Case study with dosimetric analysis: Total body irradiation to a patient with a left ventricular assist device.

Key Clinical Message: A patient presented with cardiogenic shock, requiring the implantation of a left ventricular assist device (LVAD), and acute myeloblastic leukemia. This necessitated total body irradiation (TBI) while balancing dose reduction to the LVAD components to avoid potential radiation damage. Here we outline our treatment approach and dose estimates to the LVAD. Abstract: This case report discusses the delivery of TBI to a patient with an LVAD. This treatment required radiation-dose determinations and consequential reductions for the heart, LVAD, and an external controller connected to the LVAD. The patient was treated using a traditional 16MV anterior posterior (AP)/posterior anterior (PA) technique at a source-to-surface-distance of 515 cm for 400 cGy in two fractions. A 3 cm thick Cerrobend block was placed on the beam spoiler to reduce dose to the heart and LVAD to 150 cGy. The external controller was placed in a 1 cm thick acrylic box to reduce neutron dose and positioned as far from the treatment fields as achievable. In vivo measurements were made using optically stimulated luminescence dosimeters (OSLDs) placed inside the box at distances of 2 cm, 8.5 cm, and 14 cm from the field edge, and on the patient along the central axis and centered behind the LVAD block. Further ion chamber measurements were made using a solid water phantom to more accurately estimate the dose delivered to the LVAD. Neutron dose measurements were also conducted. The total estimated dose to the controller ranged from 135.3 cGy to 91.5 cGy. The LVAD block reduced the surface dose to the patient to 271.6 cGy (68.1%). The block transmission factors of the 3 cm Cerrobend block measured in the phantom were 45% at 1 cm depth and decreased asymptotically to around 30% at 3 cm depth. Applying these transmission factors to the in vivo measurements yielded a dose of 120 cGy to the implanted device. The neutron dose the LVAD region is estimated around 0.46 cGy. Physical limitations of the controller made it impossible to completely avoid dose. Shielding is recommended. The block had limited dose reduction to the surface, due to secondary particles, but appropriately reduced the dose at 3 cm and beyond. More research on LVADs dose limits would be beneficial.

Oligoprogression in non-small cell lung cancer: a narrative review.

Background and Objective: Non-small cell lung cancer (NSCLC) accounts for 80% of lung cancers and is the most common non-cutaneous cancer world-wide. In NSCLC, oligometastatic and oligoprogressive disease (OPD) have been recognized as separate entities within the realm of metastatic disease and are emerging concepts in the context of targeted systemic therapies. Our objectives are to discuss the current literature regarding the evolving definitions of OPD in the context of oligometastatic disease (OMD) for NSCLC. Further, to discuss current and future clinical trials that have shaped our local approach with stereotactic body radiation therapy (SBRT)/stereotactic ablative radiotherapy (SABR). Methods: Literature on OPD in NSCLC and local ablative therapy (LAT) including SBRT/SABR and stereotactic radiosurgery (SRS) was reviewed. Key Content and Findings: Oligoprogression is defined as limited (usually 3-5) metastatic areas progressing while on/off systemic therapy in the background of oligometastatic or polymetastatic disease. Prognosis in OPD with treatment (such as LAT and systemic therapy) may be more favorable. Outcomes for patients progressing on tyrosine kinase inhibitors (TKIs) with molecular mutations [such as epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK)] who receive LAT are promising. Conclusions: Patients presenting with NSCLC metastasis with progression at a limited number of sites on/off a given line of systemic therapy may have favorable outcomes with aggressive LAT, which includes SBRT/SABR/SRS. Further studies need to be completed to further optimize treatment recommendations.

Pulmonary blood mass dynamics on 4DCT during tidal breathing.

We previously reported that apparent lung mass varies across the phases of 4D computed tomography (4DCT) images. We hypothesize that these variations correspond to the physiologic changes in pulmonary perfusion induced during normal tidal breathing, and should therefore be present in every breathing patient. In this study, we characterize and quantify the respiratory induced variation in pulmonary blood mass (▵PBM) on 89 patients treated with stereotactic body radiotherapy. ▵PBM was computed from the treatment planning helical 4DCT images of each patient. Conversion from Hounsfield Units (HU) to density and mass per voxel was made using the density calibration curve, applied to the lung parenchyma volume within each phase. A difference in the lung mass with breathing was found for all cases, as was a substantial individual variation in lung volume. We found that the ▵PBM increased during inhalation, and decreased during exhalation. A significant correlation between the individual ▵PBM and tidal volume was observed; ▵PBM increased with tidal volume. We further evaluated the anatomic distribution of ▵PBM variation comparing the central versus peripheral lung, cranial versus caudal, dependent versus non-dependent lung. Our observations regarding spatial distribution of the ▵PBM agree with previously reported differences among similar regions for the supine patient. These results show that a variation in pulmonary mass during respiration is apparent on 4DCT and suggest that these variations reflect respiratory induced changes in the pulmonary perfusion. Therefore, the 4DCT derived respiratory induced ▵PBM signal can provide further insight into the pulmonary circulation and advance the overall understanding and diagnosis of human health and disease.