Dose-volume effects of breast cancer radiation therapy on the risk of second oesophageal cancer

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

Organ at risk dose-volume metrics in a series of hypofractionated breast radiotherapy with integrated boost

Dose and volume metrics to organs at risk are used for evaluation and optimization in radiotherapy planning. However, the numerous choices of metrics can be confusing. In a series of patients treated with hypofractionation and an integrated boost for breast cancer, we aim to determine if a parsimonious selection of representative metrics can be identified. The dosimetries of 42 patients receiving 42 Gy to the breast, with or without nodal irradiation, and 51 Gy integrated boost to tumor bed in 15 fractions were reviewed. For each organ-heart, lungs, and contralateral breast-cumulative dose-volume histograms were used to extract values for 3 basic metric classes: Two additional classes were considered: Pearson correlation coefficient R was calculated between pairs of values within each basic class and with the 2 additional classes for each organ. The interquartile ranges of correlations for D.yy, Vrel.xx, and Vabs.xx were as follows: The mean dose correlated with all basic classes for the heart and lungs, and with dose D.yy and volumes at Vrel.10-Vabs.10 for the contralateral breast. The standard deviation correlated with Vrel.xx and Vabs.xx for the heart and lungs (R ≥ 0.70). Among the D.yy, D.50 (median dose) correlated with the mean and standard deviation for all organs (R = 0.65-0.96). The mean, standard deviation, and median doses were the preeminent correlators. These statistics appear to be parsimonious representatives of doses to organs. Further studies with other radiotherapy series will be necessary to validate these observations.

Radiation Dose-Volume-Response Relationships for Adverse Events in Childhood Cancer Survivors: Introduction to the Scientific Issues in PENTEC

At its very core, radiation oncology involves a trade-off between the benefits and risks of exposing tumors and normal tissue to relatively high doses of ionizing radiation. This trade-off is particularly critical in childhood cancer survivors (CCS), in whom both benefits and risks can be hugely consequential due to the long life expectancy if the primary cancer is controlled. Estimating the normal tissue-related risks of a specific radiation therapy plan in an individual patient relies on predictive mathematical modeling of empirical data on adverse events. The Pediatric Normal-Tissue Effects in the Clinic (PENTEC) collaborative network was formed to summarize and, when possible, to synthesize dose-volume-response relationships for a range of adverse events incident in CCS based on the literature. Normal-tissue clinical radiation biology in children is particularly challenging for many reasons: (1) Childhood malignancies are relatively uncommon-constituting approximately 1% of new incident cancers in the United States-and biologically heterogeneous, leading to many small series in the literature and large variability within and between series. This creates challenges in synthesizing data across series. (2) CCS are at an elevated risk for a range of adverse health events that are not specific to radiation therapy. Thus, excess relative or absolute risk compared with a reference population becomes the appropriate metric. (3) Various study designs and quantities to express risk are found in the literature, and these are summarized. (4) Adverse effects in CCS often occur 30, 50, or more years after therapy. This limits the information content of series with even very extended follow-up, and lifetime risk estimates are typically extrapolations that become dependent on the mathematical model used. (5) The long latent period means that retrospective dosimetry is required, as individual computed tomography-based radiation therapy plans gradually became available after 1980. (6) Many individual patient-level factors affect outcomes, including age at exposure, attained age, lifestyle exposures, health behaviors, other treatment modalities, dose, fractionation, and dose distribution. (7) Prospective databases with individual patient-level data and radiation dosimetry are being built and will facilitate advances in dose-volume-response modeling. We discuss these challenges and attempts to overcome them in the setting of PENTEC.

Radiation Therapy Technology Advances and Mitigation of Subsequent Neoplasms in Childhood Cancer Survivors

PURPOSE

In this Pediatric Normal Tissue Effects in the Clinic (PENTEC) vision paper, challenges and opportunities in the assessment of subsequent neoplasms (SNs) from radiation therapy (RT) are presented and discussed in the context of technology advancement.

METHODS AND MATERIALS

The paper discusses the current knowledge of SN risks associated with historic, contemporary, and future RT technologies. Opportunities for research and SN mitigation strategies in pediatric patients with cancer are reviewed.

RESULTS

Present experience with radiation carcinogenesis is from populations exposed during widely different scenarios. Knowledge gaps exist within clinical cohorts and follow-up; dose-response and volume effects; dose-rate and fractionation effects; radiation quality and proton/particle therapy; age considerations; susceptibility of specific tissues; and risks related to genetic predisposition. The biological mechanisms associated with local and patient-level risks are largely unknown.

CONCLUSIONS

Future cancer care is expected to involve several available RT technologies, necessitating evidence and strategies to assess the performance of competing treatments. It is essential to maximize the utilization of existing follow-up while planning for prospective data collection, including standardized registration of individual treatment information with linkage across patient databases.

Proton Beam Therapy for Early Breast Cancer: A Systematic Review and Meta-analysis of Clinical Outcomes

PURPOSE

Adjuvant proton beam therapy (PBT) is increasingly available to patients with breast cancer. It achieves better planned dose distributions than standard photon radiation therapy and therefore may reduce the risks. However, clinical evidence is lacking.

METHODS AND MATERIALS

A systematic review of clinical outcomes from studies of adjuvant PBT for early breast cancer published in 2000 to 2022 was undertaken. Early breast cancer was defined as when all detected invasive cancer cells are in the breast or nearby lymph nodes and can be removed surgically. Adverse outcomes were summarized quantitatively, and the prevalence of the most common ones were estimated using meta-analysis.

RESULTS

Thirty-two studies (1452 patients) reported clinical outcomes after adjuvant PBT for early breast cancer. Median follow-up ranged from 2 to 59 months. There were no published randomized trials comparing PBT with photon radiation therapy. Scattering PBT was delivered in 7 studies (258 patients) starting 2003 to 2015 and scanning PBT in 22 studies (1041 patients) starting 2000 to 2019. Two studies (123 patients) starting 2011 used both PBT types. For 1 study (30 patients), PBT type was unspecified. Adverse events were less severe after scanning than after scattering PBT. They also varied by clinical target. For partial breast PBT, 498 adverse events were reported (8 studies, 358 patients). None were categorized as severe after scanning PBT. For whole breast or chest wall ± regional lymph nodes PBT, 1344 adverse events were reported (19 studies, 933 patients). After scanning PBT, 4% (44/1026) of events were severe. The most prevalent severe outcome after scanning PBT was dermatitis, which occurred in 5.7% (95% confidence interval, 4.2-7.6) of patients. Other severe adverse outcomes included infection, pain, and pneumonitis (each ≤1%). Of the 141 reconstruction events reported (13 studies, 459 patients), the most prevalent after scanning PBT was prosthetic implant removal (34/181, 19%).

CONCLUSIONS

This is a quantitative summary of all published clinical outcomes after adjuvant PBT for early breast cancer. Ongoing randomized trials will provide information on its longer-term safety compared with standard photon radiation therapy.

The Pediatric Proton and Photon Therapy Comparison Cohort: Study Design for a Multicenter Retrospective Cohort to Investigate Subsequent Cancers After Pediatric Radiation Therapy

Purpose

The physical properties of protons lower doses to surrounding normal tissues compared with photons, potentially reducing acute and long-term adverse effects, including subsequent cancers. The magnitude of benefit is uncertain, however, and currently based largely on modeling studies. Despite the paucity of directly comparative data, the number of proton centers and patients are expanding exponentially. Direct studies of the potential risks and benefits are needed in children, who have the highest risk of radiation-related subsequent cancers. The Pediatric Proton and Photon Therapy Comparison Cohort aims to meet this need.

Methods and Materials

We are developing a record-linkage cohort of 10,000 proton and 10,000 photon therapy patients treated from 2007 to 2022 in the United States and Canada for pediatric central nervous system tumors, sarcomas, Hodgkin lymphoma, or neuroblastoma, the pediatric tumors most frequently treated with protons. Exposure assessment will be based on state-of-the-art dosimetry facilitated by collection of electronic radiation records for all eligible patients. Subsequent cancers and mortality will be ascertained by linkage to state and provincial cancer registries in the United States and Canada, respectively. The primary analysis will examine subsequent cancer risk after proton therapy compared with photon therapy, adjusting for potential confounders and accounting for competing risks.

Results

For the primary aim comparing overall subsequent cancer rates between proton and photon therapy, we estimated that with 10,000 patients in each treatment group there would be 80% power to detect a relative risk of 0.8 assuming a cumulative incidence of subsequent cancers of 2.5% by 15 years after diagnosis. To date, 9 institutions have joined the cohort and initiated data collection; additional centers will be added in the coming year(s).

Conclusions

Our findings will affect clinical practice for pediatric patients with cancer by providing the first large-scale systematic comparison of the risk of subsequent cancers from proton compared with photon therapy.

Beyond the heart in hypofractionated radiotherapy and in the transition from 3D to IMRT/VMAT

Background

The knowledge of the risks induced by radiation with hypofractionation regimens has only recently been estimated together with its implementation as a management standard. However, the dose to other risk organs with intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) is not clear, that is why this is only a reference study of radiation doses to organs at risk in hypofractionation in our center.

Materials and methods

We completed a retrospective and observational analysis of 1398 patients treated with adjuvant hypofractionated radiotherapy from 2015 to 2018, using the clinical records and dose-volume histogram of patients treated with moderate hypofractionated adjuvant radiotherapy. To analyze the institutional experience on the dosimetry of the esophagus and liver as risk organs in the use of moderate adjuvant hypofractionated radiotherapy in breast cancer.

Results

The dosimetry of the esophagus was 3271 cGy DMax, 177 cGy DMed, 68 cGy D50%, 500 cGy DcMAX with 3D RT and 4124 cGy DMax, 1242 cGy DMed, 934.50 cGy D50%, 3213 cGy DcMAX with IMRT/VMAT and the dosimetry for the liver was for right breast cancer 466 cGy DMed, 102 cGy D50% and 8% V20, for left breast cancer 22 cGy DMed, 6.10 cGy D50% and 0.3% V20.

Conclusion

The statistically significant differences in irradiation show the lack of consensus on the optimal restrictions in hypofractionation regimens to reduce clinical sequela; consequently, the variability in the specification of each radiation oncologist is observed; standardization in our center can lead to improvement in the quality of treatments.

Esophageal Neuroendocrine Carcinoma Presenting After Definitive Chemoradiation of Squamous Cell Carcinoma in the Same Location

Esophageal neuroendocrine carcinoma is very rare and highly aggressive. An 85-year-old man with a history of esophageal squamous cell carcinoma in remission presented 4 years after definitive chemoradiation with new-onset dysphagia. Endoscopy with biopsy revealed high-grade malignancy consistent with neuroendocrine carcinoma. Treatment options were limited to chemotherapy because of his metastatic disease, and he unfortunately died 14 months after diagnosis. The occurrence of esophageal neuroendocrine carcinoma in a site of prior squamous cell carcinoma is very uncommon, and this likely represents a case of radiation-induced malignancy. Therefore, when undergoing radiotherapy, patients and providers should discuss the possibility of this life-threatening complication.

Risk and prognosis of secondary esophagus cancer after radiotherapy for breast cancer

Although radiation therapy (RT) improves locoregional recurrence and overall survival in breast cancer (BC), it is not yet clear whether RT affects the risk of patients with BC developing second esophageal cancer (SEC). We enrolled patients with BC as their first primary cancer from nine registries in the Surveillance, Epidemiology, and End Results (SEER) database between 1975 and 2018. Fine-Gray competing risk regressions were assessed to determine the cumulative incidence of SECs. The standardized incidence ratio (SIR) was used to compare the prevalence of SECs among BC survivors to that in the general population of the US. Kaplan-Meier survival analysis was applied to calculate the 10-year overall survival (OS) and cancer-specific survival (CSS) rates for SEC patients. Among the 523,502 BC patients considered herein, 255,135 were treated with surgery and RT, while 268,367 had surgery without radiotherapy. In a competing risk regression analysis, receiving RT was associated with a higher risk of developing an SEC in BC patients than that in the patients not receiving RT (P = .003). Compared to the general population of the US, the BC patients receiving RT showed a greater incidence of SEC (SIR, 1.52; 95% confidence interval [CI], 1.34-1.71, P < .05). The 10-year OS and CSS rates of SEC patients after RT were comparable to those of the SEC patients after no RT. Radiotherapy was related to an increased risk of developing SECs in patients with BC. Survival outcomes for patients who developed SEC after RT were similar to those after no RT.

Comparison of esophagus dose in breast cancer patients undergoing supraclavicular irradiation with and without esophagus countering

CONTEXT

Esophagus toxicity and the risk of esophageal cancer are linked to radiation dose to the esophagus in breast cancer patients undergoing supraclavicular irradiation.

AIMS

The aim of this study was to evaluate the impact of esophagus contouring on the dose received in the esophagus in breast cancer patients undergoing supraclavicular irradiation.

SETTING AND DESIGN

This study included 30 treatment plans for breast cancer patients who received 50 Gy/25 fractions (2 Gy/fraction/day) using 3D-conformal radiation therapy (3D-CRT) to the whole breast or chest wall and supraclavicular.

METHODS AND MATERIALS

Our study included two groups: the non-sparing group was the treatment plan in which the esophagus was not delineated and the esophagus sparing group was generated, in which the plans were modified to spare the esophagus. The maximum dose, mean dose, and percentage of esophagus volume received, 5, 10, 15, and 20 Gy, respectively (V5, V10, V15, and V20), were used to evaluate both groups.

STATISTICAL ANALYSIS

One-way analysis of variance was used. A P value <0.05 was considered statistically significant.

RESULTS

The esophagus sparing group plans show a reduction in the esophageal mean dose Dmean (5.72 ± 5.15) Gy when compared to the non-sparing group (7.83 ± 3.31) Gy. Likewise, the maximum dose, V5, V10, V15, and V20 were reduced in the esophagus sparing group. All dosimetric parameters were significantly higher (P < 0.05) in patients with left breast cancer for both groups.

CONCLUSION

Our results suggest that it is possible to reduce the dose to the esophagus by considering the esophagus during treatment planning while maintaining plan quality. This reduction could lead to the greatest predicted decrease in acute esophagitis and esophageal cancer.

Radiotherapy-related dose and irradiated volume effects on breast cancer risk among Hodgkin lymphoma survivors

Background

Breast cancer (BC) risk is increased among Hodgkin lymphoma (HL) survivors treated with chest radiotherapy. Case-control studies showed a linear radiation dose-response relationship for estimated dose to the breast tumor location. However, these relative risks cannot be used for absolute risk prediction of BC anywhere in the breasts. Furthermore, the independent and joint effects of radiation dose and irradiated volumes are unclear. Therefore, we examined the effects of mean breast dose and various dose-volume parameters on BC risk in HL patients.

Methods

We conducted a nested case-control study of BC among 5-year HL survivors (173 case patients, 464 matched control patients). Dose-volume histograms were obtained from reconstructed voxel-based 3-dimensional dose distributions. Summary parameters of dose-volume histograms were studied next to mean and median breast dose, Gini index, and the new dose metric mean absolute difference of dose, using categorical and linear excess odds ratio (EOR) models. Interactions between dose-volume parameters and mean dose were also examined.

Results

Statistically significant linear dose-response relationships were observed for mean breast dose (EOR per Gy = 0.19, 95% confidence interval [CI] = 0.05 to 1.06) and median dose (EOR/Gy = 0.06, 95% CI = 0.02 to 0.19), with no statistically significant curvature. All metrics except Gini and mean absolute difference were positively correlated with each other. These metrics all showed similar patterns of dose-response that were no longer statistically significant when adjusting for mean dose. No statistically significant modification of the effect of mean dose was observed.

Conclusion

Mean breast dose predicts subsequent BC risk in long-term HL survivors.

Radiation-Induced Toxicity Risks in Photon Versus Proton Therapy for Synchronous Bilateral Breast Cancer

Purpose

This study compares photon and proton therapy plans for patients with synchronous bilateral early breast cancer and estimates risks of early and late radiation-induced toxicities.

Materials and Methods

Twenty-four patients with synchronous bilateral early breast cancer receiving adjuvant radiation therapy using photons, 3-dimensional conformal radiation therapy or volumetric modulated arc therapy, were included and competing pencil beam scanning proton therapy plans were created. Risks of dermatitis, pneumonitis, acute esophageal toxicity, lung and breast fibrosis, hypothyroidism, secondary lung and esophageal cancer and coronary artery events were estimated using published dose-response relationships and normal tissue complication probability (NTCP) models.

Results

The primary clinical target volume V95% and/or nodal clinical target volume V90% were less than 95% in 17 photon therapy plans and none of the proton plans. Median NTCP of radiation dermatitis ≥ grade 2 was 18.3% (range, 5.4-41.7) with photon therapy and 58.4% (range, 31.4-69.7) with proton therapy. Median excess absolute risk (EAR) of secondary lung cancer at age 80 for current and former smokers was 4.8% (range, 0.0-17.0) using photons and 2.7% (range, 0.0-13.6) using protons. Median EAR of coronary event at age 80, assuming all patients have preexisting cardiac risk factors, was 1.0% (range, 0.0-5.6) with photons and 0.2% (range, 0.0-1.3) with protons.

Conclusion

Proton therapy plans improved target coverage and reduced risk of coronary artery event and secondary lung cancer while increasing the risk of radiation dermatitis.

Exposure of the oesophagus in breast cancer radiotherapy: A systematic review of oesophagus doses published 2010-2020

BACKGROUND AND PURPOSE

Breast cancer radiotherapy can increase the risk of subsequent primary oesophageal cancer, with risk increasing according to oesophagus radiation dose. We describe oesophagus exposure from modern breast cancer regimens and discuss the risks of oesophageal cancer for women irradiated recently.

MATERIALS AND METHODS

A systematic review was undertaken of oesophagus doses from breast cancer radiotherapy regimens published during 2010-2020. Mean and maximum oesophagus doses were described for different target regions irradiated and different radiotherapy techniques.

RESULTS

In 112 published regimens from 18 countries, oesophagus doses varied with target region. For partial breast irradiation, average mean oesophagus dose was 0.2 Gy (range 0.1-0.4) in four regimens; maximum dose was not reported. For breast or chest wall radiotherapy, average oesophagus doses were mean 1.8 Gy (range 0.1-10.4) in 24 regimens and maximum 6.7 Gy (range 0.4-14.3) in seven regimens. For radiotherapy including a nodal region, average oesophagus doses were higher: mean 11.4 Gy (range <0.1-29.3) in 61 regimens and maximum 34.4 Gy (range 3.4-51.3) in 55 regimens. Average mean oesophagus doses were >10 Gy for intensity modulated nodal radiotherapy, but lower for other node techniques.

CONCLUSIONS

Mean oesophagus doses from partial breast and breast/chest wall regimens were usually less than 2 Gy, hence radiation-risks will be very small. However, for radiotherapy including lymph nodes, average mean oesophagus dose of 11.4 Gy may nearly double oesophageal cancer risk. Consideration of oesophageal exposure during nodal radiotherapy planning may reduce the risks of radiation-related oesophageal cancer for women irradiated today.