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SU‐E‐T‐56: Brain Metastasis Treatment Plans for Contrast‐Enhanced Synchrotron Radiation Therapy
Author(s) -
Obeid L,
Tessier A,
Vautrin M,
Sihanath R,
Benkebil M,
Adam J
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4888386
Subject(s) - nuclear medicine , medicine , radiation therapy , collimator , brain metastasis , radiation treatment planning , radiosurgery , skull , dosimetry , radiology , metastasis , surgery , physics , cancer , optics
Purpose: Iodine‐enhanced radiotherapy is an innovative treatment combining the selective accumulation of an iodinated contrast agent in brain tumors with irradiations using monochromatic medium energy x‐rays. The aim of this study is to compare dynamic stereotactic arc‐therapy and iodineenhanced SSRT. Methods: Five patients bearing brain metastasis received a standard helical 3D‐scan without iodine. A second scan was acquired 13 min after an 80 g iodine infusion. Two SSRT treatment plans (with/without iodine) were performed for each patient using a dedicated Monte Carlo (MC) treatment planning system (TPS) based on the ISOgray TPS. Ten coplanar beams (6×6 cm2, shaped with collimator) were simulated. MC statistical error objective was less than 5% in the 50% isodose. The dynamic arc‐therapy plan was achieved on the Iplan Brainlab TPS. The treatment plan validation criteria were fixed such that 100% of the prescribed dose is delivered at the beam isocentre and the 70% isodose contains the whole target volume. The comparison elements were the 70% isodose volume, the average and maximum doses delivered to organs at risk (OAR): brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma. Results: The stereotactic dynamic arc‐therapy remains the best technique in terms of dose conformation. Iodine‐enhanced SSRT presents similar performances to dynamic arc‐therapy with increased brainstem and brain parenchyma sparing. One disadvantage of SSRT is the high dose to the skull bone. Iodine accumulation in metastasis may increase the dose by 20–30%, allowing a normal tissue sparing effect at constant prescribed dose. Treatment without any iodine enhancement (medium‐energy stereotactic radiotherapy) is not relevant with degraded HDVs (brain, parenchyma and skull bone) comparing to stereotactic dynamic arc‐therapy. Conclusion: Iodine‐enhanced SSRT exhibits a good potential for brain metastasis treatment regarding the dose distribution and OAR criteria.