Quality assurance system to correct for errors arising from couch rotation in linac-based stereotactic radiosurgery.

PURPOSE: The purpose of this project was the development of a quality assurance (QA) system that would provide geographically accurate targeting for linac-based stereotactic radiosurgery (LBSR). METHODS AND MATERIALS: The key component of our QA system is a novel device (Alignment Tool) for expedient measurement of gantry and treatment table excursions (wobble) during rotation. The Alignment Tool replaces the familiar pencil-shaped pointers with a ball pointer that is used with the field light of the accelerator to indicate alignment of beam and target. Wobble is measured prior to each patient treatment and analyzed together with the BRW coordinates of the target by a spreadsheet. The corrections required to compensate for any imprecisions are identified, and a printout generated indicating the floor stand coordinates for each couch angle used to place the target at isocenter. RESULTS: The Alignment Tool has an inherent accuracy of measurement better than 0.1 mm. The overall targeting error of our QA method, found by evaluating 177 target simulator films of 55 foci in 40 randomly selected patients, was 0.47 +/- 0.23 mm. The Alignment Tool was also valuable during installation of the floor stand and a supplemental collimator for the accelerator. CONCLUSIONS: The QA procedure described allows accurate targeting in LBSR, even when couch rotation is imprecise. The Alignment Tool can facilitate the installation of any stereotactic irradiation system, and can be useful for annual QA checks as well as in the installation and commissioning of new accelerators.

Postsurgical recurrent carcinoma of the cervix: reassessment and results of radiation therapy options.

PURPOSE: To evaluate outcome and reassess the radiation therapy options in pelvic recurrences of cervical cancer treated initially with surgery. MATERIALS AND METHODS: In 30 patients, the prognostic factors analyzed for local control included site of recurrence (central, pelvic wall), tumor size, modality of radiation therapy, and radiation dose. Mean follow-up in survivors was 111.5 months. RESULTS: Local control was attained in (a) nine of 20 patients with central recurrence and in two of 10 with pelvic wall recurrence (p = .25); (b) none of four who received less than 50 Gy, five of nine who received 50-60 Gy, and six of 17 who received greater than 60 Gy (p = .27); and (c) five of 11 with tumor smaller than 3 cm, five of nine with tumor size 3-6 cm, and one of 10 with tumor larger than 6 cm. Multivariate analysis revealed a significant benefit of local control on survival (P = .05). Median survival for patients with central recurrence was 14.5 months compared with 9 months for those with pelvic wall recurrence. CONCLUSION: Local pelvic control depends on site and size of recurrence and radiation therapy modality and dose. Appropriate choice of brachytherapy modality is important. To improve local control and survival, more aggressive treatment is indicated, but attendant higher complications may be expected.

Resection of multiple pulmonary metastases from a recurrent intracranial meningioma.

Surgical resection of multiple pulmonary metastases from a recurrent intracranial meningioma in a 53-year-old woman is presented. The primary tumor was diagnosed in 1984 and partially excised in early 1985. The tumor recurred and was re-excised in 1989 and 1992. A fourth intracranial recurrence was noted in 1993, accompanied by multiple bilateral pulmonary metastases. The metastases were excised using staged thoracotomies in July and September 1994. The patient is surviving with cranial tumor residual.

Major geometric variations between multiple high-dose-rate applications of brachytherapy in cancer of the cervix: frequency and types of variation.

PURPOSE: To evaluate major geometric variations in multiple intracavitary applications for carcinoma of the cervix. MATERIALS AND METHODS: Orthogonal radiographs were reviewed of 17 consecutive patients with carcinoma of the cervix treated with 70 applications of high-dose-rate brachytherapy. In seven patients, conscious sedation was used for all applications. In 10 patients, general anesthesia was used for the first application and conscious sedation for subsequent applications. Major geometric variation between applications in axis, length, and slippage in tandem placement and separation, packing, and slippage in colpostats placement were reviewed. A major variation was defined as more than 1.0-cm deviation. RESULTS: Major variations between applications occurred more commonly in colpostats placement than in tandem placement. For tandems, the rates of variation were 5.7% in axis, 4.3% in length, and 1.4% in slippage. For colpostats, rates of variation were 7.1% in separation, 25.7% in vaginal packing, and 7.1% in slippage. No consistent pattern of variation was found between applications except in vaginal packing. CONCLUSION: Awareness of geometric variations should improve proper placement of intracavitary applicators for brachytherapy.

Conventional four-field pelvic radiotherapy technique without computed tomography-treatment planning in cancer of the cervix: potential geographic miss and its impact on pelvic control.

PURPOSE: To evaluate the impact of inadequate margins on pelvic control using the conventional four-field pelvic portals without computed tomography (CT)-treatment planning. METHODS AND MATERIALS: Between 1986 and 1991, 34 patients with invasive cancer of the cervix were eligible for outcome study of conventional four-field radiation therapy (10 Stage I, 16 Stage II, 8 Stage III). The eligibility for this study includes four-field pelvic technique, definitive radiation therapy, and diagnostic CT scan of the pelvis. For this study, an inadequate margin is arbitrarily defined as < or = 1.0 cm of normal tissue around the CT-defined tumor volume. RESULTS: All 34 patients had adequate margins for anterio-posterior/posterio-anterior portals. However, 19 patients had an inadequate margin at the posterior border (S2-S3 interspace) and/or custom-shaped rectal block for lateral pelvic portals. Two patients had inadequate margins at the anterior border (level of symphysis pubis) due to an enlarged uterus. With a median follow-up of 36 months, pelvic control for adequate margins and inadequate margins was 100% and 71% for Stage IB disease and 88% and 50% for Stage IIB disease, respectively. However, pelvic control for Stage IIIB disease was 50% for both groups. There was no difference in total dose to point A or point B between the two groups. CONCLUSION: Our preliminary data show higher local failure in patients with an inadequate margin. For four-field pelvic radiation therapy, we strongly recommend CT-treatment planning. Otherwise, anterio-posterior/posterio-anterior pelvic therapy is the most reliable treatment for cancer of the uterine cervix.

Conventional four-field pelvic radiotherapy technique without CT treatment planning in cancer of the cervix: potential geographic miss.

The advantage of 4-field radiation to the pelvis is the use of lateral ports which spare the small bowel anteriorly and a portion of the rectum posteriorly from radiation. However, guidelines for the lateral pelvic ports are poorly defined. This is a comparative analysis to determine adequate margins by correlating conventional lateral pelvic treatment portals with CT defined tumor volume. The study included 52 patients treated definitively for carcinoma of the uterine cervix between 1986 and 1991. The most common site of inadequate margin (< or = 1.0 cm) was at the rectal block. The incidence of inadequate margin ranged from 39% to 50% and was independent of the stage of the disease except non-bulky stage IB disease. The next most common site was at the posterior border where frequency of inadequate margin for cervical tumor depended on stage with 8% of stage IB, 27% of stage IIB and 22% of stage IIIB/IVA disease. For the anterior border, an enlarged uterus was the only reason for inadequate margin rather than cervical tumor in 8% of stage IB, 18% of stage IIB, and 27% of stage IIIB/IVA disease. Without knowledge of precise tumor volume, the 4-field pelvic technique is potentially dangerous, risking underdosing of the tumor volume. For 4-field pelvic radiotherapy, we strongly recommend CT treatment planning.