519 poster Total marrow and total lymphatic irradiation using helical tomotherapy

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decreased complications rates of organs at risk is expected. Reduction of respiratory motion can be achieved by using either breath hold techniques or respiration synchronized gating techniques. Breath hold techniques, usually at inspiration (DIBH), can be achieved with passive techniques, in which the patient voluntarily breath-hold. Synchronized gating techniques use external devices (CCD camera for the GEMS/Varian system) to predict the phase of the respiration cycles while the patient breaths freely. A new strategy is currently developed: the 4D Respiration correlated CT (4DCT). It consists of retrospectively reconstruct CT slices at different phases of the breathing cycle allowing to measure residual movements and to choose the optimal breathing phase where tumour movements are lower. This work proposes a validation of these two approaches. For the first method inter-DIBH reproducibility is measured for 5 patients by measuring the lung volume variations between 2 DIBH CT scans. Intra-DIBH motion during the beam delivery is measured on portal images in cine mode for breast and lung tumours. Results are compared to a reference free breathing (FB) CT scan. For the second technique, lung volume variations during FB, obtained with 4D-CT series, are compared to lung volume variation for different breathing phase acquisition. For one patient we have performed both DIBH-CT and 4D-CT during FB. Differences of lung volume between these 2 techniques are compared to the same value measured with a spirometer. Results: The lung volume difference between the 2 DIBH CT scans is 3%. During treatment, sup-inf motion of the lower part of the lung is 1.04cm and 0.24cm between FB and DiBH, respectively. For breast, the mean motion along ant-post direction is 0.6cm and 0.13cm for FB and DIBH respectively. Lung volume variations during El with two different phase acquisitions (20% and 40% centred on El) are 74% and 51% respectively, smaller than FB. Finally, lung volume difference between EE and DIBH CT scans is 1.37L while it was 1.4L measured with a spirometer. Conclusions: Further studies should confirm these results. Dosimetric benefits will also be evaluated for both techniques. The first results are very promising. 518 poster 3D dose distribution in tissue calculated based on PETCT imaging for high energy scanned photon therapy

J. Uhrdin ~'2, S. Janek ~, R. Svensson 1 IKarolinska Institutet, Medical radiation physics, Stockholm, Sweden 2RaySearch Laboratories AB, Stockholm, Sweden The technical improvements in combining CT with PET have opened up the possibility to use PET imaging to monitor the delivered 3D dose distribution when radiating with high energy photon beams. High energy photons, during radiation therapy, will produce PET emitting isotopes such as 150, 13N and 11C through photonuclear reactions, mainly (7, n) reactions, i.e. the PET signal distribution will represent the activation of tissue from photons above the photonuclear cross section threshold energy to maximum photon energy. The novelty of using PET imaging is that the knowledge of the actual dose delivered to the patient can be extracted during or after delivery, coupled with geometrical data from the CT. The reconstructed 3D dose distribution from PET-CT imaging, used in an optimization algorithm for adaptive radiation therapy, can be used to lower the impact of geometrical uncertainties. Here an .approximate method for calculating delivered dose based on the measured PET image after delivery will be presented. In a first approximation, the energy fluence spectra is both invariant in

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position and depth (e.g. disregarding beam hardening). Thus, the PET signal from shallow depth is proportional to the incident energy fluence distribution. The dose distribution is then calculated by folding the energy fluence, for the true scan pattern, with the energy deposition kernel corresponding to the high energy elementary bremstrahlung beam. It is assumed that the part of the energy fluence spectra that are below the threshold for activation is invariant, although this part considerably contributes to the delivered dose distribution. A full calculation takes into account the correct energy fluence distribution at all depths (i.e. the 3D PET image) as well as tissue nuclide composition. A cylindrical carbon phantom has been radiated with one homogeneous 10x10 cm field of 50 MeV scanned photons in one fraction for a prescribed dose of 10 Gy in isocenter. After 5 min the phantom has been placed in a Siemens ECAT EXACT HR PET camera and measured during a time frame of 40 minutes. The experimental CT-PET image was then used for calculating the delivered 3D dose distribution. The measured and planned dose distributions, conditioned the used approximations, showed good agreement. Thus, 3D dose reconstruction by PET-CT imaging may be an additional tool for high energy optimized adaptive therapy. 5 t 9 poster Total marrow and total lymphatic irradiation using helical tomotherapy

T. Schultheiss 1, J. Wong ~, A. LiJ, G. Olivera 2'3, J. Kapatoes 3 ~City of Hope Medical Center, Radiation Oncology, Duarte, CA, U.S.A. 2University of Wisconin, Radiation Oncology, Madison, WI, U.S.A. 3TomoTherapy, Inc., Madison, WI, U.S.A. The objective of this study is to develop a treatment technique to reduce the morbidity from TBI conditioning regimens used for leukemia, lymphoma and myeloma. We have developed a technique that uses the total marrow or marrow plus lymphatics as the target in a helical tomotherapy IMRT treatment, Using this technique, we are able to greatly reduce the dose to all visceral organs. The conventional TBI technique used at our institution uses 12 Gy in 10 fractions with an SSD of approximately 4 m. All organs receive the full dose except the lungs, which are partially blocked. The lungs receive a maximum of 12 Gy and 50% of the lung volume receives 9 Gy. Using helical tomotherapy, a beam of variable slice thickness is rotated continuously around the patient while the MLC rapidly opens and closes beamlets of 6 mm width. The patient is translated through the aperture of the unit continuously, as in a helical CT scanner. The pitch is also variable. In this study, we used slice thicknesses of 11, 25, and 50 mm with a pitch of 0.5. The treatment time for the 25 mm slice thickness is approximately 20 minutes. The instantaneous dose rate is higher using helical tomotherapy than in conventional TBI, but for normal tissue sparing low dose rates are not needed for fractionated regimens. Circulating malignant cells can be appropriately treated using chemotherapeutic agents specifically designed for that purpose in the conditioning regimen. The table below shows that the median doses to the organs responsible for the major toxicities is reduced by approximately 50%. Similar reductions are seen for all other organs. Because of this sparing, dose escalation may be possible. Furthermore, it may be possible to deliver the treatment on an outpatient basis. Late effects will be reduced drastically.

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Table: Dose (Gy) to 50% Organ Volume.

z~ ....................................................

Organ :TBI (linac)TLI (aT)TMI (HT) . . . . . . . . . . "Q"..............i . . . . . . . ]Lungs !9.0 6.3 6.7 Orbts :11.3

5,5 5.4

6.3

Liver

112.3

Bowe

12.3

i5.5

6 5

6.2

Breasts 11.5

i5.2

6.6

Thyroid :~12.1

4.2

6.4

{

520 poster

Figure 1

Investigating the correlation between surface and bony anatomy using 3D surface and portal imaging 3 M. Bidmead1, L. Corsini2 , J. Lindgren-Tumer3, N. Smith,/. MeiF, R. Howe3, H. Convery2, M. Davies2, E. Miles 2

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1Royal Marsden Hospital, Medical Physics, London, United Kingdom 2Royal Marsden Hospital, Radiotherapy, London, United Kingdom 3Vision RT Ltd, London, United Kingdom This study investigates the relationship between 3D surface contours and internal bony anatomy in order to assess the use of surface imaging for patient set-up and position verification. A group of pelvic patients were studied throughout the duration of respective courses of radical EBRT. All of the study group were positioned by aligning skin tattoos with lasers, and were treated using a Varian 2100CD Linac. Following set-up, AP and RT lat portal images ('Pl's) were taken using a Varian EPID. A 3D surface image was also captured at the same point in time using AlignRT, a real-time 3D surface imaging system. For each treatment fraction, the PIs were matched to the simulator reference using a Varian 'Vision' Portal Image workstation. The rotation and translation errors that were output were combined into a single PI error factor ('PIEF'). For each patient, the treatment surface with the minimum corresponding PI error was chosen as a reference and a region of interest ('ROI') was selected on the surface around the treatment isocentre, with care being taken to restrict the ROI to relatively rigid and stable anatomical areas. Surface data from all other fractions were projected to the reference ROI and the corresponding mean of the absolute projected distances, for each fraction, was computed. The range of PIEF values and mean ROI errors were then normalised and compared directly. Correlation factors between the PIEF and surface ROI projection errors were computed for each patient. These ranged from 0.72 to 0.95 (-1.0 to +1.0) with a mean of 0.82 and SD of 0.09. Figure 1 shows the results of the computed errors for one of the patients. The above results suggest a strong correlation between relatively rigid regions of skin surface, as computed by AlignRT, and bony anatomy detected via portal imaging. Further work is ongoing to corroborate this trend on a broader range of patients. In addition, work is planned to explore to what extent using surface imaging during patient set-up may help to reduce portal image derived systematic and random set-up errors.

Registration of CT and room coordinate systems for image-guided radiation therapy (IGRT) T. Jenkins, C. Sibata, M. Wolfe, Y. Feng, H. Mot& R. Allison The Brody School of Medicine, East Carolina Uni, Radiation Oncology, Greenville, NC, U.S.A. CT-on-rail systems (Primatom by Siemens, Inc.) are being installed beside linear accelerators to facilitate image-guided radiation therapy. With this configuration, patients can be imaged and treated on the same table. We have developed a method for registering the CT and room coordinate systems, thereby allowing the geometric relationship between any CT voxel and the linac isocenter to be determined. Using this system, corrections can be made for organ motion or setup errors without needing fiducial markers on the patient. Custom-milled "anchor points" were mounted to three walls and the ceiling of the treatment room. These anchor points allowed precise radial distances to be measured in any direction. Software was also created that could determine the x, y, and z coordinate of any point in the room based on it's distance from these anchor points. This established the "room" coordinate system. Using a phantom, the locations of various points in the room were measured using both the anchor points and CT scanner. A matrix was then determined that could translate from one coordinate system into the other. The matrix was calculated using a marching simplex algorithm that minimized a function of nine parameters (rotation, translation, and scaling along the x, y, and z axes). For the 11 points measured, the matrix was able to translate all CT coordinates to within one millimeter of the matching room coordinate. The average radial distance between room and translated CT points was 0.4 + 0.3 mm. Based on these measurements, we feel that this system is suitable for IGRT. Planning isocenters can be located using the CT scanner, translated into room coordinates, and then shifted to match the coordinates of the linac isocenter on a daily basis.

Benign disease 522 poster Painful calcaneal spur: is there any influence of radiation quality (orthovoltage vs. high voltage) on pain relief after radiotherapy? I. SchlOcker, A. Lilienthal, W. Oehler SfJdharz-Clinic Nordhausen gGmbH, Radiooncology and Radiotherapy, Nordhausen, Germany Purpose: Low dose radiotherapy (total dose 5 - 6 Gy) is a well established method for complete response of excruciating symptoms of painful spur in Germany. Most