IMRT Delivery Research Articles

Is the IROC H&N credentialing phantom an effective surrogate for different anatomical sites?: Using IROC's H&N phantom for various sites

PURPOSEThe IROC head and neck phantom is used to credential institutions for IMRT delivery for all anatomical sites where delivery of modulated therapy is a primary challenge. This study evaluated how appropriate the use of this phantom is for varied clinical anatomy by evaluating how closely the IROC head and neck phantom described clinical dose errors from beam modeling compared to various anatomical sites. METHODSThe MLC offset, transmission, PDD and seven additional beam modeling parameters for a Varian accelerator were modified in RayStation to match community data at the 2.5, 25, 50, 75 and 97.5 percentile levels. Modifications were evaluated on 25 H&N phantom cases and 25 clinical cases (H&N, prostate, lung, mesothelioma, and brain), generating 2,000 plan perturbations. Differences in mean dose delivered to clinical target volumes (CTV) and organs at risk (OAR) were compared between phantom and clinical plans to assess the relationship between dose deviations in phantom versus clinical CTVs, and as a function of 18 different complexity metrics. RESULTSPerturbations to MLC offset and transmission parameters demonstrated the greatest impact on dose accuracy for phantom and clinical plans (for all anatomic sites). The phantom demonstrated equivalent or greater sensitivity to these parameter perturbations when compared to clinical sites, largely aligning with treatment complexity. The mean MLC Gap best described the impact of errors in TPS beam modeling parameters in phantoms plan and clinical plans from various anatomical sites. CONCLUSIONWhen compared across various anatomical sites, the IROC H&N credentialing phantom exhibited similar or greater sensitivity to errors in the treatment planning system. As such, it is a suitable surrogate device for assessing institutional performance across various anatomical sites. If an institution successfully irradiates the phantom, that result confers confidence that IMRT to a wide range of anatomical sites can be successfully delivered by the institution.

Acute radiation morbidities and dosimetric evaluation of DARS structures: Results from the phase III randomized SWOAR trial.

TPS149 Background: The SWOAR is a phase III trial (ClinicalTrials.gov ID NCT05187091) evaluating sparing of dysphagia/aspiration related structures (DARS) & submandibular gland by IMRT. Methods: Patients with T1-4, N0-3, M0 of oropharynx, larynx and hypopharynx treated with radical RT were randomized to arm A (standard IMRT) or arm B (DARS IMRT) in 1:1 manner. Treatment allocation was done based on T stage, concurrent chemotherapy use (weekly 40mg/m2) & subsite. A10-point improvement in MD Anderson Dysphagia Inventory (MDADI) composite score (primary end point of study) at 6 months post RT with SD of 17, power as 90% and two-sided alpha of 5% estimated sample size. SIB IMRT delivered dose of 66Gy (gross disease+0.5cm), 54Gy (gross disease+1cms+regional lymphatics) in 30 fractions. Acute radiation morbidities were scored by RTOG scoring criteria. Aspiration prevention assessment was done by PAS measured by FEES. Results: A total of 166 patients till date have been enrolled, 81 in Arm A & 85 in Arm B. Median age was 58 years, 73.4% had oropharyngeal primary, 89% had stage III-IV & received concurrent chemotherapy. Median composite MDADI scores pre-RT in Arm A was 70.5 (IQR 56.8-75.8) & 69.5 (56.8-75.8) in arm B. Post-RT median score dropped to 54.2 (48.8-60) in arm A & 54.8 (51.6-65.3) in arm B. Reduction in MDADI score pre & post RT in arm A was median 11.1 (0-21) & arm B was 7.9 (0-20) (p=0.28). Pre RT-PAS score was similar in both arms 1 (IOR 1-2), post-RT PAS in arm A was 1 (1-2) & arm B was 1 (1-1). Median of mean dose to SCM was 56.2Gy (46.8Gy-61.2Gy) vs 48.9Gy (36Gy-57.6Gy) p<0.003, MCM 58.5Gy (52.7Gy-63.1Gy) vs 56.2Gy (47.8-63.6) p=0.11, ICM 48.5Gy (46.8Gy-57.7Gy) vs 37.8Gy (26.5-62.4) p<0.001, base of tongue 60.5Gy (53.9Gy-64.3Gy) vs 53.9Gy (40.2Gy-62.4Gy) p=0.001,supraglottic larynx 57.7Gy (49.2Gy-64.4Gy) vs 60.5Gy (46.7-64.6) p=0.63, larynx 46.0Gy(42.4Gy-53.7Gy) vs 28.3Gy (21.5Gy-49Gy) p<0.001, cricopharyngeus 46.0Gy(43.6Gy-49.9Gy) vs 32.6Gy (27.3Gy-47Gy) p<0.001, esophageal inlet 44.6Gy (41.3Gy-47.9Gy) vs 27.2Gy (22.8Gy-39.1Gy) p<0.001, contralateral submandibular gland 52.8Gy (48.5Gy-57.2Gy) vs 40.4Gy (37.3-49.6) p<0.001, all arm A vs arm B respectively. Acute grade 3 occurred in 68.4% in arm A & 54.4% arm B, p=0.07. Acute grade 3 mucositis developed in 34.2% in arm A vs 16.7% arm B, p=0.009. Conclusions: Swallowing-sparing IMRT significantly reduced dose to contralateral submandibular gland & all the DARS structures (except middle constrictor muscle & supra glottic larynx). Dosimetric advantage gained by delivery of Swallowing-sparing IMRT resulted in significant reduction in development of acute grade III mucositis & showed a trend towards reduction in all acute grade III toxicities. Clinical trial information: NCT05187091 .

Prospective Randomized Trial Comparing 2 Devices for Deep Inspiration Breath Hold Management in Breast Radiation Therapy: Results of the BRAVEHeart Trial

Aims: The BRAVEHeart trial prospectively randomized left-sided breast cancer patients to one of two deep inspiration breath hold (DIBH) biofeedback devices: a novel chest surface tracking system and an abdominal block tracking system. The primary hypothesis was that the accuracy of chest tracking would be higher than that of abdominal tracking as the chest is a more direct surrogate of the breast target.Methods: Left-sided breast cancer patients were treated in DIBH with IMRT delivery. Patients were randomized to either the novel chest surface system or abdominal block system for active management of breath hold with visual feedback. On both trial arms the unallocated system monitored passively.239,296 cine EPID images were analyzed retrospectively to extract the chest wall position. Treatment accuracy was quantified as the deviation of the internal chest wall during treatment relative to the planned position from the digitally reconstructed radiograph. The correlation between motion of the external surrogate and internal chest wall was calculated per breath hold. Ease of use was assessed with questionnaires for both radiation therapists and patients and appointment length recorded.Results: Data from 26 participants were available for analysis. No difference was found in delivered treatment accuracy between arms. Across all patients and fractions, the median correlation between internal chest wall movement and external surrogate was 0.69 for the chest surface and 0.17 for the abdominal block. Patients found it easy to follow visual feedback from both systems. No difference was found in appointment length between arms.Conclusions: No statistical evidence was found for superior treatment accuracy, satisfaction or appointment length for the novel chest surface tracking device compared to the abdominal block system. During DIBH, the median per-breath hold correlation of internal chest wall movement to the motion of the chest surface was higher than the median correlation of the abdominal block to the chest surface.

Potential Dosimetric Predictors of Patient-Reported Quality of Life for Head and Neck Cancer Following Chemoradiation IMRT

This study aims to identify both acute and late patient patient-reported salivary quality of life outcomes in patients with head and neck cancer treated with chemoradiation therapy on a prospective trial. A cohort of 40 patients with head and neck cancers were included in the study. All patients underwent concurrent chemoradiation therapy using IMRT delivery (1 patient on one Linac, 24 patients on a different Linac, and 15 on a helical delivery machine). All patients were asked to complete the University of Washington Quality of Life (UOW-QOL) questionnaire at baseline, immediately after treatment, as well as at 1 month, 3 months, 6 months, 12 month and 18 months post-treatment. For the salivary quality of life (QOL) outcome scores, the possible responses were scored on a discreet scale of 100, 70, 30, and 0, with 100 as normal and 0 as dysfunctional. Dosimetric endpoints achieved based on the treatment plan, such as maximum/mean/minimum doses, V30 (percent volume receiving 30 Gy dose), and Dy (dose received to y percent volume) were collected for the bilateral salivary glands, bilateral temporomandibular joint and bilateral submandibular glands. The associations between these dosimetric parameters and the corresponding salivary QOL scores at each time point were analyzed. A Wilcoxon test was performed to identify any differences in the dosimetry and salivary QOL scores among the four different responses. At short-term follow-up including 1- and 6-month, the distribution of the mean dose received by the right parotid was significantly different between the patients that reported a salivary QOL score of 30 and those that reported 100, with p-values of 0.007 for the 1-month comparison and 0.006 for the 6-month comparison. This was also seen for the V30, with p-values of 0.027 for the 1-month comparison and 0.013 for the 6-month comparison. At 3 months, the maximum dose received by the left temporomandibular joint was significantly different between the patients that reported 30 and those that reported 70, with a p-value of 0.038. At 6 months, the average dose distribution of the right submandibular gland received between the patients that reported a score of 30 and 100 was also significantly different, with a p-value of 0.006. At the long-term follow-up time points of 12 and 18 months, no significant differences were found. The significant differences seen in the data suggest that the dosimetry may have effects on patient reported salivary QOL at short-term follow-up but not long-term. This provides a new perspective into how a patient's QOL over a period of time could be affected by the amount of dose to critical organs. These results also serve as the basis for further investigation into the actual delivered dose, which could differ from the planned dose due to daily anatomic changes over the course of head and neck radiotherapy delivery. These daily volumetric and dosimetric changes may guide early adaptive treatment to improve patient-reported QOL outcomes.

Fixed-Field IMRT for Cervix Carcinoma Patients on an MR-LINAC Platform: Dosimetric Feasibility and Challenges

To investigate the impact of MR-LINAC performance characteristics and inverse planning implementation on the feasibility of fixed-field IMRT for cervix carcinoma patients by benchmarking MR-LINAC plans against clinically used VMAT plans in a single institution study and multi-institutional treatment planning challenge. For 10 cervix cancer patients who had previously received Linac-based VMAT, new treatment plans were optimized for MR-LINAC IMRT using 6X FFF fixed fields with maximum available field size of 27.4 x 24.1 cm2. Dose optimization was performed on the clinically used planning CT and structure set. Prescribed dose was 48.6 Gy in 27 fractions for all patients with 6 patients receiving an additional integrated boost for a total of 58.05 Gy to involved nodes. Constraints were based on our institutional protocol as per Table 1. IMRT delivery time was limited to 20 min. Original clinically used VMAT plans were generated on Eclipse (Varian Medical System) using 3 to 4 arcs. For the multi-institutional planning challenge, the data set from a single patient was anonymized and shared to participants. Participants used a single MR-based Linac planning platform to generate a plan based on our institutional constraints, with maximum treatment time limited to 20 min. For all analyses, a paired samples t-test was used to compare the significance defined at p < 0.05. For MR-LINAC plans, the mean number of fields used was 23, mean number of segments 229, and the average estimated treatment delivery time was 17.3 minutes. MR-LINAC plans showed a significantly higher heterogeneity and dose to organs at risk compared to VMAT plans (Table 1). For the planning challenge, a total of 30 participants registered interest. Of this, seven plans were submitted to the challenge. On average, participants generated a plan that would be acceptable based on our institutional constraints (Table 1). However, the volumetric dose to bowel and pelvic bones were higher on MR-LINAC plans compared to the reference VMAT plan. MR-LINAC fixed-field IMRT for cervix cancer patients is feasible but system constraints and optimization implementation result in greater dose heterogeneity and worse organ-at-risk sparing compared to Linac based VMAT. Further research is needed to determine if potential reduction of treatment margins, allowed by better MRI soft-tissue visualization, will result in MR-LINAC IMRT superior to Linac VMAT.

Patient-specific quality assurance for IMRT delivery: A multicentre study

IMRT is a commonly used technique for radiotherapy. This is the first multicentre study conducted nationally for assessing the quality of IMRT delivery in participating centres by cross-checking local QA results with on-site measurements using novel MOSkin detector and a commercial two-dimensional planar detector. By using MOSkin, 40 measurement points were evaluated, with 18% (8 points) showing deviations of more than ±5% from the predicted dose, while 82% of the results were within the recommended tolerance level of ±5% for on-site and end-to-end IMRT/VMAT audits. Most centres passed the 95% points of the gamma criteria of 3%/3 mm for planar dose measurement, which is consistent with other similar studies and within the confidence limits recommended by AAPM TG119. By benchmarking their performance with the recommended tolerance levels for IMRT delivery, participating centres can improve their quality continuously. In conclusion, the study found that participating centres generally met the international guidelines for IMRT delivery standards.

Clinical implementation of a log file-based machine and patient QA system for IMRT and VMAT treatment plans

PurposeTo determine the error detection sensitivity of a commercial log file-based system (LINACWatch®, LW) for integration into clinical routine and to compare it with a measurement device (OCTAVIUS 4D, Oct4D) for IMRT and VMAT delivery QA. Materials and methods76 VMAT/IMRT plans (H&N, prostate, rectum and breast) preliminarily classified according to their Modulation Complexity Score (MCS) calculated by LW, were considered. Receiver Operating Characteristic (ROC) Curves were used to establish gamma criteria for LW. 12 plans (3 for each site) were intentionally modified in order to introduce delivery errors regarding MLC, jaws, collimator, gantry and MU (for a total set of 168 incorrect plans) and irradiated on Oct4D; the corresponding log files were analysed by LW. Each incorrect plan was compared to the error-free plan using γ-index analysis for MLC, jaws and MU errors investigation and Root-Mean-Square (RMS) values for gantry and collimator errors investigation. ResultsMCS ranges values were: 0.10–0.20 for H&N, 0.21–0.40 for prostate and rectum, 0.41–1.00 for breast. From ROC curves, the Gamma Passing Rate (GPR) thresholds were: 87%, 92%, 99% for H&N, prostate and rectum, and breast, respectively. The 1.5%/1.5 mm/local criteria were adopted for the γ-analysis. LW sensitivity in detecting the introduced errors was higher when compared to Oct4D: 48.5% vs 30.4% respectively. ConclusionsLW can be considered useful complement to phantom-based delivery QA of IMRT/VMAT plans. The MCS tool is effective in detecting over or under modulated plans prior to pre-treatment QA. However, rigorous and routinely machine QCs are recommended.

Determinants of Commercial Prices for Common Radiation Therapy Procedures

Using hospital-reported price data, we analyzed whether various market factors including radiation oncology practice consolidation were associated with higher commercial prices for radiation therapy (RT). We evaluated commercial prices paid by private insurers for 4 common RT procedures-Intensity modulated RT (IMRT) planning, IMRT delivery, 3DRT planning, and 3DRT delivery-reported among the 2,096 U.S. hospitals that deliver RT according to the Medicare Provider of Service (POS) file. To assess price variation within hospitals, we evaluated the ratio of the 90th percentile price to the 10th percentile price among different private insurers. To assess regional variation, we similarly compared median commercial prices at the 90th and 10th percentile hospitals in each Hospital Referral Region (HRR). We generated multivariable models to test the association of various hospital, health system, regional, and market factors on median hospital commercial prices. A total of 1,004 hospitals (47.9%) reported at least one commercial price for any of the 4 RT procedures considered in this study. National median commercial prices for IMRT planning and IMRT delivery were $4,073 (IQR: $2,242-$6,305) and $1,666 (IQR: $1,014-$2,619), respectively. Prices for 3D-RT planning and 3D-RT delivery were $2,824 (IQR: $1,339-$4,738) and $616 (IQR: $419-877), respectively. Within hospitals, the 90th percentile price paid by a private insurer was 2.3 to 2.5 times higher on average than the 10th percentile price, depending on the procedure. Within each HRR, the median price at the 90th percentile hospital was between 2.4 and 3.2 times higher than at the 10th percentile hospital. On multivariable analysis, higher prices were generally observed at hospitals with for-profit ownership, teaching status, and affiliation with large health systems. Levels of radiation oncology practice consolidation were not significantly associated with any prices. Commercial prices for common RT procedures vary by more than a factor of 2 depending on a patient's private insurer and hospital of choice. Higher prices were more likely to be found at for-profit hospitals, teaching hospitals, and hospitals affiliated with large health systems.

Intensity Modulated Radiotherapy on a Novel Ring Gantry-Based Linac with Integrated Dual PET-CT Imaging Systems: Dosimetric Plan Comparison and Initial Clinical Delivery Experience

<h3>Purpose/Objective(s)</h3> This study aims to report our initial clinical experience on using a new external-beam radiotherapy delivery system on a ring gantry with dual PET-CT imaging capabilities for IMRT treatments at different anatomical sites. The study also evaluates the system's plan quality compared to an existing ring gantry-based Linac. This new external-beam radiotherapy delivery system has the potential to be used for biology-guided radiotherapy. <h3>Materials/Methods</h3> We performed a single-institution retrospective review of patients treated on the machine since commissioning. The initial five patients treated to a thoracic site and five patients treated to a pelvic site were included in this study. The dose per fraction ranged from 1.8 to 3.0 Gy. The treatment plans for the machine used a 2-cm jaw size along the longitudinal direction and used the IMRT delivery mode. A 64-leaf binary MLC was used to modulate a flattening filter free 6-MV photon beam. A helical tomotherapy plan (HT plan) using a 2.5-cm jaw size was generated for each RFX plan to serve as the backup plan in clinical treatments. Dosimetric parameters used in institutional treatment protocols were compared between RFX plans and HT plans. Daily delivery records were reviewed, and actual beam-on time was compared between the two machine types. <h3>Results</h3> On average, 12 dosimetric parameters (range: 7 – 14) for critical organs and the primary PTV were used in each treatment plan as clinically relevant planning optimization parameters and were analyzed in this study. Among the critical organ dose parameters, 19 (22.4%) dosimetric parameters were lower by more than 10% in the study's plans compared to the HT plans, while 11 (12.9%) dosimetric parameters were higher by more than 10% in the study's plans compared to the HT plans. The other dosimetric parameters had less than 10% or no clinically relevant difference between the two plans. There was no statistically significant difference in integrated dose between the new machine and HT plans. All the plans were normalized so that the prescription dose covered 95% of the primary planning target volume (PTV). The average D_mean of the primary PTV were 103.5±1.1% and 102.6±0.8% of the prescription dose in the new external-beam radiotherapy delivery system and HT plans, respectively, and the average D(1%) of the primary PTV (dose covering the hottest 1% of the PTV) were 107.1±2.0% and 105.2%±1.6% in the new external-beam radiotherapy delivery system and HT plans, respectively (two-tailed p-value = 0.06 in the paired t-test). The beam-on time was not significantly different between the two machines. The average daily beam-on time was 438.8±151.2 seconds and 427.6±183.1 seconds with the new external-beam radiotherapy delivery system and HT systems, respectively (two-tailed p-value = 0.76 in the paired t-test). <h3>Conclusion</h3> Our initial clinical experience with the external-beam radiotherapy delivery system showed that image guided IMRT could be delivered to different anatomical sites with adequate clinical workflow efficiency. The new machine achieved clinically comparable treatment plan quality compared to helical tomotherapy. The beam-on time was comparable to that on helical tomotherapy.

Clinical Implementation of Single Visit Palliative Adaptive Radiotherapy without Prior CT Simulation

<h3>Purpose/Objective(s)</h3> Standard workflows of radiotherapy for metastatic disease palliation often involve multiple clinic visits and (long) waiting times. Fast palliation completed during a single clinic visit can be achieved by omitting a treatment planning CT scan and using available diagnostic imaging for treatment planning. The use of a diagnostic CT can be challenging due to differences in patient positioning and location of target and organs at risk (OAR), but adaptive treatment platforms provide possible solutions. We integrated a fast palliative workflow using diagnostic imaging for pre-planning, with subsequent on couch contour and plan adaption based on a synthetic CT derived from cone-beam CT imaging (CBCT), and report our clinical and dosimetric experiences. <h3>Materials/Methods</h3> An ethics-approved protocol for fast palliation (FAST-METS) was implemented in November 2021. Patients referred for palliative radiotherapy of painful bony metastatic disease of any primary site, available recent diagnostic imaging (<4 weeks) with visualization of both the metastasis and OAR were eligible. The workflow was as follows: 1) a radiation oncologist consulted the patient by telephone; 2) pre-planning on the diagnostic CT, using standard planning templates; 3) in-clinic consult at day of treatment, with obtaining informed consent for questionnaires; and 4) CBCT scan with on-couch adaptation of the target, OAR and treatment plan on the Linac. Different strategies were explored for beam setup including 6-12 fields IMRT and VMAT, in order to optimize dose calculation and beam-on times. Treatment times were collected from DICOM data and patient questionnaires. <h3>Results</h3> Data of the first eight patients are presented. The treated metastases were located in the lumbar (2) or thoracic (3) spine and pelvis (3). In all patients, the on-couch re-optimized plan was used for treatment, with a PTV_V95% coverage of ≥95%. In three patients, target and OAR volumes were adapted on-couch by the radiation oncologist. All patients completed their consult and treatment within 2 hours. Plan re-optimization time was <2 min. for IMRT (N=5), and 5-7 min. for VMAT plans (N=3). However, a 12-field IMRT setup was less preferable in three patients due to longer beam-on time compared to VMAT, and was addressed by using a 6-field IMRT setup. All 8 patients indicated satisfaction with the FAST-METS procedure. <h3>Conclusion</h3> A fast workflow for a single visit palliative IMRT delivery without dedicated planning CT scan was implemented for patients with bone metastases. All patients completed consultation and treatment within 2 hours on average, and indicated satisfaction with the procedure.

Total marrow irradiation (TMI): Addressing an unmet need in hematopoietic cell transplantation - a single institution experience review.

PurposeTMI utilizes IMRT to deliver organ sparing targeted radiotherapy in patients undergoing hematopoietic cell transplantation (HCT). TMI addresses an unmet need, specifically patients with refractory or relapsed (R/R) hematologic malignancies who have poor outcomes with standard HCT regimens and where attempts to improve outcomes by adding or dose escalating TBI are not possible due to increased toxicities. Over 500 patients have received TMI at this center. This review summarizes this experience including planning and delivery, clinical results, and future directions.MethodsPatients were treated on prospective allogeneic HCT trials using helical tomographic or VMAT IMRT delivery. Target structures included the bone/marrow only (TMI), or the addition of lymph nodes, and spleen (total marrow and lymphoid irradiation, TMLI). Total dose ranged from 12 to 20 Gy at 1.5-2.0 Gy fractions twice daily.ResultsTrials demonstrate engraftment in all patients and a low incidence of radiation related toxicities and extramedullary relapses. In R/R acute leukemia TMLI 20 Gy, etoposide, and cyclophosphamide (Cy) results in a 1-year non-relapse mortality (NRM) rate of 6% and 2-year overall survival (OS) of 48%; TMLI 12 Gy added to fludarabine (flu) and melphalan (mel) in older patients (≥ 60 years old) results in a NRM rate of 33% comparable to flu/mel alone, and 5-year OS of 42%; and TMLI 20 Gy/flu/Cy and post-transplant Cy (PTCy) in haplo-identical HCT results in a 2-year NRM rate of 13% and 1-year OS of 83%. In AML in complete remission, TMLI 20 Gy and PTCy results in 2-year NRM, OS, and GVHD free/relapse-free survival (GRFS) rates of 0%, 86·7%, and 59.3%, respectively.ConclusionTMI/TMLI shows significant promise, low NRM rates, the ability to offer myeloablative radiation containing regimens to older patients, the ability to dose escalate, and response and survival rates that compare favorably to published results. Collaboration between radiation oncology and hematology is key to successful implementation. TMI/TMLI represents a paradigm shift from TBI towards novel strategies to integrate a safer and more effective target-specific radiation therapy into HCT conditioning beyond what is possible with TBI and will help expand and redefine the role of radiotherapy in HCT.

PO-1684 Fast delivery of IMRT to metastatic disease without planning CT simulation.

PO-1684 Fast delivery of IMRT to metastatic disease without planning CT simulation.

A method for in vivo treatment verification of IMRT and VMAT based on electronic portal imaging device

BackgroundIntensity-modulated radiation therapy (IMRT) and volume-modulated arc therapy (VMAT) are rather complex treatment techniques and require patient-specific quality assurance procedures. Electronic portal imaging devices (EPID) are increasingly used in the verification of radiation therapy (RT). This work aims to develop a novel model to predict the EPID transmission image (TI) with fluence maps from the RT plan. The predicted TI is compared with the measured TI for in vivo treatment verification.MethodsThe fluence map was extracted from the RT plan and corrections of penumbra, response, global field output, attenuation, and scatter were applied before the TI was calculated. The parameters used in the model were calculated separately for central axis and off-axis points using a series of EPID measurement data. Our model was evaluated using a CIRS thorax phantom and 20 clinical plans (10 IMRT and 10 VMAT) optimized for head and neck, breast, and rectum treatments.ResultsComparisons of the predicted and measured images were carried out using a global gamma analysis of 3%/2 mm (10% threshold) to validate the accuracy of the model. The gamma pass rates for IMRT and VMAT were greater than 97.2% and 94.5% at 3%/2 mm, respectively.ConclusionWe have developed an accurate and straightforward EPID-based quality assurance model that can potentially be used for in vivo treatment verification of the IMRT and VMAT delivery.

Decreases in Radiation Oncology Medicare Reimbursement Over Time: Analysis by Billing Code

Decreases in Radiation Oncology Medicare Reimbursement Over Time: Analysis by Billing Code

Dosimetric Parameters Related to Local Control and Rate of Distant Metastases in NSCLC SBRT Patients

Previous studies have suggested that the dose immediately outside the PTV may impact the incidence of distant metastases after stereotactic body radiation therapy (SBRT) for patients with early-stage non-small cell lung cancer. In particular, Diamant et al have reported a correlation between the mean EQD2 of a 30mm shell around the PTV and both local control and the rate of distant metastases in lung SBRT patients. In this study, we review this parameter and others in a series of patients with radiographically presumed or biopsy proven early-stage non-small cell lung cancer treated at our institution with SBRT between 2014 and 2019.We reviewed the dosimetry, local control and rate of distant metastases for a series of 155 patients with 165 lesions treated with SBRT at our institution. Dosimetric parameters obtained included the prescribed dose, minimum and mean doses to the PTV, conformity index, and the mean EQD2 to a 30mm shell around the PTV, as reported by Diamant et al. Time to local progression and distant metastasis were defined from date of last fraction of SBRT to date of event, with event-free patients censored at last radiographic follow-up. All plans were calculated in the Varian Eclipse treatment planning system using the AAA algorithm and treated on conventional Linac with either IMRT or VMAT delivery. Analysis of the data was performed using IBM SPSS for Windows (version 27), with analysis of time to event via Kaplan-Meier method. Univariate analysis of outcomes based on the above dosimetric parameters was performed utilizing the log-rank test. A P-value < 0.05 was considered to be statistically significant.No significant correlation was seen between the mean EQD2 dose to a 30mm shell around the PTV and either the local control or the rate of distant metastases in these patients. Positive predictors of reduced incidence of distant metastases were the prescribed dose of 54 Gy (vs 45-50 Gy, P < 0.01) and PTV < 22 cc (vs. ≥ 22 cc, P = 0.01). In the 45-50 Gy cohort, PTV mean dose ≥ 53 Gy (vs. < 53 Gy, P = 0.04) was associated with reduced incidence of distant metastases. Improved local control was also noted with prescribed dose of 54 Gy (vs 48-50 Gy, P = 0.01). In the 45-50 Gy cohort, PTV mean dose ≥ 53 Gy (vs. < 53 Gy, P = 0.03) was associated improved local control. No additional factors examined were significantly correlated with local control.We failed to replicate the correlation of the rate of distant metastases with dose outside the PTV as reported by Diamant et al. Higher prescribed and mean dose to the PTV was correlated with both local control and reduced incidence of distant metastases. References.

Evaluation of Two Intensity Modulated Radiotherapy Techniques for Total Body Irradiation: Initial Clinical Experience From an Ongoing Pilot Study

A multi-institutional pilot study is initiated to compare two IMRT delivery techniques (volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT)) for total body irradiation as conditioning regimen in patients undergoing hematopoietic stem cell transplant with an updated lung dose limit based on recently published clinical data on lung toxicities. We report comparison and initial clinical experience in dosimetric plan quality, patient setup correction techniques, and dose delivery efficiency.We reviewed treatment planning and delivery record for the initial seven patients that were prospectively enrolled in this study. TBI was given to each patient in 8 fractions at 165 cGy per fraction. Patient height ranged from 154.9 to 193.5 cm. The planning target volume (PTV) is the whole body excluding the lung volume. The total lung and 15 additional normal organs were included in plan optimization and dosimetric evaluation. In planning, mean lung dose (MLD) limit was 8 Gy and maximum dose (Dmax) to normal organs was required to be < 130% of the prescribed dose with a recommended goal of < 115%. Four patients received TBI with HT and the other three on a conventional Linac. Patients treated with HT had an upper body HT plan with a rotating gantry using a 5-cm jaw and a lower extremity HT plan using static AP/PA HT fields. Patients treated on a conventional Linac had an upper body VMAT plan using 9 to 10 VMAT fields and a lower body plan with either VMAT fields or static AP/PA fields. The virtual bolus technique was used in VMAT plans to reduce dose variation due to setup uncertainty. The VMAT fields used a 6 MV photon beam with a 90° collimator angle and had an overlap of at least 2 cm between adjacent fields along the longitudinal direction. All the plans were normalized so that 85% of the PTV received at least 13.2 Gy in total dose.In the upper body HT plans the average PTV dose was 13.6 Gy (range: 13.5 - 13.7 Gy), the MLD averaged at 7.71 Gy (range: 7.21 - 7.95 Gy), and Dmax was < 115% of prescribed dose for at least 14 normal organs. In the upper-body VMAT plans the average PTV dose was 13.95 Gy (range: 13.86 - 14.02 Gy), the MLD averaged at 7.12 Gy (range: 6.85 - 7.63 Gy), and Dmax was < 115% of prescribed dose with 1 to 9 normal organs. The Dmax limit of 130% of prescribed dose was achieved in all the plans. In HT treatments, an MVCT scan was used for daily patient setup corrections in both the upper and lower body treatments and the overall treatment time per fraction was 1.23 ± 0.21 hours (range: 0.90 - 1.88 hours). In VMAT treatments, both cone beam CT scans and orthogonal kilovoltage images were used for daily patient setup on a conventional Linac and the overall treatment time per fraction was 1.39 ± 0.20 hours.Both the HT and VMAT plans achieved adequate lung sparing under our new institutional lung dose limit in TBI. VMAT TBI is clinically feasible and could provide access to more patients for TBI treatments. The two IMRT techniques also allow selective sparing of additional organs in TBI treatments.

How Sensitive is Mass-Based Inverse Optimization to IMRT Delivery Parameters?

Purpose: To determine the sensitivity of changes to IMRT delivery parameters for mass-based optimization schemes: Dose-Mass- (DM) and Energy-based (Energy), compared to Dose-Volume-based (DV) optimization. Methods: Twelve Head-and-Neck (HN) and twelve lung cases were retrospectively optimized using DM and Energy optimization. In both optimization approaches nine equidistant, split beams were used for step-and-shoot deliverable IMRT. Changes to two parameters were investigated: the number of IMRT segments (5 and 10 per beam) and the minimum allowed segment area (2 and 6 cm²). Plans were normalized such that 95% of the PTV received the same dose. Dose Indices (DIs) were used for evaluation. For the lung cases, DIs included: 1%_cord, 33%_heart, 20% and 30%_both-lungs, and 50%_ esophagus. In the HN cases: 1%_cord, 1%_brainstem, left/right parotids_50%, 50%_larynx, and 50%_esophagus. Results: The lung cases demonstrated that the Energy plans were more sensitive to segment area; changing the segment area resulted in a statistically significant dose increase for 1%_cord, 30%_both-lungs and 50%_esophagus. Changes to the number of segments yielded on average statistically significant differences in dose to 1%_cord in Energy plans, 50%_esophagus in DM plans, and 20%_both-lungs in DV plans. When the segment area was changed, the HN cases yielded statistically significant differences in doses to 1%_cord, 1%_ brainstem, 50%_left and right parotids, and 50%_larynx for the Energy plans and 50%_larynx for DM plans. Moreover, changing the number of segments resulted in significant dose decrease for 50%_parotids and 50%_esophagus for the Energy plans and 50%_larynx for DV plans. Conclusions: This study showed that both lung and HN Energy plans exhibit larger sensitivity than DV and DM plans to changing IMRT delivery parameters, especially when increasing the minimum segment area rather than with varying the number of segments.

The technical design and concept of a PET/CT linac for biology-guided radiotherapy

This is a summary of the design and concept of the RefleXion X1, a system for biology-guided radiotherapy (BgRT). This system is a multi-modal tomography (PET, fan-beam kVCT, and MVD) treatment machine that utilizes imaging and therapy planes for optimized beam delivery of IMRT, SBRT, SRS, and BgRT radiotherapy regimens. For BgRT delivery specifically, annihilation photons emanating outward from a PET-avid tumor are used to guide the delivery of beamlets of radiation to the tumor at sub-second latency. With the integration of PET detectors, rapid beam-station delivery, real-time tracking, and high-frequency multi-leaf collimation, the BgRT system has the potential to deliver a highly conformal treatment to malignant lesions while minimizing dose to surrounding healthy tissues. Furthermore, the potential use of a single radiotracer injection to guide radiotherapy to multiple targets opens avenues for debulking in advanced and metastatic disease states.

Affordable compensator for IMRT delivery designed for low-and-middle income countries, a Monte Carlo study.

We propose a novel cost-effective compensator that can be used to facilitate access to IMRT in low-and-middle income countries. The compensator has the advantages of simplicity, less downtime, increased reliability and less impact on treatment quality from patient motion during treatment. Moreover, the system can be used with either a cobalt-60 unit or linear accelerator. In this Monte Carlo study, the dosimetric properties of the new compensator design have been evaluated. Results were obtained for different field sizes of cobalt teletherapy machine, and the dose was scored at 0.5cm depth in a water phantom. The effects of compensator thickness, filling material type and shape, and field size were identified. Furthermore, the percentage depth dose and beam profiles for various field sizes and at different depths were obtained. Beam profiles show no significant signature of the beads relative to a solid compensator; in addition, they exhibit a better flatness while preserving symmetry for all field sizes. A reusable bead-based compensator appears to be feasible, and provides dose distribution similar to a solid compensator with low cost and no hazards. Our results avail the ongoing efforts to expand the reach to IMRT in low- and middle-income countries.

Cardiac Dose Control and Optimization Strategy for Left Breast Cancer Radiotherapy With Non-Uniform VMAT Technology.

Purpose: A novel in-house technology “Non-Uniform VMAT (NU-VMAT)” was developed for automated cardiac dose reduction and treatment planning optimization in the left breast radiotherapy. Methods: The NU-VMAT model based on IGM (gantry MLC Movement coefficient index) was established to optimize the volumetric modulated arc therapy (VMAT) MLC movement and modulation intensity in certain gantry angles. The ESAPI embedded in Eclipse® was employed to connect TPS and the optimization program via I/O relevant DICOM RT files. The adjuvant whole-breast radiotherapy of 14 patients with left breast cancer was replanned using our NU-VMAT technology in comparison with VMAT and IMRT technology. Dosimetric parameters including D1%, D99%, and Dmean of PTV, V5, V10, and V20 of ipisilateral lung, V5, D20, D30, and Dmean of heart, monitor units (MUs), and delivery time derived from IMRT, VMAT, and NU-VMAT plans were evaluated for plan quality and delivery efficiency. The quality assurance (QA) was conducted using both point-dose and planar-dose measurements for all treatment plans. Results: The IGM−NU−VMAT curves with plan optimization (range from 50% to 147%) were converged more significantly than IGM-VMAT curves (range from 0% to 297%). The dose distribution requirements of the target and normal tissues could be met using IMRT, VMAT, or NU-VMAT; the lowest Dmean was achieved in NU-VMAT plans (5.38 ± 0.46 Gy vs 5.63 ± 0.61 Gy in IMRT and 7.95 ± 0.52 Gy in VMAT plans). Statistically significant differences were found in terms of delivery time and MU when comparing IMRT with VMAT and NU-VMAT plans (P < .05). In comparison with IMRT plans, the MU and delivery time in NU-VMAT plans dramatically decreased by 69.8% and 28.4%, respectively. Moreover, NU-VMAT plans showed a high gamma passing rate (96.5% ± 1.11) in plane dose verification and minimal dose difference (2.4% ± 0.19) in point absolute dose verification. Conclusion: Our non-uniform VMAT facilitated the treatment strategy optimization for left breast cancer radiotherapy with dosimetric advantage in cardiac dose reduction and delivery efficiency in comparison with the conventional VMAT and IMRT.