142 Feasibility of pathology-correlated lung imaging for accurate target definition of lung tumors

Proffered Papers obturator foramen to the superior margin of the bladder. The CT scans for each patient were fused using custom software to a reference scan for that patient, and the fusion was based solely on the rigid bones that define the pelvic girdle: sacrum, ilium, ischium, and pubis. Once the images were fused, the amount of intra- and inter-fraction bony anatomy rotation could be measured. Results: As repeated in the table below, the largest rotational variability was measured around the xaxis (front to back rotation of the hips) with the day-to-day variability being slightly larger than the same-day uncertainty. However, our measurements showed systematic changes during treatment with the patients rotating their hips forward by 0.6 degrees on average between the pre and post CT scans. Some patients seemed more prone to intra-fraction motion than others. Conclusions: Inter-fraction rotational variability was shown to be only slightly larger than intra-fraction variability. This result, when considered with our other research into organ motion, suggests that intra-fraction motion should be considered when treating prostate cancer.

140 Implementation of radiographer led planning target delineation for prostate cancer

S. Boston 1, C. Scrase 2, V. Hardy 1 1 : Suffolk Oncology Centre, Radiotherapy, Ipswich, UK 2: Suffolk Oncology Centre, Clinical Oncology, Ipswich, UK Introduction: To facilitate radiographer-led target volume delineation for prostate cancer Lo improve patient pathway and wailing times for radiotherapy treatments. Background: Prostate cancer is now the commonest male malignancy in the UK, and radical radiotherapy is one major treatment option, hence a high throughput of patients. We identified that 84% of patients did not meet the UK standard wait of 4 weeks. In addition, a delay was identified between the radiotherapy planning C'i" scan to target definition. This was considered to be due to the workload and availability of the Clinical Oncologist. We sought a radiographer led process of target volume delineation and planning, with the aim of accelerating the process, whilst ensuring a high standard was maintained. Method: A preliminary training period was undertaken including self-directed study at Masters Level, and observation of diagnostic reporting with Radiologists, attendance of relevant courses, and experience of organ at risk delineation. This was followed by practical target definition training from the Oncologist. 25 cases were outlined independently by the Oncologist and trainee. Standard 3 field prostate plans were recreated using the trainee defined target volumes. Dose volume histograms were then calculated for the Oncologist defined volumes. Successful outcome was achieved if the Oncologist volume received >95% of the prescribed dose. Protocols and trouble shooting mechanisms were also implemented to assist with the decision making process, for difficult situations. Results: Of the 25 cases 88% received a clinically acceptable dose. A learning curve was also observed showing improvement in target delineation over time. Waiting times from the radiotherapy planning CT scan to target definition were also improved by 7.5 working days. Conclusions: The training program allowed the Oncologist to be satisfied that any outline differences were due to intra observer error only, and therefore, acceptable for clinical

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use. Radiographer led target delineation was then implemented. This promoted the appropriate application of skills within the department, increasing job satisfaction for the multidisciplinary team, and also ensuring optimal treatment regimes for the patients

141 Adaptive Radiotherapy in prostate conformal dynamic treatment

C. Garibaldi 1, F. Cattani 1, S. CastiglionP, B. Tagaste I, M. Riboldi 4, R. Cambria I, P. FossatP, G. Tosi I, R. Orecchia 2 1European Institute of Oncolog, Medical Physics, Milano, Italy 2European Institute of Oncology, Radiation Oncology, Milano, Italy 4Politecnico di Milano, Bioengineering, Milano, Italy Background and purpose: To investigate the feasibility of an off-line image feedback to predict patient set-up errors and organ motion in order to re-optimise the treatment plan for prostate irradiation. Materials and methods: 10 patients (pts) were enrolled in the study. All pts underwent a planning CT scan and four repeated CT scans during the first week of treatment in order to evaluate the organ motion. All repealed CT scans were fused on the planning CT and CTV (prostate and seminal vesicles) and OARs (rectum and bladder) were delineated by the same radiation oncologist on each CT scan. The adaptive CTV (CTVadp) was defined as the envelope of the different CTVs drawn on each CT scan. PLs were daily repositioned with the ExacTrac (BrainLAB) and set-up errors were evaluated with EPID during the first five treatment sessions. A pt-specific set-up margin was added to the C-i-Vadpto create the adaptive PTV (PTVadp). Treatment plans based on two 6 MV dynamic arcs conformed the PTV and P'l-Vadp by a micromultileaf collimator (BrainLAB) were compared in terms of CTV coverage and irradiation of OARs. For CTV coverage we evaluated V95O/o(volume receiving at least 95% of prescribed dose), white for rectum, V3oo/oand Veoo/oand for bladder Vs0o/o, in relationship to our dose-volume constraints for prostate treatment. All pts received a dose of 76 Gy. Results: The use of ExacTrac led to a reduction of the set-up errors comparing to our conventional set-up technique. Setup errors (ram) were 1.7+0.5 (1 SD) in LL, 1.9 +0.7 in CC and 1.6_+0.6 in AP directions. The centre of mass of CTVad~ exhibited a displacement from that of CTV mostly in AP direction of 2.5+3.9 mm posteriorly with a maximum value of 9 mm. The PTVadp was significantly smaller than the PTV for all pLs, with a mean reduction of 37% -+9% . CTV coverage was excellent in both plans for all pts. We observed a worsening of the PTVadp coverage in the PTV-based plan in 3 out of 10 pts, leading to a mean AVgso/o=-3%+5%. The same pts exhibited a worsening of the rectum DHV, due to a displacement of the CTVadp towards the rectum. The bladder DVH for the PTVadp-based plan significantly improved compared to the P-i-V-based plan, for all pts. Conclusions. This work highlighted, beside the improvement of patient positioning with Exactrac, that the described procedure is reliable for organ motion assessment. Nevertheless, the adaptive process, being time consuming, can be applied in our dept. only in selected prostate cases. 142 Feasibility of pathology-correlated lung imaging for accurate target definition of lung tumors

J. Stroom I, H. Blaauwgeers 2, J. Belderbos 1, H. KIomp3, K. Lieske 4, R. van Pel5, L. Boersma 6, J. Lebesque 1, K. Gilhuijs 7 1The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Radiation Oncology ,Amsterdam, The Netherlands 20nze Lieve Vrouwe Hospital, Pathology, Amsterdam, The Netherlands 3The Netherlands Cancer Institute - Antoni van Leeuwenhoek

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Hospital, Surgery, Amsterdam, The Netherlands 40nze Lieve Vrouwe Hospital ,Pulmonology, Amsterdam, The Netherlands SThe Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Pathology, Amsterdam, The Netherlands 6University of Maastricht, Radiation Oncology (MAASTRO) Maastricht, The Netherlands 7The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Radiology, Amsterdam, The Netherlands Background: In order to accurately define the gross tumor volume (G-IV) and clinical target volume (C-FV) for radiotherapy, pre-treatment imaging must be correlated with hisLopathology in a patient population that undergoes surgery and is comparable to that treated by radiotherapy. For tumors in the lung, the CTV margins estimated from histopathology might be affected by lung deformations before and after surgery. We investigated the feasibility of in-vivo pathology-correlated lung imaging, thus quantifying the effect of lung deformaLions. Methods and material: High-resolution (1 mm slice distance) multi-slice CT scans were obtained from patients with NSCLC prior to Iobectomy. At pathology, the involved lung lobes were inflated with formalin. After fixation overnight, the specimens were sectioned in parallel slices orLhogonal Lo the longest axis aL approximately 5 mm slice thickness. Digital photographs were obtained from each slice. Microscopic thin sections covering the tumor and surrounding area of about 2 cm were obtained and their images overlaid onto the macroscopic images. The CT data were reformatted in the direction of sectioning. An interactive tool was built to identify corresponding cut planes and to indicate pairs of corresponding fiducial points in bronchi and blood vessels. Using this information, the macroscopic sections were warped to the corresponding CT images, hence taking into account lung deformations. Gross tumor areas corresponding to the microscopy overlay were not deformed but subject to rigid-body motion only. Results: In the figure an example of the above procedure is demonstrated. In A) fiducial points (arrows) are indicated in a reformatted CT-slice through the left upper lobe (black line). In B) the fiducials are used to warp the corresponding macroscopic slice to the CT. In C) the microscopic cuts are overlayed, indicating that the position of an islet of microscopic disease (X) relative to the GTV (solid line) is underestimated without correction for deformations. The first results of our ongoing study indicate that this underestimation may be a factor of two, even when lobes are well inflated at pathology. This will have consequences for the definition of CTV volumes.

143 4OCT intrafraction motion margin assessment breast cancer treatments S.J. Becker, R.R. Patel, T.R. Mackie University of Wisconsin, Medical Physics, Madison, USA

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Purpose: Prone positioning has the advantage of moving the breast tissue away from critical underlying structures like the heart, lung, and contralateral breast. We used 4D-CT scanning to quantify breathing motion of breast cancer patients in both the prone and supine position in order to properly determine the range of motion. Methods and Materials: 15 consecutive post-lumpectomy breast cancer patients were imaged using the cine mode of the CT machine. Contrast was injected into the surgical cavity Lo allow motion tracking with the breathing cycle. (See Image below) Both conventional supine positioning as well as prone positioning on a custom mattress was analyzed. The images were taken every second for 20 seconds. This allowed the observation of several breathing cycles. Motion was assessed by analyzing the movement of the surface of Lhe breast above the contrast-enhanced lumpectomy caviLy, the chest wall, the anterior and posterior edges of the lumpectomy cavity and the centroid of the lumpectomy cavity in each patient. Results: Motion in the prone position was less than the motion in Lhe supine position. The measurement of the motion in the prone posiLion was limited by the resolution of the CT machine (0.94 mm). The motion on the all sites in the prone position was less than 1ram. The motion in the supine was less than 2.5mm for all sites and for the centroid less than 2mm. Conclusions: The breast in the prone position moved negligibly during quiet breathing as compared Lo the supine position, which moved by 2 mm during quiet breathing. A small reduction in the PTV margin is possible with the prone position but more importantly, this study indicates that there does not need to be any flash when treating in the prone position and the use of IMRT is possible without any risk of developing hot or cold spots.

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144 Changes in respiratory pattern during radiotherapy for lung cancer 7-. N~ttrup I, S. Korreman 2, L. Aarup 2, M. Olsen 1, A.

Conclusions: The described technique demonstrated the feasibility of pathology-correlated lung imaging to improve target definition. NoL Laking into account lung volume deformations may cause profound underestimation of the size of the C'IV.

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Pedersen 1, L. Specht 1, H. NystrSm 1 1Department of Radiation Oncology, The Finsen Centre, Rigshospitalet, Copenhagen, Denmark 2Department of Oncology, The Finsen Centre, Rigshospitalet, Copenhagen, Denmark Background: Planning high-precision radiotherapy of lung tumours is extremely challenging. The tumour must remain within the radiation field irrespective of respiratory motion, requiring large treatment field margins. New therapeutic radiation equipment can adapt the radiation beam to the respiratory motion, so-called breathing adapted radiotherapy or respiratory gating. It is an innovative 4-