Assessment of set-up discrepancies using daily portal imaging during radiotherapy treatment for patients with spine and bone metastases

Abstract

It is well established that patients with bone metastases get good pain relief from radiotherapy. The aim of treatment is to achieve maximum pain relief with minimum morbidity. Accuracy and reproducibility of the patient's position are fundamental to the successful delivery of radiation therapy. It has been recognised for many years, that the accuracy of patient positioning will improve the success of radiation treatment. A previous study carried out in the department showed that the use of only a single tattoo for the set-up of palliative patients resulted in poor accuracy. The aim of this study was to assess if the addition of extra skin marks improved the set-up accuracy of palliative patients being treated for spine and bone metastases. A protocol was implemented detailing the extra skin marks to be used. Daily portal images were acquired and analysed retrospectively using anatomy matching. The results obtained were then compared with those of the previous study. The use of extra skin marks resulted in a total of 45% of images within 5 mm tolerance compared with 36% of images in patients treated with a single centre tattoo. Also, the number of images with deviations greater than 15 mm was reduced by more than 50% with the addition of extra skin marks. This study has shown that extra skin marks do increase the set-up accuracy in palliative patients treated for spine and bone metastases. Therefore, the practice of using extra skin marks has become standard protocol for all palliative patients within the department.

Set-up variation in palliative radiotherapy: one versus three skin localisation marks

“…Young and Blyth also found an increased incidence of images within 5 mm tolerance for multiple marks (45%) compared to a single skin mark set-up (36%) for bony and spinal treatment sites. 6 Deviations over 15 mm are significantly reduced using multiple skin marks, with less than 1% of images from Group 2 falling beyond this threshold, a similar finding to Young and Blyth. 6 Clinically, it is important to reduce the incidence of such large gross deviations, particularly when using a hypofractionated schedule.…”

“…6 Deviations over 15 mm are significantly reduced using multiple skin marks, with less than 1% of images from Group 2 falling beyond this threshold, a similar finding to Young and Blyth. 6 Clinically, it is important to reduce the incidence of such large gross deviations, particularly when using a hypofractionated schedule. Errors of this magnitude could result in geographic miss of the target, resulting in an excessively high dose to normal tissues, potentially increasing toxicity and reducing the efficacy of treatment.…”

“…Furthermore, the literature regarding the optimal number of skin marks to be used for accurate patient set-up is sparse. A study conducted by Young and Blyth, 6 concluded that the use of extra skin marks results in an increased accuracy in patient set-up for bone and spinal RT. Similarly, Easton et al 7 found that the addition of lateral marks reduced the rate of patient position re-adjustment for spinal RT.…”