PRECLINICAL ASSESSMENT OF VOLUMETRIC MODULATED ARC THERAPY FOR TOTAL MARROW IRRADIATION

Purpose: A preclinical investigation was undertaken to explore a treatment technique for total marrow irradiationusing RapidArc, a volumetric modulated arc technique.Materials and Methods: Computed tomography datasets of 5 patients were included. Plans with eight overlappingcoaxial arcs were optimized for 6-MV photon beams. Dose prescription was 12 Gy in 2 Gy per fraction, normalizedso that 100% isodose covered 85% of the planning target volume (PTV). The PTV consisted of the whole skeleton(including ribs and sternum), from the top of the skull to the medium distal third of the femurs. Planning objectivesfor organs at risk (OARs) were constrained to a median dose <6 to 7 Gy. OARs included brain, eyes, oral cavity,parotids, thyroid, lungs, heart, kidneys, liver, spleen, stomach, abdominal cavity, bladder, rectum, and genitals.Pretreatment quality assurance consisted of portal dosimetry comparisons, scoring the delivery to calculationagreement with the gamma agreement index.Results: The median total body volume in the study was 57 liters (range, 49–81 liters), for an average diameter of 47cm (range, 46–53 cm) and a total length ranging from 95 to 112 cm. The median PTV volume was 6.8 liters (range,5.8–10.8 liters). The mean dose to PTV was 109% (range, 107–112%). The global mean of median dose to all OARswas 4.9 Gy (range, 4.5–5.1 Gy over the 5 patients). The individual mean of median doses per organ ranged from 2.3Gy (oral cavity) to 7.3 Gy (bowels cavity). Preclinical quality assurance resulted in a mean gamma agreement indexof 94.3 ± 5.1%. The delivery time measured from quality assurance runs was 13 minutes.Conclusion: Sparing of normal tissues with adequate coverage of skeletal bones was shown to be feasible withRapidArc. Pretreatment quality assurance measurements confirmed the technical agreement between expectedand actually delivered dose distributions, suggesting the possibility of incorporating this technique in the treatmentoptions for patients.

Purpose: A preclinical investigation was undertaken to explore a treatment technique for total marrow irradiation using RapidArc, a volumetric modulated arc technique. Materials and Methods: Computed tomography datasets of 5 patients were included. Plans with eight overlapping coaxial arcs were optimized for 6-MV photon beams. Dose prescription was 12 Gy in 2 Gy per fraction, normalized so that 100% isodose covered 85% of the planning target volume (PTV). The PTV consisted of the whole skeleton (including ribs and sternum), from the top of the skull to the medium distal third of the femurs. Planning objectives for organs at risk (OARs) were constrained to a median dose <6 to 7 Gy. OARS included brain, eyes, oral cavity, parotids, thyroid, lungs, heart, kidneys, liver, spleen, stomach, abdominal cavity, bladder, rectum, and genitals. Pretreatment quality assurance consisted of portal dosimetry comparisons, scoring the delivery to calculation agreement with the gamma agreement index. Results: The median total body volume in the study was 57 liters (range, 49-81 liters), for an average diameter of 47 cm (range, 46-53 cm) and a total length ranging from 95 to 112 cm. The median PTV volume was 6.8 liters (range, 5.8-10.8 liters). The mean dose to PTV was 109% (range, 107-112%). The global mean of median dose to all OARs was 4.9 Gy (range, 4.5-5.1 Gy over the 5 patients). The individual mean of median doses per organ ranged from 2.3 Gy (oral cavity) to 7.3 Gy (bowels cavity). Preclinical quality assurance resulted in a mean gamma agreement index of 94.3 +/- 5.1%. The delivery time measured from quality assurance runs was 13 minutes. Conclusion: Sparing of normal tissues with adequate coverage of skeletal bones was shown to be feasible with RapidArc. Pretreatment quality assurance measurements confirmed the technical agreement between expected and actually delivered dose distributions, suggesting the possibility of incorporating this technique in the treatment options for patients. (C) 2011 Elsevier Inc.