Dosimetric impact of using a commercial metal artifact reduction tool in carbon ion therapy in patients with hip prostheses

Proton Therapy for Spinal Tumors: A Consensus Statement From the Particle Therapy Cooperative Group

PURPOSE

Proton beam therapy (PBT) plays an important role in the management of primary spine tumors. The purpose of this consensus statement was to summarize safe and optimal delivery of PBT for spinal tumors.

METHODS AND MATERIALS

The Particle Therapy Cooperative Group Skull Base/Central nervous system/Sarcoma Subcommittee consisting of radiation oncologists and medical physicists with specific expertise in spinal irradiation developed expert recommendations discussing treatment planning considerations and current approaches in the treatment of primary spinal tumors.

RESULTS

Computed tomography simulation: factors that require significant consideration include (1) patient comfort, (2) setup reproducibility and stability, and (3) accessibility of appropriate beam angles.

SPINE STABILIZATION HARDWARE

If present, hardware should be placed with cross-links well above/below the level of the primary tumor to reduce the metal burden at the level of the tumor bed. New materials that can reduce uncertainties include polyether-ether-ketone and composite polyether-ether-ketone-carbon fiber implants.

FIELD ARRANGEMENT

Appropriate beam selection is required to ensure robust target coverage and organ at risk sparing. Commonly, 2 to 4 treatment fields, typically from posterior and/or posterior-oblique directions, are used.

TREATMENT PLANNING METHODOLOGY

Robust optimization is recommended for all pencil beam scanning plans (the preferred treatment modality) and should consider setup uncertainty (between 3 and 7 mm) and range uncertainty (3%-3.5%). In the presence of metal hardware, use of an increased range uncertainty up to 5% is recommended.

CONCLUSIONS

The Particle Therapy Cooperative Group Skull Base/Central nervous system/Sarcoma Subcommittee has developed recommendations to enable centers to deliver PBT safely and effectively for the management of primary spinal tumors.

Feasibility of dose calculation for treatment plans using electron density maps from a novel dual-layer detector spectral CT simulator

BACKGROUND

Conventional single-energy CT can only provide a raw estimation of electron density (ED) for dose calculation by developing a calibration curve that simply maps the HU values to ED values through their correlations. Spectral CT, also known as dual-energy CT (DECT) or multi-energy CT, can generate a series of quantitative maps, such as ED maps. Using spectral CT for radiotherapy simulations can directly acquire ED information without developing specific calibration curves. The purpose of this study is to assess the feasibility of utilizing electron density (ED) maps generated by a novel dual-layer detector spectral CT simulator for dose calculation in radiotherapy treatment plans.

METHODS

30 patients from head&neck, chest, and pelvic treatment sites were selected retrospectively, and all of them underwent spectral CT simulation. Treatment plans based on conventional CT images were transplanted to ED maps with the same structure set, including planning target volume (PTV) and organs at risk (OARs), and the dose distributions were then recalculated. The differences in dose and volume histogram (DVH) parameters of the PTV and OARs between the two types of plans were analyzed and compared. Besides, gamma analysis between these plans was performed by using MEPHYSTO Navigator software.

RESULTS

In terms of PTV, the homogeneity index (HI), gradient index (GI), D2%, D98%, and Dmean showed no significant difference between conventional plans and ED plans. For OARs, statistically significant differences were observed in parotids D50%, brainstem in head&neck plans, spinal cord in chest plans and rectum D50% in pelvic plans, whereas the variance remained minor. For the rest, the DVH parameters exhibited no significant difference between conventional plans and ED plans. All of the mean gamma passing rates (GPRs) of gamma analysis were higher than 90%.

CONCLUSION

Compared to conventional treatment plans relying on CT images, plans utilizing ED maps demonstrated similar dosimetric quality. However, the latter approach enables direct utilization in dose calculation without the requirements of establishing and selecting a specific Hounsfield unit (HU) to ED calibration curve, providing an advantage in clinical applications.

Commissioning and Validation of CT Number to SPR Calibration in Carbon Ion Therapy Facility

Purpose

We performed computed tomography (CT)-stopping power ratio (SPR) calibration in a carbon-ion therapy facility and evaluated SPR estimation accuracy.

Materials and Methods

A polybinary tissue model method was used for the calibration of CT numbers and SPR. As a verification by dose calculation, we created a virtual phantom to which the CT-SPR calibration table was applied. Then, SPR was calculated from the change in the range of the treatment planning beam when changing to 19 different CT numbers, and the accuracy of the treatment planning system (TPS) calculation of SPR values from the CT-SPR calibration table was validated. As a verification by measurement, 5 materials (water, milk, olive oil, ethanol, 40% K2HPO4) were placed in a container, and the SPR was obtained by measurement from the change in the range of the beam that passed through the materials.

Results

The results of the dose calculations of the TPS showed that the results agreed within 1% for the lower CT numbers up to 1000 HU, but there was a difference of 3.0% in the higher CT number volume. The difference between the SPR calculated by TPS and the SPR caused by the difference in the energy of the incident particles agreed within 0.51%. The accuracy of SPR estimation was measured, and the error was within 2% for all materials tested.

Conclusion

These results indicate that the SPR estimation errors are within the range of errors that can be expected in particle therapy. From commissioning and verification results, the CT-SPR calibration table obtained during this commissioning process is clinically applicable.

Results of salvage treatment with CyberKnife® fractioned radiosurgery in recurrent large chordoma

AIM

Chordomas and chondrosarcomas are locally destructive tumors with high progression or recurrence rates after initial multimodality treatment. This report examined the role of radiosurgery in patients who were considered inoperable after the recurrence of large chordoma disease having undergone previous surgery and/or radiotherapy.

METHODS

All patients who were referred to Okmeydani Education and Research Hospital between 2012 and 2019 for treatment of recurrent or metastatic chordoma and considered not suitable for surgical treatment were included in the study. We included patients presenting with recurrent or metastatic chordoma, those who had undergone surgery and/or radiotherapy and were now considered to be surgically inoperable, patients whose tumors could lead to severe neurologic or organ dysfunction when resected, and those who underwent salvage treatments for definitive or palliative purposes with radiosurgery. After radiosurgical salvage therapy was performed on 13 patients using a CyberKnife® device, the effect of this treatment in terms of local control and survival and the factors that might affect it was investigated. Thirteen lesions were local (in-field) recurrence, and five lesions were closer to the primary tumor mass or seeding metastatic lesions. Tumor response was evaluated using the Response Evaluation Criteria for Solid Tumors (RECIST) system and volumetric analysis.

RESULTS

The median age of the 13 patients was 59 years, and the median tumor volume of 18 lesions was 30.506 cc (R: 6884.06-150,418.519 mL). The median dose was 35 Gy (R: 17.5-47.5), the median fraction was 5 (R: 1-5), and the median biological effective dose BED_2.45 was 135 Gy (R: 63.82-231.68). The median time for radiosurgery was 30 months after the first radiotherapy and 45 months after the last surgery. The median follow-up time was 57 (R: 15-94) months. The progression-free survival was 24 months. The median survival was 33.9 months. Local control was achieved in 84.6% of patients after 1 year, and 76.9% after 2 years, with the mass shrinking or remaining stable. Survival after recurrence was 69.2% for the 1st year, 61.5% for the 2nd year, and 53.8% for the 5th year.

CONCLUSION

In patients with recurrent and surgically inoperable chordomas, stereotactic body radiation therapy (SBRT) is a reliable and effective treatment method. Promising result has been obtained with radiosurgery treatment under local control of patients.

LEVEL OF EVIDENCE

Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.