Clinical Investigation
Evaluation of Image-Guidance Strategies in the Treatment of Localized Prostate Cancer

https://doi.org/10.1016/j.ijrobp.2007.07.2371Get rights and content

Purpose

To compare different image-guidance strategies in the alignment of prostate cancer patients. Using data from patients treated using daily image guidance, the remaining setup errors for several different strategies were retrospectively calculated.

Methods and Materials

The alignment data from 74 patients treated with helical tomotherapy were analyzed, resulting in a data set of 2,252 fractions during which a megavoltage computed tomography image was used for image guidance with intraprostatic metallic fiducials. Given the daily positional adjustments, a variety of protocols, differing in imaging frequency and method, were retrospectively studied. The residual setup errors were determined for each protocol.

Results

As expected, the systematic errors were effectively reduced with imaging. However, the random errors were unaffected. Even when image guidance was performed every other day with a running mean of the previous displacements, residual setup errors >5 mm occurred in 24% of all fractions. This frequency increased to about 40% if setup errors >3 mm were scored.

Conclusion

Setup errors increased with decreasing frequency of image guidance. However, residual errors were still significant at the 5-mm level, even with imaging was performed every other day. This suggests that localizations must be performed daily in the set up of prostate cancer patients during a course of external beam radiotherapy.

Introduction

Image guidance (IG) has become increasingly popular for the set up of patients with localized prostate cancer undergoing external beam radiotherapy. Specifically for this subset of patients, ample data is available reporting the setup variations observed with a variety of image procedures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. However, significant controversy still exists regarding the adequacy, accuracy, and method to follow for individual imaging techniques. The use of implanted markers located with a variety of imaging methods is accepted as a localization technique. The frequency of imaging throughout a fractionated course of radiotherapy and the method of processing the setup data obtained throughout the course are still being debated 13, 14. Patient- vs. population-based recipes have been suggested for different techniques 15, 16, mostly in an effort to juggle the accuracy of localization vs. the cost associated with imaging, in terms of machine time or patient imaging dose, or both.

In our current clinical practice at M.D. Anderson Cancer Center Orlando, all patients have intraprostatic metallic fiducials implanted before therapy (17). All patients underwent imaging daily before each fraction. These daily scans are used to correct the patient's position before each treatment session using the location of the metallic fiducials. However, IG affects the traditional treatment workflow and can increase the patient's radiation dose. Although the volume that is imaged and the associated imaging radiation doses are modest, daily imaging should be evaluated for whether its benefit outweighs these disadvantages. Therefore, the investigation of optimal IG schedules and strategies is important.

In this study, daily IG was compared with different IG protocols that require less-frequent imaging. The protocols were used in a previous study from our center that analyzed localization in head-and-neck cancer patients (18). Eight such imaging protocols were retrospectively studied in a large number of prostate cancer patients for whom daily localization data were available. The scenarios ranged from using no IG to using IG with every other fraction. The remaining systematic and random setup errors for the patient population were calculated for each scenario. The frequency of residual setup errors was also analyzed for each scenario. These data allowed an assessment of patient positioning accuracy and precision while tracking the imaging frequency.

Section snippets

Methods and Materials

Daily alignment data were available for 74 prostate cancer patients treated with helical tomotherapy on the Hi-Art II unit (TomoTherapy, Madison WI) (19). The range of fractions per patient was 10 to 39. The number of fractions per patient varied because of the use of different fractionation schemes. A total of 2,252 image-guided treatment sessions were available for analysis, with an average of 30 alignments per patient. All alignments were performed with intraprostatic implanted metallic

Results

A summary of the actual data from the daily image-guided sessions is provided in Table 1. These data show the setup corrections performed for the 74 patients (2,252 fractions). The systematic couch drop in the anteroposterior direction and the related systematic couch shift in the superoinferior direction were manifested in the 8.72-mm and −2.8-mm respective mean systematic setup errors M. The mean random errors were in the 2–3-mm range. These were in agreement with the random setup errors

Discussion

In the treatment of localized prostate cancer with external beam radiotherapy, controversy still exists about the need for daily localization vs. other strategies to adjust for interfraction variations of the target location 13, 16. If daily localization is considered to provide the best alignment strategy to correct for interfraction location variations, the cost of daily IG in terms of increased dose and in-room time is a consideration that must be weighed against this benefit. Multiple

Conclusion

Systematic errors throughout the treatment course can be reduced with strategies that involve infrequent imaging. However, random setup errors were not eliminated with any of the imaging strategies investigated in the present study. Investigating various imaging strategies, the proportion of fractions associated with significant localization errors increased with decreasing frequency of IG. Treatment margins would have to be increased significantly to accommodate for these positional

References (25)

Cited by (95)

  • Magnetic Resonance Imaging for Target Delineation and Daily Treatment Modification

    2018, Seminars in Radiation Oncology
    Citation Excerpt :

    Additional reductions in margin can be achieved with the use of online and offline plan adaptation techniques which may help with removing some contributing factors from the systematic component of the margin recipe.34,35 The need for daily in-room imaging to correct for interfraction motion and deformation of the target has been investigated extensively for different treatment sites, using a variety of standard in-room imaging modalities.36-41 Overall these studies have shown some level of improvement in the treatment accuracy with daily imaging with the extent of effect on the dose accuracy depending on the type of treatment (IMRT vs conformal 3D) and the treatment site.

View all citing articles on Scopus

Supported in part by a grant from Tomotherapy Inc.

The contents are solely the responsibility of the authors and do not necessarily represent the official views of TomoTherapy, Inc.

Conflict of interest: M.D. Anderson Cancer Center Orlando received a research grant from Tomotherapy Inc.

View full text