Dosimetric advantage of ring-mounted Halcyon linac in radiation therapy for lung tumors
Abstract
Objective
To systematically compare the dosimetric performance of two radiotherapy devices, Halcyon and TrueBeam, in intensity-modulated radiotherapy (IMRT) plans for non-small cell lung cancer (NSCLC), providing a reference for hospitals to optimize NSCLC radiotherapy based on different devices.
Materials and Methods
A retrospective analysis was conducted on 102 NSCLC patients who received curative radiotherapy. All initial plans were designed on the Eclipse 15.6 system based on TrueBeam parameters (6MV FF photon beam, IMRT, dose grid of 2.5mm). New plans were re-optimized using Halcyon parameters while maintaining the same field directions and other parameters. The comparison indicators included: planning target volume (PTV) dose metrics (<inline-formula> <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="25334035v1_inline1.gif"/> </inline-formula>, D2%, D98%, Dmean, V98%, conformity index CI, homogeneity index HI); dose metrics for organs at risk (OARs) (Lungs: V5-V60, MLD; Heart: V5-V60, Dmean; remaining normal tissues NT: V5-V30); monitor units (MUs) counts and plan complexity index (PCI). Differences were analyzed using paired t-tests or Wilcoxon tests in SPSS 27.0, and the correlation between MUs and PCI was assessed.
Results
The PTV conformity index (CI) of Halcyon plans was significantly superior to that of TrueBeam (0.75±0.12 vs. 0.73±0.12, P<0.001). Halcyon’s <inline-formula> <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="25334035v1_inline2.gif"/> </inline-formula> was higher than TrueBeam (6555.20±117.50 cGy vs. 6525.20±99.38 cGy, P<0.001), and V98% was slightly lower than TrueBeam (95.83±11.74% vs. 95.99±11.38%, P=0.046). There were no statistically significant differences in D2%, D98%, Dmean, and HI (P>0.05). Halcyon significantly reduced the volume of lungs, heart, and other normal tissues exposed to low and intermediate doses and lowered the mean lung dose (P<0.001). Halcyon’s MUs were significantly higher than TrueBeam’s (1323.1±374.91 vs. 1121.1±384.84, P<0.001), but its PCI was significantly lower than TrueBeam’s (0.09±0.03 vs. 0.17±0.05, P<0.001), indicating that Halcyon plans are more complex. The correlation between PCI and MUs was weak for Halcyon (R2=0.07), while the correlation was stronger for TrueBeam (R2=0.54).
Conclusion
Compared to TrueBeam, Halcyon demonstrated significant dosimetric advantages: superior target volume dose conformity and effective reduction in the volume of normal tissues (lung, heart, and remaining tissues) exposed to low and intermediate doses, especially in large PTV volumes where low-dose protection for NT was more significant. Although Halcyon plans are more complex and involve higher MUs, the complexity has a lower dependency on MUs, showing greater stability. Halcyon offers a safer treatment device choice for lung cancer patients who require precise dose control and low-dose protection.
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