Treatment Plan Parameters Research Articles

Optimizing Prostate Cancer Radiotherapy: Advanced Machine Learning in Virtual Patient-Specific Plan Verification-Review Study

Background: Virtual patient-specific plan verification in radiotherapy is critical to ensure precise dose delivery while minimizing healthy tissue exposure, particularly in prostate cancer treatments. Prior studies, however, have overlooked the physical implications of predictor features and lacked comprehensive decision support tools, leading to gaps in understanding and practical application. This research aims to bridge these gaps by providing a nuanced understanding of predictor features, exploring advanced automatic feature extraction methods, emphasizing model reliability, and proposing a comprehensive decision support tool. Our objective is to optimize radiotherapy protocols, ensuring safer and more effective treatments for patients undergoing prostate cancer therapy. Methods: This research employs a literature review approach. An extensive literature study served as the foundation. Results: Our study reveals that understanding the physical implications of predictor features significantly enhances prediction accuracy. Utilizing Convolutional Neural Networks (CNN) models for automatic feature extraction improves prediction performance, providing robust and transferable results. Conclusions: By emphasizing model reliability through the integration of treatment plan parameters, our approach ensures stable predictions across diverse patient cases. The proposed decision support tool offers clinicians detailed insights into predicted dose deliverability, facilitating informed decision-making for patient-specific treatment plans. Through these advancements, our research contributes to the optimization of radiotherapy protocols, ensuring safer and more effective treatments for patients undergoing prostate cancer therapy.

Dosiomics-based detection of dose distribution variations in helical tomotherapy for prostate cancer patients: influence of treatment plan parameters.

The stability of dosiomics features (DFs) and dose-volume histogram (DVH) parameters for detecting disparities in helical tomotherapy planned dose distributions was assessed. Treatment plans of 18 prostate patients were recalculated using the followings: field width (WF) (2.5 vs. 5), pitch factor (PF) (0.433 vs. 0.444), and modulation factor (MF) (2.5 vs. 3). From each of the eight plans per patient, ninety-three original and 744 wavelet-based DFs were extracted, using 3D-Slicer software, across six regions including: target volume (PTV), pelvic lymph nodes (PTV-LN), PTV + PTV-LN (PTV-All), one cm rind around PTV-All (PTV-Ring), rectum, and bladder. For the resulting DFs and DVH parameters, the coefficient of variation (CV) was calculated, and using hierarchical clustering, the features were classified into low/high variability. The significance of parameters on instability was analyzed by a three-way analysis of variance. All DF's were stable in PTV, PTV-LN, and PTV-Ring (average CV ( ≤0.36). Only one feature in the bladder ( =0.9), rectum ( =0.4), and PTV-All ( =0.37) were considered unstable due to change in MF in the bladder and WF in the PTV-All. The value of for the wavelet features was much higher than that for the original features. Out of 225 unstable wavelet features, 84 features had ≥1. The CVs for all the DVHs remained very small ( <0.06). This study highlights that the sensitivity of DFs to changes in tomotherapy planning parameters is influenced by the region and the DFs, particularly wavelet features, surpassing the effectiveness of DVHs.

Tomotherapy in synchronous and metachronous bilateral breast cancer: Clinical experience.

The objective of this research is to present our firsthand experience and provide up-to-date data for the further study of cases involving simultaneous breast irradiation using helical Tomotherapy, ©Accuray Inc. The radical treatment options for bilateral breast cancer are surgery, chemotherapy, and radiation therapy. Being that radiotherapy for bilateral breast cancer is challenging due to limitations in the geometry of modern radiotherapy equipment, helical Tomotherapy was chosen as an appropriate technique of irradiation. The retrospective review focused on the records of patients who underwent bilateral irradiation of the breast or chest wall and regional lymph nodes using helical Tomotherapy. Only four patients with bilateral breast cancer completed a radiation therapy course in our center from 2018 to 2023. Two patients underwent radical mastectomy with lymph node dissection on both sides before irradiation. For the other two patients, radical mastectomy was done after neoadjuvant chemotherapy. Acute radiation toxicity scoring was based on Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Only mild adverse effects, such as general weakness and slight skin irritation below Grade 3, were observed, with no instances of skin swelling, dryness, or pigmentation noted. Evaluation of late complications revealed tissue fibrosis in the area of the internal mammary nodes and respiratory failure with various severity. Complications and deterioration in the cardiovascular system were not observed during the follow-up period, which varied from 3 to 48months. Our results show the efficacy of using helical Tomotherapy considering positive outcomes, being that three out of four patients are in remission with low acute toxicity and late complications. There are a small number of articles describing bilateral breast cancer treatment with helical Tomotherapy. On this occasion, our data could contribute to the studies of tolerant doses for organs at risk and improve the parameters of treatment plans for bilateral breast cancer. Since the small sample of patients with bilateral breast cancer limits the study, a larger cohort of patients is essential to obtain statistically reliable results.

Evaluation of Radiation Therapy Treatment Plans in a Randomized Phase 2 Trial Comparing 2 Schedules of Twice-Daily Thoracic Radiation Therapy in Limited Stage Small Cell Lung Cancer

PurposeThere is limited clinical data for recommendations on how to deliver thoracic radiotherapy (TRT) concurrently with chemotherapy in limited stage (LS) small-cell lung cancer (SCLC). We reviewed radiotherapy treatment plans in a randomized phase II trial comparing high-dose with standard-dose twice-daily TRT to assess treatment planning techniques, dose-volume data for target volumes and organs at risk (OARs), evaluate compliance with the protocol, associations with radiation-induced toxicity and whether an imbalance in treatment planning parameters might be a reason for the large survival benefit of the higher dose (median overall survival 43.6 vs. 22.6 months). Methods and Materials170 patients were to receive four courses of platinum/etoposide and randomized to receive twice-daily TRT of 60 Gy/40 fractions (fx) or 45 Gy/30 fx. TRT treatment plans for those who received one or more fx of TRT (n=166) were analyzed. ResultsThe most common treatment planning technique was 3DCRT (67%). The 75th percentile of the reported dose-volume parameters for the OARs were within the protocol-recommended limits for both groups. Mean doses to the esophagus of 25.5 Gy (IQR: 20.2-31.3) [60 Gy/40 fx] and 24.3 Gy (IQR: 20.3-27.5) [45 Gy/30 fx] were associated with 21% and 18% ≥ grade 3 acute esophagitis, respectively. In the 60 Gy/40 fx group, a mean dose to the lungs of 16.5 Gy (IQR: 15.8-16.9), V20Gy of 29.5% (IQR: 28.8-30.4), and V5Gy of 65.6% (IQR: 61.5-68.7) led to ≥ grade 3 pneumonitis in 4% of the patients. There was no ≥ grade 3 pneumonitis in the 45 Gy group. Treatment planning techniques, the percentage change in volumes between original and re-delineated OARs, PTV volumes, relative doses, and laterality were well balanced between the randomly assigned groups. ConclusionConsidering that the incidences of severe radiation-induced toxicities were within the range of other recent trials, the reported doses to the OARs appear to be safe. Treatment planning parameters were well balanced between the randomly assigned groups, supporting that the survival benefit of the twice-daily 60 Gy/ 40 fx TRT schedule was due to the higher dose.

Intensity-modulated vaginal brachytherapy applicator and single- and multi-channel applicators in vaginal cuff brachytherapy.

To compare the dosimetric performance of vaginal intensity-modulated brachytherapy (IM-BRT) applicator and single- (SC-BRT) and multi-channel brachytherapy (MC-BRT) applicators for vaginal cuff brachytherapy (VC-BRT). Fifteen patients with uterine-confined endometrium cancer who received adjuvant VC-BRT were included in this study. IM-BRT, SC-BRT, and MC-BRT treatment plans were created for two different clinical target volume (CTV) definitions: 1. Standard CTV, called CTVs; and 2. Virtually defined CTV, called CTVv, with asymmetrical tumor extension > 5 mm in thickness. Plan comparison was performed using dose-volume histogram (DVH) and treatment planning parameters. According to DVH analysis, D98 for CTVv and D2 for both CTVs and CTVv showed statistically significant differences between IM-BRT and SC-BRT plans, but there was no significant difference between IM-BRT and MC-BRT plans in terms of D98 and D2 for both CTVs and CTVv. Additionally, for CTVv plans, IM-BRT was found to be significantly superior to SC-BRT for the rectum (D2cc, V5Gy, and V7Gy), bladder (D2cc and V7Gy), and small bowel (D2cc, V5Gy, and V7Gy). On the other hand, DVH parameters of the sigmoid showed large difference between IM-BRT and SC-BRT plans, but it was not statistically significant. Similarly, the use of IM-BRT applicator demonstrated a noticeable dose reduction in all defined OARs when compared with MC-BRT applicator, but statistically significant for the rectum V7Gy (p = 0.03) only. While the IM-BRT applicator is still in pre-clinical phase, our investigation demonstrated the proof-of-concept in real patient treatment plans with promising dosimetric results compared with SC-BRT and MC-BRT plans in selected patient group.

Non-elective inpatient anti-cancer therapy for solid tumors: To treat or not to treat?

234 Background: Administration of anti-cancer therapy to hospitalized patients is associated with greater treatment-related complications and reduced quality of life. We designed and implemented a standardized process to review all non-elective systemic anti-cancer therapy in solid-tumor patients with the goal of reducing aggressive end of life care and improving quality. Methods: A multidisciplinary group of quality and safety, pharmacy, physician, and nursing leadership designed a workflow to standardize the review of all inpatient anti-cancer treatment requests for non-elective solid-tumor (NEST) patients. Our NEST process begins with a formal pharmacy and nursing review, which can flag a case for further physician review. The pharmacist reviews for adequate hematologic counts, hepatic function, creatinine clearance as well as any active infections requiring IV antibiotics. Then the nursing review assesses treatment plan parameters, patient’s performance status, recent vital signs, and other clinical concerns. If either review flags one or more criteria, the case then goes to physician review. The NEST escalation process includes two levels of physician review – a single reviewer and a committee. If the review determines that there are more potential benefits than risks associated with administering anti-cancer treatment, the treatment can be approved for inpatient administration. However, if the formal review estimates significantly greater risk than potential benefit, the treatment will not be approved for inpatient administration. Results: A total of 58 requests for inpatient anti-cancer therapy occurred between initial implementation (10/31/2022) through 3/31/2023. 82.8% (48/58) were reviewed by both pharmacy and nursing and 45.8% of those were approved without need to escalate. The remaining requests had baseline patient characteristics that triggered physician review - with 13 reviewed by a single physician and 3 requiring committee review. Of the cases requiring further review, 5 did not receive their requested therapy (either denied or the family decided to not pursue treatment). 36.2% (21/58) of NEST patients died within 60 days of process initiation, 22.4% (13/58) died within 30 days, and 13.8% (8/58) died within 10 days. These outcomes were more common in individuals where NEST was denied or inpatient treatment was not pursued (77.8% died within 60 days, 44.4% died within 10 days; note 2 patients discharged to hospice with no death date on record). Conclusions: We designed a formal review process for anti-cancer therapy to be administered in the inpatient setting to solid tumor patients. This multi-disciplinary review led to 15.5% of requests not being administered to patients. Ongoing continuous improvement work focuses on further developing review criteria, exploring options for hard stops prior to treatment administration and increasing earlier goals of care discussions.

Hyperarc Vmat and Vmat planning for stereotactic radiosurgery in multiple brain metastases

Automated treatment planning systems are available for linear accelerator (LINAC) based single and more isocenter multitarget stereotactic radiosurgery (SRS) of brain metastases. HyperArc Volumetric Modulated Arc Therapy (HA-VMAT) is a relatively new isocentric Volumetric Modulated Arc Therapy (VMAT) technique developed specifically for non-coplanar, multileaf collimator (MLC)-based stereotactic radiotherapy with automatic treatment optimization and dose delivery. The HA-VMAT planning approach was developed to accommodate dosing procedures for brain metastases stereotactic radiosurgery. In this study, it was aimed to compare the dosimetric parameters of treatment plans created with single and multi-isocenter retrospectively VMAT and HA-VMAT techniques in patients with lung cancer and multiple brain metastases (4–7) who received single and multi-fraction stereotactic radiosurgery (SRS). Using VMAT and HA-VMAT techniques, two separate treatment plans were created for each case, and tumor target coverage (homogeneity index (HI); conformity index (CI); gradient index (GI)) and organ at risk (OAR) were evaluated dosimetrically. Physical properties and Monitor unit (MU) values of both treatment approaches were compared. Treatment plans were created for study purposes and patients were not treated with these plans. In the study, HI (p = 0.000), CI (p = 0.000) and GI (p = 0.002) values calculated with the HA-VMAT technique are superior to the VMAT technique. Medium-low dose spreads (V4Gy-V16Gy) were significantly reduced in HA-VMAT plans compared to plans with VMAT. HA-VMAT plans result in lower MU than VMAT plans. HA-VMAT planning has significantly less radiation necrosis indicator (V8Gy-V16Gy) compared to VMAT plans. However, there are few studies investigating the ability of the HA-VMAT technique to create high-quality treatment plans for extracranial lesions. HA-VMAT may constitute one of the new options for SRS dose delivery for both single target and multiple targets.

Predicting Local Control with Dosimetric Parameters in Patients Receiving Individualized Stereotactic Ablative Radiotherapy for Lung Tumors

Stereotactic ablative radiotherapy (SABR) is an effective treatment option for lung tumors. The individualized lung tumor SABR (iSABR) trial was a phase II single-arm study that personalized lung tumor SABR dose and fractionation based on tumor size, location, and histology with very low rates of local recurrence (LR). A secondary analysis of this trial was conducted to assess for potential dosimetric predictors of LR, in order to help guide future clinical treatment planning. From 2011 to 2018, local, regional and distant recurrence data were prospectively collected from 204 patients (261 lung SABR treatments) enrolled in a prospective trial. Baseline characteristics and treatment details were evaluated. Dosimetric and treatment plan parameters were evaluated for their potential to predict LR, using logistic regression and chi-squared analyses. The majority of treated tumors were peripheral (71%, vs 29% central), primary lesions (76%, versus 24% metastatic), and of adenocarcinoma histology (67%, versus 13% squamous cell carcinoma and 19% other). The median follow-up was 24 months (range 2-95). Twenty-seven (10.3%) LRs occurred, with a median time to LR of 15 months (range 6-81 months). There were no significant associations between the overall cohort and the dosimetric parameters. However, for the multi-fraction cohort, an increased proportion of the PTV receiving 110% and 115% of the prescription dose were associated with lower LR (p = 0.01 and p = 0.01 respectively). Specifically for the 50 Gy in 4 fraction cohort, an increased D1cc, D0.03cc, as well as the proportion of the PTV receiving 110%, 115%, and 120% of the prescription dose were associated with lower LR (p < 0.001, p = 0.001, p = 0.003, p < 0.001, p = 0.004, respectively). There was no association of LR with prescription dose expressed as biologically effective dose using an alpha/beta of 10 Gy (BED10), D99%, or single- versus multi-fraction regimens. SABR for lung tumors using the individualized protocol on this trial showed excellent LR rates. We identified dosimetric parameters that were associated with LR, including V110% and V115% within the multi-fraction cohort, as well as the 50 Gy in 4 fraction cohort the D1cc, D0.03cc, and proportions of the PTV receiving 110%, 115%, and 120% of the prescription dose in the 50 Gy in 4 fraction cohort. Optimal thresholds for these parameters will be identified in further analyses. There did not appear to be an association with LR and BED10, D99%, or comparing single- vs multi-fraction regimens.

Modeling Gamma Knife Radiosurgical Toxicity for Multiple Brain Metastases

Dosing for single fraction radiosurgery has traditionally relied on tumor measurements from a single maximum diameter. Most protocols recommend setting dosing criteria based on assumed risk of radionecrosis roughly correlating with tumor size. However, the risk of radionecrosis after radiosurgery is best modeled by a function of dose and volume treated, with the largest body of evidence supporting the use of brain tissue receiving ≥12 Gy in one fraction (V12, i.e., > 10.9 cm3). Here we show that tumor surface area (SA) and second order dimensions are superior predictors for Gamma Knife radiosurgical toxicity and can be used to estimate V12. A total of 1217 brain metastases from 245 patients treated with a prescribed dose from 13 to 27 Gy in one fraction were retrospectively reviewed. Eight independent modeling parameters were considered; 3 geometric tumor characteristics: SA, volume (V), and largest axial dimension (LAD) and 5 treatment planning variables: prescription dose (Rx), coverage, selectivity, gradient index, and number of shots. Linear regression and power-law formulations were performed to determine which parameters were the most accurate predictors of V12. The power model is dependent on a conceptualized "pseudo surface area" (PSA), defined as the surface area of a sphere with a diameter of LAD of a lesion (PSA = π*LAD2). At the aggregate patient level, the model predicts total brain V12 by summing the V12 values for each singular lesion only by using LAD and Rx as input variables. Tumor SA was the best univariate linear predictor of V12 (adjR2 = 0.770), followed by LAD (adjR2 = 0.755) and V (adjR2 = 0.745). The SA predictive model improves for lesions that have high sphericity > 0.85 (adjR2 = 0.837), with a measure of 1 indicating a perfect sphere. Using bivariable regression analysis, we formulated a single term power model that even more accurately predicts for V12 (V12 = 0.0137 * Rx1.5 * LAD2, adjR2 = 0.906) and is proportional to PSA. At the patient level, this model also accurately predicts for total brain V12 (adjR2 = 0.896) and V12 > 10.9 cm3 (Sensitivity = 99.1%, Specificity = 90.5%). Conceptually, SA univariately predicts for V12 more accurately than other tumor physical dimensions or treatment planning parameters, while the best bivariable power model involves PSA. We provide a preplan model for brain metastases that can help better estimate radionecrosis risk, determine prescription doses given a target V12, and provide safe dose escalation strategies without the use of any planning software.

Dosimetric Analysis Using Automated Tools of Trigeminal Neuralgia Treatment with Stereotactic Radiosurgery

Symptoms from trigeminal neuralgia (TGN) can be significantly debilitating. For treatment of TGN with stereotactic radiosurgery (SRS), there is some data that suggests dose and location of treatment along the trigeminal nerve (TN) pathway may be associated with improved outcomes; however, recurrence rates are widely variable. Limited data exists to evaluate dosimetric parameters of SRS for TGN in relation to patient outcome. This study evaluated the hypothesis that specific characteristics of high dose volume coverage of the TN was associated with outcomes in the treatment of TGN with SRS. Patients who underwent a non-invasive stereotactic radiosurgery instrument for the treatment of TGN at a single institution from 2008-2020 were retrospectively reviewed. Patients were selected for treatment with SRS after consensus from neurosurgery and radiation oncology teams. Patient must have undergone MR FIESTA sequence imaging for treatment planning and had at least 3mo TGN follow up after SRS. Using commercially available software, an automated script was developed to extract detailed characteristics of isodose line structures (IDL) created from the delivered radiation treatment plan. Variables evaluated included voxel volume, mean/max of the HU signal, kurtosis/skewness (a measure of non-spheroidicity) of the IDL, and HU integral of the 140-195% IDL structures, all of which could serve as possible surrogates to the degree and shape of TN pathway dosimetric coverage. Patient reported pain was graded prior and post treatment using Barrow Neurologic Institute pain scale (BNI). Post SRS BNI score I-III was considered significant symptom improvement while BNI score IV-V was considered no benefit. Univariate and multivariable analysis was performed using the cox proportional hazard model. Of the 73 patients included, 52 (71%) were female and 21 (29%) were male, and median age at time of treatment was 73 years (60-79 years). Pretreatment BNI scores were BNI III in 9 (12%) patients, BNI IV in 42 (58%) patients, and BNI V in 22 (30%) patients. After SRS, 62 (85%) patients experienced significant symptom relief (BNI I-III). Median time to symptom relief was 2mo (IQR 1-4mo) with a median duration of 12mo (2-28mo). Median time to treatment failure was 12mo (IQR 2-28mo). On multivariable analysis evaluating IDL characteristics associated with achieving symptom relief, 195% IDL kurtosis was associated with increased likelihood of achieving symptom relief (HR 1.94, p<.001), while and 180% IDL voxel size was associated with reduced likelihood of achieving symptom relief (HR 0.99, p<.001). In the treatment of TGN with SRS, these initial results suggests that high dose IDL structure characteristics, specifically the size and shape features of the dose distributions, may be associated with likelihood of achieving symptom relief. Future directions include analysis of a richer set of dosimetric features in a larger cohort to further refine significant dosimetric parameters for treatment planning.

Comparison of the dose distribution of the VMAT radiotherapy technique depending on the beam used: FFF-X10MV and FFF-X15MV.

The aim of the study was to answer the question of whether flattening filter (FF) and flattening filter-free (FFF) beams can be used alternately in the volumetric modulated arc therapy (VMAT) treatment technique, regardless of the size of the irradiated volume [small (S) or large (L) planning target volume (PTV)]. Two groups of patients were examined: a group with a S-PTV-laryngeal cancer and a group with a L-PTV - gynecological volume. For each patient, two treatment plans were made for beams (energies): FFF-X10MV and FF-X15MV. Then, a statistical analysis, nonparametric test, and independent groups were performed, comparing the beams' impact on the analyzed treatment plans. In the case of laryngeal irradiation (S-PTV), there are no statistically significant differences between the energy used and the assessed parameters of the plan. In the case of gynecological volume (L-PTV), only statistically significant differences were noted for the number of monitor units depending on the energy used. For a large irradiated volume (gynecological case), the use of FFF beams increases the number of monitor units by 39,4% in relation to the FF beam. In the case of gynecological neoplasms, statistically significant differences were found in the number of monitor units. Therefore, in the case of irradiation of L-PTV, it is recommended that flattening-filtering beams are used due to the smaller number of monitors. In the case of S-PTV, no statistically significant differences were found between the types of beams used (FF or FFF) and the treatment plan parameters analyzed in the study.

Local control and survival after stereotactic body radiation therapy of early-stage lung cancer patients in Slovenia.

Stereotactic body radiation therapy (SBRT) precisely and non-invasively delivers ablative radiation dose to tumors in early-stage lung cancer patients who are not candidates for surgery or refuse it. The aim of research was to evaluate local control, overall survival (OS), local progression free survival (LPFS), distant metastases free survival (DMFS), disease free survival (DFS) and toxicity in early-stage lung cancer patients treated with SBRT in a single tertiary cancer centre. We retrospectively evaluated medical records and radiation treatment plan parameters of 228 tumors irradiated in 206 early-stage lung cancer patients between 2016 and 2021 at the Institute of Oncology Ljubljana. After 25 months of median follow up, 68 of 206 (33%) patients died. Median OS was 46 months (CI 36-56), 1-year, 2-year and 3-year OS were 87%, 74% and 62% and 5-year OS was 31%. A total of 45 disease progressions have been identified in 41 patients. Local progress only was noticed in 5 (2%) patients, systemic progress in 32 (16%) and combined systemic and local in 4 (2%) patients. Local control rate (LCR) at 1 year was 98%, at 2 and 3 years 96% and 95% at 5 years. The 1-, 2- and 3-year LPFS were 98%, 96% and 94%, respectively and 5-year LPFS was 82%. One, 2-, 3- and 5-year DFS were 89%, 81%, 72% and 49%, respectively. Among 28 toxicities recorded only one was Grade 4 (pneumonitis), all others were Grade 1 or 2. No differences in LCR, LPFS, DFS were found in univariate analysis comparing patient, tumor, and treatment characteristics. For OS the only statistically significant difference was found in patients with more than 3 comorbidities compared to those with less comorbidities. Early lung cancer treated with SBRT at single tertiary cancer centre showed that LCR, LPFS, DFS, DMFS and OS were comparable to published studies. Patients with many comorbidities had significantly worse overall survival compared to those with less comorbidities. No other significant differences by patient, tumor, or treatment characteristics were found for DMFS, LPFS, and DFS. Toxicity data confirmed that treatment was well tolerated.

Applicator-guided proton therapy versus multichannel brachytherapy for vaginal vault irradiation.

To dosimetrically compare applicator-guided intensity-modulated proton therapy(IMPT) and multichannel brachytherapy (MC-BRT) for vaginal vault irradiation(VVI) with special focus on dose to organs at risk (OARs) and normal tissues. Ten patients with uterine confined endometrial cancer who received adjuvant vaginal cuff brachytherapy were included in this study. For each patient an additional IMPT treatment plan was created using the same computed tomography dataset and contours segmented for MC-BRT plans. Clinical target volume (CTV) was defined as the proximal 3.5 cm of the vagina including the entire thickness of vaginal wall. Planning target volume for IMPT plans was generated from the CTV with an addition isotropic 3 mm margin. OARs included rectum, bladder, sigmoid, small bowel and femoral heads. The prescribed dose was 21 Gy in 3 fractions. For simplicity, all doses were expressed in Gy and a constant relative biological effectiveness of 1.1 was used for IMPT plans. Plan comparison was performed using dose-volume histogram and treatment planning parameters. A significant improvement of the D98% coverage for CTV was reached by the applicator-guided IMPT plans (p < 0.01). IMPT also provided a dose reduction in all OARs except for femoral heads due to the lateral beam direction, especially significant reduction of V5Gy, D2cc, D0.1 cc, Dmean, V95% values for the rectum and Dmean, D0.1 cc to bladder, sigmoid, small bowel. Additionally, IMPT plans showed a significant reduction of integral dose to normal tissue with respect to MC-BRT (221.5 cGy.L vs. 653.6 cGy.L, p < 0.01). Applicator-guided IMPT has the potential for improving plan quality in VVI while maintaining the high conformity afforded by the state-of-the-art intracavitary brachytherapy.

DOSIMETRIC EVALUATION OF POST-MASTECTOMY THREE-DIMENSIONAL CONFORMAL RADIATION THERAPY (3DCRT) BREAST CANCER TREATMENT PLANS

Breast cancer is the most diagnosed cancer in women globally. External beam radiotherapy is one method to treat breast cancer, which can be given to the patients after mastectomy. The changes in anatomy of breast tissues after mastectomy makes the radiotherapy treatment very challenging to ensure the prescribed dose delivered to the tumour target while the radiation to the surrounding critical organs is kept to be low. This study aims to evaluate the dosimetric parameters of radiotherapy treatment plans for breast cancer patients after mastectomy delivered using 3DCRT technique. The evaluation includes the target coverage to the PTV, defined as the volume of PTV receiving 95% of the prescribed dose and the volume of PTV receiving 107% of the prescribed dose. The min, max and mean dose to the PTV were also recorded. The dosimetric parameters to the OARs were Dmean and V20 to the lung, Dmean and V25 to the heart, Dmean to esophagus and Dmax to the spinal cord. The result shows that target coverage is fulfilled in most of the plans, however the host spot in the PTV also observed in the most of the plans. Dose to heart, left lung, esophagus and spinal cord are relatively low and below the constraint recommended by QUANTEC, however the V20 to the right lung exceeded the constraint in the most of the plans. The combination of photon and electron beam might be useful to reduce the excessive dose to the right lung.

The Impact of Grid Size and Statistical Uncertainty on the Accuracy of VMAT Plans Based on Dosimetric Parameters for Head and Neck Cancers

Aim Grid size and Statistical Uncertainty (SU) settings have an impact on the efficiency and accuracy of the treatment plans. Hence, it is very important, to find an optimum combination of the two-dose calculation parameters for efficient treatment planning. This study aims to study the impact of Grid Size and SU on Head and Neck cancer plans which were planned using the Volumetric-Modulated Arc Therapy (VMAT) technique. Materials and Methods 15 patients were selected for this retrospective study who had undergone radiation therapy at KMC, Manipal for various Head and Neck cancers. VMAT plans were generated for each case in Monaco 5.11 Treatment Planning System (TPS) using the Monte Carlo algorithm. For each patient, nine plans were generated in which the Grid size values were taken as 2 mm, 3 mm, and 5 mm and for each Grid size, SU settings were varied as 1%, 2%, and 5%. The plans were analysed and evaluated using outcome measures such as the Homogeneity Index (HI) and the Conformity Index (CI). Results The plans were evaluated as per the ICRU guidelines. In all the plans, PTV coverage achieved was above 95% with the maximum coverage (97.009) achieved with the 3 mm/1% combination. Overall, the effect of varying Grid Size and SU was insignificant in the plans generated, but there were few variations in the dose calculation parameters. For 2 mm/1%, 2 mm/2%, 2 mm/5%, 3 mm/1%, 3 mm/2%, 3 mm/5%, 5 mm/1%, 5 mm/2%, 5 mm/5%, the mean values of HI were 1.073, 1.078,1.078, 1.075, 1.0805, 1.0805, 1.068, 1.079, 1.089, and the mean values of CI were 0.968, 0.967, 0.967, 0.968, 0.958, 0.96, 0.954, 0.946, 0.948, respectively. Among all the combinations, the results for 5 mm/1% yielded more homogeneity, whereas 2 mm/1% and 3 mm/1% combinations resulted in better conformity. The 3 mm/1% combination gave maximum target coverage and quite fewer Monitor Units (MU) as well. Conclusion 3 mm Grid Size and 1% SU is suggested for the Head and Neck carcinomas planned using the VMAT technique.

A computer-aided tool for automatic volume estimation of hematoma using non-contrast brain CT scans

The computation of hematoma volume is the key parameter for treatment planning of Intracerebral hemorrhage (ICH). Non-contrast computed tomography (NCCT) imaging is routinely used for the diagnosis of ICH. Hence, the development of computer-aided tools for three-dimensional (3D) computed tomography (CT) image analysis is essential to estimate the gross volume of hematoma. We propose a methodology for automatic estimation of the hematoma volume from 3D CT volumes. Our approach integrates two different methods, multiple abstract splitting (MAS) and seeded region growing (SRG) to develop a unified hematoma detection pipeline from pre-processed CT volumes. The proposed methodology was tested on 80 cases. The volume was estimated from the delineated hematoma region, validated against the ground-truth volumes, and compared with those obtained from the conventional ABC/2 approach. We also compared our results with the U-Net model (supervised technique) to show the applicability of the proposed method. The volume calculated from manually segmented hematoma was considered the ground truth. The R 2 correlation coefficient between the volume obtained from the proposed algorithm and the ground truth is 0.86, which is equivalent to the R 2 value resulting from the comparison between the volume calculated by ABC/2 and the ground truth. The experimental results of the proposed unsupervised approach are comparable to the deep neural architecture (U-Net models). The average computation time was 132.76 ± 14 seconds. The proposed methodology provides a fast and automatic estimation of hematoma volume, which is similar to the baseline user-guided ABC/2 approach. Implementation of our method does not demand a high-end computational setup. Thus, recommended in clinical practice for computer-assistive volume estimation of hematoma from 3D CT volumes and can be implemented in a simple computer system.

Optimizing 3DCT image registration for interfractional changes in carbon-ion prostate radiotherapy

To perform setup procedures including both positional and dosimetric information, we developed a CT–CT rigid image registration algorithm utilizing water equivalent pathlength (WEPL)-based image registration and compared the resulting dose distribution with those of two other algorithms, intensity-based image registration and target-based image registration, in prostate cancer radiotherapy using the carbon-ion pencil beam scanning technique. We used the data of the carbon ion therapy planning CT and the four-weekly treatment CTs of 19 prostate cancer cases. Three CT–CT registration algorithms were used to register the treatment CTs to the planning CT. Intensity-based image registration uses CT voxel intensity information. Target-based image registration uses target position on the treatment CTs to register it to that on the planning CT. WEPL-based image registration registers the treatment CTs to the planning CT using WEPL values. Initial dose distributions were calculated using the planning CT with the lateral beam angles. The treatment plan parameters were optimized to administer the prescribed dose to the PTV on the planning CT. Weekly dose distributions using the three different algorithms were calculated by applying the treatment plan parameters to the weekly CT data. Dosimetry, including the dose received by 95% of the clinical target volume (CTV-D95), rectal volumes receiving > 20 Gy (RBE) (V20), > 30 Gy (RBE) (V30), and > 40 Gy (RBE) (V40), were calculated. Statistical significance was assessed using the Wilcoxon signed-rank test. Interfractional CTV displacement over all patients was 6.0 ± 2.7 mm (19.3 mm maximum standard amount). WEPL differences between the planning CT and the treatment CT were 1.2 ± 0.6 mm-H2O (< 3.9 mm-H2O), 1.7 ± 0.9 mm-H2O (< 5.7 mm-H2O) and 1.5 ± 0.7 mm-H2O (< 3.6 mm-H2O maxima) with the intensity-based image registration, target-based image registration, and WEPL-based image registration, respectively. For CTV coverage, the D95 values on the planning CT were > 95% of the prescribed dose in all cases. The mean CTV-D95 values were 95.8 ± 11.5% and 98.8 ± 1.7% with the intensity-based image registration and target-based image registration, respectively. The WEPL-based image registration was CTV-D95 to 99.0 ± 0.4% and rectal Dmax to 51.9 ± 1.9 Gy (RBE) compared to 49.4 ± 9.1 Gy (RBE) with intensity-based image registration and 52.2 ± 1.8 Gy (RBE) with target-based image registration. The WEPL-based image registration algorithm improved the target coverage from the other algorithms and reduced rectal dose from the target-based image registration, even though the magnitude of the interfractional variation was increased.

Physician-driven artificial intelligence enabled planning for intraprostatic dose escalation in under ten minutes.

187 Background: Intraprostatic radiation dose escalation is an area of clinical interest. Dose escalation within the prostate must be balanced with maintaining acceptable dose to the organs at risk, OAR (bladder, rectum, and urethra). Treatment planning therefore requires simultaneous consideration of multiple competing plan optimization goals, for which iterative, interdisciplinary treatment planning tasks may take significant physician, physicist, and dosimetrist time. Semi-automated treatment planning using artificial intelligence has the potential to significantly reduce treatment planning time for technically complex treatments. Methods: A prostate SBRT planning template was created using the Varian ETHOS treatment planning system (TPS) combined with an in-house RapidPlan SBRT prostate model. Prostate dose was prescribed to 36.25 Gy over 5 fractions with 95% coverage to the PTV. To respect standard SBRT normal tissue toxicity constraints while simultaneously escalating intraprostatic dose, the TPS automatically created an intraprostatic boost structure (PTV_SIB), derived from the PTV by excluding OARs with a pre-determined margin. Physicians were trained to perform treatment planning using the prostate SBRT planning template. Treatment planning was performed on 5 unique patients. The time spent from initiation to end of treatment planning and dosimetric parameters were recorded. Results: For each patient, the ETHOS TPS generated two SBRT plans (9 field static IMRT and 3 VMAT arc) with intraprostatic dose escalation in an average of 9.3 minutes [range 8.4-11.8]. Static field and VMAT plans were comparable. PTV_SIB was escalated to above 50 Gy in all cases. Relevant dosimetry for each patient’s static IMRT plan is shown. Conclusions: Physician-driven ETHOS treatment planning was able to produce boosted internal PTV doses using autosegmented volumes. The ETHOS TPS was able to generate dose-escalated plans that reconciled complex OAR and PTV goals within 8-12 minutes. Hence, the ETHOS TPS opens the possibility of rapid physician-driven treatment planning throughput. [Table: see text]

Analysis of CyberKnife intracranial treatment plans using ICRU 91 dose reporting: A retrospective study.

ICRU 91, published in 2017, is an international standard for prescribing, recording, and reporting stereotactic treatments. Since its release, there has been limited research published on the implementation and impact of ICRU 91 on clinical practice. This work provides an assessment of the recommended ICRU 91 dose reporting metrics for their use in clinical treatment planning. A set of 180 intracranial stereotactic treatment plans for patients treated by the CyberKnife (CK) system were analyzed retrospectively using the ICRU 91 reporting metrics. The 180 plans comprised 60 trigeminal neuralgia (TGN), 60 meningioma (MEN), and 60 acoustic neuroma (AN) cases. The reporting metrics included the planning target volume (PTV) near-minimum dose ( ), near-maximum dose ( ), and median dose ( ), as well as the gradient index (GI) and conformity index (CI). The metrics were assessed for statistical correlation with several treatment plan parameters. In the TGN plan group, owing to the small targets, was greater than in 42 plans, whereas both metrics were not applicable in 17 plans. The metric was predominantly influenced by the prescription isodose line (PIDL). The GI was significantly dependent on target volume in all analyses performed, where the variables were inversely related. The CI was only dependent on target volume in treatment plans for small targets. The ICRU 91 and metrics breakdown in plans for small target volumes below 1 cm3 ; the Min and Max pixel should be reported in such cases. The metric is of limited use for treatment planning. Given their volume dependence, the GI and CI metrics could potentially serve as plan evaluation tools in the planning of the sites analyzed in this study, which would ultimately improve treatment plan quality.

Hippocampal-sparing whole-brain radiotherapy under coplanar or noncoplanar VMAT.

Whole-brain radiotherapy (WBRT) can alleviate symptoms in patients with brain metastases. However, WBRT may damage the hippocampus. Volumetric modulated arc therapy (VMAT) can achieve a suitable coverage of the target region and a more conforming dose distribution whereas decreasing the dose to organs-at-risk (OARs). Herein, we aimed to compare the differences between treatment plans utilizing coplanar VMAT and noncoplanar VMAT in hippocampal-sparing WBRT (HS-WBRT). Ten patients were included in this study. For each patient, the Eclipse A10 treatment planning system was used to generate 1 coplanar VMAT (C-VMAT) and 2 noncoplanar VMAT treatment plans with various beam angles (noncoplanar VMAT A [NC-A] and noncoplanar VMAT B [NC-B]) for HS-WBRT. The prescribed dose was 30 Gy in 12 fractions. Treatment plans were established based on the OAR dose constraints of the Radiation Therapy Oncology Group 0933 (RTOG 0933). Parameters such as the global maximum dose, dose conformity, dose homogeneity of plans, and OAR doses were evaluated. The maximum biologically equivalent doses in 2-Gy fractions (EQD2) of OARs in C-VMAT were 9.17 ± 0.61, 42.79 ± 2.00, and 42.84 ± 3.52 Gy in the hippocampus, brain stem, and optic chiasm, respectively, which were the lowest among the 3 treatment plans. There was no significant difference in dose conformity among the 3 treatment plans. However, NC-A had a slightly better conformity than C-VMAT and NC-B. NC-A had the best homogeneity, and NC-B had the worst homogeneity (p = 0.042). NC-A and NC-B had the lowest and highest global dose maximum, respectively. Therefore, NC-A, which had an intermediate performance in terms of OAR doses, had the best quality parameters. We used the quality score table based on the p-value to evaluate the significant difference between each treatment technique from the multiparameter results. In terms of treatment plan parameters, only NC-A received a score of 2; for OAR doses, C-VMAT, NC-A, and NC-B received a score of 6, 3, and 5, respectively. For the overall evaluation, C-VMAT, NC-A, and NC-B received a total score of 6, 5, and 5, respectively. Rather than noncoplanar VMAT, 3 full-arc C-VMATs should be utilized in HS-WBRT. C-VMAT can simultaneously maintain treatment plan quality and decrease patient alignment time and total treatment time.