Mean Dose Research Articles

Adaptive intensity modulated proton therapy using 4D robust planning: a proof-of-concept for the application of dose mimicking approach

Objective.A four-dimensional robust optimisation (4DRO) is usually employed when the tumour respiratory motion needs to be addressed. However, it is computationally demanding, and an automated method is preferable for adaptive planning to avoid manual trial-and-error. This study proposes a 4DRO technique based on dose mimicking for automated adaptive planning.Approach.Initial plans for 4DRO intensity modulated proton therapy were created on an average CT for four patients with clinical target volume (CTV) in the lung, oesophagus, or pancreas, respectively. These plans were robustly optimised using three phases of four-dimensional computed tomography (4DCT) and accounting for setup and density uncertainties. Weekly 4DCTs were used for adaptive replanning, using a constant relative biological effectiveness (cRBE) of 1.1. Two methods were used: (1) template-based adaptive (TA) planning and (2) dose-mimicking-based adaptive (MA) planning. The plans were evaluated using variable RBE (vRBE) weighted doses and biologically consistent dose accumulation (BCDA).Main results.MA and TA plans had comparable CTV coverage except for one patient where the MA plan had a higher D98 and lower D2 but with an increased D2 in few organs at risk (OARs). CTV D98 deviations in non-adaptive plans from the initial plans were up to -7.2 percentage points (p.p.) in individual cases and -1.8 p.p. when using BCDA. For the OARs, MA plans showed a reduced mean dose and D2 compared to the TA plans, with few exceptions. The vRBE-weighted accumulated doses had a mean dose and D2 difference of up to 0.3 Gy and 0.5 Gy, respectively, in the OARs with respect to cRBE-weighted doses.Significance.MA plans indicate better performance in target coverage and OAR dose sparing compared to the TA plans in 4DRO adaptive planning. Moreover, MA method is capable of handling both forms of anatomical variation, namely, changes in density and relative shifts in the position of OARs.

A dosimetrically motivated pathfinding approach for non-isocentric dynamic trajectory radiotherapy

Objective.Non-isocentric dynamic trajectory radiotherapy (DTRT) involves dynamic table translations in synchrony with intensity modulation and dynamic gantry, table, and/or collimator rotation. This work aims to develop and evaluate a novel dosimetrically motivated path determination technique for non-isocentric DTRT.Approach.The path determination considers all available beam directions, given on a user-specified grid of gantry angle, table angle, and longitudinal, vertical, and lateral table position. Additionally, the source-to-target distance of all beam directions can be extended by moving the table away from the gantry along the central beam axis to increase the collision-free space. The path determination uses a column generation algorithm to iteratively add beam directions to paths until a user-defined total path length is reached. A subsequent direct aperture optimization of the intensity modulation along the paths creates deliverable plans. Non-isocentric DTRT plans using the path determination and using a manual path setup were created for a craniospinal and a spinal irradiation case. Furthermore, VMAT, isocentric DTRT, and non-isocentric DTRT plans are created for a breast, head and neck (H&N), and esophagus case. Additionally, a HyperArc plan is created for the H&N case. The plans are compared in terms of the dosimetric treatment plan quality and estimated delivery time.Main results.For the craniospinal and spinal irradiation case, using path determination results in dose distributions with improved conformity but a slightly worse target homogeneity compared to manual path setup. The non-isocentric DTRT plans maintained target coverage while reducing the mean dose to organs-at-risk on average by 1.7 Gy (breast), 1.0 Gy (H&N), and 1.6 Gy (esophagus) compared to the VMAT plans and by 0.8 Gy (breast), 0.6 Gy (H&N), and 0.8 Gy (esophagus) compared to the isocentric DTRT plans.Significance.A general dosimetrically motivated path determination applicable to non-isocentric DTRT plans is successfully developed, further advancing the treatment planning for non-isocentric DTRT.

Investigation of the linear accelerator low dose rate mode for pulsed low-dose-rate radiotherapy delivery

Purpose. Pulsed volumetric modulated arc therapy (VMAT) was proposed as an advanced treatment that combines the biological benefits of pulsed low dose rate (PLDR) and the dosimetric benefits of the intensity-modulated beams. In our conventional pulsed VMAT technique, a daily fractional dose of 200 cGy is delivered in 10 arcs with 3 min intervals between the arcs. In this study, we are testing the feasibility of pulsed VMAT that omits the need to split into ten arcs and excludes any beam-off gaps. Methods. The study was conducted using computed tomographic images of 24 patients previously treated at our institution with the conventional PLDR technique. Our newly installed Elekta machine has a low dose rate option on the order of 25 MU min−1. PLDR requires an effective dose rate of 6.7 cGy min−1 with attention being paid to the maximum dose received within any point within the target not to exceed 13 cGy min−1. The quality of treatment plans was judged based on dose-volume histograms, isodose distribution, dose conformality to the target, and target dose homogeneity. The dose delivery accuracy was assessed by measurements using the MatriXX Evolution 2D array system. Results. All cases were normalized to cover 95% of the target volume with 100% of the prescription dose. The average conformity index was 1.03 ± 0.08 while the average homogeneity index was 1.05 ± 0.02. The maximum reported dose rate at any point within the target was 10.44 cGy min−1. The mean dose rate for all pulsed VMAT plans was 6.88 ± 0.1 cGy min−1. All cases passed our gamma analysis with an average passing rate of 99.00% ± 0.48%. Conclusion. The study showed the applicability of planning pulsed VMAT using Eclipse and its successful delivery on our Elekta linac. Pulsed VMAT using the machine’s low dose rate mode is more efficient than our previous pulsed VMAT delivery.

Personalized selection of unequal sub-arc collimator angles in VMAT for multiple brain metastases

PurposeInvestigating the effects of unequal sub-arc personalized collimator angle selection on the quality of Volumetric Modulated Arc Therapy (VMAT) plans for treating multiple brain metastases. MethodsThis study included 21 patients, each with 2–4 target volumes of multiple brain metastases. Two stereotactic radiotherapy (SRT) approaches were utilized: sub-arc collimator VMAT (SAC-VMAT) and fixed collimator VMAT (FC-VMAT). In the SAC-VMAT group, multi-leaf collimators (MLC) shaped the target area, dividing the full arc into four unequal sub-arcs under the beam's eye view (BEV). Each sub-arc had an appropriate collimator angle selected to mitigate ‘island blocking problems'. Conversely, the FC-VMAT group used a fixed collimator angle of 15° or 345°. A comparative analysis of the dosimetric parameters of the target volumes and normal tissues, along with the monitor units (MU), was conducted between the two groups. ResultsThe mean dose and dose-volume to normal brain tissue (2–26 Gy, with a step of 2 Gy) were significantly lower in the SAC-VMAT group (P < 0.01). There was no statistical difference between the two groups in dose to the target volumes, conformity index (CI), homogeneity index (HI), and other normal tissues (P > 0.05). Compared with the FA-VMAT group, the SAC-VMAT group significantly reduced the gradient index (GI) (4.5 ± 0.59 vs 5.2 ± 0.75, P < 0.001) and MU (1774.33 ± 181.77 vs 2001.0 ± 344.86, P < 0.001). Notably, with an increase in the number of PTV, the SAC-VMAT group demonstrated more significant improvements in the dose-volume of normal brain tissue, GI, and MU. ConclusionsIn this study, personalized selection of the unequal sub-arc collimator angle ensured the prescribed dose to the PTV, CI, and HI, while significantly reducing the GI, MU, and the dose to normal brain tissue in the VMAT plan for multi-target brain metastases in the cohort of cases with 2–4 target volumes. Particularly as the number of targets increase, the advantages of this method become more pronounced.

Geometric evaluation and quantifying dosimetric impact of diverse deformable image registration algorithms on abdomen images with biomechanically modeled deformations.

Deformable image registration (DIR) has been increasingly used in radiation therapy (RT). The accuracy of DIR algorithms and how it impacts on the RT plan dosimetrically were examined in our study for abdominal sites using biomechanically modeled deformations. Five pancreatic cancer patients were enrolled in this study. Following the guidelines of AAPM TG-132, a patient-specific quality assurance (QA) workflow was developed to evaluate DIR for the abdomen using the TG-132 recommended virtual simulation software ImSimQA (Shrewsbury, UK). First, the planning CT was deformed to simulate respiratory motion using the embedded biomechanical model in ImSimQA. Additionally, 5mm translational motion was added to the stomach, duodenum, and small bowel. The original planning CT and the deformed CT were then imported into Eclipse and MIM to perform DIR. The output displacement vector fields (DVFs) were compared with the ground truth from ImSimQA. Furthermore, the original treatment plan was recalculated on the ground-truth deformed CT and the deformed CT (with Eclipse and MIM DVF). The dose errors were calculated on a voxel-to-voxel basis. Data analysis comparing DVF from Eclipse versus MIM show the average mean DVF magnitude errors of 2.8±1.0 versus 1.1±0.7mm for stomach and duodenum, 5.2±4.0 versus 2.5±1.0mm for small bowel, and 4.8±4.1 versus 2.7±1.1mm for the gross tumor volume (GTV), respectively, across all patients. The mean dose error on stomach+duodenum and small bowel were 2.3±0.6% for Eclipse, and 1.0±0.3% for MIM. As the DIR magnitude error increases, the dose error range increase, for both Eclipse and MIM. In our study, an initial assessment was conducted to evaluate the accuracy of DIR and its dosimetric impact on radiotherapy. A patient-specific DIR QA workflow was developed for pancreatic cancer patients. This workflow exhibits promising potential for future implementation as a clinical workflow.

Investigating synergy between beta-blockers and transarterial chemoembolization in the treatment of hepatocellular carcinoma: preliminary data from a propensity matched analysis

PurposeFavorable clinical outcomes have been reported with the adjunct use of beta-blockers in cancer treatment, hypothetically secondary to their anti-angiogenic/anti-proliferative effects. Hereby, we investigate whether there is synergy between beta-blockers and TACE in the treatment of HCC. Methods36 HCC patients on beta-blockers (mean dose of 48 mg daily) at the time of first-line treatment with TACE at our institution were retrospectively identified out of a cohort of 221 patients between 2008 and 2019. Using propensity scoring, a matched cohort of 36 patients not exposed to beta-blockers was generated based on age, gender, ethnicity, etiology of liver disease, BCLC, child Pugh score, PS/ECOG, cirrhosis, largest mass treated, type of TACE and treated liver segments. Tumor response was assessed at 1st and 2nd post-TACE imaging timepoints (1.4 and 4.1 months on average respectively). Variables were compared using chi-square test and Student's t-test. Kaplan-Meier transplant-free survival plots were generated using IBM® SPSS® software. Cox regression analysis was used to evaluate survival predictors. A p values < 0.05 was considered significant. ResultsComparing the control and beta-blocker cohorts, there were no differences in baseline characteristics, post-TACE imaging timepoints, tumor response or transplant free survival (p > 0.05). Tumor size was found to be a predictor of survival when the two cohorts were combined (p = 0.03). ConclusionTransplant-free survival and HCC response to first-line TACE treatment were similar in the control and beta-blocker groups. Large tumor sizes were associated with higher mortality in combined analysis of the cohorts.

Evaluation of Inverse Planned and Forward Planned Intensity Modulated Radiotherapy Techniques in Breast Cancer

Introduction: The objective of this study is to compare the dosimetric parameters of radiation to the whole breast between the two intensity-modulated radiotherapy (IP IMRT) techniques, i.e. Inverse planned IMRT (IP IMRT) and Forward Planned IMRT (FP IMRT) with regard to target coverage (PTV) and irradiation of organs at risk (OAR). Material and Methods: Plain and Contrast enhanced computed tomography (CECT) datasets were created for 41 patients treated with whole breast radiation therapy. CT simulation and treatment is performed using deep inspiratory breath hold technique (DIBH). Radiotherapy treatment Planning is done using Eclipse Treatment Planning System (version 13.7) with a prescription dose of 40 Gy in 15#. The developed treatment plans were subjected to objective comparison of PTV and OARs using dose volume histograms (DVH). Results: IP IMRT plans provided better coverage (99.5% vs 97.6%), comparable though higher maximum dose (Dmax 45.0 VS 44.1 Gy), higher hot spot (PTV105% 49.2 vs 33), lower volumes receiving 20, 25, 30 Gy (V20, V25, V30) for heart, more homogeneous (homogeneity index 0.10 vs. 0.14) and conformal dose distribution (conformity Index 1.0 vs 0.98) compared to FP IMRT. Regarding OAR dosimetry it is observed that FP IMRT showed reduced mean dose to Coronary artery (LADCA), Contralateral Lung (CL), Contralateral breast (CB) along with reduction in low dose region (V5) to all OARs under study. It was also observed that Monitor units used and planning time were lower for FP IMRT. Conclusion: On weighing different dosimetric factors, both the techniques have displayed their own advantages and disadvantages. Choosing a planning technique needs to be customized taking into consideration various factors such as breast topography, size and volumes of breast, availability of expertise planning skills and resources.

Discordance in acute gastrointestinal toxicity between synchrotron-based proton and linac-based electron ultra-high dose rate irradiation.

Proton FLASH has been investigated using cyclotron and synchrocyclotron beamlines but not synchrotron beamlines. We evaluated the impact of dose rate (ultra-high [UHDR] vs. conventional [CONV]) and beam configuration (shoot-through [ST] vs. spread-out-Bragg-peak [SOBP]) on acute radiation-induced gastrointestinal toxicity (RIGIT) in mice. We also compared RIGIT between synchrotron-based protons and linac-based electrons with matched mean dose rates. We administered abdominal irradiation (12-14 Gy single fraction) to female C57BL/6J mice with an 87 MeV synchrotron-based proton beamline (2 cm diameter field size as a lateral beam). Dose rates were 0.2 Gy/s (S-T pCONV), 0.3 Gy/s (SOBP pCONV), 150 Gy/s (S-T pFLASH), and 230 Gy/s (SOBP pFLASH). RIGIT was assessed by the jejunal regenerating crypt assay and survival. We also compared responses to proton [pFLASH and pCONV] with responses to electron CONV (eCONV, 0.4 Gy/s) and electron FLASH (eFLASH, 188-205 Gy/s). The number of regenerating jejunal crypts at each matched dose was lowest for pFLASH (similar between S-T and SOBP), greater and similar between pCONV (S-T and SOBP) and eCONV, and greatest for eFLASH. Correspondingly, mice that received pFLASH SOBP had the lowest survival rates (50% at 50 days), followed by pFLASH S-T (80%), and pCONV SOBP (90%), but 100% of mice receiving pCONV S-T survived (log-rank P = 0.047 for the four groups). Our findings are consistent with an increase in RIGIT after synchrotron-based pFLASH versus pCONV. This negative proton-specific FLASH effect versus linac-based electron irradiation underscores the importance of understanding the physical and biological factors that will allow safe and effective clinical translation.

Stereotactic body radiotherapy using CyberKnife versus interstitial brachytherapy in accelerated partial breast irradiation on left-sided breast: A comparison of dosimetric characteristics and preliminary clinical results

IntroductionWe compared the dosimetric characteristics of the target and organs at risk (OARs) as well as the preliminary clinical outcomes between two accelerated partial breast irradiation (APBI) techniques. MethodsForty-four patients diagnosed with left-sided early breast cancer who underwent APBI using either interstitial brachytherapy (IB) or stereotactic body radiation therapy (SBRT) with CyberKnife (CK) were retrospectively reviewed. The dosimetric parameters of the target and OARs were compared. Preliminary clinical outcomes, including tumor control and acute toxicity, were analyzed. ResultsTreatment plans with CK demonstrated a better cardiac dose-sparing effect. Radiation doses to the heart at V150cGy for the CK and IB groups were 24.4 % and 60.4 %, respectively (p < 0.001), while the mean heart doses for the CK and IB groups were 107.4 cGy and 204 cGy, respectively (p < 0.001). The heart D1c.c. and the ipsilateral lung received a lower dose in the IB group, without any significant differences. The median follow-up time in the CK and IB groups was 28.6 and 61.3 months, respectively. No patients died from either breast cancer or cardiac events during follow-up. A locoregional recurrence event at the neck occurred in one patient within the IB group. ConclusionsAPBI planned by CK was shown to have a better dose-sparing effect on the heart, as well as better conformity and homogeneity to the target. CK is a non-invasive treatment which showed minimal acute toxicity and promising tumor control.

Deep learning method for predicting weekly anatomical changes in patients with nasopharyngeal carcinoma during radiotherapy.

Patients may undergo anatomical changes during radiotherapy, leading to an underdosing of the target or overdosing of the organs at risk (OARs). This study developed a deep-learning method to predict the tumor response of patients with nasopharyngeal carcinoma (NPC) during treatment. This method can predict the anatomical changes of a patient. The participants included 230 patients with NPC. The data included planning computed tomography (pCT) and routine cone-beam CT (CBCT) images. The CBCT image quality was improved to the CT level using an advanced method. A long short-term memory network-generative adversarial network (LSTM-GAN) is proposed, which can harness the forecasting ability of LSTM and the generation ability of GAN. Four models were trained to predict the anatomical changes that occurred in weeks 3-6 and named LSTM-GAN-week 3 to LSTM-GAN-week 6. The pCT and CBCT were used as input, and the tumor target volumes (TVs) and OARs were delineated on the predicted and real images (ground truth). Finally, the models were evaluated using contours and dosimetry parameters. The proposed method predicted the anatomical changes, with a dice similarity coefficient above 0.94 and 0.90 for the TVs and surrounding OARs, respectively. The dosimetry parameters were close between the prediction and ground truth. The deviations in the prescription, minimum, and maximum doses of the tumor targets were below 0.5Gy. For serial organs (brain stem and spinal cord), the deviations in the maximum dose were below 0.6Gy. For parallel organs (bilateral parotid glands), the deviations in the mean dose were below 0.8Gy. The proposed method can predict the tumor response to radiotherapy in the future such that adaptation can be scheduled on time. This study provides a proactive mechanism for planning adaptation, which can enable personalized treatment and save clinical time by anticipating and preparing for treatment strategy adjustments.

Effects of electron density force to 1.0 and fill to 1.0 on VMAT treatment plans for lung SBRT.

The aim of this study is to determine the effect of forcing and filling the electron density (ED) to 1.0 of the planning target volume (PTV) overdose distribution in lung SBRT treatment leading to shortening patient treatment time and increasing patient comfort by reducing MU/fraction due to ED manipulation effect. In this study, 36 lung SBRT plans of 12 suitable patients who prescribed a total dose of 50Gy in five fractions were generated with Monaco v.5.10 TPS using the Monte Carlo (MC) algorithm and volumetric modulated arc therapy (VMAT) technique by PTV ED values forcing as well as filling to 1.0 and comparatively assessed. The first group of plans was created by using the patient's original ED, second and third groups of plans were reoptimized by forcing and filling the ED of PTV to 1.0, respectively, therefore acquiring a new dose distribution which lead to comparatively assessment the effects of changes in ED on PTV and OAR doses. Assessment of treatment plans revealed that mean MU/fx numbers were decreased by 76% and 75.25% between Groups 1 and 2, Groups 1 and 3, respectively. The number of segments was also reduced in Group 1 by up to 15% compared with Groups 2 and 3. Maximum HI and CI differences for PTV between Groups 1 and 2 were less than 1% and Groups 1 and 3 were 1.5% which indicates all 3 group plans were comparable in terms of dose distribution within PTV. Forcing and filling the ED of PTV to 1.0 strategy has provided reduced a number of segments and MU/fx without a significant change in PTV mean and maximum doses, thereby decreasing treatment time and patient discomfort during treatment. This process should be considered in line of a potential number of patients as well as prescribed dose and MU/fx numbers.

Moving beyond mean heart dose: The importance of cardiac substructures in radiation therapy toxicity.

Normal tissue tolerance dose limits to the heart have been established to reduce the risk of radiation-induced cardiac disease (RICD). Dose constraints have been developed based on either the mean dose delivered to the whole heart (MHD) or the dose delivered to a specific volume, for example, volume of heart receiving equal to or greater than 30 Gy (V30). There is increasing evidence that the impact of thoracic radiation on cardiac morbidity and mortality has been underestimated. Consequently, there is a need to reduce the dose delivered to the heart in radical radiotherapy treatment planning. The pathophysiology of RICD may relate to dose to specific cardiac substructures (CS) rather than the traditionally observed MHD for common toxicities. The MHD or V30 Gy threshold dose rarely represents the true dose delivered to individual CS. Studies have shown the dose to specific areas may be more strongly correlated with overall survival (OS). With advances in modern radiotherapy techniques, it is vital that we develop robust, evidence-based dose limits for CS, to fully understand and reduce the risk of RICD, particularly in high-risk populations with cardiac risk factors. The following review will summarise the existing evidence of dose limits to CS, explain how dose limits may vary according to different disease sites or radiation techniques and propose how radiotherapy plans can be optimised to reduce the dose to these CS in clinical practice.

A lung SBRT treatment planning technique to focus high dose on gross disease

This study investigated a straightforward treatment planning technique for definitive stereotactic body radiation therapy (SBRT) for patients with early-stage lung cancer aimed at increasing dose to gross disease by strategically penalizing the normal tissue objective (NTO) in the EclipseTM treatment planning system. Twenty-five SBRT cases were replanned to 50 Gy in 5 fractions using static and dynamic NTO methods (50 plans total). The NTO had a start dose of 100% at the target border, end dose of 20%, fall-off rate of 0.4/mm, and a priority of 150. For the static NTO plans, a lower planning target volume (PTV) objective was placed at 52 Gy with a priority of 100. Maximum dose was not penalized. Optimization was performed without user interaction. In contrast, the planner incrementally increased the priority of the NTO on the dynamic NTO plans until 95% of the target volume was covered by the prescription dose. Further, the dynamic NTO plans used both PTV lower and upper objectives at 63-64 Gy with priorities of 50. Maximum dose was penalized to ensure that the hot spot was within ± 2% of the static NTO global maximum dose. Following optimization, all plans were normalized so that the prescription dose covered 95% of the PTV. Plans were scored based on RTOG 0813 criteria, and dose to the internal target volume (ITV) and PTV was evaluated. The Wilcoxon signed-rank test (threshold = 0.05) was used to evaluate differences between the static and dynamic NTO plans. All plans met RTOG 0813 planning guidelines. In comparison to the static NTO plans, the dynamic NTO plans exhibited statistically significant increases in PTV mean dose, ITV mean dose, and PTV-ITV mean dose. Notably, the dynamic NTO plans more effectively concentrated the high dose on gross disease at the center of the PTV. As compared to the static NTO plans, the mean dose was 4.6 Gy higher in the ITV while only 1.3 Gy higher in the PTV-ITV rind of the dynamic NTO plans. Global maximum doses were similar. There were some small yet statistically significant differences in dose conformity between plan types. Furthermore, the dynamic NTO plans demonstrated a significant reduction in total monitor units (MU). This study demonstrated an efficient optimization strategy for lung SBRT plans that concentrates the highest dose in the gross disease, which may improve local control.

233. UTILITY OF SINGLE TRANSHIATAL CHEST DRAINAGE AFTER MINIMALLY INVASIVE OESOPHAGECTOMY: A PROPENSITY-SCORE MATCHED STUDY OF FEASIBILITY

Abstract Background The routine placement of intercostal chest drains remains common practice following minimally invasive oesophagectomy (MIO). Chest drains may contribute to increased post-operative pain and morbidity. The aim of this study was to compare the outcomes of transhiatal chest drain with intercostal chest drain. We analysed use of analgesia, length of hospital stay, and postoperative pulmonary morbidity following MIO. Methods This was a retrospective case-control study of patients undergoing elective MIO at a quaternary centre in Western Australia between September 2016 and September 2023. To reduce confounding, propensity score matching was performed. All patients were identified from a prospectively maintained database. In patients undergoing MIO with exclusive transhiatal drainage, a 19 French Blake’s drain was advanced through the hiatus into the right pleural cavity and positioned adjacent to the anastomosis. Results Thirty patients were included in the study, fifteen of whom had exclusively transhiatal drain placement. Mean total daily oral morphine dose equivalent was significantly lower in the transhiatal drain group (58mg+/-35.8) compared with intercostal drain group (100.8mg+/-64.0) on day 1 (p=0.04). There is no statistically significant difference between the total oral morphine use on days 3 (p=0.44) and 6 (p=0.97). No significant difference was observed in reintervention rate (p=1.00), length of stay (p=0.78) or postoperative pulmonary complications (p=1.00). Conclusion The results of this study suggest that transhiatal drain placement following MIO is associated with a reduction in post-operative pain and no increase in pulmonary complications or length of stay. Larger, prospective studies are needed to further evaluate the safety of single transhiatal chest drain placement following MIO.

Memory Tract Sparing Using Diffusion Tensor Imaging in Radiation Planning of Primary Brain Tumors

Radiation therapy (RT) is a critical treatment modality for both primary and metastatic brain tumors, yet approximately 30% of patients experience cognitive decline post-radiotherapy. This cognitive toxicity is linked to low radiation doses affecting the hippocampal dentate gyrus. Hippocampal Avoidance (HA)-Whole Brain Radiotherapy (WBRT) combined with Memantine has shown promising outcomes in preserving cognitive function and quality of life (QOL) in patients with brain metastases. Nowadays, it is the standard of care for those with good performance status and no hippocampal metastases. We conducted a prospective trial approved by the IRB (SMC0307-23), including patients aged 18 and above with primary brain tumors post-resection or biopsy. Exclusion criteria included multifocal glioma crossing to the other hemisphere. RT was delivered to a total dose of 59.4Gy in 33. Diffusion tensor imaging (DTI) was performed to map hippocampal-associated white matter tracts. Using Eclipse treatment planning software, memory fiber tracts and hippocampi were contoured and integrated into RT planning. Dosimetric analyses compared two plans with memory fiber constraints and one without. The primary endpoints were safety and dosimetric feasibility. Twelve patients with low-grade gliomas were included, and the contouring of memory fibers and hippocampi was successful. VMAT treatment plans met-dose constraints for memory fibers, with an average mean dose of 10.1 Gy. The average MoCA score before RT was 27.1 and 26.4 at eight months post-treatment, with a p-value of 0.07. Excluding one patient, the scores were 27.1 and 26.6, respectively (p=0.13). MRI planning using DTI for memory fiber detection and incorporation into RT planning via VMAT techniques enables hippocampal and associated white fiber sparing, potentially preserving cognitive function. Preliminary cognitive data are promising, supporting the need for further validation in a larger cohort.

Impact of Isotretinoin on Blood Lipids and Liver Enzymes: A Retrospective Cohort Study in Saudi Arabia.

Isotretinoin is an effective treatment for acne but can cause side effects such as changes in blood lipids and liver enzymes. Laboratory monitoring is essential during treatment, but there is variation in monitoring practices. This study aims to investigate the relationship between isotretinoin therapy and its effects on complete blood count in Saudi Arabia to improve patient outcomes. The study was a retrospective cohort study conducted at King Khalid University Hospital in Riyadh, Saudi Arabia, between January 2016 and December 2020. Following the inclusion and exclusion criteria, 515 patients were randomly selected for the study. The data was analyzed using SPSS, and descriptive statistics and paired samples t-tests were employed to analyze the data. In this study, 515 patients were enrolled. Of these participants, 76.7% (n=395) were females and 23.3% (n=120) were males. The mean age of the study participants was 23.98±7.4 years and ranged between 16 and 65 years. The mean dose of Isotretinoin administered was 27.65±9.6 mg/day, with a range of 10-60 mg/day. The mean BMI of the study participants was 24.3±4.1 kg/m2, ranging from 14.3 to 44.8 kg/m2. Regarding the effect of Isotretinoin on laboratory measures, significant statistical differences were found in hemoglobin measurements (t=-3.379, p=0.001), platelets (t=-3.169, p=0.002), neutrophils (%) (t=3.107, p=0.002), total cholesterol (t=-13.017, p=0.000), AST (t=-6.353, p=0.000), ALT (t=-4.352, p=0.000), HDL (t=2.446, p=0.015), and LDL (t=-12.943, p=0.000). However, there were no significant statistical differences in the measurements of WBC, neutrophils (count), or triglycerides. In the Chi-square analysis and Fisher's Exact test to identify the interaction between BMI, dose, and gender on abnormal lab results, significant interaction was found between participants' BMI and abnormal HDL measurements (p=0.006). Furthermore, there were significant interactions between Isotretinoin dose (either less than 30 mg/day or 30 mg/day or more) and abnormal neutrophil count (p=0.04), abnormal HDL measurements (p=0.010), and abnormal triglycerides measurements (p=0.020). Moreover, a statistically significant interaction was found between participants' gender and abnormal hemoglobin measurements (p=0.006), abnormal total cholesterol (p=0.016), abnormal AST measurements (p=0.001), abnormal ALT measurements (p=0.000), abnormal HDL measurements (p=0.000), and abnormal triglycerides measurements (p=0.007). In conclusion, the study found that isotretinoin therapy has significant effects on several laboratory measures, including hemoglobin, platelets, neutrophils, total cholesterol, AST, ALT, HDL, and LDL. The study also revealed significant interactions between BMI, dose, gender, and abnormal lab results.

Bone marrow toxicity in patients with locally advanced cervical cancer undergoing multimodal treatment with VMAT/IMRT: are there dosimetric predictors for toxicity?

PurposeFor women with locoregionally advanced cervical cancer, the standard of care treatment is the curatively intended chemoradiation therapy (CRT). A relationship between bone marrow (BM) dose–volume histograms (DVHs) and acute hematological toxicity (HT) has been debated recently. Aim of this study was the evaluation of BM dose constraints and HT in a contemporary patient cohort.MethodsRadiation treatment plans of 31 patients with cervical cancer (FIGO stage IIB–IVB) treated with intensity-modulated radiotherapy and simultaneous chemotherapy were explored retrospective. Pelvic bones (PB) and femoral heads (FH) were contoured and DVHs were correlated with white blood cells (WBC), hemoglobin levels and platelets.ResultsComparing the absolute blood levels with the dose volumes of both FH and PB the data showed a significant correlation between WBC and the median dose of the FH and the median dose, V30Gy, V40Gy and V50Gy of the PB. A correlation between the toxicity grade of anemia and mean dose, maximum dose and V5Gy of the PB was found. Counting the highest grade of HT of all three blood levels of each patient, significant correlations were found for the mean and median dose, V30Gy, V40Gy and V50Gy of the PB.ConclusionThe results show that blood levels may correlate with distinct dosimetric subvolumes of critical bone marrow compartments with a potential impact on therapeutic outcome and treatment-related toxicity. The data presented are in line with the previous findings on the relevance of dosimetric exposure of pelvic bony subvolumes.

COMPARATIVE RADIATION DOSIMETRY OF WHOLE BREAST RADIOTHERAPY USING IMRT AND VMAT TECHNIQUES IN LEFT SIDED BREAST CANCER PATIENTS AFTER BREAST CONSERVING SURGERY

Background:The radiotherapy of left sided breast cancers is mandatory and integral part of treatment and challenging because of surrounding critical structures posing increased risk of complications. The main objective of this study was to quantify doses toorgan at risk(OARs) including left lung, heart, contralateral breast, spinal cord, and planning target volume (PTV) using different radiation techniques like Intensity modulated radiation therapy (IMRT)&amp;volumetric modulated arc therapy (VMAT) and comparison of radiation dosimetry. Methods: A prospective study of 30 patients of left sided breast cancer who had undergone Breast Conservative Surgery (BCS) and chemotherapy was done for adjuvant radiation. For every patient radiation planning was done by two different techniques IMRT and VMAT. Then the comparison of radiation dosimetry parameters was done for all the techniques including the parameters like PTV coverage, doses to OAR like heart, left lung, contralateral breast and spinal cord and head of humerus. The Homogenity Index (HI) were calculated. Result: The Mean age of the patient was 46.7 years. When comparing the doses delivered in IMRT and VMAT Technique for left sided breast cancer post breast conservation surgery there was significant difference in PTV Breast and axilla V95 Gy. It was 96.2±1.9% (IMRT) vs 94.8±1.71% (VMAT), (p=0.004). However significant sparing of Organs at Risk was seen. With ipsilateral lung dose mean V5 Gy was 77.86± 9.68% (IMRT) v/s 83.04± 9.86 % (VMAT), (p=0.0446). Also mean V30 Gy was 14.6±4.82% with IMRT vs 16.54±5.86% with VMAT, (p=0.0169). Heart mean dose was 8.8±1.49 Gy with IMRT and 10.98±3.7 Gy with VMAT, (p=0.0227). Further V30 Gy for Heart was 4.61±3.8% with IMRT and 6.72±4.0% with VMAT, (p=0.0132).No significant difference was seen with IMRT and VMAT technique for contralateral lung, contralateral breast and spinal cord. Conclusion: In treatment of patients with radiation with left breast cancer patients post BCS using IMRT and VMAT technique it is seen significant dose reduction with IMRT Technique for ipsilateral lung and Heart as compared to VMAT technique. Significant V95 coverage for PTV Breast and axilla with IMRT as compared to VMAT. Hence in our Study IMRT technique was found to be superior for better sparing of Organ at risk and better PTV coverage.

Co60 May be the Acceptable Alternative Radionuclides of Ir192 used in HDR Brachytherapy for the Treatment of Inoperable Carcinoma Cervix in the Treatment Modality of Concurrent Chemoradiation

Background: Cancer of the uterine cervix is the eighth most common cancer among women worldwide and third among all malignancies and the second most common cancers in female in Bangladesh. The treatment of cervical cancer requires multidisciplinary approaches Concurrent chemoradiation is the treatment of choice in locally advanced carcinoma cervix uteri. Radiotherapy is the primary local treatment for most patients having FIGO stage IIB to IVA diseases. The success of treatment depends on a careful balance between EBRT and Brachytherapy that optimizes the dose to tumor. Iridium192 is highly used radionuclide for modern remote after loading HDR brachytherapy till date. Recently Co60 source is available with miniature size and identical physical properties for remote after loaders. Methods: 60 patients with biopsy proven locally advanced carcinoma of the uterine cervix were enrolled in the study. Arm A was formed comprising 30 patients who were treated by Ir192 HDR brachytherapy and Arm B formed with equal number of 30 patients who received HDR brachytherapy treated with Co60 radionuclide. This prospective observational study was carried out to compare the treatment effect between two Arm. Results: 60 patients were enrolled in this study with age range from 35 to 63 years. Most of the patients presented with stage IIB disease, consisting of 39 patients (65.3%). Among them 48 patients had squamous cell carcinoma (80.60%), adenocarcinoma trailing with 9 patients (15.3%) and rest were adenoidsquamous carcinoma 2 and small cell carcinoma. In all three insertions, urinary bladder dose distribution was slightly smaller by HDR Co60 irradiation than HDR Ir192 exposure. These differences were statistically significant in first two insertions but not in third one Conclusion: In this study radiation dose distribution at OARs i.e. urinary bladder and rectum were compared between Arm A and Arm B. In all three insertions in urinary bladder the mean dose distribution was slightly smaller in HDR Co60 irradiation than HDR Iridium192 exposure. These differences were statistically significant in first two insertions but not in third one. In case of rectum point, the mean dose distribution was significantly lower in all three insertions of Co60 exposure than Ir192 exposure.

632: The FLASH Effect is dependent on Dose per Pulse and not Mean Dose Rate for Abdominal Irradiations

632: The FLASH Effect is dependent on Dose per Pulse and not Mean Dose Rate for Abdominal Irradiations