Use of skin markers and electronic portal imaging to improve verification of tangential breast irradiation

Factors impacting on patient setup analysis and error management during breast cancer radiotherapy

Radiotherapy is required to deliver an accurate dose to the tumor while protecting surrounding normal tissues. Breast cancer radiotherapy involves a number of factors that can influence patient setup and error management, including the immobilization device used, the verification system and the patient's treatment position. The aim of this review is to compile and discuss the setup errors that occur due to the above-mentioned factors. In view of this, a systematic search of the scientific literature in the Medline/PubMed databases was performed over the 1990-2021 time period, with 93 articles found to be relevant for the study. To be accessible to all, this study not only aims to identify factors impacting on patient setup analysis, but also seeks to evaluate the role of each verification device, board immobilization and position in influencing these errors.

Three-dimensional dose evaluation in breast cancer patients to define decision criteria for adaptive radiotherapy

BACKGROUND

Dose-guided adaptive radiation therapy (DGART) is the systematic evaluation and adaptation of the dose delivery during treatment for an individual patient. The aim of this study is to define quantitative action levels for DGART by evaluating changes in 3D dose metrics in breast cancer and correlate them with clinical expert evaluation.

MATERIAL AND METHODS

Twenty-three breast cancer treatment plans were evaluated, that were clinically adapted based on institutional IGRT guidelines. Reasons for adaptation were variation in seroma, hematoma, edema, positioning or problems using voluntary deep inspiration breath hold. Sixteen patients received a uniform dose to the breast (clinical target volume 1; CTV1). Six patients were treated with a simultaneous integrated boost to CTV2. The original plan was copied to the CT during treatment (re-CT) or to the stitched cone-beam CT (CBCT). Clinical expert evaluation of the re-calculated dose distribution and extraction of dose-volume histogram (DVH) parameters were performed. The extreme scenarios were evaluated, assuming all treatment fractions were given to the original planning CT (pCT), re-CT or CBCT. Reported results are mean ± SD.

RESULTS

DVH results showed a mean dose (Dmean) difference between pCT and re-CT of -0.4 ± 1.4% (CTV1) and -1.4 ± 2.1% (CTV2). The difference in V95% was -2.6 ± 4.4% (CTV1) and -9.8 ± 8.3% (CTV2). Clinical evaluation and DVH evaluation resulted in a recommended adaptation in 17/23 or 16/23 plans, respectively. Applying thresholds on the DVH parameters: D_mean CTV, V95% CTV, D_max, mean lung dose, volume exceeding 107% (uniform dose) or 90% (SIB) of the prescribed dose enabled the identification of patients with an assumed clinically relevant dose difference, with a sensitivity of 0.89 and specificity of 1.0. Re-calculation on CBCT imaging identified the same plans for adaptation as re-CT imaging.

CONCLUSIONS

Clinical expert evaluation can be related to quantitative DVH parameters on re-CT or CBCT imaging to select patients for DGART.

Actual target coverage after setup verification using surgical clips compared with external skin markers in postoperative breast cancer radiation therapy

PURPOSE

After changing from offline setup verification to online setup verification using external skin markers in breast cancer patients, we noticed an increase in localized acute skin toxicity beneath the markers. Also, in vivo 3-dimensional dose measurements showed deviations between the delivered and the planned dose distributions; therefore, we investigated the accuracy of setup verification using surgical clips in the tumor bed, with a focus on target coverage of whole breast and tumor bed.

METHODS AND MATERIALS

Orthogonal kilovoltage images were acquired before every fraction in 35 breast cancer patients, deriving an online 3-dimensional setup error by matching on external skin markers. In retrospect, a rematch was performed using surgical clips. For 155 fractions (ie, 5-6 fractions/patient), a cone beam computed tomography (CT) scan was available. Analysis concerned: (1) visibility of the clips, (2) migration of the clips, (3) comparison of setup errors according to both match methods, and (4) comparison of target coverage by recalculating the dose on the online setup-corrected cone beam CT scan with the patient setup according to both match methods. External validation of the surgical clip-based online setup verification was performed in 23 patients by analyzing kilovoltage images of 100 fractions, obtained after treatment.

RESULTS

All types of surgical clips could be visualized. The clip to center-of-mass distance decreased on average by 2 mm (standard deviation, 1) over the course of treatment. Setup differences between match methods were on average <0.5 mm in all directions. The reconstructed dose distributions showed standard deviations of volumes receiving 95% or 107% of prescribed dose and mean dose of the breast and boost planning target volume were similar for the planning CT and the cone beam CTs, for both match procedures. An external validation in 23 patients showed reassuring setup errors <2 mm.

CONCLUSIONS

Online setup verification using surgical clips results in comparable setup corrections and target volume coverage as verification using skin markers. By omitting skin markers acute skin toxicity beneath the markers is prevented.

Electronic portal images (EPIs) based position verification for the breast simultaneous integrated boost (SIB) technique

BACKGROUND AND PURPOSE

To develop a method based on electronic portal images (EPIs) for the position verification of breast cancer patients that are treated with a simultaneous integrated boost (SIB) technique.

METHOD

3D setup errors of the breast outline and the thoracic wall were determined from EPIs of the tangential treatment fields and anterior posterior (AP) verification field. The method was verified with repeated CT scans of 38 patients with an average setup error larger than 5 mm.

RESULT

The 3D position deviation of the boost volume can best be determined from the position deviation of the breast outline in the ventrodorsal direction and the thoracic wall in the lateral and longitudinal directions from the tangential and AP EPIs. The method gives an average overestimation of the deviation of the boost volume in the ventrodorsal, lateral and longitudinal directions by 28%, 20% and 6%, respectively and an average underestimation of the deviation of the whole breast by 32%, 17% and 39%.

CONCLUSIONS

The described method is superior to using tangential EPIs only and is recommended for position verification of breast cancer patients that are treated with a SIB technique if no Cone beam CT (CBCT) or fiducial markers can be used.

Correction of systematic set-up error in breast and head and neck irradiation through a no-action level (NAL) protocol

PURPOSE

To quantify systematic and random patient set-up errors in breast and head and neck conventional irradiation and to evaluate a no-action level (NAL) protocol for systematic set-up error off-line correction in head and neck cancer and breast cancer patients.

MATERIAL AND METHODS

Verification electronic portal images of orthogonal set-up fields were obtained daily for the initial four consecutive fractions for 20 patients treated for breast cancer and for 20 head and neck cancer patients. The calculated systematic error was used to shift the isocentre accordingly on the fifth treatment day. From then until the end of the treatment course, pair orthogonal portal images of set-up fields were obtained weekly. To assess the impact of the protocol, pre- and post-correction systematic errors were compared and PTV margins were estimated before and after correction using published margin recipes.

RESULTS

Population systematic set-up error decreased in the breast cancer patient group after the implementation of NAL protocol from 4.0 to 1.7 mm on the x-axis, from 4.7 to 2.1 mm on the y-axis and from 2.8 to 0.9 mm on the z axis. The percentage of patients with individual systematic set-up error reduction was 80%, 90% and 80% on the x-, y and z-axes respectively. Population systematic set-up error decreased also in the head and neck cancer patient group from 2.3 to 1.1 mm on the x-axis, from 1.6 to 1.4 mm on the y-axis and from 1.7 to 0.7 mm on the z-axis. The percentage of patients with individual systematic set-up error reduction was 70%, 65% and 85% on the x-, y- and z-axes respectively. Margin reduction achievable with NAL protocol implementation on the x-, y- and z-axes was 6.3, 7.2 and 4.8 mm for breast cancer patients and 3.3, 0.6 and 2.8 mm for head and neck cancer patients.

CONCLUSION

NAL off-line protocol is useful for systematic set-up error correction and PTV margin reduction in conventional breast and head and neck irradiation.