Daily computed tomography image guidance: Dosimetric advantages outweigh low-dose radiation exposure for treatment of mediastinal lymphoma

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.

The role of motion management and position verification in lymphoma radiotherapy

In the last decades, the substantial technical progress in radiation oncology offered the opportunity for more accurate planning and delivery of treatment. At the same time, the evolution of systemic treatment and the advent of modern diagnostic tools allowed for more accurate staging and consequently a safe reduction of radiotherapy (RT) target volumes and RT doses in the treatment of lymphomas. As a result, incidental irradiation of organs at risk was reduced, with a consequent reduction of severe late toxicity in long-term lymphoma survivors. Nevertheless, these innovations warrant that professionals pay attention to concurrently ensure precise planning and dose delivery to the target volume and safe sparing of the organs at risk. In particular, target and organ motion should be carefully managed in order to prevent any compromise of treatment efficacy. Several aspects should be taken into account during the treatment pathway to minimise uncertainties and to apply a valuable motion management strategy, when needed. These include: reliable image registration between diagnostic and planning radiologic exams to facilitate the contouring process, image guidance to limit positioning uncertainties and to ensure the accuracy of dose delivery and management of lung motion through procedures of respiratory gating and breath control. In this review, we will cover the current clinical approaches to minimise these uncertainties in patients treated with modern RT techniques, with a particular focus on mediastinal lymphoma. In addition, since uncertainties have a different impact on the dose deposition of protons compared to conventional x-rays, the role of motion management and position verification in proton beam therapy (PBT) will be discussed in a separate section.

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.