Volumetric Arc Therapy Plans Research Articles

Robustness analysis of dynamic trajectory radiotherapy and volumetric modulated arc therapy plans for head and neck cancer

Background and purposeDynamic trajectory radiotherapy (DTRT) has been shown to improve healthy tissue sparing compared to volumetric arc therapy (VMAT). This study aimed to assess and compare the robustness of DTRT and VMAT treatment-plans for head and neck (H&N) cancer to patient-setup (PS) and machine-positioning uncertainties. Materials and methodsThe robustness of DTRT and VMAT plans previously created for 46 H&N cases, prescribed 50–70 Gy to 95 % of the planning-target-volume, was assessed. For this purpose, dose distributions were recalculated using Monte Carlo, including uncertainties in PS (translation and rotation) and machine-positioning (gantry-, table-, collimator-rotation and multi-leaf collimator (MLC)). Plan robustness was evaluated by the uncertainties’ impact on normal tissue complication probabilities (NTCP) for xerostomia and dysphagia and on dose-volume endpoints. Differences between DTRT and VMAT plan robustness were compared using Wilcoxon matched-pair signed-rank test (α = 5 %). ResultsAverage NTCP for moderate-to-severe xerostomia and grade ≥ II dysphagia was lower for DTRT than VMAT in the nominal scenario (0.5 %, p = 0.01; 2.1 %, p < 0.01) and for all investigated uncertainties, except MLC positioning, where the difference was not significant. Average differences compared to the nominal scenario were ≤ 3.5 Gy for rotational PS (≤ 3°) and machine-positioning (≤ 2°) uncertainties, <7 Gy for translational PS uncertainties (≤ 5 mm) and < 20 Gy for MLC-positioning uncertainties (≤ 5 mm). ConclusionsDTRT and VMAT plan robustness to the investigated uncertainties depended on uncertainty direction and location of the structure-of-interest to the target. NTCP remained on average lower for DTRT than VMAT even when considering uncertainties.

DOSIMETRIC COMPARISON OF INTENSITY-MODULATED RADIATION THERAPY (IMRT) AND VOLUMETRIC-MODULATED ARC THERAPY (VMAT) IN RECTAL CANCER PATIENTS: A COMPREHENSIVE ANALYSIS

This study aimed to conduct a thorough dosimetric comparison between two advanced radiotherapy techniques, Intensity-Modulated Radiation Therapy (IMRT) and Volumetric-Modulated Arc Therapy (VMAT), to ascertain the superior modality in terms of dose distribution and organ-at-risk sparing for rectal cancer patients. Thirty-three patients with ECOG performance status 1, aged between 18 to 60 years, diagnosed with Stage II to III rectal cancer, were included in this prospective study. Each patient underwent treatment planning with IMRT and VMAT techniques using Varian system simulation computed tomography scans. The dosimetric analysis encompassed the evaluation of target volume dose homogeneity, conformity, and doses to at-risk organs. The dosimetric comparison was conducted utilizing seven-field IMRT and dual arc VMAT plans. Statistical analysis was performed using paired t-tests and SPSS 20 software. Treatment plan constraints adhered to the RTOG 9406 guidelines, ensuring adequate planning target volume (PTV) coverage, homogeneity index, conformity index, and dose limits for organs at risk, including small bowel V20 (&lt;200cc), bladder V45 (&lt;21Gy), and femoral head V50 (≤30 Gy). Volumetric arc therapy plans demonstrated superior dose homogeneity to fixed-field intensity-modulated plans (p-value = 0.04), particularly in femoral head dose-limiting toxicity (p-value = 0.00). However, intensity-modulated therapy exhibited equivalent or superior performance in other evaluated parameters. Our findings suggest that while VMAT offers advantages in PTV coverage homogeneity and femoral head dose-limiting toxicity, IMRT remains competitive and potentially preferable in certain dosimetric aspects. The choice between IMRT and VMAT should be carefully considered based on individual patient characteristics and treatment goals. This comprehensive dosimetric comparison contributes valuable insights into optimizing radiotherapy planning for rectal cancer patients, potentially guiding clinical decision-making and improving treatment outcomes.

Dosimetric Comparison of CPAP and DIBH for Left-sided Breast Cancer Radiation Therapy

PurposeDespite the increasing interest in using continuous positive airway pressure (CPAP) in radiotherapy (RT), direct comparisons with the more widely employed deep inspiration breath-hold (DIBH) have been limited. This planning study aimed to offer comprehensive geometric and dosimetric evidence by comparing CPAP and DIBH-based RT plans. Materials and MethodsA retrospective dataset of 35 left-sided breast cancer patients with planning CT (pCT) scans under three breathing conditions (free breathing, CPAP with 10 cmH2O pressure, and DIBH) was collected. Volumetric arc therapy plans aimed for 95% dose coverage to 95% of the planning target volume with a maximum dose below 107%. A comparative dosimetric analysis among the three plans was conducted. Additionally, geometric differences were assessed by calculating the minimum distance between the heart and the clinical target volume (CTV) in each pCT. ResultsCPAP and DIBH plans demonstrated comparable mean heart doses (1.05 Gy), which were significantly lower than the FB plan (1.34 Gy). The maximum dose to the left anterior descending artery was smallest in the CPAP plan (4.44 Gy), followed by DIBH (4.73 Gy) and FB (7.33 Gy). Other organ-at-risk doses for CPAP and DIBH were similar, with mean contralateral breast doses of 2.27 and 2.21 Gy, mean ipsilateral lung doses of 4.09 and 4.08 Gy, V20 at 6.11 and 6.31%, and mean contralateral lung doses of 0.94 and 0.92 Gy, respectively. No significant difference was found in the minimum heart-to-CTV distance between CPAP and DIBH. DIBH exhibited the greatest lung volume (3908 cc), followed by CPAP (3509 cc), and FB (2703 cc). ConclusionThe comparison between CPAP and DIBH shows their similarity in both geometric and dosimetric aspects, providing strong evidence for CPAP's effectiveness and feasibility in RT. This suggests its potential as an alternative to DIBH for left-sided breast cancer patients.

Dosimetric evaluation of VMAT automated breast treatment plans: Towards the establishment of an institutional plan acceptability criteria

Abstract Introduction: To evaluate the clinical suitability of the current facility-based treatment plan protocol in establishing acceptability criteria. Material and methods: Automated Volumetric Arc Therapy (VMAT) treatment plans were retrospectively evaluated for intact breast and chest-wall cancer patients from January 2021 to January 2023. Results: A total of 94 patients were planned and treated using automated contouring and VMAT planning technique. The number of patients planned and treated for intact breast and chest-wall were 41 (43.6%) and 53 (56.4%), respectively. The mean intact breast volumes for optimization (Brst_opt) receiving 95% and 105% of the prescribed doses were 92.80% ± 1.11 and 1.54% ± 1.02, respectively. Their corresponding mean chest-wall volumes for optimization (Chst_opt) were 90.65% ± 3.19 and 2.28% ± 2.99, respectively. For left-sided cases, the mean heart dose received was 4.61 Gy ± 1.76 and 5.18 Gy ± 1.55 for intact breast plans and that for chest-wall plans, respectively. The mean ipsilateral lung volume receiving 20 Gy of the prescribed dose was 12.22% ± 3.86 and 13.19% ± 3.74 for intact breast plans and chest-wall plans, respectively. For the Brst_opt and Chst_opt dose metrics were calculated; the mean homogeneity index (HI) was 0.14 ± 0.03 and 0.15 ± 0.04, mean uniformity index (UI) was 1.09 ± 0.03 and 1.11 ± 0.03, and mean conformity index (CI) were 0.92 ± 0.04 and 0.91 ± 0.04, respectively. Conclusions: The dosimetric evaluation shows a good dose distribution in the target volumes with minimal doses to the organs at risk (OAR). Assessment of the current data affirms the clinical usefulness of the facility-adopted protocol in achieving quality treatment plans for intact breast and chest-wall irradiations. The establishment of plan acceptability criteria will help achieve improved overall treatment outcomes.

Intensity-Modulated Proton Therapy (IMPT) Offered Advantageous Dosimetry Compared to Volumetric Arc Therapy (VMAT) or Helical Tomotherapy (HT) in Patients with Synchronous Bilateral Breast Cancer

Radiotherapy of synchronous bilateral breast cancer poses some technical challenges with regards to dose coverage and sparing of organs at risk (OAR). In this study, we aimed to evaluate dosimetric characteristics of 3 different techniques, IMPT vs photon (VMAT and HT). We hypothesized that IMPT would result in lower doses to organs at risk, as compared to the other 2 techniques. A total of 10 patients with synchronous bilateral breast cancer who were treated with VMAT at our institution were retrospectively analyzed. Clinical target volume (CTV) included chest wall and regional nodes (supraclavicular fossa and internal mammary chain) and prescription dose was 40.05 Gy in 15 daily fractions. HT and IMPT plans were generated for each patient. Dose-volume statistics, including planning target volume (PTV) coverage and dose to OAR: lungs, heart, thyroid, spinal cord, brachial plexus and esophagus, were compared between modalities using a paired T-test. Mean age of patients was 61 years (43-84). Majority of the patients (80%) were ER+ PR+ and HER2-. 40% of patients underwent breast reconstruction following surgery. All 3 techniques provided adequate target volume distribution and OAR sparing. Compared to VMAT and HT plans, IMPT had better heart and lung sparing effects, resulting in lower mean and V25 Gy heart dose; mean, V20 Gy and V5 Gy lung dose (p<0.0001). There was no significant difference in VMAT and HT plans for mean heart and lung dose. VMAT plans showed significantly lower V25 Gy heart dose on average (p = 0.04). V5 Gy lung dose was slightly lower in HT compared to VMAT plans, approaching statistical significance (p = 0.08). PTV coverage was adequate for all 3 techniques. All techniques fulfilled cord, esophagus, thyroid and brachial plexus constraints. IMPT plans showed significantly better OAR sparing compared to photon techniques. All 3 techniques met OAR constraints, and resulted in adequate target volume coverage. As IMPT is significantly more costly than VMAT or HT techniques, appropriate patient selection is important to deliver treatment in the most resource-effective manner for patients who would derive the most benefit, for example those with young age or existing heart or lung comorbidities.

Feasibility of hypofractionated pelvic radiotherapy with parametrial and nodal simultaneous integrated boost for locally advanced cervical cancers: dummy run for the HYACINCT trial

Objectives The HYACINCT trial will investigate the role of dose-adapted hypofractionated pelvic radiotherapy in patients with locally advanced cervical cancer who are ineligible for cisplatin. This dummy run evaluated the feasibility of the protocol treatment planning objectives using intensity-modulated radiotherapy (IMRT) and volumetric arc therapy (VMAT). Material and Methods The HYACINCT protocol defines a set of guidelines for image acquisition, target and organ delineation, and treatment planning objectives. Fifteen dummy cases were prepared, five each for three levels of dose requirements: 40 Gy without boost, and with boost to 45 Gy and to 48 Gy. IMRT and VMAT plans were prepared for each case, evaluated and assigned penalty and compliance scores according to planning objectives, and subjected to quality control. IMRT and VMAT plans were compared in terms of treatment plan quality (target coverage, penalty, and compliance scores), and treatment delivery. Tumor extent (T-stage, T-score), nodal status, and PTV volumes (in cc) were examined as potential determinants of penalty and compliance scores. Results IMRT was able to meet the planning objectives for all but one case; and VMAT, for all cases. All plans passed the quality control check. IMRT and VMAT were equivalent in terms of target coverage and penalty and compliance scores, but the latter was associated with better treatment delivery. T-score was a determinant for the penalty score. Conclusion The HYACINCT radiotherapy protocol is feasible with either IMRT or VMAT. VMAT may be beneficial in more extensive cases, as measured by the T-score. Trial Registration Number NCT05210270

Secondary cancer risk assessment after high-risk and intermediate-risk prostate cancer radiotherapy in Senegal

Purpose: This study aims at evaluating the excess absolute risk (EAR) of cancer in thirty patients with high and intermediate risks of prostate cancer based on the Amico’s classification, who received a three-dimensional conformal radiotherapy (3DCRT) or a modulated volumetric arc therapy (VMAT) with 6 MV photons energy. Materials and Methods: VMAT plans were performed in simultaneous integrated boost, with 76 Gy to prostate and 56 Gy to pelvic lymph node and seminal vesicle. 3DCRT planning was realized in two stages with prostate, seminal vesicles, and pelvic lymph node receiving 46 Gy, in the first stage, and in the second stage, prostate prescribed at 28 Gy. The EAR was assessed using the Schneider concept based on the equivalent dose for a given organ (OED). Thus, the EAR of the rectum, bladder, pelvic bone and healthy pelvic tissues were calculated and compared on the basis of the Mechanistic, Exponential Linear, Plateau and Sarcoma specific Mechanistic models. Results: The EAR in the rectum were found to be higher in 3DCRT than in VMAT. The EAR values ranged from 3.98-5.37 for the rectum, and from 1.05-3.76 for the bladder depending on the model used. Conclusion: The overall EARs analysis for both radiation modalities indicated that the risk of induction of carcinoma in the rectum was higher with 3DCRT, compared with VMAT. However, it would be necessary for validation of predicted models, to conduct prospective clinal trials with a larger patient cohort

Dosimetric Comparison of Unmatched Flattening Filter-free and Flattened Beams in Volumetric Arc Therapy Plans for Head-and-neck Cancer.

Conventionally, the fattened beam is being used in radiotherapy for routine clinical cases even after introduction of intensity-modulated radiotherapy with incorporation of multi-leaf collimator system. With the removal of the flattening filter (FF) from the beam's path average energy of the photon gets reduced resulting in reduced scatter, reduction in treatment time, and reduced neutron contamination for high-energy beam and ultimately resulting in treatment plan quality deviations. This study aims to investigate the usefulness of the FF-free (FFF) beam for routine head-and-neck cancer (HNC) cases treated with volumetric arc therapy (VMAT) and dosimetrically compares the result with the FF beam. In this study, 20 patients treated on HalcyonTM (unmatched 6 megavoltage [6MV] FFF beam) medical linear accelerator with VMAT of different HNC selected and for comparison with 6MV FF beam, 20 equivalent treatment plans are created for TruebeamTM configuration and the plans have been evaluated for target coverage, doses to the organ at risk (OAR), and other dose quality indices. Comparable target coverage, doses to OARs except for rest right parotid (P = 0.02) between 6MV FFF beam and 6MV FF beam is observed. Insignificant differences in conformity index, homogeneity index, and gradient index have been observed. Higher monitor unit (MU) (P ≤ 0.001) and lesser beam on time (BOT) (P = 0.003) have been observed in 6MV FFF. 6MV FFF beam provides comparable target coverage and improved dose-sparing effect to most of the OARs. 6MV FFF beam has lesser BOT, but on the other hand number of MUs is higher as compared to 6MV-FF plans.

Can Proton Linear Accelerator Beams and Minibeams Achieve Superior Plan Quality over Cyclotron-Generated Proton Beams and Photons in the Treatment of Multiple Brain Metastases?

<h3>Purpose/Objective(s)</h3> To compare plan quality and delivery timing among photon Volumetric Arc Therapy (VMAT), Intensity-Modulated Proton Therapy using cyclotron-generated proton beams (CPB), linear accelerator proton beams (LPB), and linear accelerator proton minibeams (LPMB). <h3>Materials/Methods</h3> Thirty-five brain lesions from twenty patients were planned using CPBs and compared against LPBs and LPMBs and VMAT. All proton plans were optimized with multi-field optimization technique using the Monte Carlo algorithm. Benchmarked on the photon plans, dose coverage to each lesion for each proton plan was set to 99% of the GTV receiving the prescription (Rx) dose for all plans. Conformity index (CI), gradient index (GI), V_12Gy, V_4.5Gy and mean dose of the brain were compared. To achieve similar PTV dose coverage to photons, ±2 mm setup uncertainty and ±2% range uncertainty were included in robust evaluation using V_100%Rx > 95% of the GTV for proton plans. Additionally, the plan delivery timing was assessed based on the proton modalities' energy switching and spot scanning times. <h3>Results</h3> All metrics of CI, GI, V_12Gy, V_4.5Gy, and mean brain dose for VMAT photon and three different proton plans are listed in Table 1. When compared to CPB generated plans, CI and GI were significantly better for the LPB and LPMB plans with a mean CI of 1.7 ± 0.5, 1.57 ± 0.4, and 1.4 ± 0.6 and a mean GI of 4.64 ± 1.48, 3.7 ± 1.1 and 2.8 ± 0.7, respectively. In comparison, mean CI and GI from photon VMAT plans were 2 ± 1.2, 4.7 ± 1.4. All proton plans achieved better V_4.5Gy than photon VMAT plans. LPBs reduced the mean brain dose by 17% compared to the CPB plans, and LPMB plans reduced the mean brain dose by 44%. While all plans had V_100%Rx of the GTV > 99% in the nominal scenario, in the voxel-wise worst scenario, 97.1%, 92.8% and 84.2% of the lesions had V_100%Rx > 95% for CPB, LPB, and LPMB, respectively, and in the worst-case scenario, 97.1%, 94.3% and 78.6% of the plans showed V_100%Rx > 95% among all lesions. The LPB energy switching time (5 ms) enables a rapid beam delivery, 58% faster on average than for CPB plans. LPMB beam delivery time can be further reduced by spot reduction planning (SRP) with equal plan quality. <h3>Conclusion</h3> We successfully quantified plan quality and evaluated robustness for CPBs, LPBs and LPMBs for brain metastases. The LPB and LPMB stand as an excellent alternative to CPB therapy and can significantly increase the preservation of normal tissue while ensuring fast delivery time.

Dosimetric evaluation of adult and paediatric brain tumours planned using mask-based cobalt-60 fractionated stereotactic radiotherapy compared to linear accelerator-based volumetric modulated arc therapy.

We conducted a study to evaluate the dosimetric feasibility of mask-based cobalt-60 fractionated stereotactic radiotherapy (mcfSRT) with the Leksell Gamma Knife® Icon™ device. Eleven patients with intracranial tumours were selected for this dosimetry study. These patients, previously treated with volumetric arc therapy (VMAT), were re-planned using mcfSRT. Target volume coverage, conformity/gradient indices, doses to organs at risk and treatment times were compared between the mcfSRT and VMAT plans. Two-sided paired Wilcoxon signed-rank test was used to compare differences between the two plans. The V95 for PTV was similar between fractionated mcfSRT and VMAT (P = 0.47). The conformity index and gradient indices were 0.9 and 3.3, respectively, for mcfSRT compared to 0.7 and 4.2, respectively, for VMAT (P < 0.001 and 0.004, respectively). The radiation exposure to normal brain was lower for mcfSRT across V10, V25 and V50 compared with VMAT (P = 0.007, <0.001 and <0.001, respectively). The median D0.1cc for optic nerve and chiasm as well as the median D50 to the hippocampi were lower for mcfSRT compared to VMAT. Median beam-on time for mcfSRT was 9.7 min per fraction, compared to 0.9 min for VMAT (P = 0.002). mcfSRT plans achieve equivalent target volume coverage, improved conformity and gradient indices, and reduced radiation doses to organs at risk as compared with VMAT plans. These results suggest superior dosimetric parameters for mcfSRT plans and can form the basis for future prospective studies.

Intra-arc binary collimation with dynamic axes trajectory optimization for the SRS treatment of multiple metastases with multiple prescriptions.

This work generates multi-metastases cranial stereotactic radiosurgery/radiotherapy (SRS/SRT) plans using a novel treatment planning technique in which dynamic couch, collimator, and gantry trajectories are used with periodic binary target collimation. The performance of this planning technique is evaluated against conventional volumetric arc therapy (VMAT) planning in terms of various dose and plan quality metrics. A 3D cost space (referred to herein as the combined optimization of dynamic axes or CODA cube) was calculated based on an overlap between targets and organs-at-risk (OARs) and uncollimated areas between targets (island blocking) for all combinations of couch, gantry, and collimator angles. Gradient descent through the cube was applied to determine dynamic trajectories. At each control point (CP), each target can either be conformally treated or blocked by the multi-leaf collimator (referred to as intra-arc binary collimation, iABC). Simulated annealing was used to optimize the collimation patterns throughout the arcs as well as the monitor units (MUs) delivered at each CP. Seven previously treated VMAT plans were selected for comparison against the CODA-iABC planning technique. Two CODA-iABC plans were developed: a single gantry arc plan and a plan with one gantry arc and two couch arcs. Plan quality comparison metrics included maximum and mean dose to OARs (brainstem, chiasm, optic nerves, eyes, and lenses), the volume of normal brain receiving 12Gy (V12Gy), total MUs, target conformity, and dose-gradient index. Treatment plans generated with 1-arc CODA-iABC plans delivered an average of 21% and 30% higher maximum and mean doses to brainstem, respectively, when compared to VMAT plans. Treatment plans generated with 3-arc CODA-iABC used an average of 24% fewer MUs and resulted in an average reduction of 48% maximum dose and 50% mean dose to the OARs, when compared to VMAT. Target conformity values were worse in both CODA-iABC plans than VMAT by an average of 35% and 15%, respectively. There are no significant differences in V12Gy for all three planning techniques; however, 3-arc CODA-iABC is more effective at reducing dose to normal brain in the low-dose region (<12Gy). CODA-iABC is a novel planning technique that has been developed to automatically generate patient-specific multi-axis trajectories for multiple metastases cranial SRS/SRT. This work has demonstrated the feasibility of planning with this novel method. The 1-arc CODA-iABC planning technique is slightly dosimetric inferior to VMAT. With an increased sampling of a three-dimensional CODA cube by using a 3-arc CODA-iABC technique, there was improved total dose sparing to all the OARs and increased MU efficiency, but with a cost in target conformity, when compared to VMAT.

Dosimetric comparison of normal breathing and deep inspiration breath hold technique for synchronous bilateral breast cancer using 6MV flattened beam and flattening filter free beam.

BackgroundThe present study was to investigate the usefulness of deep inspiration breath hold (DIBH) in bilateral breast patients using 6MV flattened beam (FB) and flattening filter free beam (FFFB).Materials and methodsTwenty bilateral breast cancer patients were simulated, using left breast patients treated with DIBH technique. CT scans were performed in the normal breathing (NB) and DIBH method. Three-dimensional conformal radiotherapy (3DCRT) and volumetric arc therapy (VMAT) plans were generated.ResultsIn our study the best organ at risk (OAR) sparing is achieved in the 3DCRT DIBH plan with adequate PTV coverage (V95 ≥ 47.5 Gy) as compared to 6MV FB and FFFB VMAT DIBH plans. The DIBH scan plan reduces the heart mean dose significantly at the rate of 49% in 3DCRT (p = 0.00) and 22% in VMAT (p = 0.010). Similarly, the DIBH scan plan produces lesser common lung mean dose of 18% in 3DCRT (p = 0.011) and 8% in VMAT (0.007) as compared to the NB scan. The conformity index is much better in VMAT FB (1.04 ± 0.04 vs. 1.04 ± 0.05), p =1.00 and VMAT FFFB (1.04 ± 0.05 vs. 1 ± 0.24, p = 0.345) plans as compared to 3DCRT (1.63 ± 0.2 vs. 1.47 ± 0.28, p = 0.002). The homogeneity index of all the plans is less than 0.15. The global dmax is more in VMAT FFFB DIBH plan (113.7%). The maximum MU noted in the NB scan plan (478 vs. 477MU, 1366 vs. 1299 MU and 1853 vs. 1788 MU for 3DCRT, VMAT FB and VMAT FFFB technique as compared to DIBH scan.ConclusionWe recommend that the use of DIBH techniques for bilateral breast cancer patients significantly reduces the radiation doses to OARs in both 3DCRT and VMAT plans.

Peripheral Lymphocyte Counts and Lymphocyte-Related Inflammation Indicators During Radiotherapy for Pelvic Malignancies: Temporal Characterization and Dosimetric Predictors.

Purpose: To identify the dosimetric predictors of lymphocytopenia and retrospectively analyze the changing trend of peripheral lymphocyte counts and lymphocyte-related inflammatory indicators in patients with simple pelvic radiotherapy. Methods and Materials: We retrospectively reviewed the clinical data of 188 patients with pelvic malignancies undergoing pelvic radiotherapy. The absolute count of neutrophils, lymphocytes, monocytes, and platelets at each time point was collected, and lymphocyte-related inflammation indicators were obtained, including neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), platelet-to-lymphocyte ratio (PLR), and the systemic immune-inflammation index (SII). The total pelvic bone (TPB) and the body within the 5 Gy coverage were retrospectively delineated for each patient. Dose-volume histograms corresponding to the delivered volumetric arc therapy plan were used to assess the dose volumes received by the TPB and body. A paired-samples t-test or Wilcoxon signed-rank test for matched pairs was applied for pairwise comparisons. We also established a stepwise multiple linear regression model for the peripheral lymphocyte count (PLC) value at the end of radiotherapy. Results: The PLC and lymphocyte-related inflammatory indicators changed significantly after the start of radiotherapy and persisted for 3-6 months after radiotherapy. The nadirs of PLC occurred at RT-End, and the PLC was still significantly lower than the baseline value at RT-3 months and RT-6 months. NLR, PLR, and SII at RT-End are about 3.5 times the value at RT-Baseline, while LMR is one-fourth of the basal value. In a further multiple stepwise linear regression analysis, the basal PLC (β = 0.156, p ≤ .001), gender (β = 0.096, p = .005), and TPB-V5 (β = −0.016, p ≤ .001) turned out to be the predictor of the absolute value of lymphocytes at the end of radiotherapy. Conclusions: The impact of pelvic radiotherapy on PLC and lymphocyte-related inflammatory indicators is considerable and long-lasting. Minimizing pelvic bone radiation exposure dose (5 Gy) may help to avoid severe cases of lymphocytopenia.

Comparative performance analysis of 2D and 3D gamma metrics for patient specific QA in VMAT using Octavius 4D with 2D-Array 1500.

Gamma pass percentage (GPP) is the predominant metric used for Patient Specific Quality Assurance (PSQA) in radiation therapy. The dimensionality of the measurement geometry in PSQA has evolved from 2D planar to 3D planar, and presently to state-of-the-art 3D volumetric geometry. We aim to critically examine the performance of the three-dimensional gammas vis-à-vis the older gamma metrics of lower dimensionality to determine their mutual fungibility in PSQA, using clinically approved Volumetric Arc Therapy (VMAT) plans. Gamma pass percentages derived from PSQA for VMAT plans using Octavius 4D phantom with 2D-Array 1500 and its proprietary software were recorded. 2D planar, 3D planar, and 3D volumetric gamma pass percentages were retrospectively extracted for multiple treatment plans at three sites, using three acceptance limits, and for two modes of normalization. The differences in mean pass percentages, and the pairwise correlation between geometries were calculated within limits of statistical significance. A significant increase in mean pass rates was observed from 2D planar to 3D planar geometries. The difference was less pronounced from 3D planar to 3D volumetric. 2D planar v/s 3D planar showed a significant degree of correlation among themselves, which was not seen against most of the 3D volumetric pass rates. The mean gamma pass rates show conclusive evidence of the benefits of shifting from 2D planar to higher dimensions measurement geometries, but the benefits of using 3D volumetric compared to 3D planar is not always unequivocal. The correlations show mixed results regarding the interdependence of pass percentages at different geometries.

Stereotactic Body Radiotherapy (SBRT) for Multiple Synchronous Oligometastases (< 5) Lung Lesions: Early Clinical Outcomes

Lung cancer patients with multiple oligometastases (< 5) lesions with associated co-morbidities may not retain their treatment position for the extended Stereotactic Body Radiotherapy (SBRT) treatment times with individual isocenters for each lesion due to distress or shortness of breath. SBRT of multiple lung lesions synchronously (in one course) using a single-isocenter volumetric arc therapy (VMAT) plan with flattening filter free (FFF) beam or tomotherapy will shorten treatment courses, improve patient comfort by reducing treatment time, and improve clinic efficiency. We report our early clinical results of treating oligometastatic lung disease with synchronous single-course lung SBRT.Fifty-six patients with multiple oligometastatic lung lesions (two n = 51, three n = 4, five n = 1, total 119 lesions) were treated synchronously with either highly conformal single-isocenter non-coplanar VMAT-SBRT (49 patients) or tomotherapy (7 patients). The most common prescriptions were 50-55 Gy/5 fractions or 54 Gy/3 fractions prescribed to 70-80% isodose line. The VMAT-SBRT plans were calculated with an advanced dose calculation algorithm for 6 MV-FFF beam and tomotherapy used superposition/convolution algorithm (with 6MV) for heterogeneity corrections. All plans were evaluated with RTOG-0618/0813 criteria. Treatments were delivered every other day with daily cone beam-CT/MVCT guidance. Highly conformal SBRT treatments were delivered in less than 10 min per fraction, on average. Local control rates, radiation-induced pneumonitis and rib toxicity were determined. Mean follow up interval was 11.4 months (range, 2.1 to 35.3 months).All plans met RTOG-0618/0813 requirements for target(s) coverage, dose to organs at risk including lung and ribs and all patients tolerated SBRT. Six patients died before follow up and five were lost to follow up. Five patients have initial post-treatment imaging pending. Of forty evaluable patients, all achieved complete response to SBRT in all lesions. However, 18 patients developed distant metastases. During the follow-up interval, almost 50% of the patients developed radiographic changes that were asymptomatic in nature, however no patient developed grade+2 (or higher) pneumonitis, had rib fracture or developed chest wall pain.A single course of lung SBRT to synchronous multiple lung lesions using a single-isocenter VMAT plan or tomotherapy is feasible, fast, safe and highly effective, with promising early local control rates and no adverse pulmonary side effects or rib toxicity. Although 18 patients developed distant metastases, the local control achieved in the treated lesions could preserve the patient's quality of life or delay systemic therapy even in these patients. Longer clinical follow up is warranted and planned.L. Downes: None. D. Pokhrel: None. L. Critchfield: None. M.E. Bernard: None. M.E. Randall: None. R.C. McGarry: None.

Correlation of tumour and treatment characteristics to dose received by cochlea in volumetric arc therapy.

This is a radiation field simulation study using CT images designed to see the cochlear dosimetry and its correlation with tumour and treatment characteristics during radiotherapy for head and neck cancers (HNC) for identifying the factors associated with a higher dose delivered to the cochlea. From 2018 to 2020, 80 patients with HNC underwent volumetric arc therapy (VMAT) to a dose of 66-70Gy at 2Gy per fraction with bilateral cochlea contoured for VMAT optimization as an organ at risk. Minimum, mean and maximum planned radiation dose to the cochlea based on tumour and treatment characteristics and dose-volume histogram variables of VMAT plans were analysed. Mean (standard deviation, SD) cochlear volume was 0.14(0.06) cm3 with maximum and mean planned doses of 10.3 (SD = 11.6) Gy and 8.5 (SD = 9.8) Gy, respectively. We found a statistically significant correlation between mean dose received by bilateral cochlea (P-0.000, rright-0.84, rleft-0.78, rmidline-0.92). Tumours of the paranasal sinuses, and the parotids and more advanced T stages were associated with a higher mean dose to cochlea but was not significant statistically. The dose received by the 95% target nodal volume (D95%) showed a significant correlation with the cochlear mean dose (P-0.000, rright-0.85, rleft-0.77, rmidline-0.93) CONCLUSION: With VMAT we have achieved a better sparing of cochlea. The mean dose to the cochlea of one side significantly differed from the other side in patients with lateralized cancers. D95% of nodal volume also showed a significant correlation with the cochlear mean dose.

Comparison between two different patient specific QA systems for detection of errors introduced to VMAT plans

Volumetric Arc Therapy (VMAT) technique involves varying the gantry angle, MLC position, and the dose rate as the radiation is delivered. To ensure the integrity of VMAT plans, each plan must be verified through a quality assurance (QA) process, which is known as patient-specific QA. The quality assurance system should detect the planning and machine errors. This study aims to investigate the sensitivity of two different patient specific QA systems to detect errors in VMAT plans.

Volumetric arc therapy: A viable option for right-sided breast with comprehensive regional nodal irradiation in conjunction with deep inspiration breath hold

Abstract Purpose Deep inspiration breath hold (DIBH) is an innovative technique routinely used for left-sided breast radiotherapy to significantly reduce harmful dose to the heart and ipsilateral lung. Currently, there is scant literature exploring DIBH for right-sided whole breast and regional nodal irradiation (WB & RNI). The purpose of this study is to examine if DIBH produces a clinically significant reduction in organ at risk (OAR) dose for right-sided WB + RNI, whilst comparatively analysing the use of volumetric arc therapy (VMAT) versus tangential inverse modulated radiotherapy (t-IMRT). Methods and Materials Ten patients, previously treated for left sided breast cancer (with a FB and DIBH CT scan), were selected from our database to be retrospectively replanned to the right breast and nodal regions. Planning target volumes (PTV) were marked to include the whole right breast and regional nodes, encompassing the supraclavicular fossa (SCF) and internal mammary nodes (IMN). PTVs and OARs were contoured on the Pinnacle workstation according to the Radiation Therapy Oncology Group (RTOG) guidelines. VMAT and t-IMRT plans were generated to a prescribed dose of 50 Gy in 25 fractions on both the DIBH and FB data sets for dosimetric analysis. Results Coverage of the right breast (mean, D95%) and SCF (D95%) were significantly improved with VMAT in comparison to t-IMRT, with no statistically significant variation on the IMN PTV (D95%). The use of DIBH did not impact PTV coverage compared with FB. VMAT reduced dose to the ipsilateral lung (mean, V20Gy), combined lungs (mean, V20Gy) and liver (D2cc); conversely dose to the heart (mean), left lung (mean, V5Gy) and contralateral breast (mean) were increased. For both techniques DIBH significantly improved dose to OARs including the ipsilateral lung (mean, V20Gy, V5Gy), total lung (mean, V20Gy), heart (mean, V25Gy) and liver (D2cc) when compared to FB. Conclusion DIBH could be considered for patients treated with right-sided WB and RNI due to a significant decrease in heart, ipsilateral lung, total lung and liver doses. VMAT significantly improves PTV coverage over t-IMRT whilst reducing dose to the ipsilateral lung and liver, albeit to the detriment of the left lung, contralateral breast and heart. The increase in heart dose can be mitigated by the use of DIBH. We recommend if VMAT is utilised for superior target volume coverage, DIBH should also be implemented to reduce OAR toxicity.

Proton Beam Therapy in the Treatment of Periorbital Malignancies.

PurposePeriorbital tumor location presents a significant challenge with 3-dimensional conformal radiation therapy or intensity modulated radiation therapy due to high tumor dose needed in the setting of close proximity to orbital structures with lower tolerance. Proton beam therapy (PBT) is felt to be an effective modality in such cases due to its sharp dose gradient.Materials and MethodsWe reviewed our institutional PBT registry and identified 17 patients with tumor epicenters within 2 cm of the eye and optic apparatus treated with passive scatter PBT with comparison volumetric arc therapy plans available. Maximum and mean doses to organs at risk of interest, including optic nerves, optic chiasm, lens, eye ball, pituitary, cochlea, lacrimal gland, and surrounding brain, were compared using the paired Wilcoxon signed rank test. Overall survival was determined using the Kaplan-Meier method.ResultsMedian age was 67. Median follow-up was 19.7 months. Fourteen patients underwent upfront resection and received postoperative radiation and 3 received definitive radiation. One patient received elective neck radiation, 2 underwent reirradiation, and 3 had concurrent chemotherapy. There was a statistically significant reduction in mean dose to the optic nerves and chiasm, brain, pituitary gland, lacrimal glands, and cochlea as well as in the maximum dose to the optic nerves and chiasm, pituitary gland, lacrimal glands, and cochlea with PBT. The 18-month cumulative incidence of local failure was 19.1% and 1-year overall survival was 80.9%.ConclusionProton beam therapy resulted in significant dose reductions to several periorbital and optic structures compared with volumetric arc therapy. Proton beam therapy appears to be the optimal radiation modality in such cases to minimize risk of toxicity to periorbital organs at risk.

The influence of small field output factors simulated uncertainties on the calculated dose in VMAT plans for brain metastases: a multicentre study.

This multicentric study was carried out to investigate the impact of small field output factors (OFs) inaccuracies on the calculated dose in volumetric arctherapy (VMAT) radiosurgery brain plans. Nine centres, realised the same five VMAT plans with common planning rules and their specific clinical equipment Linac/treatment planning system commissioned with their OFs measured values (OFbaseline). In order to simulate OFs errors, two new OFs sets were generated for each centre by changing only the OFs values of the smallest field sizes (from 3.2 × 3.2 cm2 to 1 × 1 cm2) with well-defined amounts (positive and negative). Consequently, two virtual machines for each centre were recommissioned using the new OFs and the percentage dose differences ΔD (%) between the baseline plans and the same plans recalculated using the incremented (OFup) and decremented (OFdown) values were evaluated. The ΔD (%) were analysed in terms of planning target volume (PTV) coverage and organs at risk (OARs) sparing at selected dose/volume points. The plans recalculated with OFdown sets resulted in higher variation of doses than baseline within 1.6 and 3.4% to PTVs and OARs respectively; while the plans with OFup sets resulted in lower variation within 1.3% to both PTVs and OARs. Our analysis highlights that OFs variations affect calculated dose depending on the algorithm and on the delivery mode (field jaw/MLC-defined). The Monte Carlo (MC) algorithm resulted significantly more sensitive to OFs variations than all of the other algorithms. The aim of our study was to evaluate how small fields OFs inaccuracies can affect the dose calculation in VMAT brain radiosurgery treatments plans. It was observed that simulated OFs errors, return dosimetric calculation accuracies within the 3% between concurrent plans analysed in terms of percentage dose differences at selected dose/volume points of the PTV coverage and OARs sparing. First multicentre study involving different Planning/Linacs about undetectable errors in commissioning output factor for small fields.