year relapse-free survival rates were 93 and 85%, respectively. The actual 5-year pelvic control rate was 94% for the two-field technique and 100% for the irregularly shaped four-field technique. Pelvic recurrence was seen in one patient treated with the two-field technique and none in the group treated with the irregularly shaped four-field technique (Table 2). Distant metastasis was observed in two patients in each group.
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Chronic edema of the legs was observed in 50% (20/40) of the patients in the two-field technique group; 25% (10/40) were grade I and 25% (10/40) were grade II and no patients experienced grade III leg edema (Table 3). Edema of the leg was observed in 9% (3/34) of the patients in the irregularly shaped four-field technique group; 6% (2/34) were grade I and 3% (1/34) were grade II. The actual 5-year complication-free rates of grade II leg edema were 71.4 and 96.9% for the two-field technique and irregularly shaped four-field technique, respectively (Fig. 2). The difference was statistically significant in a log-rank test (p = 0.0123). The time of onset of chronic bowel complication was difficult to determine, so the incidence of bowel complication after 6 months was compared without consideration of the time of its onset. Bowel complications were observed in 12 patients in the two-field technique group and six patients in the irregularly shaped four-field technique group (Table 3). The incidence of grade II–III bowel complications in the irregularly shaped four-field technique group (0.0%, 0/34) was significantly lower than that in the two-field technique group (17.5%, 7/40) (p < 0.05). No other late complication was detected during the study period. In the two-field technique group, no difference was demonstrated in survival rates, pelvic control rates or complication rates between X-ray simulation and CT simulation.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Pelvic radiotherapy for uterine cancer after surgical intervention has been associated with high morbidity (12,13). The present study suggests that irregularly shaped four-field radiotherapy is useful for reducing the complication rate. This conclusion is consistent with previous reports about pelvic radiotherapy for uterus and prostate cancers (14–17). However, the present study is still an interim report in terms of late complications because the follow-up period is shorter for patients with four-field technique. Further follow-up is required to judge whether the superiority of four-fields technique is real.
The lower incidence of bowel complications following irregularly shaped four-field radiotherapy was consistent with the well-known fact that bowel complications can be reduced by minimizing the volume of bowel structure that receives doses higher than about 45 Gy (18). Chronic leg lymph-edema after post-operative radiotherapy is induced by the blockage of the lymphatic drainage through the pelvis. The superficial abdominal lymphatic chain is a collateral route that can compensate for the blockage of the deep lymphatic chain. Radiotherapy of the anterior and posterior parallel–opposed fields may obstruct the lymphatic chain at the abdominal wall and increase the incidence of leg edema (18). A collateral drainage passageway from the leg to the anterior abdominal wall may be maintained after treatment with our irregularly shaped four-field technique. CT simulation may be useful for shielding the small bowel and anterior abdominal wall lymphatic collateral chain while still providing adequate coverage of the target volume.
The position of the aortic bifurcation, common iliac bifurcation and femoral arteries is variable from patient to patient, as Greer et al. demonstrated by surgical measurement (19). Anatomical landmarks are not optimal to cover the lymphatics and may be suboptimal for a significant percentage of patients and could be a contributing cause of failure to control cervical cancer (14,20). Zunino et al. have confirmed that using the anterior border of the lateral fields over the anterior edge of the pubic symphysis and the posterior at the S2–3 interspace as the anatomic border of the lateral fields is inadequate in radical radiotherapy for uterine cervix cancer (10). X-ray simulation following pelvic organ opacification using contrast media was shown to be effective for conformal therapy, but the technique is time consuming and uncertainty is caused by bony landmarks (2). Kim et al. have suggested that CT simulation is required to decrease the potential geographic miss when using the four-field technique in radical radiotherapy for uterine cervical cancer (21). With the irregularly shaped four-field technique, the anterior border and posterior border can be determined using internal anatomy rather than bony structure in CT simulation. In the present study, it was not possible to analyze whether CT simulation was useful for reducing geographic miss because of the low incidence of pelvic relapses in both techniques. However, the high pelvic control rate of the irregularly shaped four-field technique in our series may be due to accurate coverage of the clinical target volume.
Recent advances in the multileaf collimator on linear accelerators and 3D radiotherapy planning systems have made it practical to use more conformal fields than were employed with the technique used in this study (22). A further reduction of complication without deterioration in the tumor control rate can be expected using conformal four-field pelvic radiotherapy with a multileaf collimator.
In conclusion, irregularly shaped four-field post-operative pelvic radiotherapy using CT simulation appears to be as effective as parallel–opposed whole pelvic radiotherapy, with a lower incidence of bowel complication and chronic leg edema.
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Acknowledgment |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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The work was partly supported by a grant from the Casio Science Promotion Foundation.
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FOOTNOTES |
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+ For reprints and all correspondence: Hiroki Shirato, Department of Radiation Medicine, Hokkaido University, Graduate School of Medicine, North-15 West-7 Kita-ku, Sapporo 060-8638, Japan
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Received November 29, 1999; accepted January 31, 2000.
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