Proceedings of the 51st Annual ASTRO Meeting S605

2944 The Impact of Cardiac Pulsation Phase on Cardiac Radiation Dose in Tangential Breast Cancer

Radiotherapy

K. Yamada, K. Isogai, M. Atsumi, Y. Tonosaki, K. Shima

Seirei Mikatahara General Hospital, Hamamatsu, Japan

Purpose/Objective(s): To reduce cardiotoxicity from breast radiotherapy, innovative techniques are under investigation. In com-parison with the respiratory cycle, there have been few studies on the influence of cardiac pulsation. We studied the impact of car-diac pulsation on the cardiac radiation dose in tangential breast cancer radiotherapy.

Materials/Methods: Ten patients with left -sided breast cancer after breast conservation were enrolled in this study. Planning CTimages were acquired with electrocardiographically-gated 64-section CT (Aquilion 64, Toshiba Co.) using the deep-inspirationbreath-hold technique. A total dose of 50 Gy in 25 fractions was prescribed with 4-MV conventional tangential beams. For assess-ment of the cardiac pulsation cycle, cardiac systolic and diastolic phase images were reconstructed. Reconstructed CT images in thesystolic and diastolic phases were obtained using relative-delay ECG gating with 40 and 0% of the R-R interval occurring after theonset of R waves, respectively. The reconstructed image data for systolic and diastolic phases were transferred to the 3D-RTP sys-tem (Eclipse 7.3, Varian Co.). For each treatment plan, dose-volume histograms (DVH) of the heart and left ventricle were repro-duced using reconstructed systolic and diastolic phase images, respectively.

Results: The mean volume of the heart in the diastolic phase was 507.8±82.4 ml, and 433.9±74.4ml in the systolic phase. Themean volume of the left ventricle in the diastolic phase was 192.9±32.1 ml, and 126.0±23.4ml in the systolic phase. The meancardiac dose in the diastolic phase was 4.5 Gy on average for all patients, and 4.1 Gy in the systolic phase. The mean dose ofthe left ventricle in the diastolic phase was 6.4 Gy, and 5.7Gy in the systolic phase. The mean volume of the heart receivingover 20 Gy (V20) in the diastolic phase was 26.5±14.6 ml, and 20.9ml±13.9 ml in the systolic phase (p \ 0.01). The meanV20 of the left ventricle in the diastolic phase was 15.2±9.9 ml, and 11.3±7.8ml in the systolic phase (p \ 0.01).

Conclusions: The high dose volume (V20) of the heart and left ventricle reduced significantly in the systolic compared with thediastolic phase. The potential application of cardiac together with respiratory gating to treatment planning merits further investi-gation.

Author Disclosure: K. Yamada, None; K. Isogai, None; M. Atsumi, None; Y. Tonosaki, None; K. Shima, None.

2945 Image Guided Radiotherapy (IGRT) for Nasopharyngeal Cancer with Megavoltage Cone-beam CT

(MV-CBCT)

X. Wang, L. Li, C. Hu, Z. Xu, Y. Feng

Cancer Hospital, Fudan University, Shanghai, China

Purpose/Objective(s): To analyze changes of multiple regions of interest (ROIs) in nasopharyngeal cancer (NPC) during thecourse of radiotherapy using megavoltage cone beam computed tomography (MV-CBCT).

Materials/Methods: 21 NPC patients were immobilized with head-neck-shoulder thermoplastic mask, and they were treated withintensity modulated radiotherapy (IMRT). MV-CBCT scan was acquired for those patients once a week during the course of ra-diotherapy. Skin contours at different locations were defined: skull base, the parotid gland, C3, and C6. Three separate bony ROIswere defined: skull, styloid process, and mandible. Distances of the skin contour along the X- (right-left) and Z- (anterior-posterior)axis, and distances of the bony ROIs were measured once a week during the course of radiotherapy.

Results: Distance of the skin contour at the skull base decreased 0.25±0.06cm and 0.26±0.08cm(p . 0.05), respectively. Anddistance at the parotid level decreased 1.05±0.29cm,0.27±0.09cm(p = 0.00)along the X- and Z-axis, respectively. At the C3 level,1.11±0.28cm, 0.35±0.12cm(p = 0.00)along the X- and Z-axis, respectively. At the C6 level, 0.43±0.15cm, 0.31±0.11cm(p =0.01)along the X- and Z-axis, respectively. But changes of the distance between the bony structures like the skull base, styloidprocess, and the ascending branch of the mandible were negligible.

Conclusions: We found shrinkage of the skin contour at different regions of head-and-neck anatomy. Skin contour at the parotidgland and C3 level had the largest shrinkage. However, bony structures changed little.

Author Disclosure: X. Wang, None; L. Li, None; C. Hu, None; Z. Xu, None; Y. Feng, None.

2946 Investigation of Potential Interference of 3 Piece Penile Prostheses with Electromagnetic Localization

System

B. J. Salter, B. Wang, J. D. Tward, D. C. Shrieve

University of Utah, Salt Lake City, UT

Purpose/Objective(s): The Calypso 4D Localization System has recently emerged as an effective method of localizing and track-ing for conformal treatment of prostate. Currently, prosthetic penile implants are listed by the vendor as a contraindication to use,owing to concerns over potential interference from the small metal components within the penile implant valve. A prostate cancerpatient who recently presented for treatment in our clinic with an implanted penile prosthesis inspired us to investigate the inter-ference potential of the most popular penile prosthetic systems.

Materials/Methods: Non-sterile samples of the AMS model 700 (70.8% market share) and the Coloplast models Alpha 1 andTitan, 3 piece inflatable systems (29.2% market share) were obtained from the respective vendors. For phantom study, the penileimplants were filled with saline according to vendor instructions, as would be performed during patient implantation. The Calypsodaily QA phantom with three implanted transponders was setup to known off-sets from linac isocenter, and the ability of the systemto correctly identify required localization shifts was assessed with each of the three penile implant devices located at multiple, clin-ically relevant locations around the phantom. Errors from known required values were recorded. The QA phantom was then po-sitioned at linac isocenter and the system was placed into real-time Tracking Mode. The 3 penile implant devices were each moved

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in all directions surrounding the phantom, under the 4D Array panel. Interference in Tracking Mode would be expected to manifestas apparent phantom location changes on the Calypso tracking output data. Any system-interpreted phantom shifts were recorded.After confirming the safety of use in phantom, we implanted transponders in one patient with an AMS Model 700 inflatable penileprosthetic. For each treatment fraction, redundant stereotactic ultrasound (US) image guidance was performed to ensure agreementbetween US and Calypso guidance. Image guidance results for both systems were collected.

Results: In the phantom study, the electromagnetic tracking system was seen to correctly identify required localization shifts within±0.5 mm with each penile implant device present. Additionally, tracking data for the phantom with penile implant devices presentdid not indicate any changes of the target location beyond normal background fluctuations of ±0.5 mm. Mean target position var-iation of US guided alignment from Calypso alignment was\3 mm in all directions, thus indicating good agreement between USand Calypso alignment in the presence of penile implant device.

Conclusions: Our phantom and patient-based evaluation suggests that accurate Calypso alignments can be performed in the pres-ence of 3 piece inflatable penile implants.

Author Disclosure: B.J. Salter, None; B. Wang, None; J.D. Tward, None; D.C. Shrieve, None.

2947 Assessing the Carina as a Reliable Thoracic Landmark for Patient Setup using Four-dimensional

Computed Tomography

C. H. Matthews, E. Ford, D. Song

Johns Hopkins Hospital, Baltimore, MD

Purpose/Objective(s): The carina has often been considered a reliable landmark for patient positioning for lung cancer radiother-apy. We aimed to examine the reliability of the carina as a thoracic landmark during radiographic setup verification by assessing theextent to which the carina moves during the course of a respiratory cycle.

Materials/Methods: In 30 lung cancer patients we measured the superior-inferior excursion of the carina during the course ofa breathing cycle using respiration-correlated four-dimensional computed tomography scans acquired at the time of simulation.CT scans from ten respiratory phases were co-registered in the Pinnacle treatment planning system (Philips). At a given phasea point of interest was placed at the carina and excursions were calculated relative to the bony architecture.

Results: 20% (6/30) of the patients exhibited carina movement of more than 9 mm with one patient’s movement registering 1.5cm.The carina moved a mean of 6mm with a standard deviation of 2.72mm (range: 3mm-1.5cm).

Conclusions: These data demonstrate that the carina exhibits a clinically significant range of movement during the course ofa breathing cycle. The S/I range of motion of the carina is larger in many cases than the 5 mm margin often used for setup variation.The carina is therefore not a reliable landmark to use for precise patient positioning verification. This underscores the need for fur-ther investigation into finding a more reliable anatomical reference for port radiographic positioning.

Author Disclosure: C.H. Matthews, None; E. Ford, None; D. Song, None.

2948 A Comparative Study for Daily Localization with 3D Ultrasound, Cone Beam CT, and Implanted Prostate

Fiducial Markers for Patients undergoing IGRT for Prostate Cancer

T. Neicu, I. J. Chetty, D. Pradhan, H. Stricker, B. Movsas, M. Elshaikh

Henry Ford Health System, Detroit, MI

Purpose/Objective(s): To assess the accuracy and dosimetric implications of multimodality-based online image-guided localiza-tion methods, including intramodality 3D prostate ultrasound, cone beam CT (CBCT) and implanted prostate markers for the samepatients undergoing external beam radiation treatment with IMRT for prostate carcinoma.

Materials/Methods: Nine prostate cancer patients implanted with gold fiducial markers were imaged using the IGRT techniques:Clarity intramodality 3D U/S-IGRT system (Resonant Medical Inc., Montreal, Canada) and the On Board Imager (OBI) on a VarianTrilogy TX linac (Varian Medical Systems, Palo Alto CA). 3D U/S images, CBCT scans and orthogonal kV images were obtainedeach day prior to and once a week post daily treatment. Rigid body registrations were performed offline between the planning anddaily images to estimate daily offsets. Dosimetric differences were evaluated by computing treatment plans using the average shiftvalues generated by the image-guided localization methods.

Results: The average couch shifts of 295 treatment fractions are -2.5 ± 2.0 mm (A/P), -1.0 ± 3.3 mm (S/I) and -0.1 ± 2.3 mm (L/R)for U/S, -0.8 ± 1.5 mm (A/P), 0.2 ± 1.1 mm (S/I) and 1.8 ± 1.8 mm (L/R) for CBCT, and -3.3 ± 2.2 mm (A/P), -1.0 ± 2.1 mm (S/I)and 1.5 ± 1.3 mm (L/R) for fiducial markers. The multimodality offset probability density functions (PDFs) were found to exhibitGaussian behavior. Residual motion of the patient after setup was also calculated from the fiducial markers locations in the kVimages and was found to be: 0.0 ± 0.5 mm (A/P), 0.2 ± 0.6 mm (S /I), and 0.1 ± 0.3 mm (L/R). Differences between U/S and fiducialmarker centroids (as measured by CBCT) are: -1.5 ± 2.1 mm (A/P), -2.5 ± 2.1 mm (S/I), 0.9 ± 1.9 mm (L/R). However, it shouldalso be noted that weekly CBCTs taken before and after treatment differed as follows: -0.9 ± 2.8 mm (A/P), 0.0 ± 2.5 mm (S/I); 0.0± 1.3 mm (L/R). Changes in inter-fiducial distances between sim and treatment were found to be on average 1.5 mm (maximum of5.8 mm). This is possibly caused by rotations, migration, and/or prostate size/shape changes. DVHs for the rectum, and bladdershow in some instances significant increases in dose received when measured setup shifts were included. Dose coverage to the95% of PTV volume was also found to be several percent lower than the prescription in some cases.

Conclusions: The comparison of multimodality IGRT techniques is subject to many uncertainties, including prostate intrafractionmotion, changes in the prostate position due to bladder/rectal filling during the time between image acquisitions, migration of fi-ducial markers, etc. Future work will include the use of electromagnetic beacons (Calypso, Seattle WA) to monitor the intrafractionmotion.

Author Disclosure: T. Neicu, None; I.J. Chetty, Resonant Medical Inc., B. Research Grant; D. Pradhan, None; H. Stricker, None; B.Movsas, Resonant Medical Inc., B. Research Grant; M. Elshaikh, Resonant Medical Inc., B. Research Grant.