Air variability in maxillary sinus during radiotherapy for sinonasal carcinoma

Abstract

Introduction: The aim was to characterise patterns and predictability of aeration changes in the ipsilateral maxillary sinus during intensity-modulated radiotherapy (IMRT) for sinonasal cancer (SNC), and in a sample evaluate the dosimetric effects of aeration changes for both photon and proton therapy. Materials and methods: The study included patients treated with IMRT for SNC in a single institution in 2009-2017. The volume of air in the ipsilateral maxillary sinus was recorded in 1578 daily cone beam computer tomography (CBCT) from 53 patients. Patterns of changing air volumes were categorised as 'stable', increasing', 'decreasing', or 'erratic'. For the prediction analysis, categorisation was performed based both on the entire treatment course and the first five fractions (F1-5). Photon and proton therapy plans were generated for four patients, the one from each category with the largest aeration variation. Synthetic CT images were generated for each CBCT and all plans were recalculated on the daily synthetic CTs. Results: The absolute volume of air varied considerably during the treatment course, ranging from 0 to 25.9 cm 3 . Changes within a single participant varied in the range of 0-18.7 cm 3 . In the categorisation of patterns, most patients had increasing aeration of the sinus. Generally, patterns of aeration could not be predicted from F1-5. Patients categorised as increasing in F1-5 had the best prediction, with 78% predicted correctly as increasing for the entire treatment course. The numeric correlation coefficients for target coverage and air volume were low for 3/4 scenarios (photons 0.03-0.23, protons 0.26-0.48). No straightforward correlation between the dosimetric effect and the volume changes could be detected in the sample test of four patients for neither photon nor proton therapy. Conclusion: The variation of aeration was large and unpredictable. No clear dosimetric consequences of the aeration variation were evident for neither IMRT nor proton therapy for the patients investigated.

Evaluation of robustly optimised intensity modulated proton therapy for nasopharyngeal carcinoma

“…Efforts were also made to reduce the sensitivity of the dose distribution to uncertainties not (fully) addressed by robust optimisation, such as the variable filling of the sinuses, the reproducibility of the shoulder position, mobile soft tissues or skin folds in the neck and metallic implants or dental fillings. For example, using the 6-beam arrangement the anterior oblique beams were often prevented from shooting through the maxillary sinus, a source of potential variation [18,30], while maintaining dose contributions from the remaining 4 beams. A 4-cm water-equivalent thickness range shifter was used for beams treating shallow targets and with a minimum air gap of 5 cm.…”

Robust Angle Selection in Particle Therapy

“…Regarding the tumors located in the nasopharynx, and sinonasal region, the robustness of dose distribution should consider not only tumor shrinkage but also aeration changes. Some studies ( 60 – 62 ) have found that the high irradiation area shifts forward or backward in the direction of the beam as the aeration within the irradiated cavity increases or decreases. Shusharina et al.…”

“…Regarding the tumors located in the nasopharynx, and sinonasal region, the robustness of dose distribution should consider not only tumor shrinkage but also aeration changes. Some studies (60)(61)(62) have found that the high irradiation area shifts forward or backward in the direction of the beam as the aeration within the irradiated cavity increases or decreases. Shusharina et al (61) revealed that the non-involving beams crossing the sinus cavities were the most robust to change in aeration and that with posterior beam directions, aeration changes affect only the exit dose; therefore, the dose distribution was not substantially compromised.…”

Dose and robustness comparison of nominal, daily and accumulated doses for photon and proton treatment of sinonasal cancer

“…An important consid-eration for proton therapy is robustness of the treatment, particularly towards anatomical variations over the treatment course since these cannot easily be taken into account in the planning phase. SNC patients may experience anatomical changes, such as emptying or filling of nasal cavities and tumor shrinkage [13,14]. While photon plans are generally considered very robust towards such changes, the variations have been suggested to cause considerable problems for proton treatments [15,16].…”

“…While photon plans are generally considered very robust towards such changes, the variations have been suggested to cause considerable problems for proton treatments [15,16]. The anatomical variations during a treatment course are unpredictable [13], and their impact is not fully investigated for either photon or proton therapy.…”