Setup variations in locoregional radiotherapy for breast cancer: an electronic portal imaging study

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.

Dosimetric and isocentric variations due to patient setup errors in CT-based treatment planning for breast cancer by electronic portal imaging

BACKGROUND

Inaccuracies in treatment setup during radiation therapy for breast cancers may increase risks to surrounding normal tissue toxicities, i.e. organs at risks (OARs), and compromise disease control. This study was planned to evaluate the dosimetric and isocentric variations and determine setup reproducibility and errors using an online electronic portal imaging (EPI) protocol.

METHODS

A total of 360 EPIs in 60 patients receiving breast/chest wall irradiation were evaluated. Cumulative dose-volume histograms (DVHs) were analyzed for mean doses to lung (V20) and heart (V30), setup source to surface distance (SSD) and central lung distance (CLD), and shifts in anterior-posterior (AP), superior-inferior (SI), and medial lateral (ML) directions.

RESULTS

Random errors ranged from 2 to 3 mm for the breast/chest wall (medial and lateral) tangential treatments and 2-2.5 mm for the anterior supraclavicular nodal field. Systematic errors ranged from 3 to 5 mm in the AP direction for the tangential fields and from 2.5 to 5 mm in the SI and ML direction for the anterior supraclavicular nodal field. For right-sided patients, V20 was 0.69-3.96 Gy, maximum lung dose was 40.5 Gy, V30 was 1.4-3 Gy, and maximum heart dose was 50.5 Gy. Similarly, for left-sided patients, the CLD (treatment planning system) was 25 mm-30 mm, CLD (EPIs) was 30-40 mm, V20 was 0.9-5.9 Gy, maximum lung dose was 45 Gy, V30 was 2.4-4.1 Gy, and maximum heart dose was 55 Gy.

CONCLUSION

Online assessment of patient position with matching of EPIs with digitally reconstructed radiographs (DRRs) is a useful method in evaluation of interfraction reproducibility in breast irradiation.

Comparison of set-up errors by breast size on wing board by portal imaging

AIM

To quantify and compare setup errors between small and large breast patients undergoing intact breast radiotherapy.

METHODS

20 patients were inducted. 10 small/moderate size breast in arm I and 10 large breast in arm II. Two orthogonal and one lateral tangent portal images (PIs) were obtained and analyzed for systematic (Σ) and random (σ) errors. Effect of no action level (NAL) was also evaluated retrospectively.

RESULTS

142 PIs were analyzed. Σ(mm) was 3.2 versus 6.7 (p = 0.41) in the mediolateral (ML) direction, 2.1 versus 2.9 (p = 0.06) in the craniocaudal (CC) and 2.2 versus 3.6 (p = 0.08) in the anteroposterior (AP) direction in small and large breast, respectively. σ(mm) was 3.0, 3.3 and 3.3 for small breast and 4.1, 3.7 and 3.2 for large breast in the ML, CC and AP direction (p = 0.07, 0.86, 0.37), respectively. 3 D Σ(mm) was 2.7 versus 4.2 (p = 0.01) and σ(mm) was 2.5 versus 3.2 (p = 0.14) in arm I and II, respectively. The standard deviation (SD) of variations (mm) in breast contour depicted by central lung distance (CLD) was 5.9 versus 7.4 (p < 0.001), central flash distance (CFD) 6.6 versus 10.5 (p = 0.002), inferior central margin (ICM) 4 versus 4.9 (p < 0.001) in arm I and II, respectively. NAL showed a significant reduction of systematic error in large breast in the mediolateral direction only.

CONCLUSION

Wing board can be used in a busy radiotherapy department for setting up breast patients with a margin of 1.1 cm, 0.76 cm and 0.71 cm for small breasts and 1.96 cm, 1.12 cm and 0.98 cm for large breast in the ML, AP and CC directions, respectively. The large PTV margin in the mediolateral direction in large breast can be reduced using NAL. Further research is needed to optimize positioning of large breasted women.

A three-field monoisocentric inverse breast treatment planning technique without half-beam blocking

The purpose of this study was to introduce a three‐field monoisocentric inverse treatment planning method without half‐beam blocks for breast cancer radiation treatments. Three‐field monoisocentric breast treatment planning with half‐beam blocks limits the tangential field length to 20 cm. A dual‐isocenter approach accommodates patients with larger breasts, but prolongs treatment time and may introduce dose uncertainty at the matching plane due to daily setup variations. We developed a novel monoisocentric, three‐field treatment planning method without half‐beam blocking. The new beam‐matching method utilizes the full field size with a single isocenter. Furthermore, an open/IMRT hybrid inverse optimization method was employed to improve dose uniformity and coverage. Geometric beam matching was achieved by rotating the couch, collimator, and gantry together. Formulae for three‐field geometric matching were derived and implemented in Pinnacle scripts. This monoisocentric technique can be used for patients with larger breast size. The new method has no constraints on the length of tangential fields. Compared with the dual‐isocenter method, it can significantly reduce patient setup time and uncertainties.

PACS number: 87.55.D‐

The impact of inter-fraction set-up errors on the probability of pulmonary and cardiac complication in left-sided breast cancer patients

Purpose

This study evaluated the impact of patient set-up errors on the probability of pulmonary and cardiac complications in the irradiation of left-sided breast cancer.

Methods and materials

Using the CMS XiO Version 4·6 radiotherapy planning system's normal tissue complication probability (NTCP) algorithm and the Lyman–Kutcher–Burman model, we calculated the dose–volume histograms (DVH) indices for the ipsilateral lung and heart and the resultant NTCP for radiation-induced pneumonitis and excess cardiac mortality in 12 left-sided breast cancer patients.

Results

Isocentric shifts in the posterior direction had the greatest effect on the lung V20, heart V25, and mean and maximum doses to the lung and the heart. DVH results show that the ipsilateral lung V20 tolerance was exceeded in 58% of the patients after 1 cm posterior shifts. Similarly, the heart V25 tolerance was exceeded after 1 cm antero-posterior and left–right isocentric shifts in 70% of the patients. The baseline NTCPs for radiation-induced pneumonitis ranged from 0·73% to 3·4%, with a mean value of 1·7%. The maximum reported NTCP for radiation-induced pneumonitis was 5·8% (mean 2·6%) after 1 cm posterior isocentric shift. The NTCP for excess cardiac mortality were 0% in 100% of the patients (n = 12) before and after set-up error simulations.

Conclusions

Set-up errors in left-sided breast cancer patients have a statistically significant impact on the Lung NTCPs and DVH indices. However, with a central lung distance of 3 cm or less (CLD < 3 cm), and a maximum heart distance of 1·5 cm or less (MHD < 1·5 cm), the treatment plans could tolerate set-up errors of up to 1 cm without any change in the NTCP to the heart.

Influence of Individualized Stabilization on the Consistency of Supraclavicular Fossa Positioning in Breast Radiation Therapy: A Retrospective Study

INTRODUCTION

The accurate stabilization of breast patients who are also undergoing supraclavicular fossa treatment is essential and can be challenging. Discrepancy in setup error for these patients often lies with the position of the clavicle in relationship with other anatomic structures. This study was performed to assess how individualized stabilization can improve patient's stability and reproducibility.

METHODS

Thirty patients stabilized with an individualized vacfix located on a Civco wing board (Civco Medical Solutions, Kalona, IA) were compared with 30 patients stabilized in the traditional manner on a Civco breast board (Civco Medical Solutions). Each of these patients underwent daily imaging using the Varian Clinac iX On-board Imaging System (Varian Medical Systems, Palo Alto, CA), and image mismatch data for each session were collected. Additionally, the relationship between the clavicle and vertebrae was assessed for each stabilization solution on a daily basis. Statistical analysis of this data was then performed using a mixed effects approach to take account of data grouping by patient specifically for the displacement error in each direction.

RESULTS

The use of an individualized vacfix decreased the overall systematic and random setup errors and displayed a reduction in the standard deviation of setup error. Patients positioned using breast board stabilization with the clavicle as the match method were exposed in the longitudinal direction to a systematic error of a 95% confidence interval (CI) of 2.6-4.5 mm and a random error of a 95% CI of 2.7-3.2 mm. This was significantly reduced for vacfix stabilization with a systematic error of a 95% CI of 1.2-2.3 mm and a random error of a 95% CI of 1.8-2.3 mm. These data amount to a reduction of the systematic error by 40% (P = .02) and a random error by 25% (P = .003) when using the vacfix method compared with the breast board. The data displaying the relationship between the clavicle and other anatomy within the treatment volume appear to be more consistent with the individualized vacfix approach.

CONCLUSIONS

Reproducible and consistent stabilization for the breast/supraclavicular fossa technique is vital in terms of ensuring accurate patient position. Analysis of the setup error for clavicle and spinous process matching strongly indicates a reduction in both the systematic and random setup error achieved by the vacfix. This illustrates the increased stability and reproducibility of patient positioning when an individualized vacfix is 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.

Local relapse rates are falling after breast conserving surgery and systemic therapy for early breast cancer: can radiotherapy ever be safely withheld?

Rates of local tumour relapse after breast conservation treatment in women with early breast cancer are falling. Explanations for this decline are considered in this review including advances in breast cancer management and aging of the breast cancer population. Breast surgery has become more standardised following publication of practice guidelines and is mostly carried out by specialist surgeons. Systemic therapies (hormonal therapy and chemotherapy) are now more effective and are recommended to a higher proportion of patients than ever before. Radiotherapy techniques have also improved. The contributions of each factor are difficult to quantify precisely, but all are likely to be relevant. In order to identify a subgroup of women that might safely be spared radiotherapy, several factors are analysed, including the prognostic significance for local relapse of tumour characteristics (pathologic data, gene-expression profiles), patient characteristics and life expectancy (age and comorbidities).

Inverse-planned, dynamic, multi-beam, intensity-modulated radiation therapy (IMRT): A promising technique when target volume is the left breast and internal mammary lymph nodes

The purpose of this study was to determine the optimum beam number and orientation for inverse-planned, dynamic intensity-modulated radiation therapy (IMRT) for treatment of left-sided breast cancer and internal mammary nodes (IMNs) to improve target coverage while reducing cardiac and ipsilateral lung irradiation. Computed tomography (CT) data was used from 5 patients with left-sided breast cancer in whom the heart was close to the chest wall. The planning target volume (PTV) was the full breast plus ipsilateral IMNs. Two geometric beam arrangements were investigated, 240 degrees and 190 degrees sector angles, and the number of beams was increased from 7 to 9 to 11. Dose comparison metrics included: PTV homogeneity and conformity indices (HI, CI), heart V30, left lung V20, and mean doses to surrounding structures. To assess clinical application, the IMRT plans with 11 beams equally spaced in a 190 degrees sector angle were compared to conventional plans. Treatment times were modeled. The 190 degrees IMRT plans improved PTV HI and CI and reduced mean dose to the heart, lungs, contralateral breast, and total healthy tissue (all p < 0.05) compared to a 240 degrees sector angle. The 11-beam plan significantly improved PTV HI and CI, heart V30, left lung V20, and healthy tissue V5 compared to a 7-beam plan (all p < 0.05). The 11-beam plan reduced heart V30 and left lung V20 (p < 0.05) without compromising PTV coverage, compared to a 9-beam plan. Compared to a conventional plan, the IMRT class solution significantly improved PTV HI and CI (both p < 0.01), heart V30 (p = 0.01), and marginally reduced left lung V20 (p = 0.07) but increased contralateral breast and lung mean dose (p < 0.001) and healthy tissue V5 (p < 0.001). An 11-beam 190 degrees sector angle IMRT technique as a class solution is clinically feasible.

Impact of radiotherapy technique on the outcome of early breast cancer treated with conservative surgery: A multicenter observational study on 1,176 patients

PURPOSE

To quantify the impact of radiotherapy technique on cosmetic outcome and on 5-year local control rate of early breast cancer treated with conservative surgery and adjuvant radiation.

METHODS AND MATERIALS

A total of 1,176 patients irradiated to the breast in 1997 were entered by eight centers into a prospective, observational study. Surgical procedure was quadrantectomy in 97% of patients, with axillary dissection performed in 96%; pT-stage was T1 in 81% and T2 in 19% of cases; pN-stage was N0 in 71%, N + (1-3) in 21%, and N + (>3) in 8% of cases. An immobilization device was used in 17% of patients; external contour-based and computed tomography-based treatment planning were performed in 20% and 72% of cases, respectively; 37% of patients were treated with a telecobalt unit and 63% with a linear accelerator; portal verification was used in 55% of patients; a boost dose to the tumor bed was delivered in 60% of cases.

RESULTS

With a median follow-up of 6.2 years, local, regional, and distant control rates at 5 years are 98%, 99%, and 92%, respectively. Use of less sophisticated treatment technique was associated with a less favorable cosmetic outcome. Local control was comparable between centers despite substantial technical differences. In a multivariate analysis including clinical and technical factors, only older age and prescription of medical adjuvant treatment significantly predicted for better local control, whereas use of portal verification was of borderline significance.

CONCLUSIONS

Radiation technical factors impacted negatively on cosmetic outcome, but had relatively small effects on local control compared with other clinical factors.