A methodology for selecting the beam arrangement to reduce the intensity-modulated radiation therapy (IMRT) dose to the SPECT-defined functioning lung

Automatic planning for functional lung avoidance radiotherapy based on function-guided beam angle selection and plan optimization

Objective.This study aims to develop a fully automatic planning framework for functional lung avoidance radiotherapy (AP-FLART).Approach.The AP-FLART integrates a dosimetric score-based beam angle selection method and a meta-optimization-based plan optimization method, both of which incorporate lung function information to guide dose redirection from high functional lung (HFL) to low functional lung (LFL). It is applicable to both contour-based FLART (cFLART) and voxel-based FLART (vFLART) optimization options. A cohort of 18 lung cancer patient cases underwent planning-CT and SPECT perfusion scans were collected. AP-FLART was applied to generate conventional RT (ConvRT), cFLART, and vFLART plans for all cases. We compared automatic against manual ConvRT plans as well as automatic ConvRT against FLART plans, to evaluate the effectiveness of AP-FLART. Ablation studies were performed to evaluate the contribution of function-guided beam angle selection and plan optimization to dose redirection.Main results.Automatic ConvRT plans generated by AP-FLART exhibited similar quality compared to manual counterparts. Furthermore, compared to automatic ConvRT plans, HFL mean dose,V20, andV5were significantly reduced by 1.13 Gy (p< .001), 2.01% (p< .001), and 6.66% (p< .001) respectively for cFLART plans. Besides, vFLART plans showed a decrease in lung functionally weighted mean dose by 0.64 Gy (p< .01),fV20by 0.90% (p= 0.099), andfV5by 5.07% (p< .01) respectively. Though inferior conformity was observed, all dose constraints were well satisfied. The ablation study results indicated that both function-guided beam angle selection and plan optimization significantly contributed to dose redirection.Significance.AP-FLART can effectively redirect doses from HFL to LFL without severely degrading conventional dose metrics, producing high-quality FLART plans. It has the potential to advance the research and clinical application of FLART by providing labor-free, consistent, and high-quality plans.

Incorporation of Functional Lung Imaging Into Radiation Therapy Planning in Patients With Lung Cancer: A Systematic Review and Meta-Analysis

Our purpose was to provide an understanding of current functional lung imaging (FLI) techniques and their potential to improve dosimetry and outcomes for patients with lung cancer receiving radiation therapy (RT). Excerpta Medica dataBASE (EMBASE), PubMed, and Cochrane Library were searched from 1990 until April 2023. Articles were included if they reported on FLI in one of: techniques, incorporation into RT planning for lung cancer, or quantification of RT-related outcomes for patients with lung cancer. Studies involving all RT modalities, including stereotactic body RT and particle therapy, were included. Meta-analyses were conducted to investigate differences in dose-function parameters between anatomic and functional RT planning techniques, as well as to investigate correlations of dose-function parameters with grade 2+ radiation pneumonitis (RP). One hundred seventy-eight studies were included in the narrative synthesis. We report on FLI modalities, dose-response quantification, functional lung (FL) definitions, FL avoidance techniques, and correlations between FL irradiation and toxicity. Meta-analysis results show that FL avoidance planning gives statistically significant absolute reductions of 3.22% to the fraction of well-ventilated lung receiving 20 Gy or more, 3.52% to the fraction of well-perfused lung receiving 20 Gy or more, 1.3 Gy to the mean dose to the well-ventilated lung, and 2.41 Gy to the mean dose to the well-perfused lung. Increases in the threshold value for defining FL are associated with decreases in functional parameters. For intensity modulated RT and volumetric modulated arc therapy, avoidance planning results in a 13% rate of grade 2+ RP, which is reduced compared with results from conventional planning cohorts. A trend of increased predictive ability for grade 2+ RP was seen in models using FL information but was not statistically significant. FLI shows promise as a method to spare FL during thoracic RT, but interventional trials related to FL avoidance planning are sparse. Such trials are critical to understanding the effect of FL avoidance planning on toxicity reduction and patient outcomes.

Personal innovative approach in radiation therapy of lung cancer- functional lung avoidance SPECT-guided (ASPECT) radiation therapy: a study protocol for phase II randomised double-blind clinical trial

BACKGROUND

Radiation therapy (RT) plays a key role in curative-intent treatment for locally advanced lung cancer. Radiation induced pulmonary toxicity can be significant for some patients and becomes a limiting factor for radiation dose, suitability for treatment, as well as post treatment quality of life and suitability for the newly introduced adjuvant immunotherapy. Modern RT techniques aim to minimise the radiation dose to the lungs, without accounting for regional distribution of lung function. Many lung cancer patients have significant regional differences in pulmonary function due to smoking and chronic lung co-morbidity. Even though reduction of dose to functional lung has shown to be feasible, the method of preferential functional lung avoidance has not been investigated in a randomised clinical trial.

METHODS

In this study, single photon emission computed tomography (SPECT/CT) imaging technique is used for functional lung definition, in conjunction with advanced radiation dose delivery method in randomised, double-blind trial. The study aims to assess the impact of functional lung avoidance technique on pulmonary toxicity and quality of life in patients receiving chemo-RT for lung cancer. Eligibility criteria are biopsy verified lung cancer, scheduled to receive (chemo)-RT with curative intent. Every patient will undergo a pre-treatment perfusion SPECT/CT to identify functional lung. At radiation dose planning, two plans will be produced for all patients on trial. Standard reference plan, without the use of SPECT imaging data, and functional avoidance plan, will be optimised to reduce the dose to functional lung within the predefined constraints. Both plans will be clinically approved. Patients will then be randomised in a 2:1 ratio to be treated according to either the functional avoidance or the standard plan. This study aims to accrue a total of 200 patients within 3 years. The primary endpoint is symptomatic radiation-induced lung toxicity, measured serially 1-12 months after RT. Secondary endpoints include: a quality of life and patient reported lung symptoms assessment, overall survival, progression-free survival, and loco-regional disease control.

DISCUSSION

ASPECT trial will investigate functional avoidance method of radiation delivery in clinical practice, and will establish toxicity outcomes for patients with lung cancer undergoing curative chemo-RT.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT04676828 . Registered 1 December 2020.

Functional lung volume mapping with perfusion Single-Photon Emission Computed Tomography scan for radiotherapy planning in patients with locally advanced nonsmall cell lung cancer

OBJECTIVES

Radical chemotherapy-radiotherapy represents the standard treatment for locally-advanced nonsmall cell lung cancer (NSCLC). Conventional radiotherapy achieves limited local tumor control, but dose escalation to the primary tumor is prevented by radiotherapy-induced toxicity. The aim of this study was to evaluate feasibility of tailored intensity-modulated radiotherapy (IMRT) planning based on lung single-photon emission computed tomography (SPECT) perfusion data and to compare functional and conventional dose-volume parameters.

METHODS

A total of 21 patients were prospectively enrolled. Patients underwent IMRT treatment with 2 Gy/fraction (median total dose of 60 Gy). Lung perfusion SPECT images were acquired before radiotherapy and 3 and 6 months after radiotherapy completion. SPECT and planning computed tomography images were co-registered using MIM-MAESTRO software with 3D-PET Edge algorithm. Lung volumes were defined anatomically as total lung and functionally as total not functional lung and total functional lung. Dose-volume histograms were calculated using QUANTEC constraints [mean lung dose (MLD)<20 Gy, V20<20%]. For each patient, conventional and functional radiotherapy plans were generated and compared.

RESULTS

A total of 19 of 21 patients with NSCLC were included (mean age 66 years, 11 stage IIIA, 8 stage IIIB), 12/19 patients completed the 6-months follow-up. A significant reduction of mean V20 was observed in functional radiotherapy planning compared to conventional plan (405.9 cc, P < 0.001). Mean MLD was also lower in the SPECT-based plans, but the difference was not statistically relevant (0.8 Gy, P = 0.299). G2 radiation pneumonitis was observed in two patients.

CONCLUSIONS

Functional radiotherapy planning allowed to decrease functional lung irradiation compared to conventional planning. The possibility to limit radiotherapy-induced toxicity could allow us to perform an effective dose-escalation to target volume.

Single photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging for radiotherapy planning in patients with lung cancer: a meta-analysis

Functional imaging modalities enable practitioners to identify functional lung regions. This analysis evaluated the feasibility of nuclear medicine imaging to avoid doses to the functional lung in radiotherapy (RT) planning for patients with lung cancer. This systematic review and meta-analysis was carried out according to PRISMA-P guidelines. A search of EMBASE and PubMed for studies published throughout the last 20 years was performed using the following search criteria: (a) ‘lung cancer’ or ‘lung malignancy’ and (b) ‘radiotherapy’ or ‘radiation therapy’ or ‘RT planning’ and (c) ‘SPECT’ or ‘single positron emission computed tomography’ or ‘functional image.’ The analyzed planning parameters were the volumes of the normal lung that have received ≥ 10 Gy and ≥ 20 Gy of radiation (V10 and V20, respectively) and the mean lung dose (MLD). We compared the planning parameters obtained from anatomical RT planning and functional RT planning using perfusion or ventilation imaging (‘V10, V20 or MLD’ in anatomical plan vs. ‘fV10, fV20 or fMLD’ in functional plan). A total of 309 patients with 344 RT plan sets from 15 publications (11 perfusion SPECT, 2 ventilation SPECT, and 1 SPECT and 1 PET with both perfusion and ventilation) were included in the meta-analysis. The standard mean differences in planning parameters in functional plans using nuclear imaging were significantly reduced compared to those of anatomical plans (P < 0.01 for all): − 0.42 (95% confidence interval (CI) − 0.78 to − 0.07) for ‘V10 vs. fV10′, − 0.41 (95% CI − 0.64 to − 0.17) for ‘V20 vs. fV20′, and − 0.24 (95% CI − 0.45 to − 0.03) for ‘MLD vs. fMLD’. In subgroup analysis, the functional plan using perfusion was significantly lower than the anatomical plan in all planning parameters, but there was no significant difference for ventilation. RT planning with nuclear functional lung imaging has potential to reduce radiation-induced lung injury. Perfusion imaging seems to be more promising than ventilation imaging for all planning parameters. There were not enough studies using ventilation imaging to determine what the effect is on the lung plan parameters.

Functional perfusion image guided radiation treatment planning for locally advanced lung cancer

Background and purpose

Functional avoidance radiation therapy (RT) aims at sparing functional lung regions. The purpose of this simulation study was to evaluate the feasibility of functional lung avoidance methodology in RT of lung cancer and to characterize the achievable dosimetry of single photon emission computed tomography (SPECT) guided treatment planning.

Materials and methods

Fifteen consecutive lung cancer patients were included and planned for definitive RT of 60–66 Gy in 2-Gy fractions. Two plans were optimized: a standard CT-plan, and functional SPECT-plan. The objective was to reduce dose to the highly functional lung subvolumes without compromising tumour coverage, and respecting dose to other organs at risk. For each patient a 3D-conformal, intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy plans were created for standard and functional avoidance. Standard versus functional dose-volume parameters for functional lung (FL) subvolumes, organs at risk and tumour coverage were compared.

Results

The largest dose reduction was achieved with IMRT plans. Functional plans resulted in dose reduction from 9.0 Gy to 6.7 Gy (mean reduction of 2.3 Gy or 26%) to the highest functional subvolume FL80% (95%CI 1.1; 3.5). Dose to FL40% was reduced from 13.3 Gy to 11.6 Gy with functional planning. Dose reduction to FL40% was 1.7 Gy (95%CI 0.9; 2.6). Functional volume of lung receiving over 20 Gy improved by 5% (standard 22%, functional 17%). Dose to organs at risk and tumour coverage were not significantly different between plans.

Conclusions

SPECT/CT-guided planning resulted in improved dose-volumetric outcomes for functional lung. This methodology may lead to potential reduction in radiation-induced lung toxicity.

Functional lung imaging in radiation therapy for lung cancer: A systematic review and meta-analysis

RATIONALE

Advanced imaging techniques allow functional information to be derived and integrated into treatment planning.

METHODS

A systematic review was conducted with the primary objective to evaluate the ability of functional lung imaging to predict risk of radiation pneumonitis. Secondary objectives were to evaluate dose-response relationships on post treatment functional imaging and assess the utility in including functional lung information into treatment planning. A structured search for publications was performed following PRISMA guidelines and registered on PROSPERO.

RESULTS

814 articles were screened against review criteria and 114 publications met criteria. Methods of identifying functional lung included using CT, MRI, SPECT and PET to image ventilation or perfusion. Six studies compared differences between functional and anatomical lung imaging at predicting radiation pneumonitis. These found higher predictive values using functional lung imaging. Twenty-one studies identified a dose-response relationship on post-treatment functional lung imaging. Nineteen planning studies demonstrated the ability of functional lung optimised planning techniques to spare regions of functional lung. Meta-analysis of these studies found that mean (95% CI) functional volume receiving 20 Gy was reduced by 4.2% [95% CI: 2.3: 6.0] and mean lung dose by 2.2 Gy [95% CI: 1.2: 3.3] when plans were optimised to spare functional lung. There was significant variation between publications in the definition of functional lung.

CONCLUSION

Functional lung imaging may have potential utility in radiation therapy planning and delivery, although significant heterogeneity was identified in approaches and reporting. Recommendations have been made based on the available evidence for future functional lung trials.

Functional lung avoidance and response-adaptive escalation (FLARE) RT: Multimodality plan dosimetry of a precision radiation oncology strategy

PURPOSE

Nonsmall cell lung cancer (NSCLC) patient radiation therapy (RT) is planned without consideration of spatial heterogeneity in lung function or tumor response. We assessed the dosimetric and clinical feasibility of functional lung avoidance and response-adaptive escalation (FLARE) RT to reduce dose to [^99m Tc]MAA-SPECT/CT perfused lung while redistributing an escalated boost dose within [¹⁸ F]FDG-PET/CT-defined biological target volumes (BTV).

METHODS

Eight stage IIB-IIIB NSCLC patients underwent FDG-PET/CT and MAA-SPECT/CT treatment planning scans. Perfused lung objectives were derived from scatter/collimator/attenuation-corrected MAA-SPECT uptake relative to ITV-subtracted lung to maintain < 20 Gy mean lung dose (MLD). Prescriptions included 60 Gy to the planning target volume (PTV) and concomitant boost of 74 Gy mean to biological target volumes (BTV = GTV + PET gradient segmentation) scaled to each BTV voxel by relative FDG-PET SUV. Dose-painting-by-numbers prescriptions were integrated into commercial treatment planning systems via uptake threshold discretization. Dose constraints for lung, heart, cord, and esophagus were defined. FLARE RT plans were optimized with volumetric modulated arc therapy (VMAT), proton pencil beam scanning (PBS) with 3%-3 mm robust optimization, and combination of PBS (avoidance) plus VMAT (escalation). The high boost dose region was evaluated within a standardized SUV_peak structure. FLARE RT plans were compared to reference VMAT plans. Linear regression between radiation dose to BTV and normalized FDG PET SUV at every voxel was conducted, from which Pearson linear correlation coefficients and regression slopes were extracted. Spearman rank correlation coefficients were estimated between radiation dose to lung and normalized SPECT uptake. Dosimetric differences between treatment modalities were evaluated by Friedman nonparametric paired test with multiple sampling correction.

RESULTS

No unacceptable violations of PTV and normal tissue objectives were observed in 24 FLARE RT plans. Compared to reference VMAT plans, FLARE VMAT plans achieved a higher mean dose to BTV (73.7 Gy 98195. 61.3 Gy), higher mean dose to SUV_peak (89.7 Gy vs. 60.8 Gy), and lower mean dose to highly perfused lung (7.3 Gy vs. 14.9 Gy). These dosimetric gains came at the expense of higher mean heart dose (9.4 Gy vs. 5.8 Gy) and higher maximum cord dose (50.1 Gy vs. 44.6 Gy) relative to the reference VMAT plans. Between FLARE plans, FLARE VMAT achieved higher dose to the SUV_peak ROI than FLARE PBS (89.7 Gy vs. 79.2 Gy, P = 0.01), while FLARE PBS delivered lower dose to lung than FLARE VMAT (11.9 Gy vs. 15.6 Gy, P < 0.001). Voxelwise linear dose redistribution slope between BTV dose and FDG PET uptake was higher in magnitude for FLARE PBS + VMAT (0.36 Gy per %SUV_max ) compared to FLARE VMAT (0.27 Gy per %SUV_max ) or FLARE PBS alone (0.17 Gy per %SUV_max ).

CONCLUSIONS

FLARE RT is clinically feasible with VMAT and PBS. A combination of PBS for functional lung avoidance and VMAT for FDG PET dose escalation balanced target and normal tissue objective tradeoffs. These results provide a technical platform for testing of FLARE RT safety and efficacy within a precision radiation oncology trial.

Framework for radiation pneumonitis risk stratification based on anatomic and perfused lung dosimetry

PURPOSE

To design and apply a framework for predicting symptomatic radiation pneumonitis in patients undergoing thoracic radiation, using both pretreatment anatomic and perfused lung dose-volume parameters.

MATERIALS AND METHODS

Radiation treatment planning CT scans were coregistered with pretreatment [99mTc]MAA perfusion SPECT/CT scans of 20 patients who underwent definitive thoracic radiation. Clinical radiation pneumonitis was defined as grade ≥ 2 (CTCAE v4 grading system). Anatomic lung dose-volume parameters were collected from the treatment planning scans. Perfusion dose-volume parameters were calculated from pretreatment SPECT/CT scans. Equivalent doses in 2 Gy per fraction were calculated in the lung to account for differences in treatment regimens and spatial variations in lung dose (EQD2lung).

RESULTS

Anatomic lung dosimetric parameters (MLD) and functional lung dosimetric parameters (pMLD70%) were identified as candidate predictors of grade ≥ 2 radiation pneumonitis (AUC > 0.93, p < 0.01). Pairing of an anatomic and functional dosimetric parameter (e. g., MLD and pMLD70%) may further improve prediction accuracy. Not all individuals with high anatomic lung dose (MLD > 13.6 GyEQD2lung, 19.3 Gy for patients receiving 60 Gy in 30 fractions) developed radiation pneumonitis, but all individuals who also had high mean dose to perfused lung (pMLD70% > 13.3 GyEQD2) developed radiation pneumonitis.

CONCLUSIONS

The preliminary application of this framework revealed differences between anatomic and perfused lung dosimetry in this limited patient cohort. The addition of perfused lung parameters may help risk stratify patients for radiation pneumonitis, especially in treatment plans with high anatomic mean lung dose. Further investigations are warranted.

Priority-driven plan optimization in locally advanced lung patients based on perfusion SPECT imaging

Purpose

Limits on mean lung dose (MLD) allow for individualization of radiation doses at safe levels for patients with lung tumors. However, MLD does not account for individual differences in the extent or spatial distribution of pulmonary dysfunction among patients, which leads to toxicity variability at the same MLD. We investigated dose rearrangement to minimize the radiation dose to the functional lung as assessed by perfusion single photon emission computed tomography (SPECT) and maximize the target coverage to maintain conventional normal tissue limits.

Methods and materials

Retrospective plans were optimized for 15 patients with locally advanced non-small cell lung cancer who were enrolled in a prospective imaging trial. A staged, priority-based optimization system was used. The baseline priorities were to meet physical MLD and other dose constraints for organs at risk, and to maximize the target generalized equivalent uniform dose (gEUD). To determine the benefit of dose rearrangement with perfusion SPECT, plans were reoptimized to minimize the generalized equivalent uniform functional dose (gEUfD) to the lung as the subsequent priority.

Results

When only physical MLD is minimized, lung gEUfD was 12.6 ± 4.9 Gy (6.3-21.7 Gy). When the dose is rearranged to minimize gEUfD directly in the optimization objective function, 10 of 15 cases showed a decrease in lung gEUfD of >20% (lung gEUfD mean 9.9 ± 4.3 Gy, range 2.1-16.2 Gy) while maintaining equivalent planning target volume coverage. Although all dose-limiting constraints remained unviolated, the dose rearrangement resulted in slight gEUD increases to the cord (5.4 ± 3.9 Gy), esophagus (3.0 ± 3.7 Gy), and heart (2.3 ± 2.6 Gy).

Conclusions

Priority-driven optimization in conjunction with perfusion SPECT permits image guided spatial dose redistribution within the lung and allows for a reduced dose to the functional lung without compromising target coverage or exceeding conventional limits for organs at risk.

Should we include SPECT lung perfusion in radiotherapy treatment plans of thoracic targets? Evidences from the literature

PURPOSE

To report the available data about the potential impact of integrating lung perfusion SPECT/CT in treatment plans optimization for the irradiation of thoracic targets.

MATERIALS AND METHODS

We searched in the PubMed and Scopus databases, English-written articles published from 2000 to June 2015 dealing with the integration of perfusion SPECT/CT in radiotherapy.

RESULTS

We found and analyzed 16 research articles (10 dosimetric, 6 clinical) for a total of 578 patients. Available data suggest dosimetric and clinical improvements when perfusion SPEC/CT is integrated in the radiotherapy treatment planing of selected patients with thoracic targets. In particular, patients presenting emphysema and/or large areas of deficit of perfusion show the most important improvements. Moreover, some studies show different risk of radiation pneumonitis (RP) depending on the localization of the tumor in the lungs: patients with low-located tumors, present an increased risk of RP, and functional data could be a benefit in treatment plan optimization. Unfortunately, none of the available studies finally reports any dosimetric constraint, which could be used in the clinical practice, even if most of them used the cut-off of the 30% of the maximal perfusion value to define the well-functioning lung.

CONCLUSIONS

Published data support the integration of lung perfusion scintigraphy in some selected categories of patients. Prospective studies should be designed to define the best candidates, and to assess the clinical advantage of this kind of optimization.

High-resolution pulmonary ventilation and perfusion PET/CT allows for functionally adapted intensity modulated radiotherapy in lung cancer

BACKGROUND AND PURPOSE

To assess the utility of functional lung avoidance using IMRT informed by four-dimensional (4D) ventilation/perfusion (V/Q) PET/CT.

MATERIALS AND METHODS

In a prospective clinical trial, patients with non-small cell lung cancer (NSCLC) underwent 4D-V/Q PET/CT scanning before 60Gy of definitive chemoradiation. Both "highly perfused" (HPLung) and "highly ventilated" (HVLung) lung volumes were delineated using a 70th centile SUV threshold, and a "ventilated lung volume" (VLung) was created using a 50th centile SUV threshold. For each patient four IMRT plans were created, optimised to the anatomical lung, HPLung, HVLung and VLung volumes, respectively. Improvements in functional dose volumetrics when optimising to functional volumes were assessed using mean lung dose (MLD), V5, V10, V20, V30, V40, V50 and V60 parameters.

RESULTS

The study cohort consisted of 20 patients with 80 IMRT plans. Plans optimised to HPLung resulted in a significant reduction of functional MLD by a mean of 13.0% (1.7Gy), p=0.02. Functional V5, V10 and V20 were improved by 13.2%, 7.3% and 3.8% respectively (p-values<0.04). There was no significant sparing of dose to functional lung when adapting to VLung or HVLung. Plan quality was highly consistent with a mean PTV D95 and D5 ranging from 60.8Gy to 61.0Gy and 63.4Gy to 64.5Gy, respectively, and mean conformity and heterogeneity index ranging from 1.11 to 1.17 and 0.94 to 0.95, respectively.

CONCLUSION

IMRT plans adapted to perfused but not ventilated lung on 4D-V/Q PET/CT allowed for reduced dose to functional lung whilst maintaining consistent plan quality.

Differential hepatic avoidance radiation therapy: Proof of concept in hepatocellular carcinoma patients

PURPOSE

To evaluate the feasibility of a novel planning concept that differentially redistributes RT dose away from functional liver regions as defined by (99m)Tc-sulphur colloid (SC) uptake on patient SPECT/CT images.

MATERIALS AND METHODS

Ten HCC patients with different Child-Turcotte-Pugh scores (A5-B9) underwent SC SPECT/CT scans in treatment position prior to RT that were registered to planning CT scans. Proton pencil beam scanning (PBS) therapy plans were optimized to deliver 37.5-60.0Gy (RBE) over 5-15 fractions using single field uniform dose technique robust to range and setup uncertainty. Photon volumetrically modulated arc therapy (VMAT) plans were optimized to the same prescribed dose and minimum target coverage. For both treatment modalities, differential hepatic avoidance RT (DHART) plans were generated to decrease dose to functional liver volumes (FLV) defined by a range of thresholds relative to maximum SC uptake (43-90%) in the tumor-subtracted liver. Radiation dose was redistributed away from regions of increased SC uptake in each FLV by linearly scaling mean dose objectives during PBS or VMAT optimization. DHART planning feasibility was assessed by a significantly negative Spearman's rank correlation (RS) between dose difference and SC uptake. Patient, tumor, and treatment planning characteristics were tested for association to DHART planning feasibility using non-parametric Kruskal-Wallis ANOVA.

RESULTS

Compared to conventional plans, DHART plans achieved a 3% FLV dose reduction for every 10% SC uptake increase. DHART planning was feasible in the majority of patients with 60% of patients having RS<-0.5 (p<0.01, range -1.0 to 0.2) and was particularly effective in 30% of patients (RS<-0.9). Mean dose to FLV was reduced by up to 20% in these patients. Only fractionation regimen was associated with DHART planning feasibility: 15 fraction courses were more feasible than 5-6 fraction courses (RS<-0.93 vs. RS>-0.60, p<0.02).

CONCLUSION

Differential avoidance of functional liver regions defined on sulphur colloid SPECT/CT is achievable with either photon VMAT or proton PBS therapy. Further investigation with phantom studies and in a larger cohort of patients may validate the utility of DHART planning for HCC radiotherapy.

Ga-68 MAA Perfusion 4D-PET/CT Scanning Allows for Functional Lung Avoidance Using Conformal Radiation Therapy Planning

BACKGROUND

Ga-68-macroaggregated albumin ((68)Ga-perfusion) positron emission tomography/computed tomography (PET/CT) is a novel imaging technique for the assessment of functional lung volumes. The purpose of this study was to use this imaging technique for functional adaptation of definitive radiotherapy plans in patients with non-small cell lung cancer (NSCLC).

METHODS

This was a prospective clinical trial of patients with NSCLC who received definitive 3-dimensional (3D) conformal radiotherapy to 60 Gy in 30 fx and underwent pretreatment respiratory-gated (4-dimensional [4D]) perfusion PET/CT. The "perfused" lung volume was defined as all lung parenchyma taking up radiotracer, and the "well-perfused" lung volume was contoured using a visually adapted threshold of 30% maximum standardized uptake value (SUV max). Alternate 3D conformal plans were subsequently created and optimized to avoid perfused and well-perfused lung volumes. Functional dose volumetrics were compared using mean lung dose (MLD), V5 (volume receiving 5 Gy or more), V10, V20, V30, V40, V50, and V60 parameters.

RESULTS

Fourteen consecutive patients had alternate radiotherapy plans created based on functional lung volumes. When considering the original treatment plan, the dose to perfused and well-perfused functional lung volumes was similar to that of the conventional anatomical lung volumes with an average MLD of 12.15, 12.67, and 12.11 Gy, respectively. Plans optimized for well-perfused lung improved functional V30, V40, V50, and V60 metrics (all P values <.05). The functional MLD of well-perfused lung was improved by a median of 0.86 Gy, P < .01. However, plans optimized for perfused lung only showed significant improvement in the functional V60 dose parameter (median 1.00%, P = .04) but at a detriment of a worse functional V5 (median 3.33%, P = .05).

CONCLUSIONS

This study demonstrates proof of principle that 4D-perfusion PET/CT may enable functional lung avoidance during treatment planning of patients with NSCLC. Radiotherapy plans adapted to well-perfused but not perfused functional lung volumes allow for reduction in dose to functional lung using 3D conformal radiotherapy.

Imaging techniques for tumour delineation and heterogeneity quantification of lung cancer: overview of current possibilities

Imaging techniques for the characterization and delineation of primary lung tumours and lymph nodes are a prerequisite for adequate radiotherapy. Numerous imaging modalities have been proposed for this purpose, but only computed tomography (CT) and FDG-PET have been implemented in clinical routine. Hypoxia PET, dynamic contrast-enhanced CT (DCE-CT), dual energy CT (DECT) and (functional) magnetic resonance imaging (MRI) hold promise for the future. Besides information on the primary tumour, these techniques can be used for quantification of tissue heterogeneity and response. In the future, treatment strategies may be designed which are based on imaging techniques to optimize individual treatment.

Impact of different beam directions on intensity-modulated radiation therapy dose delivered to functioning lung tissue identified using single-photon emission computed tomography

Aim of the study

To use different beam arrangements and numbers to plan intensity-modulated radiation therapy (IMRT) and investigate their effects on low and high radiation doses delivered to the functional lung, in order to reduce radiation-induced lung damage.

Material and methods

Ten patients with stage I–III non-small cell lung carcinoma (NSCLC) underwent IMRT. Beam arrangements were selected on the basis of orientation and dose-volume histograms to create SPECT-guided IMRT plans that spared the functional lung and maintained target coverage. Four different plans, including CT-7, SPECT-7, SPECT-4, SPECT-5 with different beam arrangements, were used. The differences of conformity index (CI), heterogeneity index (HI) between the plans were analyzed, by using a paired t-test.

Results

The seven-beam SPECT (SPECT-7) plan reduced the volume of the functional lung irradiated with at least 20 Gy (FV20) and 30 Gy (FV30) by 26.02% ±15.45% and 14.41% ±16.66%, respectively, as compared to the seven-beam computed tomography (CT-7) plan. The CI significantly differed between the SPECT-7 and SPECT-4 plans and between the SPECT-5 and SPECT-4 plans, but not between the SPECT-5 and SPECT-7 plans. The CIs in the SPECT-5 and SPECT-7 plans were better than that in the SPECT-4 plan. The heterogeneity index significantly differed among the three SPECT plans and was best in the SPECT-7 plan.

Conclusions

The incorporation of SPECT images into IMRT planning for NSCLC greatly affected beam angles and number of beams. Fewer beams and modified beam angles achieved similar or better IMRT quality. The low-dose volumes were lower in SPECT-4.

Functional and molecular image guidance in radiotherapy treatment planning optimization

Functional and molecular imaging techniques are increasingly being developed and used to quantitatively map the spatial distribution of parameters, such as metabolism, proliferation, hypoxia, perfusion, and ventilation, onto anatomically imaged normal organs and tumor. In radiotherapy optimization, these imaging modalities offer the promise of increased dose sparing to high-functioning subregions of normal organs or dose escalation to selected subregions of the tumor as well as the potential to adapt radiotherapy to functional changes that occur during the course of treatment. The practical use of functional/molecular imaging in radiotherapy optimization must take into cautious consideration several factors whose influences are still not clearly quantified or well understood including patient positioning differences between the planning computed tomography and functional/molecular imaging sessions, image reconstruction parameters and techniques, image registration, target/normal organ functional segmentation, the relationship governing the dose escalation/sparing warranted by the functional/molecular image intensity map, and radiotherapy-induced changes in the image intensity map over the course of treatment. The clinical benefit of functional/molecular image guidance in the form of improved local control or decreased normal organ toxicity has yet to be shown and awaits prospective clinical trials addressing this issue.

The ESTRO Breur Lecture 2009. From population to voxel-based radiotherapy: exploiting intra-tumour and intra-organ heterogeneity for advanced treatment of non-small cell lung cancer

Evidence is accumulating that radiotherapy of non-small cell lung cancer patients can be optimized by escalating the tumour dose until the normal tissue tolerances are met. To further improve the therapeutic ratio between tumour control probability and the risk of normal tissue complications, we firstly need to exploit inter patient variation. This variation arises, e.g. from differences in tumour shape and size, lung function and genetic factors. Secondly improvement is achieved by taking into account intra-tumour and intra-organ heterogeneity derived from molecular and functional imaging. Additional radiation dose must be delivered to those parts of the tumour that need it the most, e.g. because of increased radio-resistance or reduced therapeutic drug uptake, and away from regions inside the lung that are most prone to complication. As the delivery of these treatments plans is very sensitive for geometrical uncertainties, probabilistic treatment planning is needed to generate robust treatment plans. The administration of these complicated dose distributions requires a quality assurance procedure that can evaluate the treatment delivery and, if necessary, adapt the treatment plan during radiotherapy.