Elsevier

Radiography

Volume 24, Issue 2, May 2018, Pages 142-145
Radiography

A service evaluation of on-line image-guided radiotherapy to lower extremity sarcoma: Investigating the workload implications of a 3 mm action level for image assessment and correction prior to delivery

https://doi.org/10.1016/j.radi.2017.11.007Get rights and content

Highlights

  • A service evaluation of cone beam imaging for lower limb sarcoma was performed.

  • A specified action level for image correction was used during IGRT.

  • The action level was used for daily IGRT, SE correction and weekly assessment.

  • The strategy can be used to minimise imaging frequency and concomitant exposures.

Abstract

Introduction

Although all systematic and random positional setup errors can be corrected for in entirety during on-line image-guided radiotherapy, the use of a specified action level, below which no correction occurs, is also an option. The following service evaluation aimed to investigate the use of this 3 mm action level for on-line image assessment and correction (online, systematic set-up error and weekly evaluation) for lower extremity sarcoma, and understand the impact on imaging frequency and patient positioning error within one cancer centre.

Methods

All patients were immobilised using a thermoplastic shell attached to a plastic base and an individual moulded footrest. A retrospective analysis of 30 patients was performed. Patient setup and correctional data derived from cone beam CT analysis was retrieved. The timing, frequency and magnitude of corrections were evaluated. The population systematic and random error was derived.

Results

20% of patients had no systematic corrections over the duration of treatment, and 47% had one. The maximum number of systematic corrections per course of radiotherapy was 4, which occurred for 2 patients. 34% of episodes occurred within the first 5 fractions. All patients had at least one observed translational error during their treatment greater than 0.3 cm, and 80% of patients had at least one observed translational error during their treatment greater than 0.5 cm. The population systematic error was 0.14 cm, 0.10 cm, 0.14 cm and random error was 0.27 cm, 0.22 cm, 0.23 cm in the lateral, caudocranial and anteroposterial directions. The required Planning Target Volume margin for the study population was 0.55 cm, 0.41 cm and 0.50 cm in the lateral, caudocranial and anteroposterial directions.

Conclusion

The 3 mm action level for image assessment and correction prior to delivery reduced the imaging burden and focussed intervention on patients that exhibited greater positional variability. This strategy could be an efficient deployment of departmental resources if full daily correction of positional setup error is not possible.

Section snippets

Introduction and background

Sarcoma is a relatively rare diagnosis, accounting for 1% of cancer diagnoses; with around 25% of cases occurring in the limbs.1, 2 Surgery is the primary treatment used in the management of sarcoma3 and whilst conservative surgery is the major goal, amputation is indicated in some cases.4 In cases where limb preservation is possible, lower limb sarcomas are typically treated with conservative surgery and adjuvant or neo-adjuvant radiotherapy and this combination achieves high rates of local

Methods

Approval was gained from the institution's clinical governance committee and The University of Liverpool Ethics Committee to conduct a retrospective imaging evaluation. All patients treated with radiotherapy for sarcoma of the lower limb between 25th May 2015 and 25th May 2016 were initially identified by treatment site in the MOSAIQ (Version 2.5 Elekta, Sweden) electronic booking system and the Webpublisher (V2.3.25 Phillips, The Netherlands) electronic prescription software at The Christie

Results

30 consecutive patients with complete CBCT data sets were evaluated. Treatment subsites for the 30 evaluated patients are recorded in Table 2. 18 received postoperative radiotherapy, 11 received preoperative radiotherapy and 1 patient received radiotherapy alone. 826 fractions were delivered, the mean number of fractions per patient was 27.5 (range 20–30) and dose ranged between 45 and 60 Gy.

436 CBCT images were delivered (per patient: range 8–22, median 13.5, mean of 14.5; per fraction: mean

Discussion

Although daily on-line image analysis and correction with no specified action level will achieve the largest reduction of systematic and random error, it is believed to be time consuming and labour intensive,17, 18 and there is a duty to keep concomitant exposure as low as reasonably possible.19 For sarcoma of the limb, patient specific factors such as: pre/postoperative status; tumour location in the limb; and limb swelling could potentially affect the magnitude and fluctuation of

Conclusion

This evaluation aimed to investigate the impact of a 3 mm action level for online assessment and correction in our departmental IGRT practice for lower extremity sarcoma. This strategy reduced the imaging burden and focussed intervention on patients that exhibited greater positional variability. The evaluation suggests that the impact of image matching and positional correction was greatest at the beginning of treatment, and that time trend errors were small, despite common site-specific

Conflict of interest

None.

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