Evidence-based Review on the Use of Proton Therapy in Lymphoma From the Particle Therapy Cooperative Group (PTCOG) Lymphoma Subcommittee

Proton Pencil Beam Scanning Facilitates the Safe Treatment of Extended Radiation Targets for Hodgkin Lymphoma: A Report from the Proton Collaborative Group Registry

Because proton beam therapy (PBT) can lower the dose of radiation to the heart, lungs, and breast, it is an established radiation modality for patients with Hodgkin lymphoma (HL). Pencil beam scanning (PBS) PBT facilitates the treatment of more extensive targets. This may be especially of value for lymphoma patients who require RT to both mediastinal and axillary targets, defined here as extended target RT (ETRT), given the target distribution and need to minimize the lung, heart, and breast dose. Using the Proton Collaborative Group registry, we identified patients with HL treated with PBT to both their mediastinum and axilla, for which DICOM-RT was available. All patients were treated with PBS. To evaluate the dosimetric impact of PBS, we compared delivered PBS plans with VMAT butterfly photon plans optimized to have the same target volume coverage, when feasible. Between 2016 and 2021, twelve patients (median 26 years) received PBS ETRT (median 30.6 Gy (RBE)). Despite the large superior/inferior (SI, median 22.2 cm) and left/right (LR, median 22.8 cm) extent of the ETRT targets, all patients were treated with one isocenter except for two patients (both with SI and LR > 30 cm). Most commonly, anterior beams, with or without posterior beams, were used. Compared to photons, PBS had greater target coverage, better conformity, and lower dose heterogeneity while achieving lower doses to the lungs and heart, but not to the breast. No acute grade 3+ toxicities were reported, including pneumonitis. Proton ETRT in this small cohort was safely delivered with PBS and was associated with an improved sparing of the heart and lungs compared to VMAT.

Contemporary radiation therapy use in Hodgkin lymphoma

Radiation therapy assumes a pivotal role in Hodgkin lymphoma management, especially within combined modality therapy. It serves as a cornerstone in early-stage disease and in mitigating high-risk instances of local relapse in advanced stages. Over recent decades, radiation therapy has undergone significant advancements, notably alongside diagnostic imaging improvements, facilitating the reduction of radiation field size and dosage. This progress has notably led to minimized toxicity while upholding treatment efficacy. This comprehensive review extensively evaluates the indications and advancements in radiation therapy for Hodgkin lymphoma, with a primary focus on enhancing treatment efficacy while minimizing radiation-related toxicities. The exploration encompasses a detailed examination of various radiation fields, techniques and delivery modalities employed in Hodgkin lymphoma treatment, including intensity-modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), and proton therapy. It delves into the intricacies of optimal dose selection and treatment planning strategies aimed at achieving maximal disease control while concurrently minimizing the risk of long-term side effects.

The pediatric approach to Hodgkin lymphoma

Hodgkin lymphoma (HL) occurs throughout the lifespan but is one of the most common cancers in adolescents and young adults (AYA; 15-39 years). HL has become a highly curable disease with survival rates surpassing 90%, including patients with high-risk and advanced stage disease. Unfortunately, intensive treatment carries a risk of short- and long-term toxicity. Given the decades pediatric HL survivors are expected to live after treatment, the pediatric approach to treatment has focused on improving the therapeutic index through response adapted treatment and more recently the incorporation of novel agents. The efforts of pediatric and medical oncologists in research and clinical trial development have long occurred in parallel, but recent efforts have laid the foundation for collaboration with the goal of standardizing AYA care and allowing earlier incorporation of novel therapy for younger patients. This review focuses on the evolution of the management of pediatric HL including epidemiology, biology, and approaches to upfront and salvage treatment regimens.

Pencil beam scanning proton therapy for mediastinal lymphomas in deep inspiration breath-hold: a retrospective assessment of plan robustness

PURPOSE/BACKGROUND

The aim of this study was to evaluate pencil beam scanning (PBS) proton therapy (PT) in deep inspiration breath-hold (DIBH) for mediastinal lymphoma patients, by retrospectively evaluating plan robustness to the clinical target volume (CTV) and organs at risk (OARs) on repeated CT images acquired throughout treatment.  Methods: Sixteen mediastinal lymphoma patients treated with PBS-PT in DIBH were included. Treatment plans (TPs) were robustly optimized on the CTV (7 mm/4.5%). Repeated verification CTs (vCT) were acquired during the treatment course, resulting in 52 images for the entire patient cohort. The CTV and OARs were transferred from the planning CT to the vCTs with deformable image registration and the TPs were recalculated on the vCTs. Target coverage and OAR doses at the vCTs were compared to the nominal plan. Deviation in lung volume was also calculated.

RESULTS

The TPs demonstrated high robust target coverage throughout treatment with D98%,CTV deviations within 2% for 14 patients and above the desired requirement of 95% for 49/52 vCTs. However, two patients did not achieve a robust dose to CTV due to poor DIBH reproducibility, with D98%,CTV at 78 and 93% respectively, and replanning was performed for one patient. Adequate OAR sparing was achieved for all patients. Total lung volume variation was below 10% for 39/52 vCTs.

CONCLUSION

PBS PT in DIBH is generally a robust technique for treatment of mediastinal lymphomas. However, closely monitoring the DIBH-reproducibility during treatment is important to avoid underdosing CTV and achieve sufficient dose-sparing of the OARs.

Is oligometastatic disease an applicable and useful concept in haematologic malignancies? A narrative review of radiation therapy standards, modern techniques, and innovations

PURPOSE

Haematologic malignancies are particular in that they can generally be cured, even when distant metastases are present at diagnosis, unlike solid malignancies. Systemic treatments, including chemotherapy, targeted therapies, and immunotherapy, are the standard of care with excellent results. The considerable progress made in the management of these diseases in the last 20years has redefined the role of radiation therapy as minor in many clinical situations. We propose a literature review of data, showing that radiation therapy still has a role in curative, salvage, and palliative therapy situations.

MATERIAL AND METHODS

A document and literature search was carried out in the following databases: Medline and ClinicalTrial.gov, for the terms "radiotherapy", "haematologic malignancies", "Hodgkin lymphoma", "non-Hodgkin lymphoma", "CAR T cells", "multiple myeloma", "solitary plasmocytoma", "intensity-modulated radiotherapy", "extracranial stereotactic body radiation therapy" and "proton therapy references".

RESULTS

Haemopathological malignancies include a wide range of diseases and radiation therapy indications have been assessed over the past 20years. Currently, radiation therapy is indicated for localized disease (solitary plasmocytoma), as an adjuvant (Hodgkin lymphoma), in palliative settings, or after systemic treatment in relapsed patients (chimeric antigen receptor [CAR] T-cells) with a low recurrence burden, which can therefore be considered "oligorecurrence". Radiation therapy, through total body irradiation, has important indications, thanks to its immunomodulatory and/or myeloablative effects. Moreover, recent technological developments have made possible significant improvement in safety, contributing to radiation therapy being positioned in the treatment strategy of several indications.

CONCLUSIONS

Given the effectiveness of systemic treatments in hematologic malignancies, the oligometastasis stage is of little importance. A curative intent after local radiation therapy, even advanced stage, is possible, both with residual disease for advanced Hodgkin lymphoma, aggressive non-Hodgkin lymphoma, or solitary plasmocytoma, and even without evidence of disease after chemotherapy for Hodgkin or non-Hodgkin lymphoma. The role of new treatments, such as CAR T cells, allows us to consider radiation therapy after systemic treatment of relapsed diseases with low volume recurrence, which can be considered oligorecurrence.

Breast Cancer and Mediastinal Hodgkin's Lymphomas: Multidisciplinary Discussion

Treatment for Hodgkin's lymphoma (HL) has evolved, with modern treatments combining less toxic chemotherapy and radiation, leading to improved long-term disease-free survival. However, there is a higher chance of second cancer, especially breast cancer, following effective HL treatment. The impact of reduced radiation doses and volumes, as well as the use of advanced irradiation techniques, on the risk of second malignancy is not clear. According to medical organizations, the history of chest irradiation is a relative contraindication to breast preservation therapy for women with initial breast cancer, leading to a paradigm of mastectomy. This article proposes a discussion between radiation oncologists and surgeons to review major trials and recent developments on the prevalence of breast cancer following HL therapy, the risk of contralateral cancer, the feasibility of breast conserving surgery (BCS), as well as breast reconstruction modalities.

Selecting Optimal Proton Pencil Beam Scanning Plan Parameters to Reduce Dose Discrepancy between Discrete Spot Plan and Continuous Scanning: A Proof-of-Concept Study

Pencil beam scanning delivered with continuous scanning has several advantages over conventional discrete spot scanning. Such advantages include improved beam delivery efficiency and reduced beam delivery time. However, a move dose is delivered between consecutive spots with continuous scanning, and current treatment planning systems do not take this into account. Therefore, continuous scanning and discrete spot plans have an inherent dose discrepancy. Using the operating parameters of the state-of-the-art particle therapy system, we conducted a proof-of-concept study in which we systematically generated 28 plans for cubic targets with different combinations of plan parameters and simulated the dose discrepancies between continuous scanning and a planned one. A nomograph to guide the selection of plan parameters was developed to reduce the dose discrepancy. The effectiveness of the nomograph was evaluated with two clinical cases (one prostate and one liver). Plans with parameters guided by the nomograph decreased dose discrepancy than those used standard plan parameters. Specifically, the 2%/2 mm gamma passing rate increased from 96.3% to 100% for the prostate case and from 97.8% to 99.7% for the liver case. The CTV DVH root mean square error decreased from 2.2% to 0.2% for the prostate case and from 1.8% to 0.9% for the liver case. The decreased dose discrepancy may allow the relaxing of the delivery constraint for some cases, leading to greater benefits in continuous scanning. Further investigation is warranted.

Individualised Estimation of Quality-adjusted Survival Benefit and Cost-effectiveness of Proton Beam Therapy in Intermediate-stage Hodgkin Lymphoma

AIMS

Radiotherapy for Hodgkin lymphoma leads to the irradiation of organs at risk (OAR), which may confer excess risks of late effects. Comparative dosimetry studies show that proton beam therapy (PBT) may reduce OAR irradiation compared with photon radiotherapy, but PBT is more expensive and treatment capacity is limited. The purpose of this study is to inform the appropriateness of PBT for intermediate-stage Hodgkin lymphoma (ISHL).

MATERIALS AND METHODS

A microsimulation model simulating the course of ISHL, background mortality and late effects was used to estimate comparative quality-adjusted life years (QALYs) lived and healthcare costs after consolidative pencil beam scanning PBT or volumetric modulated arc therapy (VMAT), both in deep-inspiration breath-hold. Outcomes were compared for 606 illustrative patients covering a spectrum of clinical presentations, varying by two age strata (20 and 40 years), both sexes, three smoking statuses (never, former and current) and 61 pairs of OAR radiation doses from a comparative planning study. Both undiscounted and discounted outcomes at 3.5% yearly discount were estimated. The maximum excess cost of PBT that might be considered cost-effective by the UK's National Institute for Health and Care Excellence was calculated.

RESULTS

OAR doses, smoking status and discount rate had large impacts on QALYs gained with PBT. Current smokers benefited the most, averaging 0.605 undiscounted QALYs (range -0.341 to 2.171) and 0.146 discounted QALYs (range -0.067 to 0.686), whereas never smokers benefited the least, averaging 0.074 undiscounted QALYs (range -0.196 to 0.491) and 0.017 discounted QALYs (range -0.030 to 0.086). For the gain in discounted QALYs to be considered cost-effective, PBT would have to cost at most £4812 more than VMAT for current smokers and £645 more for never smokers. This is below preliminary National Health Service cost estimates of PBT over photon radiotherapy.

CONCLUSION

In a UK setting, PBT for ISHL may not be considered cost-effective. However, the degree of unquantifiable uncertainty is substantial.

Systematic review for deep inspiration breath hold in proton therapy for mediastinal lymphoma: A PTCOG Lymphoma Subcommittee report and recommendations

PURPOSE

To systematically review all dosimetric studies investigating the impact of deep inspiration breath hold (DIBH) compared with free breathing (FB) in mediastinal lymphoma patients treated with proton therapy as compared to IMRT (intensity-modulated radiation therapy)-DIBH.

MATERIALS AND METHODS

We conducted a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline using the PubMed database to identify studies of mediastinal lymphoma patients with dosimetric comparisons of proton-FB and/or proton-DIBH with IMRT-DIBH. Parameters included mean heart (MHD), lung (MLD), and breast (MBD) doses, among other parameters. Case reports were excluded. Absolute differences in mean doses > 1 Gy between comparators were considered to be clinically meaningful.

RESULTS

As of April 2021, eight studies fit these criteria (n = 8), with the following comparisons: proton-FB vs IMRT-DIBH (n = 5), proton-DIBH vs proton-FB (n = 5), and proton-DIBH vs IMRT-DIBH (n = 8). When comparing proton-FB with IMRT-DIBH in 5 studies, MHD was reduced with proton-FB in 2 studies, was similar (<1 Gy difference) in 2 studies, and increased in 1 study. On the other hand, MLD and MBD were reduced with proton-FB in 3 and 4 studies, respectively. When comparing proton-DIBH with proton-FB, MHD and MLD were reduced with proton DIBH in 4 and 3 studies, respectively, while MBD remained similar. Compared with IMRT-DIBH in 8 studies, proton-DIBH reduced the MHD in 7 studies and was similar in 1 study. Furthermore, MLD and MBD were reduced with proton-DIBH in 8 and 6 studies respectively. Integral dose was similar between proton-FB and proton-DIBH, and both were substantially lower than IMRT-DIBH.

CONCLUSION

Accounting for heart, lung, breast, and integral dose, proton therapy (FB or DIBH) was superior to IMRT-DIBH. Proton-DIBH can lower dose to the lungs and heart even further compared with proton-FB, depending on disease location in the mediastinum, and organ-sparing and target coverage priorities.

Proton Therapy in Supradiaphragmatic Lymphoma: Predicting Treatment-Related Mortality to Help Optimize Patient Selection

PURPOSE

In some patients with Hodgkin lymphoma (HL), proton beam therapy (PBT) may reduce the risk of radiation-related cardiovascular disease (CVD) and second cancers (SC) compared with photon radiation therapy (RT). Our aim was to identify patients who benefit the most from PBT in terms of predicted 30-year absolute mortality risks (AMR30) from CVD and SC, taking into account individual background, chemotherapy, radiation, and smoking-related risks.

METHODS AND MATERIALS

Eighty patients with supradiaphragmatic HL treated with PBT between 2015 and 2019 were replanned using optimal photon RT. To identify patients predicted to derive the greatest benefit from PBT compared with photon RT, doses and AMR30 from CVD and SC of the lung, breast, and esophagus were compared for all patients and across patient subgroups.

RESULTS

For patients with mediastinal disease below the origin of the left main coronary artery (n = 66; 82%), PBT reduced the mean dose to the heart, left ventricle, and heart valves by 1.0, 2.7, and 3.6 Gy, respectively. Based on U.S. mortality rates, PBT reduced CVD AMR30 by 0.2%, from 5.9% to 5.7%. The benefit was larger if the mediastinal disease overlapped longitudinally with the heart by ≥40% (n = 23; 29%). PBT reduced the mean dose to the heart, left ventricle, and heart valves by 3.2, 5.6, and 5.1 Gy, respectively, and reduced CVD AMR30 by 0.8%, from 7.0% to 6.2%. For patients with axillary disease (n = 25; 31%), PBT reduced the mean lung dose by 2.8 Gy and lung cancer AMR30 by 0.6%, from 2.7% to 2.1%. Breast and esophageal doses were also lower with PBT, but the effects on AMR30 were negligible. The effect of smoking on CVD and lung cancer AMR30 was much larger than radiation and chemotherapy and the differences between radiation modalities.

CONCLUSIONS

The predicted benefit of PBT is not universal and limited to certain categories of patients with lymphoma and lower mediastinal or axillary disease. Smoking cessation should be strongly encouraged in smokers who require thoracic RT.

A scoping review of patient selection methods for proton therapy

The aim was to explore various national and international clinical decision-making tools and dose comparison methods used for selecting cancer patients for proton versus X-ray radiation therapy. To address this aim, a literature search using defined scoping review methods was performed in Medline and Embase databases as well as grey literature. Articles published between 1 January 2015 and 4 August 2020 and those that clearly stated methods of proton versus X-ray therapy patient selection and those published in English were eligible for inclusion. In total, 321 studies were identified of which 49 articles met the study's inclusion criteria representing 13 countries. Six different clinical decision-making tools and 14 dose comparison methods were identified, demonstrating variability within countries and internationally. Proton therapy was indicated for all paediatric patients except those with lymphoma and re-irradiation where individualised model-based selection was required. The most commonly reported patient selection tools included the Normal Tissue Complication Probability model, followed by cost-effectiveness modelling and dosimetry comparison. Model-based selection methods were most commonly applied for head and neck clinical indications in adult cohorts (48% of studies). While no 'Gold Standard' currently exists for proton therapy patient selection with variations evidenced globally, some of the patient selection methods identified in this review can be used to inform future practice in Australia. As literature was not identified from all countries where proton therapy centres are available, further research is needed to evaluate patient selection methods in these jurisdictions for a comprehensive overview.

Cellular plasticity upon proton irradiation determines tumor cell radiosensitivity

Proton radiotherapy has been implemented into the standard-of-care for cancer patients within recent years. However, experimental studies investigating cellular and molecular mechanisms are lacking, and prognostic biomarkers are needed. Cancer stem cell (CSC)-related biomarkers, such as aldehyde dehydrogenase (ALDH), are known to influence cellular radiosensitivity through inactivation of reactive oxygen species, DNA damage repair, and cell death. In a previous study, we found that ionizing radiation itself enriches for ALDH-positive CSCs. In this study, we analyze CSC marker dynamics in prostate cancer, head and neck cancer, and glioblastoma cells upon proton beam irradiation. We find that proton irradiation has a higher potential to target CSCs through induction of complex DNA damages, lower rates of cellular senescence, and minor alteration in histone methylation pattern compared with conventional photon irradiation. Mathematical modeling indicates differences in plasticity rates among ALDH-positive CSCs and ALDH-negative cancer cells between the two irradiation types.

Volumetric modulated arc therapy versus intensity-modulated proton therapy in the irradiation of infra diaphragmatic Hodgkin Lymphoma in female patients

PURPOSE

To investigate the role of infra diaphragmatic intensity-modulated proton therapy (IMPT) compared to volumetric modulated arc therapy (VMAT) for female Hodgkin Lymphoma (HL) patients and to estimate the risk of secondary cancer and ovarian failure.

METHODS

A comparative treatment planning study was performed on 14 patients, and the results were compared according to conventional dose-volume metrics. In addition, estimates of the excess absolute risk (EAR) of secondary cancer induction were determined for the bowel, the bladder and the rectum. For the ovaries, the risk of ovarian failure was estimated.

RESULTS

The dosimetric findings demonstrate the equivalence between VMAT and IMPT in terms of target coverage. A statistically significant reduction of the mean and near-to-maximum doses was proven for the organs at risk. The EAR ratio estimated for IMPT to VMAT was 0.51 ± 0.32, 0.32 ± 0.35 and 0.05 ± 0.11 for the bowel, bladder and rectum, respectively. Concerning the risk of ovarian failure for the chronologic age ranging from 18 to 46 years, the expected net loss in fertility years ranged from 4.8 to 3.0 years for protons and 12.0 to 5.7 years for photons.

CONCLUSION

This in-silico study confirmed the beneficial role of IMPT from a dosimetric point of view. Mathematical models suggested that the use of protons might be further advantageous due to the expected reduction of the risk of secondary cancer induction and its milder impact on the reduction of fertility.

Impact of lung block shape on cardiac dose for total body irradiation

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Partial cardiac shielding in TBI is not commonly reported and varies among clinics.

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We evaluated the effects of cardiac shielding in TBI using 3D beam modeling in a commercial TPS.

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Partial cardiac shielding can reduce mean heart dose and reduce LAD dose up to 30%.

Evaluating cardiac dose during total body irradiation (TBI) is of increasing interest. A three-dimensional beam model for TBI was commissioned and lung shielding was simulated in a treatment planning system with the cardiac silhouette partially blocked and unblocked. When blocked, the median heart dose decreased by 6% (IQR = 6%) and the median cardiac V12Gy decreased by 27% (IQR = 17%). The median left anterior descending artery dose decreased 20% (IQR = 12%) for blocked cases. Because using partial heart shielding may result in considerable changes in dose to cardiac structures, TBI protocols should explicitly consider lung block design parameters and their potential effects.

Radiation-Induced Heart Disease

Cancer incidence and survivorship have had a rising tendency over the last two decades due to better treatment modalities. One of these is radiation therapy (RT), which is used in 20-55% of cancer patients, and its basic principle consists of inhibiting proliferation or inducing apoptosis of cancer cells. Classically, photon beam RT has been the mainstay therapy for these patients, but, in the last decade, proton beam has been introduced as a new option. This newer method focuses more on the tumor and affects less of the surrounding normal tissue, i.e., the heart. Radiation to the heart is a common complication of RT, especially in patients with lymphoma, breast, lung, and esophageal cancer. The pathophysiology is due to changes in the microvascular and macrovascular milieu that can promote accelerated atherosclerosis and/or induce fibrosis of the myocardium, pericardium, and valves. These complications occur days, weeks, or years after RT and the risk factors associated are high radiation doses (>30 Gy), concomitant chemotherapy (primarily anthracyclines), age, history of heart disease, and the presence of cardiovascular risk factors. The understanding of these mechanisms and risk factors by physicians can lead to a tailored assessment and monitorization of these patients with the objective of early detection or prevention of radiation-induced heart disease. Echocardiography is a noninvasive method which provides a comprehensive evaluation of the pericardium, valves, myocardium, and coronaries, making it the first imaging tool in most cases; however, other modalities, such as computed tomography, nuclear medicine, or cardiac magnetic resonance, can provide additional value.

Comparable Efficacy of Reduced Dose Radiation Therapy for the Treatment of Early Stage Gastric Extranodal Marginal Zone Lymphoma of Mucosa-Associated Lymphoid Tissue

Purpose

This study compares reduced (<27 Gy) to standard dose (≥30 Gy) radiation therapy (RT) in the treatment of gastric extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (gMALT lymphoma).

Methods and Materials

Forty-two patients with stage I or II disease were retrospectively reviewed. Response to RT was assessed with endoscopy after RT. Complete response rate (CR), freedom from treatment failure, and overall survival (OS) were calculated.

Results

All patients were stage I (n = 40) or II (n = 2). All patients had residual biopsy proven gMALT lymphoma before RT. Twenty-six patients (61.9%) were treated with standard dose RT, 30 to 36 Gy, and 16 (38.1%) with the reduced dose RT, 23.5 to 27 Gy. The median follow-up was 29.5 months (range, 6-85). Thirty-six patients (86%) achieved complete response (CR), and 6 patients (14%) achieved partial response (PR). The complete response rate (CR) at the first endoscopic assessment, median time of 3 months, was 81% (95% confidence interval, 0.61%-0.93%) for standard RT, and 94% (confidence interval, 0.69%-0.99%) for reduced RT. Among CR patients, one patient had locally relapsed disease at 50 months. The 1-year overall survival (OS) was 100% in both groups. The 1-year freedom from treatment failure (FFTF) was 100% in the reduced RT group and 92% in the standard RT group. The 2-year FFTF and OS of the whole cohort were 92% and 96%, respectively. There was no significant difference in the OS, FFTF, and CR between the 2 treatment groups (P = .38, P = .18, and P = .267, respectively). For toxicity, the mean liver dose and the mean V20 heart dose were significantly lower in the reduced RT group (P <.001 and P = .001, respectively). However, incidence and severity of reported toxicities were similar between the 2 groups.

Conclusions

Reduced dose RT (23.5-27 Gy) achieved excellent complete response rates with minimal toxicity, comparable with standard dose RT (30-36 Gy), for gMALT.

What can space radiation protection learn from radiation oncology?

Protection from cosmic radiation of crews of long-term space missions is now becoming an urgent requirement to allow a safe colonization of the moon and Mars. Epidemiology provides little help to quantify the risk, because the astronaut group is small and as yet mostly involved in low-Earth orbit mission, whilst the usual cohorts used for radiation protection on Earth (e.g. atomic bomb survivors) were exposed to a radiation quality substantially different from the energetic charged particle field found in space. However, there are over 260,000 patients treated with accelerated protons or heavier ions for different types of cancer, and this cohort may be useful for quantifying the effects of space-like radiation in humans. Space radiation protection and particle therapy research also share the same tools and devices, such as accelerators and detectors, as well as several research topics, from nuclear fragmentation cross sections to the radiobiology of densely ionizing radiation. The transfer of the information from the cancer radiotherapy field to space is manifestly complicated, yet the two field should strengthen their relationship and exchange methods and data.

Establishing cost-effective allocation of proton therapy for patients with mediastinal Hodgkin lymphoma

PURPOSE

For curative treatment of Hodgkin lymphoma, radiotherapy benefit must be weighed against toxicity. Although more costly, proton radiotherapy reduces dose to healthy tissue, potentially improving the therapeutic ratio compared to photons. We sought to determine the cost-effectiveness of proton versus photon therapy for mediastinal Hodgkin lymphoma (MHL) based on reduced heart disease.

METHODS

Our model approach was two-fold: (1) Utilize patient-level dosimetric information for a cost-effectiveness analysis using a Markov cohort model. (2) Utilize population-based data to develop guidelines for policy-makers to determine thresholds of proton therapy favorability for a given photon dose. The HD14 trial informed relapse risk; coronary heart disease risk was informed by the Framingham risk calculator modified by the mean heart dose (MHD) from radiation. Sensitivity analyses assessed model robustness and identified the most influential model assumptions. A 30-year-old adult with MHL was the base case using 30.6-Gy proton therapy versus photon intensity-modulated radiotherapy.

RESULTS

Proton therapy was not cost-effective in the base case for male ($129K/QALY) or female patients ($196/QALY). A 5-Gy MHD decrease was associated with proton therapy incremental cost-effectiveness ratio<$100K/QALY in 40% of scenarios. The hazard ratio associating MHD and heart disease was the most influential clinical parameter.

CONCLUSION

Proton therapy may be cost-effective a select minority of patients with MHLbased on age, sex, and MHD reduction. We present guidance for clinicians utilizing MHD to aid decision-making for radiotherapy modality.

Current Situation of Proton Therapy for Hodgkin Lymphoma: From Expectations to Evidence

Consolidative radiation therapy (RT) is of prime importance for early-stage Hodgkin lymphoma (HL) management since it significantly increases progression-free survival (PFS). Nevertheless, first-generation techniques, relying on large irradiation fields, delivered significant radiation doses to critical organs-at-risk (OARs, such as the heart, to the lung or the breasts) when treating mediastinal HL; consequently, secondary cancers, and cardiac and lung toxicity were substantially increased. Fortunately, HL RT has drastically evolved and, nowadays, state-of-the-art RT techniques efficiently spare critical organs-at-risks without altering local control or overall survival. Recently, proton therapy has been evaluated for mediastinal HL treatment, due to its possibility to significantly reduce integral dose to OARs, which is expected to limit second neoplasm risk and reduce late toxicity. Nevertheless, clinical experience for this recent technique is still limited worldwide. Based on current literature, this critical review aims to examine the current practice of proton therapy for mediastinal HL irradiation.

Selection of Mediastinal Lymphoma Patients for Proton Therapy Within the Proton Collaborative Group Registry: Concordance With the ILROG Guidelines

PURPOSE

As patients with mediastinal lymphoma are typically young with curable disease, advanced radiation techniques such as proton therapy are often considered to minimize subacute and late toxicity. However, it is unclear which mediastinal lymphoma patients are treated with proton therapy. Within a prospective, multi-institutional proton registry, we characterized mediastinal lymphoma patients treated with proton therapy and assessed concordance with consensus recommendations published in 2018 by the International Lymphoma Radiation Oncology Group (ILROG).

METHODS

Eligible patients included those with lymphoma of the mediastinum treated exclusively with proton therapy for whom digital imaging and communications in medicine (DICOM) treatment data were available for review. Given the challenge with reliably visualizing the left mainstem coronary artery, the inferior-most aspect of the left pulmonary artery (PA) was used as a surrogate. Extent of disease was characterized as upper mediastinum (above level of left PA), middle mediastinum (below left PA but at or above level of T8), or low mediastinum (below T8).

RESULTS

Between November 2012 and April 2019, 56 patients were treated and met inclusion criteria. Patients treated with proton therapy were young (median, 24 y; range: 12 to 88), with over half being female (55%). Patients were most commonly treated at initial diagnosis (86%) and had Hodgkin lymphoma (79%). Most patients (96%) had mediastinal disease that extended down to the level of the heart: 48% had middle and 48% had low mediastinal involvement. Nearly all patients (96%) met the ILROG consensus recommendations: 95% had lower mediastinal disease, 46% were young females, and 9% were heavily pretreated. Heart (mean) and lung dose (mean, V5, V20) were significantly associated with lowest extent of mediastinal disease.

CONCLUSIONS

Mediastinal lymphoma patients treated with proton therapy are typically young with lower mediastinal involvement. Within a prospective, multi-institutional proton registry, nearly all treated patients fit the ILROG consensus recommendations regarding which mediastinal lymphoma patients may most benefit from proton therapy.

Radiotherapy for Non-Hodgkin Lymphomas

Radiotherapy (RT) plays a diverse and essential role in the contemporary management of non-Hodgkin lymphoma (NHL) and remains the single most powerful monotherapeutic intervention for both aggressive and indolent subtypes. Over the past decade, there have been significant advancements in radiation oncology practice, which have made modern treatments safer and more conformal. Despite this sophistication and evidence supporting a continued role for RT, numerous data suggest that utilization is on the decline. In this review, we discuss the rationale for RT in 4 commonly encountered scenarios: combined modality therapy for limited-stage aggressive NHL, consolidation therapy for advanced-stage aggressive NHL, and the changing roles of salvage RT for relapsed/refractory NHL in an era of new frontiers such as cellular therapies. We also evaluate current strategies to treat indolent histologies. We conclude with perspectives on how RT for the hematological malignancies may continue to evolve.

On the Importance of Individualized, Non-Coplanar Beam Configurations in Mediastinal Lymphoma Radiotherapy, Optimized With Automated Planning

Background and Purpose

Literature is non-conclusive regarding selection of beam configurations in radiotherapy for mediastinal lymphoma (ML) radiotherapy, and published studies are based on manual planning with its inherent limitations. In this study, coplanar and non-coplanar beam configurations were systematically compared, using a large number of automatically generated plans.

Material and Methods

An autoplanning workflow, including beam configuration optimization, was configured for young female ML patients. For each of 25 patients, 24 plans with different beam configurations were generated with autoplanning: 11 coplanar CP_x plans and 11 non-coplanar NCP_x plans with x = 5 to 15 IMRT beams with computer-optimized, patient-specific configurations, and the coplanar VMAT and non-coplanar Butterfly VMAT (B-VMAT) beam angle class solutions (600 plans in total).

Results

Autoplans compared favorably with manually generated, clinically delivered plans, ensuring that beam configuration comparisons were performed with high quality plans. There was no beam configuration approach that was best for all patients and all plan parameters. Overall there was a clear tendency towards higher plan quality with non-coplanar configurations (NCP_x≥12 and B-VMAT). NCP_x≥12 produced highly conformal plans with on average reduced high doses in lungs and patient and also a reduced heart Dmean, while B-VMAT resulted in reduced low-dose spread in lungs and left breast.

Conclusions

Non-coplanar beam configurations were favorable for young female mediastinal lymphoma patients, with patient-specific and plan-parameter-dependent dosimetric advantages of NCP_x≥12 and B-VMAT. Individualization of beam configuration approach, considering also the faster delivery of B-VMAT vs. NCP_x≥12, can importantly improve the treatments.

Primary Mediastinal B Cell Lymphoma in the Positron-Emission Tomography Era Executive Summary of the American Radium Society Appropriate Use Criteria

PURPOSE

Primary mediastinal B cell lymphoma (PMBCL) is a highly curable subtype of non-Hodgkin lymphoma that is diagnosed predominantly in adolescents and young adults. Consequently, long-term treatment-related morbidity is critical to consider when devising treatment strategies that include different chemoimmunotherapy strategies with or without radiation therapy. Furthermore, adaptive approaches using the end-of-chemotherapy (EOC) positron emission tomography (PET)/computed tomography (CT) scanning may help to determine which patients may benefit from additional therapies. We aimed to develop evidence-based guidelines for treating these patients.

METHODS AND MATERIALS

We conducted a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline using the PubMed database. The ARS expert committee, composed of radiation oncologists, hematologists, and pediatric oncologists, developed consensus guidelines using the modified Delphi framework.

RESULTS

Nine studies met the full criteria for inclusion based on reporting outcomes on patients with primary mediastinal B cell lymphoma with EOC PET/CT response scored with the 5-point Deauville scale. These studies formed the evidence for these guidelines in managing patients with PMBCL according to the EOC PET response, including after a 5-point Deauville scale of 1 to 3, 4, or 5, and for patients with relapsed and refractory disease. The expert group also developed guidance on radiation simulation, treatment planning, and plan evaluation based on expert opinion.

CONCLUSIONS

Various treatment approaches exist in the management of PMBCL, including different chemoimmunotherapy regimens, the use of consolidative radiation therapy, and adaptive approaches based on EOC PET/CT response. These guidelines can be used by practitioners to provide appropriate treatment according to different disease scenarios.

Extranodal Natural Killer/T-cell Lymphoma, Nasal Type: Diagnosis and Treatment

The aggressive lymphoma, extranodal natural killer/T-cell lymphoma-nasal type, is strongly associated with Epstein-Barr virus (EBV) and is most common in Asia and in South and Central America. By contrast, incidence is low in the United States and Europe, where extranodal natural killer/T-cell lymphoma represents only 0.2%-0.4% of all newly diagnosed non-Hodgkin lymphomas. At diagnosis, it is important to test for EBV DNA in plasma by polymerase chain reaction and to carry out positron emission tomography/computer tomography and magnetic resonance imaging of the nasopharynx. In stage I/II disease, radiotherapy is the most important treatment modality, but in high-risk stage I/II disease (stage II, age > 60 y, elevated lactate dehydrogenase, Eastern Cooperative Oncology Group performance score ≥2, primary tumor invasion), it should be combined with chemotherapy. The most optimal responses are reached with nonmultidrug resistance-based therapy (eg, asparaginase- or platinum-based therapy). Therapeutic approaches consist of either platinum-based concurrent chemoradiotherapy or sequential chemoradiotherapy. The minimum dose of radiotherapy should be 50-56 Gy. Treatment of stage III/IV disease consists of 3 cycles of chemotherapy followed by autologous hematopoietic cell transplantation. Allogeneic hematopoietic cell transplantation should only be considered in case of relapsed disease or after difficulty reaching complete remission. During treatment and follow-up, plasma EBV levels should be monitored as a marker of tumor load.

Proton therapy for thoracic malignancies: a review of oncologic outcomes

Introduction: Radiotherapy is an integral component in the treatment of the majority of thoracic malignancies. By taking advantage of the steep dose fall-off characteristic of protons combined with modern optimization and delivery techniques, proton beam therapy (PBT) has emerged as a potential tool to improve oncologic outcomes while reducing toxicities from treatment.Areas covered: We review the physical properties and treatment techniques that form the basis of PBT as applicable for thoracic malignancies, including a brief discussion on the recent advances that show promise to enhance treatment planning and delivery. The dosimetric advantages and clinical outcomes of PBT are critically reviewed for each of the major thoracic malignancies, including lung cancer, esophageal cancer, mesothelioma, thymic cancer, and primary mediastinal lymphoma.Expert opinion: Despite clear dosimetric benefits with PBT in thoracic radiotherapy, the improvement in clinical outcomes remains to be seen. Nevertheless, with the incorporation of newer techniques, PBT remains a promising modality and ongoing randomized studies will clarify its role to determine which patients with thoracic malignancies receive the most benefit. Re-irradiation, advanced disease requiring high cardio-pulmonary irradiation volume and younger patients will likely derive maximum benefit with modern PBT.

Differential transcriptome response to proton versus X-ray radiation reveals novel candidate targets for combinatorial PT therapy in lymphoma

BACKGROUND AND PURPOSE

Knowledge of biological responses to proton therapy (PT) in comparison to X-ray remains in its infancy. Identification of PT specific molecular signals is an important opportunity for the discovery of biomarkers and synergistic drugs to advance clinical application. Since PT is used for the treatment of lymphoma, we report here transcriptomic responses of lymphoma cell lines to PT vs X-ray and identify potential therapeutic targets.

MATERIALS AND METHODS

Two lymphoma cell lines of human (BL41) and murine (J3D) origin were irradiated by X-ray and PT. Differential transcriptome regulation was quantified by RNA sequencing for each radiation type at 12 hours post irradiation. Gene-set enrichment analysis revealed deregulated molecular pathways and putative targets for lymphoma cell sensitization to PT.

RESULTS

Transcriptomic gene set enrichment analyses uncovered pathways that contribute to the unfolded protein response (UPR) and mitochondrial transport. Functional validation at multiple time points demonstrated increased UPR activation and decreased protein translation, perhaps due to increased oxidative stress and oxidative protein damage after PT. PPARgamma was identified as a potential regulator of the PT transcriptomic response. Inhibition of PPARgamma by two compounds, T0070907 and SR2595, sensitized lymphoma cells to PT.

CONCLUSIONS

Proton vs X-ray radiation leads to the transcriptional regulation of a specific subset of genes in line with diminished protein translation and UPR activation that may be due to oxidative stress. This study demonstrates that different radiation qualities trigger distinct cellular responses in lymphoma cells, and identifies PPARgamma inhibition as a potential strategy for the sensitization of lymphoma to PT.

Proton Therapy as a Bridging Treatment in CAR T-Cell Therapy for Relapsed and Refractory Large B-Cell Lymphoma: Is There a Role?

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. Since the relapse rate of DLBCL to frontline chemoimmunotherapy and salvage autologous hematopoietic cell transplant is high, CD19-directed chimeric antigen receptor (CAR) T-cell therapy was adopted. Given the time interval needed for CAR T cells to be manufactured (3-5 weeks) and the aggressiveness of these relapsed/refractory lymphomas, some patients do not make it to the CAR T-cell infusion phase. This calls for a bridging therapy to control, debulk, and sensitize the disease during this period. Radiation therapy can serve this purpose and has shown promising results in some studies. Proton therapy, compared to standard radiation therapy, in some locations, can reduce the radiation dose to the organs at risk, which may lead to fewer side effects for patients with lymphomas. Thus, we hypothesize that proton therapy may serve as a promising bridging strategy to CAR T-cell therapy for some patients.

The impact of proton therapy on cardiotoxicity following radiation treatment

Cardiac disease following radiation therapy represents a major consideration in the treatment of a variety of malignancies. Damage to the heart can manifest in a variety of pathologies including ischemic cardiac disease, cardiomyopathy, valvular dysfunction, arrhythmias, and pericarditis. This damage has been shown to directly relate to cardiac radiation dose and to stem from a range of cellular pathways that are often related to fibrosis. The importance of minimizing radiation dose to the heart is especially critical in the pediatric population and when treating disease sites adjacent to the heart. Proton therapy represents a promising approach to minimize dose to normal tissues such as the heart. The cardiac dosimetry reductions due to proton therapy have been demonstrated in multiple cancers and further long-term follow-up will determine the clinical significance of these reductions to cardiac structures. Future approaches using advanced techniques such as FLASH therapy could provide even further benefit by reducing post-radiation fibrosis.

Risk of Pneumonitis and Outcomes After Mediastinal Proton Therapy for Relapsed/Refractory Lymphoma: A PTCOG and PCG Collaboration

PURPOSE

Despite high response rates, there has been reluctance to use radiation therapy for patients with relapsed/refractory (r/r) Hodgkin (HL) or aggressive non-Hodgkin lymphoma (NHL) given concerns for subacute and late toxicities. Symptomatic pneumonitis, a subacute toxicity, has an incidence of 17% to 24% (≥grade 2) even with intensity modulated radiation therapy. Proton therapy (PT), which has no exit radiation dose, is associated with a lower dose to lung compared with other radiation techniques. As risk of radiation pneumonitis is associated with lung dose, we evaluated whether pneumonitis rates are lower with PT.

METHODS AND MATERIALS

Within an international, multi-institutional cohort, we retrospectively evaluated the incidence and grade of radiation pneumonitis (National Cancer Institute Common Terminology Criteria for Adverse Events v4) among patients with r/r HL or NHL treated with PT.

RESULTS

A total of 85 patients with r/r lymphoma (66% HL, 34% NHL; 46% primary chemorefractory) received thoracic PT from 2009 to 2017 in the consolidation (45%) or salvage (54%) setting. Median dose was 36 Gy(RBE). Before PT, patients underwent a median of 1 salvage systemic therapy (range, 0-4); 40% received PT within 4 months of transplant. With a median follow-up of 26.3 months among living patients, 11 patients developed symptomatic (grade 2) pneumonitis (12.8%). No grade 3 or higher pneumonitis was observed. Dose to lung, including mean lung dose, lung V5, and V20, significantly predicted risk of symptomatic pneumonitis, but not receipt of brentuximab, history of bleomycin toxicity, sex, or peritransplant radiation.

CONCLUSIONS

PT for relapsed/refractory lymphoma was associated with favorable rates of pneumonitis compared with historical controls. We confirm that among patients treated with PT, pneumonitis risk is associated with mean lung and lung V20 dose. These findings highlight how advancements in radiation delivery may improve the therapeutic ratio for patients with relapsed/refractory lymphoma. PT may be considered as a treatment modality for patients with relapsed/refractory lymphoma in the consolidation or salvage setting.

Irradiating Residual Disease to 30 Gy with Proton Therapy in Pediatric Mediastinal Hodgkin Lymphoma

Background:

Local relapse is a predominant form of recurrence among pediatric patients with Hodgkin lymphoma (PHL). Although PHL radiotherapy doses have been approximately 20 Gy, adults with Hodgkin lymphoma receiving 30 to 36 Gy experience fewer in-field relapses. We investigated the dosimetric effect of such a dose escalation to the organs at risk (OARs).

Materials and Methods:

Ten patients with PHL treated with proton therapy to 21 Gy involved-site radiation therapy (ISRT_21Gy) were replanned to deliver 30 Gy by treating the ISRT to 30 Gy (ISRT_30Gy), delivering 21 Gy to the ISRT plus a 9-Gy boost to postchemotherapy residual volume (rISRT_boost), and delivering 30 Gy to the residual ISRT target only (rISRT_30Gy). Radiation doses to the OARs were compared.

Results:

The ISRT_30Gy escalated the dose to the target by 42% but also to the OARs. The rISRT_boost escalated the residual target dose by 42%, and the OAR dose by only 17% to 26%. The rISRT_30Gy escalated the residual target dose by 42% but reduced the OAR dose by 25% to 46%.

Conclusion:

Boosting the postchemotherapy residual target dose to 30Gy can allow for dose escalation with a slight OAR dose increase. Treating the residual disease for the full 30Gy, however, would reduce the OAR dose significantly compared with ISRT_21Gy. Studies should evaluate these strategies to improve outcomes and minimize the late effects.

Long-Term Outcomes in 10-Year Survivors of Early-Stage Hodgkin Lymphoma

PURPOSE

Although radiation therapy improves progression-free survival in early-stage Hodgkin lymphoma (HL), substantial concerns remain regarding the impact of delayed normal tissue effects on quality of life and survival. We hypothesized that treatment with combined-modality therapy (CMT; chemotherapy and radiation therapy) improves overall survival among 10-year survivors compared with treatment with radiation therapy or chemotherapy alone.

METHODS AND MATERIALS

We compared patients in the Surveillance, Epidemiology, and End Results database who received a diagnosis of stage I/II HL between 1983 and 2006 who received chemotherapy and/or external beam radiation and survived at least 10 years. Our primary study outcome was overall survival; we also analyzed cause-specific and other-cause-specific survival.

RESULTS

Of 10,443 ten-year survivors of stage I/II classical HL, 33.6% received chemotherapy alone, 23.8% radiation therapy alone, and 42.6% CMT. Median follow-up was 16.1 years. On multivariate analysis including race, stage, sex, age, and "modern" treatment in 1995 and later, 10-year survivors who received CMT had improved overall survival relative to survivors who received RT alone (hazard ratio, 1.41; 95% confidence interval, 1.21-1.64; P < .01) or chemotherapy alone (hazard ratio, 1.35; 95% confidence interval, 1.16-1.57; P < .01).

CONCLUSIONS

This survival difference was driven by an increase in death from both HL and non-HL causes in those treated with chemotherapy alone. Our analysis suggests that CMT offers optimal survivorship for patients with stage I/II HL.

Pencil beam scanning proton therapy of Hodgkin's lymphoma in deep inspiration breath-hold: A case series report

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A combination of proton therapy and deep inspiration breath-hold can reduce normal tissue dose.

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The first patients treated showed clinically acceptable inter breath-hold variations.

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The treatment strategy is robust and works well at a proton center.

Background

Most patients with Hodgkin’s lymphoma are young and have a favourable prognosis, therefore it is of high importance to decrease the radiation doses to normal tissues received during radiotherapy. A combination of proton therapy and deep inspiration breath-hold technique (DIBH) can improve the sparing effect and thereby reduce the risk of late effects.

Case presentation

The two first patient cases treated with proton therapy in DIBH at the Skandion Clinic, Uppsala, Sweden, are presented here. Proton treatment plans were compared to photon plans based on doses to target and organs at risk. Several CT scans were acquired during the treatment course and inter breath-hold variations were evaluated based on anatomical distances and dosimetric comparisons.

Conclusions

The results from our first patients treated with proton therapy in DIBH imply that the treatment strategy is robust and has the potential to reduce dose to normal tissue.

The role of proton therapy in pediatric malignancies: Recent advances and future directions

Proton radiotherapy has promised an advantage in safely treating pediatric malignancies with an increased capability to spare normal tissues, reducing the risk of both acute and late toxicity. The past decade has seen the proliferation of more than 30 proton facilities in the United States, with increased capacity to provide access to approximately 3,000 children per year who will require radiotherapy for their disease. We provide a review of the initial efforts to describe outcomes after proton therapy across the common pediatric disease sites. We discuss the main attempts to assess comparative efficacy between proton and photon radiotherapy concerning toxicity. We also discuss recent efforts of multi-institutional registries aimed at accelerating research to better define the optimal treatment paradigm for children requiring radiotherapy for cure.

Association of Combined Modality Therapy vs Chemotherapy Alone With Overall Survival in Early-Stage Pediatric Hodgkin Lymphoma

Importance

To date, there is no well-defined standard of care for early-stage pediatric Hodgkin lymphoma (HL), which may include chemotherapy alone or combined modality therapy (CMT) with chemotherapy followed by radiotherapy. Although the use of radiotherapy in pediatric HL is decreasing, this strategy remains controversial.

Objective

To examine the use of CMT in pediatric HL and its association with improved overall survival using data from a large cancer registry.

Design, Setting, and Participants

This observational cohort study used data from the National Cancer Database to evaluate clinical features and survival outcomes among 5657 pediatric patients (age, 0.1-21 years) who received a diagnosis of stage I or II HL in the United States from January 1, 2004, to December 31, 2015. Statistical analysis was conducted from May 1 to November 1, 2018.

Exposures

Patients received definitive treatment with chemotherapy or CMT, defined as chemotherapy followed by radiotherapy.

Main Outcomes and Measures

Kaplan-Meier survival curves were used to examine overall survival. The association between CMT use, covariables, and overall survival was assessed in multivariable Cox proportional hazards regression models. Use of radiotherapy was assessed over time.

Results

Among the 11 546 pediatric patients with HL in the National Cancer Database, 5657 patients (3004 females, 2596 males, and 57 missing information on sex; mean [SD] age, 17.1 [3.6] years) with stage I or II classic HL were analyzed. Of these patients, 2845 (50.3%) received CMT; use of CMT vs chemotherapy alone was associated with younger age (<16 years, 1102 of 2845 [38.7%] vs 856 of 2812 [30.4%]; P < .001), male sex (1369 of 2845 [48.1%] vs 1227 of 2812 [43.6%]; P < .001), stage II disease (2467 of 2845 [86.7%] vs 2376 of 2812 [84.5%]; P = .02), and private health insurance (2065 of 2845 [72.6%] vs 1949 of 2812 [69.3%]; P = .002). The 5-year overall survival was 94.5% (confidence limits, 93.8%, 95.8%) for patients who received chemotherapy alone and 97.3% (confidence limits, 96.4%, 97.9%) for those who received CMT, which remained significant in the intention-to-treat analysis and multivariate analysis (adjusted hazard ratio for CMT, 0.57; 95% CI, 0.42-0.78; P < .001). In the sensitivity analysis, the low-risk cohort (stage I-IIA) and adolescent and young adult patients had the greatest benefit from CMT (adjusted hazard ratio, 0.47; 95% CI, 0.40-0.56; P < .001). The use of CMT decreased by 24.8% from 2004 to 2015 (from 59.7% [271 of 454] to 34.9% [153 of 438]).

Conclusions and Relevance

In this study, pediatric patients with early-stage HL receiving CMT experienced improved overall survival 5 years after treatment. There is a nationwide decrease in the use of CMT, perhaps reflecting the bias of ongoing clinical trials designed to avoid consolidation radiotherapy. This study represents the largest data set to date examining the role of CMT in pediatric HL.

Intensity modulated proton therapy compared to volumetric modulated arc therapy in the irradiation of young female patients with hodgkin's lymphoma. Assessment of risk of toxicity and secondary cancer induction

Background

To investigate the role of intensity modulated proton therapy (IMPT) compared to volumetric modulated arc therapy (VMAT) for advanced supradiaphragmatic Hodgkin’s lymphoma (HL) in young female patients by assessing dosimetric features and modelling the risk of treatment related complications and radiation-induced secondary malignancies.

Methods

A group of 20 cases (planned according to the involved-site approach) were retrospectively investigated in a comparative planning study. Intensity modulated proton plans (IMPT) were compared to VMAT RapidArc plans (RA). Estimates of toxicity were derived from normal tissue complication probability (NTCP) calculations with either the Lyman or the Poisson models for a number of endpoints. Estimates of the risk of secondary cancer induction were determined for lungs, breasts, esophagus and thyroid. A simple model-based selection strategy was considered as a feasibility proof for the individualized selection of patients suitable for proton therapy.

Results

IMPT and VMAT plans resulted equivalent in terms of target dose distributions, both were capable to ensure high coverage and homogeneity. In terms of conformality, IMPT resulted ~ 10% better than RA plans. Concerning organs at risk, IMPT data presented a systematic improvement (highly significant) over RA for all organs, particularly in the dose range up to 20Gy. This lead to a composite average reduction of NTCP of 2.90 ± 2.24 and a reduction of 0.26 ± 0.22 in the relative risk of cardiac failures. The excess absolute risk per 10,000 patients-years of secondary cancer induction was reduced, with IMPT, of 9.1 ± 3.2, 7.2 ± 3.7 for breast and lung compared to RA. The gain in EAR for thyroid and esophagus was lower than 1. Depending on the arbitrary thresholds applied, the selection rate for proton treatment would have ranged from 5 to 75%.

Conclusion

In relation to young female patients with advanced supradiaphragmatic HL, IMPT can in general offer improved dose-volume sparing of organs at risk leading to an anticipated lower risk of early or late treatment related toxicities. This would reflect also in significantly lower risk of secondary malignancies induction compared to advanced photon based techniques. Depending on the selection thresholds and with all the limits of a non-validated and very basic model, it can be anticipated that a significant fraction of patients might be suitable for proton treatments if all the risk factors would be accounted for.

Comparative photon and proton dosimetry for patients with mediastinal lymphoma in the era of Monte Carlo treatment planning and variable relative biological effectiveness

Background

Existing pencil beam analytical (PBA) algorithms for proton therapy treatment planning are not ideal for sites with heterogeneous tissue density and do not account for the spatial variations in proton relative biological effectiveness (vRBE). Using a commercially available Monte Carlo (MC) treatment planning system, we compared various dosimetric endpoints between proton PBA, proton MC, and photon treatment plans among patients with mediastinal lymphoma.

Methods

Eight mediastinal lymphoma patients with both free breathing (FB) and deep inspiration breath hold (DIBH) CT simulation scans were analyzed. The original PBA plans were re-calculated with MC. New proton plans that used MC for both optimization and dose calculation with equivalent CTV/ITV coverage were also created. A vRBE model, which uses a published model for DNA double strand break (DSB) induction, was applied on MC plans to study the potential impact of vRBE on cardiac doses. Comparative photon plans were generated on the DIBH scan.

Results

Re-calculation of FB PBA plans with MC demonstrated significant under coverage of the ITV V99 and V95. Target coverage was recovered by re-optimizing the PT plan with MC with minimal change to OAR doses. Compared to photons with DIBH, MC-optimized FB and DIBH proton plans had significantly lower dose to the mean lung, lung V5, breast tissue, and spinal cord for similar target coverage. Even with application of vRBE in the proton plans, the putative increase in RBE at the end of range did not decrease the dosimetric advantages of proton therapy in cardiac substructures.

Conclusions

MC should be used for PT treatment planning of mediastinal lymphoma to ensure adequate coverage of target volumes. Our preliminary data suggests that MC-optimized PT plans have better sparing of the lung and breast tissue compared to photons. Also, the potential for end of range RBE effects are unlikely to be large enough to offset the dosimetric advantages of proton therapy in cardiac substructures for mediastinal targets, although these dosimetric findings require validation with late toxicity data.

Proton therapy in the most common pediatric non-central nervous system malignancies: an overview of clinical and dosimetric outcomes

Radiation therapy represents an important approach in the therapeutic management of children and adolescents with malignant tumors and its application with modern techniques – including Proton Beam Therapy (PBT) – is of great interest. In particular, potential radiation-induced injuries and secondary malignancies – also associated to the prolonged life expectancy of patients – are still questions of concern that increase the debate on the usefulness of PBT in pediatric treatments. This paper presents a literary review of current applications of PBT in non-Central Nervous System pediatric tumors (such as retinoblastoma, Hodgkin Lymphoma, Wilms tumor, bone and soft tissues sarcomas). We specifically reported clinical results achieved with PBT and dosimetric comparisons between PBT and the most common photon-therapy techniques. The analysis emphasizes that PBT minimizes radiation doses to healthy growing organs, suggesting for reduced risks of late side-effects and radiation-induced secondary malignancies. Extended follow up and confirms by prospective clinical trials should support the effectiveness and long-term tolerance of PBT in the considered setting.

Cardiotoxicity of mediastinal radiotherapy

Aim

To explore available recent literature related to cardiotoxicity following mediastinal radiation.

Background

Radiotherapy-related heart injury is well documented, with no apparent safety threshold dose. The number of long-term cancer survivors exposed to mediastinal radiotherapy at some point of their treatment is increasing. Heart dosimetric parameters are of great importance in developing a treatment plan, but few data are available regarding radiosensitivity and dose-volume constraints for specific heart structures.

Materials and Methods

In October 2018, we identified articles published after 1990 through a PubMed/MEDLINE database search. The authors examined rough search results and manuscripts not relevant for the topic were excluded. We extracted clinical outcomes following mediastinal radiotherapy of childhood cancers, lymphoma, medulloblastoma, thymic cancers and hematopoietic cell transplantation survivors and evaluated treatment planning data, whenever available.

Results

A total of 1311 manuscripts were identified in our first-round search. Of these manuscripts, only 115 articles, matching our selection criteria, were included.

Conclusions

Studies uniformly show a linear radiation dose-response relationship between mean absorbed dose to the heart (heart-D_mean) and the risk of dying as a result of cardiac disease, particularly when heart-D_mean exceeds 5 Gy. Limited data are available regarding dose-volume predictors for heart substructures and the risk of subsequent cardiac toxicity. An individual patient's cardiotoxicity risk can be modified with advanced treatment planning techniques, including deep inspiration breath hold. Proton therapy is currently showing advantages in improving treatment planning parameters when compared to advanced photon techniques in lymphoma, thymic malignancies, malignant mesothelioma and craniospinal irradiation.

Hematologic Malignancies

Radiation therapy plays a critical role in the management of a wide range of hematologic malignancies. The optimal radiation dose and target volume, and safe and effective ways of integrating radiation with systemic agents, vary depending on the histologic subtypes, stage at presentation, patient performance status, response to systemic therapy if given, treatment intent, and patient preferences. Limiting doses to surrounding organs without sacrificing disease control is of paramount importance. Reducing radiation doses and treatment volume in selected cases, and the use of advanced radiotherapy technology, can improve the therapeutic ratio of patients receiving radiation therapy for hematologic malignancies.