Target Volume Dose Research Articles

A dosimetric comparative analysis of Brainlab elements and Eclipse RapidArc for spine SBRT treatment planning

Purpose. This is a dosimetric study comparing stereotactic body radiotherapy (SBRT) plans of spine tumors using Brainlab Elements Spine planning module against Eclipse RapidArc plans. Dose conformity, dose gradient, dose fall-off, and patient-specific quality assurance (QA) metrics were evaluated. Methods:Twenty patients were immobilized in supine position using half Vac-Lok. A prescription dose of 16 Gy in a single fraction was planned for Varian TrueBeam. Conformal arc plans were generated with Pencil beam (PB), MonteCarlo (MC) in Elements, and RapidArc with Acuros XB algorithm in Eclipse using identical treatment geometry. Results. Eclipse, Elements PB, and Elements MC generated dosimetrically conformal plans having Inverse Paddick Conformity Index (IPCI) <1.3. All plans satisfied the dose constraints to target and OARs. Elements PB had a sharper gradient than Elements MC with average GI of 3.67(95% CI: 3.52–3.82) and 4.06 (95% CI: 3.93–4.20) respectively. Eclipse plans were more homogeneous with mean HI = 1.22 (95% CI: 1.20–1.23) that is lower than others. Average maximum clinical target volume (CTV) doses were higher in Elements MC with 22.31 Gy (95% CI: 21.87–22.74), while PB plans have 21.15 Gy (95% CI: 20.36–21.96), respectively. Elements MC and PB plans had lower average dose to 0.35 c.c. of spinal cord (D0.35cc) of 7.60 Gy (95% CI: 7.18–8.02) and 8.42 Gy (95% CI: 7.83–9.01). All plans had >95% points passing the gamma QA criteria at 3%/2 mm. Conclusion. All treatment plans achieved clinically acceptable target coverage >95% and meet spinal cord dose limits. Smart optimization in Brainlab Elements spine module produced dosimetrically superior plans by better spinal cord sparing.

Adaptive dose escalated radiotherapy in oropharyngeal cancers: a treatment planning feasibility study

BackgroundA significant proportion of patients with poor prognosis squamous cell cancer of the oropharynx relapse loco-regionally despite radical (chemo)radiotherapy. If a predictive biomarker for disease control can be identified during treatment then individualised and adaptive treatment strategies may be employed. The aim of this study is to assess the feasibility of adaptive and dose-escalated RT to the gross tumour volume without increasing surrounding planning target volume doses and maintaining clinically acceptable organs at risk doses.Materials and methodsTwenty representative patients with poor prognosis locally advanced OPSCC who were known to have relapsed post RT, were re-planned retrospectively using Eclipse TPS v15.5, RapidPlan™ and multi-criteria optimisation. In our centre, PTV65 is treated with 65 Gy in 30 fractions while areas at risk of containing microscopic disease (PTV54) are treated synchronously to 54 Gy in 30 fractions. The original clinical plans were re-optimised to act as controls (Group I). These plans were split into two plans of 15 fractions each, with the latter 15 fractions used to escalate the dose to the GTV to 73 Gy (Group II) and 82 Gy (Group III). Plan sums were created for the total 30 fractions to record plan evaluation parameters along with assessments of plan deliverability.ResultsFor all groups, the dose coverage at D98% and D50% for the PTVs were comparable. The D2% dose levels for PTV65-GTV increased. All dose levels associated with PTV54 remained largely unaffected by the dose escalation regimens. Conformity indices for PTV65 and PTVAll (PTV65 plus PTV54) reveal comparable target volume coverage across all three groups. Despite the GTV being escalated by 12.3% and 26.2% in groups II and III, the volume of GTV receiving > 84 Gy was considerably less than 1.75 cc. While OAR doses increased for the escalated groups, these increases were not clinically significant.ConclusionThis planning feasibility study exploring RapidPlan™ combined with multi-criteria optimisation has demonstrated that doses to the GTV may be escalated without increasing PTV65-GTV, PTV54 or OAR doses considerably, suggesting an interventional clinical trial using this approach would be feasible.

Conformity and Homogeneity Indices for Brain Cancer Patients Using 3DCRT Technique

Background: 3D conformal radiotherapy 3DCRT technique are used to treat patients with brain cancer. Goal: this study aims to compare conformity and homogeneity indices for eight patients of brain cancer by using three-dimension conformal radiotherapy (3DCRT) technique on planning target volume (PTV) located in brain. Methods: Comparative study of Conformity and Homogeneity indices for ten brain cancer patients during period from October 2019 to March 2020 that carried out at ZCC (Zhianawa Cancer Center) in Sulaimany-Iraq. 3DECRT technique was applied to get the heist dosage to the target volume (tumor) and lowest dose to the healthy structures around the tumor. By using Linear Accelerator machine- LINAC, Elekta synergy type with 6MV photon beam. SPSS-version 22 was applied for analyzing and caring out the data measurements. Results: It has been observed from the results, in both techniques the highest conformity and homogeneity indices have the acceptable values, in this study with 3D-CRT plan technique showed that the mean conformity and homogeneity indices were (0.1999 ± 0.03, 0.9457 ± 0.05) respectively. The mean dose values for organs at risk spinal cord and brain stem were (41.98 ± 2.23, 26.01 ± 16.62) respectively, for ten right and left parotid glands were (23.52 ± 3.99, 23.34 ± 3.93) respectively. In both plans, the average dose values for all organs at risk mentioned above were less than tolerance radiation doses. Conclusion: This study also supports that indices of homogeneity and conformity are important tools for improving the long-term quality of life of brain cancer patients using 3DCRT technology.

Correlation of 3DCRT and Open Field Treatment Techniques in Advanced Head and Neck Cancer Patients Treated by Chemoradiation.

Background: Multimodality treatment is required for the management of head and neck cancer. Functional impairment and toxicities associated with surgery and radiation accentuate the need to develop innovative therapeutic strategies in the management of these patients to improve survival and reduce toxicity. In this study, we have compared treatment effects in patients of advanced head and neck squamous cell cancer treated by open field and 3DCRT treatment planning techniques.Objective: This study aims to evaluate open field and 3DCRT treatment planning techniques in advanced head and neck squamous cell cancer patients managed by chemoradiation in the scenario of limited resources.Material and Methods: In this analytical study, 40 histologically proven unresectable advanced squamous cell carcinoma patients of oropharynx and larynx were allocated in two groups to receive 70 Gy in 35 fractions in 7 weeks with concurrent cisplatinum35 mg/m2 weekly either with open-field technique or three dimensional conformal radiotherapy (3DCRT) by ElektaSynergy linear accelerator. Target volume coverage and dose received by organ at risk (OARs) were compared. Clinical outcome in terms of response and toxicities is also evaluated in this study.Results: Plans with best possible coverage of the target volume were obtained. No significant difference was found in the dose received by the spinal cord; however, it was possible to prevent higher dose to brain stem with 3DCRTin node negative patients of oropharynx cancer and larynx cancer. Skin toxicities were significantly lower in 3DCRT arm.Conclusion: In low resource settings with increased burden of locally advanced disease, both open-field and 3DCRT treatment techniques are comparable in terms of target coverage, OARs preservation, toxicity and treatment response.

Role of the Neuroradiologist and Neurosurgeon in Contouring with the Clinical Oncologist for Stereotactic Radiosurgery

AimTo evaluate the value of a multidisciplinary team (MDT), including a neuroradiologist and a neurosurgeon, review of contouring in stereotactic radiosurgery (SRS). Materials and methodsA sequential audit of all patients receiving intracranial SRS at local institution was conducted. Lesions were contoured first by a clinical oncologist, then reviewed/edited by the MDT. The initial contour was compared with the final contour using Jaccard conformity (JCI) and geographical miss indices (GMI). The dosimetric impact of a contouring change was assessed using plan metrics to both original and final contours. ResultsIn total, 113 patients and 142 lesions treated over 22 months were identified. The mean JCI was 0.92 (0.32–1.00) and 38% needed significant editing (JCI <0.95). The mean GMI was 0.03 (0.0–0.65) and 17% showed significant miss (GMI >0.05). Resection cavities showed more changes, with lower JCI and higher GMI (P < 0.05). There was no significant improvement on JCI or GMI shown over time. The dosimetric analysis indicated a strong association of conformity metrics with planning target volume dose metrics; a 0.1 change in gross tumour volume conformity metric association with a 6–17% change in dose to 95% of the resulting planning target volume. Greater association was seen in the resection cavity, suggesting the geographical nature of a typical contouring error gives rise to greater potential change in dose. Clinical outcomes compared well with published series. The median survival was 20 months; the local relapse-free rate in the treated areas was 0.89 (0.8–0.94) at 40 months; the radionecrosis-free rate at 40 months was 0.9 (0.83–0.95) with a median of 17 months to developing radionecrosis. ConclusionsThis work highlights that MDT contour review adds significant value to SRS and the approach translates into reduced local recurrence rates at the local institution compared with previously published data. No improvement in clinical oncologist contouring over time was shown, indicating that a collaborative approach is needed regardless of the experience of the clinical oncologist. MDT input is recommended in particular for contouring of resection cavities.

Adjustment of multi-leaf collimator parameters in 4-MV and 6-MV IMRT: A study of veterinary clinical cases.

Background:For optimal treatment, it is important to maintain optimal multi-leaf collimator (MLC) transmission in intensity-modulated radiation therapy (IMRT). However, adjustment of transmissions has not been reported in veterinary medicine.Aim:To demonstrate that appropriate MLC parameter adjustment for IMRT using 4- and 6-MV energy can reduce the need for quality assurance revalidation in real companion animal clinical cases.Methods:The MLC parameters (leaf transmission and leaf offset) of the treatment planning system were adjusted by evaluating seven plans (10 × 10 cm, 3ABUT, DMLC, 7segA, FOURL, HDMLC, and HIMRT) and 20 preclinical cases (10 cases each in 4- and 6-MV groups). Subsequently, 101 IMRT plans of 88 cases (77 dogs and 11 cats) were evaluated for absolute dose of plan target volume (PTV) and organs at risk (OAR) and were analyzed for the relative dose distribution by gamma analysis (3%/3 mm, >10%) using EBT3 film.Results:After adjustment of the MLC parameters (leaf transmission and leaf offset, 4 MV: 0.008 and 0, 6 MV: 0.005 and 0, respectively), the data from 101 plans (4 MV: 64 plans and 6 MV: 37 plans) treated with IMRT showed PTV <3%, OAR <5%, and gamma analysis pass rates ≥95% in all cases.Conclusion:Clinically meaningful dose distributions can be created even with a limited validation device if the treatment parameters are adjusted appropriately, even for tumors in canines and felines, where the irradiation field is small, the target is adjacent to the OAR, and the target is often superficial.

Dosimetric Influence of Acuros XB Dose-to-Medium and Dose-to-Water Reporting Modes on Carcinoma Cervix Using Intensity-Modulated Radiation Therapy and Volumetric RapidArc Technique.

Aim:We aimed to evaluate the dosimetric influence of Acuros XB (AXB) dose-to-medium (Dm) and dose-to-water (Dw) reporting mode on carcinoma cervix using intensity-modulated radiation therapy (IMRT) and RapidArc (RA) technique.Materials and Methods:A cohort of thirty patients cared for carcinoma cervix was retrospectively selected for the study. Plans were computed using analytical anisotropic algorithm (AAA), AXB-Dm, and AXB-Dw algorithms for dosimetric comparison. A paired t-test and Pitman–Morgan dispersion test were executed to appraise the difference in mean values and the inter-patient variability of the differences.Results:The dose–volume parameters were higher for AXB-Dw in contrast to AAA for IMRT and RA plans, excluding D98%, minimum dose to planning target volume (PTV) and rectum mean dose (RA). There was no systematic trend observed in dose–volume parameters for PTV and organs at risk (OARs) between AXB-Dm and AXB-Dw for IMRT and RA plans. The dose–volume parameters for target were higher for AXB-Dm in comparison to AAA in IMRT and RA plans, except D98% and minimum dose to PTV. Analysis envisaged less inter-patient variability while switching from AAA to AXB-Dm in comparison to those switching from AAA to AXB-Dw.Conclusions:The present study reveals the important difference between AAA, AXB-Dm, and AXB-Dw computations for cervix carcinoma using IMRT and RA techniques. The inter-patient variability and systematic difference in dose–volume parameters computed using AAA, AXB-Dm, and AXB-Dw algorithms present the possible impact on the dose prescription to PTV and their relative constraints to OARs for IMRT and RA techniques. This may help in the decision-making in clinic while switching from AAA to AXB (Dm or Dw) algorithm for cervix carcinoma using IMRT and RA techniques.

Dose Estimation Using Optically Stimulated Luminescence Dosimeter and EBT3 Films for Various Treatment Techniques in Alderson Rando Phantom and Estimation of Secondary Cancer Incidence for Carcinoma of Left Breast.

The aim of this study was to measure the dose to planning target and organ at risk (OAR) using Alderson Rando phantom for various treatment techniques in left breast radiotherapy and to estimate the secondary cancer incidence. Eleven different combinations of plans containing four techniques (three dimensional conformal radiotherapy, intensity-modulated radiation therapy [IMRT], volumetric modulated arc therapy [VMAT], and combination of 3DCRT and VMAT plans (HYBRID)) were created with 6 MV FF and 6 MV FFF (flattening filter and flattening filter-free) photon energies in phantom. Planned target volume and OAR doses in 23 different locations were measured using optically stimulated luminescence dosimeter (OSLD) and EBT3 films. Assuming the age of exposure as 30 years, lifetime attributable risk (LAR) was estimated based on excess absolute risk (EAR) models outlined in the Biological Effects of Ionizing Radiation VII report. Film showed maximum deviations of 6.15% with IMRT_C_FF plan when compared with treatment planning system (TPS). The maximum percentage difference of 1.7% was found with OSLD measurement when compared with TPS for VMAT_T_FFF plan. EAR estimation was done for all the OARs including target. The LARs for left lung, right lung, and right breast were evaluated. The maximum LAR values of 2.92 ± 0.14 were found for left lung with VMAT_C_FFF plans. This study shows that both OSLD and EBT3 films are suitable for dose measurements using Rando phantom. OSLD shows superior results when compared with films, especially with relatively larger distances. Maximum LAR values were found with VMAT_C_FFF plans. Considering the secondary cancer risk associated with the patients treated in the younger age group, it is suggested that in vivo dose estimation should be a part of treatment quality audit whenever possible.

COMPARISON OF TWO RADIOTHERAPY TECHNIQUES IN TREATMENT OF PATIENTS WITH DIAGNOSED INOPERABLE CERVICAL CANCER

Advanced cervical cancer is treated with radiotherapy, target therapy, chemotherapy or a combination of those. Standardized accepted treatment of inoperable cervical cancer is concurrent chemo-radiotherapy (CCRT) followed by brachytherapy. Radiotherapy techniques used are three-dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiation therapy (IMRT). In this study participated 30 female patients, average age of 52 at the time of irradiation.3D-CRT plans were made, patients were treated on linear accelerator (LINAC) with 3D-CRT. IMRT plans were made additionally. Planning target volume (PTV) dose coverage was 105.36% for 3D-CRT and 105.64% for IMRT. Homogeneity index (HI) was 0.062 for 3D-CRT and 0.048 for IMRT. Conformity index (CI) for 3D-CRT was 1.93 for PTV of 2990.77 ccm. CI for IMRT&nbsp; was 1.305 for PTV of 2019.83 ccm. Bladder V40 (%) for 3D-CRT averaged 96.61%, while IMRT averaged 73.11%. Rectal V50 (%) for 3D-CRT was 72.55% and for IMRT was 17.80%. Rectal V40 (%) for 3D-CRT and IMRT averaged 92.12% and 73.49% respectively. Quantitative Analysis of normal Tissue Effects in the Clinic (QUANTEC) – V45 for 3D-CRT was 228.80ccm and for IMRT was 104.55ccm. Femoral heads dose for 3D-CRT was 51.50Gy for left and 51.29Gy for right. Absorbed doses for IMRT were 47.28Gy for left and 47.32Gy for right femoral head, respectively. 13 patients had grade 1 cystitis and urethritis, 2 with grade 2. 7 patients developed grade 1 diarrhea, 1 with grade 2. It can be concluded that dosimetrically IMRT is superior to 3D-CRT in patients treating cervical cancer. Keywords: cervical cancer, 3D-CRT, IMRT. &nbsp;

Flattening Filter-Free Volumetric-Modulated Arc Radiotherapy for Left-Sided Whole-Breast, Partial-Breast, and Postmastectomy Irradiations.

Purpose:Unflattened photon beams exhibit many benefits over traditional flattened beams for radiotherapy (RT), but comprehensive evaluations of dosimetric results and beam-on time using flattening filter-free (FFF) beams for all types of breast irradiations are still lacking. The purpose of this study was to investigate if FFF RT can maintain equal or better dose coverage than standard flattened-beam RT while reducing doses to organs at risk (OARs) and beam-on time for various types of breast cancer irradiations.Methods and Materials:FFF volumetric-modulated arc therapy (FFF-VMAT) and standard VMAT (STD-VMAT) treatment plans were created for 15 whole-breast irradiation (WBI) patients with 50 Gy/25 fractions, 13 partial-breast irradiation (PBI) patients with 38.5 Gy/10 fractions, and 9 postmastectomy irradiation (PMI) patients with 50 Gy/25 fractions. Planning target volume (PTV) coverage and dose to OARs were evaluated.Results:Both techniques produced clinically acceptable plans for all three types of irradiations. For WBI, FFF-VMAT plans exhibited similar PTV and OARs evaluation metrics as STD-VMAT. For PBI, FFF-VMAT plans showed significantly lower mean and maximum doses for ipsilateral and contralateral lungs, contralateral breast, and heart. For PMI, FFF-VMAT plans showed significantly lower mean dose and V5 for contralateral breast but significantly higher Dmean, Dmax, and V20 for ipsilateral lung and significantly higher Dmean, V22.5, and V30 for heart. FFF-VMAT techniques significantly reduced beam-on time than STD-VMAT for all cases.Conclusion:This work has shown that FFF beams are most beneficial for small-field irradiation such as PBI, and breast cancer patients could potentially benefit from the shortened beam-on time.

DOSIMETRIC ANALYSIS OF ADAPTIVE RADIOTHERAPY(ART) IN LOCALLY ADVANCED HEAD AND NECK CANCER

PURPOSE/OBJECTIVE: The objective of this study is to evaluate the dosimetric parameters in adaptive radiotherapy for locally advanced head and neck cancers METHODS AND MATERIALS: This is a Hospital-based Prospective study conducted in the period from Dec 2020 to March 2021. Histologically proven Head and Neck Carcinoma patients with Stage III to IV (locally advanced) were selected for the study. A total of 10 patients receiving denitive, conformal radiation therapy to the head and neck region were evaluated for the study. After the acquisition of CT images, target volumes, OARs were contoured in the planning CT. Images were again acquired midway during the planned course of radiation therapy. Body contours, target volumes, and organs at risk were redrawn on the new set of images. Two sets of additional treatment plans were generated: 1) a non-optimized plan (plan 2), which is an overlay of the original plan (plan 1) on the new set of contours, and 2) an optimized plan(plan 3) with the new set of contours. These 3 sets of plans were then compared for dosimetric differences. RESULTS: Four patients had locally advanced nasopharyngeal cancers, 4 patients had locally advanced oropharyngeal cancers, 2 patients had locally advanced hypopharyngeal cancer. The average reduction in gross tumour volume was 37.1 ml. The average changes in right and left parotid volume were 5.94 and 5.49 ml, respectively. With the non-optimized plan, the average increase in the maximum dose to the spinal cord was 9.8% (58.96-68.76; p= 0.156). With reoptimization, the maximum dose to the spinal cord decreased from 68.76% to 54.97% (mean difference, -13.79%, p=0.03). The average D99 for the planning target volume( dose received by 99% of the target volume) was 98.68% and 98.65% with the original and reoptimized plans, respectively. Most of the patients during radiation had Grade 2 skin toxicity and Grade 2 mucositis which was managed conservatively. CONCLUSIONS: This study demonstrates that during radiation there is gross changes of volumes in locally advanced head and neck cancers and thus adaptive radiation therapy plays a pivotal role in locally advanced head and neck cancer

Dosimetric Comparison of Helical Tomotherapy, Volume-Modulated Arc Therapy, and Fixed-Field Intensity-Modulated Radiation Therapy in Locally Advanced Nasopharyngeal Carcinoma.

ObjectiveTo compare the dosimetric parameters of different radiotherapy plans [helical tomotherapy (HT), volume-modulated arc therapy (VMAT), and fixed-field intensity-modulated radiation therapy (FF-IMRT)] for locally advanced nasopharyngeal carcinoma (NPC).MethodsA total of 15 patients with locally advanced NPC were chosen for this retrospective analysis and replanned for HT, VMAT, and FF-IMRT. The prescribed planning target volume (PTV) dose for the primary tumor and metastatic lymph nodes was 70 Gy (2.12 Gy/fraction, delivered over 33 fractions). The prescribed PTV dose for the high-risk subclinical region was 59.4 Gy (1.8 Gy/fraction, delivered over 33 fractions). The dosimetric parameters of the PTV and organs at risk (OARs) and the efficiency of radiation delivery were assessed and compared using the paired-samples t-test.ResultsCompared with VMAT and FF-IMRT plans, HT plans significantly improved the mean conformity index (CI) and homogeneity index (HI). The HT plans reduced the maximum doses delivered to OARs, such as the brainstem, spinal cord, and optic nerves, and significantly reduced the volume delivered to the high-dose region, especially when examining the V 30 value of the parotid glands. However, VMAT reduced the treatment time and improved the efficiency of radiation delivery compared with HT.ConclusionsFor locally advanced NPC, the results showed that HT and VMAT possessed better target homogeneity and conformity, reducing the dose delivered to OARs compared with conventional FF-IMRT, with HT achieving the best effect. Among the techniques studied, VMAT had the shortest radiation delivery time. The results of this study can provide guidance for the selection of appropriate radiation technologies used to treat patients with locally advanced NPC who are undergoing concurrent chemoradiotherapy.

Cumulative Target Volume Dose and Locoregional Failure in Pancreatic Cancer Patients With Treated With Ablative Stereotactic MR-Guided Adaptive Radiation Therapy (SMART)

<h3>Purpose/Objective(s)</h3> Emerging data suggest that ablative stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) for inoperable pancreas cancer (PCa) achieves favorable local control (LC) and overall survival (OS) compared to non-ablative dose. In the current SMART workflow, each adaptive fraction is reoptimized without accounting for previously delivered dose. Cumulative target volume (TV) dose from all SMART fractions has not previously been evaluated with respect to clinical outcomes. <h3>Materials/Methods</h3> We evaluated 44 inoperable PCa patients who were prescribed 50 Gy in 5 daily fractions on a 0.35T-MR LINAC. 33 patients (75%) were treated with elective nodal irradiation, typically including the celiac axis and superior mesenteric artery. PTV margin was 3 mm. On-table adaptive replanning was performed to primarily satisfy gastrointestinal (GI) organ at risk (OAR) constraints, and secondarily maximize TV coverage. Cumulative dose for all fractions was summed onto a TRUFI MR fractional scan (i.e., fraction 5). A rigid transformation was performed for fractions 1 to 4 scans onto the fraction 5 frame of reference (FOR) based on alignment of gross disease. Each fractional dose was transformed onto fraction 5 FOR and summed cumulatively for all 5 fractions. Locoregional failure (LRF) was delineated on follow-up imaging by a diagnostic radiologist with PCa expertise. Cumulative TV dose metrics (D80, D90, mean, max) were evaluated with respect to LRF. Diagnostic scans were rigidly registered to the fraction 5 FOR based on recurrence region to investigate recurrence characteristics and target dose metrics. A Spearman correlation was used to investigate LRF and (1) ENI vs. no ENI, (2) TV coverage metrics, (3) planning TV (PTV) volume. <h3>Results</h3> The median PTV volume for all patients, with ENI, and without ENI was 125.9 cc (range: 20.6-356.8), 137.3 cc (range: 72.8-356.8, and 55.4 (range: 20.6-280.15), respectively. LRF occurred in 12 patients (27.3%); the median LRF volume was 10.9 cc (range: 1.1-145.5cc). The median Dice similarity coefficient taken to characterize LRF overlap with PTV was 0.05 (range: 0-0.45). Moderate negative correlation coefficients were noted between recurrence to ENI [-0.59 (<i>P</i> < 0.001)], recurrence to PTV volume [-0.41 (<i>P</i> < 0.001)] and recurrence to max PTV dose [–0.47 (<i>P</i> < 0.001)]. No correlation was observed for cumulative D80, D90, mean dose to recurrence. <h3>Conclusion</h3> To our knowledge, this is the first analysis of cumulative TV dose from 5-fraction SMART for PCa. While use of ENI is controversial, moderate and statistically significant correlations were noted between LRF and ENI, in addition to PTV volume and maximum dose. Additional investigation is warranted to better understand whether specific dose thresholds exist for gross disease and electively treated volumes with respect to long-term LC and OS.

Treatment Outcomes Following Proton Therapy for High Grade Spinal Cord Ependymoma in Children

There is limited information published on the outcome of children treated with radiation for high-grade ependymoma of the spinal cord. Thus, little evidence is available to inform decisions of target volume or prescription dose. Moreover, there is virtually no mature outcome data on proton therapy, despite theoretical advantages in normal tissue exposure. We therefore performed a bicentric retrospective study to better inform treatment of this rare tumor in children.Between 2008 and 2019, 14 consecutive pediatric patients with a non-metastatic grade II or III spinal ependymoma were treated with proton therapy at the University of Florida and Massachusetts General Hospital. The median age of the children at the time of radiation was 14 years old (range, 1.5-18 years). Five tumors arose within the cervical cord (C1-5, C1-2, C1-T1, C3-T1, C4-C6), 3 within the thoracic spine (C7-T4, T7-L1, T11-T12), and 6 within the lumbosacral spine (L3-L5, L3-L5, L4-S2, S2-S5, L2-L3, L2-L3). Six tumors were grade II histology and 8 were grade III. Prior to radiotherapy, 3 patients had undergone a subtotal resection while the other 11 had a gross total or near total resection. One patient received chemotherapy according to the International Society of Pediatric Oncology (SIOP) infant regimen and 1 patient received chemotherapy according to Children's Oncology Group (COG) ACNS0831. For radiation, the gross tumor volume (GTV) was defined by the gross disease and/or tumor bed at the time of radiation. The CTV was defined by the GTV + 5-10 mm. The CTV received 50.4 Gy (n = 8), 52.2 (n = 1), or 54 Gy (n = 5), with the latter undergoing boost to just the GTV following the initial 50.4 Gy to respect spinal cord tolerance. For the cohort, the median maximum point dose to the spinal cord was 52.4 Gy (range, 0-53.9 Gy). The median maximum dose to 0.1 cc of spinal cord was 51.3 Gy (range, 0-52.5 Gy). The median volume of cord receiving ≥50.4 Gy was 3.4 cc (range, 0-17.1 cc).With a median follow-up of 6.3 years (range, 1.5 - 14.8 years), no tumors have progressed and all patients are alive. Serious acute toxicity was limited to 1 case of grade 2 nausea. While most patients experienced neurologic sequela following surgery, only 1 patient developed additional neurologic deficits following radiation: An 18-year-old male who received 54 Gy following gross total resection of a lumbosacral tumor developed grade 2 erectile dysfunction. There were 2 cases of chronic musculoskeletal toxicity attributable to surgery and radiation in survivors. No patients have developed cardiac, pulmonary, or other visceral organ complications, nor has any patient developed a second malignancy.These outcomes suggest that radiation to a dose of 50-54 Gy can be safely delivered and plays a beneficial role in the multidisciplinary management of children with grade II/III spinal cord ependymoma. Proton therapy may reduce the late radiation effects and is not associated with unexpected spinal cord toxicity.

Small Non-Rigid Variations Can Assist Robust IMPT Plan Selection for Head and Neck Patients

Interfraction anatomical variability increases dosimetric discrepancy during delivery of intensity-modulated proton therapy (IMPT). Small non-rigid variations (sNRVs) such as neck extension, spinal flexion, jaw and shoulder position occur during IMPT for head & neck cancer. We assess dosimetric discrepancies caused by sNRVs and suggest a population-based model to incorporate sNRVs into robust evaluation of IMPT plans.A total of 20 nasopharynx and 15 oropharynx radiotherapy patients were retrospectively analyzed, each with weekly CT scans. Anatomical variations during the first week of treatment are predominately due to sNRV, when progressive changes (weight-loss, tumor shrinkage) are less significant. Using deformable image registration, we obtained deformations between week 0/week 1 of treatment for all 35 patients, creating a distribution of possible sNRVs. The deformations from this distribution are then applied to the planning CT of two patients. Patient 1 has a laterally located gross tumor volume (GTV), patient 2 has a central GTV, both with bilateral low-risk clinical target volume (CTV). For both patients, IMPT plans using 3-field, 4-field, and 5-field beam arrangements were generated (nominal dose) and dose was forward calculated on the 35 deformed CT images representing the possible sNRV dose (n = 210) to assess dose degradation. Dose-volume histogram (DVH) bandwidths for sNRV doses were calculated per patient and beam arrangement to evaluate the robustness of the nominal plans with respect to the sNRVs.Among both patients (210 scenarios), we observe a maximum difference to the nominal dose of: 7% degradation of CTV D95, increase in parotid Dmean 10.6 Gy (RBE), increase in brainstem Dmax 14.8 Gy (RBE), increase in chiasm Dmax 18 Gy (RBE), increase in larynx Dmean15 Gy (RBE). For both patients, the 4-field plan shows the narrowest bandwidth and thus best robustness against sNRV in terms of CTV coverage (tab 1). For patient 1, the 4-field plan appears most robust in terms of organ at risk dose. For patient 2, the 3-field plan shows the best parotid sparing while dose metrics for brainstem and chiasm are similar for all beam arrangements.We demonstrate that sNRVs can substantially degrade the dose to the target volume and increase OAR doses. Including the influence of sNRVs during robust evaluation may assist in plan selection, providing information on clinical uncertainties additional to the conventional rigid isocenter shift and CT number uncertainty.

Assessing the impact of magnetic resonance treatment simulation (MRSIM) on target volume delineation and dose to organs at risk for oropharyngeal radiotherapy.

IntroductionAssessing the use of a radiation therapy (RT) planning MRI performed in the treatment position (pMRI) on target volume delineation and effect on organ at risk dose for oropharyngeal cancer patients planned with diagnostic MRI (dMRI) and CT scan.MethodsDiagnostic MRI scans were acquired for 26 patients in a neutral patient position using a 3T scanner (dMRI). Subsequent pMRI scans were acquired on the same scanner with a flat couch top and the patient in their immobilisation mask. Each series was rigidly registered to the patients planning CT scan and volumes were first completed with the CT/dMRI. The pMRI was then made available for volume modification. For the group with revised volumes, two IMRT plans were developed to demonstrate the impact of the modification. Image and registration quality was also evaluated.ResultsThe pMRI registration led to the modification of target volumes for 19 of 26 participants. The pMRI target volumes were larger in absolute volume resulting in reduced capacity for organ sparing. Predominantly, modifications occurred for the primary gross tumour volume (GTVp) with a mean Dice Similarity Coefficient (DSC) of 0.7 and the resulting high risk planning target volume, a mean DSC of 0.89. Both MRIs scored similarly for image quality, with the pMRI demonstrating improved registration quality and efficiency.ConclusionsA pMRI provides improvement in registration efficiency, quality and a higher degree of oncologist confidence in target delineation. These results have led to a practice change within our department, where a pMRI is acquired for all eligible oropharyngeal cancer patients.

Implementation and experimental validation of a robust hybrid direct aperture optimization approach for mixed-beam radiotherapy.

PurposeThe objectives of the work presented in this paper were to (1) implement a robust‐optimization method for deliverable mixed‐beam radiotherapy (MBRT) plans within a previously developed MBRT planning framework; (2) perform an experimental validation of the delivery of robust‐optimized MBRT plans; and (3) compare PTV‐based and robust‐optimized MBRT plans in terms of target dose robustness and organs at risk (OAR) sparing for clinical head and neck and brain patient cases.MethodsA robust‐optimization method, which accounts for translational setup errors, was implemented within a previously developed treatment planning framework for MBRT. The framework uses a hybrid direct aperture optimization method combining column generation and simulated annealing. A robust plan was developed and then delivered to an anthropomorphic head phantom using the Developer Mode of a TrueBeam linac. Planar dose distributions were measured and compared to the planned dose. Robust‐optimized and PTV‐based plans were developed for three clinical patient cases consisting of two head and neck cases and one brain case. The plans were compared in terms of the robustness to 5 mm shifts of the target volume dose as well as in terms of OAR sparing.ResultsUsing a gamma criterion of 3%/2 mm and a dose threshold of 10%, the agreement between film measurements and dose calculations was better than 97.7% for the total plan and better than 95.5% for the electron component of the plan. For the two head and neck patient cases, the average clinical target volume (CTV) dose homogeneity index (V95%–V107%) over all the considered setup error scenarios was on average 19% lower for the PTV‐based plans and it had a larger standard deviation. The robust‐optimized plans achieved, on average, a 20% reduction in the OAR doses compared to the PTV‐based plans. For the brain patient case, the CTV dose homogeneity index was similar for the two plans, while the OAR doses were 22% lower, on average, for the robust‐optimized plan. No clear trend in terms of electron contributions was found across the three patient cases, although robust‐optimized plans tended toward higher electron beam energies.ConclusionsA framework for robust optimization of deliverable MBRT plans has been developed and validated. PTV‐based MBRT were found to not be robust to setup errors, while the dose delivered by the robust‐optimized plans were clinically acceptable for all considered error scenarios and had better OAR sparing. This study shows that the robust optimization is a promising alternative to conventional PTV margins for MBRT.

Potential Morbidity Reduction for Lung Stereotactic Body Radiation Therapy Using Respiratory Gating.

Simple SummaryLung stereotactic body radiotherapy (SBRT) is the standard of care for early-stage lung cancer and oligometastases. For SBRT, motion has to be considered to avoid misdosage. Respiratory phase gating, meaning to irradiate the target volume only in a predefined gating motion phase window, can be applied to mitigate motion-induced effects. The aim of this study was to exploit the clinical benefit of gating for lung SBRT. For the majority of 14 lung tumor patients and various gating windows, we could prove a reduced dose to normal tissue by gating simulation. A normal tissue complication probability (NTCP) model analysis revealed a major reduction of normal tissue toxicity for moderate gating window sizes. The most beneficial effect of gating was found for those patients with the highest prior toxicity risk. The presented results are useful for personalized risk assessment prior to treatment and may help to select patients and optimal gating windows.We investigated the potential of respiratory gating to mitigate the motion-caused misdosage in lung stereotactic body radiotherapy (SBRT). For fourteen patients with lung tumors, we investigated treatment plans for a gating window (GW) including three breathing phases around the maximum exhalation phase, GW40–60. For a subset of six patients, we also assessed a preceding three-phase GW20–40 and six-phase GW20–70. We analyzed the target volume, lung, esophagus, and heart doses. Using normal tissue complication probability (NTCP) models, we estimated radiation pneumonitis and esophagitis risks. Compared to plans without gating, GW40–60 significantly reduced doses to organs at risk without impairing the tumor doses. On average, the mean lung dose decreased by 0.6 Gy (p < 0.001), treated lung V20Gy by 2.4% (p = 0.003), esophageal dose to 5cc by 2.0 Gy (p = 0.003), and maximum heart dose by 3.2 Gy (p = 0.009). The model-estimated mean risks of 11% for pneumonitis and 12% for esophagitis without gating decreased upon GW40–60 to 7% and 9%, respectively. For the highest-risk patient, gating reduced the pneumonitis risk from 43% to 32%. Gating is most beneficial for patients with high-toxicity risks. Pre-treatment toxicity risk assessment may help optimize patient selection for gating, as well as GW selection for individual patients.

Bicentric Treatment Outcomes After Proton Therapy for Nonmyxopapillary High-Grade Spinal Cord Ependymoma in Children

Few studies report outcomes in children treated with radiation for nonmyxopapillary ependymoma of the spinal cord, and little evidence exists to inform decisions regarding target volume and prescription dose. Moreover, virtually no mature outcome data exist on proton therapy for this tumor. We describe our combined institutional experience treating pediatric classical/anaplastic ependymoma of the spinal cord with proton therapy. Between 2008 and 2019, 14 pediatric patients with nonmetastatic nonmyxopapillary grade II (n=6) and grade III (n=8) spinal ependymoma received proton therapy. The median age at radiation was 14 years (range, 1.5-18 years). Five tumors arose within the cervical cord, 3 within the thoracic cord, and 6 within the lumbosacral cord. Before radiation therapy, 3 patients underwent subtotal resection, and 11 underwent gross-total or near total resection. Two patients received chemotherapy. For radiation, the clinical target volume received 50.4 Gy (n=8), 52.2 (n=1), or 54 Gy (n=5), with the latter receiving a boost to the gross tumor volume after the initial 50.4 Gy, modified to respect spinal cord tolerance. With a median follow-up of 6.3 years (range, 1.5-14.8 years), no tumors progressed. Although most patients experienced neurologic sequela after surgery, only 1 developed additional neurologic deficits after radiation: An 18-year-old male who received 54 Gy after gross total resection of a lumbosacral tumor developed grade 2 erectile dysfunction. There were 2 cases of musculoskeletal toxicity attributable to surgery and radiation. At analysis, no patient had developed cardiac, pulmonary, or other visceral organ complications or a second malignancy. Radiation to a total dose of 50 to 54 Gy can be safely delivered and plays a beneficial role in the multidisciplinary management of children with nonmyxopapillary spinal cord ependymoma. Proton therapy may reduce late radiation effects and is not associated with unexpected spinal cord toxicity.

A dosimetric and radiobiological evaluation of VMAT following mastectomy for patients with left-sided breast cancer

BackgroundTo compare the dosimetric, normal tissue complication probability (NTCP), secondary cancer complication probabilities (SCCP), and excess absolute risk (EAR) differences of volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) for left-sided breast cancer after mastectomy.Methods and materialsThirty patients with left-sided breast cancer treated with post-mastectomy radiation therapy (PMRT) were randomly enrolled in this study. Both IMRT and VMAT treatment plans were created for each patient. Planning target volume (PTV) doses for the chest wall and internal mammary nodes, PTV1, and PTV of the supraclavicular nodes, PTV2, of 50 Gy were prescribed in 25 fractions. The plans were evaluated based on PTV1 and PTV2 coverage, homogeneity index (HI), conformity index, conformity number (CN), dose to organs at risk, NTCP, SCCP, EAR, number of monitors units, and beam delivery time.ResultsVMAT resulted in more homogeneous chest wall coverage than did IMRT. The percent volume of PTV1 that received the prescribed dose of VMRT and IMRT was 95.9 ± 1.2% and 94.5 ± 1.6%, respectively (p < 0.001). The HI was 0.11 ± 0.01 for VMAT and 0.12 ± 0.02 for IMRT, respectively (p = 0.001). The VMAT plan had better conformity (CN: 0.84 ± 0.02 vs. 0.78 ± 0.04, p < 0.001) in PTV compared with IMRT. As opposed to IMRT plans, VMAT delivered a lower mean dose to the ipsilateral lung (11.5 Gy vs 12.6 Gy) and heart (5.2 Gy vs 6.0 Gy) and significantly reduced the V5, V10, V20, V30, and V40 of the ipsilateral lung and heart; only the differences in V5 of the ipsilateral lung did not reach statistical significance (p = 0.409). Although the volume of the ipsilateral lung and heart encompassed by the 2.5 Gy isodose line (V2.5) was increased by 6.7% and 7.7% (p < 0.001, p = 0.002), the NTCP was decreased by 0.8% and 0.6%, and SCCP and EAR were decreased by 1.9% and 0.1% for the ipsilateral lung. No significant differences were observed in the contralateral lung/breast V2.5, V5, V10, V20, mean dose, SCCP, and EAR. Finally, VMAT reduced the number of monitor units by 31.5% and the treatment time by 71.4%, as compared with IMRT.ConclusionsCompared with IMRT, VMAT is the optimal technique for PMRT patients with left-sided breast cancer due to better target coverage, a lower dose delivered, NTCP, SCCP, and EAR to the ipsilateral lung and heart, similar doses delivered to the contralateral lung and breast, fewer monitor units and a shorter delivery time.