The Association of Incidental Radiation Dose to the Heart Base with Overall Survival and Cardiac Events after Curative-intent Radiotherapy for Non-small Cell Lung Cancer: Results from the NI-HEART Study

AIMS

Cardiac disease is a dose-limiting toxicity in non-small cell lung cancer radiotherapy. The dose to the heart base has been associated with poor survival in multiple institutional and clinical trial datasets using unsupervised, voxel-based analysis. Validation has not been undertaken in a cohort with individual patient delineations of the cardiac base or for the endpoint of cardiac events. The purpose of this study was to assess the association of heart base radiation dose with overall survival and the risk of cardiac events with individual heart base contours.

MATERIALS AND METHODS

Patients treated between 2015 and 2020 were reviewed for baseline patient, tumour and cardiac details and both cancer and cardiac outcomes as part of the NI-HEART study. Three cardiologists verified cardiac events including atrial fibrillation, heart failure and acute coronary syndrome. Cardiac substructure delineations were completed using a validated deep learning-based autosegmentation tool and a composite cardiac base structure was generated. Cox and Fine-Gray regressions were undertaken for the risk of death and cardiac events.

RESULTS

Of 478 eligible patients, most received 55 Gy/20 fractions (96%) without chemotherapy (58%), planned with intensity-modulated radiotherapy (71%). Pre-existing cardiovascular morbidity was common (78% two or more risk factors, 46% one or more established disease). The median follow-up was 21.1 months. Dichotomised at the median, a higher heart base Dmax was associated with poorer survival on Kaplan-Meier analysis (20.2 months versus 28.3 months; hazard ratio 1.40, 95% confidence interval 1.14-1.75, P = 0.0017) and statistical significance was retained in multivariate analyses. Furthermore, heart base Dmax was associated with pooled cardiac events in a multivariate analysis (hazard ratio 1.75, 95% confidence interval 1.03-2.97, P = 0.04).

CONCLUSIONS

Heart base Dmax was associated with the rate of death and cardiac events after adjusting for patient, tumour and cardiovascular factors in the NI-HEART study. This validates the findings from previous unsupervised analytical approaches. The heart base could be considered as a potential sub-organ at risk towards reducing radiation cardiotoxicity.

Implementation of 26 Gy in five fractions over 1 week adjuvant radiotherapy for breast cancer: Prospective report of acute skin toxicity and consideration of resource implications

PURPOSE

In March 2020, a 1-week adjuvant breast radiotherapy schedule, 26 Gy in 5 fractions, was adopted to reduce the risk of COVID19 for staff and patients. This study quantifies acute toxicity rates and the effect on linac capacity.

MATERIALS AND METHODS

This is a report of consecutive patients receiving ultrafractionated breast radiotherapy ( ± sequential boost) Mar-Aug 2020. Virtual consultations assessed acute skin toxicity during treatment and weeks 1, 2, 3 and 4 post treatment using CTCAE V5 scoring criteria. The number of linac minutes saved was estimated accounting for boost and DIBH use.

RESULTS

In total, 128/135 (95%) patients, including 31/33 boost patients, completed at least 3/5 assessments. 0/128 (0%) reported moist desquamation not confined to skin folds or minor bleeding (Grade 3), 41/128 (32%) reported brisk erythema, moist desquamation confined to skin folds or breast swelling (Grade 2), 62/128 (48%) reported faint erythema or dry desquamation (Grade 1) as their worst skin toxicity, with the remaining 20% reporting no skin toxicity. The highest prevalence of grade 2 toxicity occurred week 1 following treatment (20%), reducing to 3% by week 4. There was no difference in toxicity between those who received a boost versus not (p = 1.00). Delivering this schedule to 135 patients over six months saved 21,300 linac minutes and 1485 hospital visits compared to a 3-week schedule.

CONCLUSION

Rapidly implementing ultrahypofractionated breast radiotherapy is feasible and acute toxicity rates are acceptable even when followed by boost.

Resource implications of evolving breast cancer radiotherapy treatment protocols

•Updated breast cancer adjuvant radiotherapy treatment protocols resulted in a reduction of staff time (linac and non-linac) and overall resource costs. •The introduction of ultrahypofractionated 26Gy/5 radiotherapy resulted in the greatest saving of resource costs, €47,489, and staff time, 13,820 min. •Expanded use of IMN radiotherapy resulted in the largest increase in resource costs, €7,612, and staff time, 11,345 min. •After implementing all treatment protocols changes, the overall resource cost was reduced by €62,477 (11.5 %). •Overall linac time was reduced by 9700 min (12.9 %) and non-linac time was reduced by 1315 min (1.1 %).

Estimated Doses to the Heart, Lungs and Oesophagus and Risks From Typical UK Radiotherapy for Early Breast Cancer During 2015-2023

PURPOSE

Breast cancer radiotherapy can increase the risks of heart disease, lung cancer and oesophageal cancer. At present, the best dosimetric predictors of these risks are mean doses to the whole heart, lungs and oesophagus, respectively. We aimed to estimate typical doses to these organs and resulting risks from UK breast cancer radiotherapy.

METHODS

A systematic review and meta-analysis was conducted of planned or delivered mean doses to the whole heart, lungs or oesophagus from UK breast cancer radiotherapy in studies published during 2015-2023. Average mean doses were summarised for combinations of laterality and clinical targets. Heart disease and lung cancer mortality risks were then estimated using established models.

RESULTS

For whole heart, thirteen studies reported 2893 doses. Average mean doses were higher in left than in right-sided radiotherapy and increased with extent of clinical targets. For left-sided radiotherapy, average mean heart doses were: 2.0 Gy (range 1.2-8.0 Gy) breast/chest wall, 2.7 Gy (range 0.6-5.6 Gy) breast/chest wall with either axilla or supraclavicular nodes and 2.9 Gy (range 1.3-4.7 Gy) breast/chest wall with nodes including internal mammary. For right-sided radiotherapy, average mean heart doses were: 1.0 Gy (range 0.3-1.0 Gy) breast/chest wall and 1.2 Gy (range 1.0-1.4 Gy) breast/chest wall with either axilla or supraclavicular nodes. There were no whole heart dose estimates from right internal mammary radiotherapy. For whole lung, six studies reported 2230 doses. Average mean lung doses increased with extent of targets irradiated: 2.6 Gy (range 1.4-3.0 Gy) breast/chest wall, 3.0 Gy (range 0.9-5.1 Gy) breast/chest wall with either axilla or supraclavicular nodes and 7.1 Gy (range 6.7-10.0 Gy) breast/chest wall with nodes including internal mammary. For whole oesophagus, two studies reported 76 doses. Average mean oesophagus doses increased with extent of targets irradiated: 1.4 Gy (range 1.0-2.0 Gy) breast/chest wall with either axilla or supraclavicular nodes and 5.8 Gy (range 1.9-10.0 Gy) breast/chest wall with nodes including internal mammary.

CONCLUSIONS

The typical doses to these organs may be combined with dose-response relationships to estimate radiation risks. Estimated 30-year absolute lung cancer mortality risks from modern UK breast cancer radiotherapy for patients irradiated when aged 50 years were 2-6% for long-term continuing smokers, and <1% for non-smokers. Estimated 30-year mortality risks for heart disease were <1%.

Financial Implications of Evolving Breast Cancer Radiotherapy Treatment Protocols

PURPOSE/OBJECTIVE(S)

Adjuvant radiotherapy for breast cancer represents a significant portion of radiotherapy (RT) treatments. The resource implications of evidence-based changes in treatment protocols must be defined to facilitate RT service planning. We designed a study to calculate the impact of past changes and create a model to allow prediction of costs implications for future changes.

MATERIALS/METHODS

Changes in RT treatment (shown in table 1) in the past 3 years were identified in consultation with clinical staff and by reviewing institutional treatment guidelines. Resource and infrastructure costs were calculated for each protocol. Staff time was calculated using standard time slots where known (e.g., CT simulation appointment) and estimates based on discussion with staff (e.g., time to plan whole breast RT). Cost / Gy was calculated based on Linac cost of €2.5M, 10% annual service charge over 12-year lifetime, 2.7 patients treated / hour (verified institutional metric) and standard 2Gy fraction, giving €37.72 / Gy. We did not include facilities costs nor account for differing treatment outcomes. We collected relevant data on a consecutive 6-month sample (Jan - Jun 2019) of women receiving adjuvant RT for breast cancer (n = 224). Total costs were calculated by applying costs for each protocol change to the women in this cohort eligible for the changes.

RESULTS

Protocol changes and costs are summarized in table 1. The use of DIBH for women <60 years receiving IMN RT (left and right sided) added a cost. The largest cost saving resulted from more selective tumor bed boost, a saving of €462,138. The potential impact of a 5-fraction boost for women with non-low risk DCIS was estimated.

CONCLUSION

In the cohort analyzed, identified changes in adjuvant breast radiotherapy resulted in overall savings due to updated indications for boost and the implementation of ultra-hypofractionated radiotherapy. We are now analyzing the impact of introducing simultaneous integrated boost and partial breast radiotherapy.