PTV Conformity Research Articles

Multi-institutional evaluation of a Pareto navigation guided automated radiotherapy planning solution for prostate cancer

BackgroundCurrent automated planning solutions are calibrated using trial and error or machine learning on historical datasets. Neither method allows for the intuitive exploration of differing trade-off options during calibration, which may aid in ensuring automated solutions align with clinical preference. Pareto navigation provides this functionality and offers a potential calibration alternative. The purpose of this study was to validate an automated radiotherapy planning solution with a novel multi-dimensional Pareto navigation calibration interface across two external institutions for prostate cancer.MethodsThe implemented ‘Pareto Guided Automated Planning’ (PGAP) methodology was developed in RayStation using scripting and consisted of a Pareto navigation calibration interface built upon a ‘Protocol Based Automatic Iterative Optimisation’ planning framework. 30 previous patients were randomly selected by each institution (IA and IB), 10 for calibration and 20 for validation. Utilising the Pareto navigation interface automated protocols were calibrated to the institutions’ clinical preferences. A single automated plan (VMATAuto) was generated for each validation patient with plan quality compared against the previously treated clinical plan (VMATClinical) both quantitatively, using a range of DVH metrics, and qualitatively through blind review at the external institution.ResultsPGAP led to marked improvements across the majority of rectal dose metrics, with Dmean reduced by 3.7 Gy and 1.8 Gy for IA and IB respectively (p < 0.001). For bladder, results were mixed with low and intermediate dose metrics reduced for IB but increased for IA. Differences, whilst statistically significant (p < 0.05) were small and not considered clinically relevant. The reduction in rectum dose was not at the expense of PTV coverage (D98% was generally improved with VMATAuto), but was somewhat detrimental to PTV conformality. The prioritisation of rectum over conformality was however aligned with preferences expressed during calibration and was a key driver in both institutions demonstrating a clear preference towards VMATAuto, with 31/40 considered superior to VMATClinical upon blind review.ConclusionsPGAP enabled intuitive adaptation of automated protocols to an institution’s planning aims and yielded plans more congruent with the institution’s clinical preference than the locally produced manual clinical plans.

Comparative Dosimetric Analysis of conventional 3DCRT and VMAT for Head and Neck Cancer

Introduction: Advancements in radiation oncology improve the outlook for patients with head and neck cancer which allowed to escalate the dose of radiation to tumours while minimizing the dose to surrounding healthy tissues. This study aims comparison of radiotherapy treatment planning of 3 DCRT and VMAT for head and neck cancer.Methods: Prospective study conducted on fifty patients of head and neck cancer in which 25 patients were treated with 3 DCRT and 25 patients treated with VMAT. Both plans were evaluated to compare the efficiency of VMAT and 3 DCRT dosimetrically in terms of PTV volume, homogeneity index, conformity index and doses to organs at risk. Results: Dose D98% for PTV66 was 59.39 Gy and 51.82 for VMAT and 3DCRT respectively. Conformity index was 1.0816 and 1.4472 for VMAT and 3DCRT plans respectively and the difference was statistically significant. Homogeneity index was 0.1473 for VMAT and 0.2997 for 3DCRT which proves that VMAT was more homogeneous. OARs sparing was also better with VMAT compared to 3DCRT especially the OARs which were very close to target volume especially parotid glands, Brainstem and optic nerve. Conclusion: Compared to 3DCRT plans, VMAT plan produced significantly better target coverage, homogeneous as well as dose conformity. Doses to organs at risk such as spinal cord and parotid glands were also reduced. Besides, the delivery of VMAT treatment was more efficient.

Dosimetric comparison in sparing normal tissue dosage by using auto-SBRT planning in oligo liver tumors.

The study aimed to compare the dosimetric distribution of VMAT plans by increasing the number of half arcs in liver SBRT and investigate the effect by using automatic plan software in plan optimization. Thirty-one patients with oligo liver tumors were randomly selected. VMAT treatment plans with different numbers of coplanar half arcs were generated. Adding arcs significantly increased the PTV, D2%, D50%, and CI, but sacrificed the plan homogeneity. It also decreased the maximum dose of normal tissues such as the stomach, duodenum, and spinal cord and reduced Dmean, D500cc, and D700cc for the liver. Nevertheless, the diminishing effect gradually decayed into three arcs. Meanwhile, the addition of arcs substantially extended the beam-on time. In the context of SBRT for oligo liver tumors, increasing the number of coplanar half arcs will improve PTV conformity and offer better protection for OARs, albeit at the expense of increased treatment duration. Considering the trade-off between plan quality and treatment efficiency, a three-arc plan may be more suitable for clinical implementation.

Comparative analysis of dose calculation algorithms for CyberKnife-based stereotactic radiotherapy in lung cancer.

The accuracy of dose calculation is the prerequisite for CyberKnife (CK) to implement precise stereotactic body radiotherapy (SBRT). In this study, CK-MLC treatment planning for early-stage non-small cell lung cancer (NSCLC) were compared using finite-size pencil beam (FSPB) algorithm, FSPB with lateral scaling option (FSPB_LS) and Monte Carlo (MC) algorithms, respectively. We concentrated on the enhancement of accuracy with the FSPB_LS algorithm over the conventional FSPB algorithm and the dose consistency with the MC algorithm. In this study, 54 cases of NSCLC were subdivided into central lung cancer (CLC, n=26) and ultra-central lung cancer (UCLC, n=28). For each patient, we used the FSPB algorithm to generate a treatment plan. Then the dose was recalculated using FSPB_LS and MC dose algorithms based on the plans computed using the FSPB algorithm. The resultant plans were assessed by calculating the mean value of pertinent comparative parameters, including PTV prescription isodose, conformity index (CI), homogeneity index (HI), and dose-volume statistics of organs at risk (OARs). In this study, most dose parameters of PTV and OARs demonstrated a trend of MC > FSPB_LS > FSPB. The FSPB_LS algorithm aligns better with the dose parameters of the target compared to the MC algorithm, which is particularly evident in UCLC. However, the FSPB algorithm significantly underestimated the does of the target. Regarding the OARs in CLC, differences in dose parameters were observed between FSPB and FSPB_LS for V10 of the contralateral lung, as well as between FSPB and MC for mean dose (Dmean) of the contralateral lung and maximum dose (Dmax) of the aorta, exhibiting statistical differences. There were no statistically significant differences observed between FSPB_LS and MC for the OARs. However, the average dose deviation between FSPB_LS and MC algorithms for OARs ranged from 2.79% to 11.93%. No significant dose differences were observed among the three algorithms in UCLC. For CLC, the FSPB_LS algorithm exhibited good consistency with the MC algorithm in PTV and demonstrated a significant improvement in accuracy when compared to the traditional FSPB algorithm. However, the FSPB_LS algorithm and the MC algorithm showed a significant dose deviation in OARs of CLC. In the case of UCLC, FSPB_LS showed better consistency with the MC algorithm than observed in CLC. Notwithstanding, UCLC's OARs were highly sensitive to radiation dose and could result in potentially serious adverse reactions. Consequently, it is advisable to use the MC algorithm for dose calculation in both CLC and UCLC, while the application of FSPB_LS algorithm should be carefully considered.

Towards Biology-Guided Radiotherapy Planning and Delivery on a Novel O-Ring PET-Linac Platform: Extended Beyond Bone and Lung Lesions

Biology-guided radiotherapy (BgRT) with FDG signal collected via an on-board positron emission tomography (PET) system integrated in an O-ring gantry Linac was recently cleared by the FDA for lung and bone lesions. This study aims to determine if BgRT plans, guided via PET signal, are clinically acceptable for FDG-avid lesions in disease sites beyond bone and lung. Ten patients previously treated for lesions in the liver, head and neck (HN), pancreas, renal and pelvic-abdominal lymph nodes were identified. Diagnostic PET/CT images of these treatment sites were first collected and processed/converted to mimic PET images that are acquired on PET-Linac and would be used to guide the delivery. For BgRT planning, the PTV was generated with 5 mm margin from GTV and a Biology Tracking Zone was generated including the anticipated full range of target motion. BgRT plans, guided by the emulated PET signal, were generated with 46Gy in 3 fractions for liver and 40Gy in 5 fractions for all other sites. BgRT plan deliverability was first assessed by evaluating the Activity Concentration (AC) and Normalized Target Signals (NTS) on converted PET images with the goal to meet NTS >2 (hard constraint) and AC >5kBq/ml (goal). BgRT plan quality was then evaluated with institutional guidelines on PTV coverage, OAR doses, conformity index (CI) and Heterogeneity index (HI). BgRT plans were successfully generated for 11 target lesions among ten patients. The average diagnostic PET SUV, derived NTS and AC on converted PET images were 12.62, 9.33 and 12.10 kBq/ml, respectively. All images met the NTS constraints, and 8/11 plans met the AC goal for deliverability. All plans met the OAR hard constraints such as max dose on duodenum, small bowel, large bowel and spinal cord. Five of 11 plans had a limiting GI structure that resulted in an expected reduction in PTV coverage with an average PTV V100% = 77.9%, CI of 1.4, HI of 1.36 and max dose of 133.8%. The other 6 of 11 cases met the PTV V100% = 95%, had an average CI of 1.1, HI of 1.28 and Dmax of 127.67%. The estimated average time for BgRT delivery was 17 mins 25 secs. Although these plan parameters are deemed to be clinically acceptable, heterogeneity was detected inside the target region and suboptimal dose fall off was observed in some cases that may be caused by current implementation. This preliminary study showed that BgRT plans were generated successfully with emulated PET images on 11 treatment sites covering HN, abdominal and pelvic regions. All plans met NTS constraints and 8 out of 11 met AC goals for deliverability. The plan quality of all BgRT plans were clinically acceptable based on institutional constraints. Further investigations are required to test more patients/sites for BgRT plan feasibility. Dosimetric benefit from margin reduction of BgRT target should also be investigated in future study.

Development and Assessment of a Multi-Purpose Knowledge-Based Planning Model (RapidPlan) for Prostate Radiation

RapidPlan (RP) is a knowledge-based planning (KBP) tool to improve plan quality, planning speed, and reduce inter-patient plan variability. For small to medium institutions, it is difficult to find sufficient patient numbers to configure a reliable KBP-RP model. This study aimed to build a multi-purpose KBP-RP model for prostate cancers. A total of 124 prostate plans from 2018-2022 at our institution were selected to configure the initial RP model. After model training, outliers were removed. 77 patients were used for the final RP model. Three fine-tuned RP sub-models with different optimized constraints corresponding to prostate bed, prostate + seminal vesicles (SV), and prostate boost plans were generated. RP models were validated by comparing plan quality with the original manually optimized plans (MP). 54 independent plans were selected to validate the RP models. Validation included: dose to 99% and 2% of PTV (D99%, D2%), PTV conformity index (CI); for organs at risk (OARs), volume receiving >70Gy and >60Gy (V70Gy, V60Gy) to bladder and rectum, maximum dose (Dmax) to femur heads (FHs) and small bowel. Statistical t-test analysis was performed with a significance of p<0.05. A total of 48/54 model-based plans were clinically approved after single RP optimization. 6/54 failed plans were prostate bed plans and were deemed acceptable after additional minor constraint adjustments. For PTV, D99%, D2%, and CI were comparable (p>0.05) to MP. Bladder and rectum V70Gy were comparable (p>0.05), and V60Gy were significantly lower to MP (p<0.05), with an average Dmean of 23.21±14.58Gy and 16.41±10.63Gy vs 26.36±16.89Gy and 18.24±12.81Gy for RP and MP. RP significantly reduced Dmax to FHs and small bowel (p<0.05), with average Dmax of 34.95±6.06Gy and 35.62±18.99Gy vs 36.81±7.05Gy and 38.14±17.81Gy, respectively. Multi-purpose prostate RP model was configured and approved plans were generated after single optimization. Prostate RP plans had equivalent PTV coverage with better or comparable OAR constraints.

Knowledge Based Planning for Lung SBRT: Model Transferability between Treatment Systems and Calculation Algorithms

Knowledge based planning (KBP) is known to be effective and clinically feasible in achieving high quality treatment plans with less variability between planners and reduced planning time. A KBP model is highly dependent on characteristics of the training data. Our institution developed and validated a lung SBRT KBP model from plans treated with a C-arm linear accelerator (Linac). This study aims to evaluate the quality of lung SBRT plans with a KBP model when this model is used for an O-ring Linac with different MLC design, beam quality, and calculation algorithm. Two academic hospitals in the same healthcare network were included in this study. One hospital trained a KBP model for five-fraction lung SBRT using 43 plans calculated using the Eclipse AcurosXB v15.6 algorithm for a C-arm Linac. The model was developed to prioritize dose gradient outside the PTV while satisfying institutional critical organ limits and validated using an additional set of 12 plans. A cohort of 10 patients (11 plans) previously treated with lung SBRT using the O-ring Linac at the second hospital was selected. These plans were calculated using the Eclipse AAA v15.6 algorithm with prescription doses of 30-50 Gy in five fractions. Each plan was re-optimized using the KBP model, without manual adjustment of the optimization objectives, using the same beam geometry as in the clinical plans. KBP plans were normalized to achieve the same PTV coverage as the clinical plans. Clinical and KBP plans were evaluated for ITV D98%, PTV conformity index (CI), R50 and maximum dose at 2 cm from the PTV (D2cm). All clinical and KBP plans met critical organ dose constraints. The range of CI was 1-1.13 vs. 0.96-1.05 for clinical plans and KBP plans, respectively. R50 and D2cm were lower with KBP plans (p = 0.007 and p = 0.05, respectively). ITV D98% range was 105-120% vs. 117-122% of the PTV prescription dose for clinical plans and KBP plans, respectively, and higher with KBP plans (p<0.001). For plans where the PTV overlaps the chest wall (n = 7), the maximum chest wall doses (D0.03cc) from KBP plans were higher than the clinical plans (p = 0.16), with an absolute chest wall D0.03cc difference of 9 Gy (54 Gy vs 63 Gy). The KBP model includes an ITV SIB of 120% of the PTV prescription, whereas the clinical plans reduced the ITV SIB when the PTV overlapped the chest wall, highlighting a difference in clinical practice between the two hospitals in this study. This study supports that a lung SBRT KBP model trained using plans for one Linac system and the AcurosXB algorithm can be used to generate clinically acceptable plans without manual planner intervention for a different Linac system and the AAA calculation algorithm, indicating the potential of a KBP model use for centralized planning process across different Linac systems and calculation algorithms.

Intensity Modulated Radiotherapy (IMRT) Versus Helical Tomotherapy (HT) in Esophageal Cancer: A Comparative Analysis

Purpose/Objectives: Definitive chemoradiation is an accepted alternative treatment in the management of esophageal cancer in patients who are not candidates for surgery. The location of esophagus poses a challenge because of its close proximity to the critical organs. Various modern techniques of radiation planning offer the advantage of better dose conformality and increased sparing of organs at risk. This study aims to compare the dosimetric parameters of Intensity Modulated Radiotherapy (IMRT) and Helical Tomotherapy (HT) planning techniques in radical radiotherapy for esophageal cancer patients. Materials/Methods: A total of 38 patients of esophageal squamous cell carcinoma with clinical staging cT2-T4/N0-N2/M0 planned for definitive chemoradiation were enrolled from June 2021 till November 2022. CT simulation was done with intravenous and oral contrast, and contouring of tumor volumes and organs at risk were done according to RTOG contouring guidelines. All patients were planned for a total dose of 50.4Gy in 28 fractions. Radiation plans of IMRT and HT were generated for each patient. Dosimetric parameters of PTV D98, D2, Dmean, V95, V110, Homogeneity Index (HI) and Conformity Index (CI) were noted for both the plans. Organs at risk (OAR) parameters such as Lung (V20, V30, V5, Dmean), Heart (V25, V30, Dmean), Spinal Cord Dmax, Larynx (Dmax, Dmean) and Liver Dmean were noted. All parameters of the two different planning techniques were compared and analyzed using SPSS software v23 with paired t-test.Results: The coverage of the PTV in IMRT and HT was similar in terms of PTV V95 and PTV D98. The regions receiving more than 107% and 110% of the prescribed dose was significantly higher in IMRT compared to HT, on assessing V107, V110 and D2 (p=0.001). HI was similar in both the groups, but the CI was significantly better in HT compared to IMRT (0.9 ± 0.02 vs 1.03 ± 0.01; p=0.002). Doses to the lungs, heart and liver were similar between the two groups. IMRT had higher spinal cord (39.1 ± 3.2 vs 34.2 ± 5.5; p=0.001) and laryngeal dose (9.6 ± 5.5 vs 5.6 ± 3.7; p=0.009) compared to HT.Conclusion: HT offers better dose conformality and uniformity when compared to IMRT with lesser dose to spinal cord and larynx. As this is a dosimetric study, a larger sample size and patient follow up is essential for clinical correlation and assessment of benefit of different radiation modalities.

Dosimetric Comparison of 3-Dimensional Conformal Radiotherapy (3DCRT), Intensity Modulated Radiotherapy (IMRT) and Volumetric-Arc Radiotherapy (VMAT) in Cervical Cancer Treatment

Background: Cervical cancer being the fourth most frequently diagnosed cancer, concurrent chemoradiation forms the mainstay of the treatment from stage IB3 to IVA. As we witnessed advancement in radiotherapy technologies, attempts had been taken to reduce the dose to the OARs without compromising the tumor coverage. In this study we will compare the PTV coverage, conformity index and doses received by the OARs (urinary bladder, rectum, bowel bag, bilateral head of femur) by all the three techniques namely 3DCRT, IMRT and VMAT for carcinoma cervix patients undergoing concurrent Chemoradiotherapy (CRT) at our institution and further implement the results in our clinical practice. Material and Methods: Forty-five of biopsy-proven carcinoma cervix in stage IIA to IIIB were taken up for the study. Following imaging, contouring was carried out using the principal clinical findings and conventional RTOG recommendations. Dose prescription to the cervix was 50 Gy in 25 fraction and planned with all three modalities, 3DCRT, IMRT and VMAT. The patient was treated with the 3DCRT plan and the IMRT and VMAT plans were made for dosimetric purpose only. Results: Quantitative dose evaluation performed of three techniques V40, V45, V50, Dmean for Bladder and Rectum, Dmean and D100 for Femur, V30, V40, D195 CC, Dmean for Bowel. Results show that VMAT plan is preferable than IMRT for sparing Bladder and rectum. Conclusion: IMRT and VMAT both could be advocated for practice was tumor coverage was almost similar in both of them and decision could be made on patient specific logistics.

Investigation of Isotoxic Dose Escalation and Plan Quality with TDABC Analysis on a 0.35 T MR-Linac (MRL) System in Ablative 5-Fraction Stereotactic Magnetic Resonance-Guided Radiation Therapy (MRgRT) for Primary Pancreatic Cancer.

This study investigates plan quality generated by an MR-Linac (MRL) treatment planning system (TPS) for 5-fraction stereotactic body radiation therapy (SBRT) of primary pancreatic cancer (PCa). In addition, an isotoxic dose escalation was investigated with the MRL TPS based on stereotactic MR-guided adaptive radiation therapy (SMART) trial constraints. A clinical workflow was developed for adaptive and non-adaptive treatments with the MRL, on which a time-driven activity-based costing (TDABC) analysis was performed to quantify clinical efficacy. Fifteen PCa patients previously treated with a conventional Linac were retrospectively re-planned for this study. Three plans were generated for each patient using the original prescription dose (PD) and organ at risk (OAR) constraints (Plan 1), following SMART trial’s OAR constraints but with the original PD (Plan 2), starting with Plan 2, following an isotoxic dose escalation strategy where the dose was escalated until any one of the SMART trial’s OAR constraints reached its limit (Plan 3). Conformity index (CI) and the ratio of the 50% isodose volume to PTV (R50%) conformity metrics were calculated for all 45 MRL plans, in addition to standard dose-volume indices. Forty-five MRL plans were created which met their respective dosimetric criteria described above. For Plan 1, the MRL TPS successfully achieved equivalent or lower OAR doses while maintaining the prescribed PTV coverage for the 15 plans. A maximum dose to the small bowel was reduced on average by 4.97 Gy (range: 1.11–10.58 Gy). For Plan 2, the MRL TPS successfully met all SMART trial OAR constraints while maintaining equivalent PTV coverage. For Plan 3, the MRL TPS was able to escalate the prescription dose from the original 25–33 Gy by, on average, 36 Gy (range: 15–70 Gy), and dose to the PTV was successfully escalated to at least 50 Gy for all 15 plans. These achievements were made possible, in part, due to the omission of the ITV afforded by the MRL’s real-time target tracking technology and sharper dose penumbra due to its unique dual-focus MLC design. The 0.35T MRL TPS can generate plans that are equivalent to conventional Linac-based plans for SBRT of PCa. Through analyzing Plan 2 and 3 strategies, and due to the real-time target localization capabilities of the MRL system, increased OAR sparing and/or target dose escalation are possible.

Dosimetric Comparison of Arms Up Versus Arms Down Positions for Lung SBRT

<h3>Purpose/Objective(s)</h3> Reproducible patient positioning is integral to the safe and accurate delivery of radiation therapy. Commonly, lung patients are simulated with their arms up (AU) to improve dose conformality by utilizing lateral gantry angles. However, the AU position can be uncomfortable and difficult to maintain, especially in the early stage lung SBRT patient cohort, who tend to be older and less physically fit. For these patients, the physical discomfort from the AU position can lead to decreased accuracy in patient positioning and possibly treatment delivery. We sought to evaluate any potential dosimetric differences between simulating and treating SBRT lung patients in the standard AU position versus a more comfortable arms down (AD) position. <h3>Materials/Methods</h3> A sample of 10 patients undergoing lung SBRT on a noncoplanar robotic radiosurgery platform were selected. Patients were originally simulated, planned, and treated in the AD position. For ease of comparison, all treatments were replanned to 50 Gy (10 Gy x 5 fractions) regardless of tumor location. For each patient a new plan was then generated subtracting out the arms to reproduce the commonly used AU simulation position. Dosimetric quantities such as PTV coverage, PTV conformality, and other commonly accepted normal tissue constraints were compared. <i>Paired t-tests</i> of various plan metrics were calculated with a <0.05 threshold of significance. <h3>Results</h3> All plans were able to achieve adequate target coverage without violating any standard normal tissue constraints. There was no statistically significant differences observed for plans calculated in the AD versus AU positions for PTV V50Gy, lung V20Gy, esophagus D0.03cc, chest wall V30Gy, proximal bronchus D0.03cc, and distal bronchus D0.03cc. There was a statistically significant difference observed for the cord 0.03cc and cord 0.35cc doses in favor of the AD position, though in all cases the cord constraints were met. The median cord D0.35cc was 557cGy for AU verses 216cGy for AD. The median cord D0.03cc was 606cGy for AU verses 252cGy for AD. <h3>Conclusion</h3> There is no major dosimetric difference between treatment plans generated in the AU and AD positions. The exception was cord dose metrics, which showed a favorable decrease in median D0.03cc and D0.35cc in the AD position. Given the increased ease of positioning, which we believe leads to improved reproducibility and ultimately accuracy of treatment, we believe that simulating and treating patients in the AD position can be advantageous for lung SBRT treatments.

Alopecia and neurocognitive dysfunction in Glioblastoma multiforme patients- Prevention feasibillity by dosimetric analysis in conformal radiotherapy techniques

Background: The survival rates of GBM patients have shown improvement. This increases the likelihood of manifesting radiation induced sequelae such as neurocognitive dysfunction, alopecia, and memory loss. This increases the focus on dosimetry of hippocampus, scalp, and normal brain. The present study was designed to compare the dosimetric efficacy of two conformal techniques in terms of OAR’s sparing and PTV coverage. Materials and Methods: A total of 10 patients with GBM who had received radical radiotherapy by 3DCRT technique were selected. A corresponding IMRT plan was generated for study purpose (n=20 plans). The dose prescribed to the PTV was 60 Gy in 30 fractions. Other than critical structures, additional delineation of hippocampus, normal brain and skin was done. The dosimetric parameters of PTV and OAR’s were compared amongst the two techniques. Results: The IMRT technique led to significant advantage in PTV coverage, dose homogeneity and conformity. A clear advantage with either technique could not be demonstrated in terms of point dose of critical structures. The normal brain and scalp showed significant reduction in doses with IMRT technique. The contralateral Hippocampal avoidance Zone also showed better sparing with IMRT technique but significant difference could not be demonstrated. Conclusion: The better coverage with IMRT technique was particularly observed in cases where PTV was overlapping with critical OAR’S while in rest of the cases coverage was comparable amongst both the techniques. The better sparing of scalp and normal brain may decrease the incidence of alopecia, neurocognitive dysfunction that needs to be clinically validated in future studies. Keywords: GBM, 3DCRT, IMRT.

Which Bone Marrow Sparing Strategy and Radiotherapy Technology Is Most Beneficial in Bone Marrow-Sparing Intensity Modulated Radiation Therapy for Patients With Cervical Cancer?

BackgroundTo evaluate the dosimetric parameters of different bone marrow sparing strategies and radiotherapy technologies and determine the optimal strategy to reduce hematologic toxicity associated with concurrent chemoradiation (cCRT) for cervical cancer.MethodsA total of 15 patients with Federation International of Gynecology and Obsterics (FIGO) Stage IIB cervical cancer treated with cCRT were re-planned for bone marrow (BM)-sparing plans. First, we determined the optimal BM sparing strategy for intensity modulated radiotherapy (IMRT), including a BMS-IMRT plan that used total BM sparing (IMRT-BM) as the dose-volume constraint, and another plan used os coxae (OC) and lumbosacral spine (LS) sparing (IMRT-LS+OC) to compare the plan without BM-sparing (IMRT-N). Then, we determined the optimal technology for the BMS-IMRT, including fixed-field IMRT (FF-IMRT), volumetric-modulated arc therapy (VMAT), and helical tomotherapy (HT). The conformity and homogeneity of PTV, exposure volume of OARs, and efficiency of radiation delivery were analyzed.ResultsCompared with the IMRT-N group, the average volume of BM that received ≥10, ≥20, ≥30, and ≥40 Gy decreased significantly in both two BM-sparing groups, especially in the IMRT-LS+OC group, meanwhile, two BMS-IMRT plans exhibited the similar effect on PTV coverage and other organs at risk (OARs) sparing. Among three common IMRT techniques in clinic, HT was significantly less effective than VMAT and FF-IMRT in the aspect of BM-Sparing. Additionally, VMAT exhibited more efficient radiation delivery.ConclusionWe recommend the use of VMAT with OC and LS as separate dose-volume constraints in cervical cancer patients aiming at reducing hematologic toxicity associated with cCRT, especially in developing countries.

Impact of Field Number and Beam Angle on ERE for Lung Cancers Radiotherapy Planning in 1.5 T MR-Linac

The MR-Linac offers great potential for high-precision delivery of radiation therapy and allows for direct monitoring of intrafraction motion without being invasive, needing surrogates, or exposing the patient to additional radiation. However, the electron deflection resulting from presence of a transverse magnetic field (TMF) can affect the dose distribution, particularly the electron return effect (ERE) at tissue interface. The purpose of the study is to investigate the dose effects of ERE at lung tissue interface and reduce the ERE by increasing the field number and optimizing the beam angle during intensity-modulated radiation therapy (IMRT) planning for lung patents. IMRT plans for four representative lung cases were generated following commonly used clinical dose volume criteria and using TPS Monaco 5.40. In each case, three types of plans were generated: (1) the plans with 5 fields and beam angle in tumor side generated with or without a TMF (5Fside); (2) the plans with 9 fields and beam angle in tumor side generated with or without a TMF (9Fside); (3) the plans with 9 fields and beam angle in the opposite direction generated with or without a TMF (9Fopposite). These plans were compared using a variety of dose-volume-parameters (DVPs), including V100%, Dmean, Heterogeneity Index (HI), Conformity Index (CI), Dmax, and D1cc in OARs (organ at risk) and tissue interface. All the optimizations and calculations in this work were performed on static data. Results showed that no significantly differences for 5 and 9 fields plans generated without the presence of the 1.5 T TMF. The 5Fside and 9Fside plans with TMF had slightly worsened homogeneity and conformity of PTV than plans without TMF, with the mean HI and CI difference being more than 50% and 16% respectively. Similarly, the 5Fside and 9Fside TMF plans results in considerable increase in Dmax and Dmean on PTV, mostly between 10% and 25%. And the Dmax and D1cc on tissue interface also increased by 10% to 25%. However, the 9Fopposite TMF plans lead to much smaller dose effects from ERE compared 5Fside and 9Fside TMF plans. Additionally, there was no significantly difference in DVPs of PTV and tissue interface in 9Fopposite TMF plans in comparison to the plans without TMF, with the difference being less than 1%. The doses on PTV and tissue interface can be significantly changed by the presence of a 1.5 T TMF for lung patient in MR-Linac. The selection of optimal fields number and beam angle can substantially reduce or even eliminated these changes, without deteriorating overall plan quality.

Yüksek Dereceli Glial Tümörlerin Radyoterapisinde VMAT Tekniği İle IMRT Tekniğinin Karşılaştırılması

The aim of radiotherapy is to protect critical organs sensitive to radiation and surrounding healthy tissues as much as possible, while giving the most appropriate dose on the specified target volume. The aim of this study is to provide the best plans of 10 brain tumor patients, whose computed tomography (CT) image was taken, using the best plans created using the VMAT technique in the Eclipse treatment planning system and the best plans created using the seven-field IMRT technique to compare doses in terms of target volume, duration of treatment and monitor unit (MU) values. The study is a retrospective study and patients were not treated with the plans and techniques used in the studies. Plans have been made so that 100% of the dose defined for the target volume will take at least 95% of the target volume. Using the Radiation Therapy Oncology Group (RTOG) protocol, the results obtained with the minitab program were statistically evaluated using the t-test for the matched data. PTV coverage, conformity and homogeneity index were equivalent for VMAT and IMRT plans. VMAT plans compared to IMRT, PTV max. 64,835±0,504 (p=0,039), Brain max. 64,378±0,565 (p=0,025), and Eye L. max. 20,39± 12,17 (p=0,046) The difference between the mean doses is statistically significant. Brain mean 26,74±3,42 (p=0,096), Brainstem max. 32,44±18,70 (p=0,178), Eye R. max. 32,90± 16,84 (p=0,076), Optic Nerve L.max. 23,17± 15,45 (p=0,851), Optic Nerve R. max. 22,63± 17,98 (p=0,688), Optic Chiasma max. 25,25± 20,24 (p=0,531) were found lower in VMAT plans but it was not statistically significant. It may be preferred in plans made with the VMAT technique due to less monitor units (MU) and shorter treatment time.

Results of the ACCEL trial: Dosimetry in accelerated partial breast irradiation

PurposeTo report the achieved dosimetry in the ACCEL trial and compare the results to reported dosimetry from the major accelerated partial breast irradiation (APBI) phase III trials. MethodsThe ACCEL trial was a single arm, phase II, prospective cohort study. A five-field, inverse-planned, IMRT strategy was employed using a class solution technique to increase planning consistency including high dose conformity and low normal tissue dose to the ipsilateral breast. ResultsBetween 2016 and 2019, 283 patients were treated with 27 Gy in five fractions in consecutive days. The average PTV conformity index was 1.1. For the ipsilateral breast, the median (range) volume receiving 95% and 50% of the prescription dose was 9.7% (3.2–22.4) and 30.3% (11.1–54.6), respectively. Compared to major APBI phase III trial constraints, this reduction in irradiated volume at the 95% and 50% isodose levels represents a reduction of 209 cm3 and 265 cm3, respectively. ConclusionThe IMRT planning strategy employed in the ACCEL trial demonstrated consistent and superior dosimetry by comparison to conventionally used 3D CRT techniques. Future APBI trials should update dosimetric constraints.

A dosimetric study using split x-jaw planning technique for the treatment of endometrial carcinoma

The aim of this retrospective study was to determine if the split x-jaw planning technique could be used with Varian linear accelerators to improve plan conformity and limit dose to organs at risk (OAR) for planning target volumes that require field sizes larger than the 15 cm extent of the multileaf collimator in the x-jaw position. Traditional planning techniques include limited and open x-jaw methods. The study population included 20 randomly selected patients with endometrial carcinoma. Treatment plans for each patient were designed using split, limited, and open x-jaw volumetric modulated arc radiotherapy for comparison purposes. Dose statistics including the PTV conformity index and dose to OAR were used to evaluate plan performance. The split x-jaw planning method had the most consistent conformity index (0.98 ± 0.02), followed by the open (01 ± 0.03), and the limited (1.04 ± 0.05) techniques. On average, the split method better spared the OAR. In comparison to the limited and open techniques, the split method reduced the dose to the bowel by 3.8%, rectum by 3.2%, sigmoid by 2.1%, right femoral head by 3.5%, and left femoral head by 3.9%. The split and open techniques showed comparable bladder results and were superior over the limited method. The monitor units were highest with the split method leading to increased treatment times. The split x-jaw planning technique should be used with Varian linear accelerators to produce superior volumetric modulated arc radiotherapy plans for planning target volumes larger than the maximum extent of the multileaf collimator in the x-jaw direction.

A hybrid automated treatment planning solution for esophageal cancer

ObjectiveThis study aims to investigate a hybrid automated treatment planning (HAP) solution that combines knowledge-based planning (KBP) and script-based planning for esophageal cancer.MethodsIn order to fully investigate the advantages of HAP, three planning strategies were implemented in the present study: HAP, KBP, and full manual planning. Each method was applied to 20 patients. For HAP and KBP, the objective functions for plan optimization were generated from a dose–volume histogram (DVH) estimation model, which was based on 70 esophageal patients. Script-based automated planning was used for HAP, while the regular IMRT inverse planning method was used for KBP. For full manual planning, clinical standards were applied to create the plans. Paired t-tests were performed to compare the differences in dose-volume indices among the three planning methods.ResultsAmong the three planning strategies, HAP exhibited the best performance in all dose-volume indices, except for PTV dose homogeneity and lung V5. PTV conformity and spinal cord sparing were significantly improved in HAP (P < 0.001). Compared to KBP, HAP improved all indices, except for lung V5. Furthermore, the OAR sparing and target coverage between HAP and full manual planning were similar. Moreover, HAP had the shortest average planning time (57 min), when compared to KBP (63 min) and full manual planning (118 min).ConclusionHAP is an effective planning strategy for obtaining a high quality treatment plan for esophageal cancer.

Hyperpolarized 129xe Gas MRI Pulmonary Ventilation Imaging-Based Functional Avoidance for Lung Cancer Radiotherapy

For patients undergoing lung cancer radiotherapy, functional lung imaging can be incorporated into treatment planning to achieve differential sparing between the viable and defective non-target lung regions. Hyperpolarized 129Xe gas MRI is a powerful tool for evaluating the pulmonary function due to the extremely high enhancement in spin polarization using spin-exchange optical pumping. As the first implementation of hyperpolarized 129Xe gas MRI pulmonary ventilation imaging-guided functional treatment planning in China, this study aimed to quantify its dosimetric impact on sparing the high-functional lung regions. Ten locally advanced lung cancer patients with a median PTV volume of 233.2 cm3 (range: 119.2-667.9 cm3) were included in this study. Before radiotherapy, each patient underwent an MRI scan with 1 liter (L) xenon-inhalation and a simulation CT scan with 1L air-ventilation. The CT and MRI was then registered in a commercially available deformable registration algorithm where the GTV, CTV, and regular OARs were contoured on the CT and the high-functional lungs contoured on the MRI. Two IMRT plans (64Gy/35fractions) were designed for each patient: an anatomic plan (Plan-A) using the simulation CT alone and a functional plan (Plan-F) using the hyperpolarized 129Xe gas MRI in addition. The two plans were created using a treatment planning system with the same dose optimization objectives except that the lung dose objectives in Plan-A were placed on the high-functional lung instead in Plan-F. These lung dose goals focused on V20Gy, V5Gy and the mean dose. Finally, the dose-volume histograms were compared between the two plans for the PTV and OARs using the Wilcoxon signed-rank test. All plans were judged as clinically acceptable. Plan-A and Plan-F showed similar PTV dose homogeneity index and conformity index. Similarly, the doses to all OARs except the high-functional lungs showed no statistical difference. Compared with Plan-A, the V5Gy, V10Gy, V15Gy, V20Gy, V25Gy, V30Gy, and Dmean of high-functional lungs were significantly reduced in Plan-F (P＜0.05 for all indices), from 34.0±13.5%, 24.2±10.8%, 16.7±7.6%, 12.8±6.2%, 9.5±4.8%, 6.4±3.8%, and 7.4±3.0Gy in Plan-A, to 31.8±12.3%, 21.7±8.6%, 14.9±6.2%, 11.1±4.8%, 8.2±4.0%, 5.7±3.4%, and 6.9±2.6Gy in Plan-F, respectively. The sparing is more significant when the high-functional lung is adjacent to the PTV, with the above indices reduced from 46.8%, 39.2%, 32.2%, 26.5%, 19.7%, 15.2%, and 13.6Gy in Plan-A, to 41.8%, 33.4%, 24.8%, 19.4%, 14.2%, 11.8%, and 10.2Gy in Plan-F, for one patient. An emerging technology, hyperpolarized 129Xe gas MRI has been translated into the clinic and used in functional image-guided radiotherapy in China for the first time. Our findings indicate the potential of functional planning in lung functional avoidance for IMRT, particularly for patients who have high-functional lung adjacent to the PTV.

Utilisation of Pareto navigation techniques to calibrate a fully automated radiotherapy treatment planning solution.

Background and purposeCurrent automated radiotherapy planning solutions do not allow for the intuitive exploration of different treatment options during protocol calibration. This work introduces an automated planning solution, which aims to address this problem through incorporating Pareto navigation techniques into the calibration process.Materials and methodsFor each tumour site a set of planning goals is defined. Utilising Pareto navigation techniques an operator calibrates the solution through intuitively exploring different treatment options: selecting the optimum balancing of competing planning goals for the given site. Once calibrated, fully automated plan generation is possible, with specific algorithms implemented to ensure trade-off balancing of new patients is consistent with that during calibration. Using the proposed methodology the system was calibrated for prostate and seminal vesicle treatments. The resultant solution was validated through quantitatively comparing the dose distribution of automatically generated plans (VMATAuto) against the previous clinical plan, for ten randomly selected patients.ResultsVMATAuto yielded statistically significant improvements in: PTV conformity indices, high dose bladder metrics, mean bowel dose, and the majority of rectum dose metrics. Of particular note was the reduction in mean rectum dose (median 25.1 Gy vs. 27.5 Gy), rectum V24.3Gy (median 41.1% vs. 46.4%), and improvement in the conformity index for the primary PTV (median 0.86 vs. 0.79). Dosimetric improvements were not at the cost of other dose metrics.ConclusionsAn automated planning methodology with a Pareto navigation based calibration has been developed, which enables the complex balancing of competing trade-offs to be intuitively incorporated into automated protocols.