Individualized estimates of second cancer risks after contemporary radiation therapy for Hodgkin lymphoma

Toward a paradigm shift in prognostication and treatment of early-stage Hodgkin lymphoma

Twenty years after the conceptual revolution that occurred in the millennium turnaround upon the introduction of PET/CT in lymphoma staging, restaging, and prognostication, a number of new parameters for PET reading have been proposed: (1) the shift from a qualitative to a semi-quantitative reading for PET reporting, (2) an international consensus on these novel interpretation keys, (3) a standardized and agreed procedure to measure the total metabolic tumour volume (TMTV), and (4) the proposition of new indexes to portray the tumour spread: (D-Max and Total Lesion Surface -TLS). These proved to be very powerful prognosticators, able to revolutionize the traditional Ann Arbor four-stage lymphoma staging. During the 17° Lugano meeting on lymphoma, one main question was asked to experts attending a closed workshop dedicated to new metrics for lymphoma diagnosis, staging, restaging, and prognostication: "Should the traditional 4-stage anatomic staging system be simplified to a more clinically relevant 2-stage system (e.g., limited vs. extensive disease)?" Early-stage HL is an example of how these new metrics could fit with this proposal.

A Case Report on Breast Cancer Following Mantle Radiation for Hodgkin Lymphoma: Screening and Management

Hodgkin lymphoma survivors who received mantle radiation are at risk of developing secondary malignant neoplasms. There is no established recommended screening guideline for this population. We discuss the case of a patient with a history of Hodgkin lymphoma status post-mantle field radiation, thyroid cancer status post-thyroidectomy, and now breast cancer following mantle radiation. The risk of adverse effects from mantle field radiation is well documented and includes secondary cancers of the thyroid, breast, lung, and cardiovascular disease. Advances in technology have led to an international paradigm shift in the management of Hodgkin lymphoma to reduce the diameter and dose of radiation based on the patient's anatomy. However, there is no consensus regarding the optimal frequency or modality of breast cancer screening in patients with Hodgkin lymphoma status post-mantle radiation who are now in remission. We discuss screening methods for this population, which has a high risk of developing breast cancer, and emphasize the need for personalized medicine.

Harnessing multi-source data for individualized care in Hodgkin Lymphoma

Hodgkin lymphoma is a rare, but highly curative form of cancer, primarily afflicting adolescents and young adults. Despite multiple seminal trials over the past twenty years, there is no single consensus-based treatment approach beyond use of multi-agency chemotherapy with curative intent. The use of radiation continues to be debated in early-stage disease, as part of combined modality treatment, as well as in salvage, as an important form of consolidation. While short-term disease outcomes have varied little across these different approaches across both early and advanced stage disease, the potential risk of severe, longer-term risk has varied considerably. Over the past decade novel therapeutics have been employed in the retrieval setting in preparation to and as consolidation after autologous stem cell transplant. More recently, these novel therapeutics have moved to the frontline setting, initially compared to standard-of-care treatment and later in a direct head-to-head comparison combined with multi-agent chemotherapy. In 2018, we established the HoLISTIC Consortium, bringing together disease and methods experts to develop clinical decision models based on individual patient data to guide providers, patients, and caregivers in decision-making. In this review, we detail the steps we followed to create the master database of individual patient data from patients treated over the past 20 years, using principles of data science. We then describe different methodological approaches we are taking to clinical decision making, beginning with clinical prediction tools at the time of diagnosis, to multi-state models, incorporating treatments and their response. Finally, we describe how simulation modeling can be used to estimate risks of late effects, based on cumulative exposure from frontline and salvage treatment. The resultant database and tools employed are dynamic with the expectation that they will be updated as better and more complete information becomes available.

Best practice & research clinical haematology: Screening for breast cancer in hodgkin lymphoma survivors

Childhood and young adult survivors of Hodgkin lymphoma are at an elevated risk of developing breast cancer. Breast cancer risk is felt to originate from chest wall radiation exposure prior to the third decade of life, with incidence beginning to rise approximately eight to ten years following Hodgkin lymphoma treatment. Although incidence varies according to age at radiation exposure, dosage, and treatment fields, cohort studies have documented a cumulative incidence of breast cancer of 10-20% by 40 years of age. Women with a history of chest radiation for Hodgkin lymphoma are counselled to begin screening with bilateral breast MRI at 25 years of age, or eight years after radiation, whichever occurs later. Outside of high-risk surveillance, the optimal management approach for women with prior radiation exposure continues to evolve. When diagnosed with breast malignancy, evidence supports consideration of unilateral therapeutic and contralateral prophylactic mastectomy, although breast conserving surgery may be considered following multidisciplinary assessment. This review will address the epidemiology, characteristics, screening and management guidelines, and breast-cancer prevention efforts for Hodgkin lymphoma survivors treated with radiation therapy in adolescence and young adulthood.

Colorectal Cancer Risk and Recommendations for Colorectal Cancer Surveillance in Adult Survivors of Childhood Cancer

While many organizations have published guidance on the approach to colorectal cancer (CRC) screening in average-risk and certain high-risk groups, adult survivors of childhood cancer (ASCC) who have a heightened risk of CRC are rarely included as a target group for enhanced CRC surveillance. The population of ASCC continues to grow due to increasingly effective cancer therapies and improved survival. With this increased survival comes an increased risk for subsequent malignant neoplasms, including CRC. Since there is little published guidance for CRC surveillance in ASCC and limited awareness of increased CRC risk among both physicians and patients, the objectives of our paper are to review the incidence of and risk factors for colorectal neoplasia in ASCC, describe the clinical phenotypes of colorectal neoplasia in ASCC, review published surveillance strategies based on consensus-based survivorship guidelines, and outline areas for future research to optimize surveillance strategies.

Radiation doses to mediastinal organs at risk in early-stage unfavorable Hodgkin lymphoma- a risk stratified analysis of the GHSG HD17 trial

Introduction

The German Hodgkin Study Group (GHSG) HD17 trial established the omission of radiotherapy (RT) for patients with early-stage unfavorable Hodgkin lymphoma being PET-negative after 2 cycles of BEACOPP escalated plus 2 cycles of ABVD. This patient group reveals heterogeneity in characteristics and disease extent which prompted us to perform a decisive dosimetric analysis according to GHSG risk factors. This may help to tailor RT individually balancing risks and benefits.

Methods

For quality assurance, RT-plans were requested from the treating facilities (n= 141) and analyzed centrally. Dose-volume histograms were scanned either paper-based or digitally to obtain doses to mediastinal organs. These were registered and compared according to GHSG risk factors.

Results

Overall, RT plans of 176 patients were requested, 139 of which had dosimetric information on target volumes within the mediastinum. Most of these patients were stage II (92.8%), had no B-symptoms (79.1%) and were aged < 50 years (89.9%). Risk factors were present in 8.6% (extranodal involvement), 31.7% (bulky disease), 46.0% (elevated erythrocyte sedimentation rate) and 64.0% (three involved areas), respectively. The presence of bulky disease significantly affected the mean RT doses to the heart (p=0.005) and to the left lung (median: 11.3 Gy vs. 9.9 Gy; p=0.042) as well as V5 of the right and left lung, respectively (median right lung: 67.4% vs. 51.0%; p=0.011; median left lung: 65.9% vs. 54.2%; p=0.008). Significant differences in similar organs at risk parameters could be found between the sub-cohorts with the presence or absence of extranodal involvement, respectively. In contrast, an elevated erythrocyte sedimentation rate did not deteriorate dosimetry significantly. No association of any risk factor with radiation doses to the female breast was found.

Conclusion

Pre-chemotherapy risk factors may help to predict potential RT exposure to normal organs and to critically review treatment indication. Individualized risk-benefit evaluations for patients with HL in early-stage unfavorable disease are mandatory.

Radiation-induced soft tissue sarcoma of the neck after radiation therapy for Hodgkin's lymphoma: a clinical case

Background. Radiation-induced malignancies are one of the long-term complications of radiation therapy, which is widely used to treat some tumors. The latency period before a second tumor develops varies from 3 to 60 years. Epithelial tumors and hemoblastoses occur after low-dose radiation therapy and sarcomas after high-dose radiation therapy. Aim. To present a case of radiation-induced soft tissue angiosarcoma of the neck after the cure of Hodgkin's disease. Materials and methods. A 41-year-old patient with Hodgkin's nodular lymphoma with the lymphoid predominance of stage IIIA with involvement of the right cervical and clavicular lymph nodes, mediastinum, and abdominal lymph nodes was followed-up. In 2004 the patient underwent four cycles of polychemotherapy per ABVD regimen followed by radiotherapy of the right cervical and clavicular lymph nodes and mediastinum, with a total focal dose of 40 Gy. Results. Seventeen years after the treatment for Hodgkin's disease, including radiation therapy, the patient presented with painful swelling of the neck soft tissues in the radiation area with the transition to the anterior thoracic wall and an enlarged cervical lymph node. A lymph node dissection was performed. According to the combined positron emission tomography and X-ray computed tomography (PET/CT), histological and immunohistochemical studies, epithelioid angiosarcoma of soft tissues of the neck and thoracic wall stage IV cT2N1M1G3 with metastases to the skeleton bones, neck lymph nodes, left adrenal gland was established. Surgical treatment was not performed due to advanced disease. The patient received six cycles of polychemotherapy with doxorubicin + ifosfamide. PET/CT confirmed partial tumor regression. Conclusion. Radiation-induced soft tissue sarcoma is a late iatrogenic complication of radiation therapy for Hodgkin's lymphoma. The tumor occurred in the radiation area. PET/CT is the method of choice in diagnosing and evaluating the extent of cancer and response to treatment. Chemotherapy, as an option for complex treatment, can achieve adequate disease control when surgery is not feasible.

[Hematological pathologies: the most successful model of de-escalation in radiotherapy]

The proportion of patients irradiated in the context of malignant hematological pathologies decreased over the last decades. The main causes are the late side effects of the historical series and the new therapeutic strategies aiming to relay radiotherapy to the rank of option. At the same time, radiotherapy has been modernised, target volumes and total doses have been drastically reduced. Hodgkin's lymphomas, indolent follicular lymphomas and primary cerebral lymphomas are the main witnesses of this therapeutic deflation.

Second Malignancies in Patients with Hodgkin’s Lymphoma: Half a Century of Experience

Purpose

Therapeutic improvements for Hodgkin’s Lymphoma (HL) has resulted in excellent survival outcomes. Thus, patients are increasing susceptible to developing secondary malignancy (SM) a feared iatrogenic complication.

Materials & Methods

We evaluated the SM risk in a cohort of patients with HL treated over a 50-year period. In total, 1653 patients were treated for HL from 1956 to 2009 at a tertiary-cancer-center. A cumulative incidence function was used to quantify SM risk and the Fine and Gray competing risk model was used to identify disease and treatment related correlates.

Results

Two-hundred-ninety patients (19%) developed SMs. Paradoxically, SM risk was higher in the modern era with 20-year cumulative incidence rates of 11.1%, 11.9%, 17% and 21.8%, for patients treated <1970, 1971–1986, 1986–1995 and 1996–2009, respectively. We hypothesized that the disproportionately high rate of early deaths in the early era may skew the assessment of SM risks, a much-delayed event. When the analysis was restricted to patients with early-stage favorable HL treated >1980, we found a reversal of the trend, especially on the risk of solid tumor, with a hazard ratio of 0.57 (p = 0.0651) in patients treated after 1996.

Conclusion

Our findings highlight the limitations of comparing the risk of a late event between groups with disparate rates of early deaths, despite the use of a competing risk model. When partially corrected for, patients treated in the more recent time period experienced a lower solid tumor risk.

Treatment-related peripheral small cell lung carcinoma in a Hodgkin lymphoma survivor

Hodgkin lymphoma (HL) survivors have an increased risk of developing subsequent treatment-related primary malignancies. In the last few decades, advances in knowledge, radiotherapy, chemotherapy and autologous stem cell transplantation have led to the transformation of lethal malignancy into highly curable malignancy, thereby improving outcomes. With prolonged survival, the risk of developing subsequent treatment-related late adverse effects, such as malignancies, steadily increases over time. Herein, we present the first case of a treatment-related second primary stage IV peripheral small cell lung carcinoma in a female HL survivor who was also diagnosed with right breast cancer 13 years after HL treatment and 1 year before her lung cancer diagnosis.

Second Cancers in Classical Hodgkin Lymphoma and Diffuse Large B-Cell Lymphoma: A Systematic Review by the Fondazione Italiana Linfomi

BACKGROUND

The increase of lymphoma patient survival led to a modification of the incidence of long-term sequelae, including second malignancies (SM). Several groups have dealt with the incidence of SM, according to the primary treatment; however, a standardized approach for the early detection and screening of SM in the population of lymphoma survivors should be implemented.

METHODS

A systematic review was conducted by Fondazione Italiana Linfomi (FIL), in order to define the incidence of SM, the impact of modern radiotherapy on SM risk, and the usefulness of tailored follow-up and screening strategies for early diagnosis of SM. Classical Hodgkin lymphoma (cHL) and diffuse large B-cell lymphoma (DLBCL) survivors were investigated. The MEDLINE, Embase, and Cochrane Library databases were checked for relevant reports published up to January 2020. The selection process was reported according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines.

RESULTS

A total of 27 full-text manuscripts resulted as eligible for the analysis. The incidence of SM in cHL patients treated with ABVD was higher compared to the general population and was even higher in patients treated with intensified regimens. The risk increased over time, as well as after 10-15 years from therapy, and was augmented by radiotherapy exposure. In DLBCL, more intensive regimens (i.e., R-CHOEP or R-MegaCHOEP) vs. R-CHOP were associated with a higher SM incidence. Salvage chemotherapy and autologous stem cell transplants increased the risk of SM in both cHL and DLBCL cohorts. A lower incidence of SM, particularly of breast cancer (BC), was shown in cohorts of cHL survivors treated with reduced radiation volumes and doses (involved fields vs. extended fields), but robust trials are still lacking. Considering the advantage of a structured screening for early detection of SM, all the included studies regarded cHL survivors and screening strategy for early BC detection. Moreover, the authors discuss additional papers, to guide the early diagnosis of lung, colorectal, skin, and thyroid cancer in patients at risk due to family history, drug or RT exposure, or unhealthy lifestyles. These screening strategies all passed through patient awareness.

CONCLUSION

A modern approach to chemotherapy and radiotherapy led to a lower risk of SM, which should be confirmed over time. Early detection of secondary cancers could be achieved through a tailored screening program, according to the individual risk profile.

Clinicopathologic features of breast cancers diagnosed in women treated with prior radiation therapy for Hodgkin lymphoma: Results from a population-based cohort

BACKGROUND

Childhood and young adult survivors of Hodgkin lymphoma (HL) are at elevated risk of developing breast cancer, yet little data exist on the tumor characteristics that develop in this high-risk patient population.

METHODS

The National Cancer Institute's Surveillance, Epidemiology, and End Results database was used to identify breast cancers diagnosed between 1990 and 2016 in women who had received prior radiation therapy for HL at age 30 years or younger. Clinicopathologic features of subsequent breast cancers (breast cancer after radiation therapy for HL [BC-HL]) were examined and compared with breast cancers diagnosed in women who had no prior malignancy (breast cancer with no prior malignancy [BC-NPM]).

RESULTS

In total, 321 breast cancers were identified in 257 women who had a history of radiation therapy for HL. The median age at HL diagnosis was 22 years (interquartile range, 18-26 years), and nearly all patients in the BC-HL group (97.9%) were diagnosed ≥8 years after radiation therapy. Overall, 56 patients in the BC-HL group (21.8%) developed bilateral breast cancer. Compared with women who had BC-NPM, those who had BC-HL were younger (43 vs 60 years; P < .001) and were less likely to present with ductal carcinoma in situ (8.4% vs 14.9%; P = .001). On multivariable analysis that included adjustment for age, invasive BC-HL was associated with smaller (≤2 cm) tumor size (odds ratio, 1.64; 95% CI, 1.25-2.15) and upper outer quadrant tumors (odds ratio, 1.37; 95% CI, 1.04-1.81) compared with BC-NPM. In a subset analysis of 102 women who had HER2/neu status available, the distribution of biologic subtype was not significantly different between BC-HL and BC-NPM (P = .16).

CONCLUSIONS

Breast cancers in women who previously received radiation therapy for HL are characterized by earlier onset disease, although most remain estrogen receptor-positive and have early stage disease at presentation.

LAY SUMMARY

Women who have had radiation therapy for Hodgkin lymphoma at a young age are at increased risk of developing early onset breast cancer; however, most of these breast cancers are sensitive to hormones (estrogen receptor-positive) and are diagnosed at early stages. Because these breast tumors are estrogen receptor-positive, medications that prevent breast cancer by blocking the effect of or lowering hormone levels (also termed endocrine prevention) may be useful in this group of high-risk women.

Involved-Field Radiation Therapy Prevents Recurrences in the Early Stages of Hodgkin Lymphoma in PET-Negative Patients After ABVD Chemotherapy: Relapse Analysis of GHSG Phase 3 HD16 Trial

PURPOSE

The HD16 trial of the German Hodgkin Study Group (NCT00736320) demonstrated that radiation therapy in early-stage Hodgkin lymphoma without risk factors cannot be safely omitted, and therefore combined modality therapy (CMT) remains the standard treatment. To demonstrate the local effect of consolidating involved-field radiation therapy (IF-RT), we performed an analysis of the recurrence pattern of positron emission tomography (PET)-negative HD16 patients.

METHODS AND MATERIALS

Between 2009 and 2015, 1150 patients with early-stage Hodgkin lymphoma without risk factors were randomly assigned to PET guided to 20 Gy IF-RT after 2 cycles of doxorubicin, bleomycin, vinblastine, and dacarbazine chemotherapy in the HD16 study of the German Hodgkin Study Group. The study was designed as a prospective randomized controlled trial. We correlated the localization of recurrence with the panel-based IF-RT plan, which was drawn up for all patients prospectively, blinded to treatment allocation. Accordingly, we were able to identify recurrences that occurred at least in part inside or outside of the (potential) radiation field (in-field and out-field, respectively).

RESULTS

There were 328 and 300 PET-negative patients assigned to CMT and PET-guided treatment (ie, chemotherapy alone), respectively. Within a median 47-month follow-up, disease progression or recurrence was documented for 15 and 29 patients treated with and without IF-RT, respectively. Relapse localization was unknown in 1 CMT patient. Without IF-RT, 5-year incidence of in-field relapses was 10.5% (95% confidence interval, 6.5-14.6) compared with 2.4% (0.5-4.3) with CMT (P = .0008). There were no relevant differences in out-field recurrences (5-year incidence 4.1% [1.7-6.6] vs 6.6% [3.0-10.3], P = .54). There was no grade 4 toxicity observed during IF-RT, and incidence of second primary malignancies was similar in both groups.

CONCLUSIONS

PET-negative patients of the HD16 study showed no significant toxicity after 20 Gy IF-RT, and we demonstrated that omission of IF-RT resulted in more, particularly local, recurrences. Therefore, consolidation IF-RT should still be considered as standard therapy in this setting.

Younger North Americans are exposed to more radon gas due to occupancy biases within the residential built environment

Residential buildings can concentrate radioactive radon gas, exposing occupants to particle radiation that increases lung cancer risk. This has worsened over time in North America, with newer residences containing greater radon. Using data from 18,971 Canadian households, we calculated annual particle radiation dose rates due to long term residential radon exposure, and examined this as a function of occupant demographics. The current particle radiation dose rate to lungs from residential radon in Canada is 4.08 mSv/y from 108.2 Bq/m3, with 23.4% receiving 100-2655 mSv doses that are known to elevate human cancer risk. Notably, residences built in the twenty-first century are occupied by significantly younger people experiencing greater radiation dose rates from radon (mean age of 46 at 5.01 mSv/y), relative to older groups more likely to occupy twentieth century-built properties (mean age of 53 at 3.45-4.22 mSv/y). Newer, higher radon-containing properties are also more likely to have minors, pregnant women and an overall higher number of occupants living there full time. As younger age-of-exposure to radon equates to greater lifetime lung cancer risk, these data reveal a worst case scenario of exposure bias. This is of concern as, if it continues, it forecasts serious future increases in radon-induced lung cancer in younger people.

Harnessing genome-wide association studies to minimize adverse radiation-induced side effects

Radiotherapy is used as definitive treatment in approximately two-thirds of all cancers. However, like any treatment, radiation has significant acute and long-term side effects including secondary malignancies. Even when similar radiation parameters are used, 5%–10% of patients will experience adverse radiation side effects. Genomic susceptibility is thought to be responsible for approximately 40% of the clinical variability observed. In the era of precision medicine, the link between genetic susceptibility and radiation-induced side effects is further strengthening. Genome-wide association studies (GWAS) have begun to identify single-nucleotide polymorphisms (SNPs) attributed to overall and tissue-specific toxicity following radiation for treatment of breast cancer, prostate cancer, and other cancers. Here, we review the use of GWAS in identifying polymorphisms that are predictive of acute and long-term radiation-induced side effects with a focus on chest, pelvic, and head-and-neck irradiation. Integration of GWAS with “omic” data, patient characteristics, and clinical correlates into predictive models could decrease radiation-induced side effects while increasing therapeutic efficacy.

Fondazione Italiana Linfomi (FIL) expert consensus on the use of intensity-modulated and image-guided radiotherapy for Hodgkin's lymphoma involving the mediastinum

Aim

Advances in therapy have resulted in improved cure rates and an increasing number of long-term Hodgkin's lymphoma (HL) survivors. However, radiotherapy (RT)-related late effects are still a significant issue, particularly for younger patients with mediastinal disease (secondary cancers, heart diseases). In many Centers, technological evolution has substantially changed RT planning and delivery. This consensus document aims to analyze the current knowledge of Intensity-Modulated Radiation Therapy (IMRT) and Image-Guided Radiation Therapy (IGRT) for mediastinal HL and formulate practical recommendations based on scientific evidence and expert opinions.

Methods

A dedicated working group was set up within the Fondazione Italiana Linfomi (FIL) Radiotherapy Committee in May 2018. After a first meeting, the group adopted a dedicated platform to share retrieved articles and other material. Two group coordinators redacted a first document draft, that was further discussed and finalized in two subsequent meetings. Topics of interest were: 1) Published data comparing 3D-conformal radiotherapy (3D-CRT) and IMRT 2) dose objectives for the organs at risk 3) IGRT protocols and motion management.

Results

Data review showed that IMRT might allow for an essential reduction in the high-dose regions for all different thoracic OAR. As very few studies included specific dose constraints for lungs and breasts, the low-dose component for these OAR resulted slightly higher with IMRT vs. 3D-CRT, depending on the technique used. We propose a set of dose objectives for the heart, breasts, lungs, and thyroid. The use of IGRT is advised for margin reduction without specific indications, such as the use of breath-holding techniques. An individual approach, including comparative planning and considering different risk factors for late morbidity, is recommended for each patient.

Conclusions

As HL therapy continues to evolve, with an emphasis on treatment reduction, radiation oncologists should use at best all the available tools to minimize the dose to organs at risk and optimize treatment plans. This document provides indications on the use of IMRT/IGRT based on expert consensus, providing a basis for clinical implementation and future development.

Times Not to Forget Radiotherapy When Treating Patients With Lymphoma

Radiation therapy remains an important component of lymphoma treatment. It has evolved with improvements in technology and a better understanding of how to successfully integrate it into lymphoma treatment. There are specific clinical presentations where omission of radiation therapy could adversely affect patient outcome and should not be overlooked. Radiation therapy may serve an important role as primary treatment, as a component of combined modality therapy, as adjuvant therapy to maximize local control, and as an important component of salvage therapy for relapsed or primary refractory lymphoma and in the successful palliation of lymphoma. This review identifies those clinical presentations where the use of radiation therapy should not be overlooked or should at least be considered.

Modelling recurrence and second cancer risks induced by proton therapy

In the past few years, proton therapy has taken the centre stage in treating various tumour types. The primary contribution of this study is to investigate the tumour control probability (TCP), relapse time and the corresponding secondary cancer risks induced by proton beam radiation therapy. We incorporate tumour relapse kinetics into the TCP framework and calculate the associated second cancer risks. To calculate proton therapy-induced secondary cancer induction, we used the well-known biologically motivated mathematical model, initiation-inactivation-proliferation formalism. We used the available in vitro data for the linear energy transfer (LET) dependence of cell killing and mutation induction parameters. We evaluated the TCP and radiation-induced second cancer risks for protons in the clinical range of LETs, i.e. approximately 8 $\mathrm{keV/\mu m}$ for the tumour volume and 1-3 $\mathrm{keV/\mu m}$ for the organs at risk. This study may serve as a framework for further work in this field and elucidates proton-induced TCP and the associated secondary cancer risks, not previously reported in the literature. Although studies with a greater number of cell lines would reduce uncertainties within the model parameters, we argue that the theoretical framework presented within is a sufficient rationale to assess proton radiation TCP, relapse and carcinogenic effects in various treatment plans. We show that compared with photon therapy, proton therapy markedly reduces the risk of secondary malignancies and for equivalent dosing regimens achieves better tumour control as well as a reduced primary recurrence outcome, especially within a hypo-fractionated regimen.

Second cancers in Hodgkin's lymphoma long-term survivals: A 60-year single institutional experience with real-life cohort of 871 patients

BACKGROUND AND PURPOSE

Appropriate surveillance guidelines for patients after successful treatment of Hodgkin's lymphoma (HL) are needed to reduce mortality of iatrogenic secondary cancers (SC). This large single institutional retrospective study analyses the risk of SC in HL patients treated outside of clinical trials over past decades.

MATERIAL AND METHODS

Consecutive series of HL patients were analysed with median follow-up 12 years. Standardised incidence ratio (SIR) and absolute excess risk (AER) were calculated for site-specific risk of SC.

RESULTS

In total of 871 patients (491 men; median age 34 years), chemotherapy alone, radiotherapy alone, and combined treatment underwent 36%, 40%, and 24% patients. 154 SC were found with significantly increased SIR = 2.9 and AER = 80.8 for all cancers except of nonmelanoma-skin cancer. SC-related death occurred in 71 patients (15% of those who died, 8% of whole cohort). The most common SC were lung (17.5% of all malignancies, SIR = 3.2), breast carcinoma (15.6%, SIR = 4.4), and haematological malignancy (non-Hodgkin's lymphoma SIR = 13.1; leukaemia SIR = 5.8). For SC within radiation field, the highest AER was in breast (AER = 46.9), colorectal (AER = 22.8), and lung cancer (AER = 17).

CONCLUSIONS

Patients with HL are generally at great risk of developing SC, which is significantly increased especially by the use of radiotherapy. We suggested special follow-up schema for patients after initial HL treatment suitable for daily real-world clinical practice. The system depends on gender, form of HL treatment and especially the form of radiation therapy in terms of location of radiation fields.

Prognostic factors and patterns of failure in advanced stage Hodgkin lymphoma treated with combined modality therapy

BACKGROUND AND PURPOSE

The role of irradiation to non-bulky and bulky sites of disease in advanced stage Hodgkin lymphoma is controversial. We aimed to review the long-term outcomes of patients treated with combined modality therapy to clarify the role of consolidative radiotherapy.

MATERIALS AND METHODS

Patients with stage III or IV Hodgkin lymphoma treated with Stanford V chemotherapy and consolidative radiotherapy to initial sites of disease ≥5 cm were analyzed retrospectively to determine patient outcomes, patterns of failure, and factors associated with treatment failure.

RESULTS

A total of 170 patients were analyzed. Overall survival was 91.2%, freedom from progression was 80.6%, and progression-free survival was 78.9% at 10 years. 5 patients (2.9%) had refractory disease and 27 patients (15.9%) relapsed after treatment. Only an International Prognostic Score (IPS) greater than 2 predicted disease progression. 19 out of 27 relapses occurred exclusively outside of the radiation treatment field, and 17 out of 27 relapses occurred exclusively at original sites of disease. However, only 11 of 170 patients (6.5%) relapsed exclusively at original, non-bulky sites of disease not treated with radiation therapy. The cumulative incidence of local failure at 10 years was 4.6% for unirradiated sites and 2.6% for irradiated sites.

CONCLUSION

Patients with advanced stage Hodgkin lymphoma treated with combined modality therapy including consolidative radiotherapy to bulky disease sites had excellent long-term outcomes. Given the low frequency of isolated failures at initial sites, our results suggest that selective radiation therapy to sites at high risk of relapse may be feasible.

Early-stage Hodgkin lymphoma in the modern era: simulation modelling to delineate long-term patient outcomes

We developed a novel simulation model integrating multiple data sets to project long-term outcomes with contemporary therapy for early-stage Hodgkin lymphoma (ESHL), namely combined modality therapy (CMT) versus chemotherapy alone (CA) via ¹⁸ F-fluorodeoxyglucose positron emission tomography response-adaption. The model incorporated 3-year progression-free survival (PFS), probability of cure with/without relapse, frequency of severe late effects (LEs), and 35-year probability of LEs. Furthermore, we generated estimates for quality-adjusted life years (QALYs) and unadjusted survival (life years, LY) and used model projections to compare outcomes for CMTversusCA for two index patients. Patient 1: a 25-year-old male with favourable ESHL (stage IA); Patient 2: a 25-year-old female with unfavourable ESHL (stage IIB). Sensitivity analyses assessed the impact of alternative assumptions for LE probabilities. For Patient 1, CMT was superior to CA (CMT incremental gain = 0·11 QALYs, 0·21 LYs). For Patient 2, CA was superior to CMT (CA incremental gain = 0·37 QALYs, 0·92 LYs). For Patient 1, the advantage of CMT changed minimally when the proportion of severe LEs was reduced from 20% to 5% (0·15 QALYs, 0·43 LYs), whereas increasing the severity proportion for Patient 2's LEs from 20% to 80% enhanced the advantage of CA (1·1 QALYs, 6·5 LYs). Collectively, this detailed simulation model quantified the long-term impact that varied host factors and alternative contemporary treatments have in ESHL.

Radiation-Induced Malignancies Making Radiotherapy a "Two-Edged Sword": A Review of Literature

Radiotherapy is one of the modalities of treatment of malignancies. Radiation-induced malignancies (RIMs) are late complications of radiotherapy, seen among the survivors of both adult and pediatric cancers. Mutagenesis of normal tissues is the basis for RIMs. The aim of this review of literature was to discuss epidemiology, factors affecting and different settings in which RIM occur.

Effects of Radiotherapy on the Risk of Developing Secondary Malignant Neoplasms in Hodgkin's Lymphoma Survivors

Extended follow-up of Hodgkin lymphoma (HL) survivors indicates that these patients are at high risk of secondary malignant neoplasms (SMNs) contributing to increased morbidity and mortality. This study examined the characteristics of HL survivors who developed SMNs with the aim to report any correlation with radiotherapy (RT) dose. In this retrospective multi-center cohort study of HL patients treated between 1990 and 2011 at three major teaching hospitals in Lebanon, classification was into two groups including those treated with combined modality (RT and chemotherapy-CHT) and those treated with CHT alone. Approval from the University Institutional Review Board (IRB) was obtained. Of the 112 patients evaluated, 52.7% (59) received the combined modality while 47.3% (53) received CHT alone. There were 6 cases of SMNs in the combined modality cohort and 5 cases in the CHT cohort. The mean RT dose in the combined modality cohort was 34.5 Gray (Gy) (SD ± 5.3). A statistically significant increase (1.5 fold) in the risk of developing SMNs was observed among patients who received a dose higher than 41 Gy compared to a dose between 20 to 30 Gy (OR= 1.5; 95% confidence interval= 0.674 to 3.339, p=0.012). The risk of SMNs was not significantly higher among patients who received extended field compared to involved field RT (p=0.964). This study showed that the risk of developing SMNs is higher among patients treated with RT dose greater than 31 Gy, independent of the RT type used.

Estimation of second cancer risk after radiotherapy for rectal cancer: comparison of 3D conformal radiotherapy and volumetric modulated arc therapy using different high dose fractionation schemes

Purpose

To investigate second cancer risk (SCR) comparing volumetric modulated arc therapy (VMAT) and 3D conformal radiotherapy (3DCRT) with different high dose fractionation schemes.

Methods

VMAT and 3DCRT virtual treatment plans for 25 patients previously treated with radiotherapy for rectal cancer were evaluated retrospectively. Doses prescribed were 25 × 1.8 Gy and 5 × 5 Gy, respectively. SCR was estimated using a carcinogenesis model and epidemiological data for carcinoma and sarcoma induction. SCR was determined by lifetime attributable risk (LAR).

Results

Mean excess LAR was highest for organs adjacent to the PTV. Total LAR for VMAT and 3DCRT was 2.3–3.0 and 2.0–2.7 %, respectively. For 5 × 5 Gy, LAR was 1.4–1.9 % for VMAT and 1.2–1.6 % for 3DCRT. Organ-specific excess LAR was significantly higher for VMAT, and highest for bladder and colon. Size and shape of the PTV influenced SCR and was highest for age ≤ 40 years. For a patient with an additional lifetime risk of 60 years, LAR was 10 % for 25 × 1.8 Gy and 6 % for 5 × 5 Gy.

Conclusions

No statistically significant difference was detected in SCR using VMAT or 3DCRT. For bladder and colon, organ-specific excess LAR was statistically lower using 3DCRT, however the difference was small. Compared to epidemiological data, SCR was smaller when using a hypofractionated schedule. SCR was 2 % higher at normal life expectancy.

Trial registration

ClinicalTrials.gov Identifier NCT02572362. Registered 4 October 2015. Retrospectively registered.

Secondary Breast Cancer Risk by Radiation Volume in Women With Hodgkin Lymphoma

PURPOSE

To determine whether the risk of secondary breast cancer (SBC) is reduced in women with Hodgkin lymphoma (HL) treated with smaller field radiation therapy (SFRT) versus mantle field radiation therapy (MRT).

METHODS AND MATERIALS

We used the BC Cancer Agency (BCCA) Lymphoid Cancer Database to identify female patients treated for HL between January 1961 and December 2009. Radiation therapy volumes were categorized as MRT or SFRT, which included involved field, involved site, or involved nodal radiation therapy. SBC risk estimates were compared using competing risk analysis and Fine and Gray multivariable model: MRT ± chemotherapy, SFRT ± chemotherapy, or chemotherapy-only.

RESULTS

Of 734 eligible patients, 75% of the living patients have been followed up for more than 10 years, SBC has developed in 54, and 15 have died of breast cancer. The 20-year estimated risks (competing risk cumulative incidence) for SBC differed significantly: MRT 7.5% (95% confidence interval [CI] 4.4%-11.5%), SFRT 3.1% (95% CI 1.0%-7.7%), and chemotherapy-only 2.2% (95% CI 1.0%-4.8%) (P=.01). Using a Fine and Gray model to control for death and patients lost to follow-up, MRT was associated with a higher risk of SBC (hazard ratio [HR] = 2.9; 95% CI 1.4%-6.0%; P=.004) compared with chemotherapy-only and with SFRT (HR = 3.3; 95% CI 1.3%-8.4%; P=.01). SFRT was not associated with a greater risk of SBC compared with chemotherapy-only (HR = 0.87; 95% CI 0.28%-2.66%; P=.80).

CONCLUSION

This study confirms that large-volume MRT is associated with a markedly increased risk of SBC; however, more modern small-volume RT is not associated with a greater risk of SBC than chemotherapy alone.

Treatment of Early-Stage Unfavorable Hodgkin Lymphoma: Efficacy and Toxicity of 4 Versus 6 Cycles of ABVD Chemotherapy With Radiation

PURPOSE

The German Hodgkin Study Group HD11 trial validated 4 cycles of doxorubicin, bleomycin, vinblastine, dacarbazine (ABVD) chemotherapy followed by involved field radiation therapy (IFRT) for early unfavorable Hodgkin lymphoma (HL) patients. However, practitioners often recommend 6 cycles followed by RT, especially for bulky disease. We compared patient outcomes after treatment with 4 or 6 cycles of ABVD followed by RT (IFRT and involved site RT [ISRT]).

METHODS AND MATERIALS

We identified 128 patients treated for early unfavorable HL (GHSG criteria) between 2000 and 2013. Clinical outcomes (overall survival [OS] and freedom from relapse [FFR]) were estimated using Kaplan-Meier analysis. Toxicities were evaluated.

RESULTS

The median follow-up time was 5.0 years. Patients received 4 (70 patients, 55%) or 6 (58 patients, 45%) cycles of chemotherapy. Bulky disease was present in 22 patients (31%; 0 stage IA, 3 stage IB, 19 stage IIA) of the 4-cycle group and 42 patients (72%; 5 stage IA, 3 stage IB, 34 stage IIA) of the 6-cycle group. For patients receiving 4 and 6 cycles, the 6-year OS was 100% and 97% (P=.35), respectively, and the 6 year FFR was 100% and 98% (P=.28), respectively. More patients received 6 cycles if they were treated before 2010 (HD11 report) (P=.01) and if they had bulky disease (P<.01). Sixty-eight percent of patients received ISRT. The 6-year FFR was 99% and 100% for patients receiving ISRT and IFRT, respectively (P=.58). More patients experienced bleomycin pulmonary toxicity in the 6-cycle group (20% vs 31%, P=.16). For patients with bulky disease, the 4-year FFR was similar with receipt of 4 (100%) or 6 (98%) cycles (P=.48) and IFRT (100%) or ISRT (98%) (P=.52). There were no deaths among patients with bulky disease.

CONCLUSIONS

Patients with early unfavorable HL have excellent outcomes with 4 cycles of ABVD chemotherapy followed by ISRT. Six cycles of chemotherapy does not appear superior for disease control, even for bulky disease.

Late mortality, secondary malignancy and hospitalisation in teenage and young adult survivors of Hodgkin lymphoma: report of the Childhood/Adolescent/Young Adult Cancer Survivors Research Program and the BC Cancer Agency Centre for Lymphoid Cancer

Late complications affecting Hodgkin lymphoma (HL) survivors are well described in paediatric and adult-based publications. This study determined the late morbidity and mortality risk for 442 teenage and young adult (TYAs) 5-year HL survivors, diagnosed at 15-24 years of age between 1970 and 1999, identified from the British Columbia Cancer Registry. Treatment details were abstracted from charts. Survivors and a matched comparison cohort were linked to provincial administrative health datasets until December 2006 and regression analysis was performed, providing risk ratios regarding mortality, secondary malignancy and morbidity causing hospitalisation. Sixty (13·6%) survivors experienced late mortality with excess deaths from secondary cancer [standardised mortality ratio (SMR) 18·6; 95% confidence interval (CI) 11-29·4] and non-malignant disease (SMR 3·6; 95% CI 2·2-5·5). Excess secondary cancers (standardised incidence ratio 7·8; 95% CI 5·6-10·5) were associated with radiotherapy [Hazard ratio (HR) 2·7; 95% CI 1-7·7] and female gender (HR 1·8; 95% CI 1-3·4). Of 281 survivors treated between 1981 and 1999, 143 (51%) had morbidity resulting in hospitalisation (relative risk 1·45; 95% CI 1·22-1·73). Hospitalisation significantly increased with combined modality therapy, chemotherapy alone and recent treatment era. TYA HL survivors have excess risk of mortality and secondary malignancy continuing 30 years from diagnosis. Radiotherapy is associated with secondary malignancy and current response-adapted protocols attempt to minimise exposure, but late morbidity causing hospitalisation remains significant.

Outcomes After Chemotherapy Followed by Radiation for Stage IIB Hodgkin Lymphoma With Bulky Disease

BACKGROUND

Treatment of stage IIB bulky Hodgkin lymphoma (HL) is controversial, with treatment varying by institution. We evaluated patients with IIB bulky disease treated with combined-modality therapy at our institution by describing their long-term outcomes.

PATIENTS AND METHODS

We identified 149 consecutive patients with stage IIB bulky HL treated between 1971 and 2012. Clinical, pathologic, and treatment characteristics were extracted from medical records. Actuarial overall survival (OS) and relapse-free survival (RFS) were calculated by the Kaplan-Meier method. Independent factors associated with these outcomes were identified by a multivariate Cox regression model. Outcomes were further compared against comparison groups of both advanced-stage and stage IIB patients treated between 1971 and 2009.

RESULTS

The 8-year OS rate for patients with stage IIB bulky disease who received combined-modality ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine) and radiation was 88.8%; the 8-year RFS rate was 76.8%. On multivariate analysis, age < 40 years (hazard ratio [HR], 0.28; 95% confidence interval [CI], 0.14-0.57; P = .001), receipt of ABVD (vs. MOPP [mechlorethamine, vincristine, procarbazine, prednisone]; HR, 0.32; 95% CI, 0.10-0.88; P = .028), and radiation dose ≥ 30.1 Gy (HR, 0.25; 95% CI, 0.11-0.65; P = .006) were associated with improved OS. Cardiac events (n = 11) and secondary malignancies (n = 11) only occurred in patients treated before 1995. A subgroup analysis demonstrated significantly improved survival in IIB bulky versus advanced-stage patients (8-year OS, 73.4% vs. 57.4%; P = .008). Improved outcomes in patients with in IIB bulky disease were especially evident in the modern era (> 1995; P = .004).

CONCLUSION

Patients with stage IIB bulky HL had excellent outcomes after combined-modality therapy. Treatment strategies have changed substantially over time, with concomitant improvements in disease outcomes and long-term toxicities.

Involved site radiation therapy for the treatment of early-stage Hodgkin lymphoma in adolescents and young adults

Radiation therapy technology has permitted the development of new treatment planning techniques. Involved field, involved node, and involved site radiotherapy fields are discussed and compared. Indications for and implications of combined modality therapy are examined, particularly as pertinent to the adolescent and young adult population.

Radiotherapy for benign disease; assessing the risk of radiation-induced cancer following exposure to intermediate dose radiation

Most radiotherapy (RT) involves the use of high doses (>50 Gy) to treat malignant disease. However, low to intermediate doses (approximately 3-50 Gy) can provide effective control of a number of benign conditions, ranging from inflammatory/proliferative disorders (e.g. Dupuytren's disease, heterotopic ossification, keloid scarring, pigmented villonodular synovitis) to benign tumours (e.g. glomus tumours or juvenile nasopharyngeal angiofibromas). Current use in UK RT departments is very variable. This review identifies those benign diseases for which RT provides good control of symptoms with, for the most part, minimal side effects. However, exposure to radiation has the potential to cause a radiation-induced cancer (RIC) many years after treatment. The evidence for the magnitude of this risk comes from many disparate sources and is constrained by the small number of long-term studies in relevant clinical cohorts. This review considers the types of evidence available, i.e. theoretical models, phantom studies, epidemiological studies, long-term follow-up of cancer patients and those treated for benign disease, although many of the latter data pertain to treatments that are no longer used. Informative studies are summarized and considered in relation to the potential for development of a RIC in a range of key tissues (skin, brain etc.). Overall, the evidence suggests that the risks of cancer following RT for benign disease for currently advised protocols are small, especially in older patients. However, the balance of risk vs benefit needs to be considered in younger adults and especially if RT is being considered in adolescents or children.

Long-Term Course of Patients With Stage IA Nodular Lymphocyte-Predominant Hodgkin Lymphoma: A Report From the German Hodgkin Study Group

Purpose

The optimal treatment of stage IA nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is not well defined. Thus, we performed an analysis using the database of the German Hodgkin Study Group.

Patients and Methods

The long-term outcome of 256 patients with stage IA NLPHL was evaluated. Patients had received combined-modality treatment (CMT; n = 72), extended-field radiotherapy (EF-RT; n = 49), involved-field radiotherapy (IF-RT; n = 108), or four weekly standard doses of rituximab (n = 27) within German Hodgkin Study Group clinical trial protocols between 1988 and 2009.

Results

The median age at NLPHL diagnosis was 39 years (range, 16 to 75 years). Most patients were male (76%). The whole patient group had a median follow-up of 91 months (CMT: 95 months; EF-RT: 110 months; IF-RT: 87 months; rituximab: 49 months). At 8 years, progression-free survival and overall survival rates were 88.5% and 98.6% for CMT, 84.3% and 95.7% for EF-RT, and 91.9% and 99.0% for IF-RT, respectively. Patients treated with rituximab had 4-year progression-free and overall survival rates of 81.0% and 100%, respectively. A second malignancy during the course of follow-up was diagnosed in 17 (6.6%) of 256 patients. A total of 12 deaths occurred. However, only one patient died from NLPHL.

Conclusion

Tumor control in this analysis was equivalent with CMT, EF-RT, and IF-RT. Therefore, IF-RT, which is associated with the lowest risk for the development of toxic effects, should be considered as standard of care for patients with stage IA NLPHL. Rituximab alone is associated with an increased risk of relapse in this patient population.

Optimized volumetric modulated arc therapy versus 3D-CRT for early stage mediastinal Hodgkin lymphoma without axillary involvement: a comparison of second cancers and heart disease risk

PURPOSE

The purpose of this study was to evaluate the risks of second cancers and cardiovascular diseases associated with an optimized volumetric modulated arc therapy (VMAT) planning solution in a selected cohort of stage I/II Hodgkin lymphoma (HL) patients treated with either involved-node or involved-site radiation therapy in comparison with 3-dimensional conformal radiation therapy (3D-CRT).

METHODS AND MATERIALS

Thirty-eight patients (13 males and 25 females) were included. Disease extent was mediastinum alone (n=8, 21.1%); mediastinum plus unilateral neck (n=19, 50%); mediastinum plus bilateral neck (n=11, 29.9%). Prescription dose was 30 Gy in 2-Gy fractions. Only 5 patients had mediastinal bulky disease at diagnosis (13.1%). Anteroposterior 3D-CRT was compared with a multiarc optimized VMAT solution. Lung, breast, and thyroid cancer risks were estimated by calculating a lifetime attributable risk (LAR), with a LAR ratio (LAR(VMAT)-to-LAR(3D-CRT)) as a comparative measure. Cardiac toxicity risks were estimated by calculating absolute excess risk (AER).

RESULTS

The LAR ratio favored 3D-CRT for lung cancer induction risk in mediastinal alone (P=.004) and mediastinal plus unilateral neck (P=.02) presentations. LAR ratio for breast cancer was lower for VMAT in mediastinal plus bilateral neck presentations (P=.02), without differences for other sites. For thyroid cancer, no significant differences were observed, regardless of anatomical presentation. A significantly lower AER of cardiac (P=.038) and valvular diseases (P<.0001) was observed for VMAT regardless of disease extent.

CONCLUSIONS

In a cohort of patients with favorable characteristics in terms of disease extent at diagnosis (large prevalence of nonbulky presentations without axillary involvement), optimized VMAT reduced heart disease risk with comparable risks of thyroid and breast cancer, with an increase in lung cancer induction probability. The results are however strongly influenced by the different anatomical presentations, supporting an individualized approach.

Modeling age-dependent radiation-induced second cancer risks and estimation of mutation rate: an evolutionary approach

Although the survival rate of cancer patients has significantly increased due to advances in anti-cancer therapeutics, one of the major side effects of these therapies, particularly radiotherapy, is the potential manifestation of radiation-induced secondary malignancies. In this work, a novel evolutionary stochastic model is introduced that couples short-term formalism (during radiotherapy) and long-term formalism (post-treatment). This framework is used to estimate the risks of second cancer as a function of spontaneous background and radiation-induced mutation rates of normal and pre-malignant cells. By fitting the model to available clinical data for spontaneous background risk together with data of Hodgkin's lymphoma survivors (for various organs), the second cancer mutation rate is estimated. The model predicts a significant increase in mutation rate for some cancer types, which may be a sign of genomic instability. Finally, it is shown that the model results are in agreement with the measured results for excess relative risk (ERR) as a function of exposure age and that the model predicts a negative correlation of ERR with increase in attained age. This novel approach can be used to analyze several radiotherapy protocols in current clinical practice and to forecast the second cancer risks over time for individual patients.

Late morbidity and mortality in patients with Hodgkin's lymphoma treated during adulthood

BACKGROUND

Survivors of Hodgkin's lymphoma (HL) treated as adults are at risk for late effects of therapy. However, the burden of late morbidity and mortality among adults treated for HL remains incompletely characterized.

METHODS

Vital status and, for deceased, cause of death were determined for 746 adults treated on a first-line trial at a single center from 1975 to 2000. Survivors completed a detailed survey describing their physical and mental health. A severity score (grades 1-4, ranging from mild to life-threatening or disabling) was assigned to self-reported conditions.

RESULTS

At a median follow-up of 22 years, 227 of patients (30.4%) had died, 107 (47.1%) from HL, 120 (52.9%) from other causes, including second primary malignancies (SPMs) (n = 52) and cardiovascular disease (n = 27). Across the duration of follow-up, all-cause and SPM-specific risk of death remained higher than predicted by normative data. Among survivors, late morbidity survey data are available for 238 patients (45.9%). Ninety-four-point-one percent of respondents reported at least one morbidity, and 47.5% reported at least one grade 3 or 4 morbidity; 20.2% reported two or more grade 3 morbidities. Commonly reported morbidities included cardiovascular (54.6%), endocrine (68.5%), pulmonary disease (21.4%), and nonfatal second malignancy (23.1%). Anxiety, depression, and fear of recurrence were frequently reported.

CONCLUSIONS

Among a large cohort of patients treated for HL with extensive follow-up, risk of late mortality from causes other than HL and prevalence of late medical morbidity are high. Guidelines for prevention, screening, and management of late effects in adult survivors of HL are needed.

The effect of radiation quality on the risks of second malignancies

Abstract Purpose: Numerous studies have implicated elevated second cancer risks as a result of radiation therapy. Our aim in this paper was to contribute to an understanding of the effects of radiation quality on second cancer risks. In particular, we developed a biologically motivated model to study the effects of linear energy transfer (LET) of charged particles (including protons, alpha particles and heavy ions Carbon and Neon) on the risk of second cancer.

MATERIALS AND METHODS

A widely used approach to estimate the risk uses the so-called initiation-inactivation-repopulation model. Based on the available experimental data for the LET dependence of radiobiological parameters and mutation rate, we generalized this formulation to include the effects of radiation quality. We evaluated the secondary cancer risks for protons in the clinical range of LET, i.e., around 4-10 (KeV/μm), which lies in the plateau region of the Bragg peak.

RESULTS

For protons, at a fixed radiation dose, we showed that the increase in second cancer risks correlated directly with increasing values of LET to a certain point, and then decreased. Interestingly, we obtained a higher risk for proton LET of 10 KeV/μm compared to the lower LET of 4 KeV/μm in the low dose region. In the case of heavy ions, the risk was higher for Carbon ions than Neon ions (even though they have almost the same LET). We also compared protons and alpha particles with the same LET, and it was interesting to note that the second cancer risks were higher for protons compared to alpha particles in the low-dose region.

CONCLUSION

Overall, this study demonstrated the importance of including LET dependence in the estimation of second cancer risk. Our theoretical risk predictions were noticeably high; however, the biological end points should be tested experimentally for multiple treatment fields and to improve theoretical predictions.