A retrospective evaluation of the dosimetric parameters; Conformity Index and Gradient Index for patients with spine metastases treated with SBRT

Congress:

2023 ASM

Poster Number:

C-285

Type:

Scientific Exhibit

Keywords:

Oncology, Cone beam CT, Dosimetry, Cancer

Authors:

N. Mitina, T. Peterson, R. Guidi, C. Hargrave

DOI:

10.26044/ranzcr2023/C-285

DOI-Link:

https://dx.doi.org/10.26044/ranzcr2023/C-285

Purpose

Stereotactic body radiation therapy (SBRT) is an established, effective treatment for spinal metastases [8].It utilises advanced imaging technology and delivery techniques to deliver high doses of radiation over a shorter course. SBRT offers patients rapid and durable pain reliefwhileachievingsteeper dose gradients near critical structures such as the spinal cord, cauda equina and nerve roots. Parameters used for plan evaluation in SBRT include Conformity Index (CI) and Gradient Index (GI) [1]. CI is a metric used to evaluate how tightly the prescription dose is conforming to...

Methods and materials

A systematic literature review was conducted on the PubMed MEDLINE database search to assess current published CI and GI values for spine metastases treated with SBRT. Collection of data included a retrospective analysis of 49 SBRT treatment plans for patients treated for spine metastases at ROPART from April 2016 until March 2023. Human research ethics committee (EC00167) classified the project as exempt from ethical approval. The following data was collected: CI and GI for all plans were calculated using equations seen in Figure 1 and...

Results

Literature review: The systematic literature review employed a key word search including the following; ‘stereotactic spine radiotherapy conformity index’ and ‘stereotactic spine radiotherapy conformation’. The review (Figure 5) identified four suitable articles [2,3,4,5]. Only articles that included the Paddick Conformity Index were included. These articles confirmed significant discrepancy in reported CI and GI values for SBRT spine treatment plans. Only one study [2] reported results for Cervical, Thoracic and Lumbar spine treatments separately. Published mean CI and GI values in these articles ranged from 0.52...

Conclusion

The results of this pilot study are subect to following limiting factors: Small sample size – in paticular once sub-catagorised into vertabral body level and complexity rating. Some volumes included in this study featured characteristics that may have affected the CI and GI values achieved. For example soft tissue extension of GTV, post surgical hardware, destructive lesions encompassing entire segments, rib involvment, additional adjacent previously treated PTVs. Date range for collected data – the departmental level of experience with planning VMAT SBRT spine lesions has...

Personal information

References

ICRU report 91 on prescribing, recording, and reporting of stereotactic treatments with small photon beams. Oxford University press July 2017 H. Acar et al. Dosimetric comparison of robotic- and LINAC-based treatment of spine stereotactic body radiotherapy. Medical Dosimetry 47 (2022) 348–355 J. Yang et al. Dosimetric evaluation of 4 different treatment modalities for curative-intent stereotactic body radiation therapy for isolated thoracic spinal metastases. Medical Dosimetry 41(2016)105–112 F. Li et al. Is Halcyon feasible for single thoracic or lumbar vertebral segment SBRT? J Appl Clin Med...

Fig 1: Figure 1 CI Equation - ICRU 91 [1]

Fig 2: Figure 2 GI Equation - ICRU 91 [1]

Fig 3: Figure 3 ISRC Bony anatomic classification - Cox et al. (2012) [6]

Fig 4: Figure 4 Examples of complexity rating for PTV volumes of SBRT spine plans at...

Fig 5: Figure 5 Literature Review

Table 1: Table 1 CI and GI of SBRT spine plans separated by spine level (Radiation...

Table 2: Table 2 CI and GI of SBRT spine plans separated by complexity level (Radiation...