Baseline shift corrections towards the heart: External validation of the impact on survival in early-stage NSCLC patients

PURPOSE

To externally validate Johnson-Hart et al. findings: the association of tumor baseline shifts towards the heart with overall survival (OS) in SBRT for NSCLC. Further analysis included investigating the presence of interfractional heart baseline shifts and the association of OS with heart dose change during treatment.

METHODS

Data from 416 SBRT early-stage NSCLC patients was collected. Pearson's correlations (PCCs) between clinical variables and treatment-averaged tumor shifts towards/away from the heart were explored. Validation of published multivariable Cox model was performed. PCCs between heart and tumor baseline shifts were analyzed. Dose accumulation was performed following daily CBCT-to-pCT deformable registration. Maximum heart dose (D0) was computed for planned and accumulated doses. Differences in OS according to shifts towards/away from the heart or D0 increase/decrease were analyzed. Significant D0 differences between patients with D0 increase/decrease and different tumor locations were explored.

RESULTS

Tumor shifts towards/away from the heart showed no significant association with OS (p = 0.91). Distance between PTV and heart correlated significantly (PCC = 0.18) with shifts to the heart. Cox model did not validate in our cohort. Heart presented baseline shifts positively correlated with tumor baseline shifts in all three directions (PCC ≥ 0.38; p < 0.001). Counterintuitively, patients experiencing increased D0 during treatment showed significantly better OS (p = 0.0077). Upper-lobe tumor patients with increased D0 had lower D0 than those with decreased D0 (right-upper-lobe p ≤ 0.018).

CONCLUSIONS

In our SBRT cohort, the shifts towards the heart were not associated with worse OS. Moderate correlations were found between tumor and heart baseline shifts in each direction. Moreover, the distance between the PTV and the heart showed a significant correlation with shifts to the heart.

DIBH reduces right coronary artery and lung radiation dose in right breast cancer loco-regional radiotherapy

To determine whether deep inspiratory breath-hold (DIBH) reduces dose to organs-at-risk (OAR), in particular the right coronary artery (RCA), in women with breast cancer requiring right-sided post-mastectomy radiotherapy (PMRT) including internal mammary chain (+IMC) radiotherapy (RT). Fourteen consecutive women requiring right-sided PMRT + IMC were retrospectively identified. Nodal delineation was in accordance with European Society for Radiology and Oncology (ESTRO) guidelines and tangential chest wall fields marked. Patients were planned with Anisotropic Analytical Algorithm using free-breathing (FB) and DIBH datasets. Dose was calculated using Acuros External Beam algorithm. FB and DIBH dose comparisons were analyzed for heart, RCA and right lung, as were chest wall and IMC planning target volumes (PTVs). DIBH vs FB resulted in median decreases of: the RCA mean dose by 0.6Gray (Gy) (interquartile range (IQR) 0.1, 1.9) (p = 0.002), RCA max dose by 1.8Gy (IQR 0.8, 6.1) (p = 0.002), and V5Gy by 2.9% (IQR 0.0, 37.2) (p = 0.016). RCA data indicated no statistically significant dosimetric reduction ≥10Gy. A median reduction of 1.7Gy (c -0.0, 7.1) (p = 0.019) in maximum heart dose was recorded with DIBH vs FB; no significant difference was observed in other heart and left anterior descending coronary artery parameters. The median reduction in right lung mean dose was 2.8Gy for DIBH vs FB plans (IQR 1.6, 3.6) (p = 0.001); significant median reductions of V5Gy, V20Gy, and V30Gy were all achieved with DIBH. Chest wall PTV coverage did not significantly differ between DIBH and FB plans; IMC dosimetric coverage improved with use of DIBH (V47.5Gy, V45Gy, V42Gy). DIBH reduced OAR dose in right-sided PMRT + IMC patients. A novel finding was that DIBH decreased RCA dose. Heart and right lung dose were also decreased with DIBH, whilst optimally dosed PTVs were maintained.

Heart and Lung Dose as Predictors of Overall Survival in Patients With Locally Advanced Lung Cancer. A National Multicenter Study

Introduction

It is an ongoing debate how much lung and heart irradiation impact overall survival (OS) after definitive radiotherapy for lung cancer. This study uses a large national cohort of patients with locally advanced NSCLC to investigate the association between OS and irradiation of lung and heart.

Methods

Treatment plans were acquired from six Danish radiotherapy centers, and patient characteristics were obtained from national registries. A hybrid segmentation tool automatically delineated the heart and substructures. Dose-volume histograms for all structures were extracted and analyzed using principal component analyses (PCAs). Parameter selection for a multivariable Cox model for OS prediction was performed using cross-validation based on bootstrapping.

Results

The population consisted of 644 patients with a median survival of 26 months (95% confidence interval [CI]: 24-29). The cross-validation selected two PCA variables to be included in the multivariable model. PCA1 represented irradiation of the heart and affected OS negatively (hazard ratio, 1.14; 95% CI: 1.04-1.26). PCA2 characterized the left-right balance (right atrium and left ventricle) irradiation, showing better survival for tumors near the right side (hazard ratio, 0.92; 95% CI: 0.84-1.00). Besides the two PCA variables, the multivariable model included age, sex, body-mass index, performance status, tumor dose, and tumor volume.

Conclusions

Besides the classic noncardiac risk factors, lung and heart doses had a negative impact on survival, while it is suggested that the left side of the heart is a more radiation dose-sensitive region. The data indicate that overall heart irradiation should be reduced to improve the OS if possible.

Association of radiation dose to cardiac substructures with major ischaemic events following breast cancer radiotherapy

BACKGROUND AND AIMS

Patients with left-sided breast cancer receive a higher mean heart dose (MHD) after radiotherapy, with subsequent risk of ischaemic heart disease. However, the optimum dosimetric predictor among cardiac substructures has not yet been determined.

METHODS AND RESULTS

This study retrospectively reviewed 2158 women with breast cancer receiving adjuvant radiotherapy. The primary endpoint was a major ischaemic event. The dose-volume parameters of each delineated cardiac substructure were calculated. The risk factors for major ischaemic events and the association between MHD and major ischaemic events were analysed by Cox regression. The optimum dose-volume predictors among cardiac substructures were explored in multivariable models by comparing performance metrics of each model. At a median follow-up of 7.9 years (interquartile range 5.6-10.8 years), 89 patients developed major ischaemic events. The cumulative incidence rate of major ischaemic events was significantly higher in left-sided disease (P = 0.044). Overall, MHD increased the risk of major ischaemic events by 6.2% per Gy (hazard ratio 1.062, 95% confidence interval 1.01-1.12; P = 0.012). The model containing the volume of the left ventricle receiving 25 Gy (LV V25) with the cut-point of 4% presented with the best goodness of fit and discrimination performance in left-sided breast cancer. Age, chronic kidney disease, and hyperlipidaemia were also significant risk factors.

CONCLUSION

Risk of major ischaemic events exist in the era of modern radiotherapy. LV V25 ≥ 4% appeared to be the optimum parameter and was superior to MHD in predicting major ischaemic events. This dose constraint could aid in achieving better heart protection in breast cancer radiotherapy, though a further validation study is warranted.

Heart atlas for retrospective cardiac dosimetry: a multi-institutional study on interobserver contouring variations and their dosimetric impact

PURPOSE

Cardiac effects after breast cancer radiation therapy potentially affect more patients as survival improves. The heart's heterogeneous radiation exposure and composition of functional structures call for establishing individual relationships between structure dose and specific late effects. However, valid dosimetry requires reliable contouring which is challenging for small volumes based on older, lower-quality computed tomography imaging. We developed a heart atlas for robust heart contouring in retrospective epidemiologic studies.

METHODS AND MATERIALS

The atlas defined the complete heart and geometric surrogate volumes for six cardiac structures: aortic valve, pulmonary valve, all deeper structures combined, myocardium, left anterior myocardium, and right anterior myocardium. We collected treatment planning records from 16 patients from 4 hospitals including dose calculations for 3D conformal tangential field radiation therapy for left-sided breast cancer. Six observers each contoured all patients. We assessed spatial contouring agreement and corresponding dosimetric variability.

RESULTS

Contouring agreement for the complete heart was high with a mean Jaccard similarity coefficient (JSC) of 89%, a volume coefficient of variation (CV) of 5.2%, and a mean dose CV of 4.2%. The left (right) anterior myocardium had acceptable agreement with 63% (58%) JSC, 9.8% (11.5%) volume CV, and 11.9% (8.0%) mean dose CV. Dosimetric agreement for the deep structures and aortic valve was good despite higher spatial variation. Low spatial agreement for the pulmonary valve translated to poor dosimetric agreement.

CONCLUSIONS

For the purpose of retrospective dosimetry based on older imaging, geometric surrogate volumes for cardiac organs at risk can yield better contouring agreement than anatomical definitions, but retain limitations for small structures like the pulmonary valve.

Increasing Heart Dose Reduces Overall Survival in Patients Undergoing Postoperative Radiation Therapy for NSCLC

Introduction

Given the concern for cardiopulmonary toxicity in patients with NSCLC undergoing postoperative radiation therapy (PORT), the purpose of this study was to evaluate the association between heart dose and overall survival (OS) in patients undergoing PORT with modern techniques.

Methods

This is a retrospective study of consecutive patients with NSCLC treated with PORT between May 2004 and January 2017. Clinical records were reviewed and radiation dose distributions were analyzed for association with OS.

Results

A total of 284 patients were analyzed. At the time of surgery, most patients had pathologic American Joint Committee on Cancer seventh edition stage III disease (91.2 %) and received either preoperative or adjuvant chemotherapy (92.3 %). Most patients underwent a lobectomy (81.3 %) and had R0 (80.6 %) or R1 (19.4 %) resection. PORT was delivered with a median radiation dose of 54 Gy, and 70.4 % of patients were treated with intensity-modulated radiation therapy. Dosimetric variables across a large range of doses to the heart were highly significant (p < 0.05) for OS. The volume of the heart receiving 8 Gy (HV8) was the most significant dosimetric variable (p < 0.001), and the median HV8 was 35.5 %. The median OS was 33.2 versus 53.6 months (p < 0.005) for patients with HV8 above or below 35.5 %, respectively. On multivariable analysis accounting for other potential prognostic confounders, HV8 remained highly significant (p < 0.001).

Conclusions

The data reveal a strong correlation between increasing heart dose and OS in patients with NSCLC undergoing PORT. Taken together with the recently presented LungART trial, lowering heart dose in PORT patients may help to decrease the risk of morbidity and mortality and improve the therapeutic ratio of PORT.

Cardiac sub-volume targeting demonstrates regional radiosensitivity in the mouse heart

BACKGROUND AND PURPOSE

Radiation-induced cardiac toxicity (RICT) remains one of the most critical dose limiting constraints in radiotherapy. Recent studies have shown higher doses to the base of the heart are associated with worse overall survival in lung cancer patients receiving radiotherapy. This work aimed to investigate the impact of sub-volume heart irradiation in a mouse model using small animal image-guided radiotherapy.

MATERIALS AND METHODS

C57BL/6 mice were irradiated with a single fraction of 16 Gy to the base, middle or apex of the heart using a small animal radiotherapy research platform. Cone beam CT and echocardiography were performed at baseline and at 10 week intervals until 50 weeks post-treatment. Structural and functional parameters were correlated with mean heart dose (MHD) and volume of heart receiving 5 Gy (V5).

RESULTS

All irradiated mice showed a time dependent increase in left ventricle wall thickness in diastole of ~0.2 mm detected at 10 weeks post-treatment, with the most significant and persistent changes occurring in the heart base-irradiated animals. Similarly, statistically different functional effects (p < 0.01) were observed in base-irradiated animals which showed the most significant decreases compared to controls. The observed functional changes did not correlate with MHD and V5 (R2 < 0.1), indicating that whole heart dosimetry parameters do not predict physiological changes resulting from cardiac sub-volume irradiation.

CONCLUSIONS

This is the first report demonstrating the structural and functional consequences of sub-volume targeting in the mouse heart and reverse translates clinical observations indicating the heart base as a critical radiosensitive region.

The effect of deep inspiration breath-hold technique on left anterior descending coronary artery and heart dose in left breast irradiation

Purpose

To determine the effect of the deep inspiration breath-hold (DIBH) technique on left anterior descending coronary artery (LAD) region and heart dose in left breast cancer irradiation.

Materials and Methods

Twenty-five left breast cancer patients who previously received breast-conserving surgery underwent computed tomography (CT) simulation with both free-breathing (FB) and DIBH techniques and four radiation treatment plans. The plan comprised the following with both the FB and DIBH techniques: whole breast (WB), and WB with internal mammary lymph nodes (WB+IMNs). The prescription dose was 50 Gy in 25 fractions. The doses to the LAD region, heart and lungs were compared. Moreover, in-field maximum heart distance (maxHD) and breast volume were analyzed for correlations with the mean heart dose (MHD).

Results

In the WB plan with DIBH vs. FB techniques, the mean radiation doses to the LAD region, MHD, and the left lung V20 were 11.48 Gy vs. 19.84 Gy (p < 0.0001), 2.95 Gy vs. 5.38 Gy (p < 0.0001), and 19.72% vs. 22.73% (p = 0.0045), respectively. In the WB+IMNs plan, the corresponding values were 23.88 Gy vs. 31.98 Gy (p < 0.0001), 6.43 Gy vs. 10.24 Gy (p < 0.0001), and 29.31% vs. 32.1% (p = 0.0009), respectively. MHD correlated with maxHD (r = 0.925) and breast volume (r = 0.6).

Conclusion

The use of the DIBH technique in left breast cancer irradiation effectively reduces the radiation doses to the LAD region, heart and lungs. MHD is associated with maxHD and breast size.

Decreased heart dose with deep inspiration breath hold for the treatment of gastric lymphoma with IMRT

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Radiation therapy to the stomach can result in unintended radiation to the heart.

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Deep inspiration breath-hold can provide spatial separation between the heart and stomach.

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Deep inspiration breath-hold permits decreased dose to organs at risk when treating the stomach.

We hypothesized that deep inspiration breath-hold (DIBH) and computed-tomography image-guided radiotherapy (CT-IGRT) may be beneficial to decrease dose to organs at risk (OARs), when treating the stomach with radiotherapy for lymphoma. We compared dosimetric parameters of OARs from plans generated using free-breathing (FB) versus DIBH for 10 patients with non-Hodgkin lymphoma involving the stomach treated with involved site radiotherapy. All patients had 4DCT and DIBH scans. Planning was performed with intensity modulated radiotherapy (IMRT) to 30.6 Gy in 17 fractions. Differences in target volume and dosimetric parameters were assessed using a paired two-sided t-test. All heart and left ventricle parameters including mean dose, V30, V20, V10, and V5 were statistically significantly lower with DIBH. For IMRT-FB plans the average mean heart dose was 4.9 Gy compared to 2.6 Gy for the IMRT-DIBH group (p < 0.001). There was a statistically significant decrease in right kidney dose with DIBH. For lymphoma patients treated to the stomach with IMRT, DIBH provides superior OAR sparing compared to FB-based planning, most notably reducing dose to the heart and left ventricle. This strategy could be considered when treating other gastric malignancies.

Impact of positioning errors in the dosimetry of VMAT left-sided post mastectomy irradiation

Background

Volumetric modulated arc therapy (VMAT) adopted in post-mastectomy radiation therapy (PMRT) has the capacity to achieve highly conformal dose distributions. The research aims to evaluate the impact of positioning errors in the dosimetry of VMAT left-sided PMRT.

Methods

A total of 18 perturbations where introduced in 11 VMAT treatment plans that shifted the isocenter from its reference position of 3, 5, 10 mm in six directions. The thoracic wall and supraclavicular clinical target volumes (CTVs), the heart and the left lung dose volume histograms (DVHs) of 198 perturbed plans were calculated. The absolute differences (∆) of the mean dose (Dm) and DVH endpoints Vx and Dy (percentage volume receiving x Gy, and dose covering y% of the volume, respectively) were used to compare the dosimetry of the reference vs perturbed plans.

Results

Isocenter shifts in the anterior and lateral directions lead to maximum disagreement between the CTVs dosimetry of perturbed vs reference plans. Isocenter shifts of 10 mm shown a decrease of D95, D98 and Dm of 12.8, 18.0, and 2.9% respectively, for the CTVs. For 5 mm isocenter shifts, these differences decreased to 3.2, 5.2, and 0.9%, respectively, and for 3 mm shifts to 1.0, 1.7, and 0.6%, respectively. For the organs at risk (OARs), only isocenter shifts in the right, posterior and inferior directions worsen the plan dosimetry, nevertheless not negligible lung ∆ V20 of + 2.6%, and heart ∆ V25 of + 1.6% persist for 3 mm shifts.

Conclusions

Inaccuracy in isocenter positioning for VMAT left-sided PMRT irradiation may impact the dosimetry of the CTVs and OARs to a different extent, depending on the directions and magnitude of the perturbation. The acquired information could be useful for planning strategies to guarantee the accuracy of the treatment delivered.

Impact of small residual setup errors after image guidance on heart dose and survival in non-small cell lung cancer treated with curative-intent radiotherapy

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Residual errors following treatment setup result in a change in dose from planned.

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The change in dose in a region in the heart is related to overall survival.

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No relationship between the change in dose and other clinical variables was found.

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Increased heart dose explains the relationship between residual errors and survival.

Background and purpose

A recent study of NSCLC patients showed small residual setup errors (shifts) in the direction of the heart following image-guidance were significantly related to overall survival. This study of the dosimetric effects of these residual shifts investigates the hypothesis that observed survival differences were related to a change in heart dose.

Materials and methods

Accumulated doses including shifts for each fraction were determined for 475 NSCLC patients. Planning CTs and corresponding dose distributions were deformed to a reference. Image-based data-mining techniques were then applied to the difference between the planned and accumulated dose (Δdose) to determine where Δdose relates to 1-year survival. The significance of Δdose in the identified region was assessed using multivariable Cox analysis. The cohort was then split into octiles, based upon planned dose to the region, and multivariable Cox analysis performed for each sub-cohort to explore the dose response relationship. The identified dose threshold for damage was then tested in an independent validation cohort of 1482 NSCLC patients from the same institution.

Results

Permutation testing identified a small region in the heart base where Δdose significantly correlated with 1-year survival. Δdose in this region showed no correlation with common clinical variables, and was significant in multivariable Cox regression (p < 0.001, hazard ratio 1.221/Gy), with increasing change in dose from plan resulting in greater risk of death. Octile analysis revealed Δdose to be significant only in the 7th octile, planning dose 16.2–23.4 Gy, suggesting a steep dose–effect relation for heart damage in this range. Taking 16.2 Gy as a conservative threshold dose, this result was successfully validated, with a significant difference being seen between patients with a region dose above or below 16.2 Gy.

Conclusions

This study suggests the relation between residual set-up errors and survival is explained by changes in cardiac dose, and identifies an area at the heart base where dose is correlated with survival. Our results suggest the dose threshold for cardiac damage is between 16.2 and 23.4 Gy in the base of the heart, which was validated in an independent cohort. However, the dose effect in other regions of the heart should also be investigated.

Effects of Preparatory Coaching and Home Practice for Deep Inspiration Breath Hold on Cardiac Dose for Left Breast Radiation Therapy

AIMS

Deep inspiration breath hold (DIBH) reduces cardiac radiation exposure by creating cardiac-chest wall separation in breast cancer radiotherapy. DIBH requires sustaining chest wall expansion for up to 40 s and involves complex co-ordination of thoraco-abdominal muscles, which may not be intuitive to patients. We investigated the effect of in-advance preparatory DIBH coaching and home practice on cardiac doses.

MATERIALS AND METHODS

Successive patients from 1 February 2015 to 31 December 2016 with left-sided breast cancer who underwent tangential field radiotherapy utilising the DIBH technique were included. The study cohort consisted of patients treated by a physician who routinely provided DIBH coaching and home practice instructions at least 5 days before simulation. The control group included non-coached patients under another physician's care. Minimum, maximum and mean cardiac doses and V5, V10 and V30 from DIBH and free breathing simulation computed tomography scans were obtained from the planning system. DIBH and free breathing cardiac doses and volume exposures were compared between the coached and non-coached groups using the two-sample t-test, Fisher's exact test and the Mann-Whitney U-test.

RESULTS

Twenty-seven coached and 42 non-coached patients were identified. The DIBH maximum cardiac dose was lower in coached patients at 13.1 Gy compared with 19.4 Gy without coaching (P = 0.004). The percentage cardiac volume exposure in DIBH was lower in coached patients; the DIBH V10 was 0.5% without coaching and 0.1% with coaching (P = 0.005). There was also a trend towards lower DIBH V5 in the coached group compared with the non-coached group (1.2% versus 1.9%, P = 0.071). No significant differences in patient cardiopulmonary comorbidity factors that might influence cardiac doses were found between the groups.

CONCLUSIONS

Our results suggest that cardiac dose sparing can potentially be further improved with a 5 day regimen of preparatory DIBH coaching and in-advance home practice before simulation. These hypothesis-generating findings should be confirmed in a larger study.

Volumetric Modulated Arc Therapy After Lung Sparing Surgery for Malignant Pleural Mesothelioma: A Single Institution Experience

INTRODUCTION

We investigated the possible role of volumetric modulated arc therapy (VMAT) in the setting of adjuvant treatment of malignant pleural mesothelioma (MPM) after lung-sparing surgery with pleurectomy and decortication.

MATERIALS AND METHODS

Patients affected by MPM who had undergone pleurectomy and decortication and adjuvant radiotherapy with VMAT were included. The endpoints of the present analysis were local control, progression-free survival, and overall survival. Assessment of the variables affecting survival was performed using univariate and multivariate Cox proportional hazard models.

RESULTS

A total of 49 patients were included in the present study. Of the 49 patients, 96% had been treated with a trimodality approach. Radiotherapy was delivered to a median dose of 44 Gy in 22 fractions (range, 22-59.4 Gy). The treatment was well tolerated, with just 2 grade 3 acute toxicities, 1 grade 5, and 2 grade 4 toxicities recorded during the follow-up period. The median follow-up period was 27.4 months. The local control rate at 12, 24, and 36 months was 75.2%, 67.4%, and 56.5%, respectively. The median progression-free survival was 14.9 months (95% confidence interval [CI], 7.5-25.2). The median overall survival was 21.5 months (95% CI, 15.3-37.1). On multivariate analysis, the administration of carboplatin- instead of cisplatin-based chemotherapy (hazard ratio, 2.97; 95% CI, 1.22-7.26; P = .017) and R2 resection (hazard ratio, 1.95; 95% CI, 1.27-2.99; P = .002) showed a negative correlation with overall survival. On univariate analysis, the percentage of the heart receiving >20 Gy and >30 was associated with the occurrence of late pneumonitis (P = .018 and P = .077).

CONCLUSION

VMAT is feasible in the setting of MPM after lung-sparing surgery. The toxicity rates were reduced with this technique compared with historical data of older techniques. Local and distant failure remain a major issue to be addressed in future trials.

Impact of patient and treatment characteristics on heart and lung dose in adjuvant radiotherapy for left-sided breast cancer

PURPOSE

The heart and lungs are routinely exposed to incidental irradiation during adjuvant radiotherapy (RT) of breast cancer. We analyzed the impact of patient and treatment characteristics on heart and lung dose in left-sided breast RT.

METHODS

We analyzed 332 female patients treated with left-sided breast RT between 2013 and 2018. Mean heart dose (MHD), left mean lung dose (MLD) and heart / lung V20Gy were collected from treatment plans. Patients were stratified by RT technique (3D-conformal RT, 3DCRT; intensity-modulated RT, IMRT; volumetric modulated arc therapy, VMAT) and target volumes, including lymph node RT (LN-RT). Patient characteristics (body mass index (BMI), heart and lung volume) were assessed using correlation analyses.

RESULTS

LN-RT was performed in 111 patients with increased MHD (median 4.6 vs. 3.3 Gy; p < .01), left MLD (14.8 vs. 7.7 Gy; p < .01) and left lung V20Gy (30.0% vs. 14.4%; p < .01) compared to treatment without LN-RT. Internal mammary LN-RT further increased organ doses compared to RT involving only supraclavicular +/- axillary LN (p < .01 for all values; MHD 6.9 vs. 4.2 Gy). In 221 patients treated without LN-RT, IMRT/VMAT was associated with higher left lung doses (MLD 9.1 vs. 7.4 Gy, p < .01; V20Gy 18.8% vs. 14.0%, p < .01) compared to 3DCRT. A negative correlation between total lung volume and both MHD (r = - 0.38; p < .01) and heart V20Gy (r = - 0.37; p < .01), as well as a weak positive correlation of BMI and MHD (r = 0.27; p < .01) were observed.

CONCLUSIONS

In adjuvant RT for left-sided breast cancer, LN-RT is associated with a marked increase in heart and lung doses, particularly with internal mammary LN-RT. Potential advantages of IMRT/VMAT for breast or chest wall RT need to be weighed against a moderately increased lung dose.

Deep inspiration breath-hold for left-sided breast irradiation: Analysis of dose-mass histograms and the impact of lung expansion

Background

The aim of this study was to compare dose-volume histogram (DVH) with dose-mass histogram (DMH) parameters for treatment of left-sided breast cancer in deep inspiration breath-hold (DIBH) and free breathing (FB). Additionally, lung expansion and anatomical factors were analyzed and correlated to dose differences.

Methods

For 31 patients 3D conformal radiation therapy plans were retrospectively calculated on FB and DIBH CTs in the treatment planning system. The calculated doses, structures and CT data were transferred into MATLAB and DVHs and DMHs were calculated. Mean doses (Dmean), volumes and masses receiving certain doses (Vx, Mx) were determined for the left lung and the heart. Additionally, expansion of the left lung was evaluated using deformable image registration. Differences in DVH and DMH dose parameters between FB and DIBH were statistically analyzed and correlated to lung expansion and anatomical factors.

Results

DIBH reduced Dmean (DVH) and relative V20 (V20 [%]) of the left lung in all patients, on average by − 19 ± 9% (mean ± standard deviation) and − 24 ± 10%. Dmean (DMH) and M20 [%] were also significantly reduced (− 12 ± 11%, − 16 ± 13%), however 4 patients had higher DMH values in DIBH than in FB. Linear regression showed good correlations between DVH and DMH parameters, e.g. a dosimetric benefit smaller than 8.4% for Dmean (DVH) in DIBH indicated more irradiated lung mass in DIBH than in FB. The mean expansion of the left lung between FB and DIBH was 1.5 ± 2.4 mm (left), 16.0 ± 4.0 mm (anterior) and 12.2 ± 4.6 mm (caudal). No significant correlations were found between expansions and differences in Dmean for the left lung. The heart dose in DIBH was reduced in all patients by 53% (Dmean) and this dosimetric benefit correlated to lung expansion in anterior.

Conclusions

Treatment of left-sided breast cancer in DIBH reduced dose to the heart and in most cases the lung dose, relative irradiated lung volume and lung mass. A mass related dosimetric benefit in DIBH can be achieved as long as the volume related benefit is about ≥8–9%. The lung expansion (breathing pattern) showed no impact on lung dose, but on heart dose. A stronger chest breathing (anterior expansion) for DIBH seems to be more beneficial than abdominal breathing.

Doses of radiation to the pericardium, instead of heart, are significant for survival in patients with non-small cell lung cancer

BACKGROUND AND PURPOSE

Higher cardiac dose was associated with worse overall survival in the RTOG0617 study. Pericardial effusion (PCE) is a common cardiac complication of thoracic radiation therapy (RT). We investigated whether doses of radiation to the heart and pericardium are associated with PCE and overall survival in patients treated with thoracic radiation for non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

A total of 94 patients with medically inoperable/unresectable NSCLC treated with definitive RT in prospective studies were reviewed for this secondary analysis. Heart and pericardium were contoured consistently according to the RTOG1106 Atlas, with the great vessels and thymus of the upper mediastinal structures included in the upper part of pericardium, only heart chambers included in the heart structure. Clinical factors and dose-volume parameters associated with PCE or survival were identified via Cox proportional hazards modeling. The risk of PCE and death were mapped using DVH atlases.

RESULTS

Median follow-up for surviving patients was 58 months. The overall rate of PCE was 40.4%. On multivariable analysis, dosimetric factors of heart and pericardium were significantly associated with the risk of PCE. Pericardial V30 and V55 were significantly correlated with overall survival, but presence of PCE and heart dosimetric factors were not.

CONCLUSION

PCE was associated with both heart and pericardial doses. The significance of pericardial dosimetric parameters, but not heart chamber parameters, on survival suggests the potential significance of radiation damage to the cranial region of pericardium.

Dosimetric comparison of deep-inspiration breath-hold and free-breathing treatment delivery techniques for left-sided breast cancer using 3D surface tracking

INTRODUCTION

While radiation therapy has been shown to increase local control and overall survival for breast cancer, late cardiac toxicity remains a concern. Morbidity and mortality have been shown to increase proportionally to the mean heart dose. Deep inspiration breath-hold (DIBH) can reduce heart dose compared to free-breathing (FB) by increasing the heart-to-chest wall distance, especially in left-sided breast cancer. We present our clinical experience with DIBH in left breast and chest-wall irradiation using 3D optical surface tracking.

MATERIALS & METHODS

29 patients were treated with DIBH using a surface tracking system that provides a real time 3D surface image of the patient. Comparisons of maximum and mean heart dose, heart-chest wall separation, and the percentage of lung volume that receives 20 or more Gy (V20) between the DIBH and hypothetical FB treatment plans were conducted with the Student's t-test. Correlation coefficients were also calculated for heart-chest wall separation, heart volume, and lung volume.

RESULTS

Comparing DIBH and FB plans showed a decrease in mean and maximum heart doses in all patients. Individual mean heart doses decreased by an average of 1.12 Gy, and the average mean heart dose for DIBH plans was significantly lower than corresponding FB plans (1.02 vs. 2.12 Gy; p < 0.0001). Maximum heart dose decreased by an average of 11.88 Gy and was significantly lower in DIBH versus FB plans (28.33 vs. 43.7 Gy; p = 0.0001). The average difference in heart to chest-wall separation between DIBH and FB images was 2.41 cm. DIBH left lung volume and measured increases in volume on inspiration inversely correlated with maximum heart dose (R = 0.39) and left lung V20 (R = 0.32).

CONCLUSIONS

DIBH with 3D surface tracking can significantly benefit patients with left sided disease by limiting the mean and maximum heart dose. DIBH appears to viably reduce heart dose for left-breast cancer patients and thus potentially reduce long-term complications without prolonging treatment delivery.

Comparison of heart dose in early-stage left-sided breast cancers treated with intraoperative radiation therapy or whole-breast irradiation with deep inspiratory breath hold

PURPOSE

To compare heart dose between patients treated with lumpectomy and either intraoperative radiation therapy (IORT) with CT-guided high-dose-rate brachytherapy (precision breast IORT [PB-IORT]) or whole-breast irradiation with deep inspiratory breath hold (WBI-DIBH) for early-stage left-sided breast cancers.

METHODS AND MATERIALS

We retrospectively identified the 17 patients with left-sided breast cancers treated with PB-IORT on a phase I clinical trial and 17 patients with left-sided tumors who had undergone lumpectomy and adjuvant WBI-DIBH. Dosimetric data were obtained. T-testing was performed and biologically effective doses (BEDs) were calculated using an α/β ratio of 2 Gy.

RESULTS

Mean heart dose was significantly lower with WBI-DIBH compared with PB-IORT (0.61 vs. 0.87 Gy, p = 0.006). Mean heart BED was lower with WBI-DIBH (0.62 vs. 1.3 Gy₂, p = 0.0001). Nominal maximum heart dose was higher with WBI-DIBH (11.37 vs. 4.81 Gy, p = 0.004). Maximum heart dose BED was similar between WBI-DIBH and IORT, 16.63 vs. 19.36 Gy (p = 0.64), respectively. No difference was found in mean left anterior descending artery dose: 2.18 Gy with WBI-DIBH and 1.89 Gy with IORT (p = 0.446). The maximum left anterior descending doses were 9.63 Gy and 3.62 Gy with WBI-DIBH and IORT, respectively (p = 0.016). Distance from the heart to the lumpectomy cavity was inversely associated with heart dose for PB-IORT, but not for WBI-IORT.

CONCLUSIONS

Heart doses were low in both groups. Expected increase in cardiac risk at these doses is minimal. It is unlikely that there will be a clinically significant difference in cardiac toxicity in patients treated with WBI-DIBH or PB-IORT. Further research is needed to evaluate the actual clinical impact of the observed cardiac doses delivered with these modalities.

Cardiac dose is associated with immunosuppression and poor survival in locally advanced non-small cell lung cancer

PURPOSE

Studies have associated increased radiation therapy (RT) heart dose with cardiac toxicity. Others have correlated RT-related immunosuppression with worsened survival. Given the large vascular volumes irradiated during locally advanced non-small cell lung cancer (LA-NSCLC) treatment, we hypothesized an association between increased heart dose and immunosuppression.

METHODS

We identified 400 LA-NSCLC patients treated with definitive RT ± chemotherapy between 2001 and 2016. Absolute lymphocyte counts (ALC), absolute neutrophil counts (ANC), and neutrophil-to-lymphocyte ratio (NLR = ANC/ALC) were analyzed pre-RT, during RT, and post-RT. Multivariable analysis (MVA) was performed to correlate Clinical factors with both hematologic toxicity and overall survival. An upper tertile threshold to increase specificity of NLR was chosen to dichotomize continuous hematologic variables.

RESULTS

Median follow up was 17 months (range 0.2-174 months) in all patients and 46 months (range 0.2-161 months) in survivors. A total of 94% of patients had stage III disease and 77% received concurrent chemo radiation. Two-year overall survival (OS), freedom from local recurrence (FFLR), and freedom from distant metastases (FFDM) was 42%, 60% and 45%, respectively. Median survival was 18 months. On MVA for OS (n = 207), male gender (Hazard Ratio [HR] 1.7; 95% CI 1.2-2.3), RT alone (HR 2.1; 95% CI 1.9-4.0), the percentage of heart receiving ≥50 Gy (V50) (HR 1.02; 95% CI 1.01-1.03), and higher NLR at 4 months (HR 1.02, 95% CI 1.01-1.03) were associated with reduced OS. ALC nadir was not associated with treatment outcomes. NLR >10.5 was associated with decreased OS (p < 0.001) and decreased FFDM (p = 0.04). On MVA evaluating factors associated with hematological toxicity (n = 247), adjuvant chemotherapy (HR 2.6; 95% CI 1.3-5.0; p = 0.006), RT alone (HR 3.6; 95% CI 1.1-12; p = 0.04), and heart V50 >25% (HR 2.0; 95% CI 1.1-3.5; p = 0.02) were associated with a NLR >10.5 4 months post-RT.

CONCLUSION

RT related immunosuppression is associated with worse patient outcomes, and may represent a source of increased mortality beyond cardiac toxicity alone.

Spatial orientation of coronary arteries and its implication for breast and thoracic radiotherapy-proposing "coronary strip" as a new organ at risk

OBJECTIVES

Radiotherapy for breast cancer has been associated with various side effects including cardiac sequelae. Our study aimed to define the spatial arc of spread of coronary vessels in a radian angle.

MATERIALS AND METHODS

We analysed the records of 51 CT coronary angiographies done in our hospital from January 2016 to July 2016. Left anterior descending (LAD) and right coronary (RC) were contoured for each patient. In each axial section, the radial spread of each artery was noted. A 5 mm brush tool was used to join the start and stop angles for making the summated "coronary strips".

RESULTS

Start and end angle of LAD with 95% confidence interval (CI) (in clockwise direction) were 23.9 ± 4° and 79.0 ± 6.6°, respectively. Mean LAD arc length ± SD (standard deviation) noted was 55.1° ± 7.7° (95% CI). For RC the smallest start angle and the largest end angle in all patients was 297.6° and 322.6°, respectively. RC start angle, end angle and arc length for 95% confidence interval were 322.2 ± 6.1°, 292.4 ± 11.6° and 29.8 ± 13.1°, respectively.

CONCLUSIONS

Our study provides a measure of the radial spread of the coronary arteries, especially from the perspective of breast radiotherapy. We have proposed a new organ at risk (OAR) of coronary strip. This should provide an easy and cost-effective way to delineate the coronary vasculature in breast cancer patients undergoing radiotherapy.

Evaluation of Heart Dose for Left-Sided Breast Cancer Patients Over an 11-Year Period Spanning the Transition From 2-Dimensional to 3-Dimensional Planning

INTRODUCTION/BACKGROUND

We evaluated heart dose from left breast radiotherapy with 2-dimensional (2D) versus 3-dimensional (3D) plans.

PATIENTS AND METHODS

Treatment plans from patients treated with standard fractionation for left breast cancer from 2003 to 2013 were reviewed, with patients grouped into 3 cohorts: 2003 to 2004 ("2D", with computed tomography scans for dose calculation but fields defined using simulation films; n = 29), 2005 to 2006 ("2D-post," after several influential articles on heart dose were published; n = 31), and 2007 to 2013 ("3D"; n = 256). All patients were treated with free-breathing technique. Heart volumes were retrospectively contoured for the earlier 2 cohorts. Mean heart dose (MHD) and percentage of structure receiving at least 25 Gy (V25 Gy) and percentage of structure receiving at least 5 Gy for the whole heart, left ventricle (LV), right ventricle (RV), and both ventricles were recorded and compared among cohorts.

RESULTS

MHD was 345 cGy (2D), 213 cGy (2D-post) and 213 cGy (3D). LV V25 Gy was 6.3%, 1.5%, and 1.1%, respectively. Lower doses were seen over time for all indices (analysis of variance, P < .0001). Post hoc tests indicated significantly higher doses for 2D versus 2D-post or 3D cohorts (P ≤ .001) for all parameters except RV V25 Gy (P = .24).

CONCLUSION

Heart doses were higher with 2D versus 3D plans. Cardiac doses and resulting toxicity with modern 3D planning might be lower than those in previous reports.

Treatment of breast cancer with simultaneous integrated boost in hybrid plan technique : Influence of flattening filter-free beams

OBJECTIVE

The present study compares in silico treatment plans using hybrid plan technique during hypofractionated radiation of mammary carcinoma with simultaneous integrated boost (SIB). The influence of 6 MV photon radiation in flattening filter free (FFF) mode against the clinical standard flattening filter (FF) mode is to be examined.

PATIENTS AND METHODS

RT planning took place with FF and FFF radiation plans for 10 left-sided breast cancer patients. Hybrid plans were realised with two tangential IMRT fields and one VMAT field. The dose prescription was in line with the guidelines in the ARO-2010-01 study. The dosimetric verification took place with a manufacturer-independent measurement system.

RESULTS

Required dose prescriptions for the planning target volumes (PTV) were achieved for both groups. The average dose values of the ipsi- and contralateral lung and the heart did not differ significantly. The overall average incidental dose to the left anterior descending artery (LAD) of 8.24 ± 3.9 Gy in the FFF group and 9.05 ± 3.7 Gy in the FF group (p < 0.05) were found. The dosimetric verifications corresponded to the clinical requirements. FFF-based RT plans reduced the average treatment time by 17 s/fraction.

CONCLUSION

In comparison to the FF-based hybrid plan technique the FFF mode allows further reduction of the average LAD dose for comparable target volume coverage without adverse low-dose exposure of contralateral structures. The combination of hybrid plan technique and 6 MV photon radiation in the FFF mode is suitable for use with hypofractionated dose schemes. The increased dose rate allows a substantial reduction of treatment time and thus beneficial application of the deep inspiration breath hold technique.

Uncertainties in estimating heart doses from 2D-tangential breast cancer radiotherapy

Background and purpose

We evaluated the accuracy of three methods of estimating radiation dose to the heart from two-dimensional tangential radiotherapy for breast cancer, as used in Denmark during 1982–2002.

Material and methods

Three tangential radiotherapy regimens were reconstructed using CT-based planning scans for 40 patients with left-sided and 10 with right-sided breast cancer. Setup errors and organ motion were simulated using estimated uncertainties. For left-sided patients, mean heart dose was related to maximum heart distance in the medial field.

Results

For left-sided breast cancer, mean heart dose estimated from individual CT-scans varied from <1 Gy to >8 Gy, and maximum dose from 5 to 50 Gy for all three regimens, so that estimates based only on regimen had substantial uncertainty. When maximum heart distance was taken into account, the uncertainty was reduced and was comparable to the uncertainty of estimates based on individual CT-scans. For right-sided breast cancer patients, mean heart dose based on individual CT-scans was always <1 Gy and maximum dose always <5 Gy for all three regimens.

Conclusions

The use of stored individual simulator films provides a method for estimating heart doses in left-tangential radiotherapy for breast cancer that is almost as accurate as estimates based on individual CT-scans.

Radiation dose distribution in functional heart regions from tangential breast cancer radiotherapy

BACKGROUND AND PURPOSE

To analyze the distribution of individually-determined radiation dose to the heart and its functional sub-structures after radiotherapy in breast cancer patients treated in Germany during 1998-2008.

MATERIAL AND METHODS

We obtained electronic treatment planning records for 769 female breast cancer patients treated with megavoltage tangential field radiotherapy. All dose distributions were re-calculated using Eclipse with the anisotropic analytical algorithm (AAA) for photon fields, and the electron Monte Carlo algorithm for electron boost fields. Based on individual dose volume histograms for the complete heart and several functional sub-structures, we estimated various dose measures in patient groups.

RESULTS

Mean heart dose spanned a range of 0.9-19.1Gy for left-sided radiotherapy and 0.3-11.6Gy for right-sided radiotherapy. Average (median) mean heart dose was 4.6Gy (3.7Gy) for left-sided radiotherapy, and 1.7Gy (1.4Gy) for right-sided RT. With left-sided radiotherapy, 66% of the patients had 2cm(3) of the complete heart exposed to at least 40Gy. Younger age, higher body mass index, tumor location in a medial quadrant, and presence of a parasternal field were also associated with higher heart dose.

CONCLUSION

Tumor location and treatment choices influence cardiac dose with complex interactions. There is considerable variability in heart dose, with dose metrics of different cardiac sub-structures showing different patterns in their dependency on external influences. Dose-response analysis of late cardiac effects after radiotherapy requires detailed individual dosimetry.

Anatomic features of interest in women at risk of cardiac exposure from whole breast radiotherapy

BACKGROUND AND PURPOSE

Left-sided breast radiotherapy (RT) can result in cardiac exposure. This study aims to identify predictive anatomic features in women requiring breath-hold (RT(BH)) for cardiac sparing during adjuvant whole breast RT.

MATERIAL AND METHODS

We retrospectively reviewed free-breathing (FB) CT scans of 80 women previously treated with left-sided breast RT. Unfavourable cardiac anatomy was defined as the number of consecutive axial CT slices (2 mm) in which the anterior chest wall contacted the heart (Contact(Heart)) or left ventricle (Contact(LV)). The sternal angle and Haller Index (HI) were used to measure chest concavity. Position and volume of post-operative cavity was also quantified.

RESULTS

Heart mean dose (D(mean)) was strongly correlated with Contact(LV) (r=0.625, p<0.001) and Contact(Heart) (r=0.524, p<0.001) but not significantly correlated with tumor size, cavity volume, heart volume, cavity distance to chest wall, sternal angle, or HI. ROC analysis of Contact(Heart) was most predictive of the need for breath-hold (RT(BH)) technique [Area Under Curve=0.815 (SE: 0.048; 95% CI: 0.721-0.91)] and ⩾25 Contact(Heart) CT slices predicted for heart D(mean) ⩾1.7 Gy (68% sensitivity and 82% specificity).

CONCLUSION

Contact(Heart) on FB CT of ⩾25 axial slices (2 mm), ⩾50 mm of para-sagittal heart contact, was predictive of higher heart D(mean) and suggest a potential need for RT(BH).