measurements were performed with 6 MV photon beams of our Novalis accelerator. MC calculations were performed with an ''Ac- curacy optimized'' model with ...
I. J. Radiation Oncology d Biology d Physics
S674
3097
Volume 75, Number 3, Supplement, 2009
Salvage Stereotactic Body Radiotherapy for Locally Recurrent Head and Neck Carcinomas
M. Cengiz, G. Ozyigit, E. Karakaya, A. Dogan, H. Beyaz, F. Yıldız, F. Akyol, M. Gurkaynak, F. Zorlu Hacettepe University School of Med, Ankara, Turkey Purpose/Objective(s): The purpose of this study is to determine the efficacy and toxicity of stereotactic body radiotherapy (SBRT) as a salvage treatment in patients with locally persistent and recurrent head and neck carcinomas (HNC). Materials/Methods: Between July 2007 and November 2008, 35 patients with locally recurrent HNC were treated by SBRT. The sites of disease distribution were as follows: nasopharyngeal cancer, 16; paranasal sinus cancer, 7; oral cavity cancer, 3; hypopharyngeal cancer, 4; laryngeal cancer, 1; thyroid cancer, 1; tracheal cancer,1; lacrimal gland cancer, 1; and parotid cancer; 1. All patients had previously received full dose radical external beam radiotherapy. Median first line radiotherapy dose was 65,5 Gy (range, 30 Gy-77,4 Gy. Time from the previous radiotherapy to SBRT was median 66 months (range, 7-300 months). Ten patients were treated for two or more recurrences and five of these had taken second re-irradiation before SBRT. Median SBRT dose was 30 Gy (18-35 Gy) in median 5 fractions (1-5 fractions) in median 5 days (1-8 days) to typically 75-85% prescription isodoses. Median follow up time was 8 months (range, 4-18 months). Results: Seven patients had complete regression of tumor after SBRT, eleven had partial response, ten had stable disease, and six had progression of tumor. The overall response rate was 51.4% (n = 18). SBRT established ultimate disease control in 80 % (n = 28) of the patients. Disease progression in six patients occurred in median 6 months (range, 2-9 months) after SBRT. One year survival is 66.7%. Thirteen patients (%37) were complained of grade II-III toxicities; mucositis, dysphagia, feeding tube, fistula, myelitis and soft tissue necrosis. Moreover, three of four patients who have presented with profuse bleeding as life threatening toxicity after 2-3 months of SBRT were died. Conclusions: Our early result is encouraging that SBRT is an effective treatment modality with relatively good disease control for recurrent head and neck cancer. Major treatment related mortality is bleeding. Longer follow up with increased number of patients is essential to determine the definitive role of SBRT in this group of patients. Author Disclosure: M. Cengiz, None; G. Ozyigit, None; E. Karakaya, None; A. Dogan, None; H. Beyaz, None; F. Yıldız, None; F. Akyol, None; M. Gurkaynak, None; F. Zorlu, Honoraria, D. Speakers Bureau/Honoraria.
3098
Evaluation and Implementation of iPlan RT Monte Carlo Dose Algorithm for Head and Neck and Lung Cancer Patients
A. L. Petoukhova, R. G. J. Wiggenraad, P. J. M. van de Vaart, K. van Wingerden, J. van Egmond, E. Franken, J. P. C. van Santvoort Medical Centre Haaglanden, The Hague, Netherlands Purpose/Objective(s): To evaluate and implement iPlan RT Monte Carlo Dose Algorithm (MC) (BrainLab) for stereotactic radiotherapy. This study compares doses calculated with MC with doses measured and/or calculated with Pencil Beam algorithm (PB) using phantoms or patient data. Materials/Methods: MC calculations were compared to verification measurements and PB calculations in home made phantoms with lung equivalent material or air cavities or bone equivalent material to mimic head-and-neck and thorax. An Alderson anthropomorphic phantom was used for comparison of the measured and calculated clinical plans. Additional dosimetric accuracy of MC to benchmark the micro-MLC (Multileaf Collimator) transport was tested in an acrylic phantom (IMRT Phantom, BrainLab). All measurements were performed with 6 MV photon beams of our Novalis accelerator. MC calculations were performed with an ‘‘Accuracy optimized’’ model with a spatial resolution of 2 mm and a variance of 1%. To compare dose distributions a gamma analysis was performed with the DoseLab software with 3% dose difference and 1mm distance-to-agreement criteria. For the dosimetric measurements, we used a 0.14 cc ionization chamber and Kodak EDR2 films. Results: For fields larger than the dimensions of the inhomogeneities the MC calculation results show excellent agreement (within 3%/1mm) with the experimental data for phantoms with a lung equivalent material, a bone equivalent material and air cavities. Only for small field sizes some deviations were found within and a few mm behind the air cavities. Comparison of the dose distributions measured by film and calculated with MC method in the homogeneous phantom gives excellent agreement for an oval, C and squiggle shaped-fields (according to the AAPM TG-53) and a clinical IMRT plan. For the MLC blocked field, the experimental results are still much closer to MC than PB calculations. Results of measurements and MC calculations in the anthropomorphic phantom give good agreement for conformal beam plans and reasonable agreement for Dynamic Arc and IMRT plans. For five head-and-neck and ten lung patients a comparison of the plan calculated using MC with the plan calculated using PB was performed. For lung patients a difference up to 22% was observed within the Planning Target Volume. For head-and-neck patients dose deviations between PB and MC were smaller. Conclusions: Our results demonstrate that iPlan RT Monte Carlo Dose Algorithm is able to accurately predict the dose in the presence of inhomogeneities typical for head-and-neck and thorax regions with reasonable calculation times (5-20 minutes). Even for small field sizes the lateral electron transport is well reproduced in MC calculations. We are planning to implement MC calculations for head-and-neck and lung cancer patients. Author Disclosure: A.L. Petoukhova, None; R.G.J. Wiggenraad, None; P.J.M. van de Vaart, None; K. van Wingerden, None; J. van Egmond, None; E. Franken, None; J.P.C. van Santvoort, None.
3099
A Variable Circular Collimator: A Time-efficient Alternative for a Multi-leaf Collimator in Robotic Radiosurgery?
B. Heijmen, S. van de Water, S. Breedveld, J. J. M. E. Nuyttens, M. S. Hoogeman Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, Netherlands Purpose/Objective(s): The CyberKnife robotic radiosurgery unit uses small, non-isocentric cone beams for dose delivery. Clinical treatment plans are designed with one or two fixed collimators, requiring the tumor to be painted with many beams to obtain a highly
