P. Warde

Magnetic resonance imaging (MRI) for localization of the prostatic apex: comparison to computed tomography (CT) and urethrography

BACKGROUND AND PURPOSE It is necessary to include the entire prostate in the high dose treatment volume when planning radical radiation for patients with prostate cancer. We prospectively compared magnetic resonance imaging (MRI) to computed tomography (CT) and urethrography as means of localizing the prostatic apex. MATERIALS AND METHODS Thirty patients with clinically localized prostate cancer had a sagittal T2-weighted MRI scan and a conventional axial CT scan performed in the treatment position prior to the start of radiotherapy. Twenty of these patients had a static retrograde urethrogram performed at simulation. The position of the MRI and CT apices were localized independently by two radiation oncologists. In addition, the MRI apex was localized independently by a diagnostic radiologist. The urethrogram apex, defined as the tip of the urethral contrast cone, was easily identified and was therefore localized by only one observer. RESULTS There was good interobserver agreement in the position of the MRI apex. Interobserver agreement was significantly better with MRI than with CT. There were no systematic differences in the position of the MRI and CT apices. However, the MRI apex was located significantly above and behind the urethrogram apex. There was poor correlation between MRI and CT and between MRI and urethrogram in the height of the apex above the ischial tuberosities. There was 83% agreement between MRI and CT and 80% agreement between MRI and urethrogram in the identification of patients with a low-lying apex. The apex, as determined by MRI, was <2 cm above the ischial tuberosities and therefore potentially under-treated in 17% of the patients. CONCLUSIONS MRI is superior to CT and urethrography for localization of the prostatic apex. All patients undergoing radiotherapy for prostate cancer should have localization of the apex using MRI or a technique of equal precision to assure adequate dose delivery to the entire prostate and to minimize the unnecessary irradiation of normal tissues.

ETHMOID SINUS CANCER: TWENTY-NINE CASES MANAGED WITH PRIMARY RADIATION THERAPY

PURPOSE To describe the outcome of patients with carcinoma of the ethmoid sinus managed with a policy of primary radiation therapy with surgery for salvage of persistent or progressive disease. METHODS AND MATERIALS A retrospective chart review was undertaken of 29 patients with the diagnosis of carcinoma of the ethmoid complex who underwent treatment in the period between January 1976 and December 1994 at the Princess Margaret Hospital. Analysis was confined to those patients with epithelial invasive histology (squamous carcinoma, adenocarcinoma, or undifferentiated carcinoma) managed with curative intent with primary radiation therapy. The median patient age was 62, with a median follow-up time of 4 years. Staging was assigned according to a modification of the UICC 1997 system with 19 (66%) of patients presenting with T4 category tumors. The most common radiation dose regimes were 60 Gy in 30 daily fractions over 6 weeks, or 50 Gy in 20 daily fractions over 4 weeks. Outcome was analyzed with respect to overall survival, cause-specific survival, and local progression-free survival. The influence of a variety of clinical and therapeutic factors on outcome is discussed, the patterns of disease failure are described, and the rationale for this treatment approach is outlined. RESULTS The 5-year rates of overall survival, cause-specific survival, and local progression-free survival were 39%, 58%, and 41%, respectively. A total of 18 of 29 patients died during the period of review. Of these, 12 deaths were due to ethmoid cancer, one was due to a second primary lung cancer, and five were attributed to nononcologic causes. No patients died due to treatment-related toxicity. Increasing T category predicted for worse outcome on univariate analysis. Local progression was the major cause of treatment failure and was documented in 15 of 29 patients treated (52%). Six patients were offered salvage surgery for local progression, of whom two remained disease free at 15 and 17 months follow-up. CONCLUSIONS Outcome of patients with ethmoid cancer managed with primary radiation therapy with surgery for salvage is comparable to that achieved with planned combined modality approaches. Nevertheless, outcome remains poor and is dependent on the local extent of tumor, with 40-50% of patients eventually succumbing to disease.

OC-0046 SHORT TERM HORMONE THERAPY AND DOSE ESCALATED RADIATION FOR LOCALIZED PROSTATE CANCER: A RANDOMIZED PHASE III STUDY

consequences of rotational errors, which remain uncorrected if six degree of freedom couches are missing, and intra-fractional patient motion, which appears larger compared to the invasive frame-based approach, are unknown. It was the purpose of this study to investigate geometric and dosimetric accuracy of frame-less IG-RS for brain metastases. Materials and Methods: Single fraction IG-RS was practiced in 72 patients with 98 brain metastases. Patient positioning and immobilization used either double(n=72) or single-layer (n=27) thermoplastic masks. Pre-treatment set-up errors (n=98) were evaluated with cone-beam CT (CBCT) based IG and were corrected in six degrees of freedom without an action level. CBCT imaging after treatment measured intra-fractional errors (n=64). Preand posttreatment errors were simulated in the Pinnacle planning system based on the patient-specific RS treatment plans and target coverage and Paddick conformity index were evaluated. Three scenarios of 0mm, 1mm and 2mm GTV-to-PTV (gross / planning tumor volume) safety margins (SM) were simulated. Results: Errors prior to IG were 3.9mm±1.7mm (3D vector) and the maximum rotational error was 1.7°±0.8° on average. The posttreatment 3D error was 0.9mm±0.6mm. No significant differences between the more rigid double-layer (0.8mm±0.6mm) and single-layer (1.0mm±0.6mm) masks were observed. Simulation of RS without IG reduced target coverage and conformity by 25% and 40% for 0mm SM, respectively. Each 3D set-up error of 1mm decreased target coverage and dose conformity by 6% and 10% on average, respectively. After simulation of 1mm and 2mm GTV-to-PTV SM, target coverage was still reduced by 18% and 10% on average, respectively, if no IG was practiced. Pre-treatment correction of translations only but not rotations did not affect target coverage and conformity, irrespective of the SM. Post-treatment errors reduced target coverage by >5% in 14% and 0% of the patients for a 0mm and 1mm GTV-to-PTV SM, respectively. Conclusions: IG-RS with online correction of translational errors achieved high accuracy with residual errors of about 1mm on average after treatment. Application of 1mm GTV-to-PTV safety margins ensured target coverage within a 5% range compared to the planned dose distributions in all patients.

85 T1/T2 glottic cancer managed by extermal beam radiotherapy — the influence of pretreatment hemoglobin on local control

PURPOSE Pretreatment hemoglobin (Hb) level has been reported to be an important prognostic factor for local control and survival in various malignancies. However, in many settings, the adverse effect of a low Hb may be related to more advanced disease. The purpose of this analysis was to assess the influence of pretreatment Hb on local control in a large series of patients with a localized cancer (T1/T2 glottic cancer, AJCC 1992) treated in a standard fashion. MATERIALS AND METHODS Between January 1981 and December 1989, 735 patients (median age 63; 657 males, 78 females) with T1/T2 glottic cancer were treated with radiation therapy (RT). The standard RT prescription was 50 Gy in 20 fractions over 4 weeks (97% of patients). Factors studied for prognostic importance for local failure included pretreatment Hb, age, sex, T category, anterior commissure involvement, subglottic extension, and tumor bulk (presence of visible tumor vs. subclinical disease). RESULTS With a median follow-up of 6.8 years (range 0.2-14.3), 131 patients have locally relapsed for an actuarial 5-year relapse-free rate of 81.7%. The 5-year actuarial survival was 75.8%. The mean pretreatment hemoglobin level was 14.8 g/dl and was similar in all prognostic categories. On multivariate analysis, using the Cox proportional hazards model, pretreatment Hb predicted for local failure after RT. The hazard ratio (HR) for relapse was calculated for various Hb levels. For example, the HR for a Hb of 12 g/dl vs. a Hb of 15 g/dl was 1.8 (95% confidence interval 1.2-2.5). Previously established factors, including gender, T category, subglottic extension, as well as tumor bulk, were also prognostically important for local control. CONCLUSIONS This analysis, in a large number of similarly treated patients, indicates that pretreatment Hb is an independent prognostic factor for local control in patients with T1/T2 carcinoma of the glottis treated with RT. The underlying biology of this observation needs to be explored, and using this information, it may be possible to develop strategies to improve treatment outcome.