Intensity-modulated Radiation Therapy Treatment Plans Research Articles

Prediction of Optimal Dosimetry for Intensity-Modulated Radiotherapy With a Cascaded Auto-Content Deep Learning Model

<h3>Purpose/Objective(s)</h3> The treatment planning of intensity-modulated radiotherapy (IMRT) is often time-consuming and needs multiple rounds of trials and errors. The unknown optimal dosimetry of anatomy mainly causes the difficulty. This study aims to develop a deep learning model to predict the dose distribution of a new patient, which has a similar diametric quality to previous clinical plans. <h3>Materials/Methods</h3> The dataset comes from the international competition for the dosimetry prediction of head and neck patients (2020 OpenKBP) with three target prescriptions (56 Gy, 63 Gy, and 70 Gy). The evaluation criterion is pixel-by-pixel dose discrepancy and point-by-point DVH difference. The organizer provides 200 training cases. Each has one planning CT image, one dose distribution, and one segmentation mask of seven organs-at-risks (OARs, brainstem, spinal cord, right parotid, left parotid, larynx, esophagus, and mandible). 40 cases are provided as a validation set with CT and segmentation mask only. The organizer reported the prediction quality for these 40 validation patients to help the model refining, but did not disclose the ground truth dosimetry. Finally, 100 testing cases were used to evaluate the model performance. We proposed a triple-stage cascaded U-Net to predict the dose distribution in a coarse-to-fine manner using the auto-context mechanism. Specifically, the first U-Net takes the CT image and structure contours as input and outputs a coarse dose distribution. This distribution is then fed into the second U-Net together with the CT image and contours, to predict a refined dose distribution. Finally, the third U-Net takes both dose distribution predicted by the first and second U-Net together with the CT image and contours to generate the final dose distribution, which is a refinement of the previous two predictions. The network is fully implemented in 3D manners (which means it takes the 3D CT volume as input, not 2D CT slices). It takes about 17 hours to train the model for 400 epochs, using a batch size of 6 and Adam optimizer with a base learning rate of 0.0005 on a GPU server equipped with six NVIDIA TITAN Xp graphic cards with 12 GBytes of memory each. The prediction is almost instantaneous, about 0.2 seconds per case. <h3>Results</h3> We found the proposed method's performance is better with 200 training cases than with 160 cases, which demonstrated the data reliance of the deep learning-based methods. The dose similarity score and DVH similarity score from 100 testing cases are 2.753 and 1.559, respectively. Our model has one of the best performances among the participants. The predicted dosimetry is similar to the realistic one, with no clinically meaningful difference. <h3>Conclusion</h3> We developed a novel cascaded auto-context deep learning model to predict optimal dosimetry of a head and neck patient. The model achieved satisfactory performance for clinical use.

Non-Coplanar vs. Coplanar Intensity-Modulated Radiation Therapy (IMRT) for Protection of Lip and Buccal Mucosa

In this study, by comparing the coplanar and non-coplanar intensity-modulated radiation therapy (IMRT) treatment planning in treating tongue cancer, the significance of non-coplanar fields in the protection of lip and buccal mucosa was determined, and a reasonable solution was selected.48 tongue cancer patients treated from June 2019 to Feb 2021 were selected and divided into coplanar field group and non-coplanar field group randomly: the former one used divided nine fields on average while the latter one adopted seven fields meanly with two other fields which needed to turn the bed 270 degrees for making the angle of radiation ray tangent to the region of mucous membrane. The mucosal dose limit changed from 15 Gy to 45 Gy for comparison of the two treatment plans. The evaluating indicators including conformal index (CI), homogeneity index (HI), D5, D50, D98 of the target volume. The dose of normal tissues and organs including spine, throat, bilateral parotid gland, pharyngeal constrictor and oral mucosa (lip, upper and lower buccal mucosa) were calculated under different mucosal dose limit. The clinical manifestations of lip and buccal mucositis of 48 cases were recorded and graded by NCI-CTCAE 4.0. Corresponding statistical analysis were performed.The difference of CI, HI, D98, D50 and D5 between two groups in the target volume has the tendency to become smaller when the mucosal dose limit is less than 30 Gy, with significant statistical difference (P < 0.05). When the limit exceeds 30 Gy, there are still statistical differences in other indicators except CI (P < 0.05). In terms of normal tissue, a certain gap of doses on normal tissues between two groups exists when the mucosal limit is lower than 20 Gy, with significant statistical difference (P < 0.05). When the limit exceeds 20 Gy, there was no statistical difference. There are statistical differences (P < 0.05) in D98, D50, D5, CI and HI of the target area between the two groups when the mucosal function setting is less than 30 Gy. When the mucosal function setting exceeds 30 Gy, there is no statistical difference in CI, but there were still statistical differences in others (P < 0.05). In normal tissue, there is statistical difference (P < 0.05) between two treatment plans when mucosal function setting is smaller than 20 Gy; if it exceeds, there is no statistical difference. The patients of non-coplanar group showed better results in terms of the radiation-related toxicity of lip and cheek membrane: the incidence rate and classification of severity were much lower. Patients usually developed lip and buccal mucositis after the fourth week during the radiotherapy, and symptoms of most cases were classified mild. 21 cases ranked grade I while the remaining 3 ranked grade II.Compared with coplanar field, non-coplanar field radiotherapy can effectively reduce the exposure dose of lip and buccal mucosa. The application of non-coplanar treatment plan has good clinical significance and deserves to be promoted.

Longitudinal Remote IMRT Training in Africa: A Prospective Cohort Study

<h3>Purpose/Objective(s)</h3> Intensity-modulated radiation therapy (IMRT) can significantly enhance patient outcomes compared to 3D-conformal radiotherapy (3D-CRT), yet African patients' access to IMRT is sparse. Limited opportunities for continuing education and training for radiation oncology professionals has been identified as a significant problem. We aimed to evaluate a telehealth training curriculum for clinicians and medical physicists in low- and middle- income countries in Africa. <h3>Materials/Methods</h3> A 30-session remote training program on transitioning from 3D to IMRT was provided at no cost to radiation oncology centers in Africa and one sister institution in Pakistan. The program consisted of twice weekly 1-hour live video conferencing sessions for 4 months with interactive didactics and case-based learning utilizing a cloud-based contouring platform. 15 radiation oncology centers across Africa were invited to participate, of which 13 were transitioning to, or had recently began, IMRT programs. A Likert scale (1-5) confidence evaluation on 7 foundational domains of IMRT treatment planning and delivery, 8 physics-specific domains, and 3 physician-specific domains was electronically administered to enrolled individuals pre- and post- curriculum. Participation was tracked for each session. <h3>Results</h3> A total of 12 centers (9 public, 2 private, and 1 semi-private) formally enrolled in training. Of these, 4 began IMRT in the last 3 years and 8 had plans to transition from 3D-CRT to IMRT. 128 individuals participated: 47 medical physicists (36.7%), 21 radiation oncologists (16.4%), 16 radiation therapists (12.5%), 30 residents (23.4%), 9 medical physics trainees (7.0%), and 5 other staff (3.9%). Average participation per session was 31 (range 17–83, SD = 16.6), and 36 individuals attended 10 sessions or more. 30 respondents, who attended 12/30 sessions on average (range 4 to 21, SD = 5.2), completed both pre- and post- surveys and were eligible for paired analysis. Overall pre- and post-curriculum mean self-confidence scores were 2.51 (n = 142) and 4.1 (n = 30), respectively, out of a possible 5. Paired pre- vs. post- analysis for 30 individuals revealed statistically significantly (<i>P</i> < 0.05) higher scores for 7 of 7 foundational domains (n = 30), 5 of 8 physics-specific domains (n = 15), and 3 of 3 physician-specific domains (n = 13). Higher attendance rates significantly correlated with larger gains in confidence scores (<i>P</i> = 0.047). <h3>Conclusion</h3> Longitudinal telehealth training integrating cloud-based tools for radiation oncology professionals is a viable and efficient method for continuing education in Africa. Despite low attendance rates, this program significantly and comprehensively improved confidence in IMRT across multiple training domains, with confidence improving with greater course participation. Future work remains to facilitate and explore the efficacy of similar programs and to assess concordance of participant confidence with clinical knowledge and skill.

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.

Dosimetric comparison of MR-linac-based IMRT and conventional VMAT treatment plans for prostate cancer

BackgroundThe aim of this study was to evaluate and compare the performance of intensity modulated radiation therapy (IMRT) plans, planned for low-field strength magnetic resonance (MR) guided linear accelerator (linac) delivery (labelled IMRT MRL plans), and clinical conventional volumetric modulated arc therapy (VMAT) plans, for the treatment of prostate cancer (PCa). Both plans used the original planning target volume (PTV) margins. Additionally, the potential dosimetric benefits of MR-guidance were estimated, by creating IMRT MRL plans using smaller PTV margins.Materials and methods20 PCa patients previously treated with conventional VMAT were considered. For each patient, two different IMRT MRL plans using the low-field MR-linac treatment planning system were created: one with original (orig.) PTV margins and the other with reduced (red.) PTV margins. Dose indices related to target coverage, as well as dose-volume histogram (DVH) parameters for the target and organs at risk (OAR) were compared. Additionally, the estimated treatment delivery times and the number of monitor units (MU) of each plan were evaluated.ResultsThe dose distribution in the high dose region and the target volume DVH parameters (D98%, D50%, D2% and V95%) were similar for all three types of treatment plans, with deviations below 1% in most cases. Both IMRT MRL plans (orig. and red. PTV margins) showed similar homogeneity indices (HI), however worse values for the conformity index (CI) were also found when compared to VMAT. The IMRT MRL plans showed similar OAR sparing when the orig. PTV margins were used but a significantly better sparing was feasible when red. PTV margins were applied. Higher number of MU and longer predicted treatment delivery times were seen for both IMRT MRL plans.ConclusionsA comparable plan quality between VMAT and IMRT MRL plans was achieved, when applying the same PTV margin. However, online MR-guided adaptive radiotherapy allows for a reduction of PTV margins. With a red. PTV margin, better sparing of the surrounding tissues can be achieved, while maintaining adequate target coverage. Nonetheless, longer treatment delivery times, characteristic for the IMRT technique, have to be expected.

Radiation-induced hypothyroidism in patients with nasopharyngeal carcinoma treated with intensity-modulated radiation therapy with or without chemotherapy: Development of a nomogram based on the equivalent dose

ObjectiveThe aim of this study was to establish a nomogram for predicting radiation-induced hypothyroidism (RHT) based on an equivalent dose at 2 Gy per fraction (EQD2) in patients with nasopharyngeal carcinoma (NPC) treated with intensity-modulated radiation therapy (IMRT) with or without chemotherapy. MethodsTwo hundred forty-four eligible patients with NPC were recruited for this study. Patients’ clinical factors and dose-volume parameters of the thyroid gland were retrieved from medical records and the IMRT treatment planning system, respectively. The irradiation doses were converted into EQD2 for analysis. Least absolute shrinkage and selection operator (LASSO) regression analysis and multivariate logistic regression analysis were performed to identify optimal predictors of RHT for constructing the nomogram. ResultsWith a median follow-up of 63.0 months, the cumulative incidence rates of RHT at 3 months and 1-, 2-, 3-, 4- and 5- year after IMRT were 10.2%, 36.2%, 47.6%, 54.2%, 58.8% and 69.4%, respectively. Four independent factors for predicting RHT, including gender, age, pretreatment volume of the thyroid gland and V35Gy(3Gy) of the thyroid gland, were identified and incorporated into the nomogram. The area under the ROC curve of the nomogram was 0.747 (95% confidence interval 0.685 – 0.809). Calibration curves and DCA curves showed that the nomogram was in good agreement with the actual observations and clinical usefulness. ConclusionsThe nomogram proposed in this study provides a reliable estimate of RHT risk in patients with NPC after IMRT and appears to have the potential to be a useful tool for widespread clinical applications.

Tree-based exploration of the optimization objectives for automatic cervical cancer IMRT treatment planning.

To develop and evaluate a practical automatic treatment planning method for intensity-modulated radiation therapy (IMRT) in cervical cancer cases. A novel algorithm named as Optimization Objectives Tree Search Algorithm (OOTSA) was proposed to emulate the planning optimization process and achieve a progressively improving IMRT plan, based on the Eclipse Scripting Application Programming Interface (ESAPI). 30 previously treated cervical cancer cases were selected from the clinical database and comparison was made between the OOTSA-generated plans and clinical treated plans and RapidPlan-based (RP) plans. In clinical evaluation, compared with plan scores of the clinical plans and the RP plans, 22 and 26 of the OOTSA plans were considered as clinically improved in terms of plan quality, respectively. The average conformity index (CI) for the PTV in the OOTSA plans was 0.86 ± 0.01 (mean ± 1 standard deviation), better than those in the RP plans (0.83 ± 0.02) and the clinical plans (0.71 ± 0.11). Compared with the clinical plans, the mean doses of femoral head, rectum, spinal cord and right kidney in the OOTSA plans were reduced by 2.34 ± 2.87 Gy, 1.67 ± 2.10 Gy, 4.12 ± 6.44 Gy and 1.15 ± 2.67 Gy. Compared with the RP plans, the mean doses of femoral head, spinal cord, right kidney and small intestine in the OOTSA plans were reduced by 3.31 ± 1.55 Gy, 4.25 ± 3.69 Gy, 1.54 ± 2.23 Gy and 3.33 ± 1.91 Gy, respectively. In the OOTSA plans, the mean dose of bladder was slightly increased, with 2.33 ± 2.55 Gy (versus clinical plans) and 1.37 ± 1.74 Gy (vs RP plans). The average elapsed time of OOTSA and clinical planning were 59.2 ± 3.47 min and 76.53 ± 5.19 min. The plans created by OOTSA have been shown marginally better than the manual plans, especially in preserving OARs. In addition, the time of automatic treatment planning has shown a reduction compared to a manual planning process, and the variation of plan quality was greatly reduced. Although improvement on the algorithm is warranted, this proof-of-concept study has demonstrated that the proposed approach can be a practical solution for automatic planning. The proposed method is novel in the emulation strategy of the physicists' iterative operation during the planning process. Based on the existing optimizers, this method can be a simple yet effective solution for automated IMRT treatment planning.

Comparison of helical tomotherapy with multi-field intensity-modulated radiotherapy treatment plans using simultaneous integrated boost in high-risk prostate cancer

Abstract Purpose: The aim of this study is to compare the dosimetric results of Helical Tomotherapy (HT) and Multi-field IMRT treatment plans using a Simultaneous Integrated Boost (SIB) technique in the treatment of High-Risk Prostate Cancer (HRPCa) with pelvic nodal radiation. Methods: Seventeen patients planned with HT and 7,8 and 9 fields IMRT were investigated. All plans were designed with the prescribed dose of 54.0 Gy to the PTVln while simultaneously delivering 74.0 Gy to the PTVPS in 30 fractions. Dosimetric data of PTV and OARs were compared. Results: HT gives a better CI and HI of PTVPS compared to multi-field IMRT plans. HT plans significantly improved target coverage (HT:0.95 vs multi-field IMRT: 0.52, 0.49 and 0.49 respectively, p &lt; 0.001). Bladder mean dose(Gy) (HT: 45.6 vs multi-field IMRT: 53.6, 53.3 and 52.7 respectively, p = 0.004) and D66%(Gy) dose (HT: 35.3 vs multi-field IMRT: 46.7, 47.0 and 44.9 respectively, p = 0.006) were lower in HT. But multi-field IMRT plans significantly reduced the rectum volume receiving more than 75 Gy; (HT V75% (%) 2.7 vs multi-field IMRT 0.8, 1.4 and 0.9 respectively, p = 0.008). HT provided better sparing of the right and left femoral head receiving a mean dose. The penile bulb and small bowel doses were the highest in HT compared with multi-field IMRT. Conclusions: HT achieved better dose distribution to target compared to multi-field IMRT. This study suggests HT as a reasonable option for the treatment of HRPCa patients.

Comprehensive Patient-Specific Intensity-Modulated Radiation Therapy Quality Assurance Comparing Mobius3D/FX to Conventional Methods of Evaluation.

PurposeTo determine the appropriateness of implementing Mobius3D/FX (Varian Medical Systems, Inc., Palo Alto, CA, USA) as not only a pretreatment secondary check but as an alternative to measurement-based patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA).MethodsMobius3D/FX was commissioned and stock beam models were tweaked so that an independent recalculated 3D dose distribution can be obtained. Then, 50 patient-specific treatment plans for various indications were delivered across a 2D ion chamber array, radiochromic film setup, and electronic portal imager and analyzed with MobiusFX and gamma analysis. The concordance of plans scored as passing between MobiusFX and the conventional methods of QA was determined.ResultsAll analyzed treatment plans passed with a gamma passing rate >90% across all conventional QA methods, most commonly using a 3%/3mm gamma criterion except for film measurements where a 5%/3mm criterion was applied. There was good agreement and concordance between MobiusFX and conventional methods when using a 3%/3mm criteria for MobiusFX, whereas a 2%/2mm criteria appeared too stringent as it failed treatment plans deemed clinically acceptable using conventional methods.ConclusionsUsing a 50-sample subset of clinically delivered treatment plans this non-inferiority-type comparison shows Mobius3D/FX based on log file analysis to be a suitable alternative to conventional QA methods when utilizing the 3%/3mm gamma criterion. Methods based on log file analysis can provide an opportunity for resource sparing, improving the efficiency, and workflow for evaluating IMRT treatment plans.

Comparison of a Hybrid IMRT/VMAT technique with non-coplanar VMAT and non-coplanar IMRT for unresectable olfactory neuroblastoma using the RayStation treatment planning system—EUD, NTCP and planning study

The purpose of this study was to compare hybrid intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (Hybrid IMRT/VMAT), with non-coplanar (nc) IMRT and nc-VMAT treatment plans for unresectable olfactory neuroblastoma (ONB). Hybrid IMRT/VMAT, nc-IMRT and nc-VMAT plans were optimized for 12 patients with modified Kadish C stage ONB. Dose prescription was 65 Gy in 26 fractions. Dose–volume histogram parameters, conformation number (CN), homogeneity index (HI), integral dose and monitor units (MUs) delivered per fraction were assessed. Equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) based on the EUD model (NTCPLogit) and the Lyman–Kutcher–Burman model (NTCPLKB) were also evaluated. We found that the Hybrid IMRT/VMAT plan significantly improved the CN for clinical target volume (CTV) and planning treatment volume (PTV) compared with the nc-VMAT plan. In general, sparing of organs at risk (OARs) is similar with the three techniques, although the Hybrid IMRT/VMAT plan resulted in a significantly reduced Dmax to contralateral (C/L) optic nerve compared with the nc-IMRT plan. The Hybrid IMRT/VMAT plan significantly reduce EUD to the ipsilateral (I/L) and C/L optic nerve in comparison with the nc-IMRT plan and nc-VMAT plan, but the difference in NTCP between the three technique was <1%. We concluded that the Hybrid IMRT/VMAT technique can offer improvement in terms of target conformity and EUD for optic nerves, while achieving equal or better OAR sparing compared with nc-IMRT and nc-VMAT, and can be a viable radiation technique for treating unresectable ONB. However, the clinical benefit of these small differences in dosimetric data, EUD and NTCP of optic nerves may be minimal.

Noncoplanar Versus Coplanar Intensity-Modulated Radiation Therapy (IMRT) for Protection of the Lip and Buccal Mucosa

Objective:In this study, by comparing coplanar and noncoplanar intensity-modulated radiation therapy (IMRT) treatment planning in treating tongue cancer, the significance of noncoplanar fields in the protection of the lip and buccal mucosa was determined, and a reasonable solution was selected.Methods:Forty-eight tongue cancer patients treated from June 2019 to February 2021 were selected and randomly divided into a coplanar field group and a noncoplanar field group. The mucosal dose limit changed from 15 Gy to 45 Gy for comparison of the two treatment plans. The evaluation indicators (conformal index (CI); homogeneity index (HI); D5, D50, and D98 of the target volume; and the dose of normal tissues) were calculated under different mucosal dose limits. The clinical observation of the lip and buccal mucosa of 48 cases was monitored and graded carefully according to NCI-CTCAE V4.0. Statistical analyses were performed.Results:The differences in CI, HI, D98, D50 and D5 between the two groups in the target volume tended to decrease when the mucosal dose limit was less than 30 Gy, with a significant difference (P < 0.05). When the limit exceeded 30 Gy, significant differences in other indicators except CI (P < 0.05) were still noted. In normal tissue, differences in doses between the two groups existed when the mucosal limit was less than 20 Gy, with a significant difference (P < 0.05). When the limit exceeded 20 Gy, no significant difference was noted. Patients in the noncoplanar group showed significantly better results than those in the other group in terms of the radiation-related toxicity of the lip and cheek membrane(P < 0.001).Conclusions:Compared with coplanar field radiotherapy, noncoplanar field radiotherapy can effectively reduce the exposure dose to the lip and buccal mucosa. The application of noncoplanar treatment plans exhibits good clinical significance and deserves to be promoted.

Technical Note: Cumulative dose modeling for organ motion management in MRI-guided radiation therapy.

To develop a method for continuous online dose accumulation during irradiation in MRI-guided radiation therapy (MRgRT) and to demonstrate its application in evaluating the impact of internal organ motion on cumulative dose. An intensity-modulated radiation therapy (IMRT) treatment plan is partitioned into its unique apertures. Dose for each planned aperture is calculated using Monte Carlo dose simulation on each phase of a four-dimensional computed tomography (4D-CT) dataset. Deformable image registration is then performed both (a) between each frame of a cine-MRI acquisition obtained during treatment and a reference frame, and (b) between each volume of the 4D-CT phases and a reference phase. These registrations are used to associate each cine image with a 4D-CT phase. Additionally, for each 4D-CT phase, the deformation vector field (DVF) is used to warp the pre-calculated dose volumes per aperture onto the reference CT dataset. To estimate the dose volume delivered during each frame of the cine-MRI acquisition, we retrieve the pre-calculated warped dose volume for the delivered aperture on the associated 4D-CT phase and adjust it by a rigid translation to account for baseline drift and instances where motion on the cine image exceeds the amplitude observed between 4D-CT phases. The proposed dose accumulation method is retrospectively applied to a liver cancer case previously treated on an MRgRT platform. Cumulative dose estimated for free-breathing and respiration-gated delivery is compared against dose calculated on static anatomy. In this sample case, the target minimum dose and varied by as much as 5% and 7%, respectively. We demonstrate a technique suitable for continuous online dose accumulation during MRgRT. In contrast to other approaches, dose is pre-calculated per aperture and phase and then retrieved based on a mapping scheme between cine MRI and 4D-CT datasets, aiming at reducing the computational burden for potential real-time applications.

3D conformal, IMRT and VMAT for the treatment of head and neck cancer: a brief literature review

AbstractAim:The objective of this study has been to identify monitor unit (MU) and treatment time variations, volume coverage dissimilarity among 3D conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) treatment plans for head and neck cancer (HNC) based on literature review.Methods:A number of HNC cases were studied with the investigation of conformity and homogeneity index.Results:When high-dose modulation was required around small organs at risk (OARs), a clinically acceptable IMRT plan was achieved as VMAT usually required longer dose optimisation time. The greatest benefit of VMAT has been rapid treatment delivery allowing improved patient comfort, reduced intra-fraction motion and increased patient throughput. In some papers, 3D-CRT was shown not to meet well the requirements on parotid glands. One paper showed that cerebellum dose was lower for 3D-CRT than IMRT. However, it was found in other papers that OAR sparing with 3D-CRT was reasonable but in complex cases not enough.Conclusions:IMRT usually consists of several treatment fields with different directions, hundreds of beam lets with modulated intensity, an advantage over 3D-CRT, whereas VMAT has advantage over IMRT due to rotating beam utilisation. VMAT has lower total MU and treatment times than IMRT and 3D-CRT, while maintaining similar dosimetric endpoints.

Pelvic organ motion and dosimetric implications during horizontal patient rotation for prostate radiation therapy.

Gantry-free radiation therapy systems utilizing patient rotation would be simpler and more cost effective than the conventional gantry-based systems. Such a system could enable the expansion of radiation therapy to meet global demand and reduce capital costs. Recent advances in adaptive radiation therapy could potentially be applied to correct for gravitational deformation during horizontal patient rotation. This study aims to quantify the pelvic organ motion and the dosimetric implications of horizontal rotation for prostate intensity-modulated radiation therapy (IMRT) treatments. Eight human participants who previously received prostate radiation therapy were imaged in a clinical magnetic resonance imaging (MRI) scanner using a bespoke patient rotation system (PRS). The patients were imaged every 45 degrees during a full roll rotation (0-360 degrees). Whole pelvic bone, prostate, rectum, and bladder motion were compared to the supine position using dice similarity coefficient (DSC) and mean absolute surface distance (MASD). Prostate centroid motion was compared in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) direction prior to and following pelvic bone-guided rigid registration. Seven-field prostate IMRT treatment plans were generated for each patient rotation angles under three adaption scenarios: No plan adaption, rigid planning target volume (PTV)-guided alignment to the prostate, and plan re-optimization. Prostate, rectum, and bladder doses were compared for each adaption scenario. Pelvic bone motion within the PRS of up to 53mm relative to the supine position was observed for some participants. Internal organ motion was greatest at the 180-degree PRS couch angle (prone), with prostate centroid motion range<2mm LR, 0mm to 14mm SI, and -11mm to 4mm AP. Rotation with no adaption of the treatment plan resulted in an underdose to the PTV -- in some instances up to 75% (D95%: 78±0.3Gy at supine to 20±15.0Gy at the 225-degree PRS couch angle). Bladder dose was reduced during the rotation by up to 98% (V60Gy: 15.0±9.4% supine to 0.3±0.5% at the 225-degree PRS couch angle). In some instances, the rectum dose increased during rotation (V60Gy: 20.0±4.5% supine to 25.0±15.0% at the 135-degree PRS couch angle). Rigid PTV-guided alignment resulted in PTV coverage which, though statistically lower (P<0.05 for all D95% values), was within 1Gy of the supine plans. Plan re-optimization resulted in a statistically equivalent PTV coverage compared to the supine plans (P>0.05 for all D95% metrics and all within ±0.4Gy). For both rigid PTV-guided alignment and plan re-optimization, rectum dose volume metrics were reduced compared to the supine position between the 90- and 225-degree PRS couch angles (P<0.05). Bladder dose volume metrics were not impacted by rotation. Pelvic bone and internal organ motion are present during patient rotation. Rigid PTV-guided alignment to the prostate will be a requirement if prostate IMRT is to be safely delivered using patient rotation. Plan re-optimization for each PRS couch angle to account for anatomical deformations further improves the PTV coverage.

Investigation of 3D-Conformal and Intensity-Modulated Therapy Techniques to Determine the Absorbed Fetal Dose in Patients With Nasopharyngeal Cancer During Pregnancy

The aim of this research was to investigate the fetal doses of pregnant patients undergoing conformal radiotherapy or intensity-modulated radiation therapy (IMRT) for nasopharyngeal cancers at various times during pregnancy. In this work, the head and neck cancer treatment of a pregnant patient was experimentally simulated. Two treatment plans were calculated using a female RANDO anthropomorphic phantom. This phantom was irradiated using the Clinac DHX linear accelerator, according to the Standard treatment plans of both three-dimensional conformal radiation therapy (3-DCRT) and IMRT techniques. During pregnancy, the height of the fundus at different weeks was determined and a sign was placed on the phantom. OSLD (optically stimulated luminescence dosimeter) and MOSFET (Metal oxide semiconductor field effect transistor) dosimeters were used to measure the dose of virtually designated uterus area at various times during pregnancy. The data carried out by TPS were compared with measured data. PBC calculation method in the treatment planning system (TPS) was unable to estimate the peripheral doses in uterus area. TPS showed a dose of 0 cGy at many points. On the contrary, OSLD measurement results revealed that the uterus (fetus) doses were ranging from 14.46–43.05 cGy (mean 27.9 ± 10.1 cGy) for 7-field IMRT treatment plan and 6,12–27,3 cGy (mean 14,7 ± 7,97 cGy) for 3-DCRT in Alderson anthropomorphic female RANDO phantom. MOSFET measurements showed that the uterus (fetus) doses were ranging from 15–50.1 cGy (mean 36.25 ± 11.7 cGy) for 7-field IMRT treatment plan and 10–36.3 cGy (mean 21.3 ± 9.54 cGy) for 3-DCRT treatment plan. All the observed fetal dose for the measurements and TPS data for two techniques are given in the Table below. In summary, comparing two techniques, it is clear that IMRT causes higher fetal radiation dose than 3-D CRT due to its higher MU value. Considering that fetal radiogenic effects are seen at 5-10 cGy (American Association of Physicists in Medicine Radiation Therapy Committee Task Group 36), 3-D CRT is a more reliable method. The TPS is unable to estimate peripheral doses accurately. Since the TPS underestimates the fetal dose, relying on the dose calculated by TPS does not seem possible under the current circumstances. The fetal dose from radiotherapy may vary depending on the gestational age at the time of treatment. The use of special shielding devices can considerably reduce the fetal dose from radiation therapy.Tabled 1Abstract 2597; TableIMRT3DMOSFETOSLDTPSMOSFETOSLDTPS12weeks15 cGy14.46cGy0.0cGy12weeks10cGy6.12cGy0.0cGy16 weeks32.2cGy22cGy0.0cGy16 weeks12.3cGy8.68cGy0.0cGy20-22 weeks32.55cGy23.1 cGy0.7cGy20-22 weeks15.6cGy10.5cGy0.0cGy24-26 weeks36.5 cGy25.69 cGy0.7cGy24-26 weeks21.5cGy12.25cGy0.0cGy28 weeks39.6 cGy27.09 cGy11cGy28 weeks23.4cGy14.03cGy0.0cGy36 weeks50.1 cGy43.05 cGy15cGy36 weeks36.3cGy27.3cGy9.7cGy40 weeks47.8 cGy40.01cGy11.6cGy40 weeks30cGy24.1cGy9.7cGy Open table in a new tab

Physician review of image registration and normal structure delineation.

IntroductionImage registration and delineation of organs at risk (OARs) are key components of three‐dimensional conformal (3DCRT) and intensity‐modulated radiotherapy (IMRT) treatment planning. This study hypothesized that image registration and OAR delineation are often performed by medical physicists and/or dosimetrists and are not routinely reviewed by treating physicians.MethodsAn anonymous, internet‐based survey of medical physicists and dosimetrists was distributed via the MEDPHYS and MEDDOS listserv groups. Participants were asked to characterize standard practices for completion and review of OAR contouring, target volume contouring, and image registration at their institution along with their personal training in these areas and level of comfort performing these tasks. Likert‐type scales are reported as Median [Interquartile range] with scores ranging from 1 = “Extremely/All of the time” to 5 = “Not at all/Never.”ResultsTwo hundred and ninety‐seven individuals responded to the survey. Overall, respondents indicated significantly less frequent physician review (3 [2–4] vs 2 [1–3]), and less confidence in the thoroughness of physician review (3 [2–4] vs 2 [1–3], P < 0.01) of OAR contours compared to image registration. Only 19% (95% CI 14–24%) of respondents reported a formal process by which OAR volumes are reviewed by physicians in their clinic. The presence of a formal review process was also associated with significantly higher perceived thoroughness of review of OAR volumes compared to clinics with no formal review process (2 [2–3] vs 3 [2–4], P < 0.01).ConclusionDespite the critical role of OAR delineation and image registration in the 3DCRT and IMRT treatment planning process, physician review of these tasks is not always optimal. Radiotherapy clinics should consider implementation of formal processes to promote adequate physician review of OARs and image registrations to ensure the quality and safety of radiotherapy treatment plans.

Intensity-Modulated Radiation Therapy Optimization for Acceptable and Remaining-One Unacceptable Dose-Volume and Mean-Dose Constraint Planning.

We give a novel approach for obtaining an intensity-modulated radiation therapy (IMRT) optimization solution based on the idea of continuous dynamical methods. The proposed method, which is an iterative algorithm derived from the discretization of a continuous-time dynamical system, can handle not only dose-volume but also mean-dose constraints directly in IMRT treatment planning. A theoretical proof for the convergence to an equilibrium corresponding to the desired IMRT planning is given by using the Lyapunov stability theorem. By introducing the concept of “acceptable,” which means the existence of a nonempty set of beam weights satisfying the given dose-volume and mean-dose constraints, and by using the proposed method for an acceptable IMRT planning, one can resolve the issue that the objective and evaluation are different in the conventional planning process. Moreover, in the case where the target planning is totally unacceptable and partly acceptable except for one group of dose constraints, we give a procedure that enables us to obtain a nearly optimal solution close to the desired solution for unacceptable planning. The performance of the proposed approach for an acceptable or unacceptable planning is confirmed through numerical experiments simulating a clinical setup.

Dose-Volume Comparison of IMRT and PSPT Treatment Plans for Early-Stage Glottic Cancer.

PurposeTo clarify the dose distribution characteristics for early-stage glottic cancer by comparing the dose distribution between intensity-modulated radiation therapy (IMRT) and passive scattering proton therapy (PSPT) and to examine the usefulness of PSPT for early-stage glottic cancer.Materials and MethodsComputed tomography datasets of 8 patients with T1-2 glottic cancer who had been treated by PSPT were used to create an IMRT plan in Eclipse with 7 fields and a PSPT plan in XiO-M with 2 fields. Organs at risk (OARs) included the carotid arteries, arytenoids, inferior constrictor muscles, strap muscles, thyroid cartilage, cricoid cartilage, and spinal cord. The prescription dose was 66 GyRBE in 33 fractions to the planning target volume (PTV). All plans were optimized such that 95% of the PTV received 90% of the prescription dose considering that the skin was slightly spared.ResultsThe superiority of the PSPT was confirmed in all OARs. In the PSPT, the dose to the contralateral carotid artery and the spinal cord, which is slightly distant from the PTV, was dramatically reduced while maintaining the dose distribution uniformity of the PTV by comparison with IMRT.ConclusionPSPT for early-stage glottic cancer resulted in good target dose homogeneity and significantly spared the OARs as compared with the IMRT. PSPT is expected to be effective in reducing late effects and particularly useful for young people.

A technique for quantifying the sensitivity of dosimetric tool gamma with 2D detector array in pretreatment IMRT plans by segment deletion method.

Motivation of this study is to check the sensitivity of dosimetric tool gamma with 2D detector array combination when unexpected errors occur while transferring intensity-modulated radiation therapy treatment plans from planning system to treatment unit. This study consists of 17 head and neck cancer patient's treatment plans. Nine types of verification plans are created for all 17 clinically approved treatment plans by consecutively deleting different segments (up to eight) one by one from each field of the plan. Decrement factor (χ) is introduced in our study which illustrated the degree of decay of gamma passing rate when intentional errors are introduced. We analyzed the data by two different methods-one without selecting the region of interest (ROI) in dose distributions and the other by selecting the region of interest. By linear regression, the absolute value of slopes is 0.025, 0.024 and 0.015 without ROI and 0.030, 0.027 and 0.015 with ROI for 2%/2mm, 3%/3mm and 5%/5mm criteria, respectively. The higher absolute value of the fitted slope indicates the higher sensitivity of this method to identify erroneous plan in treatment unit. The threshold value for 2%/2mm equivalent to 95% passing criteria in 3%/3mm used in clinical practice is obtained as 83.44%. The 2D detector array with dosimetric tool gamma is less sensitive in detecting errors when unprecedented errors of segment deletion occur within the treatment plans.

Quality assurance of IMRT treatment plans for a 1.5 T MR-linac using a 2D ionization chamber array and a static solid phantom

MR-guided radiotherapy requires novel quality assurance (QA) methods for intensity-modulated radiotherapy treatment plans (TPs). Here, an optimized method for TPs for a 1.5 T MR-linac was developed and implemented clinically.A static solid phantom and an MR-compatible 2D ionization chamber array were used. The array’s response with respect to the incident beam gantry angles was characterized for four different orientations of the array relative to the beam. A lookup table was created identifying the optimum orientation for each gantry angle. For the QA of clinical MR-linac TPs, beams were grouped according to their gantry angles and measured with up to four setups. The method was applied to n = 106 clinical TPs of 54 patients for different tumour entities. Reference plans and plans created in the online adaptive workflow were analysed, using a local 3%/3 mm gamma criterion for dose values larger than 30% of the maximum. Pass rates were averaged over all beam groups.The array’s response strongly depends on the beam incidence angle. Optimum angles typically range from −10° to 80° around the phantom setup angle. Consequently, plan verification required up to four setups. For clinical MR-linac TPs, the overall median pass rate was 98.5% (range 88.6%–100%). Pass rates depended on the tumour entity. Median pass rates were for liver metastases stereotactic body radiotherapy 99.2%, prostate cancer 99%, pancreatic cancer 98.9%, lymph node metastases 98.7%, partial breast irradiation (PBI) 98%, head-and-neck cancer 97.7%, rectal cancer 94% and others 96.6%. 85% of plans were accepted straightaway, with pass rates above 95%. A single plan with a pass rate below 90% was subsequently verified with a modified method. Off-axis target volumes, e.g. PBI, were verified successfully using a lateral shift of the phantom.The method is suitable to verify reference and online adapted TPs for a 1.5 T MR-linac, including plans for off-axis target volumes.