Rationale for and preliminary results of proton beam therapy for mediastinal lymphoma

Radiotherapy dose de-escalation in patients with high grade non-Hodgkin lymphoma in a real-world clinical practice

PURPOSE

The standard treatment of non-Hodgkin lymphoma (NHL) comprises combined modality treatment, radiotherapy (RT), and chemotherapy with rituximab which has significantly improved both disease-free survival (DFS) and overall survival (OS). However, there is no uniformity in radiation dose usage in these patients. In this retrospective study, we compared lower radiation dose with higher in patients with aggressive NHL.

MATERIALS AND METHODS

From 2007 to 2017, treatment records of all high-grade NHL or diffuse large B-cell lymphoma and non-central nervous system NHL were included. We compared response rates, OS and DFS of patients who received ≤30 Gy RT to those with >30 Gy. Univariate and multivariate analyses were done to determine factors affecting prognosis, i.e., age, sex, stage, International Prognostic Index (IPI), adding rituximab, and radiation dose.

RESULTS

A total of 184 NHL patients treated with combined modality or radiation alone having complete follow-up details were analyzed. At median follow-up of 66.8 months, 5-year OS was 72.8% in high-dose group versus 69.9% in low-dose group (p = 0.772) and 5-year DFS 64.7% versus 64.1% (p = 0.871). Patients having early-stage disease receiving low dose and those with advanced disease treated with >30 Gy had better OS and DFS though not statistically significant. Adding rituximab was associated with significantly better OS and DFS irrespective of radiation dose delivered. High IPI score and omitting rituximab were the only factors that significantly worsened both OS and DFS. Acute radiation toxicities were comparable in both groups (p = 0.82). Among late toxicities, no patient developed a second malignancy and 5% died due to cardiovascular complications (p = 0.595) though only two patients (1.1%) had received thoracic radiation.

CONCLUSION

The two groups had comparable response rates, acute toxicities, DFS and OS. This study suggests that RT dose reduction may be possible in high-grade NHL without compromising the DFS and OS.

NCCN Guidelines® Insights: Hodgkin Lymphoma, Version 2.2022

Hodgkin lymphoma (HL) is an uncommon malignancy of B-cell origin. Classical HL (cHL) and nodular lymphocyte-predominant HL are the 2 main types of HL. The cure rates for HL have increased so markedly with the advent of modern treatment options that overriding treatment considerations often relate to long-term toxicity. These NCCN Guidelines Insights discuss the recent updates to the NCCN Guidelines for HL focusing on (1) radiation therapy dose constraints in the management of patients with HL, and (2) the management of advanced-stage and relapsed or refractory cHL.

Modern Radiation Oncology: From IMRT to Particle Therapy—Present Status and the Days to Come

There has been tremendous technological development in the field of radiation oncology, mainly during the last few decades. Parallel advancements in imaging and accelerator technologies have contributed significantly to the same. Present-day radiation therapy is aimed at precision, in terms of physical accuracy of both its planning and delivery. This has been made possible by improvements in defining the target (use of various radiological and functional imaging modalities), advanced radiotherapy planning methods (intensity-modulated radiation therapy and recent emergence of particle therapy), and robust verification techniques (image-guided radiation therapy). These developments have enabled delivery of adequate tumoricidal doses conforming to the target, thereby improving disease control with reduced normal tissue toxicity in a wide range of malignancies. Elucidation of molecular pathways determining radioresistance or systemic effects of radiotherapy and strategies for therapeutic manipulation of the same are also being explored. Overall, we look forward to ensuring basic radiotherapy access to all patients, and precision radiation therapy to appropriate candidates (triaged by disease anatomy or biology and associated cost-effectiveness).

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.

Hodgkin Lymphoma, Version 2.2020, NCCN Clinical Practice Guidelines in Oncology

The NCCN Clinical Practice Guidelines in Oncology for Hodgkin Lymphoma (HL) provide recommendations for the management of adult patients with HL. The NCCN panel meets at least annually to review comments from reviewers within their institutions, examine relevant data, and reevaluate and update their recommendations. Current management of classic HL involves initial treatment with chemotherapy alone or combined modality therapy followed by restaging with PET/CT to assess treatment response. Overall, the introduction of less toxic and more effective regimens has significantly advanced HL cure rates. This portion of the NCCN Guidelines focuses on the management of classic HL.

Percussion assisted radiation therapy in Hodgkin lymphoma allows a marked reduction in heart dose

BACKGROUND AND PURPOSE

Early-stage Hodgkin lymphoma (HL) is a highly curable disease but the treatment can induce late complications many years later. Irradiation of the healthy heart is inevitable during radiation treatment of mediastinal sites. We developed a novel method to induce a prolonged apnea-like state that can help decrease the dose to organs at risk during radiation therapy. We present the results of the first 8 HL patients treated routinely with percussion assisted radiation therapy (PART) in our clinic.

MATERIAL AND METHODS

We used a newly developed high-frequency non-invasive ventilation system to suppress respiratory motion for prolonged periods and push the heart away from the treated volume.

RESULTS

All 8 patients were able to rapidly learn the technique and had an advantage to be treated by PART. We lowered the mean heart dose by an average of 3 Gy with similar target coverage compared to a classical free breathing treatment plan. They were all treated for 15 radiotherapy sessions by PART without any notable side effects.

CONCLUSIONS

Percussion assisted radiation therapy can be used routinely to reduce the dose to the heart in Hodgkin lymphoma.

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.

Proton Therapy For Lymphomas: Current State Of The Art

The combination of brief chemo-radiotherapy provides high cure rates and represents the first line of treatment for many lymphoma patients. As a result, a high proportion of long-term survivors may experience treatment-related toxic events many years later. Excess and unintended radiation dose to organs at risk (particularly heart, lungs and breasts) may translate in an increased risk of cardiovascular events and second cancers after a few decades. Minimizing dose to organs at risk is thus pivotal to restrain the risk of long-term complications. Proton therapy, with its peculiar physic properties, may help to better spare organs at risk and consequently to reduce toxicities especially in patients receiving mediastinal radiotherapy. Herein, we review the physical basis of proton therapy and the rationale for its implementation in lymphoma patients, with a detailed description of the clinical data. We also discuss the potential disadvantages and uncertainties of protons that may limit their application and critically review the dosimetric studies comparing the risk of late complications between proton and photon radiotherapy.

Comparative treatment planning study for mediastinal Hodgkin's lymphoma: impact on normal tissue dose using deep inspiration breath hold proton and photon therapy

BACKGROUND

Late effects induced by radiotherapy (RT) are of great concern for mediastinal Hodgkin's lymphoma (HL) patients and it is therefore important to reduce normal tissue dose. The aim of this study was to investigate the impact on the normal tissue dose and target coverage, using various combinations of intensity modulated proton therapy (IMPT), volumetric modulated arc therapy (VMAT) and 3-dimensional conformal RT (3D-CRT), planned in both deep inspiration breath hold (DIBH) and free breathing (FB).

MATERIAL AND METHODS

Eighteen patients were enrolled in this study and planned with involved site RT. Two computed tomography images were acquired for each patient, one during DIBH and one during FB. Six treatment plans were created for each patient; 3D-CRT in FB, 3D-CRT in DIBH, VMAT in FB, VMAT in DIBH, IMPT in FB and IMPT in DIBH. Dosimetric impact on the heart, left anterior descending (LAD) coronary artery, lungs, female breasts, target coverage, and also conformity index and integral dose (ID), was compared between the different treatment techniques.

RESULTS

The use of DIBH significantly reduced the lung dose for all three treatment techniques, however, no significant difference in the dose to the female breasts was observed. Regarding the heart and LAD doses, large individual variations were observed. For VMAT, the mean heart and LAD doses were significantly reduced using DIBH, but no significant difference was observed for 3D-CRT and IMPT. Both IMPT and VMAT resulted in improved target coverage and more conform dose distributions compared to 3D-CRT. IMPT generally showed the lowest organs at risk (OAR) doses and significantly reduced the ID compared to both 3D-CRT and VMAT.

CONCLUSIONS

The majority of patients benefited from treatment in DIBH, however, the impact on the normal tissue dose was highly individual and therefore comparative treatment planning is encouraged. The lowest OAR doses were generally observed for IMPT in combination with DIBH.

Proton therapy for adults with mediastinal lymphomas: the International Lymphoma Radiation Oncology Group guidelines

Among adult lymphoma survivors, radiation treatment techniques that increase the excess radiation dose to organs at risk (OARs) put patients at risk for increased side effects, especially late toxicities. Minimizing radiation to OARs in adults patients with Hodgkin and non-Hodgkin lymphomas involving the mediastinum is the deciding factor for the choice of treatment modality. Proton therapy may help to reduce the radiation dose to the OARs and reduce toxicities, especially the risks for cardiac morbidity and second cancers. Because proton therapy may have some disadvantages, identifying the patients and the circumstances that may benefit the most from proton therapy is important. We present modern guidelines to identify adult lymphoma patients who may derive the greatest benefit from proton therapy, along with an analysis of the advantages and disadvantages of proton treatment.

[Radiation therapy planning for Hodgkin lymphoma: Focus on intensity-modulated radiotherapy, gating, protons. Which techniques to best deliver radiation?]

The optimization of radiotherapy in these young and long-lived survivors raises the question about the interest of using modern techniques to allow a better distribution of the dose. The choice of the irradiation technique must take into account the incidence of side effects related to radiation. In this context, the definition of the target volumes as well as the verification and monitoring of the delivered processing are essential. International recommendations for treatment fields are based on the "involved node radiotherapy" concept. The best irradiation technique to use remains to be defined. The use of intensity-modulated radiotherapy improves the coverage and reduces the dose to the organs at risk with a variable gain depending on the topography of the lymph nodes: upper or lower mediastinum, right or left lateralization, the techniques used. The deep inspiration breath-hold technique allows an increase of the pulmonary volume, extension of the mediastinum with an up down of the heart which make possible to move the planning target volume away from the cardiac structures. The volumetric-modulated arctherapy technique with several arches can be particularly interesting to reduce the dose to the breasts, as well as tomotherapy when bulky disease. Proton therapy with the Bragg peak specificity can play a key role in limiting doses to organs at risk, when robust planning that will take into account geometric and physical uncertainties is available. The heterogeneity of Hodgkin lymphomas in terms of volume, shape and initial location are the key elements to take into account when choosing the preferred radiotherapy technique.

Proton versus photon deep inspiration breath hold technique in patients with hodgkin lymphoma and mediastinal radiation : A PLANNING COMPARISON OF DEEP INSPIRATION BREATH HOLD INTENSITY MODULATION RADIOTHERAPY AND INTENSITY MODULATED PROTON THERAPY

BACKGROUND

The benefits of proton therapy in the treatment of patients with Hodgkin lymphoma (HL) are controversially discussed. Therefore we compared intensitiy modulated proton therapy (IMPT) with intensity modulated radiotherapy (IMRT), in the form of volumetric modulated arc therapy (VMAT) in patients with Hodgkin lymphoma (HL), through a comparative treatment planning study.

METHODS

Radiation plans for 21 patients with Hodgkin Lymphoma (HL) were computed for IMPT and deep inspiration breath hold (DIBH) VMAT. Plans were optimized and computed assuming deep inspiration breath holding conditions. Dosimetric comparison on standard metrics from dose volume histograms was performed to appraise the relative merits of the two techniques, while proton plan robustness was assessed by re-computing the dose distribution of each plan by varying the Hounsfield Units to stopping power calibration by applying a ± 3 and 4% error.

RESULTS

DIBH-VMAT and IMPT both provided excellent coverage, conformity and heterogeneity of the clinical target volume (CTV) and planning target volume (PTV). IMPT reduced mean doses to the breasts, lungs, heart and normal tissue by 38-83%. IMPT significantly reduced mean doses to the heart to < 5 Gy despite bulky mediastinal disease and decreased breast doses in female patients to < 1 Gy. Despite the simulated 3 and 4% miscalibration errors, no remarkable or measurable impact was observed on the organs at risk (OARs).

CONCLUSIONS

This is the first comparison between DIBH-VMAT and IMPT in HL treatment. We could demonstrate statistically significant decreases in all dose/volume metrics of the OARs. Regardless of the planning paradigm used, range uncertainties can substantially under dose the PTV, while perhaps not leading to clinically significant deterioration of CTV coverage. With the geometry applied no impact was observed for OARs, suggesting IMPT as a superior technique for potentially reducing future health risks for HL patients.

Life years lost attributable to late effects after radiotherapy for early stage Hodgkin lymphoma: The impact of proton therapy and/or deep inspiration breath hold

BACKGROUND AND PURPOSE

Due to the long life expectancy after treatment, the risk of late effects after radiotherapy (RT) is of particular importance for patients with Hodgkin lymphoma (HL). Both deep inspiration breath hold (DIBH) and proton therapy have been shown to reduce the dose to normal tissues for mediastinal HL, but the impact of these techniques in combination is unknown. The purpose of this study was to compare the life years lost (LYL) attributable to late effects after RT for mediastinal HL using intensity modulated radiation therapy (IMRT) in free breathing (FB) and DIBH, and proton therapy in FB and DIBH.

MATERIALS AND METHODS

Plans for each technique were created for 22 patients with HL. Doses were extracted and the risk of late effects and LYL were estimated.

RESULTS

We found that the use of DIBH, proton therapy, and the combination significantly reduced the LYL compared to IMRT in FB. The lowest LYL was found for proton therapy in DIBH. However, when IMRT in DIBH was compared to proton therapy in FB, no significant difference was found.

CONCLUSIONS

Patient-specific plan comparisons should be used to select the optimal technique when comparing IMRT in DIBH and proton therapy in FB.

Risk of major cardiac events following adjuvant proton versus photon radiation therapy for patients with thymic malignancies

BACKGROUND

While often managed with surgery alone, patients with thymic malignancies with high-risk features may benefit from adjuvant radiation therapy but are at risk for late toxicities. Previously, the risk of major cardiac events (MCEs) was reported to increase by 7% per one Gray (Gy) to the heart. In this study, we compare dose to organs at risk (OARs) with intensity-modulated (IMRT) versus proton beam therapy (PBT). We hypothesize a decrease risk of predicted MCEs with PBT.

MATERIAL AND METHODS

Patients requiring adjuvant therapy for thymic malignancies were treated with double scattered proton beam therapy (DS-PBT). Clinical backup IMRT plans were generated. Predicted MCEs were calculated based on median dose to the heart. A Wilcoxon rank sum test was used for statistical comparisons.

RESULTS

Twenty-two consecutive patients were evaluated. DS-PBT resulted in statistically significant decreases in dose to the heart, lungs, left ventricle, esophagus, and spinal cord (all p ≤ .01). The increase in risk of MCEs from 0 to ≥20 years was lower with PBT (74% versus 135%, p = .04).

DISCUSSION

DS-PBT results in decreased dose to OARs and may reduce the risk of MCEs compared with IMRT. Long-term follow-up is required to assess for clinical benefit from DS-PBT.

Optimal Therapy for Early-Stage Hodgkin's Lymphoma: Risk Adapting, Response Adapting, and Role of Radiotherapy

PURPOSE OF REVIEW

The aim of this article is to discuss the current role of radiotherapy (RT) for early-stage Hodgkin's lymphoma (HL) in the context of risk-adapted and response-adapted treatment strategy, and describe changes in RT technical approach.

RECENT FINDINGS

In low-risk patients, RT could be omitted but, at the price of a lower progression-free survival, and its role is still debated. Ongoing trials are combining new agents with chemotherapy alone or response-adapted combined modality therapy, and results are awaited. Modern RT incorporates lower doses and smaller fields, together with the implementation of sophisticated delivery techniques aimed to reducing the dose to critical structures such as the heart. The role of RT for early-stage HL is still under debate, and new combinations are emerging; an individualized approach should be recommended, considering all RT technical opportunities to minimize toxicity while maintaining efficacy.

Proton Therapy for Pediatric Hodgkin Lymphoma

BACKGROUND

Compared to X-ray radiation therapy, proton therapy (PT) reduces the radiation dose to organs at risk, which is expected to translate into fewer second cancers and less cardiac morbidity decades after treatment. The Children's Oncology Group high-risk pediatric Hodgkin lymphoma (PHL) protocol, AHOD1331, allows the use of PT, yet limited data exist on the use of PT in PHL.

PROCEDURE

Between 2010 and 2014, 22 pediatric patients were treated with PT for PHL at our institution: 7 intermediate-risk patients, 11 high-risk patients, and 4 relapsed patients. The patients' age ranged from 6 to 18 years old. Median follow-up was 36 months. All patients received chemotherapy before PT.

RESULTS

The 2-year and 3-year overall survival rates were both 94%, and the progression-free survival rate was 86%. Recurrences occurred in three high-risk patients: one isolated in-field cervical lymph node and two in-field and out-of-field. All recurrences occurred within 5 months of completing PT. No PT-related grade 3 or higher acute or late complications were observed.

CONCLUSION

PT for PHL showed no short-term severe toxicity and yields similar short-term control to recently published large multi-institutional clinical trials.

Proton pencil beam scanning for mediastinal lymphoma: treatment planning and robustness assessment

BACKGROUND

Modern radiotherapy (RT) for lymphoma is highly personalized. While advanced imaging is largely employed to define limited treatment volumes, the use of proton pencil beam scanning (PBS) for highly conformal lymphoma RT is still in its infancy. Here, we assess the dosimetric benefits and feasibility of PBS for mediastinal lymphoma (ML).

MATERIALS AND METHODS

Ten patients were planned using PBS for involved-site RT. The initial plans were calculated on the average four-dimensional computed tomography (4D-CT). PBS plans were compared with 3D conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and proton double scattering (DS). In order to evaluate the feasibility of PBS and the plan robustness against inter- and intra-fractional uncertainties, the 4D dose was calculated on initial and verification CTs. The deviation of planned dose from delivered dose was measured. The same proton beamline was used for all patients, while another beamline with larger spots was employed for patients with large motion perpendicular to the beam.

RESULTS

PBS provided the lowest mean lung dose (MLD) and mean heart dose (MHD) for all patients in comparison with 3D-CRT, IMRT, and DS. For eight patients, internal target volume (ITV) D_98% was degraded by <3%; and the MLD and MHD deviated by <10% of prescription over the course of treatment when the PBS field was painted twice in each session. For one patient with target motion perpendicular to the beam (>5 mm), the degradation of ITV D_98% was 9%, which was effectively mitigated by employing large spots. One patient exhibited large dose degradation due to pericardial effusion, which required replanning across all modalities.

CONCLUSIONS

This study demonstrates that PBS plans significantly reduce MLD and MHD relative to 3D-CRT, IMRT, and DS and identifies requirements for robust free-breathing ML PBS treatments, showing that PBS plan robustness can be maintained with repainting and/or large spots.

Comparison of passive-beam proton therapy, helical tomotherapy and 3D conformal radiation therapy in Hodgkin's lymphoma female patients receiving involved-field or involved site radiation therapy

PURPOSE

Second cancers and cardiovascular toxicities are long term radiation toxicity in locally advanced Hodgkin's lymphomas. In this study, we evaluate the potential reduction of dose to normal tissue with helical tomotherapy and proton therapy for Hodgkin's lymphoma involved-field or involved-site irradiation compared to standard 3D conformal radiation therapy.

PATIENTS AND METHODS

Fourteen female patients with supradiaphragmatic Hodgkin's lymphoma were treated at our institution with 3D conformal radiation therapy or helical tomotherapy to a dose of 30Gy in 15 fractions. A planning comparison was achieved including proton therapy with anterior/posterior passive scattered beams weighted 20Gy/10Gy.

RESULTS

Mean doses to breasts, lung tissue and heart with proton therapy were significantly lower compared to helical tomotherapy and to 3D conformal radiation therapy. Helical tomotherapy assured the best protection of lungs from doses above 15Gy with the V20Gy equal to 16.4%, compared to 19.7% for proton therapy (P=0.01) or 22.4% with 3D conformal radiation therapy (P<0.01). Volumes of lung receiving doses below 15Gy were significantly larger for helical tomotherapy than for proton therapy or 3D conformal radiation therapy, with respective lung doses V10Gy=37.2%, 24.6% and 27.4%. Also, in the domain of low doses, the volumes of breast that received more than 10Gy or more than 4Gy with helical tomotherapy were double the corresponding volumes for proton therapy, with V4Gy representing more than a third of one breast volume with helical tomotherapy.

CONCLUSIONS

Helical tomotherapy achieved a better protection to the lungs for doses above 15Gy than passive proton therapy or 3D conformal radiation therapy. However, dose distributions could generally be improved by using protons even with our current passive-beam technology, especially allowing less low dose spreading and better breast tissue sparing, which is an important factor to consider when treating Hodgkin's lymphomas in female patients. Prospective clinical study is needed to evaluate the tolerance and confirm these findings.

Proton therapy in the management of lymphoma

Hodgkin lymphoma and non-Hodgkin lymphoma are common hematologic malignancies with such a favorable prognosis that many survivors live decades after combined chemotherapy and radiotherapy. These survivors, however, are at risk of developing late treatment adverse effects from collateral damage, including secondary malignancies, cardiac toxicities, and ischemic heart diseases. Recent efforts have successfully reduced the radiation dose and treatment field without compromising cure rates. Proton therapy has the potential of further lowering the treatment-related toxicity owing to its ability to deposit a high dose only at the target. Although this finding has been supported by several current dosimetric studies, its utilization in the management of lymphoma has been limited during the past 5 years because of the paucity of facilities and the difficulty of obtaining insurance coverage. With diligent follow-up, the clinical impact of proton therapy will be established to improve the therapeutic ratio and to reduce late treatment-related morbidity.

Proton therapy for Hodgkin lymphoma

Hodgkin lymphoma has gone from an incurable disease to one for which the majority of patients will be cured. Combined chemotherapy and radiotherapy achieves the best disease control rates and results in many long-term survivors. As a result, a majority of long-term Hodgkin lymphoma survivors live to experience severe late treatment-related complications, especially cardiovascular disease and second malignancies. The focus of research and treatment for Hodgkin lymphoma is to maintain the current high rates of disease control while reducing treatment-related morbidity and mortality. Efforts to reduce late treatment complications focus on improvements in both systemic therapies and radiotherapy. Herein we review the basis for the benefits of proton therapy over conventional X-ray therapy. We review outcomes of Hodgkin lymphoma treated with proton therapy, and discuss the ability of protons to reduce radiation dose to organs at risk and the impact on the most significant late complications related to the treatment.

Proton therapy in the management of non-Hodgkin lymphoma

Proton therapy (PT) is a highly conformal type of radiation therapy that can target the tumor while sparing dose to surrounding normal tissues. This study reviews a single institution's experience managing patients with non-Hodgkin lymphoma (NHL) treated with PT. Eleven patients with NHL were treated with PT from January 2008 to January 2014 on an institutional review board-approved outcomes tracking protocol, and included patients with indolent orbital lymphoma (n = 4), primary mediastinal B-cell lymphoma (n = 3), plasmablastic lymphoma (n = 2) and natural killer (NK) T-cell lymphoma (n = 2). The median follow-up was 38 months. The 2-year rate of local control was 91%, with one patient with NK T-cell lymphoma having recurrence in-field. Toxicities were limited to grade 2 at highest, during follow-up. PT is a feasible and effective treatment for NHL. Early outcomes are favorable. Longer follow-up and more patients are needed to confirm our findings.

The role of radiotherapy in Hodgkin's lymphoma: what has been achieved during the last 50 years?

Currently, Hodgkin's lymphoma (HL) has an excellent clinical outcome, with overall survival of approximately 90% in early stages of the disease. Based on young age of the majority of patients at the time of diagnosis and their long survival time, increased attention has been focused on long-term toxicity of therapy. While novel, directly targeting antitumor agents, with an excellent safety profile, have been developed for HL treatment, the role of radiotherapy is still debated. Radiotherapy may induce cardiovascular disease and impairment of thyroid or pulmonary function and, most importantly, may lead to development of secondary cancers. As a consequence, the current radiation therapy planning paradigm is mainly focused on a reduction of field size. As it was investigated in clinical trials regional therapy is as effective as extended field radiotherapy, but less toxic. Although chemotherapy is the mainstay of HL treatment, consolidative involved field radiation therapy is still considered to be the standard of care in both early and advanced stages. Recently, further field reduction has been investigated to further decrease the late radiation-induced toxicity. In this paper we describe the role and safety profile of radiotherapy in the past and present and hope for the novel techniques in the future.

Novel radiotherapy techniques for involved-field and involved-node treatment of mediastinal Hodgkin lymphoma: when should they be considered and which questions remain open?

PURPOSE

Hodgkin lymphoma (HL) is a highly curable disease. Reducing late complications and second malignancies has become increasingly important. Radiotherapy target paradigms are currently changing and radiotherapy techniques are evolving rapidly.

DESIGN

This overview reports to what extent target volume reduction in involved-node (IN) and advanced radiotherapy techniques, such as intensity-modulated radiotherapy (IMRT) and proton therapy-compared with involved-field (IF) and 3D radiotherapy (3D-RT)- can reduce high doses to organs at risk (OAR) and examines the issues that still remain open.

RESULTS

Although no comparison of all available techniques on identical patient datasets exists, clear patterns emerge. Advanced dose-calculation algorithms (e.g., convolution-superposition/Monte Carlo) should be used in mediastinal HL. INRT consistently reduces treated volumes when compared with IFRT with the exact amount depending on the INRT definition. The number of patients that might significantly benefit from highly conformal techniques such as IMRT over 3D-RT regarding high-dose exposure to organs at risk (OAR) is smaller with INRT. The impact of larger volumes treated with low doses in advanced techniques is unclear. The type of IMRT used (static/rotational) is of minor importance. All advanced photon techniques result in similar potential benefits and disadvantages, therefore only the degree-of-modulation should be chosen based on individual treatment goals. Treatment in deep inspiration breath hold is being evaluated. Protons theoretically provide both excellent high-dose conformality and reduced integral dose.

CONCLUSION

Further reduction of treated volumes most effectively reduces OAR dose, most likely without disadvantages if the excellent control rates achieved currently are maintained. For both IFRT and INRT, the benefits of advanced radiotherapy techniques depend on the individual patient/target geometry. Their use should therefore be decided case by case with comparative treatment planning.

New strategies in radiation therapy: exploiting the full potential of protons

Protons provide significant dosimetric advantages compared with photons because of their unique depth-dose distribution characteristics. However, they are more sensitive to the effects of intra- and intertreatment fraction anatomic variations and uncertainties in treatment setup. Furthermore, in the current practice of proton therapy, the biologic effectiveness of protons relative to photons is assumed to have a generic fixed value of 1.1. However, this is a simplification, and it is likely higher in different portions of the proton beam. Current clinical practice and trials have not fully exploited the unique physical and biologic properties of protons. Intensity-modulated proton therapy, with its ability to manipulate energies (in addition to intensities), provides an entirely new dimension, which, with ongoing research, has considerable potential to increase the therapeutic ratio.

Charged particle therapy--optimization, challenges and future directions

The use of charged particle therapy to control tumours non-invasively offers advantages over conventional radiotherapy. Protons and heavy ions deposit energy far more selectively than X-rays, allowing a higher local control of the tumour, a lower probability of damage to healthy tissue, low risk of complications and the chance for a rapid recovery after therapy. Charged particles are also useful for treating tumours located in areas that surround tissues that are radiosensitive and in anatomical sites where surgical access is limited. Current trial outcomes indicate that accelerated ions can potentially replace surgery for radical cancer treatments, which might be beneficial as the success of surgical cancer treatments are largely dependent on the expertise and experience of the surgeon and the location of the tumour. However, to date, only a small number of controlled randomized clinical trials have made comparisons between particle therapy and X-rays. Therefore, although the potential advantages are clear and supported by data, the cost:benefit ratio remains controversial. Research in medical physics and radiobiology is focusing on reducing the costs and increasing the benefits of this treatment.

Hodgkin's lymphoma emerging radiation treatment techniques: trade-offs between late radio-induced toxicities and secondary malignant neoplasms

BACKGROUND

Purpose of this study is to explore the trade-offs between radio-induced toxicities and second malignant neoplasm (SMN) induction risk of different emerging radiotherapy techniques for Hodgkin's lymphoma (HL) through a comprehensive dosimetric analysis on a representative clinical model.

METHODS

Three different planning target volume (PTVi) scenarios of a female patient with supradiaphragmatic HL were used as models for the purpose of this study. Five treatment radiation techniques were simulated: an anterior-posterior parallel-opposed (AP-PA), a forward intensity modulated (FIMRT), an inverse intensity modulated (IMRT), a Tomotherapy (TOMO), a proton (PRO) technique. A radiation dose of 30 Gy or CGE was prescribed. Dose-volume histograms of PTVs and organs-at-risk (OARs) were calculated and related to available dose-volume constraints. SMN risk for breasts, thyroid, and lungs was estimated through the Organ Equivalent Dose model considering cell repopulation and inhomogeneous organ doses.

RESULTS

With similar level of PTVi coverage, IMRT, TOMO and PRO plans generally reduced the OARs' dose and accordingly the related radio-induced toxicities. However, only TOMO and PRO plans were compliant with all constraints in all scenarios. For the IMRT and TOMO plans an increased risk of development of breast, and lung SMN compared with AP-PA and FIMRT techniques was estimated. Only PRO plans seemed to reduce the risk of predicted SMN compared with AP-PA technique.

CONCLUSIONS

Our model-based study supports the use of advanced RT techniques to successfully spare OARs and to reduce the risk of radio-induced toxicities in HL patients. However, the estimated increase of SMNs' risk inherent to TOMO and IMRT techniques should be carefully considered in the evaluation of a risk-adapted therapeutic strategy.

Proton Therapy: Ever Shifting Sands and the Opportunities and Obligations within

Proton therapy is associated with significant benefit in terms of normal tissue sparing and potential radiation dose escalation for many patients with malignant diseases. Due to recognition of these qualities, the availability of this technology is increasing rapidly, both through increased availability of large centers, and with the possibility of smaller, lower cost proton therapy centers. Such expansion is associated with increased opportunity to provide this beneficial technology to larger numbers of patients; however, the importance of careful treatment planning and delivery, deliberate patient selection, rigorous scientific investigation including comparison to other technologies when possible, and mindfulness of ethical issues and cost effectiveness must not be forgotten. The obligation to move forward responsibly rests on the shoulders of radiation oncologists around the world. In this article, we discuss current use of proton therapy worldwide, as well as many of the factors that must be taken into account during rapid expansion of this exciting technology.