Brilliant article! Must read! Luckily its open access.
Here’s the link: Mid-treatment adaptive planning during thoracic radiation using 68 Ventilation-Perfusion Positron emission tomography
Original PDF here
Notes:
“A number of advanced imaging modalities including positron emission tomography (PET), magnetic resonance imaging (MRI) and single photon emission computed tomography (SPECT) that have developed in the last decade are able to provide detailed information about the underlying geographical distribution of functional sub-units of lung.” (Bucknell et al., 2023, p. 2)
“he 68Ga-4D-V/Q PET/CT technique has been correlated with pulmonary function tests and has been used as the basis to validate other functional imaging techniques such as CT Ventilation” (Bucknell et al., 2023, p. 2)
“Dose-response relationships have been demonstrated in patients with baseline and post-treatment functional lung imaging.[2,6,8,20,21] For perfusion imaging, the slope of this curve has been shown to approximate 0.6–0.75 % per Gy” (Bucknell et al., 2023, p. 2)
“This phenomenon of treatmentrelated re-perfusion and re-ventilation does require careful assessment in patients being treated with functional lung adaptation. Treatment plans performed to preferentially reduce dose to functional lung may increase the dose to non-functional lung as it appears at baseline; if nonfunctional lung re-perfuses/ventilates during treatment, any gains in dose reduction to functional lung may be offset by the increased dose to re-perfused/ventilated lung.” (Bucknell et al., 2023, p. 2)
“All planning was performed on the average CT dataset of the 68Ga4D-V/Q PET/CT. Mid-treatment 68Ga-4D-V/Q PET/CT images were rigidly registered to the pre-treatment planning 68Ga-4D-V/Q PET/CT image in the region of the tumour.” (Bucknell et al., 2023, p. 2)
“If the GTV decreased in size, target volumes were not altered however if there were clear geographic shifts or progressive disease on the repeat planning scan the target volumes were adjusted to account for this. Functional lung volumes were delineated on the baseline and week 4 datasets as ‘highly perfused’ (HPLung) and ‘highly ventilated’ (HVLung), using a 70th centile threshold. These volumes were reviewed and adjusted by a nuclearmedicine physician using a semi-automated method” (Bucknell et al., 2023, p. 2)
“Functional dose volumetrics were assessed using the parameters of mean lung dose (MLD), functional MLD (fMLD) and both the anatomical lung volume receiving 5, 20 Gy (V5, V20) and the functional lung volume receiving 5, 20 Gy (fV5, fV20). Plan quality was assessed for consistency with respect to conformity indices, and doses to critical structures.” (Bucknell et al., 2023, p. 2)
(Bucknell et al., 2023, p. 2)
(Bucknell et al., 2023, p. 3)
“Two patients were noted to have an increase in lung volume that was attributed due to a difference in the breathing pattern at the time of the 4D PET/CT. In both patients, the entire lung volume was different between the two-time points. This was most pronounced around the liver.” (Bucknell et al., 2023, p. 3)
“Three patients were noted to have tumour response and therefore re-perfusion these patients had an increase in their perfused volumes. These patients were not excluded. Excluding the three outliers, a decrease in the size of this HPLung volume at 4 weeks was noted of 135 ± 393 cc.” (Bucknell et al., 2023, p. 3)
“The HVLung volume increased by on average 112 ± 590 cc [±SD, range 1424 cc to 950 cc]. The HVLung volumed increased in 13/25 patients.” (Bucknell et al., 2023, p. 3)
“With the outliers excluded, the HVLung increased by on average 251 ± 479 cc. The increase in functional volume for the majority of patients was due to treatment response resulting in a decrease in tumour-related airway obstruction.” (Bucknell et al., 2023, p. 3)
(Bucknell et al., 2023, p. 3)
(Bucknell et al., 2023, p. 4)
“A subgroup analysis was performed to attempt to identify which patients derive most benefit from functional adaptive planning. This analysis involved repeating the analysis with the exclusion of patients with earlier stage disease. Six patients had stage III disease and five had oligometastic (stage IV) disease but with high thoracic disease burden (total n = 11). A majority of these patients benefitted from functional lung sparing with results shown in Fig. 4. Some patients benefited from plans optimised to HPLung only others to HVLung only and a majority achieved gains from both.” (Bucknell et al., 2023, p. 4)
“Perfusion changes following radiation are attributed to changes including endothelial proliferation, microvascular changes and fibrosis which typically occur months following radiation. [29] The aetiology of the acute reduction in pulmonary perfusion is therefore unclear and deserves further evaluation. For select patients where tumour is causing vascular compression and airway obstruction both ventilation and perfusion improve.” (Bucknell et al., 2023, p. 5)
“extensive disease may derive more benefit from a mid-treatment replanning approach. Conversely those with small tumours or no gross tumour (such as patients receiving adjuvant radiation therapy) appeared to derive less benefit from adaptive replanning.” (Bucknell et al., 2023, p. 5)
“A major limitation of this work is that there is no established clinical benefit of adapting radiation therapy plans to avoid functional lung. Current trials underway use a single baseline time point to perform functional avoidance. To our knowledge this study is the first of its kind to consider adapting at a mid-treatment time point. Another limitation of functional lung avoidance is differences in definitions of functional lung volumes.” (Bucknell et al., 2023, p. 5)
“n this paper we used our previously published method to define functional lung, In addition to this there are no known dose constraints for functional lung volumes.[26] Most current work aims to achieve dose as low as reasonably achievable.” (Bucknell et al., 2023, p. 5)
“This work demonstrates the geographic distribution of lung function is dynamic over the course of radiation treatment. Some patients experience large changes in the geographic distribution of lung function due to re-perfusion and re-ventilation” (Bucknell et al., 2023, p. 5)
“Patients with larger volume tumour and higher nodal burden appeared to derive most dosimetric benefit from our functional avoidance technique” (Bucknell et al., 2023, p. 5)
“Selection of patients with more advanced disease has two major benefits a) these patients have a higher risk of radiationpneumonitis due to higherlung doses and use of systemic therapies and b) this group has been observed to derive more benefit from FLA planning.” (Bucknell et al., 2023, p. 6)
RadOncNotes 