Dosimetric, Radiobiological and Secondary Cancer Risk Evaluation in Head-and-Neck Three-dimensional Conformal Radiation Therapy, Intensity-Modulated Radiation Therapy, and Volumetric Modulated Arc Therapy: A Phantom Study.

This analysis estimated secondary cancer risks after volumetric modulated arc therapy (VMAT) and compared those risks to the risks associated with other modalities of head-and-neck (H&N) radiotherapy. Images of H&N anthropomorphic phantom were acquired with a computed tomography scanner and exported via digital imaging and communications in medicine (DICOM) standards to a treatment planning system. Treatment plans were performed using a VMAT dual-arc technique, a nine-field intensity-modulated radiation therapy (IMRT) technique, and a four-field three-dimensional conformal therapy (3DCRT) technique. The prescription dose was 66.0 Gy for all three techniques, but to accommodate the range of dosimeter responses, we delivered a single dose of 6.60 Gy to the isocenter. The lifetime risk for secondary cancers was estimated according to National Council on Radiation Protection and Measurements (NCRP) Report 116. VMAT delivered the lowest maximum doses to esophagus (23 Gy), and normal brain (40 Gy). In comparison, maximum doses for 3DCRT were 74% and 40%, higher than those for VMAT for the esophagus, and normal brain, respectively. The normal tissue complication probability and equivalent uniform dose for the brain (2.1%, 0.9%, 0.8% and 3.8 Gy, 2.6 Gy, 2.3 Gy) and esophagus (4.2%, 0.7%, 0.4% and 3.7 Gy, 2.2 Gy, 1.8 Gy) were calculated for the 3DCRT, IMRT and VMAT respectively. Fractional esophagus OAR volumes receiving more than 20 Gy were 3.6% for VMAT, 23.6% for IMRT, and 100% for 3DCRT. The calculations for mean doses, NTCP, EUD and OAR volumes suggest that the risk of secondary cancer induction after VMAT is lower than after IMRT and 3DCRT.

Cyclic-RGD penta-peptides cRGDyK derivatized with cyclopentadienyl complexes of technetium and rhenium as radiopharmaceutical probes.

The present study reports the syntheses of half-sandwich complexes of the type [M(η5 -C5 H4 CONH-R)(CO)3 ] (M═Re,99m Tc;R═cyclic RGD peptide (cRGDyK) for potential imaging of αv ß3 integrin expression. The 99m Tc complex was prepared directly from the reaction of [99m Tc(OH2 )3 (CO)3 ]+ with cRGDyK, doubly conjugated to Thiele's acid [(C5 H5 COOH)2 ] in water. This approach extends the viability of metal-mediated retro Diels-Alder reactions for the preparation of small molecules such as linear tripeptides to a more complex cyclic peptide carrying a [(η5 -C5 H4 )99m Tc(CO)3 ] tag. The Diels-Alder product [(C5 H5 CONH-cRGDyK)2 ] was prepared from Thiele's acid via double peptide coupling. The Re-complex [Re(η5 -C5 H4 CONH-cRGDyK)(CO)3 ] was obtained by attaching [Re(η5 -C5 H4 COOH)(CO)3 ] directly to the N-terminus of cRGDyK. The identity of the 99m Tc-complex is confirmed by chromatographic comparison with the corresponding rhenium complex, fully characterized by spectroscopic techniques.