Dynamic Jaws and Dynamic Couch in Helical Tomotherapy

Proceedings of the 51st Annual ASTRO Meeting aspects for radiotherapy planning. We present the first report of dosimetric data of patients treated with electron arc (EA) therapy. Materials/Methods: Ten patients requiring bilateral chest wall irradiation for bilateral breast cancer were considered suitable for EA therapy. After positioning and immobilization, patients underwent CT scans from neck to upper abdomen. PTV included bilateral chest wall while OARs included bilateral lungs and heart. EA plans were generated using the PLATO RTS (V1.8.2 Nucletron) Treatment Planning System. Electron energy was chosen depending upon the depth and thickness of the PTV. Combinations of electron energies (6-9) MeV with bolus were used to account for differential chest wall thickness. For all patients, the arc angle ranged between 80-160 degrees. The source to skin distance remained between 80 -90cm. The electron applicator was designed to have a fixed field width of 5cm and varying field length depending on PTV. The aim was to cover the entire target with the 85% isodose line. Homogeneity Index (HI), Coverage Index (CI) and doses to OARs were evaluated. Patient specific dosimetry was carried out and output was measured in terms of MU/ Gy/degree. In addition, Thermoluminescence surface dosimetry (TLD) was done for all patients. The total planned dose to the PTV was 50Gy/25 fractions with a fraction size of 2Gy per fraction delivered over 5 fractions per week. Results: The mean PTV (± Standard Deviation) volume was 568.9 (±116) cc. Mean PTV coverage was 88(±5.8) % of the prescribed dose. The mean volume of right lung was 974 (±228.6) cc. The mean value of D1, D5, D10 and V20 were 46(±7.6) Gy, 36(±9) Gy and 29(±9) Gy and 28.4±10.5% respectively. The mean volume of left lung was 826(±220) cc. The mean value of D1, D5, D10 and V20 were 45.6(±7) Gy, 36(±9) Gy, 28(±8) Gy and 25.8±7.6% respectively. The mean volume of heart was 381(±78) cc. The mean value of D1, D5 and D10 were 24.6(±15) Gy, 16(±12) Gy and 11(±9) Gy respectively. Mean HI and CI of the PTV was found to be 24 (± 6.6) and 0.88(±0.05) respectively. The mean values of TLD at various pre specified locations on the chest wall surface (right, left, center, superior and inferior) were 1.83Gy, 1.82Gy, 1.85Gy, 1.89Gy and 1.78Gy respectively. Conclusions: EA technique for treating bilateral chest wall is a feasible and pragmatic technique. This technique has the twin advantages of adequate coverage of the target volume and sparing of adjacent normal structures. However, comparing with other techniques, it needs a firm quality assurance protocol for dosimetry and treatment delivery. Author Disclosure: P.K. Sharma, None; A. Munshi, None; A. Budrukkar, None; S.V. Jamema, None; C.M. Tambe, None; R. Jalali, None; R. Sarin, None; D.D. Deshpande, None; S.K. Shrivastava, None.

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Dynamic Jaws and Dynamic Couch in Helical Tomotherapy 1

F. Sterzing , M. Uhl1, G. Sroka-Perez1, K. Schubert1, Y. Chen2, W. Lu2, T. R. Mackie2, J. Debus1, G. Oliveira2, K. Herfarth1 1

Department of Radiation Oncology, University of Heidelberg, Germany, 2Tomotherapy Inc., Madison, WI

Purpose/Objective(s): To investigate the next generation technique of helical tomotherapy delivery with dynamic jaw and dynamic couch movement. Materials/Methods: The new technique of dynamic jaws and dynamic couch movement is described and the prototype software planning station version 6.1 is used to do a comparative planning study. Ten nasopharyngeal cancer patients with skull base infiltration close to the optic pathways and lymph node metastases were chosen to analyze the characteristics of the longitudinal dose profile comparing regular tomotherapy delivery, running-start-stop treatment and dynamic jaw and dynamic couch delivery. Target coverage, conformity and homogeneity as well as organ at risk sparing, integral dose and radiation delivery time are evaluated for 5 different plans for each patient. Within a multifocal simultaneous integrated boost concept a median dose of 70.4 Gy to the primary tumor and involved lymph nodes and a median dose of 57.4 Gy to the bilateral cervical lymphatic drainage pathways were prescribed in 32 fractions. Results: Mean parotid dose for all different deliveries was between 24.8 and 26.1 Gy without significant differences. The mean integral dose was lowered by 6.3% using the dynamic jaw and dynamic couch technique in comparison with 2.5 cm field width regular delivery and by 16.7% in comparison with 5cm regular delivery. Dose to optic pathways, brain and lung was lowered significantly with the new technique. Using dynamic jaw and couch movement the calculated radiation time was reduced to 33% of the time required with regular delivery using 2.5cm field width (199 seconds vs. 595 seconds, p \ 0.001). Conclusions: The current delivery mode of helical tomotherapy produces excellent dose distributions with conformal avoidance of parotid glands, brain stem and spinal cord for this challenging patient group. The new technology with dynamic jaw and couch movement improves the plan quality by reducing the dose penumbra and by a reducing the integral dose. In addition, radiation time is reduced to 33% of the regular delivery and patient throughput can be increased. Author Disclosure: F. Sterzing, research collaboration with Tomotherapy Inc., B. Research Grant; speaker for tomotherapy, D. Speakers Bureau/Honoraria; M. Uhl, None; G. Sroka-Perez, None; K. Schubert, None; Y. Chen, employee of tomotherapy, A. Employment; W. Lu, employee of tomotherapy, A. Employment; T.R. Mackie, employee of tomotherapy, A. Employment; J. Debus, None; G. Oliveira, employee of tomotherapy, A. Employment; K. Herfarth, research collaboration, B. Research Grant.

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A Prospective Trial of Helical Tomotherapy (HT) in Patients with Head and Neck Cancer (HNC): Results of Dosimetric Comparisons with Three-Dimensional Conformal Radiotherapy (3D-CRT)

A. Haddad, S. El-Sayed, R. Zohr, J. Belec, L. Eapen, B. Esche, L. Grimard The Ottawa Hospital Cancer Centre, Ottawa, ON, Canada Purpose/Objective(s): Intensity-modulated radiotherapy (IMRT) has been shown to provide better sparing of organs at risk (OAR), especially the parotid glands, when treating patients with head and neck malignancies. Using HT inverse planning, we set out to quantify the differences in the dose distribution to multiple target volumes, OAR and to integral dose. Materials/Methods: OTT 05-06 is an ongoing single institution study looking to prospectively evaluate toxicity patterns, quality of life (QoL) and tumor control in 80 patients with HNC treated with IMRT using HT. Patients received 50Gy to an initial low-risk volume and a boost of 20Gy to gross disease, for a total of 35 fractions. This 2-phase approach was used to allow for a more appropriate comparison with previous 3D-CRT outcomes. The plans for an initial 19 patients were selected and parallel 3D-CRT

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