Automated noncoplanar treatment planning strategy in stereotactic radiosurgery of multiple cranial metastases: HyperArc and CyberKnife dose distributions.

The purpose of this study was to evaluate and compare the dosimetric effects of HyperArc-based stereotactic radiosurgery (SRS) and a robotic radiosurgery system-based planning using CyberKnife for multiple cranial metastases. In total, 11 cancer patients with multiple cranial metastases (3 to 5 tumors) treated with CyberKnife were examined. These patients were replanned using HyperArc (Varian Medical Systems, Palo Alto, USA). HyperArc plan were designed using 4 noncoplanar arc single-isocenter VMAT in 6 MV flattening filter free mode for simulated delivery with the True beam STx (Varian). The prescription dose was 23 Gy at single fraction. Dosimetric differences and blinded clinician scoring differences were evaluated. Conformity index (CI) and gradient index (GI) were 0.60 ± 0.11 and 3.94 ± 0.74, respectively, for the CyberKnife plan and 0.87 ± 0.08 and 5.31 ± 1.42, respectively, for the HyperArc plan (p < 0.05). Total brain V12-gross tumor volumes (GTVs) for the CyberKnife and HyperArc plans were 5.26 ± 2.83 and 4.02 ± 1.71 cm3, respectively. These results indicate that HyperArc plan showed better CI and total brain V12-GTV, while CyberKnife plan showed better GI. A blinded physician scoring evaluation did not show significant differences between CyberKnife and HyperArc plans. The HyperArc-based SRS plan is comparable with the CyberKnife plan, suggesting a greater potential to emerge as a suitable tool for SRS of multiple brain metastases.

Effect of anatomical change on dose distribution during radiotherapy for maxillary sinus carcinoma: passive scattering proton therapy versus volumetric-modulated arc therapy.

OBJECTIVE:: Maxillary sinus carcinomas are anatomically situated next to many organs at risk (OARs), and anatomical change is often observed during radiotherapy. We analyzed the effect of anatomical change on dose distribution of passive scattering proton therapy (PSPT) and volumetric-modulated arc therapy (VMAT) for 20 patients. METHODS:: The first plans were generated based on the first CT images. The second CT images were acquired after 3 weeks, and the second plans were generated by copying the first plans to the second CT images. The effect of anatomical change was estimated by comparing both plans. RESULTS:: Target volume change was observed in all cases, however, the influence on dose coverage of clinical target volume tended to be small. Alternatively, the doses to almost all OARs were increased. In particular, the increase in the dose to brainstem (p < 0.001) and optic chiasm (p < 0.001) was significantly higher in the second PSPT plan than in the first PSPT plan. Although PSPT is sensitive to anatomical change, the dose to OARs remained significantly lower in PSPT plans than that in VMAT plans. CONCLUSION:: PSPT was confirmed to be more effective than VMAT even the effect of anatomical change was taken into account. Therefore, it is expected that the contralateral vision can be preserved reliably while optimal target coverage is provided. ADVANCES IN KNOWLEDGE:: PSPT allowed significant sparing of OARs even in the result of the second plans affected by the anatomical change. PSPT offers benefits over VMAT in reducing dose to several OARs.

Effect of DIR uncertainty on prostate passive-scattering proton therapy dose accumulation.

Deformable image registration (DIR) is important in dose accumulation. Currently, the impact of DIR-algorithm-associated uncertainties in proton therapy is unclear. Here, we quantify the effect of DIR uncertainties on prostate passive-scattering proton therapy (PSPT) dose accumulation. Ten patients with an intermediate risk for prostate cancer formerly treated by PSPT (PTV D95=78GyE) were studied. Dose distributions from all verification CT images (five images per patient) were warped and accumulated in the planning CT geometries with DIR. The dose-volume histogram parameters (Dmean, V40, and V70) for rectum and bladder were calculated. Two commercially available DIR software packages were employed: Velocity AI (Varian Medical Systems) and RayStation (RaySearch Laboratories). The dice similarity coefficient (DSC) and surface distance, which were calculated between planning CT contours and deformed contours, were used for DIR validation, with the relationship between the dose parameter and DIR uncertainty ultimately investigated. On average, when using RayStation, the DSC increased by 0.14 and surface distance decreased by 6.4mm, as compared to Velocity. For Dmean, V40, and V70 to the rectum, the average differences between the RayStation and Velocity were 3.9GyE, 5.5%, and 3.2%, respectively. For the bladder, the differences were 5.2GyE, 5.8%, and 5.4%, respectively. The maximum differences in V40 between RayStation and Velocity were 14.4% and 22.8% for the rectum and bladder, respectively, when the average DSC and surface distance differences were more than 0.14 and 6.4mm, respectively. Such results suggest that DIR uncertainties might significantly affect prostate PSPT dose accumulations.

Feasibility of CBCT-based proton dose calculation using a histogram-matching algorithm in proton beam therapy.

The aim of this study was to confirm On-Board Imager cone-beam computed tomography (CBCT) using the histogram-matching algorithm as a useful method for proton dose calculation. We studied one head and neck phantom, one pelvic phantom, and ten patients with head and neck cancer treated using intensity-modulated radiation therapy (IMRT) and proton beam therapy. We modified Hounsfield unit (HU) values of CBCT and generated two modified CBCTs (mCBCT-RR, mCBCT-DIR) using the histogram-matching algorithm: modified CBCT with rigid registration (mCBCT-RR) and that with deformable image registration (mCBCT-DIR). Rigid and deformable image registration were applied to match the CBCT to planning CT. To evaluate the accuracy of the proton dose calculation, we compared dose differences in the dosimetric parameters (D2% and D98%) for clinical target volume (CTV) and planning target volume (PTV). We also evaluated the accuracy of the dosimetric parameters (Dmean and D2%) for some organs at risk, and compared the proton ranges (PR) between planning CT (reference) and CBCT or mCBCTs, and the gamma passing rates of CBCT and mCBCTs. For patients, the average dose and PR differences of mCBCTs were smaller than those of CBCT. Additionally, the average gamma passing rates of mCBCTs were larger than those of CBCT (e.g., 94.1±3.5% in mCBCT-DIR vs. 87.8±7.4% in CBCT). We evaluated the accuracy of the proton dose calculation in CBCT and mCBCTs for two phantoms and ten patients. Our results showed that HU modification using the histogram-matching algorithm could improve the accuracy of the proton dose calculation.