Neurocognition and mean radiotherapy dose to vulnerable brain structures: new organs at risk?

BACKGROUND: Children with brain tumors are at high risk of neurocognitive decline after radiotherapy (RT). However, there is a lack of studies on how RT doses to organs at risk (OARs) impacts neurocognition. The aim of this study was to examine dose-risk relationships for mean RT dose to different brain structures important for neurocognitive networks. We explored previously established OARs and potentially new OARs. METHODS: A sample of 44 pediatric brain tumor survivors who had received proton and/or photon RT were included. Correlations between mean RT doses to OARs and IQ were analyzed. Previously established OARs were cochleae, optic chiasm, optic nerve, pituitary gland, hypothalamus, hippocampus and pons. Potential new OARs for RT-induced neurocognitive decline were cerebellum, vermis and thalamus. RESULTS: Mean RT dose to different OARs correlated with several IQ subtests. Higher mean RT dose to cochleae, optic nerve, cerebellum, vermis and pons was correlated with lower performance on particularly full-scale IQ (FIQ), Perceptual Reasoning (PRI), Working Memory (WMI) and Processing Speed Index (PSI). Higher mean RT dose to hippocampus correlated with lower performance on processing speed and working memory. For those receiving whole brain RT (WBRT), higher mean RT dose to the pituitary gland correlated with lower performance on working memory. CONCLUSION: A high dose-risk correlation was found between IQ subtests and mean RT dose in established and potential new OARs. Thus, in the lack of validated dose constraints for vulnerable brain structures, a parsimonious approach in RT planning should be considered to preserve neurocognitive networks.

[Reducing the risk of radiation-induced cardiotoxicity in patients with left breast tumor]. / A sugárkezelés okozta cardiotoxicitas kockázatának csökkentése bal oldali emlotumoros betegek kezelése során.

INTRODUCTION: Breast cancer is one of the most common malignancies affecting women. Treatment with drugs and radiotherapy increases the incidence of late cardiovascular disease. It is therefore particularly important to protect the heart from radiation exposure. METHOD: We prepared an irradiation plan for 45 patients with left breast cancer using deep breathing and normal breathing techniques. The plans were compared and analyzed. The irradiation plans were created in the Philips Pinnacle v. 16 planning system. RESULTS: At the same target volume coverage, the use of the deep breathing technique leads to a reduction of the dose burden to the heart and to the left descending coronary branch, thus reducing the incidence of late cardiovascular complications. DISCUSSION: The results obtained show that the use of the deep breathing technique during adjuvant radiotherapy of left-sided breast cancer patients has a beneficial effect on the radiation exposure of the heart. Our results are in good agreement with similar data from national centres. We were not only able to maintain planning target volume coverage, but also to achieve an improvement of 1%. There is a significant difference in dose to the heart and coronary artery. By using the deep breathing technique, we were able to reduce the average cardiac dose by almost half (deep breathing: 2.87 Gy, normal breathing: 5.4 Gy). The coronary exposure was reduced from 19.5 Gy to 10.98 Gy. CONCLUSION: The accuracy of treatment can be further improved by using a respiratory gating system with a surface-guided radiotherapy system. The successful use of deep breathing technique requires professionalism of the treatment staff and good patient cooperation. It is less equipment intensive than a respiration-guided system. The deep breathing technique is no longer considered state-of-the-art in the era of breath-holding, but the experience gained in our department is worth describing because of its relevance to oncocardiology. Orv Hetil. 2023; 164(11): 420-425.

Multi-center dosimetric predictions to improve plan quality for brachytherapy for cervical cancer treatment.

BACKGROUND AND PURPOSE: Image-guided adaptive brachytherapy (IGABT) is an important modality in the cervical cancer treatment, and plan quality is sensitive to time pressure in the workflow. Patient anatomy-based quality-assurance (QA) with overlap volume histograms (OVHs) has been demonstrated to detect suboptimal plans (outliers). This analysis quantifies the possible improvement of plans detected as outliers, and investigates its suitability as a clinical QA tool in a multi-center setting. MATERIALS AND METHODS: In previous work OVH-based models were investigated for the use of QA. In this work a total of 160 plans of 68 patients treated in accordance with the current state-of-the-art IGABT protocol from Erasmus MC (EMC) were analyzed, with a model based on 120 plans (60 patients) from UMC Utrecht (UMCU). Machine-learning models were trained to define QA thresholds, and to predict dose D2cm3 to bladder, rectum, sigmoid and small bowel with the help of OVHs of the EMC cohort. Plans out of set thresholds (outliers) were investigated and retrospectively replanned based on predicted D2cm3 values. RESULTS: Analysis of replanned plans demonstrated a median improvement of 0.62 Gy for all Organs At Risk (OARs) combined and an improvement for 96 % of all replanned plans. Outlier status was resolved for 36 % of the replanned plans. The majority of the plans that could not be replanned were reported having implantation complications or insufficient coverage due to tumor geometry. CONCLUSION: OVH-based QA models can detect suboptimal plans, including both unproblematic BT applications and suboptimal planning circumstances in general. OVH-based QA models demonstrate potential for clinical use in terms of performance and user-friendliness, and could be used for knowledge transfer between institutes. Further research is necessary to differentiate between (sub)optimal planning circumstances.

Should organs at risk (OARs) be prioritized over target volume coverage in stereotactic ablative radiotherapy (SABR) for oligometastases? a secondary analysis of the population-based phase II SABR-5 trial.

BACKGROUND AND PURPOSE: Stereotactic ablative radiotherapy (SABR) for oligometastases may improve survival, however concerns about safety remain. To mitigate risk of toxicity, target coverage was sacrificed to prioritize organs-at-risk (OARs) during SABR planning in the population-based SABR-5 trial. This study evaluated the effect of this practice on dosimetry, local recurrence (LR), and progression-free survival (PFS). METHODS: This single-arm phase II trial included patients with up to 5 oligometastases between November 2016 and July 2020. Theprotocol-specified planning objective was to cover 95 % of the planning target volume (PTV) with 100 % of the prescribed dose, however PTV coverage was reduced as needed to meet OAR constraints. This trade-off was measured using the coverage compromise index (CCI), computed as minimum dose received by the hottest 99 % of the PTV (D99) divided by the prescription dose. Under-coverage was defined as CCI < 0.90. The potential association between CCI and outcomes was evaluated. RESULTS: 549 lesions from 381 patients were assessed. Mean CCI was 0.88 (95 % confidence interval [CI], 0.86-0.89), and 196 (36 %) lesions were under-covered. The highest mean CCI (0.95; 95 %CI, 0.93-0.97) was in non-spine bone lesions (n = 116), while the lowest mean CCI (0.71; 95 % CI, 0.69-0.73) was in spine lesions (n = 104). On multivariable analysis, under-coverage did not predict for worse LR (HR 0.48, p = 0.37) or PFS (HR 1.24, p = 0.38). Largest lesion diameter, colorectal and 'other' (non-prostate, breast, or lung) primary predicted for worse LR. Largest lesion diameter, synchronous tumor treatment, short disease free interval, state of oligoprogression, initiation or change in systemic treatment, and a high PTV Dmax were significantly associated with PFS. CONCLUSION: PTV under-coverage was not associated with worse LR or PFS in this large, population-based phase II trial. Combined with low toxicity rates, this study supports the practice of prioritizing OAR constraints during oligometastatic SABR planning.

The New Kid on the Block: Online Adaptive Radiotherapy in the Treatment of Gynecologic Cancers.

Online adaptive radiation is a new and exciting modality of treatment for gynecologic cancers. Traditional radiation treatments deliver the same radiation plan to cancers with large margins. Improvements in imaging, technology, and artificial intelligence have made it possible to account for changes between treatments and improve the delivery of radiation. These advances can potentially lead to significant benefits in tumor coverage and normal tissue sparing. Gynecologic cancers can uniquely benefit from this technology due to the significant changes in bladder, bowel, and rectum between treatments as well as the changes in tumors commonly seen between treatments. Preliminary studies have shown that online adaptive radiation can maintain coverage of the tumor while sparing nearby organs. Given these potential benefits, numerous clinical trials are ongoing to investigate the clinical benefits of online adaptive radiotherapy. Despite the benefits, implementation of online adaptive radiotherapy requires significant clinical resources. Additionally, the timing and workflow for online adaptive radiotherapy is being optimized. In this review, we discuss the history and evolution of radiation techniques, the logistics and implementation of online adaptive radiation, and the potential benefits of online adaptive radiotherapy for gynecologic cancers.

Radiobiological and dosimetric comparison of 60Co versus 192Ir high-dose-rate intracavitary-interstitial brachytherapy for cervical cancer.

BACKGROUND: High-dose-rate (HDR) intracavitary-interstitial brachytherapy (IC-ISBT) is an effective treatment for bulky, middle, and advanced cervical cancer. In this study, we compared the differences between 60Co and 192Ir HDR IC-ISBT plans in terms of radiobiological and dosimetric parameters, providing a reference for clinical workers in brachytherapy. METHODS: A total of 30 patients with cervical cancer receiving HDR IC-ISBT were included in this study, and IC-ISBT plans for each individual were designed with both 60Co and 192Ir at a prescribed dose of CTV D90 = 6 Gy while keeping the dose to OARs as low as possible. Physical dose and dose-volume parameters of CTV and OARs were extracted from TPS. The EQD2, EUBED, EUD, TCP, and NTCP were calculated using corresponding formulas. The differences between the 60Co and 192Ir IC-ISBT plans were compared using the paired t-test. RESULTS: In each patient's 60Co and 192Ir IC-ISBT plan, the average physical dose and EQD2 of 60Co were lower than those of 192Ir, and there were statistically significant differences in D2cc and D1cc for the OARs (p < 0.05); there were statistically significant differences in D0.1 cc for the bladder (p < 0.05) and no significant differences in D0.1 cc for the rectum or intestines (p > 0.05). The EUBED ratio (60Co/192Ir) at the CTV was mostly close to 1 when neither 60Co or 192Ir passed their half-lives or when both passed two half-lives, and the difference between them was not significant; at the OARs, the mean value of 60Co was lower than that of 192Ir. There was no statistical difference between 60Co and 192Ir in the EUD (93.93 versus 93.92 Gy, p > 0.05) and TCP (97.07% versus 97.08%, p > 0.05) of the tumors. The mean NTCP value of 60Co was lower than that of 192Ir. CONCLUSIONS: Considering the CTV and OARs, the dosimetric parameters of 60Co and 192Ir are comparable. Compared with 192Ir, the use of 60Co for HDR IC-ISBT can ensure a similar tumor control probability while providing better protection to the OARs. In addition, 60Co has obvious economic advantages and can be promoted as a good alternative to 192Ir.

The feasibility of dose escalation using intensity-modulated radiotherapy (IMRT) and intensity-modulated proton therapy (IMPT) with FDG PET/CT guided in esophageal cancer.

Context: Previous studies show that dose escalation for gross tumor volume (GTV) improves local control of esophageal cancer (EC). However, optimal boosting remains uncertain. Recently, functional imaging guidance to achieve dose escalation in high-risk areas of tumors has been proposed. Aims: This study evaluated the feasibility of dose escalation in tumor regions with high fluorodeoxyglucose (FDG) uptake using intensity-modulated radiotherapy (IMRT) and intensity-modulated proton therapy (IMPT). Settings and Design: GTVPET was defined as a high FDG uptake region with 50% SUVmax threshold for dose escalation. IMRT and IMPT plans were generated for three boosting modes: plan 50.4 (50.4 Gy in clinical target volume, CTV), plan 63 (50.4 Gy in CTV, 63 Gy in GTV), plan 70 (50.4 Gy in CTV, 63 Gy in GTV, and 70 Gy in GTVPET). Methods and Material: Eleven patients with squamous cell carcinoma were evaluated. Dose parameters for heart, lung, and spinal cord were compared based on the dose-volume histogram (DVH). Statistical Analysis Used: Paired t-test was performed on the doses to organs-at-risk (OARs) among plan 50.4, plan 63, and plan 70 for IMRT and IMPT. Results: Dosimetric parameters for IMRT for heart, lung, and spinal cord increased significantly for plan 63 and some parameters even exceeded dose limits for OARs. Further dose escalation in GTV-PET did not increase dosimetric parameters significantly. Most dosimetric parameters of OARs in IMPT exhibited no statistical change compared with plan 50.4, and doses to OARs were far less than dose constraints. Conclusions: Dose escalation by IMRT may lead to increased risk of radiation-related injury. Further dose escalation in high FDG uptake regions did not increase doses to OARs. This dose escalation is ideal for achieving better outcomes for EC treatment.

Validation of a simple technique for accurate treatment delivery for bilateral breast irradiation using the electronic portal imaging device.

Background and Aims: While bilateral breast cancer is rare, the challenge for the radiation oncologist is to limit the dose to multiple important organs-at-risk and reducing the chance of overlapping tangential fields to limit hotspots. In this study, we present a simple technique to verify the setup accuracy of breast tangential fields using the electronic portal imaging device (EPID) for bilateral breast cancer. Patients and Methods: A 74-year-old female, with bilateral breast cancers, right staged as T1N0M0 and the left T2N1M0, received postoperative radiotherapy following bilateral breast conservative surgery. Standard CT-based simulation and target delineation were done, followed by treatment planning using classical field arrangements with two separate isocenters, one for each breast (keeping identical anteroposterior and superior-inferior coordinates). The planned doses were 45 Gy/25 # for whole breasts, plus tumor bed boost of 15 Gy/6 # and 50 Gy/25 # to left supraclavicular fossa. After setting up the patient, two small lead wires were placed at the medial borders of medial tangents (as seen on light fields) of each breast (longer one for left), followed by EPID imaging (dual exposure: One lateral tangent field image and other larger to include lead wires) of respective contralateral lateral tangential fields to verify that there was no actual overlapping with the opposite medial tangential field, as indicated by the lead wires. Conclusion: The study has validated a simple EPID-based technique for routine use in the field matching for radiotherapy of bilateral breast cancer.

Effect of stomach size on organs at risk in pancreatic stereotactic body radiotherapy.

BACKGROUND: In clinical practice, the organs at risk (OARs) should be carefully determined when performing pancreatic stereotactic body radiotherapy (SBRT). We conducted a simulation study to examine the effect of the stomach size on the radiation dose to the OARs when performing pancreatic SBRT. METHODS: Twenty-five cases were included in this study. Pancreatic head and body tumors were 2-cm-sized pseudotumors, which were included as gross target volume (GTV) contours. The stomach, pancreas, small intestine, liver, kidneys, and spinal cord were considered as the OARs. The prescription dose for planning target volume (PTV) was 40 Gy/5fx, and the dose limit for the OARs was determined. The dose to X% of the OAR volume at X values of 0.1, 5.0, and 10.0 cc (DX) and the percentage of the OAR volume that received more than X Gy were recorded. RESULTS: In terms of the radiation dose to the pancreatic body tumors, the stomach size was positively correlated with a dose of D10cc [correlation coefficient (r) = 0.5516) to the stomach. The r value between the radiation dose to the pancreatic head tumor and the stomach size was 0.3499. The stomach size and radiation dose to the head and body of the pancreas were positively correlated (pancreatic head D10cc: r = 0.3979, pancreatic body D10cc: r = 0.3209). The larger the stomach, the larger the radiation dose to the healthy portion of the pancreas outside the PTV. CONCLUSIONS: When performing pancreatic SBRT, the dose to the OARs depends on the stomach size. Reducing the dose to the stomach and pancreas can be achieved by shrinking the stomach.

Consolidative active scanning proton therapy for mediastinal lymphoma: selection criteria, treatment implementation and clinical feasibility.

AIMS: Proton therapy (PT) represents an advanced form of radiotherapy with unique physical properties which could be of great advantage in reducing long-term radiation morbidity for cancer survivors. Here, we aim to describe the whole process leading to the clinical implementation of consolidative active scanning proton therapy treatment (PT) for mediastinal lymphoma. METHODS: The process included administrative, technical and clinical issues. Authorization of PT is required in all cases as mediastinal lymphoma is currently not on the list of diseases reimbursable by the Italian National Health Service. Technically, active scanning PT treatment for mediastinal lymphoma is complex, due to the interaction between actively scanned protons and the usually irregular and large volumes to be irradiated, the nearby healthy tissues and the target motion caused by breathing. A road map to implement the technical procedures was prepared. The clinical selection of patients was of utmost importance and took into account both patient and tumor characteristics. RESULTS: The first mediastinal lymphoma was treated at our PT center in 2018, four years after the start of the clinical activities. The treatment technique implementation included mechanical deep inspiration breath-hold simulation computed tomography (CT), clinical target volume (CTV)-based multifield optimization planning and plan robustness analysis. The ultimate authorization rate was 93%. In 4 cases a proton-photon plan comparison was required. Between May 2018 and February, 2021, 14 patients were treated with consolidative PT. The main clinical reasons for choosing PT over photons was a bulky disease in 8 patients (57%), patient's age in 11 patients (78%) and the proximity of the lymphoma to cardiac structures in 10 patients (71%). With a median follow-up of 15 months (range, 1-33 months) all patients but one (out-of-field relapse) are without evidence of disease, all are alive and no late toxicities were observed during the follow-up period. CONCLUSIONS: The clinical implementation of consolidative active scanning PT for mediastinal lymphoma required specific technical procedures and a prolonged experience with PT treatments. An accurate selection of patients for which PT could be of advantage in comparison with photons is mandatory.

Ureter dose optimization during image guided brachytherapy for cervical cancer.

PURPOSE: In the era of image guided radiotherapy and interstitial needle use, radiation dose to ureters can cause toxicity. METHODS: A retrospective analysis of 106 patients with cervical cancer was performed to investigate ureter dose in brachytherapy patients. Re-optimization of brachytherapy treatment plans in 20 MRI planned patients was performed to reduce ureter dose whilst maintaining HRCTV D90 and OAR dose constraints. RESULTS: A total of 212 ureters were contoured and dose recorded. The crude incidence of ureteric stenosis was 6.6%. Ureter dose for all patients was 75.8 Gy and 74.4 Gy on the right and left respectively. A cohort of 20 MRI planned patients were reoptimized to reduce dose to ureters. Ureter dose was reduced from 91.1 Gy to 84.4 Gy and 73.9 Gy to 67.8 Gy on the right and left side respectively. A subgroup of patients with HRCTV D90 ≥84.3 Gy prior to reoptimisation saw a greater reduction in ureter dose of 13.3%. These were smaller tumours with better HRCTV coverage at the outset. Larger tumours with poorer HRCTV coverage (<84.3 Gy) saw a smaller reduction in ureter dose of 6.4%. Organ at risk dose to rectum, sigmoid and bladder were also significantly reduced. CONCLUSIONS: Patients treated with MRI guided brachytherapy and interstitial needles are at risk of ureteric stenosis. Contouring ureters and setting dose constraints should be considered to reduce ureteric dose while tracking HRCTV coverage.

Dose prediction via distance-guided deep learning: Initial development for nasopharyngeal carcinoma radiotherapy.

BACKGROUND AND PURPOSE: Geometric information such as distance information is essential for dose calculations in radiotherapy. However, state-of-the-art dose prediction methods use only binary masks without distance information. This study aims to develop a dose prediction deep learning method for nasopharyngeal carcinoma radiotherapy by taking advantage of the distance information as well as the mask information. MATERIALS AND METHODS: A novel transformation method based on boundary distance was proposed to facilitate the prediction of dose distributions. Radiotherapy datasets of 161 nasopharyngeal carcinoma patients were retrospectively collected, including binary masks of organs-at-risk (OARs) and targets, planning CT, and clinical plans. The patients were randomly divided into 130, 11 and 20 cases for training, validating, and testing the models, respectively. Furthermore, 40 patients from an external cohort were used to test the generalizability of the models. RESULTS: The proposed method shows superior performance. The predicted dose error and dose-volume histogram (DVH) error of our method were 7.51% and 11.6% lower than the mask-based method, respectively. For the inverse planning, compared with mask-based methods, our method provided similar performances on the GTVnx and OARs and outperformed on the GTVnd and the CTV, the pass rates of which increased from 89.490% and 90.016% to 96.694% and 91.189%, respectively. CONCLUSION: The preliminary results on nasopharyngeal carcinoma radiotherapy cases showed that our proposed distance-guided method for dose prediction achieved better performance than mask-based methods. Further studies with more patients and on other cancer sites are warranted to fully validate the proposed method.

Evaluation of auto-planning in VMAT for locally advanced nasopharyngeal carcinoma.

The aim of this study is to demonstrate the feasibility of a commercially available Auto-Planning module for the radiation therapy treatment planning for locally advanced nasopharyngeal carcinoma (NPC). 22 patients with locally advanced NPC were included in this study. For each patient, volumetric modulated arc therapy (VMAT) plans were generated both manually by an experienced physicist and automatically by the Auto-Planning module. The dose distribution, dosimetric parameters, monitor units and planning time were compared between automatic plans (APs) and manual plans (MPs). Meanwhile, the overall stage of disease was factored into the evaluation. The target dose coverage of APs was comparable to that of MPs. For the organs at risk (OARs) except spinal cord, the dose parameters of APs were superior to that of MPs. The Dmax and V50 of brainstem were statistically lower by 1.0 Gy and 1.32% respectively, while the Dmax of optic nerves and chiasm were also lower in the APs (p < 0.05). The APs provided a similar or superior quality to MPs in most cases, except for several patients with stage IV disease. The dose differences for most OARs were similar between the two types of plans regardless of stage while the APs provided better brainstem sparing for patients with stage III and improved the sparing of the parotid glands for stage IV patients. The total monitor units and planning time were significantly reduced in the APs. Auto-Planning is feasible for the VMAT treatment planning for locally advanced NPC.

Vital organ sparing with proton therapy for pediatric Hodgkin lymphoma: Toxicity and outcomes in 50 patients.

BACKGROUND AND PURPOSE: With high survival rates for pediatric Hodgkin lymphoma (HL), attention has turned to minimizing treatment-related morbidity and mortality. Chemotherapy and dose of radiation to organs at risk (OARs) contribute to elevated risks of secondary malignancy and cardiopulmonary disease. We sought to characterize the radiation dose to OARs, toxicities, and outcomes for pediatric HL patients treated with proton therapy (PT). MATERIALS AND METHODS: Fifty patients aged 11-21 with HL consecutively treated with PT were evaluated 1-2 months following completion of PT and every 6 months thereafter. Acute and late toxicities were captured retrospectively using CTCAE v5. Patterns of relapse were characterized, and survival was assessed using Kaplan-Meier method. RESULTS: Most (47, 94%) patients received PT to the mediastinum. Median mean heart dose was 4.3 Gy (RBE) and median bilateral lung V20Gy was 5.8%. Median integral dose was 1.7 Gy. For the 27 female patients, a median mean dose of 0.4 and 0.3 Gy (RBE) was delivered to ipsilateral and contralateral breast tissue, respectively. No on-treatment grade 3-5 toxicities were seen. At a median follow-up of 5.3 years, no PT-related grade 3-5 toxicities or secondary malignancies developed. Five patients relapsed at a median time of 9.2 months after PT (range 2.5-24.9 months; 5-year recurrence free survival 90%). Recurrences were both in- and out-of-field in all 5 cases with no marginal failures. All relapsed patients were successfully salvaged (5-year overall survival 100%). CONCLUSION: For pediatric HL patients, proton treatment resulted in marked dose sparing of OARs with low rates of toxicity, no marginal failures, and excellent 5-year survival.

Ultrahypofractionated radiotherapy for localized prostate cancer with simultaneous boost to the dominant intraprostatic lesion: a plan comparison.

OBJECTIVE: To compare different stereotactic body techniques-intensity-modulated radiotherapy with photons and protons, applied to radiotherapy of prostatic cancer-with simultaneous integrated boost (SIB) on the dominant intraprostatic lesion (DIL). METHODS: Ten patients were selected for this planning study. Dosimetric results were compared between volumetric modulated arc therapy, intensity-modulated radiation therapy (IMRT), and intensity-modulated proton therapy both with two (IMPT 2F) and five fields (IMPT 5F) planning while applying the prescription schemes of 7.25 Gy/fraction to the prostate gland and 7.5 Gy/fraction to the DIL in 5 fractions. RESULTS: Comparison of the coverages of the planning target volumes showed that small differences exist. The IMPT-2F-5F techniques allowed higher doses in the targets; conformal indexes resulted similar; homogeneity was better in the photon techniques (2%-5%). Regarding the organs at risk, all the techniques were able to maintain the dose well below the prescribed constraints: in the rectum, the IMPT-2F-5F and IMRT were more efficient in lowering the intermediate doses; in the bladder, the median dose was significantly better in the case of IMPT (2F-5F). In the urethra, the best sparing was achieved only by IMPT-5F. CONCLUSIONS: Stereotactic radiotherapy with SIB for localized prostate cancer is feasible with all the investigated techniques. Concerning IMPT, the two-beam technique does not seem to have a greater advantage compared to the standard techniques; the 5-beam technique seems more promising also accounting for the range uncertainty.

[68Ga]Ga-PSMA-11 PET imaging as a predictor for absorbed doses in organs at risk and small lesions in [177Lu]Lu-PSMA-617 treatment.

INTRODUCTION: Patient eligibility for [177Lu]Lu-PSMA therapy remains a challenge, with only 40-60% response rate when patient selection is done based on the lesion uptake (SUV) on [68Ga]Ga-PSMA-PET/CT. Prediction of absorbed dose based on this pre-treatment scan could improve patient selection and help to individualize treatment by maximizing the absorbed dose to target lesions while adhering to the threshold doses for the organs at risk (kidneys, salivary glands, and liver). METHODS: Ten patients with low-volume hormone-sensitive prostate cancer received a pre-therapeutic [68Ga]Ga-PSMA-11 PET/CT, followed by 3 GBq [177Lu]Lu-PSMA-617 therapy. Intra-therapeutically, SPECT/CT was acquired at 1, 24, 48, 72, and 168 h. Absorbed dose in organs and lesions (n = 22) was determined according to the MIRD scheme. Absorbed dose prediction based on [68Ga]Ga-PSMA-PET/CT was performed using tracer uptake at 1 h post-injection and the mean tissue effective half-life on SPECT. Predicted PET/actual SPECT absorbed dose ratios were determined for each target volume. RESULTS: PET/SPECT absorbed dose ratio was 1.01 ± 0.21, 1.10 ± 0.15, 1.20 ± 0.34, and 1.11 ± 0.29 for kidneys (using a 2.2 scaling factor), liver, submandibular, and parotid glands, respectively. While a large inter-patient variation in lesion kinetics was observed, PET/SPECT absorbed dose ratio was 1.3 ± 0.7 (range: 0.4-2.7, correlation coefficient r = 0.69, p < 0.01). CONCLUSION: A single time point [68Ga]Ga-PSMA-PET scan can be used to predict the absorbed dose of [177Lu]Lu-PSMA therapy to organs, and (to a limited extent) to lesions. This strategy facilitates in treatment management and could increase the personalization of [177Lu]Lu-PSMA therapy.

Once Daily Versus Twice Daily External Beam Accelerated Partial Breast Irradiation: A Randomized Prospective Study.

PURPOSE: The aim of the current study was to compare toxicity, cosmesis, and local control between the once daily and the twice daily fractionation schemes for external beam accelerated partial breast irradiation. METHODS AND MATERIALS: From December 2012 to June 2018, we enrolled 113 patients with ductal carcinoma in situ or invasive breast cancer, node negative disease, and tumors less than 3 cm in size to receive accelerated partial breast irradiation (APBI) to a total dose of 38.5 Gy over 10 fractions given either once (oAPBI) or twice daily (tAPBI). Sixty patients were included in the tAPBI arm and 53 patients were included in the oAPBI arm. RESULTS: Median follow-up was 74 months (range, 24-105). The median pain score during treatment was 3 out of 10 in the oAPBI and 5 in the tAPBI (P = .001). No differences were observed in GIII early skin toxicity (P = .4) or GI early pulmonary toxicity (P = 1.0) between the 2 treatment arms. GIII late skin toxicity developed in 3.8% and 11.7% of patients in the oAPBI and tAPBI arms, respectively (P = .001). GIII subcutaneous fibrosis developed in 1.9% and 8.3% of patients in the oAPBI and tAPBI, respectively (P = .001). The rate of patients with adverse cosmesis (poor/fair) was 7.5% at 12 months and at 24 months in the oAPBI arm compared with 21.7% and 26.7% in the tAPBI arm (P = .03 and .008, respectively). CONCLUSIONS: oAPBI is a safe, well-tolerated schedule with more favorable outcomes than the tAPBI schedule with regards to late toxicity and cosmesis.

A comparison of radiotherapy treatment planning techniques in patients with rectal cancers by analyzing testes doses.

PURPOSE: To evaluate the target volume (TV) and critical organ doses with priority of testes with the comparison of conformal radiotherapy (CRT), dynamic intensity-modulated radiotherapy (DIMRT), and volumetric modulated arc therapy (VMAT) techniques. MATERIALS AND METHODS: CRT, DIMRT, and VMAT techniques were generated on computed tomography images in prone position of 10 male patients with distal rectal cancer. Conformity index (CI), heterogeneity index (HI), treatment time, and monitor units were examined; dose-volume-histograms (DVHs) for the TV and the organs at risk (OARs) were evaluated. RESULTS: Target dose coverage of all treatment plans was similar. HI and CI values for DIMRT and VMAT were closer to "1" compared to CRT. DVH parameters for OARs were decreased with DIMRT and VMAT compared to CRT. The percent volume (Vx) of 3 Gy dose of testes was 62.01% (±25.45%), 42.68% (±16.42%), and 35.89% (±14.97%) in the CRT, DIMRT, and VMAT techniques, respectively. V3 of testes decreased with VMAT compared to CRT and DIMRT (P = 0.008 and P = 0.051, respectively). CONCLUSION: Modern radiotherapy techniques are superior to conformal techniques in planning quality parameters and sparing OARs. DIMRT and VMAT could be considered instead of CRT in the desire to preserve fertility of patients with rectal cancer.