88 Tomotherapy for recurrent carotid body tumour treated previously with radiation therapy

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Background: Lung tumours move with respiration during radiotherapy treatment. A number of sophisticated techniques exist to minimize tumour motion yet these require resources not widely available. The impact of prone positioning on lung turnout motion has not been documented and may represent a simple method to decrease respiratory movement. Objective: To evaluate the effect of prone positioning on radiotherapy treatment planning of lung cancer. Methods: Patients with lung cancer were prospectively recruited for the study. Following a standard planning CT, patients underwent two slow CT scans (pitch=l, slice thickness 3mm) in the prone and supine positions, designed to capture the tumour in all phases of respiratory motion. Subjects completed user-satisfaction surveys (linear-analog rating scale) regarding the tolerability of the positions. Two radiation oncologists independently contoured the turnout volumes in a random order on the supine and prone scans. Volumes were analyzed for change in absolute volume and geometric parameters. Results: Twelve patients with lung cancer undergoing palliative and curative treatment were recruited. The mean tumour volume on the supine scans (mean=136cc range 45-357cc) was consistently larger then the mean gross tumour volume contoured on the prone scans (mean=110cc, range 26-314cc) (p=0.02). The larger volume on the supine scans reflected increased tumour excursion in the supine position. Geometric analysis showed tumour volumes were an average of 1.29cm larger (range 0.4-3.23cm) in all directions on the supine compared to the prone scans (p=0.02). Survey results indicated that patients found both the supine and prone positions equally comfortable. Conclusions: Lung tumour movement during radiotherapy may be decreased by prone positioning. This simple measure has potential for widespread use in lung cancer patients and a significant impact on treatment. 86 A Randomized Cross-Over Study Comparing Two Immobilization Devices for the Treatment of Prostate Cancer Patients Using Megavoltage CT Scanning to Evaluate Set Up Accuracy 7-. Sexton, G. Rodrigues, T. Kron, G. Bauman, J. HarrimonDuke London Regional Cancer Program, London, Ontario tracy, sexton @lhsc. on. ca

Objectives: Many studies have evaluated different immobilization devices for prostate cancer patients. Which device has superior immobilization, patient comfort and set up time is still unclear. Our institution recently acquired a new immobilization device (Combifix). This study evaluates patient comfort and immobilization of the Combifix compared to the conventional leg cushion system. Methods: This prospective randomized cross-over study consisted of 18 high risk prostate cancer patients who received whole pelvic plus prostate radiotherapy. Phase I consisted of a prostate boost phase using one immobilization device followed by phase II whole pelvic radiation using - the second immobilization device. Our primary endpoint was ease of use and patient comfort. This was assessed by weekly questionnaires for the patients and radiotherapy staff. Our secondary endpoints included time for treatment and set-up accuracy. Results: While our patients found both immobilization devices equally comfortable (p=0.60) and easy to use (p=0.48), the radiation therapists preferred the leg cushion device for ease of set up. The length of time for patient treatment was not significantly different for the two devices (p=0.50). The mean deviation from the isocentre was significantly different between the leg cushion and the Combifix (p=0.01) as measured by EPID but was not statistically different when measured by MVCT scanning (p=0.80). There was a statistically significant difference in the mean isocentre deviation. Conclusions: There were no observed large clinical differences between the two immobilization devices. Therapists preferred the leg cushion device for ease of set up and the overall

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isocentre deviation slightly favoured the leg cushion. The MVCT/computer registrations calculated greater isocentre shifts than the EPID/human registrations. The technical/clinical significance of this finding is currently unknown. 87 A Comparison of Seroma Formation and Clip Placement to Define the Surgical Bed in Patients with Segmental Mastectomies Z. Gabos, S. Chafe, J. Hanson Cross Cancer Institute, University of Alberta, Edmonton, Alberta zgabos@ualberta, ca

Background: Novel breast radiotherapy techniques, such as partial breast irradiation (PBI), depend on accurate tumour bed definition for accurate treatment delivery. No standard exists as to how to best delineate the target volume (the tumour bed) post segmental resection. Objectives: To compare the location and extent of the tumour bed as defined by surgical clips and seroma formation on CT scan, after lumpectomy. Methods: Planning CT scans of 28 patients with multiple surgical clips were reviewed after lumpectomy. The mean surgery to CT interval was 32 days (range 14-56 days). All CT scans were pre-chemotherapy. The transverse and longitudinal dimensions of the clips and seroma were measured. The coronal area and geometric centre of the turnout bed defined by the two methods was compared. Seroma tumour bed volume, as calculated by the ACQSim treatment planning program (v.4.9.1, Philips), was also recorded. Results: Coronal tumour bed area was verified to correlate strongly with tumour bed volume, correlation coefficient 0.818. Conclusions: Tumour bed definition post-lumpectomy, as defined by surgical clips and seroma formation, varies significantly. Radiation oncologists should incorporate the seroma and surgical clips in defining the tumour bed. Future studies will be required to define volumetric changes over time. 88 Tomotherapy for Recurrent Carotid Body Tumour Treated Previously with Radiation Therapy E. Senan, A. Hammond, S. Yartsev, T. Coad London Regional Cancer Program, London, Ontario essamsenan@yahoo, corn Objectives: To report tomotherapy treatment of recurrent carotid body tumour with minimal doses to organ at risk, mainly brain stem and spinal cord. Methods and Materials: The 85-year old man with history of progressive right-sided neck swelling diagnosed to be benign carotid body tumour. He was inoperable medically because of other co-morbid conditions. That was treated 10 years ago with radiotherapy where he did receive 45 Gy in 25 fractions. The patient tolerated the treatment well. In the follow-up the tumour did show little shrinkage but was stable. However, ten years later the mass started to grow again. Surgery and immobilization were out of options because of significant comorbid conditions. He was re-treated by helical tomotherapy with intention to spare surrounding normal structures as much as possible in the area, which was treated ten years ago to avoid potential side effects in previously irradiated area in the head and neck. Results: Ninety-five percent of the PTV volume received at least 30 Gy in ten fractions. In tomotherapy treatment with 40cm wide fan beam with binary multi-leaf collimator of 64 leaves, the field width was 2.5, the pitch 0.286 and the planning modulation factor 3.00. Prior to each treatment, the patient was positioned according to external markings, followed by megavoltage computer tomography imaging. The position adjustment were in superior/anterior direction max 2.7ram, median 0.3ram, SDlmm: in anterior/ posterior direction max 6.3ram, median 5.6mm, SDlmm:in lateral direction max 3mm, median 1.2mm, SD 0.6mm. These adjustments allowed account for daily variations in initial setup. Conclusions: Helical tomotherapy improves both conformity of the radiation dose to the turnout and avoidance of critical

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structures in the head and neck tumour. Such improvement leads to better tumour control and minimal side effects from treatment. 89 Clinical Impact of F-18 Fluorodeoxyglucose Positron Emission Tomography (PET) on the Management of Primary Tumours of the Thymus J. Lee I, D. Ball2, R. Hicks2, A. Hogg2, M. MacManus 2 Princess Margaret Hospital, Toronto, Ontario1; Peter MacCallum Cancer Institute, Melbourne, Victoria, Australia 2 justin, lee@rmp, uhn. on. ca

Objectives: To evaluate the impact of PET on the management of primary tumours of the thymus. Methods: Patients with a primary tumour of the thymus who underwent PET were identified from a prospective database. Prior to PET, referring physicians recorded the scan indication, disease extent by conventional imaging and pathology, and the proposed treatment plan. The impact of PET on clinical management was assessed. Follow-up data was used to measure the accuracy of conventional imaging and PET findings. Results: From 1997 to 2005, a total of 43 PET scans were performed on 26 patients with primary thymic turnouts. The median age was 53 and median follow-up from first PET scan was 2.7 years. Indications for PET were surveillance (n=20), suspected recurrence (n=12), therapeutic monitoring (n=6) and staging (n=5). Conventional imaging and PET findings were discordant in ten cases (23%), of which PET findings were either true positive (n=3), true negative (n=2), false negative (n=3) or could not be validated or refuted by clinical outcomes (n=2). PET appropriately changed patient management in four cases (9.3%) based on accurate results that differed from prePET imaging. The treatment modality changed from surgery to observation ( n = l ) and from chemotherapy to observation ( n = l ) . The radiotherapy dose ( n = l ) and target volume ( n = l ) were also influenced by PET results. Treatment was inappropriately changed by PET in one case (2.3%); chemotherapy was withheld based on a false-negative PET result. In five cases, discordant PET results were ignored and did not change management due to patient co-morbidity (n=2), pre-planned surgery (n=2), or lack of treatment options ( n = l ) . Conclusions: The majority of PET scans performed (88%) did not influence clinical management. When conventional and PET findings differed, there was a 30% false negative rate associated with PET. In comparison with other disease sites, the clinical impact of PET on the management of primary tumours of the thymus is limited. 90 Correlation Between Intrinsic Sensitivity of Normal Tissues and Tumour Tissues in Men Undergoing HighDose External Beam Radiotherapy for Prostate Cancer: Initial Data Pertaining to Genetic Factors of Response D. Vesprini, C. Catton, G. Lockwood, A. Nichol, M. Skala, A. Bayley, P. Cheung, J. Crook, M. Gospodarowicz, C. Menard, M. McLean, M. Milosevic, P. Ward, R. Bristow Princess Margaret Hospital, Toronto, Ontario danny, vesorini(~rmo, uhn. on. ca

Purpose: To test the hypothesis that intrinsic sensitivity of normal tissues is associated with that of tumour tissues in prostate cancer, we asked if acute toxicity is correlated with biochemical failure (BF) in men treated with external beam radiotherapy. Methods: We retrospectively analysed BF in 449 patients treated with 3D-conformal and IMRT radiotherapy (181 men were treated with 75.6 Gy and 268 with 79.8 Gy). We compared BF with prospectively-collected acute GI and GU toxicity (RTOG) scores. Median follow-up for all patients was 36.7 months (74.7 months for 75.6 Gy cohort, 29.6 months for 79.8 Gy cohort). Patients reporting RTOG acute GU or GI toxicity of >1 were considered sensitive (n=164, 37%), otherwise they were considered non-sensitive (n=285, 63%). BF rates were calculated and compared between the sensitive

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and non-sensitive groups using log-rank tests and Cox regression models. Results: When calculating time to BF using the ASTRO 3 consecutive rises definition at five years, 25% (C! 19-32%) of the non-sensitive patients had failed, while 44% (CI 33-55%) of the sensitive patients had failed (log rank test, p=0.01). This difference was also observed using a nadir + 2.0 definition (non-sensitive five year BF = 22% CI 15-31% vs sensitive BF = 31%, CI 22-43%, log rank test p=0.04). The difference between groups remained significant when controlled for radiation dose cohort (75.6 vs 79.8Gy), prostate risk stratification (T category, PSA and Gleason score) and prostate volume. Formal DVH studies are ongoing. Conclusions: This study suggests that prostate cancer patients who develop acute toxicity during radiotherapy are more likely, rather than less likely, to experience BF at five years. If this observation is confirmed in other data sets, biological studies are needed to evaluate whether intrinsic genetic factors (e.g. SNPs in DNA repair genes) that lead to increased toxicity also lead to resistance (via genetic instability) in malignant cells. 91 A Phase I / I I Study of 3-D Conformal Radiotherapy and Low Dose Cisplatin for the Treatment of Recurrent Malignant Gliomas L. VanderSpek 1, G. Bauman 1, D. Macdonald 1, G. Cairncross2, B. Fisher~ London Regional Cancer Program, London, Ontario1; University of Calgary, Calgary, Alberta 2 lauren.lukasvanderspek@lhsc, on. ca

Objectives: To determine the response of recurrent malignant gliomas to 3D conformal fractionated radiotherapy with low dose Cisplatin and to assess toxicity. Methods: From March 1999 to June 2003, nine patients with recurrent malignant glioma received fractionated radiotherapy and Cisplatin (20 mg/m2/d IV on days 1-5) in an IRB approved Phase I/II radiation dose escalation trial. The median dose of radiation was 30 (25-35) Gy in 5 Gy/fraction. Recurrences were documented by imaging alone in 5/9 and also with pathology in 4/9. All patients received prior external beam radiation (median dose 59.4 [20-60] Gy) and five patients received prior chemotherapy. Results: Six male and three female patients were enrolled with a median age of 52 (24-75), and a median Karnofsky performance status score of 70. The median re-irradiated tumour volume was 18.9 (0.1-78.5) cm 3. From the start of reirradiation, the median follow-up was 8.8 months (3.2-31.2), the median overall survival was 8.8 months (95% CI 8.0-9.9), and the median disease-free interval was 2.0 months (95% CI 1.4-4.4). Two patients experienced Grade 3 toxicity (decreased level of consciousness), one during treatment and one 18 days post-treatment. These toxicities were possibly treatmentrelated; however, tumour progression, recurrence was diagnosed at symptom onset or shortly thereafter. A third patient experienced Grade 3 toxicity 17 days post-treatment (confusion/weakness) secondary to radiation necrosis requiring surgery. Another patient with Grade 2 toxicity had recurrent tumour with a component of radiation necrosis at re-operation. Altogether, two patients had surgery and seven patients received chemotherapy following re-irradiation and Cisplatin. Conclusions: 3D conformal fractionated radiotherapy with low dose Cisplatin demonstrated only modest efficacy in the treatment of recurrent malignant glioma. The survival is comparable to other salvage regimens in the literature, as are the rates of radiation necrosis. 92 Treatment Planning Comparison of Fractionated Stereotactic Radiotherapy, 3D Conformal Radiotherapy, and Helical Tomotherapy for Benign Tumours in the Base of Skull A. Cheung, S. Malone, J. Szanto, B. Clark, M. MacPherson, B. Nyiri, G. Fox, L. Montgomery, K. Carty, Y. Deshaies, R. Zohr, J. Spaans