Effect of Deep Inspiration Breath Hold on Normal Tissue Sparing With Intensity Modulated Radiation Therapy Versus Proton Therapy for Mediastinal Lymphoma

A review of the clinical introduction of 4D particle therapy research concepts

Background and purpose

Many 4D particle therapy research concepts have been recently translated into clinics, however, remaining substantial differences depend on the indication and institute-related aspects. This work aims to summarise current state-of-the-art 4D particle therapy technology and outline a roadmap for future research and developments.

Material and methods

This review focused on the clinical implementation of 4D approaches for imaging, treatment planning, delivery and evaluation based on the 2021 and 2022 4D Treatment Workshops for Particle Therapy as well as a review of the most recent surveys, guidelines and scientific papers dedicated to this topic.

Results

Available technological capabilities for motion surveillance and compensation determined the course of each 4D particle treatment. 4D motion management, delivery techniques and strategies including imaging were diverse and depended on many factors. These included aspects of motion amplitude, tumour location, as well as accelerator technology driving the necessity of centre-specific dosimetric validation. Novel methodologies for X-ray based image processing and MRI for real-time tumour tracking and motion management were shown to have a large potential for online and offline adaptation schemes compensating for potential anatomical changes over the treatment course. The latest research developments were dominated by particle imaging, artificial intelligence methods and FLASH adding another level of complexity but also opportunities in the context of 4D treatments.

Conclusion

This review showed that the rapid technological advances in radiation oncology together with the available intrafractional motion management and adaptive strategies paved the way towards clinical implementation.

Radiotherapy for mediastinal lymphoma in breath hold using surface monitoring and nasal high flow oxygen: Clinical experiences and breath hold stability

PURPOSE

In this study we describe the clinical introduction and evaluation of radiotherapy in mediastinal lymphoma in breath hold using surface monitoring combined with nasal high flow therapy (NHFT) to prolong breath hold duration.

MATERIALS AND METHODS

11 Patients with mediastinal lymphoma were evaluated. 6 Patients received NHFT, 5 patients were treated in breath hold without NHFT. Breath hold stability as measured by a surface scanning system was evaluated, as well as internal movement based on cone beam computed tomography (CBCT) before and after treatment. Based on internal movement, margins were determined. In a parallel planning study we compared free breathing plans with breath hold plans using the determined margins.

RESULTS

Average inter breath hold stability was 0.6 mm for NHFT treatments, and 0.5 mm for non-NHFT treatments (p > 0.1). Intra breath hold stability was 0.8 vs. 0.6 mm (p > 0.1) on average. Using NHFT, average breath hold duration increased from 34 s to 60 s (p < 0.01). Residual CTV motion derived from CBCTs before and after each fraction was 2.0 mm for NHFT vs 2.2 mm for non-NHFT (p > 0.1). Combined with inter-fraction motion, a uniform mediastinal margin of 5 mm appears to be sufficient. In breath hold, mean lung dose is reduced by 2.6 Gy (p < 0.001), while mean heart dose is reduced by 2.0 Gy (p < 0.001).

CONCLUSION

Treatment of mediastinal lymphoma in breath hold is feasible and safe. The addition of NHFT approximately increases breath hold durations with a factor two while stability is maintained. By reducing breathing motion, margins can be decreased to 5 mm. A considerable dose reduction in heart, lungs, esophagus, and breasts can be achieved with this method.

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.

Deep inspiration breath-hold for mediastinal lymphoma patients: Evaluation of a 5-year service

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There is little published data on the use of DIBH and Butterfly volumetric arc therapy for the treatment of mediastinal lymphoma.

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Experience of a 5 year service was analysed looking into immobilisaiton, IGRT, patient compliance, and completion of the patient pathway without interruption.

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It is noted that a successful service has been implemented with minimal disruption to the patient pathway and optimal treatment delivered.

Deep inspiration breath-hold (DIBH) is an advanced radiotherapy technique that has been shown to have dosimetric benefits in the treatment of patients with mediastinal lymphoma. Whilst there is much published data on the use of DIBH in breast radiotherapy, reports on the use of the technique in mediastinal lymphoma patients remain limited. As the first NHS centre in the UK to implement DIBH in this pt group, we have evaluated our experience and success in using this technique over a 5 year period.

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.

Dosimetry, Efficacy, Safety, and Cost-Effectiveness of Proton Therapy for Non-Small Cell Lung Cancer

Non-small cell lung cancer (NSCLC) is the most common malignancy which requires radiotherapy (RT) as an important part of its multimodality treatment. With the advent of the novel irradiation technique, the clinical outcome of NSCLC patients who receive RT has been dramatically improved. The emergence of proton therapy, which allows for a sharper dose of build-up and drop-off compared to photon therapy, has potentially improved clinical outcomes of NSCLC. Dosimetry studies have indicated that proton therapy can significantly reduce the doses for normal organs, especially the lung, heart, and esophagus while maintaining similar robust target volume coverage in both early and advanced NSCLC compared with photon therapy. However, to date, most studies have been single-arm and concluded no significant changes in the efficacy for early-stage NSCLC by proton therapy over stereotactic body radiation therapy (SBRT). The results of proton therapy for advanced NSCLC in these studies were promising, with improved clinical outcomes and reduced toxicities compared with historical photon therapy data. However, these studies were also mainly single-arm and lacked a direct comparison between the two therapies. Currently, there is much emerging evidence focusing on dosimetry, efficacy, safety, and cost-effectiveness of proton therapy for NSCLC that has been published, however, a comprehensive review comparing these therapies is, to date, lacking. Thus, this review focuses on these aspects of proton therapy for NSCLC.

A Planning Comparison of IMRT vs. Pencil Beam Scanning for Deep Inspiration Breath Hold Lung Cancers

Deep inspiration breath hold (DIBH) has dosimetric advantages for lung cancer patients treated with external beam therapy, but is difficult for many patients to perform. Proton therapy permits sparing of the downstream organs at risk (OAR). We compared conventionally fractionated proton (p) and photon(x) plans on both free breathing (FB) and DIBH planning CTs to determine the effect of DIBH with proton therapy. We evaluated 24 plans from 6 lung cancer patients treated with photon DIBH on a prospective protocol. All patients were re-planned using pencil beam scanning (PBS) proton therapy. New plans were generated for FB datasets with both modalities. All plans were renormalized to 60 Gy. We evaluated dosimetric parameters for heart, lung and esophagus. We also compared FB_p to DIBH_x parameters to quantify how FB_p plans compare to DIBH_x plans. Significant differences were found for lung metrics V20 and mean lung dose between FB and DIBH plans regardless of treatment modality. Furthermore, lung metrics for FB_p were comparable or superior to DIBH_x, suggesting that FB protons may be a viable alternative for those patients that cannot perform DIBH with IMRT. The heart dose metrics were significantly different for the 5 out of 6 patients where the PTV overlapped the heart as DIBH moved heart out of the high dose volume. Heart dose metrics were further reduced by proton therapy. DIBH offers similar relative advantages for lung sparing for PBS as it does for IMRT but the magnitude of the DIBH related gains in OAR sparing were smaller for PBS than IMRT. FB_p plans offer similar or better lung and heart sparing compared to DIBH_x plans. For IMRT patients who have difficulty performing DIBH, FB protons may offer an alternative.

Harnessing benefit of highly conformal RT techniques for lymphoma patients

This status article describes current state-of-the-art radiotherapy for lymphomas and new emerging techniques. Current state-of-the-art radiotherapy is sophisticated, individualised, CT-based, intensity-modulated treatment, using PET/CT to define the target. The concept of involved site radiotherapy should be used, delineating the target using the exact same principles as for solid tumours. The optimal treatment delivery includes motion management and online treatment verification systems, which reduce intra- and interfractional anatomical variation. Emerging radiotherapy techniques in lymphomas include adaptive radiotherapy in MR- and CT-based treatment systems and proton therapy. The next generation linear accelerators have the capability to deliver adaptive treatment and allow relatively quick online adaptation to the daily variations of the anatomy. The computer systems use machine leaning to facilitate rapid automatic contouring of the target and organs-at-risk. Moreover, emerging MR-based planning and treatment facilities allow target definition directly from MR scans and allow intra-fractional tracking of structures recognisable on MR. Proton facilities are now being widely implemented. The benefits of proton therapy are due to the physical properties of protons, which in many cases allow sparing of normal tissue. The variety of techniques in modern radiotherapy means that the radiation oncologist must be able to choose the right technique for each patient. The choice is mainly based on experience and standard protocols, but new systems calculating risks for the patients with a specific treatment plan and also systems integrating clinical factors and risk factors into the planning process itself are emerging.

Development and Implementation of Proton Therapy for Hodgkin Lymphoma: Challenges and Perspectives

Simple Summary

Hodgkin lymphoma (HL) is a highly curable disease; proton therapy for mediastinal HL irradiation might theoretically reduce late toxicities compared with classical radiotherapy techniques. However, optimal patient selection for this technique is subject to debate. While implementation at a larger scale of proton therapy for HL may face organizational, political, and societal challenges, new highly effective systematic drugs are being widely evaluated for this disease.

Abstract

Consolidative radiation therapy for early-stage Hodgkin lymphoma (HL) improves progression-free survival. Unfortunately, first-generation techniques, relying on large irradiation fields, were associated with an increased risk of secondary cancers, and of cardiac and lung toxicity. Fortunately, the use of smaller target volumes combined with technological advances in treatment techniques currently allows efficient organs-at-risk sparing without altering tumoral control. Recently, proton therapy has been evaluated for mediastinal HL treatment due to its potential to significantly reduce the dose to organs-at-risk, such as cardiac substructures. This is expected to limit late radiation-induced toxicity and possibly, second-neoplasm risk, compared with last-generation intensity-modulated radiation therapy. However, the democratization of this new technique faces multiple issues. Determination of which patient may benefit the most from proton therapy is subject to intense debate. The development of new effective systemic chemotherapy and organizational, societal, and political considerations might represent impediments to the larger-scale implementation of HL proton therapy. Based on the current literature, this critical review aims to discuss current challenges and controversies that may impede the larger-scale implementation of mediastinal HL proton therapy.