Clinical performance evaluation of O-Ring Halcyon Linac: A real-world study

BACKGROUND

Radiation therapy, especially the development of linear accelerators, plays a key role in cancer management. The fast-rotating coplanar O-ring Halcyon Linac has demonstrated many advantages. The previous literature has mainly focused on the machine parameters and plan quality of Halcyon, with a lack of relevant research on its clinical application.

AIM

To evaluate the clinical performance of the O-ring Halcyon treatment system in a real-world application setting.

METHODS

Data from sixty-one patients who were treated with the Halcyon system throughout the entire radiotherapy process in Peking Union Medical College Hospital between August 2019 and September 2020 were retrospectively reviewed. We evaluated the target tumour response to radiotherapy and irradiation toxicity from 1 to 3 mo after treatment. Dosimetric verification of Halcyon plans was performed using a quality assurance procedure, including portal dosimetry, ArcCHECK and point dose measurements for verification of the system delivery accuracy.

RESULTS

Of the 61 patients in the five groups, 16, 12, 7 and 26 patients had complete response, partial response, progressive disease and stable disease, respectively. No increase in the irradiated target tumour volume was observed when separately evaluating the local response. Regarding irradiation toxicity, no radiation-induced deaths were observed. Thirty-eight percent (23/61 patients) had no radiation toxicity after radiotherapy, 56% (34/61 patients) experienced radiation toxicity that resolved after treatment, and 6% (4/61 patients) had irreversible adverse reactions. The average gamma passing rates with a 2% dose difference and 2-mm distance to agreement for IMRT/VMAT/SRT plans were ArcCHECK at 96.4% and portal dosimetry at 96.7%, respectively. All of the validated clinical plans were within 3% for point dose measurements, and Halcyon’s ArcCHECK demonstrated a high pass rate of 99.1% ± 1.1% for clinical gamma passing criteria of 3%/3 mm.

CONCLUSION

The O-ring Halcyon Linac could achieve a better therapeutic effect on the target volume by providing accurate treatment delivery plans with tolerable irradiation toxicity.

Liver phantom design and dosimetric verification in participating institutions for a proton beam therapy in patients with resectable hepatocellular carcinoma: Japan Clinical Oncology Group trial (JCOG1315C)

BACKGROUND AND PURPOSE

In Japan, the first domestic clinical trial of proton beam therapy for the liver was initiated as the Japan Clinical Oncology Group trial (JCOG1315C: Non-randomized controlled study comparing proton beam therapy and hepatectomy for resectable hepatocellular carcinoma). Purposes of this study were to develop a new dosimetric verification system and to carry out a credentialing for the JCOG1315C clinical trial.

MATERIALS AND METHODS

Accuracy and differences in doses in proton treatment planning among participating institutions were surveyed and investigated. We designed and developed a suitable water tank-type liver phantom for a dosimetric verification of proton beam therapy for liver. In a visiting survey of five institutions participating in the clinical trial, we performed the dosimetric verification using the liver phantom and an air-filled ionization chamber.

RESULTS

The shape of the dose distributions calculated in proton treatment planning was characteristic and dependent on the manufacturers of the proton beam therapy system, the proton treatment planning system and the setup at the participating institutions. Widths of the lateral penumbra were 5.8-12.7 mm among participating institutions. The accuracy between the calculated and the measured doses in the proton irradiation was within 3% at five measurement points including both points on the isocenter and off the isocenter.

CONCLUSIONS

These findings confirmed the accuracy of the delivery doses in the institutions participating in the clinical trial, and the clinical trial with integration of all institutions (five institutions) could be initiated.

Simple index for validity of the evaluation point for dosimetric verification results of intensity-modulated radiation therapy using a Farmer-type ionization chamber

PURPOSE

Based on a retrospective analysis, this study aims to develop a simple index for validity of the evaluation point for the dosimetric verification of intensity-modulated radiation therapy (IMRT).

METHODS

The results for the dosimetric verifications of a total of 69 IMRT plans were analyzed in this study. A Farmer-type ion chamber was used as a dose detector, and a solid water-equivalent phantom was used. Index values were obtained by dividing the difference between the maximum and minimum dosages by the mean dosage of the 69 plans, and the values were classified into five groups with index value <4, 4-8, 8-12, 12-16, and >16. A t-test was used to assess the statistical significance of the mean differences of the absolute values of the relative errors among these groups.

RESULTS

We found that there was no significant difference between the groups with index value <4 and 4-8 (p = 0.152); however, there were significant differences between the other groups (p < 0.01). In addition, when the index values were smaller than 8, the pass ratio of 3% tolerance was 96.2% and the pass ratio of 5% tolerance was 99.9%. We observed that the smaller the index value, the smaller the uncertainty of the dose measurement.

CONCLUSIONS

The results obtained in this study may prove to be useful for accurate dosimetric verifications of IMRTs when ion chambers are used.