Dosimetric Results Research Articles

Computed Dosimeter Dose Index on a 16-Slice Computed Tomography Scanner.

A computed tomography dose index can be used to quantify the radiation dose received during a CT scan and it is an indicator of the radiation dose to the polymetaylenmetaAcrylate (PMMA) standardized phantom. The objective of this study was 2-fold. The first was to measure the computed tomography (CT) radiation dose for the head and body polymetaylelenmetaAcrylate (PMMA) phantoms and to determine the accuracy of the CT radiation dose parameter displayed on the CT scanner console; these were measured in this investigation and compared with the dose displayed on the CT scanner console. The dose was calculated using the formalism described in the American Association of Physics in Medicine (AAPM) Report 96. The second was to compare the dosimetric results of the head and body polymetaylelenmetaAcrylate (PMMA) phantoms with dose reference levels published in international journals, as well as to measure the central cumulative dose (DL′ (0)), as recommended by the American Association of Physics in Medicine (AAPM) report 111. This is a new, cutting-edge methodology for estimating the CT radiation dosage provided by the abdomen, thorax, and head of a PMMA phantom. We used a Philips Big Bore CT scanner with 16 slices. A CT dosimeter head phantom with a diameter of 16 cm, a CT dosimeter body phantom with a diameter of 32 cm, a 100 mm pencil chamber (PC), and a 20 mm short chamber (SC) were employed. These were coupled to an electrometer and a dosimetric readout device. The measured volume computed tomography dose index (CTDIvol) values were in good agreement with the CT radiation dose displayed on the corresponding CT scanner console. The percentage disagreement was less than 10%, with a maximal difference of 1.7% and 5.5% for the body and head phantom, respectively. The central cumulative dose (DL (0)) measurements (for L′ = 100 mm) also matched nominal or the corresponding computed tomography dose index (CT) scanner console volume computed tomography dose index (CTDIvol) values. In this case, the agreement is always below 3% for abdomen scans and 1.0% for head examinations. This result implies that the radiation dose supplied by the 16-slice computed tomography (CT) system was in good agreement with the international dose reference level and we observed something different.

Dosimetric Effect of Injection Ports in Tissue Expanders on Post-Mastectomy Volumetric Modulated Arc Therapy (VMAT) Planning for Left-Sided Breast Cancer

This study aimed to compare the dosimetric effect of traditional metallic ports and radio frequency identification (RFID) ports (Motiva Flora®) on post-mastectomy volumetric modulated arc therapy (VMAT) planning for left-sided breast cancer. Computed tomography (CT) simulation was performed on an anthropomorphic torso phantom by attaching two types of tissue expander on the left chest wall. For the comparison of CT artifacts, five points of interest were selected and compared: point A = central chest wall, B = medial chest wall, point C = lateral chest wall, point D = axilla, and point E = left anterior descending artery. VMAT planning using two partial arcs with a single isocenter was generated, and dosimetric parameters were investigated. Compared to metallic ports, RFID ports tremendously decreased distortion on CT images, with the exception of point D. The V5Gy, V10Gy, V15Gy, V20Gy, V30Gy, and Dmean values of the heart in RFID ports were lower than those in metallic ports. The V5Gy, V15Gy, V20Gy, V30Gy, and Dmean values of the ipsilateral lung in RFID ports were also lower than those in metallic ports. RFID ports showed superior dosimetric results for doses to the heart and lungs as compared to that in metallic ports.

Endovascular Juxtarenal Aortic Aneurysm Repair Using the ALTO Abdominal Stent Graft System: The First Case Series

The ALTO abdominal stent graft system (Endologix Inc., Irvine, CA, USA) is a latest-generation polymer-based device used to treat patients with abdominal aortic aneurysms. The present study describes the first case series of patients with abdominal aortic aneurysms, including two patients with juxtarenal aneurysms, treated using the ALTO stent graft system. Six males were treated using the ALTO device at a single public center. All procedures were uneventful, and the dosimetric results recorded in terms of kerma-area product and fluoroscopy time were similar to those reported in previous studies. At the 1-month follow-up, computed tomography angiography showed no evidence of endoleak, device migration, thrombosis, or structural graft failure. This clinical series demonstrates that the use of the ALTO stent graft system is associated with promising patient outcomes. Lifelong postoperative imaging surveillance may highlight possible late failures and suggest potential graft improvements.

Pulsed-Reduced Dose Rate (PRDR) Radiotherapy for Recurrent Primary Central Nervous System Malignancies: Dosimetric and Clinical Results.

Simple SummaryPulsed-reduced dose rate (PRDR) is a technique used to safely deliver re-irradiation by targeting dividing neoplastic cells while permitting intra-therapy sublethal damage repair in previously irradiated normal tissues. However, treatment-related toxicities are not uniformly reported in previous PRDR studies; thus, it is unclear whether the cumulative thresholds (EQD2) for CNS organs-at-risk (OARs) can be designated in a “safe” category. In this study, we evaluated dosimetric data for patients treated with PRDR IMRT for recurrent primary CNS malignancies, generated accumulated equivalent uniform doses with rigid registration of all intracranial treatments, and investigated toxicity as a function of cumulative EQD2. We found that PRDR IMRT re-irradiation is a safe and feasible strategy for appropriately selected recurrent primary CNS tumor patients after exhausting other options. The clinical outcomes were favorable given the unique population treated with this approach (ineligible for other salvage treatments or enrollment onto clinical trials), and the toxicities observed were mild to moderate.Purpose: The objective was to describe PRDR outcomes and report EQD2 OAR toxicity thresholds. Methods: Eighteen patients with recurrent primary CNS tumors treated with PRDR at a single institution between April 2017 and September 2021 were evaluated. The radiotherapy details, cumulative OAR doses, progression-free survival (PFS), overall survival (OS), and toxicities were collected. Results: The median PRDR dose was 45 Gy (range: 36–59.4 Gy); the median cumulative EQD2 prescription dose was 102.7 Gy (range: 93.8–120.4 Gy). The median cumulative EQD2 D0.03cc for the brain was 111.4 Gy (range: 82.4–175.2 Gy). Symptomatic radiation necrosis occurred in three patients, for which the median EQD2 brain D0.03cc was 115.9 Gy (110.4–156.7 Gy). The median PFS and OS after PRDR were 6.3 months (95%CI: 0.9–11.6 months) and 8.6 months (95%CI: 4.9–12.3 months), respectively. The systematic review identified five peer-reviewed studies with a median cumulative EQD2 prescription dose of 110.3 Gy. At a median follow-up of 8.7 months, the median PFS and OS were 5.7 months (95%CI: 2.1–15.4 months) and 6.7 months (95%CI: 3.2–14.2 months), respectively. Conclusion: PRDR re-irradiation is a relatively safe and feasible treatment for recurrent primary CNS tumors. Despite high cumulative dose to OARs, the risk of high-grade, treatment-related toxicity within the first year of follow-up remains acceptable.

Sequential treatment with gemcitabine/nab-paclitaxel (GA) and FOLFIRINOX (FFX) followed by stereotactic MRI-guided adaptive radiation therapy (SMART) in patients with locally advanced pancreatic cancer (LAPC): GABRINOX-ART phase 2, multicenter trial.

TPS4191 Background: LAPC represents a major challenge with no standardized chemotherapy (CT) and radiotherapy (RT) treatment. Phase 2 studies (LAPACT/NEOLAP) indicated efficacy of FFX and GA, although addition of conventionally fractionated RT remains controversial. Phase 3 LAP07 trial obtained a reduction of progression free survival (PFS), albeit with no overall survival (OS) advantage. Since in metastatic pancreatic cancer we recently attained with GA/FFX sequential combination (GABRINOX) high objective response rate and promising OS with acceptable toxicity and no limiting neurotoxicity, we proposed in LAPC to complement GABRINOX with SMART, recently recognized beneficial in pancreatic tumors by a retrospective multicenter study (OS at 2 years) and our prospective registry study (dosimetric benefit of adaptation). In a first step (SEQ1), we will evaluate GABRINOX efficacy and select patients without progression for a second step (SEQ2), to evaluate feasibility and tolerance in patients without disease progression after SEQ1. Secondarily we will evaluate CT tolerance (SEQ1), acute toxicities and dosimetric results (SEQ2) and for both SEQ1+2, late toxicities, response to treatment, PFS, OS and quality of life (QoL). Methods: Naive patients with confirmed non-metastatic unresectable adenocarcinoma by centralized reading (WHO 0/1) and adequate organ function will receive in SEQ1 two cycles of GABRINOX, GA (1000 mg/m2, 125 mg/m2) on days 1, 8, and 15 followed by FFX on day 29 and 43. After 3-4 weeks, patients without progression or unacceptable toxicity will benefit from SMART (5 fractions of 10 Gy/day over 5 consecutive days). Specific dummy-run, contouring quality assurance and dosimetric plans will precede post-treatment monitoring every 6 weeks for 6 months for non-progressive patients and then every 2 months until progression: radiological assessment, biological markers (circulating tumor DNA) and QoL evaluation. Co-primary endpoints include success of SEQ1 (non-progression at 4 months, RECIST v1.1) and that of SEQ2 as absence of acute digestive non-toxicity rate > grade 3 (NCI-CTCAE v5.0) within 90 days. Based on Fleming design with maximal inefficacy (p0) of 70% and 90% (α = 2.5% and β = 5%) we need 98 and 70 patients (SEQ1 and SEQ2), and total of 103 cases considering those entering in SEQ 2 (70%) and non-evaluable patients. Success rate, toxicities (by treatment sequences) and safety (System Organ Class) by patient and cycle will be considered while dosimetry will be correlated with gastro-intestinal toxicities. Median follow-up, OS and PFS will be expressed as medians and rates with 95% CI while QoL will be explored by QLQ-C30 and QLQ-PAN26 analyses using the time to definitive deterioration. From 2021, we included 5 patients (NCT04570943). Clinical trial information: NCT04570943.

Ultra-Hypofractionated vs. Moderate Fractionated Whole Breast Three Dimensional Conformal Radiotherapy during the COVID-19 Pandemic.

Background and Objectives: Reducing time of treatment during COVID-19 outbreaks has been recommended by the leading Radiation Oncology societies. Still minimizing radiation induced tissue toxicity is one of the most important issues in breast cancer patients. The study aimed to investigate compliance, clinical and dosimetry normal tissue toxicity, and cosmetic results between moderated and ultra-fractionated regimes for breast cancer patients during COVID-19 pandemic. Materials and Methods: This pilot prospective randomized study included 60 patients with early breast cancer after preserving surgery, 27 patients advocated to ultra-hypofractionated whole-breast three dimensional (3D) conformal radiotherapy of 26 Gy in 5 fractions over 1 week and 33 patients with moderate fractionated breast 3D conformal radiotherapy patients between March 2020 and July 2020, during the COVID pandemic outbreak. The compliance to treatment, dosimetric parameters, acute and late skin toxicity, subcutaneous tissue toxicity, cosmetic results and clinical follow up for 18 months for the two regimes were analyzed and compared. Results: When two regimes were compared 5 fraction group had significantly lower prevalence of newly infected cases of SARS-CoV-2 and thus delayed/interrupted treatment (p = 0.05), comparable grade 1 CTCAE v5, acute skin toxicity (p = 0.18), Grade 1 Radiation Morbidity Scoring Scheme (RESS) subcutaneous tissue toxicity (p = 0.18), Grade 1 RESS late skin toxicity (p = 0.88) and cosmetic results (p = 0.46). Dosimetric results reveled that patients in 5 fraction group received significantly lower median ipsilateral lung doses (p < 0.01) in addition to left breast cancer patients that received significantly lower median heart dose (p < 0.01) and median left anterior descending artery (LAD) dose (p < 0.01). Conclusion: Ultra-hypofractionated radiotherapy for breast cancer is comparable to moderate hypofractionation regimen regarding grade 1 acute skin toxicity, grade 1 subcutaneous tissue toxicity, late skin toxicity and cosmetic results. Application of ultra-hypofractionated radiotherapy with significantly lower radiation doses for lung and heart could be crucial in reducing the risk of acute/late pulmonary and heart radiation-induced toxicity.

SBRT for Localized Prostate Cancer: CyberKnife vs. VMAT-FFF, a Dosimetric Study.

In recent years, stereotactic body radiation therapy (SBRT) has gained popularity among clinical methods for the treatment of medium and low risk prostate cancer (PCa), mainly as an alternative to surgery. The hypo-fractionated regimen allows the administration of high doses of radiation in a small number of fractions; such a fractionation is possible by exploiting the different intrinsic prostate radiosensitivity compared with the surrounding healthy tissues. In addition, SBRT treatment guaranteed a better quality of life compared with surgery, avoiding risks, aftermaths, and possible complications. At present, most stereotactic prostate treatments are performed with the CyberKnife (CK) system, which is an accelerator exclusively dedicated for stereotaxis and it is not widely spread in every radiotherapy centre like a classic linear accelerator (LINAC). To be fair, a stereotactic treatment is achievable also by using a LINAC through Volumetric Modulated Arc Therapy (VMAT), but some precautions must be taken. The aim of this work is to carry out a dosimetric comparison between these two methodologies. In order to pursue such a goal, two groups of patients were selected at Instituto Nazionale Tumori—IRCCS Fondazione G. Pascale: the first group consisting of ten patients previously treated with a SBRT performed with CK; the second one was composed of ten patients who received a hypo-fractionated VMAT treatment and replanned in VMAT-SBRT flattening filter free mode (FFF). The two SBRT techniques were rescaled at the same target coverage and compared by normal tissue sparing, dose distribution parameters and delivery time. All organs at risk (OAR) constraints were achieved by both platforms. CK exhibits higher performances in terms of dose delivery; nevertheless, the general satisfying dosimetric results and the significantly shorter delivery time make VMAT-FFF an attractive and reasonable alternative SBRT technique for the treatment of localized prostate cancer.

Oligorecurrent nodal prostate cancer: Radiotherapy quality assurance of the randomized PEACE V-STORM phase II trial

PurposeAim of this study is to report the results of the radiotherapy quality assurance program of the PEACE V-STORM randomized phase II trial for pelvic nodal oligorecurrent prostate cancer (PCa). Material and methodsA benchmark case (BC) consisting of a postoperative case with 2 nodal recurrences was used for both stereotactic body radiotherapy (SBRT, 30 Gy/3 fx) and whole pelvic radiotherapy (WPRT, 45 Gy/25 fx + SIB boost to 65 Gy). ResultsBC of 24 centers were analyzed. The overall grading for delineation variation of the 1st BC was rated as ‘UV’ (Unacceptable Variation) or ‘AV’ (Acceptable Variation) for 1 and 7 centers for SBRT (33%), and 3 and 8 centers for WPRT (46%), respectively. An inadequate upper limit of the WPRT CTV (n = 2), a missing delineation of the prostate bed (n = 1), and a missing nodal target volume (n = 1 for SBRT and WPRT) constituted the observed ‘UV’. With the 2nd BC (n = 11), the overall delineation review showed 2 and 8 ‘AV’ for SBRT and WPRT, respectively, with no ‘UV’. For the plan review of the 2nd BC, all treatment plans were per protocol for WPRT. SBRT plans showed variability in dose normalization (Median D90% = 30.1 Gy, range 22.9–33.2 Gy and 30.6 Gy, range 26.8–34.2 Gy for nodes 1 and 2 respectively). ConclusionsUp to 46% of protocol deviations were observed in delineation of WPRT for nodal oligorecurrent PCa, while dosimetric results of SBRT showed the greatest disparities between centers. Repeated BC resulted in an improved adherence to the protocol, translating in an overall acceptable contouring and planning compliance rate among participating centers.

Assessment of Twin Fetal Exposure to Environmental Magnetic and Electromagnetic Fields.

Fetal development is vital in the human lifespan. Therefore, it is essential to characterize exposure by a series of typical environmental magnetic and electromagnetic fields. In particular, there has recently been a sharp increase in the twin birth rate. However, lack of appropriate models has prohibited dosimetric evaluation, restricting characterization of the impact of these environmental factors on twins. The present study developed two whole-body pregnant models of 31 and 32 weeks of gestation with twin fetuses and explored several typical exposure scenarios, including 50-Hz uniform magnetic field exposure, local 125-kHz magnetic field (MF), and 13.56-MHz electromagnetic field exposure, as well as wideband planewave radiofrequency (RF) exposure from 20 to 6000 MHz. Finally, dosimetric results were derived. Compared to the singleton pregnancy with similar weeks of gestation, twin fetuses were overexposed at 50-Hz uniform MF, but they were probably underexposed in the RF scenarios with frequencies for wireless communications. Furthermore, the twin fetuses manifested large dosimetric variability compared to the singleton, which was attributed to the incident direction and fetal position. Based on the analysis, the dosimetric results over the entire gestation period were estimated. The results can be helpful to estimate the risk of twin-fetal exposure to electromagnetic fields and examine the conservativeness of the international guidelines.© 2022 Bioelectromagnetics Society.

A novel analytical method for computing dose from kilovoltage beams used in Image-Guided radiation therapy

PurposeA modified convolution/superposition algorithm is proposed to compute dose from the kilovoltage beams used in IGRT. The algorithm uses material-specific energy deposition kernels instead of water-energy deposition kernels. MethodsMonte Carlo simulation was used to model the Elekta XVI unit and determine dose deposition characteristics of its kilovoltage beams. The dosimetric results were compared with ion chamber measurements. The dose from the kilovoltage beams was then computed using convolution/superposition along with material-specific energy deposition kernels and compared with Monte Carlo and measurements. The material-specific energy deposition kernels were previously generated using Monte Carlo. ResultsThe obtained gamma indices (using 2%/2mm criteria for 95% of points) were lower than 1 in almost all instances which indicates good agreement between simulated and measured depth doses and profiles. The comparisons of the algorithm with measurements in a homogeneous solid water slab phantom, and that with Monte Carlo in a head and neck CT dataset produced acceptable results. The calculated point doses were within 4.2% of measurements in the homogeneous phantom. Gamma analysis of the calculated vs. Monte Carlo simulations in the head and neck phantom resulted in 94% of points passing with a 2%/2mm criteria. ConclusionsThe proposed method offers sufficient accuracy in kilovoltage beams dose calculations and has the potential to supplement the conventional megavoltage convolution/superposition algorithms for dose calculations in low energy range.

Evaluation of Auto-Contouring and Dose Distributions for Online Adaptive Radiation Therapy of Patients With Locally Advanced Lung Cancers

PurposeRetrospective studies were performed to evaluate the accuracy of automatically mapped structures and dosimetric consequences of daily online adaptive radiation therapy (ART) for lung cancer treatments. Methods and MaterialsTen patients with locally advanced lung cancer (prescription = 2 Gy × 30) with 297 fractions of treatment were selected for this retrospective study on a research emulator (Ethos, Varian Medical Systems). All adaptive treatments were simulated twice: automatic-ART (A-ART), automatic contours were used without modification, and supervised-ART (S-ART), automatic contours were modified manually by physicians and physicists. Dosimetric results were analyzed by relating supervised scheduled (S-SCH) dose (initial baseline reference plan delivered on daily anatomy and supervised contour correction without any adaptation), A-ART and S-ART to the initial baseline reference dose. ResultsTwo hundred ninety (of 297) fractions were analyzed. Comparing target volumes between A-ART and S-ART, dice similarity coefficient was 0.93 ± 0.05, mean contour distance was 1.5 ± 1.2 mm, and Hausdorff distance was 4.0 ± 2.3 mm. Analysis of daily results over 290 fractions of treatment showed that average target coverage improved from 0.96 ± 0.04 (S-SCH) to 1.00 ± 0.02 (A-ART) and 1.02 ± 0.04 (S-ART); average upper dose constraint was reduced from 1.01 ± 0.11 (S-SCH) to 0.94 ± 0.10 (A-ART) and 0.93 ± 0.12 (S-ART). A-ART and S-ART improved planning target volume minimum doses by 4.85 ± 3.03 Gy (P = .049) and 4.46 ± 8.99 Gy (P = .058), respectively. Statistical analysis shows that A-ART and S-ART significantly improved cumulative target dose by 0.033 ± 0.087 (P = .002) and 0.032 ± 0.086 (P = .003) and reduced upper constraints by 0.033 ± 0.072 (P < .001) and 0.032 ± 0.072 (P < .001) relative to S-SCH dose results, respectively. ConclusionsAccuracy of Ethos automatic contouring for lung cancer is considered clinically acceptable. The online adaptive radiation therapy improves target coverage and spares organs-at-risk significantly.

Implementation of volumetric-modulated arc therapy for locally advanced breast cancer patients: Dosimetric comparison with deliverability consideration of planning techniques and predictions of patient-specific QA results via supervised machine learning

PurposeThe aim of this study was to implement a clinically deliverable VMAT planning technique dedicated to advanced breast cancer, and to predict failed QA using a machine learning (ML) model to optimize the QA workload. MethodsFor three planning methods (2A: 2-partial arc, 2AS: 2-partial arc with splitting, 4A: 4-partial arc), dosimetric results were compared with patient-specific QA performed with the electronic portal imaging device of the linac. A dataset was built with the pass/fail status of the plans and complexity metrics. It was divided into training and testing sets. An ML metamodel combining predictions from six base classifiers was trained on the training set to predict plans as ‘pass’ or ‘fail’. The predictive performances were evaluated using the unseen data of the testing set. ResultsThe dosimetric comparison highlighted that 4A was the highest dosimetric performant method but also the poorest performant in the QA process. 2AS spared the best heart, but provided the highest dose to the contralateral breast and lowest node coverage. 2A provides a dosimetric compromise between organ at risk sparing and PTV coverage with satisfactory QA results. The metamodel had a median predictive sensitivity of 73% and a median specificity of 91%. ConclusionsThe 2A method was selected to calculate clinically deliverable VMAT plans; however, the 2AS method was maintained when the heart was of particular importance and breath-hold techniques were not applicable. The metamodel provides promising predictive performance, and it is intended to be improved as a larger dataset becomes available.

An evaluation of the use of EBT-XD film for SRS/SBRT commissioning of a 1.5 Tesla MR-Linac system

PurposeThe goal of this study was to evaluate the use of EBT-XD film for SRS/SBRT commissioning in a 1.5T hybrid MR-Linac (MRL). MethodThe output factors (St), from 1x1, 2x2, 3x3 cm2, were measured with film in solid water. The results were compared with (1) the measurements by a PTW diamond detector (CVD) and an Exradin® A26MR ion chamber in 3D water phantom; (2) Monte Carlo calculation by Monaco TPS (MTPS) in water. The inline (IN) and crossline (CR) profiles, measured by films and the CVD, were also compared. An SRS plan with two targets was created in MTPS and was measured with EBT-XD film in a StereoPHANTM phantom serving as an end-to-end test. The 3x3 cm2 was used for film calibration with doses ranging from 0 to 28 Gy. Water was added to the phantom-film-phantom interface to reduce the electron-return-effect (ERE). Films were calibrated with One-scan-dosimetry protocol. ResultsThe film St were within 1.2% and 2.2% compared to other detectors and MTPS respectively. At the central B-field induced asymmetric region, films were within 0.6% between the CVD and the MTPS, but 5–8% differences were observed in the 40%-5% gradient region in CR due to ERE. The differences in localization and dose were found to be 0.6 mm and 3.3%. The γ(3%/2mm), γ (5%/2mm), γ (5%/1mm) were 97.7%, 99.3%, 94.6%. ConclusionsFilms can provide accurate dosimetric results under ERE and are valuable for commissioning MRL. Using the One-scan-dosimetry protocol with EBT-XD film for MRL increases accuracy and efficiency in commissioning and QA of SRS/SBRT.

Brain stereotactic radiosurgery using MR-guided online adaptive planning for daily setup variation: An end-to-end test.

Online magnetic resonance (MR)‐guided radiotherapy is expected to benefit brain stereotactic radiosurgery (SRS) due to superior soft tissue contrast and capability of daily adaptive planning. The purpose of this study was to investigate daily adaptive plan quality with setup variations and to perform an end‐to‐end test for brain SRS with multiple metastases treated with a 1.5‐Tesla MR‐Linac (MRL). The RTsafe PseudoPatient Prime brain phantom was used with a delineation insert that includes two predefined structures mimicking gadolinium contrast‐enhanced brain lesions. Daily adaptive plans were generated using six preset and six random setup variations. Two adaptive plans per daily MR image were generated using the adapt‐to‐position (ATP) and adapt‐to‐shape (ATS) workflows. An adaptive patient plan was generated on a diagnostic MR image with simulated translational and rotational daily setup variation and was compared with the reference plan. All adaptive plans were compared with the reference plan using the target coverage, Paddick conformity index, gradient index (GI), Brain V12 or V20, optimization time and total monitor units. Target doses were measured as an end‐to‐end test with two ionization chambers inserted into the phantom. With preset translational variations, V12 from the ATS plan was 17% lower than that of the ATP plan. With a larger daily setup variation, GI and V12 of the ATS plan were 10% and 16% lower than those of the ATP plan, respectively. Compared to the ATP plans, the plan quality index of the ATS plans was more consistent with the reference plan, and within 5% in both phantom and patient plans. The differences between the measured and planned target doses were within 1% for both treatment workflows. Treating brain SRS using an MRL is feasible and could achieve satisfactory dosimetric goals. Setup uncertainties could be accounted for using online plan adaptation. The ATS workflow achieved better dosimetric results than the ATP workflow at the cost of longer optimization time.

Estimation of pelvic lymph node dose contribution from HDR ICBT in cervical cancer

Context: Dose received to each pelvic group of lymph nodes, namely obturator (OB), internal iliac (II), and external iliac (EI), is less certain. This study is conducted to evaluate the dose delivered to these nodal groups so that this can be considered while planning external beam radiotherapy external beam radiation therapy (EBRT) boost in patients with gross pelvic lymph nodes. Aims: This study aimed to estimate the dose contribution to pelvic lymph nodes in three-dimensional high-dose-rate intracavitary radiotherapy (HDR-ICRT) of cervical cancer patients. Settings and Design: This was a single-arm retrospective observational study among 25 locally advanced carcinoma cervix patients treated with definitive chemoradiation. Materials and Methods: EI, II, and OB groups of lymph nodes were delineated on computed tomography data sets of selected 25 patients, and D100, D50, and D2cc to each lymph node were analyzed. The dose received by each pelvic lymph node group from all the 3 fractions of HDR-ICRT, corresponding equivalent 2 Gy dose, and percentage of brachytherapy (BT) contribution to each pelvic lymph node were calculated. Results: Mean D100 received by EI, II, and OB lymph node groups after summation across 3 fractions was 1.1 Gy, 2.34 Gy, and 3.11 Gy, respectively. Mean 2 Gy equivalent doses (D100) were 1.66 Gy, 3.41 Gy, and 4.53 Gy, respectively. Corresponding percentage of the dose received by EI, II, and OB was 4.89%, 10.43%, and 13.83% when 7.5 Gy per fraction for 3 fractions was prescribed to Point A. Conclusions: There is a significant contribution from HDR intracavitary BT to the pelvic lymph nodes in the radical treatment of cervical cancer. The dosimetric results given in this work can be used by a radiation oncologist to estimate BT doses to affected lymph nodes and integrate them into the preceding EBRT planning phase.

Dosimetric comparison of robotic- and LINAC-based treatment of spine stereotactic body radiotherapy.

To determine which treatment technique and modality would offer better dosimetric results and be preferable for spinal stereotactic body therapy (SBRT) depending on the three different regions of the vertebrae. Linear accelerator (LINAC)- and CyberKnife (CK)-based treatment techniques were compared in terms of their dosimetric quality, treatment efficiency, and delivery accuracy. Thirty previously treated patients were included in this study. Intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques were used for LINAC-based treatment, whereas CK-based treatment plans were generated for two different collimator systems: fixed and multileaf collimator (MLC). The plans were compared based on spinal cord sparing, dose homogeneity, conformity index (CI), gradient index (GI), monitor unit (MU), and beam-on time. The percentage volumes of V2Gy, V5Gy (representing volume low of the dose spillage region), V10Gy, and V20Gy (representing the volume of the high-dose spillage region) of the healthy tissue were analyzed. The CI and GI of the VMAT plans were better than those of the IMRT plans. For spinal cord sparing, the VMAT and MLC-based CK (CK-MLC) techniques were superior. The percentage of low-dose spillage regions was the lowest for IMRT and fixed cone-based CK (CK-FIX) plans. The percentage of the high-dose spillage region was the lowest for the VMAT and CK-MLC plans. In terms of treatment efficiency, the VMAT and CK-MLC plans were superior to the IMRT and CK-FIX plans. The VMAT technique lowered the MU and beam-on time values. The plan delivery accuracy of the VMAT and CK-FIX plans was better than that of the IMRT plans. VMAT is the best option for LINAC-based spinal SBRT. For CK-based spinal SBRT, MLC-based plans are preferred. If the clinic has both treatment modalities and the patient can tolerate long treatment times, CK-MLC-based treatment should be chosen because of its superiority in sparing the spinal cord and sharp dose fall-off.

Commissioning and Dosimetric Results of an Indigenously Developed Intra-Vaginal Template for Interstitial Plus Intracavitary High dose Rate Image-Guided Brachytherapy of Advanced Cervix Cancer.

The goal of this study is to discuss the commissioning and dosimetric parameters achieved during the clinical implementation of an indigenously developed intracavitary (IC) plus interstitial (IS) template for high dose rate (HDR) image-guided brachytherapy (IGBT) in cancer (Ca) cervix. We want to discuss our achieved values of cumulative equi-effective doses (EQD2) for high-risk clinical target volume (HRCTV) and organ at risk (OAR) and compare it with available published results. Medanta anterior oblique/lateral oblique template has a total of 19 needles including the central tandem. For commissioning the template with needles, the indigenously made acrylic phantom was used. Oblique and straight needles were placed inside the acrylic phantom and a computed tomography (CT) scan was performed. Sixteen patients were treated in HDR IGBT using this template after external-beam radiotherapy. The IGBT plans were evaluated based on EQD2 of target coverage i.e., dose received by 98% (D98%_HRCTV), 90% (D90%_HRCTV), and 50% (D50%_HRCTV) volume of HRCTV, and dose received by 2 cc (D2cc) and 0.1 cc (D0.1cc) of OAR using linear quadratic (LQ) radiobiological model. The autoradiographic in radiochromic film shows that the distance between the needle tip and the middle of the source position is 6 mm. The mean D98%_HRCTV and D90%_HRCTV was 76.8 Gy (range: 70-87.7 Gy, P < 0.01) and 84.49 Gy (range: 76.6-96.7 Gy, P < 0.01), respectively. Mean EQD2 of D2cc of the bladder, rectum, and sigmoid was 85.6 Gy (range: 77.5-99.6 Gy, P < 0.03), 74.3 Gy (range: 70.9-76.7 Gy, P < 0.05), and 58.3 Gy (range: 50.6-67.9 Gy, P = 0.01), respectively. The mean total reference air kerma at a 1 m distance is 0.489cGy (range: 0.391-0.681cGy). The indigenously developed template could attain satisfactory standards in terms of set parameters for commissioning and acceptable dose volume relations in our clinical use for treating the advanced Ca cervix patients who need IC + IS type of HDR IGBT. The comparative analysis with contemporary applicators was acceptable.

Quantitative Comparison of Dosimetric Data Between the Indigenous Baseplate and Commercially Available Carbon Fiber Baseplate for 6 and 15 MV Photon Energy.

Background:This study aims to design an indigenous baseplate (ID baseplate) that is economically viable and dosimetrically comparable for radiotherapy patient treatment. An ID baseplate was designed and manufactured using wood plastic composition materials that are readily available in the market and were compared dosimetrically with the commercially available carbon fiber baseplate (CF baseplate).Materials and Methods:Surface dose and beam attenuation properties of both the baseplates (ID and CF) were measured using a parallel plate chamber and compared with the dose calculated from the treatment planning system (TPS). Separate computer tomography images of both the baseplates were acquired by placing solid water phantoms. These images were used for surface dose calculation in the TPS and were validated with experimental measurements. Proper densities were assigned to the couch and baseplates to avoid uncertainties in dose calculations. All measurements were performed at field sizes 10 cm × 10 cm for 6 MV and 15 MV photon beams.Results:The percentage surface dose measured for the ID baseplate and CF baseplate was found to be matching for 6 MV beam (98.2% and 97%, respectively); however, for the 15 MV beam, the ID baseplate showed a higher surface dose of 98.6% compared to CF baseplate (87.4%). For the ID baseplate, the percentage difference in the surface dose between that TPS calculated value and the measured values were 1.6% and 1.4% for 6MV and 15MV, respectively. The ID baseplate showed higher beam attenuation than the CF baseplate by 2.2% for the 6MV beam and 3.4% for the 15MV beam when proper electron densities were not assigned. The difference between the TPS calculated dose and delivered dose was achieved within 3% after assigning proper electron density to the couch and baseplate.Conclusions:The ID baseplate has shown acceptable dosimetric results and can be an economically viable alternative to the commercially available CF baseplates. The manufacturing cost of the ID baseplate was ten times cheaper than the CF baseplate.

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.

Convolution neural network toward Monte Carlo photon dose calculation in radiation therapy.

The Monte Carlo (MC) algorithm has been widely accepted as the most accurate algorithm for dosimetric calculations under various conditions in radiotherapy. However, the calculation time remains an important obstacle hindering the routine use of MC in clinical settings. In this study, full MC three-dimensional dose distributions were obtained with the inputs of the total energy release per unit mass (TERMA) distributions and the electron density (ED) distributions using a convolutional neural network (CNN). A new Dose-mixup data augmentation routine and training strategy are proposed and applied in the training process. Attempts were made to reduce the calculation time while ensuring that the calculation accuracy is comparable to that of the MC. Datasets were generated via the MC with random rectangular field sizes, random iso-centers, and random gantry angles for head and neck computed tomography (CT) images with Mohan 6-MV spectrum photon beams. 1500 samples were generated for the training set, and 150 samples were generated for the validation set. The T-MC Net model was obtained with the Dose-mixup data augmentation routine. The new CTs were used to test the performance of the model in the rectangular fields and the intensity-modulated radiation therapy (IMRT) fields. The mean ± 95% confidence interval of gamma pass rates were calculated. For 150 rectangular field test samples, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 90.11% ± 0.65%, 97.65% ± 0.31%, and 99.16% ± 0.19%, respectively. For the 100 IMRT field test samples, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 96.48% ± 0.28%, 99.14% ± 0.10%, and 99.63% ± 0.06%, respectively. For the 7-fields IMRT plan, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 97.06%, 99.10%, and 99.52%, respectively. For the 9-fields IMRT plan, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 98.16%, 99.61%, and 99.89%, respectively. The feasibility of calculating dose distribution using a CNN with the TERMA three-dimensional distribution and ED distribution was established. The dosimetric results were comparable to those of the full MC. The accuracy and speed of the proposed approach make it a potential solution for full MC in radiotherapy. This method may be used as an acceleration engine for the dose algorithm and shows great potential for cases where fast dose calculations are needed.