Automated Non-coplanar Volumetric Modulated Arc Therapy Planning for Maxillary Sinus Carcinoma.

Dosimetric parameters in volumetric modulated arc therapy (VMAT), non-coplanar VMAT (NC-VMAT), and automated NC-VMAT (HyperArc, HA) were compared for patients with maxillary sinus carcinoma (MSC). Twenty HA plans were generated to deliver 70.4, 64, and 46 Gy for planning target volumes with high (PTV1), intermediate (PTV2), and low risk (PTV3), respectively. The VMAT and NC-VMAT plans were retrospectively generated using the same optimized parameters as those used in the HA plans. For PTV1, the three treatment plans provided comparable target coverages. For PTV2, the D95%, D99%, and Dmin in the HA plans (64.7±1.2, 62.7±2.1 and 54.6±6.2 Gy, respectively) were significantly higher (p<0.05) than those in the VMAT plans (64.3±1.7, 61.9±2.4 and 52.9±6.4 Gy, respectively). The NC-VMAT and HA plans provided significantly higher (p<0.05) dosimetric parameters for PTV3 than those in the VMAT plans, and D99% in the HA was significantly higher than that in the NC-VMAT plans (52.5±3.0 vs. 51.8±2.7 Gy, p<0.05). The doses to the brain and brainstem were lowest in the HA plans (p<0.05). Moreover, dosimetric parameters of the contralateral organs (lens, optic nerve, retina, and parotid) were lower in the HA plans than in the VMAT and NC-VMAT plans. The HA plans provided the best target coverage and OAR sparing compared with VMAT and NC-VMAT plans for patients with MSC.

Ohira S ，Inui S ，Kanayama N ，Ueda Y ，Miyazaki M ，Koizumi M ，Konishi K ... -  《-》

Dose reduction of hippocampus using HyperArc planning in postoperative radiotherapy for primary brain tumors.

To compare dosimetric parameters for the hippocampus, organs at risk (OARs), and targets of volumetric modulated arc therapy (VMAT), noncoplanar VMAT (NC-VMAT), and HyperArc (HA) plans in patients undergoing postoperative radiotherapy for primary brain tumors. For 20 patients, HA plans were generated to deliver 40.05 to 60 Gy for the planning target volume (PTV). In addition, doses for the hippocampus and OARs were minimized. The VMAT and NC-VMAT plans were retrospectively generated using the same optimization parameters as those in the HA plans. For the hippocampus, the equivalent dose to be administered in 2 Gy fractions (EQD2) was calculated assuming α/β = 2. Dosimetric parameters for the PTV, hippocampus, and OARs in the VMAT, NC-VMAT, and HA plans were compared. For PTV, the HA plans provided significantly lower Dmax and D1% than the VMAT and NC-VMAT plans (p < 0.05), whereas the D99% and Dmin were significantly higher (p < 0.05). For the contralateral hippocampus, the dosimetric parameters in the HA plans (8.1 ± 9.6, 6.5 ± 7.2, 5.6 ± 5.8, and 4.8 ± 4.7 Gy for D20%, D40%, D60% and D80%, respectively) were significantly smaller (p < 0.05) than those in the VMAT and NC-VMAT plans. Except for the optic chiasm, the Dmax in the HA plans (brainstem, lens, optic nerves, and retinas) was the smallest (p < 0.05). In addition, the doses in the HA plans for the brain and skin were the smallest (p < 0.05) among the 3 plans. HA planning, instead of coplanar and noncoplanar VMAT, significantly reduces the dosage to which the contralateral hippocampus as well as other OARs are exposed without compromising on target coverage.

Ohira S ，Ikawa T ，Kanayama N ，Inui S ，Ueda Y ，Miyazaki M ，Nishio T ，Koizumi M ，Konishi K ... -  《-》

A dosimetric comparison of volumetric modulated arc therapy (VMAT) and non-coplanar intensity modulated radiotherapy (IMRT) for nasal cavity and paranasal sinus cancer.

Jeong Y ，Lee SW ，Kwak J ，Cho I ，Yoon SM ，Kim JH ，Park JH ，Choi EK ，Song SY ，Kim YS ，Kim SS ，Joo JH ，Ahn SD ... -  《Radiation Oncology》

Improvement of target coverage using automated non-coplanar volumetric modulated arc therapy planning in stereotactic radiotherapy for cervical metastatic spinal tumors.

This study aimed to compare dosimetric parameters for targets and organs at risk (OARs) between volumetric modulated arc therapy (VMAT) and automated VMAT (HyperArc, HA) plans in stereotactic radiotherapy for patients with cervical metastatic spine tumors. VMAT plans were generated for 11 metastases using the simultaneous integrated boost technique to deliver 35 to 40 and 20 to 25 Gy for high dose and elective dose planning target volume (PTVHD and PTVED), respectively. The HA plans were retrospectively generated using 1 coplanar and 2 noncoplanar arcs. Subsequently, the doses to the targets and OARs were compared. The HA plans provided significantly higher (p < 0.05) Dmin (77.4 ± 13.1%), D99% (89.3 ± 8.9%), and D98% (92.5 ± 7.7%) for gross tumor volume (GTV) than those of the VMAT plans (73.4 ± 12.2%, 84.2 ± 9.6 and 87.3 ± 8.8% for Dmin, D99% and D98%, respectively). In addition, D99% and D98% for PTVHD were significantly higher in the HA plans, whereas dosimetric parameters were comparable between the HA and VMAT plans for PTVED. The Dmax values for the brachial plexus, esophagus, and spinal cord were comparable, and no significant difference was observed in the Dmean for the larynx, pharyngeal constrictor, thyroid, parotid grand (left and right), and Submandibular gland (left and right). The HA plans provided significantly higher target coverage of GTV and PTVHD, with a comparable dose for OARs with VMAT plans. The results of this study may contribute to the improvement of local control in clinical practice.

Ohira S ，Ikawa T ，Inui S ，Kanayama N ，Ueda Y ，Miyazaki M ，Nishio T ，Koizumi M ，Konishi K ... -  《-》

A dosimetric comparison of the use of equally spaced beam (ESB), beam angle optimization (BAO), and volumetric modulated arc therapy (VMAT) in head and neck cancers treated by intensity modulated radiotherapy.

Previous studies have shown that the beam arrangement had significant influence on plan quality in intensity modulated radiotherapy (IMRT). This study aimed to evaluate the dosimetric performance of beam arrangement methods by employing equally spaced beams (ESB), beam angle optimization (BAO), and volumetric modulated arc therapy (VMAT) in the planning of five types of head and neck (H&N) cancers treated by IMRT. Five plans of different beam arrangement methods were optimized for 119 H&N cancer patients with the prescription of 66-70 Gy for high-risk planning target volume (PTV), 60 Gy for intermediate risk PTV, 54 Gy for low-risk PTV using a simultaneously integrated boost method. The five-beam arrangement methods were: ESB, coplanar BAO (BAOc), noncoplanar BAO (BAOnc), two-arc VMAT (VMAT2), and three-arc VMAT (VMAT3). The H&N cancers included cancers of nasopharynx, oral cavity, larynx, maxillary sinus, and parotid. Although the partial arc VMAT could be used in cases where the PTVs were situated at one side of the head such as the parotid, this arrangement was not included because it was intended to include only the beam arrangements that were applicable to all the types of head and neck cancers in the study. The plans were evaluated using a "figure-of-merit" known as uncomplicated target conformity index (UTCI). In addition, PTV conformation number and homogeneity index, normal tissue integral dose, and organ at risk (OAR) doses were also used. The mean values of these parameters were compared among the five plans. All treatment plans met the preset dose requirements for the target volumes and OARs. For nasopharyngeal cancer, VMAT3 and BAOnc demonstrated significantly higher UTCI. For cancer of oral cavity, most beam arrangement showed similar UTCI except ESB, which was relatively lower. For cancer of larynx, there was no significant difference in UTCI among the five-beam arrangement methods. For cancers of maxillary sinus and parotid gland, the two BAO methods showed marginally higher UTCI among all the five methods. Individual methods showed dosimetric advantages on certain aspects, and the UTCI of the BAO treatment plans are marginally greater in the case of maxillary sinus and parotid gland. However, if treatment time was included into consideration, VMAT plans would be recommended for cancers of the nasopharynx, oral cavity, and larynx.

Leung WS ，Wu VWC ，Liu CYW ，Cheng ACK ... -  《Journal of Applied Clinical Medical Physics》