Comparison of Radiotherapy Treatment Plans for Left-sided Breast Cancer Patients based on Three- and Four-dimensional Computed Tomography Imaging

Dosimetric effect of respiratory motion on planned dose in whole-breast volumetric modulated arc therapy using moderate and ultra-hypofractionation

Background and purpose

The interplay effect of respiratory motion on the planned dose in free-breathing right-sided whole-breast irradiation (WBI) were studied by simulating hypofractionated VMAT treatment courses.

Materials and methods

Ten patients with phase-triggered 4D-CT images were included in the study. VMAT plans targeting the right breast were created retrospectively with moderately hypofractionated (40.05 Gy in 15 fractions of 2.67 Gy) and ultra-hypofractionated (26 Gy 5 fractions of 5.2 Gy) schemes. 3D-CRT plans were generated as a reference. All plans were divided into respiratory phase-specific plans and calculated in the corresponding phase images. Fraction-specific dose was formed by deforming and summing the phase-specific doses in the planning image for each fraction. The fraction-specific dose distributions were deformed and superimposed onto the planning image, forming the course-specific respiratory motion perturbed dose distribution. Planned and respiratory motion perturbed doses were compared and changes due to respiratory motion and choice of fractionation were evaluated.

Results

The respiratory motion perturbed PTV coverage (V95%) decreased by 1.7% and the homogeneity index increased by 0.02 for VMAT techniques, compared to the planned values. Highest decrease in CTV coverage was 0.7%. The largest dose differences were located in the areas of steep dose gradients parallel to respiratory motion. The largest difference in DVH parameters between fractionation schemes was 0.4% of the prescribed dose. Clinically relevant changes to the doses of organs at risk were not observed. One patient was excluded from the analysis due to large respiratory amplitude.

Conclusion

Respiratory motion of less than 5 mm in magnitude did not result in clinically significant changes in the planned free-breathing WBI dose. The 5 mm margins were sufficient to account for the respiratory motion in terms of CTV dose homogeneity and coverage for VMAT techniques. Steep dose gradients near the PTV edges might decrease the CTV coverage. No clinical significance was found due to the choice of fractionation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13014-022-02014-5.

Dosimetric comparison between three- and four-dimensional computerised tomography radiotherapy for breast cancer

At present, methods of radiotherapy simulation for breast cancer based on four-dimensional computerised tomography (4D-CT) or three-dimensional CT (3D-CT) simulation remain controversial. In the present study, 7 patients with residual breast tissue received whole breast radiotherapy based on 3D-CT and 4D-CT simulation. For the 4D-CT plan, four types of CT images were produced, including images of the end of inspiration and the end of expiration, and images acquired by the maximal intensity projection (MIP) and average intensity projection (AIP). In the 3D-CT plan, the clinical target volume (CTV) and plan target volume (PTV) were marginally higher compared with the 4D-CT plan. In addition, the minimum point dose of the target volume (D_min), the maximum point dose of the target volume (D_max) and the mean point dose of the target volume (D_mean) of the CTV and PTV in the MIP and AIP plans were marginally higher compared with the 3D-CT plan. For the contralateral breast (C-B), volumes of the 4D-CT plan were markedly lower compared with the 3D-CT plan. Furthermore, D_min, D_max and D_mean of the 3D-CT plan were higher compared with the AIP and MIP plans. For the ipsilateral lungs (I-L), volumes of the 3D-CT and AIP plans were higher compared with the MIP plan. Furthermore, when breast lesions were on the left side, for the heart, the volume receiving no less than 40% of the prescription dose (V₄₀) and the volume receiving no less than 30% of the prescription dose (V₃₀) of the MIP and AIP plans were slightly lower compared with those of the 3D plan. In conclusion, 4D-CT radiotherapy based on the MIP and AIP plans provides a slightly smaller radiation area and slightly higher radiotherapy dosage of the CTV and PTV compared with 3D-CT radiotherapy for breast radiotherapy. Therefore, the MIP and AIP plans prevent C-B radiation exposure and improve sparing of the heart and I-L.

Reproducibility of heart and thoracic wall position in repeated deep inspiration breath holds for radiotherapy of left-sided breast cancer patients

BACKGROUND

Deep inspiration breath hold (DIBH) for radiotherapy of left-sided breast cancer patients can effectively move the heart away from the target and reduce the heart dose compared to treatments in free breathing. This study aims to investigate the positional reproducibility of heart edge (HE) and thoracic wall (TW) during repeated DIBHs.

MATERIAL AND METHODS

At three occasions, 11 left-sided breast cancer patients were CT imaged during 6 minutes of repeated DIBHs with 60 cine CT series. The series were evenly distributed over three bed positions and for each bed position, the heart edge associated maximum heart distance (MHD) and thoracic wall-associated maximum lung distance (MLD) from a reference line were retrospectively analyzed. The high temporal resolution of the CT series enabled intrinsic heart movements to be resolved from breath hold variations. A body surface laser scanning system continuously extracted the thorax height and displayed it in a pair of goggles for patient feedback. To check for 'fake-breathing' movements, e.g. that the patient lifts its back from the couch to reach DIBH, the couch-to-spine distance was also measured in all CT series.

RESULTS

The analysis was done for 1432 cine CTs captured during 292 breath holds. The DIBH moved the heart on average 15 mm in medial direction compared with free breathing. For the three bed positions studied, the mean value of the max range, across all patients, was between 11-13 mm for the MHD and 4-8 mm for the MLD. The MHD variation due to breath hold variation was twice as large as the MHD variation due to intrinsic heart movement. The couch-to-spine distance varied less than 3 mm for all fractions, i.e., no fake-breathing was discovered.

CONCLUSIONS

The heart edge and thoracic wall reproducibility was high in relation to the medial heart displacement induced by the DIBH.

Three-dimensional intrafractional internal target motions in accelerated partial breast irradiation using three-dimensional conformal external beam radiotherapy

PURPOSE

We evaluated three-dimensional intrafractional target motion, divided into respiratory-induced motion and baseline drift, in accelerated partial breast irradiation (APBI).

METHODS

Paired fluoroscopic images were acquired simultaneously using orthogonal kV X-ray imaging systems at pre- and post-treatment for 23 patients who underwent APBI with external beam radiotherapy. The internal target motion was calculated from the surgical clips placed around the tumour cavity.

RESULTS

The peak-to-peak respiratory-induced motions ranged from 0.6 to 1.5mm in all directions. A systematic baseline drift of 1.5mm towards the posterior direction and a random baseline drift of 0.3mm in the lateral-medial and cranial-caudal directions were observed. The baseline for an outer tumour cavity drifted towards the lateral and posterior directions, and that for an upper tumour cavity drifted towards the cranial direction. Moderate correlations were observed between the posterior baseline drift and the patients' physical characteristics. The posterior margin for intrafractional uncertainties was larger than 5mm in patients with greater fat thickness due to the baseline drift.

CONCLUSIONS

The magnitude of the intrafractional motion was not uniform according to the direction, patients' physical characteristics, or tumour cavity location due to the baseline drift. Therefore, the intrafractional systematic movement should be properly managed.

Regional recurrence in breast cancer patients with one to three positive axillary lymph nodes treated with breast-conserving surgery and whole breast irradiation

Radiotherapy with breast-conserving therapy plays a crucial role in the treatment of early breast cancer. However, optimal radiotherapy targets have been controversial. We therefore evaluated regional recurrence in breast cancer patients with one to three positive lymph nodes (LNs) treated with breast-conserving surgery (BCS) followed by whole-breast irradiation (WBI). From 1993 to 2010, 121 breast cancer patients with one to three positive LNs who underwent BCS followed by WBI were analyzed. All patients underwent radiotherapy with two tangential fields to the whole breast. To evaluate the radiation dose to the axillary LNs, we contoured axillary LNs area and evaluated the dose-volumetric parameters. The median follow-up time was 112.4 months (range, 15.6-248.1 months). The 5-year overall survival and disease-free survival rates were 95.6% and 86.6%, respectively. The 5-year regional recurrence-free rate (RRFR) was 97.4%. During follow-up, six patients had regional recurrence. The pathological T stage was the factor best associated with the 5-year RRFR using the log-rank test, with 100.0% in the pT1 cohort versus 94.7% in the pT2-4 cohort (P < 0.01). The radiation dose to the axillary LNs did not contribute to the RRFR. In conclusion, while the pathological T stage was the prognostic factor best associated with regional recurrence, few regional recurrences were observed in early breast cancer patients with one to three LNs treated with BCS followed by WBI. Unintentional radiation doses to the axillary LNs using standard WBI were not related to the RRFR after axillary dissection.

A comparison of dosimetric variance for external-beam partial breast irradiation using three-dimensional and four-dimensional computed tomography

Purpose

To investigate the potential dosimetric benefits from four-dimensional computed tomography (4DCT) compared with three-dimensional computed tomography (3DCT) in radiotherapy treatment planning for external-beam partial breast irradiation (EB-PBI).

Patients and methods

3DCT and 4DCT scan sets were acquired for 20 patients who underwent EB-PBI. The volume of the tumor bed (TB) was determined based on seroma or surgical clips on 3DCT images (defined as TB_3D) and the end inhalation (EI) and end exhalation (EE) phases of 4DCT images (defined as TB_EI and TB_EE, respectively). The clinical target volume (CTV) consisted of the TB plus a 1.0 cm margin. The planning target volume (PTV) was the CTV plus 0.5 cm (defined as PTV_3D, PTV_EI, and PTV_EE). For each patient, a conventional 3D conformal plan (3D-CRT) was generated (defined as EB-PBI_3D, EB-PBI_EI, and EB-PBI_EE).

Results

The PTV_3D, PTV_EI, and PTV_EE were similar (P=0.549), but the PTV coverage of EB-PBI_3D was significantly less than that of EB-PBI_EI or EB-PBI_EE (P=0.001 and P=0.025, respectively). There were no significant differences in the homogeneity or conformity indexes between the three treatment plans (P=0.125 and P=0.536, respectively). The EB-PBI_3D plan resulted in the largest organs at risk dose.

Conclusion

There was a significant benefit for patients when using 3D-CRT based on 4DCT for EB-PBI with regard to reducing nontarget organ exposure. Respiratory motion did not affect the dosimetric distribution during free breathing, but might result in poor dose coverage when the PTV is determined using 3DCT.

Four-dimensional computed tomography in accelerated partial breast irradiation planning: single series from a phase III trial

PURPOSE

The aim of our study was to evaluate the usefulness of the four-dimensional computed tomography (4DCT) in accelerated partial breast irradiation (aPBI) planning.

MATERIALS AND METHODS

At our Institute, we have been treating the index quadrant with external intensity-modulated radiation therapy in a phase III trial. For this study, we selected a sample of 10 patients with right- or left-sided breast cancer and surgical clips at the excision site. Contouring of the target was performed both using three-dimensional computed tomography (3DCT) and 4DCT imaging. On both 3DCT and 4DCT, we recorded the clinical target volume (CTV) and the planning target volume (PTV) and the coordinates of the PTV centroid. We calculated the treatment plans, according to our protocol, using the contours drawn on the 3DCT and 4DCT and evaluated target coverage and sparing of organs at risk (OAR).

RESULTS

Median age of the patients was 63.5 years (range 52-75). The comparison between the 3DCT and 4DCT PTV volumes was not statistically significant (p = 0.79). Concerning centroid coordinates, the average absolute differences were 0.1 mm in the latero-lateral, 0.7 mm in the antero-posterior and 0.3 mm in the supero-inferior direction. No statistically significant differences were observed both in PTV coverage and OAR sparing; the 4D PTV contour is adequately covered when the plan based on the 3D contours is used. Target coverage was reduced on average by 1 % and no statistically significant difference was observed (p = 0.93).

CONCLUSIONS

In our experience, no significant differences between PTV volumes, PTV coverage, OAR sparing and centroid position are evidenced when comparing 3DCT and 4DCT plans. Conventional 3DCT-based planning is adequate for aPBI.

Determination of the optimal matching position for setup images and minimal setup margins in adjuvant radiotherapy of breast and lymph nodes treated in voluntary deep inhalation breath-hold

BACKGROUND

Adjuvant radiotherapy (RT) of left-sided breast cancer is increasingly performed in voluntary deep inspiration breath-hold (vDIBH). The aim of this study was to estimate the reproducibility of breath-hold level (BHL) and to find optimal bony landmarks for matching of orthogonal setup images to minimise setup margins.

METHODS

1067 sets of images with an orthogonal setup and tangential field from 67 patients were retrospectively analysed. Residual position errors were determined in the tangential treatment field images for different matches of the setup images. Variation of patient posture and BHL were analysed for position errors of the vertebrae, clavicula, ribs and sternum in the setup and tangential field images. The BHL was controlled with a Varian RPM® system. Setup margins were calculated using the van Herk's formula. Patients who underwent lymph node irradiation were also investigated.

RESULTS

For the breast alone, the midway compromise of the ribs and sternum was the best general choice for matching of the setup images. The required margins were 6.5 mm and 5.3 mm in superior-inferior (SI) and lateral/anterior-posterior (LAT/AP) directions, respectively. With the individually optimised image matching position also including the vertebrae, slightly smaller margins of 6.0 mm and 4.8 mm were achieved, respectively. With the individually optimised match, margins of 7.5 mm and 10.8 mm should be used in LAT and SI directions, respectively, for the lymph node regions. These margins were considered too large. The reproducibility of the BHL was within 5 mm in the AP direction for 75% of patients.

CONCLUSIONS

The smallest setup margins were obtained when the matching position of the setup images was individually optimised for each patient. Optimal match for the breast alone is not optimal for the lymph node region, and, therefore, a threshold of 5 mm was introduced for residual position errors of the sternum, upper vertebrae, clavicula and chest wall to retain minimal setup margins of 5 mm. Because random interfraction variation in patient posture was large, we recommend daily online image guidance. The BHL should be verified with image guidance.

Audit of radiation dose delivered in time-resolved four-dimensional computed tomography in a radiotherapy department

INTRODUCTION

To review the dose delivered to patients in time-resolved computed tomography (4D CT) used for radiotherapy treatment planning.

METHODS

4D CT is used at Peter MacCallum Cancer Centre since July 2007 for radiotherapy treatment planning using a Philips Brilliance Wide Bore CT scanner (16 slice, helical 4D CT acquisition). All scans are performed at 140 kVp and reconstructed in 10 datasets for different phases of the breathing cycle. Dose records were analysed retrospectively for 387 patients who underwent 4D CT procedures between 2007 and 2013.

RESULTS

A total of 444 4D CT scans were acquired with the majority of them (342) being for lung cancer radiotherapy. Volume CT dose index (CTDIvol) as recorded over this period was fairly constant at approximately 20 mGy for adults. The CTDI for 4D CT for lung cancers of 19.6 ± 9.3 mGy (n = 168, mean ± 1SD) was found to be 63% higher than CTDIs for conventional CT scans for lung patients that were acquired in the same period (CTDIvol 12 ± 4 mGy, sample of n = 25). CTDI and dose length product (DLP) increased with increasing field of view; however, no significant difference between DLPs for different indications (breast, kidney, liver and lung) could be found. Breathing parameters such as breathing rate or pattern did not affect dose.

CONCLUSION

4D CT scans can be acquired for radiotherapy treatment planning with a dose less than twice the one required for conventional CT scanning.

Combined photon-electron beams in the treatment of the supraclavicular lymph nodes in breast cancer: A novel technique that achieves adequate coverage while reducing lung dose

Radiation pneumonitis is a well-documented side effect of radiation therapy for breast cancer. The purpose of this study was to compare combined photon-electron, photon-only, and electron-only plans in the radiation treatment of the supraclavicular lymph nodes. In total, 13 patients requiring chest wall and supraclavicular nodal irradiation were planned retrospectively using combined photon-electron, photon-only, and electron-only supraclavicular beams. A dose of 50Gy over 25 fractions was prescribed. Chest wall irradiation parameters were fixed for all plans. The goal of this planning effort was to cover 95% of the supraclavicular clinical target volume (CTV) with 95% of the prescribed dose and to minimize the volume receiving ≥ 105% of the dose. Comparative end points were supraclavicular CTV coverage (volume covered by the 95% isodose line), hotspot volume, maximum radiation dose, contralateral breast dose, mean total lung dose, total lung volume percentage receiving at least 20 Gy (V(20 Gy)), heart volume percentage receiving at least 25 Gy (V(25 Gy)). Electron and photon energies ranged from 8 to 18 MeV and 4 to 6 MV, respectively. The ratio of photon-to-electron fractions in combined beams ranged from 5:20 to 15:10. Supraclavicular nodal coverage was highest in photon-only (mean = 96.2 ± 3.5%) followed closely by combined photon-electron (mean = 94.2 ± 2.5%) and lowest in electron-only plans (mean = 81.7 ± 14.8%, p < 0.001). The volume of tissue receiving ≥ 105% of the prescription dose was higher in the electron-only (mean = 69.7 ± 56.1 cm(3)) as opposed to combined photon-electron (mean = 50.8 ± 40.9 cm(3)) and photon-only beams (mean = 32.2 ± 28.1 cm(3), p = 0.114). Heart V(25 Gy) was not statistically different among the plans (p = 0.999). Total lung V(20 Gy) was lowest in electron-only (mean = 10.9 ± 2.3%) followed by combined photon-electron (mean = 13.8 ± 2.3%) and highest in photon-only plans (mean = 16.2 ± 3%, p < 0.001). As expected, photon-only plans demonstrated the highest target coverage and total lung V(20 Gy). The superiority of electron-only beams, in terms of decreasing lung dose, is set back by the dosimetric hotspots associated with such plans. Combined photon-electron treatment is a feasible technique for supraclavicular nodal irradiation and results in adequate target coverage, acceptable dosimetric hotspot volume, and slightly reduced lung dose.

Estimation of optimal matching position for orthogonal kV setup images and minimal setup margins in radiotherapy of whole breast and lymph node areas

AIM

The aim was to find an optimal setup image matching position and minimal setup margins to maximally spare the organs at risk in breast radiotherapy.

BACKGROUND

Radiotherapy of breast cancer is a routine task but has many challenges. We investigated residual position errors in whole breast radiotherapy when orthogonal setup images were matched to different bony landmarks.

MATERIALS AND METHODS

A total of 1111 orthogonal setup image pairs and tangential field images were analyzed retrospectively for 50 consecutive patients. Residual errors in the treatment field images were determined by matching the orthogonal setup images to the vertebrae, sternum, ribs and their compromises. The most important region was the chest wall as it is crucial for the dose delivered to the heart and the ipsilateral lung. Inter-observer variation in online image matching was investigated.

RESULTS

The best general image matching position was the compromise of the vertebrae, ribs and sternum, while the worst position was the vertebrae alone (p ≤ 0.03). The setup margins required for the chest wall varied from 4.3 mm to 5.5 mm in the lung direction while in the superior-inferior (SI) direction the margins varied from 5.1 mm to 7.6 mm. The inter-observer variation increased the minimal margins by approximately 1 mm. The margin of the lymph node areas should be at least 4.8 mm.

CONCLUSIONS

Setup margins can be reduced by proper selection of a matching position for the orthogonal setup images. To retain the minimal margins sufficient, systematic error of the chest wall should not exceed 4 mm in the tangential field image.

Impact of respiratory motion on breast tangential radiotherapy using the field-in-field technique compared to irradiation using physical wedges

Background

This study aimed to evaluate whether the field-in-field (FIF) technique was more vulnerable to the impact of respiratory motion than irradiation using physical wedges (PWs).

Patients and methods

Ten patients with early stage breast cancer were enrolled. Computed tomography (CT) was performed during free breathing (FB). After the FB-CT data set acquisition, 2 additional CT scans were obtained during a held breath after light inhalation (IN) and light exhalation (EX). Based on the FB-CT images, 2 different treatment plans were created for the entire breast for each patient and copied to the IN-CT and EX-CT images. The amount of change in the volume of the target receiving 107%, 95%, and 90% of the prescription dose (V107%, V95%, and V90%, respectively), on the IN-plan and EX-plan compared with the FB-plan were evaluated.

Results

The V107%, V95%, and V90% were significantly larger for the IN-plan than for the FB-plan in both the FIF technique and PW technique. While the amount of change in the V107% was significantly smaller in the FIF than in the PW plan, the amount of change in the V95% and V90% was significantly larger in the FIF plan. Thus, the increase in the V107% was smaller while the increases in the V95% and V90% were larger in the FIF than in the PW plan.

Conclusions

During respiratory motion, the dose parameters stay within acceptable range irrespective of irradiation technique used although the amount of change in dose parameters was smaller with FIF technique.