Feasibility of surface guided radiotherapy for patient positioning in breast radiotherapy versus conventional tattoo-based setups- a systematic review

Abstract

Background: Traditionally tattoos are used for patient setup in radiotherapy. However they may pose challenges for the radiotherapists to achieve precise patient alignment, and serve as a permanent visual reminder of the patient's diagnosis and often challenging cancer journey. The psychological impact of tattoos has been recognized in recent years. The increasing complexity of treatment techniques and the utilization of hypofractionated regimes, requires an enhanced level of accuracy and safety. Surface guided radiotherapy (SGRT) enables improvements in the accuracy and reproducibility of patient isocentric and postural alignment, enhanced efficiency, and safety in breast radiotherapy.

Purpose: The aim of this review was to compare the accuracy and reproducibility of SGRT to conventional tattoo-based setups in free-breathing breast radiotherapy and to determine if SGRT can reduce the frequency of routine image guided radiotherapy (IGRT).

Materials and methods: A systematic literature review was performed as per PRISMA guidelines. Papers identified through PubMed, Embase, Web of Science and Google Scholar database searches between 2010 and 2021, were critically appraised. Systematic, random, mean residual errors and 3D vector shifts as determined by IGRT verification were analysed.

Results: A review of 13 full papers suggests SGRT improves the accuracy and reproducibility of patient setup in breast radiotherapy with consistent reductions in the residual errors. There appears to be a good correlation between SGRT setups and radiographic imaging. The frequency of IGRT and the corresponding dose could potentially be reduced. Additionally, SGRT improves treatment efficiency.

Conclusion: SGRT appears to have improved the accuracy and reproducibility of patient setup and treatment efficiency of breast radiotherapy compared to conventional tattoo/laser-based method, with the potential to reduce the frequency of routine IGRT. The reliance on tattoos in breast radiotherapy are likely to become obsolete with positive implications for both patients and clinical practice.

Keywords: Breast cancer; Setup accuracy; Surface guided radiotherapy; Tattooless; Tattoos.

Fig. 1

Flowcharts depicting the steps in a typical breast radiotherapy patient setup using conventional tattoos and lasers (process A) vs SGRT (process B).

Fig. 2

PRISMA flow diagram of information through the phases of the systematic review and corresponding results of the database search, screening and exclusion.

Fig. 3

Mean systematic errors are displayed for both setup modalities (tattoo/laser and SGRT). Mean is representative of the mean of all the individual patient mean errors in the 3 translational directions (VERT- vertical, LNG- longitudinal, LAT-lateral). A reduction in the mean systematic errors in the vertical, longitudinal, and lateral directions are seen when SGRT is utilised (indicated by the striped bars). The treatment sites include whole breast, partial breast irradiation, and proton beam chest wall irradiation. Significant improvements are noted in the lateral direction for Cravo et al and all 3 directions for Batin et al.

Fig. 4

The histogram indicates the mean translational random errors for tattoo (solid) and SGRT setups (striped bars). Random error is defined as the mean or root mean square (RMS) of the standard deviation (SD) of all the individual patients' means. Similar to the mean systematic errors, there is a corresponding reduction in the magnitude of the random errors in all 3 directions when SGRT is used to correct the initial patient position.

Fig. 5

Group mean residual setup errors and its SD for the studies reviewed. The histogram represents the mean of all the mean individual patients’ errors. The SD deviation is indicated by the error bars. SD is not reported by Liu et al. The mean patient positional discrepancies are reduced for SGRT setups however in Jimenez et al and Kügele et al (tangent cohort) an improvement in the vertical direction is seen with tattoo/laser-based setups. The distribution and variability of the shifts are consistently lower for SGRT assisted setup. The methodology and analysis used by Liu et al varies from other studies which explains the directional variations despite a reduction in the mean residual setup errors with SGRT.

Fig. 6

3D vector shifts for free-breathing breast radiotherapy patients. A reduction in the average magnitude of the 3D shift corrections were seen with SGRT setups, suggesting improved setup accuracy. Residual setup errors for tattoos were in the range of 2.4–14 mm and 1.8–6 mm with SGRT. Statistically significant differences were noted for Kügele et al (Tangents and locoregional groups) p < 0.01, Stanley et al (p < 0.01), Chang et al (p = 0.02, <0.05)), Kost et al (Tangents- skin mean) p < 0.001) and in lateral direction for Hattel et al (P = 0.0009).

Fig. 7

Group mean residual translational errors + SD for SGRT and IGRT. A good correlation of SGRT to IGRT is seen in Ma et al with comparable residual setup errors and SD for both methods. Similarly, in Deantonio et al, a paired t-test showed non-significant systematic error in the longitudinal (p = 0.69) and lateral (p = 0.67) directions. Only vertical and longitudinal errors were reported as MV portal images were used for image verification. Chang et al observed improved setup accuracy with SGRT compared to tattoo/laser-based setup supported with a substantial reduction in the residual setup errors. The difference in the vector spatial deviation between both methods is statistically significant for SGRT setups (P < 0.05). A higher degree of variability is seen with tattoo-based setups.