Sonja L. Schoeppel

Treatment planning issues related to prostate movement in response to differential filling of the rectum and bladder

Conventional stimulation for patients with localized prostatic carcinoma often includes opacification of the dose limiting adjacent normal tissues. However, CT-based treatment planning is performed with the bladder and the rectum naturally filled or emptied. These latter conditions more closely approximate those in place at treatment Comparison of these CT-based treatment plans to simulator films taken with the rectum and bladder opacified yielded indirect evidence of movement of the prostate gland by 0.5 cm or more in 31 of 50 consecutive patients. The range of motion was 0 to 2 cm with an average of 0.5 cm (1.0 cm in the 31 patients). Six additional patients (five with local recurrence following I-125 seed implantation) were analyzed separately using CT scans. Registered CT images (3 mm slices) taken with the rectum and bladder full and/or empty provided direct evidence of prostate movement in 3 of the 6 patients. The dosimetric consequences of this movement are demonstrated using 3-dimensional dose distributions.

Three-dimensional treatment planning of intracavitary gynecologic implants: Analysis of ten cases and implications for dose specification

PURPOSE Results of 3-dimensional treatment planning for ten intracavitary gynecologic implants and implications for dose specification are presented. METHODS AND MATERIALS Using a computed tomographic (CT) compatible intracavitary applicator we have performed CT scans during gynecologic brachytherapy in 10 cases. A CT-based treatment planning system with 3-dimensional capabilities was used to calculate and display dose in three dimensions. Conventional point doses including the estimated bladder and rectal maximum doses and dose to Point A were acquired from orthogonal simulation films. CT maximum bladder and rectal doses and minimum cervix doses were ascertained from isodose lines displayed on individual CT images. Dose volume histograms for the bladder, rectum and cervix were generated and used to obtain volume of the cervix target volume receiving less than the prescribed dose and the volume of bladder and rectum receiving more than the orthogonal maximum doses. The 5 cc volume of bladder and rectum receiving the highest dose were also calculated. RESULTS Average values of CT point doses and volumes are compared with the traditionally obtained doses. As demonstrated by others, much higher bladder and rectal doses are found using the CT information. The minimum dose to the cervix target volume is lower than the dose to Point A in each case. CT maximum bladder and rectum and minimum cervix target doses may not be the best index doses to correlate with outcome because of the small volumes receiving the dose. CONCLUSION We hypothesize that clinically useful bladder, rectal and cervix target volume doses will include volume information which is obtainable with dose volume histogram analysis.

Analysis of localization errors in the definition of the mantle field using a beam's eye view treatment-planning system.

PURPOSE Reports of the treatment of Hodgkins disease (HD) with radiotherapy using the mantle field technique have demonstrated that coverage of disease by the field blocks significantly compromises outcome. It is our hypothesis that the availability of computerized tomography images reduces the incidence of localization error, and that the use of beams eye view treatment planning techniques may further improve localization. The purpose of this report is to assess the possible contribution of a three-dimensional treatment-planning system to tumor localization and mantle block drawing in patients with HD. MATERIALS AND METHODS We evaluated the localization error rate of four experienced radiation oncologists as they drew the lung blocks for the mantle field. The analysis included 16 patients treated with mantle fields in our department between 1989 and 1991. In each case our computerized three-dimensional treatment planning system was used to generate a beams eye view display of tumor volumes. Simulation radiographs for all 16 patients were overlaid with acetate film, and lung blocks were drawn by clinicians using only the simulation radiographs for reference. The process was repeated with the thoracic CT scans available for reference. The mantle block contours for each trial were then superimposed upon the beams eye view plots of tumor volumes. The beams eye view plot was our benchmark for the evaluation of errors of tumor localization. Localization errors were defined as touching or overlap of the shielding blocks onto tumors. RESULTS There was a high degree (p < 0.0003) of consistency in scoring across all pairing of clinicians and the results from all four were polled for the analysis. The overall error rate using the simulation radiographs alone was 18%. The rate was significantly lower (13%) when the CT images were available (p = 0.038). The axillary region had the highest localization error rate (41.7% with CT available and 27.1% with CT available) and the superior mediastinum had the lowest error rate (10.7% without CT, 8.5% with CT). Compared with a system such as beams eye view, which could reduce the localization error rate to zero, the error rate with CT scans available is still significant [95% confidence interval (CI = 10-17.1%)]. Localization errors were more likely with increasing tumor size when CT scans were not available (p = 0.029). A similar trend was not seen when CT scans were available (p = 0.2). In a multivariate analysis, the use of CT scans predicted for reduced localization error rate (p = 0.03). Tumors in the axilla and inferior mediastinum had a greater relative risk than those in the superior mediastinum (p = 0.0001) CONCLUSION The availability of CT imaging offers an advantage in the outlining of the mantle field in the treatment of Hodgkins disease. When the error rate is evaluated using a beams eye view treatment planning system, a significant proportion of tumors may be overlapped by the outlined mantle blocks even when CT images are available for reference. The use of beams eye view treatment planning in mantle field definition, especially for tumors in the axillary region, may reduce the incidence of geographic misses.

Continuous infusion of low-dose 5-fluorouracil and radiation therapy for poor-prognosis squamous cell carcinoma of the uterine cervix

Ten patients with squamous cell carcinoma of the cervix metastatic to periaortic lymph nodes were treated with external-beam radiation therapy and synchronous infusion of intravenous 5-fluorouracil (5-FU) chemotherapy at doses of 350 mg/m2/day. The overall response rate was 90% with four complete responses (CR) and five partial responses (PR). The median duration of response was 11.8 months for CRs and 3.6 months for PRs. Toxicity was tolerable, with gastrointestinal symptoms and myelosuppression being noted most frequently. No patient experienced life-threatening toxicity. Median survival was 7.6 months, with only one patient being alive and free of disease at 2 years. In this pilot study we were unable to demonstrate a beneficial effect of continuous infusion of low doses of 5-FU chemotherapy concurrent with radiation therapy when compared to conventional radiotherapy in patients with advanced squamous cell carcinoma of the cervix.