Fiducial marker position affects target volume in stereotactic lung irradiation

Abstract

Real-time tracking systems of moving respiratory targets such as CyberKnife,Radixact,or Vero4DRT are an advanced robotic radiotherapy device used to deliver stereotactic body radiotherapy (SBRT). The internal target volume (ITV) of lung tumors is assessed through a fiducial marker fusion using four-dimensional computed tomography (CT). It is important to minimize the ITV to protect normal lung tissue from exposure to radiation and the associated side effects post SBRT. However, the ITV may alter if there is a change in the position of the fiducial marker with respect to the tumor. This study investigated the relationship between fiducial marker position and the ITV in order to prevent radiation exposure of normal lung tissue, and correct target coverage. Materials and methods: This study retrospectively reviewed 230 lung cancer patients who received a fiducial marker for SBRT between April 2015 and September 2021. The distance of the fiducial marker to the gross tumor volume (GTV) in the expiratory (d ex ) and inspiratory (d in ) CT, and the ratio of the ITV/V(GTV ex ), were investigated. Results: Upon comparing each lobe, although there was no significant difference in the d diff and the ITV/V(GTV ex ) between all lobes for d ex < 10 mm, there was significant difference in the d diff and the ITV/V(GTV ex ) between the lower and upper lobes for d ex ≥ 10 mm (p < 0.05). Moreover, there was significant difference in the d diff and the ITV/V(GTV ex ) between d ex ≥10 mm and d ex < 10 mm in all lung regions (p < 0.05). Conclusion:The ITV that had no margin from GTVs increased when d ex was ≥10 mm for all lung regions (p < 0.05). Furthermore, the increase in ITV tended to be greater in the lower lung lobe. These findings can help decrease the possibility of adverse events post SBRT, and correct target coverage.

Intra‐ and inter‐fractional variations of tumors with fiducial markers measured using respiratory‐correlated computed tomography images for respiratory gated lung stereotactic body radiation therapy

“…They suggested that an FM inserted within 30 mm of the lung tumor represented tumor motion with an error within 3 mm in many patients. These reports 25,30,31 on intrafractional variation support our findings: D max values of the FMs for D p ≤ 26 mm were smaller than those of the FMs for D p > 26 mm in all directions. Considering our results, the prior reports on intra-fractional variation, 25,30,31 and the distance from the tumor where the FM can be inserted into the bronchus, 26 mm may be a reasonable distance between the FM and the lung tumor.…”

“…Only a few studies have indicated the specific distances between tumors and FMs. 25,30,31 Akasaka et al 25 analyzed the three-dimensional distance of the coiled FM to the lung tumor in CT scans for planning at the expiratory and inspiratory phases (D diff ) and the ratio of ITV to gross tumor volume (GTV) (ITV/V GTV ) created by 4D-CT and CT scans at the inspiratory phase for treatment planning. They showed that D diff and ITV/V GTV were smaller when the distance between the edges of the tumor and the FM was less than 10 mm.…”

“…Only a few studies have indicated the specific distances between tumors and FMs. 25 , 30 , 31 Akasaka et al. 25 analyzed the three‐dimensional distance of the coiled FM to the lung tumor in CT scans for planning at the expiratory and inspiratory phases (D diff ) and the ratio of ITV to gross tumor volume (GTV) (ITV/V GTV ) created by 4D‐CT and CT scans at the inspiratory phase for treatment planning.…”

“…Only a few studies have indicated the specific distances between tumors and FMs 25,30,31 . Akasaka et al 25 .…”

“…A strong correlation was defined as a Pearson's | R | > 0.70. The Wilcoxon rank‐sum test was used to compare D max values between the two D p groups 25 . To compare inter‐fractional variation between the three groups, based on the two D p groups and the vertebral group, the Kruskal–Wallis test with Steel–Dwass test was used for analysis.…”