Conventional 3-D versus intensity modulated radiotherapy for the adjuvant treatment of gynecologic malignancies: a comparative study of dose-volume histograms and the potential impact on toxicities

Intensity-modulated radiation therapy in gynecologic malignancies

Radiation therapy occupies an important role in the treatment of gynecologic malignancies. Unfortunately, traditional approaches result in the irradiation of large volumes of normal tissues exposing patients to many toxicities and precluding dose escalation in select patients. A novel approach to the planning and delivery of radiation therapy, known as intensity-modulated radiation therapy (IMRT), has been introduced. Unlike conventional approaches, IMRT conforms the prescription dose to the shape of the target in three dimensions, thus sparing the surrounding normal tissues. Multiple studies have demonstrated the clear superiority of IMRT planning in these patients in terms of normal tissue sparing. Promising clinical results have also been published, suggesting that IMRT reduces the incidence of acute and chronic toxicity in these women. Ongoing studies are focusing on tumor control and patient outcome. Although further work is needed, these results suggest that IMRT may represent a major advancement in the planning and delivery of radiation therapy in patients with gynecologic malignancies.

A dosimetric analysis of acute gastrointestinal toxicity in women receiving intensity-modulated whole-pelvic radiation therapy

PURPOSE

To identify dosimetric factors correlated with acute gastrointestinal (GI) toxicity in gynecology patients undergoing intensity-modulated whole pelvic radiation therapy (IM-WPRT).

MATERIAL AND METHODS

Fifty gynecology patients received IM-WPRT (45-1.8Gy/fraction) between 2/00 and 3/02. All patients were treated to a clinical target volume (CTV) consisting of the upper vagina, parametria, uterus, presacral region and pelvic lymph nodes. Grade 2 acute GI toxicity requiring frequent medications and grade 3-5 toxicities were designated as clinically significant and analyzed as a function of patient and dosimetric variables. The most significant volumetric factors were fit to a normal tissue complication probability (NTCP) function.

RESULTS

Fourteen women (28%) developed clinically significant acute GI toxicity. None of the patient factors were correlated with acute GI toxicity. In addition, the volume of rectum receiving 25, 50, 75, 90, 100 and 110% of the prescription dose did not reach statistical significance. In contrast, a correlation was observed between the volume of small bowel (SB) irradiated and acute GI toxicity, particularly the SB volumes receiving 90 and 100% of the prescription dose (p=0.009 and p=0.009, respectively). Controlling for patient and other dosimetric factors, the SB volume receiving the 100% (Vol(SB,100)) of the prescription dose remained the sole significant factor on multivariate analysis (p=0.012). Subsequently, a NTCP curve, quantifying the risk of acute GI toxicity, was generated based on the Vol(SB,100).

CONCLUSIONS

The most significant factor correlated acute GI toxicity in gynecology patients undergoing IM-WPRT is Vol(SB,100).

Intensity-modulated radiotherapy as a means of reducing dose to bone marrow in gynecologic patients receiving whole pelvic radiotherapy

PURPOSE

To evaluate intensity-modulated whole pelvis radiotherapy (IM-WPRT) (with bone marrow [BM] as a planning constraint) as a means to reduce the volume of pelvic BM irradiated.

METHODS AND MATERIALS

Ten women with cervical or endometrial cancer previously treated using IM-WPRT were selected for this analysis. Using the treatment planning CT scan, the clinical target volume was defined to encompass the gross tumor, parametrial tissues, uterus (if present), and regional lymph nodes. The clinical target volume was expanded by a 1-cm margin to form the planning target volume (PTV). The bladder, rectum, small bowel, and pelvic BM were delineated in each patient. Three plans were created for each patient: a standard four-field WPRT plan, an IM-WPRT treatment plan designed to conform the dose to the PTV while minimizing dose to the normal tissues (excluding BM), and a BM-sparing (BMS) IM-WPRT plan that included the BM as an additional treatment planning constraint. Dose-volume histograms for the PTV, small bowel, and BM were compared for each patient.

RESULTS

For each of the 10 patients, BMS IM-WPRT treatment plans demonstrated a significant reduction of the volume of BM receiving >40% (18 Gy) of the prescription dose (45 Gy) compared with both IM-WPRT and four-field treatment. On average, BMS IM-WPRT resulted in only 60% of the BM volume irradiated to >50% of the dose compared with 87.4% (p <0.001) of the BM volume in a four-field plan and 75.7% (p < 0.003) of the volume in an IM-WPRT plan. Furthermore, the BMS IM-WPRT plans resulted in significant sparing of all other normal tissues that was comparable to the original IM-WPRT. In all 10 cases, the BMS IM-WPRT treatment plan did not result in any significant differences in the PTV and small bowel dose-volume histograms compared with the IM-WPRT treatment plans.

CONCLUSION

BMS IM-WPRT significantly reduces the volume of pelvic BM irradiated compared with conventional WPRT. In addition, BMS IM-WPRT did not compromise the improvements previously seen in IM-WPRT treatment plans that did not consider BM. Clinical studies are necessary to assess the significance of BMS IM-WPRT in reducing hematologic toxicity.

Preliminary analysis of chronic gastrointestinal toxicity in gynecology patients treated with intensity-modulated whole pelvic radiation therapy

PURPOSE

To provide a preliminary analysis of chronic gastrointestinal (GI) toxicity in gynecology patients treated with intensity-modulated whole pelvic radiation therapy (IM-WPRT).

METHODS AND MATERIALS

Between February 2000 and August 2001, 36 gynecology patients received IM-WPRT. All patients underwent a contrast-enhanced computed tomography scan, and a clinical target volume (CTV) was contoured consisting of the upper vagina, parametria, uterus (if present), and presacral and pelvic lymph node regions. The CTV was expanded by 1 cm to create a planning target volume (PTV). Seven or 9-field IM-WPRT plans were generated. IM-WPRT plans were highly conformal, providing excellent coverage of the PTV and considerable sparing of normal tissues, including the small bowel and rectum. Chronic GI toxicity was scored: 0 (no symptoms), 1 (mild symptoms, no medications required), 2 (moderate symptoms, medications required), and 3 (severe symptoms, hospitalization, surgery required). Chronic GI toxicity in 30 gynecology patients treated with conventional WPRT patients before the implementation of IM-WPRT was also evaluated. Median follow-up in the IM-WPRT and WPRT groups were 19.6 and 30.2 months, respectively.

RESULTS

The IM-WPRT and WPRT groups were well balanced in terms of most patient and treatment factors, including age, site, stage, chemotherapy, WPRT dose, and brachytherapy, except for a higher frequency of surgery (75 vs. 54%, p = 0.02) in the IM-WPRT group. Overall, IM-WPRT patients had a lower rate of chronic GI toxicity (11.1 vs. 50.0%, p = 0.001) than WPRT patients. The percentage of IM-WPRT patients with Grade 1, 2, and 3 toxicity were 8.3%, 2.8%, and 0%, respectively. Corresponding percentages in the WPRT group were 30.0%, 16.7%, and 3.3%, respectively. The only other factor correlated with chronic GI toxicity was age (p = 0.02). On multivariate (logistic regression) analysis controlling for age and other clinical factors, IM-WPRT retained its statistical significance (p = 0.01; odds ratio 0.16; 95% confidence interval 0.04, 0.67)

CONCLUSIONS

Our results suggest that IM-WPRT is associated with less chronic GI toxicity than conventional WPRT in patients with gynecologic malignancies. However, longer follow-up and more patients are clearly needed to ascertain whether the benefits of IM-WPRT treatment seen here translate into true long-term reductions in chronic GI toxicity.

Impact of intensity-modulated radiotherapy on acute hematologic toxicity in women with gynecologic malignancies

PURPOSE

To evaluate the impact of intensity-modulated whole pelvic radiotherapy (IM-WPRT) on acute hematologic toxicity (HT) in gynecology patients.

METHODS AND MATERIALS

Between February 2000 and June 2001, 36 patients (24 cervix, 12 uterus) received IM-WPRT. The target consisted of the upper vagina, parametria, uterus, and presacral and pelvic lymph nodes. Using commercially available software, seven or nine coplanar IM-WPRT plans were generated. The planning goals were to irradiate the target while minimizing the dose to the small bowel, bladder, and rectum. Pelvic bone marrow (BM) was not a constraint in the planning process. The variables analyzed included white blood count (WBC), absolute neutrophil count (ANC), platelets, and hemoglobin (Hgb) obtained before and weekly during RT. As a comparison, the HT in 88 patients (44 cervix, 44 uterus) treated to the same target volume and total dose (45 Gy) with conventional four-field WPRT was analyzed. In addition, the medullary spaces within the pelvic bones in 10 women were contoured and the average dose-volume histograms representing the pelvic BM were compared between the two groups.

RESULTS

IM-WPRT patients had a lower median age (p = 0.008), higher percentage of squamous histologic features (p = 0.04), and were more likely to receive chemotherapy (CTX) (p = 0.02) than were the WPRT patients. No differences were seen in the baseline WBC, ANC, platelet, or Hgb levels between the two groups. Grade 2 or greater WBC, ANC, and Hgb toxicity was seen in 19.4%, 9.1%, and 8.6% of the IM-WPRT patients, respectively. Comparable rates were seen in the WPRT patients (WBC 21.6%, p = 0.79; ANC 8.3%, p = 0.91; Hgb 9.2%, p = 0.94). No Grade 2 or greater platelet toxicity was seen in either group. Significant HT was infrequent in women treated with RT alone and was comparable in the two groups. In contrast, WPRT + CTX patients experienced more Grade 2 or greater WBC toxicity (60% vs. 31.2%, p = 0.08) and developed lower median WBC (2.8 vs. 3.6 microg/dL, p = 0.05) and ANC (1874 vs. 2669, p = 0.04) nadirs than did IM-WPRT + CTX patients. Moreover, CTX was held more often in the WPRT group secondary to HT (40% vs. 12.5%, p = 0.06). Although Grade 2 or greater ANC (23.5% vs. 15.3%) and Hgb (35.2% vs. 15.2%) toxicity were lower in the IM-WPRT + CTX group, these differences did not reach statistical significance (p = 0.58 and p = 0.22, respectively). The comparison of pelvic BM dose-volume histograms revealed that IM-WPRT planning resulted in significantly less BM volume being irradiated compared with WPRT planning, particularly within the iliac crests.

CONCLUSION

IM-WPRT has a favorable impact on the risk of acute HT in gynecology patients, particularly in those receiving CTX. Future work is needed to optimize BM sparing in these patients to reduce the risk of significant HT further.

Intensity-modulated whole pelvic radiotherapy in women with gynecologic malignancies

PURPOSE

To describe our initial clinical experience with intensity-modulated whole pelvic radiotherapy (IM-WPRT) in women with gynecologic malignancies.

METHODS AND MATERIALS

Between February 2000 and August 2001, 40 gynecology patients underwent IM-WPRT. After fabrication of customized immobilization, all patients underwent contrast-enhanced CT, and a clinical target volume was contoured consisting of the upper vagina, parametria, uterus (if present), and presacral and pelvic lymph node regions. The clinical target volume was expanded by 1 cm to create a planning target volume (PTV). Using commercially available software, 7- or 9-field, 6-MV, coplanar IM-WPRT plans were generated for all patients. The worst acute gastrointestinal and genitourinary toxicity during treatment was scored on a 4-point scale: 0, none; 1, mild, no medications required; 2, moderate, medications required; and 3, severe, treatment breaks or cessation, hospitalization. As a comparison, acute toxicities in 35 previously treated conventional WPRT patients were analyzed. No significant differences were noted in the clinicopathologic and treatment factors between the two groups.

RESULTS

IM-WPRT plans provided excellent PTV coverage, with considerable sparing of the surrounding normal tissues. On average, 98.1% of the PTV received the prescription dose. The average percentage of the PTV receiving 110% and 115% of the prescription dose was 9.8% and 0.2%, respectively. IM-WPRT was well tolerated, with no patient developing Grade 3 toxicity. Grade 2 acute gastrointestinal toxicity was less common in the IM-WPRT group (60 vs. 91%, p = 0.002) than in the conventional WPRT group. Moreover, the percentage of IM-WPRT and WPRT patients requiring no or only infrequent antidiarrheal medications was 75% and 34%, respectively (p = 0.001). Although less Grade 2 genitourinary toxicity was seen in the IM-WPRT group (10% vs. 20%), this difference was not statistically significant (p = 0.22).

CONCLUSION

IM-WPRT is a promising approach in gynecology patients. IMRT planning resulted in excellent PTV coverage, with considerable sparing of normal tissues. Treatment was well tolerated and associated with less acute gastrointestinal sequelae than conventional WPRT. Longer follow-up and more patients are needed, however, to evaluate the full merits of this novel approach.