Planning analysis for locally advanced lung cancer: dosimetric and efficiency comparisons between intensity-modulated radiotherapy (IMRT), single-arc/partial-arc volumetric modulated arc therapy (SA/PA-VMAT)

Dose-volume metric-based prediction of radiotherapy-induced lymphocyte loss in patients with non-small-cell lung cancer treated with modern radiotherapy techniques

Background and Purpose

Radiation-induced lymphopenia (RIL) is a common side effect of radiotherapy (RT) that may negatively impact survival. We aimed to identify RIL predictors in patients with non-small-cell lung cancer (NSCLC) treated intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT).

Materials and Methods

We retrospectively analysed data of 306 patients who underwent radical RT for NSCLC. Absolute lymphocyte count (ALC) loss was evaluated for each patient by fitting an exponential decay curve to data from first 45 days since treatment start, and percentage ALC loss relative to baseline was calculated based on area under the decay curve and baseline ALC. We compared IMRT and VMAT treatment plans and used linear regression to predict ALC loss.

Results

ALC decreased during RT in the whole patient group, while neutrophil counts remained stable and decreased only in those treated with concurrent chemoradiotherapy (CRT). Percentage ALC loss ranged between 11 and 78 % and was more strongly than lymphocyte nadir correlated with dose-volume metrics for relevant normal structures. We found evidence for the association of high radiation dose to the lungs, heart and body with percentage ALC loss, with lung volume exposed to 20-30 Gy being most important predictors in patients treated with IMRT. A multivariable model based on CRT use, baseline ALC and first principal component (PC1) of the dose-volume predictors showed good predictive performance (bias-corrected R2 of 0.40).

Conclusion

Percentage lymphocyte loss is a robust measure of RIL that is predicted by baseline ALC, CRT use and dose-volume parameters to the lungs, heart and body.

Intensity-modulated proton and carbon-ion radiotherapy using a fixed-beam system for locally advanced lung cancer: dosimetric comparison with x-ray radiotherapy and normal tissue complication probability (NTCP) evaluation

Objective. To assess the dosimetric consequences and the normal tissue complication probability (NTCP) for the organs at risk (OARs) in intensity-modulated particle radiotherapy of proton (IMPT) and carbon-ion (IMCT) using a fixed-beam delivery system when compared with intensity-modulated photon radiotherapy (IMRT) for locally advanced small-cell lung cancer.Approach. The plans were all designed under the same total relative biological effectiveness (RBE)-weighted prescription dose, in which the planning target volume (PTV) of the internal gross target volume(IGTV) and the PTV of the clinical target volume was irradiated with 69.3 Gy (RBE) and 63 Gy (RBE), respectively, using a simultaneously integrated boosting (SIB) technique. NTCPs were estimated for heart, lung, esophagus and spinal cord by Lyman-Kutcher-Burman (LKB) and logistic models. Dose escalation was simulated under the desired NTCP values (0.05, 0.10 and 0.50) of the three radiation techniques.Main results. Under the similar target coverage, almost all OARs were significantly better spared (p< 0.05) when using the particle radiotherapy except for D1cc (the dose to 1 cm3of the volume) of the proximal bronchial tree (p> 0.05). At least 57.6% of mean heart dose, 28.8% of mean lung dose and 19.1% of mean esophageal dose were reduced compared with IMRT. The mean NTCP of radiation-induced pneumonitis (RP) in the ipsilateral lung was 0.39 ± 0.33 (0.39 ± 0.31) in IMPT plans and 0.36 ± 0.32 (0.35 ± 0.30) in IMCT plans compared with 0.66 ± 0.30 (0.64 ± 0.28) in IMRT plans by LKB (logistic) models. The target dose could be escalated to 78.3/76.9 Gy (RBE) in IMPT/IMCT plans compared with 61.7 Gy (RBE) in IMRT plans when 0.50 of NTCP in terms of RP in the ipsilateral lung was applied.Significance. This study presents the potential of better control of the side effects and improvement of local control originating from the dosimetric advantage with the application of IMPT and IMCT with the SIB technique for locally advanced lung cancer, even with limited beam directions.

Application research on reducing radiation-induced lung injury with a trigger operator based on overlap volume histogram (OVH) in breast cancer postoperative radiotherapy

This study aims to develop a trigger operator based on the Overlap Volume Histogram (OVH) and examined its effectiveness in enhancing plan quality to minimize radiation-induced lung injury in postoperative radiotherapy for breast cancer. This trigger operator was applied for plan re-optimization to the previous Volumetric Modulated Arc Therapy (VMAT) plans of 16 left breast conserving surgery cases. These cases were categorized into a Contiguous Group (CG) and a Separated Group (SG) based on the relative position between the target and the Left-Lung (L-Lung). We investigated the changes in Vx, mean dose, and Normal Tissue Complication Probability (NTCP) values of organs-at-risk (OARs) before and after using the trigger operator. The Pairwise Sample T test was employed to evaluate the differences in indices between the two groups before and after optimizations. The trigger operator effectively initiated plan re-optimization. The values of V5, V10, V20, V30, and V40 of the L-Lung, as well as the mean dose of the heart, all decreased after re-optimization. The Pairwise Sample T test results showed statistically significant differences in the V20, V30, and V40 of the L-Lung in the CG (P < 0.01), and in the V5, V10, V20, V30, and V40 of the L-Lung in the SG (P < 0.01). Our findings suggest that the proposed trigger operator can improve plan quality, thereby reducing radiation-induced lung injury in postoperative radiotherapy for breast cancer.

Dosimetric comparison of free-breathing versus respiratory motion-managed radiotherapy via four-dimensional computed tomography-based volumetric-modulated arctherapy for lung cancer

PURPOSE

The aim of this study is to use respiratory motion-managed radiotherapy (RT) to reduce side effects and to compare dosimetric factors with free-breathing planning in patients with lung cancer.

MATERIALS AND METHODS

Simulation images were obtained in 10 respiratory phases with free breathing using four-dimensional computed tomography (4D-CT) scanner. Planning target volume (PTV) was created with 5mm margins in each direction of the internal target volume delineated using the maximum intensity projection. A volumetric arc treatment (VMAT) plan was created so that the prescribed dose would cover 98% of the PTV. Target volumes for the free-breathing VMAT plan were created according to ICRU Reports 62 and the same prescribed dose was used.

RESULTS

Patients were evaluated during January 2020. Median 63Gy (59.4-64) RT was administered. Median PTV volumes were 173.53 and 494.50cm3 (P=0.008) and dose covering 95% of PTV volume was 62.97 and 60.51Gy (P=0.13) in 4D-CT based and free-breathing VMAT plans, respectively. The mean and V50 heart dose was 6.03Gy (vs. 10.36Gy, P=0.043) and 8.2% (vs. 33.9%, P=0.007), and significantly lower in 4D-CT based VMAT plans and there was also found a non-significant reduction for other risky organ doses.

CONCLUSION

Ten patients treated with respiratory motion-managed RT with 4D-CT based VMAT technique. It was observed that PTV did not increase, the target was covered with 95% accuracy, and with statistical significance in heart doses, all risky organ doses were found to be less.

Dosimetric comparison of five different radiotherapy treatment planning approaches for locally advanced non-small cell lung cancer with sequential plan changes

BACKGROUND

The purpose of this study was to compare the dosimetric characteristics of five different treatment planning techniques for locally advanced non-small cell lung cancer (LA-NSCLC) with sequential plan changes.

METHODS

A total of 13 stage III NSCLC patients were enrolled in this study. These patients had both computed tomography (CT) images for initial and boost treatment plans. The latter CT images were taken if tumor shrinkage was observed after 2 weeks of treatment. The prescription dose was 60 Gy/30 Fr (initial: 40 Gy/20 Fr, and boost: 20 Gy/10 Fr). Five techniques (forward-planed 3-dimensional conformal radiotherapy [F-3DCRT] on both CT images, inverse-planned 3DCRT [I-3DCRT] on both CT images, volumetric modulated arc therapy [VMAT] on both CT images, F-3DCRT on initial CT plus VMAT on boost CT [bVMAT], and hybrid of fixed intensity-modulated radiotherapy [IMRT] beams and VMAT beams on both CT images [hybrid]) were recalculated for all patients. The accumulated doses between initial and boost plans were compared among all treatment techniques.

RESULTS

The conformity indexes (CI) of the planning target volume (PTV) of the five planning techniques were 0.34 ± 0.10, 0.57 ± 0.10, 0.86 ± 0.08, 0.61 ± 0.12, and 0.83 ± 0.11 for F-3DCRT, I-3DCRT, VMAT, bVMAT, and hybrid, respectively. In the same manner, lung volumes receiving >20 Gy (V20Gy ) were 21.05 ± 10.56%, 20.86 ± 6.45, 19.50 ± 7.38%, 19.98 ± 10.04%, and 17.74 ± 7.86%. There was significant improvement about CI and V20Gy for hybrid compared with F-3DCRT (p < 0.05).

CONCLUSION

The IMRT/VMAT hybrid technique for LA-NSCLC patients improved target CI and reduced lung doses. Furthermore, if IMRT was not available initially, starting with 3DCRT might be beneficial as demonstrated in the bVMAT procedure of this study.

Comparison of photon intensity modulated, hybrid and volumetric modulated arc radiation treatment techniques in locally advanced non-small cell lung cancer

Background and purpose

There is no consensus on the best photon radiation technique for non-small cell lung cancer (NSCLC). This study quantified the differences between commonly used treatment techniques in NSCLC to find the optimal technique.

Materials and methods

Treatment plans were retrospectively generated according to clinical guidelines for 26 stage III NSCLC patients using intensity modulated radiation therapy (IMRT), hybrid, and volumetric modulated arc therapy (VMATC, and VMATV5 optimized for lower lung and heart dose). Plans were evaluated for target coverage, organs at risk dose (including heart substructures) and normal tissue complication probabilities (NTCP).

Results

The comparison showed significant and largest median differences (>1 Gy or >5%) in favor of IMRT for the mediastinal envelope and heart (maximum dose), in favor of the hybrid technique for the lungs (V5Gy of the total lungs and V5Gy of the contralateral lung) and in favor of VMATC for the heart (Dmean), most of the substructures of the heart, and the spinal cord (maximum dose). The VMATV5 technique had significantly lower heart dose compared to the hybrid technique and significantly lower lung dose compared to the VMATC, combining both advantages in one technique. The mean ΔNTCP did not exceed the 2 percent point (pp) for grade 5 (mortality), and 10 pp for grade ≥2 toxicities (radiation pneumonitis and acute esophageal toxicity), but ΔNTCP was mostly in favor of VMATC/V5 for individual patients.

Conclusion

This planning study showed that VMATV5 was preferred as it achieved low lung and heart doses, as well as low NTCPs, simultaneously.

Computed tomography and radiation dose images-based deep-learning model for predicting radiation pneumonitis in lung cancer patients after radiation therapy

PURPOSE

To develop a deep learning model that combines CT and radiation dose (RD) images to predict the occurrence of radiation pneumonitis (RP) in lung cancer patients who received radical (chemo)radiotherapy.

METHODS

CT, RD images and clinical parameters were obtained from 314 retrospectively-collected patients (training set) and 35 prospectively-collected patients (test-set-1) who were diagnosed with lung cancer and received radical radiotherapy in the dose range of 50 Gy and 70 Gy. Another 194 (60 Gy group, test-set-2) and 158 (74 Gy group, test-set-3) patients from the clinical trial RTOG 0617 were used for external validation. A ResNet architecture was used to develop a prediction model that combines CT and RD features. Thereafter, the CT and RD weights were adjusted by using 40 patients from test-set-2 or 3 to accommodate cohorts with different clinical settings or dose delivery patterns. Visual interpretation was implemented using a gradient-weighted class activation map (grad-CAM) to observe the area of model attention during the prediction process. To improve the usability, ready-to-use online software was developed.

RESULTS

The discriminative ability of a baseline trained model had an AUC of 0.83 for test-set-1, 0.55 for test-set-2, and 0.63 for test-set-3. After adjusting CT and RD weights of the model using a subset of the RTOG-0617 subjects, the discriminatory power of test-set-2 and 3 improved to AUC 0.65 and AUC 0.70, respectively. Grad-CAM showed the regions of interest to the model that contribute to the prediction of RP.

CONCLUSION

A novel deep learning approach combining CT and RD images can effectively and accurately predict the occurrence of RP, and this model can be adjusted easily to fit new cohorts.

High-risk patients with locally advanced non-small cell lung cancer treated with stereotactic body radiation therapy to the peripheral primary combined with conventionally fractionated volumetric arc therapy to the mediastinal lymph nodes

Introduction

A very narrow therapeutic window exists when delivering curative chemoradiotherapy for inoperable locally advanced non-small cell lung cancer (NSCLC), particularly when large distances exist between areas of gross disease in the thorax. In the present study, we hypothesize that a novel technique of stereotactic body radiation therapy (SBRT) to the primary tumor in combination with volumetric arc therapy (VMAT) to the mediastinal lymph nodes (MLN) is a suitable approach for high-risk patients with large volume geographically distant locally advanced NSCLC.

Patients and methods

In this single institutional review, we identified high-risk patients treated between 2014 and 2017 with SBRT to the parenchymal lung primary as well as VMAT to the involved MLN using conventional fractionation. Dosimetrically, comparative plans utilizing VMAT conventionally fractionated delivered to both the primary and MLN were analyzed. Clinically, toxicity (CTCAE version 5.0) and oncologic outcomes were analyzed in detail.

Results

A total of 21 patients were identified, 86% (n=18) of which received chemotherapy as a portion of their treatment. As treatment phase was between 2014 and 2017, none of the patients received consolidation immunotherapy. Target volume (PTV) dose coverage (99 vs. 87%) and CTV volume (307 vs. 441 ml) were significantly improved with SBRT+MLN vs. for VMAT alone (p<0.0001). Moreover, low-dose lung (median V5Gy [%]: 71 vs. 77, p<0.0001), heart (median V5Gy [%]: 41 vs. 49, p<0.0001) and esophagus (median V30Gy [%]: 54 vs. 55, p=0.03) dose exposure were all significantly reduced with SBRT+MLN. In contrast, there was no difference observed in high-dose exposure of lungs, heart, and spinal cord. Following SBRT+MLN treatment, we identified only one case of high-grade pneumonitis. As expected, we observed a higher rate of esophagitis with a total of seven patients experience grade 2+ toxicity. Overall, there were no grade 4+ toxicities identified. After a median 3 years follow up, disease progression was observed in 70% of patients irradiated using SBRT+MLN, but never in the spared 'bridging' tissue between pulmonary SBRT and mediastinal VMAT.

Conclusion

For high risk patients, SBRT+MLN is dosimetrically feasible and can provide an alternative to dose reductions necessitated by otherwise very large target volumes.

Predictors of high-grade radiation pneumonitis following radiochemotherapy for locally advanced non-small cell lung cancer: analysis of clinical, radiographic and radiotherapy-related factors

Purpose:

In this study, the relation between radiation pneumonitis (RP) and a wide spectrum of clinical, radiographic and treatment-related factors was investigated. As scoring of low-grade RP can be subjective, RP grade ≥3 (RP ≥ G3) was chosen as a more objective and clinically significant endpoint for this study.

Methods and Materials:

105 consecutive patients with locally advanced non-small cell lung cancer underwent conventionally fractionated radio-(chemo-)therapy to a median dose of 64 Gy. A retrospective analysis of 25 clinical (gender, race, pulmonary function, diabetes, statin use, smoking history), radiographic (emphysema, interstitial lung disease) and radiotherapy dose- and technique-related factors was performed to identify predictors of RP ≥ G3. Following testing of all variables for statistical association with RP using univariate analysis (UVA), a forward selection algorithm was implemented for building a multivariate predictive model (MVA) with limited sample size.

Results:

Median follow-up of surviving patients was 33 months (9–132 months). RP ≥ G3 was diagnosed in 10/105 (9·5%) patients. Median survival was 28·5 months. On UVA, predictors for RP ≥ G3 were diabetes, lower lobe location, planning target volume, volumetric modulated arc therapy (VMAT), lung V5 Gy (%), lung Vspared5 Gy (mL), lung V20 Gy (%) and heart V5 Gy (% and mL). On MVA, VMAT was the only significant predictor for RP ≥ G3 (p = 0·042). Lung V5 Gy and lung V20 Gy were borderline significant for RP ≥ G3. Patients with RP ≥ 3 had a median survival of 10 months compared to 29·5 months with RP < G3 (p = 0·02).

Conclusions:

In this study, VMAT was the only factor that was significantly correlated with RP ≥ G3. Avoiding RP ≥ G3 is important as a toxicity per se and as a risk factor for poor survival. To reduce RP, caution needs to be taken to reduce low-dose lung volumes in addition to other well-established dose constraints.

Symptomatic Radiation Pneumonitis in NSCLC Patients Receiving EGFR-TKIs and Concurrent Once-daily Thoracic Radiotherapy: Predicting the Value of Clinical and Dose-volume Histogram Parameters

BACKGROUND

The incidence of symptomatic radiation pneumonitis (RP) and its relationship with dose-volume histogram (DVH) parameters in non-small cell lung cancer (NSCLC) patients receiving epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) and concurrent once-daily thoracic radiotherapy (TRT) remain unclear. We aim to analyze the values of clinical factors and dose-volume histogram (DVH) parameters to predict the risk for symptomatic RP in these patients.

METHODS

Between 2011 and 2019, we retrospectively analyzed and identified 85 patients who had received EGFR-TKIs and once-daily TRT simultaneously (EGFR-TKIs group) and 129 patients who had received concurrent chemoradiotherapy (CCRT group). The symptomatic RP was recorded according to the Common Terminology Criteria for Adverse Event (CTCAE) criteria (grade 2 or above). Statistical analyses were performed using SPSS 26.0.

RESULTS

In total, the incidences of symptomatic (grade≥2) and severe RP (grade≥3) were 43.5% (37/85) and 16.5% (14/85) in EGFR-TKIs group vs 27.1% (35/129) and 10.1% (13/129) in CCRT group respectively. After 1:1 ratio between EGFR-TKIs group and CCRT group was matched by propensity score matching, chi-square test suggested that the incidence of symptomatic RP in the MATCHED EGFR-TKIs group was higher than that in the matched CCRT group (χ2=4.469, P=0.035). In EGFR-TKIs group, univariate and multivariate analyses indicated that the percentage of ipsilateral lung volume receiving ≥30 Gy (ilV30) [odds ratio (OR): 1.163, 95%CI: 1.036-1.306, P=0.011] and the percentage of total lung volume receiving ≥20 Gy (tlV20) (OR: 1.171, 95%CI: 1.031-1.330, P=0.015), with chronic obstructive pulmonary disease (COPD) or not (OR: 0.158, 95%CI: 0.041-0.600, P=0.007), were independent predictors of symptomatic RP. Compared to patients with lower ilV30/tlV20 values (ilV30 and tlV20<cut-off point values) and without COPD, patients with higher ilV30/tlV20 values (ilV30 and tlV20>cut-off point values) and COPD had a significantly higher risk for developing symptomatic RP, with a hazard ratio (HR) of 1.350 (95%CI: 1.190-1.531, P<0.001).

CONCLUSIONS

Patients receiving both EGFR-TKIs and once-daily TRT were more likely to develop symptomatic RP than patients receiving concurrent chemoradiotherapy. The ilV30, tlV20, and comorbidity of COPD may predict the risk of symptomatic RP among NSCLC patients receiving EGFR-TKIs and conventionally fractionated TRT concurrently.

Planning evaluation of a novel volume-based algorithm for personalized optimization of lung dose in VMAT for esophageal cancer

Radiotherapy treatment planning (RTP) is time-consuming and labor-intensive since medical physicists must devise treatment plans carefully to reduce damage to tissues and organs for patients. Previously, we proposed the volume-based algorithm (VBA) method, providing optimal partial arcs (OPA) angle to achieve the low-dose volume of lungs in dynamic arc radiotherapy. This study aimed to implement the VBA for esophageal cancer (EC) patients and compare the lung dose and delivery time between full arcs (FA) without using VBA and OPA angle using VBA in volumetric modulated arc therapy (VMAT) plans. We retrospectively included 30 patients diagnosed with EC. RTP of each patient was replanned to 4 VMAT plans, including FA plans without (FA-C) and with (FA + C) dose constraints of OARs and OPA plans without (OPA-C) and with (OPA + C) dose constraints of OARs. The prescribed dose was 45 Gy. The OARs included the lungs, heart, and spinal cord. The dose distribution, dose-volume histogram, monitor units (MUs), delivery time, and gamma passing rates were analyzed. The results showed that the lung V₅ and V₁₀ in OPA + C plans were significantly lower than in FA + C plans (p < 0.05). No significant differences were noted in planning target volume (PTV) coverage, lung V₁₅, lung V₂₀, mean lung dose, heart V₃₀, heart V₄₀, mean heart dose, and maximal spinal cord dose between FA + C and OPA + C plans. The delivery time was significantly longer in FA + C plans than in OPA + C plans (237 vs. 192 s, p < 0.05). There were no significant differences between FA + C and OPA + C plans in gamma passing rates. We successfully applied the OPA angle based on the VBA to clinical EC patients and simplified the arc angle selection in RTP. The VBA could provide a personalized OPA angle for each patient and effectively reduce lung V₅, V_10, and delivery time in VMAT.

Radiation Therapy Planning of Thoracic Tumors: A Review of Challenges Associated With Lung Toxicities and Potential Perspectives of Gallium-68 Lung PET/CT Imaging

Despite the introduction of new radiotherapy techniques, such as intensity modulated radiation therapy or stereotactic body radiation therapy, radiation induced lung injury remains a significant treatment related adverse event of thoracic radiation therapy. Functional lung avoidance radiation therapy is an emerging concept in the treatment of lung disease to better preserve lung function and to reduce pulmonary toxicity. While conventional ventilation/perfusion (V/Q) lung scintigraphy is limited by a relatively low spatial and temporal resolution, the recent advent of ⁶⁸Gallium V/Q lung PET/CT imaging offers a potential to increase the accuracy of lung functional mapping and to better tailor lung radiation therapy plans to the individual's lung function. Lung PET/CT imaging may also improve our understanding of radiation induced lung injury compared to the current anatomical based dose–volume constraints. In this review, recent advances in radiation therapy for the management of primary and secondary lung tumors and in V/Q PET/CT imaging for the assessment of functional lung volumes are reviewed. The new opportunities and challenges arising from the integration of V/Q PET/CT imaging in radiation therapy planning are also discussed.

Comparison of combinations of irradiation techniques and jaw conditions in intensity-modulated radiotherapy for lung cancer

Purpose

To assist in the selection of a suitable combination of an irradiation technique and jaw condition in intensity‐modulated radiotherapy (IMRT) and volumetric‐modulated arc radiotherapy (VMAT) for lung cancer treatment plans.

Materials and methods

Thirty patients with lung cancer who underwent radiotherapy were enrolled retrospectively. They were categorized as having central lung cancer, peripheral lung cancer with mediastinal lymph node metastasis (peripheral E lung cancer), and peripheral lung cancer without mediastinal lymph node metastasis (peripheral N lung cancer). Four treatment plans were designed for each patient: fixed jaw and adaptive jaw IMRT technique (FJ‐IMRT and JA‐IMRT), and fixed jaw and jaw tracking VMAT technique (FJ‐VMAT and JT‐VMAT). The dose parameters of the four group plans were compared and analyzed.

Results

Compared to FJ‐IMRT, JA‐IMRT significantly reduced the mean dose (D_mean) and volume percentage of 5 Gy (V_5Gy) of the total lung in central and peripheral N lung cancer. Similarly, compared to FJ‐VMAT, JT‐VMAT provided better protection to most organs at risk (OARs), particularly for total lung and heart. In comparison with IMRT, VMAT significantly improved the conformity index (CI) of the planning target volume for the three lung cancer classifications, and it reduced the dose of almost all OARs except V_5Gy and D_mean of the total lung. Moreover, the mean monitor units of the VMAT groups were far lower than the IMRT groups.

Conclusion

Based on the dosimetric findings and considering clinical data published on lung and heart side effects, we propose recommendations on the preferred treatment technique based on tumor location and pulmonary function. For central lung cancer with normal pulmonary function, we advise JT‐VMAT techniques. Conversely, for central lung cancer with poor pulmonary function, we recommend JA‐IMRT techniques. We advocate JA‐IMRT for peripheral E lung cancer. For peripheral N lung cancer, JT‐VMAT techniques are strongly recommended.

The status of medical physics in radiotherapy in China

PURPOSE

To present an overview of the status of medical physics in radiotherapy in China, including facilities and devices, occupation, education, research, etc. MATERIALS AND METHODS: The information about medical physics in clinics was obtained from the 9-th nationwide survey conducted by the China Society for Radiation Oncology in 2019. The data of medical physics in education and research was collected from the publications of the official and professional organizations.

RESULTS

By 2019, there were 1463 hospitals or institutes registered to practice radiotherapy and the number of accelerators per million population was 1.5. There were 4172 medical physicists working in clinics of radiation oncology. The ratio between the numbers of radiation oncologists and medical physicists is 3.51. Approximately, 95% of medical physicists have an undergraduate or graduate degrees in nuclear physics and biomedical engineering. 86% of medical physicists have certificates issued by the Chinese Society of Medical Physics. There has been a fast growth of publications by authors from mainland of China in the top international medical physics and radiotherapy journals since 2018.

CONCLUSIONS

Demand for medical physicists in radiotherapy increased quickly in the past decade. The distribution of radiotherapy facilities in China became more balanced. High quality continuing education and training programs for medical physicists are deficient in most areas. The role of medical physicists in the clinic has not been clearly defined and their contributions have not been fully recognized by the community.

Changes on myocardial perfusion scintigraphy and contrast-enhanced cardiac magnetic resonance imaging after definitive radiotherapy in patients with lung cancer

Aim:

To determine whether myocardial perfusion scintigraphy (MPS) changes in lung cancer patients treated with radiotherapy (RT) were detectable with late gadolinium enhancement cardiac magnetic resonance imaging (LGE CMR).

Materials and methods:

Twenty-one patients with lung cancer were evaluated pre-RT and at 2 and 6 months post-RT follow-up (FU) with MPS and LGE CMR. MPS changes in the left ventricle (LV) were analysed using the semi-quantitative summed rest score method (20 segments) and the Bull’s-eye-view technique. The LGE CMR studies were analysed for visual signs of myocardial damage (fibrosis), that is, focal LGE in the LV and cardiac function parameters.

Results:

MPS changes were detected in 7/20 patients at 2 months FU and in 8/13 patients at 6 months FU. Only one patient had a new irreversible defect judged to be caused by direct irradiation. MPS changes in two cases were deemed to be caused by attenuation. All new MPS defects were minor and no corresponding myocardial damage, or any functional changes, were evident on LGE CMR.

Findings:

The extent of MPS changes at 6 months FU appeared less prominent than in previous reports. No visual signs or functional changes corresponding to myocardial damage were detected on LGE CMR. A risk for false-positive MPS changes caused by attenuation is evident.

Optimal beam angle selection and knowledge-based planning significantly reduces radiotherapy dose to organs at risk for lung cancer patients

BACKGROUND

Lung cancer patients struggle with high toxicity rates. This study investigates if IMRT plans with individually set beam angles or uni-lateral VMAT plans results in dose reduction to OARs. We investigate if introduction of a RapidPlan model leads to reduced dose to OARs. Finally, the model is validated prospectively.

MATERIAL AND METHODS

Seventy-four consecutive lung cancer patients treated with IMRT were included. For all patients, new IMRT plans were made by an experienced dose planner re-tuning beam angles aiming for minimized dose to the lungs and heart. Additionally, VMAT plans were made. The IMRT plans were selected as input for a RapidPlan model, which was used to generate 74 new IMRT plans. The new IMRT plans were used as input for a second RapidPlan model. This model was clinically implemented and used for generation of clinical treatment plans. Dosimetric parameters were compared using a Wilcoxon signed rank test or a 1-sided student's t-test. p < .05 was considered significant.

RESULTS

IMRT plans significantly reduced mean doses to lungs (MLD) and heart (MHD) by 1.6 Gy and 1.7 Gy in mean compared to VMAT plans. MLD was significantly (p < .001) reduced from 10.8 Gy to 9.4 Gy by using the second RapidPlan model. MHD was significantly (p < .001) reduced from 4.9 Gy to 3.9 Gy. The model was validated in prospectively collected treatment plans showing significantly lower MLD after the implementation of the second RapidPlan model.

CONCLUSION

Introduction of RapidPlan and beam angles selected based on the target and OARs position reduces dose to OARs.

Toxicity after volumetric modulated arc therapy for lung cancer: a monocentric retrospective study

Background

Intensity-modulated radiotherapy (RT) is now widely implemented and has replaced classical three-dimensional (3D)-RT in many tumor sites, as it allows a better target dose conformity and a better sparing of organs a risk (OAR), at the expense, however, of increasing the volume of low dose to normal tissues. Clinical data on toxicities using volumetric modulated arc therapy (VMAT) in lung cancer remain scarce. We aimed to report both acute (APT) and late (LPT) pulmonary and acute (AET) and late (LET) oesophageal toxicities in such setting.

Methods

All patients treated for a primary lung cancer with VMAT +/- chemotherapy (ChT) in our center from 2014 to 2018 were retrospectively included. Usual clinical, treatment and dosimetric features were collected. Univariate analysis was performed using the receiver operative characteristics approach while multivariate analysis (MVA) relied on logistic regression, calculated with Medcalc 14.8.1.

Results

In total, 167 patients were included, with a median age of 66 years (39-88 years). Median radiation dose was 66 Gy (30-66 Gy); 82% patients received concomitant (32.3%), induction (25.7%) or induction followed by concomitant ChT (24%). After a median follow-up of 14.0 months, the G ≥2 APT, AET, LPT and LET rates were 22.2%, 30.0%, 16.8% and 5.4%, respectively with low grade ≥3 toxicity rates (respectively, 3%, 6.6%, 3% and 0%). On MVA, APT was significantly associated with V30 to the homolateral lung, AET with age, LPT with MEVS while no feature remained significantly correlated with LET.

Conclusions

Low rates of pulmonary and esophageal toxicity were observed in our cohort. Larger prospective studies are needed to confirm these results.

Single-arm prospective interventional study assessing feasibility of using gallium-68 ventilation and perfusion PET/CT to avoid functional lung in patients with stage III non-small cell lung cancer

BACKGROUND

In the curative-intent treatment of locally advanced lung cancer, significant morbidity and mortality can result from thoracic radiation therapy. Symptomatic radiation pneumonitis occurs in one in three patients and can lead to radiation-induced fibrosis. Local failure occurs in one in three patients due to the lungs being a dose-limiting organ, conventionally restricting tumour doses to around 60 Gy. Functional lung imaging using positron emission tomography (PET)/CT provides a geographic map of regional lung function and preclinical studies suggest this enables personalised lung radiotherapy. This map of lung function can be integrated into Volumetric Modulated Arc Therapy (VMAT) radiotherapy planning systems, enabling conformal avoidance of highly functioning regions of lung, thereby facilitating increased doses to tumour while reducing normal tissue doses.

METHODS AND ANALYSIS

This prospective interventional study will investigate the use of ventilation and perfusion PET/CT to identify highly functioning lung volumes and avoidance of these using VMAT planning. This single-arm trial will be conducted across two large public teaching hospitals in Australia. Twenty patients with stage III non-small cell lung cancer will be recruited. All patients enrolled will receive dose-escalated (69 Gy) functional avoidance radiation therapy. The primary endpoint is feasibility with this achieved if ≥15 out of 20 patients meet pre-defined feasibility criteria. Patients will be followed for 12 months post-treatment with serial imaging, biomarkers, toxicity assessment and quality of life assessment.

DISCUSSION

Using advanced techniques such as VMAT functionally adapted radiation therapy may enable safe moderate dose escalation with an aim of improving local control and concurrently decreasing treatment related toxicity. If this technique is proven feasible, it will inform the design of a prospective randomised trial to assess the clinical benefits of functional lung avoidance radiation therapy.

ETHICS AND DISSEMINATION

This study was approved by the Peter MacCallum Human Research Ethics Committee. All participants will provide written informed consent. Results will be disseminated via publications.

TRIALS REGISTRATION NUMBER

NCT03569072; Pre-results.

Toxicity and dosimetric analysis of nasopharyngeal carcinoma patients undergoing radiotherapy with IMRT or VMAT: A regional center's experience

OBJECTIVES

To observe the differences of dosimetric parameters and late toxicities in Nasopharyngeal Carcinoma (NPC) patients treated with intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT), which may provide the selective basis about radiation technology in clinical practices.

METHODS AND MATERIALS

Dosimetric parameters and late toxicities were collected and retrospectively analyzed from 627 NPC patients (stage as I-IVA/IVB) between January 2010 and December 2015.

RESULTS

The median D2 of all targets and D50 of PGTVnd (regional lymph nodes) were lower in VAMT than those in IMRT, while the median D95 and D98 of PGTVnx (primary lesions) were higher in VMAT than those in IMRT (p < 0.05). Superior sparing of the organs at risk were observed in VMAT. The maximum dose of the brainstem, spinal cord, temporal lobes, temporomandibular joint, optic chiasm, and lens were lower in VMAT than those in IMRT, where the median dose reduction ranged from 0.56 to 3.56 Gy (p < 0.05). Meanwhile, the median parotid glands V30 in VMAT was reduced by approximately 2% compared to that in IMRT (p = 0.027). Regarding the late toxicities, ototoxicity, trismus, and temporal lobe injury were reduced by VMAT (p < 0.05). Furthermore, the late toxicities were correlative with the radiation dose of the corresponding OARs (p < 0.05).

CONCLUSION

For NPC treatment plans, the VMAT might provide not only more favorable dose distributions of targets but also better sparing of normal tissue than observed in IMRT. Furthermore, VMAT possibly provides less treatment-related late toxicities such as ototoxicity, trismus, and temporal lobe injury.

Oesophageal Cancer: Conformal Radiotherapy vs. Hybrid-VMAT Technique With Two Different Treatment Planning Systems

BACKGROUND/AIM

Traditionally, the radiotherapy of oesophageal cancer has been conformal radiotherapy (CRT). We sought to compare dosimetric parameters of conformal radiotherapy (CRT) with those of two treatment planning systems for hybrid-volumetric modulated arc therapy (h-VMAT) for the treatment of oesophageal cancer.

PATIENTS AND METHODS

In 11 patients, we compared: i) planning target volume coverage, ii) dose to organs at risk, and iii) the dose rate (DR) of the three techniques. We evaluated two treatment planning systems: i) Eclipse and ii) RayStation.

RESULTS

The Conformity Index of the CRT plan was significantly higher for the h-VMAT plans, compared to all other parameters. Normal lung tissue volumes receiving >5, 13, or 20 Gy were lower with the RayStation plan compared to Eclipse. The volume of cardiac tissue receiving >40 Gy was highest with the CRT plan. The minimum DR in VMAT was lowest for the RayStation plan (49.5 MU/min).

CONCLUSION

The h-VMAT plan using RayStation is the appropriate choice for reducing lung dose.

A longitudinal evaluation of improvements in treatment plan quality for lung cancer with volumetric modulated arc therapy

Purpose

To investigate planning time and number of optimizations in routine clinical lung cancer plans based on the plan quality improvements following each optimization.

Materials and method

We selected 40 patients with lung cancer who were treated with conventional fractionated radiotherapy (CFRT). The 40 plans (divided into two groups with one or two target volumes) were completed by 9 planners using volumetric modulated arc therapy (VMAT). A planning strategy, including technique script for each group and a planning process for data collection, was introduced. The total planning time, number of optimizations, and dose–volume parameters of each plan were recorded and analyzed. A plan quality metric (PQM) was defined according to the clinical constraints. Statistical analysis of parameters of each plan following each optimization was performed for evaluating improvements in plan quality.

Results

According to the clinical plans generated by different planners, the median number of optimizations of each group was 4, and the median planning time was approximately 1 h (68.6 min and 62.0 min for plans with one or two target volumes, respectively). The dose deposited in organs at risk (OARs) gradually decreased, and the PQM values gradually improved following each optimization. The improvements were significant only between adjacent optimizations from the first optimization (Opt1) to the third optimization (Opt3).

Conclusion

Increasing the number of optimizations was associated with significantly improved sparing of OARs with slight effects on the dose coverage and homogeneity of target volume. Generally, based on the designed planning strategy, there was no significant improvement of the plan quality for more than three optimizations.

Salvage stereotactic body radiotherapy for post-operative oligo-recurrence of non-small cell lung cancer: A single-institution analysis of 59 patients

A standard treatment for patients with early-stage non-small cell lung cancer (NSCLC) who undergo surgery, and subsequently develop local failure or intrathoracic oligo-recurrence, has not yet been established. The present study aimed to assess the feasibility of stereotactic body radiotherapy (SBRT) for this subgroup of patients. Consequently, a retrospective analysis was conducted of patients with NSCLC recurrence who were treated with SBRT, and previously underwent curative surgical resection between October 2011 and October 2016. Post-SBRT survival [overall survival (OS); progression-free survival (PFS); and local control (LC)] and toxicity were analyzed. Prognostic factors for OS were identified using univariate and multivariate analysis. A total of 52 patients and 59 tumors were analyzed. The median follow-up time was 25 months (35 months for surviving patients), and median OS following salvage SBRT was 32 months. The 1- and 3-year OS rates were 84.4 and 67.8%, respectively. 1- and 3-year PFS rates were 80.8 and 58.7%, respectively. Only 4 patients (7.7%) developed local failure. Median LC was 71 months and 1- and 3-year LC rate were 97.9 and 94.9%, respectively. A total of 4 patients experienced grade 3 or higher adverse events (AEs) and two experienced grade 5 AEs (pneumonitis and hemoptysis). Central tumor location and the possibility of re-operation were independent prognostic factors for OS. The present study indicated that post-operative salvage SBRT is a promising therapeutic option for patients with NSCLC with locoregional or intrathoracic oligo-recurrence. We regard toxicity was also acceptable. However, further research is required on the appropriate selection of subjects, and stratification of the analysis by certain risk factors would increase the accuracy of the conclusions.

Acute severe radiation pneumonitis among non-small cell lung cancer (NSCLC) patients with moderate pulmonary dysfunction receiving definitive concurrent chemoradiotherapy: Impact of pre-treatment pulmonary function parameters

PURPOSE

Severe acute radiation pneumonitis (SARP) is a life-threatening complication of thoracic radiotherapy. Pre-treatment pulmonary function (PF) may influence its incidence. We have previously reported on the incidence of SARP among patients with moderate pulmonary dysfunction who received definitive concurrent chemoradiotherapy (dCCRT) for non-small cell lung cancer (NSCLC).

METHODS

The clinical outcomes, dose-volume histograms (DVH), and PF parameters of 122 patients (forced expiratory volume in 1 s [FEV1%]: 60-69%) receiving dCCRT between 2013 and 2019 were recorded. SARP was defined as grade ≥3 RP occurring during or within 3 months after CCRT. Logistic regression, receiver operating characteristics curves (ROC), and hazard ratio (HR) analyses were performed to evaluate the predictive value of each factor for SARP.

RESULTS

Univariate and multivariate analysis indicated that the ratio of carbon monoxide diffusing capacity (DLCO%; odds ratio [OR]: 0.934, 95% confidence interval [CI] 0.896-0.974, p = 0.001) and mean lung dose (MLD; OR: 1.002, 95% CI 1.001-1.003, p = 0.002) were independent predictors of SARP. The ROC AUC of combined DLCO%/MLD was 0.775 (95% confidence interval [CI]: 0.688-0.861, p = 0.001), with a sensitivity and specificity of 0.871 and 0.637, respectively; this was superior to DLCO% (0.656) or MLD (0.667) alone. Compared to the MLD-low/DLCO%-high group, the MLD-high/DLCO%-low group had the highest risk for SARP, with an HR of 9.346 (95% CI: 2.133-40.941, p = 0.003).

CONCLUSION

The DLCO% and MLD may predict the risk for SARP among patients with pre-treatment moderate pulmonary dysfunction who receive dCCRT for NSCLC. Prospective studies are needed to validate our findings.

Radiation pneumonitis in lung cancer treated with volumetric modulated arc therapy

Background

Few studies to date have assessed the incidence of radiation pneumonitis (RP) in lung cancer patients who have been treated with volumetric modulated arc therapy (VMAT). This study is aimed at reporting the RP incidence rate and the risk factors associated with a symptomatic RP in patients with lung cancer treated with VMAT.

Methods

A total of 77 consecutive lung cancer patients treated with VMAT from 2013 through 2015 were reviewed. RP severity was graded according to the Common Terminology Criteria for Adverse Events (CTCEA) v.4. Univariate and multivariate analyses were performed to identify the significant factors associated with RP.

Results

VMAT allowed us to achieve most planning objectives on the target volumes and organs at risk, for PTV V_95% =96.8%±3.1%, for lung V₅ =41.3%±8.7%, V₁₀ =30.0%±7.1%, V₂₀ =20.9%±5.7%, for heart V₅ =43.2%±29.9%, for esophagus V₆₀ =8.1%±12.9%. The maximum dose of spinal cord was 34.4±9.5 Gy. The overall incidence of symptomatic RP (grade ≥2 by CTCAE) was 28.6% in the entire cohort, and the rate of grade ≥3 RP was 11.7%. Based on the multivariate analysis, factors predictive of symptomatic RP included lung volume receiving ≥10 Gy (V₁₀) (P=0.019) and C-reactive protein changing level (P=0.013).

Conclusions

Our data showed that the incidence rate of RP was acceptable in lung cancer patients treated with VMAT. Additionally, we found that V₁₀ might be an important factor for predicting the development of RP when VMAT was used; but this observation needs to be validated in future studies.

Dosimetric and radiobiological comparison in different dose calculation grid sizes between Acuros XB and anisotropic analytical algorithm for prostate VMAT

To investigate feasible treatment planning parameters, we aimed to evaluate the dosimetric and radiobiological impact of the dose calculation algorithm and grid size in the volumetric modulated arc therapy (VMAT) plan for prostate cancer. Twenty patients were selected, and the treatment plans were initially generated with anisotropic analytical algorithm (AAA) and recalculated with Acuros XB (AXB) algorithm. Various dose grids were used for AXB (1, 2, and 3 mm) and AAA (1, 3, and 5 mm) plan. Dosimetric parameters such as homogeneity index (HI) and conformity index (CI), and radiobiological parameters such as tumor control probability (TCP) and normal tissue complication probability (NTCP) were calculated. Significant differences were observed in the planning target volume (PTV) coverage between both algorithms, and the V95%, HI, and CI of AAA were significantly affected by grid (p < 0.01). On 1 mm grid, the mean rectal dose difference between both algorithms was 2.87% of the prescription dose (p < 0.01), which was the highest among the critical organs. The TCP and NTCP of the AAA were higher than those of AXB (p < 0.01). Compared to AXB with 1 mm grid, the 2 mm grid showed comparable dose calculation accuracy with short calculation time. This study found that the PTV and rectum show significant differences according to dose calculation algorithm and grid. Considering the dose calculation performance for heterogeneous area, we recommend AXB with 2 mm grid for improving treatment efficiency of prostate VMAT.

Evaluation of the hybrid-dynamic conformal arc therapy technique for radiotherapy of lung cancer

Purpose

A hybrid-dynamic conformal arc therapy (HDCAT) technique consisting of a single half-rotated dynamic conformal arc beam and static field-in-field beams in two directions was designed and evaluated in terms of dosimetric benefits for radiotherapy of lung cancer.

Materials and Methods

This planning study was performed in 20 lung cancer cases treated with the VERO system (BrainLAB AG, Feldkirchen, Germany). Dosimetric parameters of HDCAT plans were compared with those of three-dimensional conformal radiotherapy (3D-CRT) plans in terms of target volume coverage, dose conformity, and sparing of organs at risk.

Results

HDCAT showed better dose conformity compared with 3D-CRT (conformity index: 0.74 ± 0.06 vs. 0.62 ± 0.06, p < 0.001). HDCAT significantly reduced the lung volume receiving more than 20 Gy (V₂₀: 21.4% ± 8.2% vs. 24.5% ± 8.8%, p < 0.001; V₃₀: 14.2% ± 6.1% vs. 15.1% ± 6.4%, p = 0.02; V₄₀: 8.8% ± 3.9% vs. 10.3% ± 4.5%, p < 0.001; and V₅₀: 5.7% ± 2.7% vs. 7.1% ± 3.2%, p < 0.001), V₄₀ and V₅₀ of the heart (V₄₀: 5.2 ± 3.9 Gy vs. 7.6 ± 5.5 Gy, p < 0.001; V₅₀: 1.8 ± 1.6 Gy vs. 3.1 ± 2.8 Gy, p = 0.001), and the maximum spinal cord dose (34.8 ± 9.4 Gy vs. 42.5 ± 7.8 Gy, p < 0.001) compared with 3D-CRT.

conclusions

HDCAT could achieve highly conformal target coverage and reduce the doses to critical organs such as the lung, heart, and spinal cord compared to 3D-CRT for the treatment of lung cancer patients.

Advanced radiation techniques for locally advanced non-small cell lung cancer: intensity-modulated radiation therapy and proton therapy

Radiation therapy (RT) represents an integral part of a multimodality treatment plan in the definitive, preoperative and postoperative management of non-small cell lung cancer (NSCLC). Technological advances in RT have enabled a shift from two-dimensional radiotherapy to more conformal techniques. Three-dimensional conformal radiotherapy (3DCRT), the current minimum technological standard for treating NSCLC, allows for more accurate delineation of tumor burden by using computed tomography-based treatment planning instead of two-dimensional radiographs. Intensity-modulated RT (IMRT) and proton therapy represent advancements over 3DCRT that aim to improve the conformity of RT and provide the possibility for dose escalation to the tumor by minimizing radiation dose to organs at risk. Both techniques likely confer benefits to certain anatomic subgroups of NSCLC requiring RT. This article reviews pertinent studies evaluating the use of IMRT and proton therapy in locally advanced NSCLC, and outlines challenges, indications for use, and areas for future research.

A dosimetric phantom study of thoracic radiotherapy based on three-dimensional modeling of mediastinal lymph nodes

The aim of the present study was to investigate the optimal strategy and dosimetric measurement of thoracic radiotherapy based on three-dimensional (3D) modeling of mediastinal lymph nodes (MLNs). A 3D model of MLNs was constructed from a Chinese Visible Human female dataset. Image registration and fusion between reconstructed MLNs and original chest computed tomography (CT) images was conducted in the Eclipse™ treatment planning system (TPS). There were three plans, including 3D conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), which were designed based on 10 cases of simulated lung lesions (SLLs) and MLNs. The quality of these plans was evaluated via examining indexes, including conformity index (CI), homogeneity index and clinical target volume (CTV) coverage. Dose-volume histogram analysis was performed on SLL, MLNs and organs at risk (OARs). A Chengdu Dosimetric Phantom (CDP) was then drilled at specific MLNs according to 20 patients with thoracic tumors and of a medium-build. These plans were repeated on fused MLNs and CDP CT images in the Eclipse™ TPS. Radiation doses at the SLLs and MLNs of the CDP were measured and compared with calculated doses. The established 3D MLN model demonstrated the spatial location of MLNs and adjacent structures. Precise image registration and fusion were conducted between reconstructed MLNs and the original chest CT or CDP CT images. IMRT demonstrated greater values in CI, CTV coverage and OAR (lungs and spinal cord) protection, compared with 3D-CRT and VMAT (P<0.05). The deviation between the measured and calculated doses was within ± 10% at SLL, and at the 2R and 7th MLN stations. In conclusion, the 3D MLN model can benefit plan optimization and dosimetric measurement of thoracic radiotherapy, and when combined with CDP, it may provide a tool for clinical dosimetric monitoring.

Integration of radiobiological modeling and indices in comparative plan evaluation: A study comparing VMAT and 3D-CRT in patients with NSCLC

PURPOSE

The purpose of this article was to generate an algorithm to calculate radiobiological endpoints and composite indices and use them to compare volumetric modulated arc therapy (VMAT) and 3-dimensional conformal radiation therapy (3D-CRT) techniques in patients with locally advanced non-small cell lung cancer.

METHODS AND MATERIALS

The study included 25 patients with locally advanced non-small cell lung cancer treated with 3D-CRT at our center between January 1, 2010, and December 31, 2014. The planner generated VMAT plans using clones of the original computed tomography scans and regions of interest volumes, which did not include the original 3D plans. Both 3D-CRT and VMAT plans were generated using the same dose-volume constraint worksheet. The dose-volume histogram parameters for planning target volume and relevant organs at risk (OAR) were reviewed. The calculation engine was written in the R programming language; the user interface was developed with the "shiny" R Web library. Dose-volume histogram data were imported into the calculation engine and tumor control probability (TCP), normal tissue complication probability (NTCP), composite cardiopulmonary toxicity index (CPTI), morbidity index: MI = ∑_j = 1^{#ofrelevantOARs}(w_j ∗ NTCP_j), uncomplicated TCP (UTCP=TCP∗∏k=1#ofOARs1-NTCP_K100, and therapeutic gain (TG): ie, TG = TCP ∗ (100 - MI) were calculated.

RESULTS

TCP was better with 3D-CRT (12.62% vs 11.71%, P < .001), whereas VMAT demonstrated superior NTCP esophagus (4.45% vs 7.39%, P = .02). NTCP spinal cord (0.001% vs 0.009%, P = .001), and NTCP heart/perfusion defect (44.57% vs 56.42%, P = .016). There was no difference in NTCP lung (6.27% vs 7.62%, P = .221) and NTCP heart/pericarditis (0.001% vs 0.15%, P = .129) between 2 techniques. VMAT showed substantial improvement in morbidity index (11.06% vs. 14.31%, P = 0.01), CPTI (47.59% vs 59.41%, P = .03), TG (P = .035), and trend toward superiority in UTCP (5.89 vs 4.75, P=.057).

CONCLUSION

The study highlights the utility of the radiobiological algorithm and summary indices in comparative plan evaluation and demonstrates benefits of VMAT over 3D-CRT.

Intensity-modulated radiation therapy versus volumetric-modulated arc therapy in non-small cell lung cancer: assessing the risk of radiation pneumonitis

Purpose

This study aimed to compare intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) regarding plan quality and healthy lung sparing, in stage III non-small cell lung cancer (NSCLC) patients.

Materials and methods

The plans of 60 patients were allocated either to the IMRT (n=30) or the VMAT (n=30) group. The dose prescribed to the planning target volume (PTV) was evaluated at the 95% level and the mean lung dose (MLD) and the healthy lung receiving 5, 10 and 20 Gy (V5, V10and V20, respectively) were analysed. The normal tissue complication probability (NTCP) for radiation pneumonitis was calculated with the Lyman–Kutcher–Burman model.

Results

Both techniques achieved comparable results for target coverage (V95%=97·87 versus 97·18%,p>0·05) and homogeneity. The MLD (15·57 versus 16·98 Gy,p>0·05), V5(60·35 versus 67·25%,p>0·05) and V10(45·22 versus 53·14%,p=0·011) were lower for IMRT, whereas VMAT reduced V20(26·44 versus 25·90%,p>0·05). The NTCP for radiation pneumonitis was higher for VMAT, but no statistical significance was observed (11·07 versus 12·75,p>0·05).

Conclusion

Both techniques seemed suitable for NSCLC treatment, but IMRT presented better results regarding lung sparing thus being beneficial in reducing the risk of radiation-induced pneumonitis.

Dosimetric comparison between IMRT and VMAT in irradiation for peripheral and central lung cancer

The aim of the present study was to compare intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in irradiation of lung cancer. Plans of 14 patients were compared. The results demonstrated that in peripheral lung cancer, V5 (%) of the lung in partial-arc (PA)-VMAT was decreased compared with IMRT, single-arc (SA)-, and double partial-arc (2PA)-VMAT. V30 (%) of the lung in IMRT was decreased compared with SA-, PA- and 2PA-VMAT. In the case of planning target volume (PTV) not encompassing the mediastinum in central lung cancer, the conformality index (CI) and heterogeneity index (HI) of SA-VMAT was improved compared with IMRT, PA-, and 2PA-VMAT. The received dose of heart in SA-VMAT was higher compared with IMRT, PA- and 2PA-VMAT. V30 (%) and V5 (%) of the lung in IMRT was higher compared with SA-, PA- and 2PA-VMAT; V10 (%) of the lung in 2PA was decreased compared with IMRT, SA- and PA. In the case of PTV encompassing the mediastinum in central lung cancer, the HI and CI of 2PA was improved compared with IMRT, SA- and PA-VMAT. The received dose of heart in 2PA was higher compared with IMRT, SA- and PA-VMAT. V30 (%) and V5 (%) of the lung in 2PA-VMAT was higher compared with IMRT, SA- and PA-VMAT. V20 (%) of the lung in 2PA was decreased compared with IMRT, SA- and PA-VMAT. In conclusion, it may be necessary to classify the radiotherapy plans of lung cancer into three categories including peripheral lung cancer, PTV not encompassing the mediastinum of central lung cancer, and PTV encompassing the mediastinum of central lung cancer. Each of IMRT, SA-VMAT, PA-VMAT, 2PA-VMAT strategy had individual advantages, and therefore it may be crucial to employ different planning techniques for different disease classifications and OAR requirements.

Comparison of outcomes of stereotactic body radiation therapy delivered with three different technologies to the lung

PURPOSE/OBJECTIVES

Since the inception of stereotactic body radiation therapy (SBRT), treatment delivery has been performed with volumetric modulated arc therapy (VMAT), helical tomotherapy (HT) and noncoplanar static fields (SF). The purpose of this study is to compare SBRT delivery among these treatment modalities to the lung.

MATERIALS/METHODS

A retrospective review of SBRT treatments of 30 to 60 Gy in 1 to 5 fractions from 2007 to 2015 was performed. Dosimetric parameters included V5, V20, D2cm, gross tumor volume (GTV) and planning target volume (PTV) size and coverage, rib/esophageal minimum/maximum doses, R30Gy, R50%, and the conformality index (CI). Clinical outcomes evaluated included local control, pneumonitis and other toxicities. ANOVA, Student's t-test and Kruskal-Wallis test were used to compare the parameters among modalities. Kaplan-Meier estimates of time-to-local failure were produced.

RESULTS

176 Treatments included 106 SF, 36 VMAT and 34 HT. HT had better PTV coverage (p=0.0166) but higher lung V5 and esophageal doses (p<0.001 and p=0.0032). R30Gy, R50%, and CI were significantly better with VMAT SBRT (p<0.001). Clinically, Grade 2+ pneumonitis was associated with larger median GTV's of 21.39 cc versus 7.65 cc (p=0.0016), larger median PTV's of 65.62 cc versus 31.75 cc (p=0.0030), and higher V20 6.62% versus 4.08% (p=0.0408). For patients surviving >1 year, overall local failure rate was 9.4%. Actuarial control rates trended toward statistical significance with time to local failure with VMAT being the most favorable group on the Kaplan-Meier curve (p=0.0733).

CONCLUSION

VMAT showed superior conformality compared to the other modalities. Among the modalities examined, HT had higher values for parameters associated with toxicity such as V5 and maximum esophageal dose, but all were within acceptable limits. There was a trend to better local control with VMAT.

A Dose Falloff Gradient Study in RapidArc Planning of Lung Stereotactic Body Radiation Therapy

Introduction:

Radiation Therapy Oncology Group (RTOG) report #0813 and 0915 recommends using D_2cm and R_50% as plan quality metrics for evaluation of normal tissue sparing in stereotactic body radiation therapy (SBRT) of lung lesion. This study introduces dose falloff gradient (DFG) as a tool for analyzing the dose beyond the planning target volume (PTV) extending into normal tissue structures. In ascertaining the impact of PTV size and SBRT planning techniques in DFG, this study questions the independence of the RTOG recommended metrics.

Materials and Methods:

In this retrospective study, 41 RapidArc lung SBRT plans with 2 or 3 complete or partial arcs were analyzed. PTV volumes ranged between 5.3 and 113 cm³ and their geographic locations were distributed in both lungs. 6MV, 6 MV-FFF, 10 MV, or 10 MV-FFF energies were used. RTOG-0915 metrics conformity index, homogeneity index, D_2cm, R_50%, and HD_loc were evaluated. DFG was computed from the mean and maximum dose in seven concentric 5 mm wide rings outside the PTV. DFG was investigated against the volume of normal lung irradiated by 50% isodose volume. Treatment plans with alternate energy and couch rotations were generated.

Results:

The dose falloff beyond PTV was modeled using a double exponential fit and evaluated for relationship with intermediate lung dose. Photon energy and beam configuration had a minimal impact on the dose falloff outside. The product of normalized D_2cm and R_50% was estimated to have a slowly varying value.

Conclusions:

Dose falloff outside PTV has been studied as a function of radial distance and ascertained by intermediate dose to normal lung. DFG can serve as a complementary plan quality metric.

Evaluation of MLC leaf transmission on IMRT treatment plan quality of patients with advanced lung cancer

The purpose of this paper was to evaluate the impact of leaf treatment of multileaf collimator (MLC) in plan quality of intensity-modulated radiotherapy (IMRT) of patients with advanced lung cancer. Five MLCs with different leaf transmissions (0.01%, 0.5%, 1.2%, 1.8%, and 3%) were configured for an accelerator in a treatment planning system. Correspondingly, 5 treatment plans with the same optimization setting were created and evaluated quantitatively for each patient (11 patients total) who was diagnosed with advanced lung cancer. All of the 5 plans for each patient met the dose requirement for the planning treatment volumes (PTVs) and had similar target dose homogeneity and conformity. On average, the doses to selected organs were as follows: (1) V₅, V₂₀, and the mean dose of total lung; (2) the maximum and mean dose to spinal cord planning organ-at-risk volume (PRV); and (3) V₃₀ and V₄₀ of heart, decreased slightly when MLC transmission was decreased, but with no statistical differences. There is a clear grouping of plans having total quality score (S_D) value, which is used to evaluate plan quality: (1) more than 1 (patient nos. 1 to 3, 5, and 8), and more than 2.5 (patient no. 6); (2) less than 1 (patient nos. 7 and 10); (3) around 1 (patient nos. 4, 9, and 11). As MLC transmission increased, overall S_D values increased as well and plan dose requirement was harder to meet. The clinical requirements were violated increasingly as MLC transmission became large. Total S_D with and without normal tissue (NT) showed similar results, with no statistically significant differences. Therefore, decrease of MLC transmission did have minimum impact on plan, and it improved target coverage and reduced normal tissue radiation slightly, with no statistical significance. Plan quality could not be significantly improved by MLC transmission reduction. However, lower MLC transmission may have advantages on lung sparing to low- and intermediate-dose exposure. Besides conventional fraction, hyperfraction, or stereotactic body radiotherapy (SBRT), the reduction on lung sparing is still essential because it is highly relevant to radiation pneumonitis (RP). It has potential to diminish incidence of RP and improve patient's quality of life after irradiation with lowered MLC transmission.

Study for reducing lung dose of upper thoracic esophageal cancer radiotherapy by auto-planning: volumetric-modulated arc therapy vs intensity-modulated radiation therapy

This study aimed to investigate the dosimetric differences and lung sparing between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) in the treatment of upper thoracic esophageal cancer with T3N0M0 for preoperative radiotherapy by auto-planning (AP). Sixteen patient cases diagnosed with upper thoracic esophageal cancer T3N0M0 for preoperative radiotherapy were retrospectively studied, and 3 plans were generated for each patient: full arc VMAT AP plan with double arcs, partial arc VMAT AP plan with 6 partial arcs, and conventional IMRT AP plan. A simultaneous integrated boost with 2 levels was planned in all patients. Target coverage, organ at risk sparing, treatment parameters including monitor units and treatment time (TT) were evaluated. Wilcoxon signed-rank test was used to check for significant differences (p < 0.05) between datasets. VMAT plans (pVMAT and fVMAT) significantly reduced total lung volume treated above 20 Gy (V₂₀), 25 Gy (V₂₅), 30 Gy (V₃₀), 35 Gy (V₃₅), 40 Gy (V₄₀), and without increasing the value of V₁₀, V₁₃, and V₁₅. For V₅ of total lung value, pVMAT was similar to aIMRT, and it was better than fVMAT. Both pVMAT and fVMAT improved the target dose coverage and significantly decreased maximum dose for the spinal cord, monitor unit, and TT. No significant difference was observed with respect to V₁₀ and V₁₅ of body. VMAT AP plan was a good option for treating upper thoracic esophageal cancer with T3N0M0, especially partial arc VMAT AP plan. It had the potential to effectively reduce lung dose in a shorter TT and with superior target coverage and dose homogeneity.

Normal lung sparing Tomotherapy technique in stage III lung cancer

PURPOSE

Radiation pneumonitis (RP) has been a challenging obstacle in treating stage III lung cancer patients. Beam angle optimization (BAO) technique for Tomotherapy was developed to reduce the normal lung dose for stage III non-small cell lung cancer (NSCLC). Comparative analyses on plan quality by 3 different Intensity-modulated radiation therapy (IMRT) methods with BAO were done.

MATERIALS AND METHODS

Ten consecutive stage IIIB NSCLC patients receiving linac-based static IMRT (L-IMRT) with total 66 Gy in 33 fractions to the PTV were selected. Two additional Tomotherapy-based IMRT plans (helical beam (TH-IMRT) and static beam (TD-IMRT)) were generated on each patient. To reduce the normal lung dose, Beam angles were optimized by using complete and directional block functions in Tomotherapy based on knowledge based statistical analysis. Plan quality was compared with target coverage, normal organ sparing capability, and normal tissue complication probability (NTCP). Actual beam delivery times and risk of RP related with planning target volume (PTV) were also evaluated.

RESULTS

The best PTV coverage measured by conformity index and homogeneity index was achievable by TH-IMRT (0.82 and 1.06), followed by TD-IMRT (0.81 and 1.07) and L-IMRT (0.75 and 1.08). Mean lung dose was the lowest in TH-IMRT plan followed by TD-IMRT and L-IMRT, all of which were ≤20 Gy. TH-IMRT plan could significantly lower the lung volumes receiving low to medium dose levels: V5~30 when compared to L-IMRT plan; and V5~20 when compared to TD-IMRT plan, respectively. TD-IMRT plan was significantly better than L-IMRT with respects to V20 and V30 and there was no significant difference with respect to V40 among three plans. The NTCP of the lung was the lowest in TH-IMRT plan, followed by TD-IMRT and L-IMRT (6.42% vs. 6.53% vs. 8.11%). Beam delivery time was the shortest in TD-IMRT plan followed by L-IMRT. As PTV length increased, NTCP and Mean lung dose proportionally increased significantly in all three plans.

CONCLUSION

Advantageous profiles by TH-IMRT could be achieved by BAO by complete and directional block functions. Current observation could help radiation oncologists to make wise selection of IMRT method for stage IIIB NSCLC.

A study of the dosimetric characteristics between different fixed-field IMRT and VMAT in early-stage primary mediastinal B-cell lymphoma

This analysis was designed to compare dosimetric parameters among different fixed-field intensity-modulated radiation therapy (IMRT) solutions and volumetric-modulated arc therapy (VMAT) to identify which can achieve the lowest risk of organs at risk (OARs) and treatment delivery efficiently. A total of 16 patients (8 male and 8 female) with early-stage primary mediastinal large B-cell lymphoma (PMBCL) were enrolled with planned gross tumor volume (PGTV) 45 Gy and planning target volume (PTV) 40 Gy. Four different plans were generated: 5-, 7, 9-field IMRT, and VMAT. The dose distributions for PGTV and PTV OARs (lungs, left ventricle, heart, thyroid gland, and breasts) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. Mean conformity index (CI) and homogeneity index (HI) for PGTV in 5F-, 7F-, 9F-IMRT, and VMAT were 1.01 and 1.10, 1.01 and 1.10, 1.01 and 1.10, and 1.01 and 1.11 (p = 0.963 and 0.843), whereas these 2 indices for PTV were 1.04 and 1.22, 1.03 and 1.19, 1.03 and 1.17, and 1.08 and 1.14 (p = 0.964 and 0.969), respectively. D_mean (Gy), V4 (%), D50 (Gy), and D80 (Gy) to the left and right breasts increased by 0.7 Gy and 0.1 Gy, 6.8% and 7.7%, 0.9 Gy and 1.7 Gy, and 1.0 Gy and 1.5 Gy in VMAT, respectively. The 9-beam IMRT plan had the highest MUs (25,762.4 MUs) and the longest treatment delivery time (10.7 minutes); whereas, the VMAT had the lowest MUs (13,345.0) and the shortest treatment delivery time (5.9 minutes). Seven- and 9-field IMRT and VMAT provide improved tumor coverage compared with 5F-IMRT, whereas VMAT shows higher treatment delivery efficiency than IMRT technique. Seven- and 9-field IMRT slightly reduce the low dose radiation exposure of breasts compared with VMAT technique. The 7- and 9-field IMRT and VMAT techniques both can be safely and efficiently delivered to patients with PMBCL.

Efficacy of robust optimization plan with partial-arc VMAT for photon volumetric-modulated arc therapy: A phantom study

This study investigated position dependence in planning target volume (PTV)-based and robust optimization plans using full-arc and partial-arc volumetric modulated arc therapy (VMAT). The gantry angles at the periphery, intermediate, and center CTV positions were 181°-180° (full-arc VMAT) and 181°-360° (partial-arc VMAT). A PTV-based optimization plan was defined by 5 mm margin expansion of the CTV to a PTV volume, on which the dose constraints were applied. The robust optimization plan consisted of a directly optimized dose to the CTV under a maximum-uncertainties setup of 5 mm. The prescription dose was normalized to the CTV D_99% (the minimum relative dose that covers 99% of the volume of the CTV) as an original plan. The isocenter was rigidly shifted at 1 mm intervals in the anterior-posterior (A-P), superior-inferior (S-I), and right-left (R-L) directions from the original position to the maximum-uncertainties setup of 5 mm in the original plan, yielding recalculated dose distributions. It was found that for the intermediate and center positions, the uncertainties in the D_99% doses to the CTV for all directions did not significantly differ when comparing the PTV-based and robust optimization plans (P > 0.05). For the periphery position, uncertainties in the D_99% doses to the CTV in the R-L direction for the robust optimization plan were found to be lower than those in the PTV-based optimization plan (P < 0.05). Our study demonstrated that a robust optimization plan's efficacy using partial-arc VMAT depends on the periphery CTV position.

Impacts of lung and tumor volumes on lung dosimetry for nonsmall cell lung cancer

The purpose of this study was to determine the impacts of lung and tumor volumes on normal lung dosimetry in three-dimensional conformal radiotherapy (3DCRT), step-and-shoot intensity-modulated radiotherapy (ssIMRT), and single full-arc volumetric-modulated arc therapy (VMAT) in treatment of nonsmall cell lung cancers (NSCLC). All plans were designed to deliver a total dose of 66 Gy in 33 fractions to PTV for the 32 NSCLC patients with various total (bilateral) lung volumes, planning target volumes (PTVs), and PTV locations. The ratio of the lung volume (total lung volume excluding the PTV volume) to the PTV volume (LTR) was evaluated to represent the impacts in three steps. (a) The least squares method was used to fit mean lung doses (MLDs) to PTVs or LTRs with power-law function in the population cohort (N = 32). (b) The population cohort was divided into three groups by LTRs based on first step and then by PTVs, respectively. The MLDs were compared among the three techniques in each LTR group (LG) and each PTV group (PG). (c) The power-law correlation was tested by using the adaptive radiation therapy (ART) planning data of individual patients in the individual cohort (N = 4). Different curves of power-law function with high R² values were observed between averaged LTRs and averaged MLDs for 3DCRT, ssIMRT, and VMAT, respectively. In the individual cohort, high R² values of fitting curves were also observed in individual patients in ART, although the trend was highly patient-specific. There was a more obvious correlation between LTR and MLD than that between PTV and MLD.

Small-arc volumetric-modulated arc therapy: A new approach that is superior to fixed-field IMRT in optimizing dosimetric and treatment-relevant parameters for patients undergoing whole-breast irradiation following breast-conserving surgery

Volumetric-modulated arc therapy (VMAT) is considered to deliver a better dose distribution and to shorten treatment time. There is a lack of research regarding breast irradiation after breast-conserving surgery (BCS) using VMAT with prone positioning. We developed a new small-arc VMAT methodology and compared it to conventional (fixed-field) intensity-modulated radiation therapy (IMRT) in the dosimetric and treatment relevant parameters for breast cancer patients in the prone position.Ten early-stage breast cancer patients were included in this exploratory study. All patients underwent computed tomography (CT) simulation scan in the prone position and for each patient, IMRT and VMAT plans were generated using the Monaco planning system. Two symmetrical partial arcs were applied in the VMAT plans. The angle ranges of the 2 arcs were set to approximately 60° to 100° and 220° to 260°, with small adjustments to maximize target coverage, while minimizing lung and heart exposure. The IMRT plans used 4 fixed fields. Prescribed doses were 50 Gy in 25 fractions. The target coverage, homogeneity, conformity, dose to organs at risk (OAR), treatment time, and monitor units (MU) were evaluated.Higher median conformal index (CI) and lower homogeneity index (HI) of the planning target volume (PTV) were respectively observed in VMAT and plans group (CI, 95% vs 91%; HI, 0.09 vs 0.12; P < 0.001). The volumes of ipsilateral lung receiving 30, 20, 10, and 5 Gy were lower for VMAT (P < 0.01), being 10%, 14.9%, 25.9%, and 44.9%, respectively, compared to 11.79%, 17.32%, 30.27%, and 50.58% for the IMRT plans. The mean lung dose was also reduced from 10.6 ± 1.8 to 9.6 ± 1.4 Gy (P = 0.001). The volumes of the heart receiving 30 and 40 Gy were similar for the 2 methods. In addition, the median treatment time (161 vs 412 seconds; P < 0.001) and the mean MU (713 vs 878; P < 0.001) were lower for VMAT.Small-arc VMAT plan improved CI and HI for the target, spared the dose of lung, and reduced treatment time and MU, compared to IMRT. It is a more promising irradiation technique for post-BCS radiotherapy.

Statistical Determination of the Gating Windows for Respiratory-Gated Radiotherapy Using a Visible Guiding System

Respiratory-gated radiation therapy (RGRT) is used to minimize the radiation dose to normal tissue in lung-cancer patients. Although determining the gating window in the respiratory phase of patients is important in RGRT, it is not easy. Our aim was to determine the optimal gating window when using a visible guiding system for RGRT. Between April and October 2014, the breathing signals of 23 lung-cancer patients were recorded with a real-time position management (RPM) respiratory gating system (Varian, USA). We performed statistical analysis with breathing signals to find the optimal gating window for guided breathing in RGRT. When we compared breathing signals before and after the breathing training, 19 of the 23 patients showed statistically significant differences (p < 0.05). The standard deviation of the respiration signals after breathing training was lowest for phases of 30%–70%. The results showed that the optimal gating window in RGRT is 40% (30%–70%) with respect to repeatability for breathing after respiration training with the visible guiding system. RGRT was performed with the RPM system to confirm the usefulness of the visible guiding system. The RPM system and our visible guiding system improve the respiratory regularity, which in turn should improve the accuracy and efficiency of RGRT.

Optimization of stereotactic body radiotherapy treatment planning using a multicriteria optimization algorithm

PURPOSE

To provide high-quality and efficient dosimetric planning for various types of stereotactic body radiotherapy (SBRT) for tumor treatment using a multicriteria optimization (MCO) technique fine-tuned with direct machine parameter optimization (DMPO).

METHODS AND MATERIALS

Eighteen patients with lung (n=11), liver (n=5) or adrenal cell cancer (n=2) were treated using SBRT in our clinic between December 2014 and June 2015. Plans were generated using the RayStation™ Treatment Planning System (TPS) with the VMAT technique. Optimal deliverable SBRT plans were first generated using an MCO algorithm to find a well-balanced tradeoff between tumor control and normal tissue sparing in an efficient treatment planning time. Then, the deliverable plan was post-processed using the MCO solution as the starting point for the DMPO algorithm to improve the dose gradient around the planning target volume (PTV) while maintaining the clinician's priorities. The dosimetric quality of the plans was evaluated using dose-volume histogram (DVH) parameters, which account for target coverage and the sparing of healthy tissue, as well as the CI100 and CI50 conformity indexes.

RESULTS

Using a combination of the MCO and DMPO algorithms showed that the treatment plans were clinically optimal and conformed to all organ risk dose volume constraints reported in the literature, with a computation time of approximately one hour. The coverage of the PTV (D99% and D95%) and sparing of organs at risk (OAR) were similar between the MCO and MCO+DMPO plans, with no significant differences (p>0.05) for all the SBRT plans. The average CI100 and CI50 values using MCO+DMPO were significantly better than those with MCO alone (p<0.05).

CONCLUSIONS

The MCO technique allows for convergence on an optimal solution for SBRT within an efficient planning time. The combination of the MCO and DMPO techniques yields a better dose gradient, especially for lung tumors.