Higher Tumor Control Probability Research Articles

Proton versus photon therapy for high-risk prostate cancer with dose escalation of dominant intraprostatic lesions: a preliminary planning study.

This study aimed to investigate the feasibility of safe-dose escalation to dominant intraprostatic lesions (DILs) and assess the clinical impact using dose-volume (DV) and biological metrics in photon and proton therapy. Biological parameters defined as late grade ≥ 2 gastrointestinal (GI) and genitourinary (GU) derived from planned (D P) and accumulated dose (D A) were utilized. In total, 10 patients with high-risk prostate cancer with multiparametric MRI-defined DILs were investigated. Each patient had two plans with a focal boost to the DILs using intensity-modulated proton therapy (IMPT) and volumetric-modulated arc therapy (VMAT). Plans were optimized to obtain DIL coverage while respecting the mandatory organ-at-risk constraints. For the planning evaluation, DV metrics, tumor control probability (TCP) for the DILs and whole prostate excluding the DILs (prostate-DILs), and normal tissue complication probability (NTCP) for the rectum and bladder were calculated. Wilcoxon signed-rank test was used for analyzing TCP and NTCP data. IMPT achieved a higher Dmean for the DILs compared to VMAT (IMPT: 68.1 GyRBE vs. VMAT: 66.6 Gy, p < 0.05). Intermediate-high rectal and bladder doses were lower for IMPT (p < 0.05), while the high-dose region (V60 Gy) remained comparable. IMPT-TCP for prostate-DIL were higher compared to VMAT (IMPT: 86%; α/β = 3, 94.3%; α/β = 1.5 vs. VMAT: 84.7%; α/β = 3, 93.9%; α/β = 1.5, p < 0.05). Likewise, IMPT obtained a moderately higher DIL TCP (IMPT: 97%; α/β = 3, 99.3%; α/β = 1.5 vs. VMAT: 95.9%; α/β = 3, 98.9%; α/β = 1.5, p < 0.05). Rectal D A-NTCP displayed the highest GI toxicity risk at 5.6%, and IMPT has a lower GI toxicity risk compared to VMAT-predicted Quantec-NTCP (p < 0.05). Bladder D P-NTCP projected a higher GU toxicity than D A-NTCP, with VMAT having the highest risk (p < 0.05). Dose escalation using IMPT is able to achieve a high TCP for the DILs, with the lowest rectal and bladder DV doses at the intermediate-high-dose range. The reduction in physical dose was translated into a lower NTCP (p < 0.05) for the bladder, although rectal toxicity remained equivalent.

Dosimetric and radiobiological comparison between conventional and hypofractionated breast treatment plans using the Halcyon system.

The objective of this research is to compare the efficacy of conventional and hypofractionated radiotherapy treatment plans for breast cancer patients, with a specific focus on the unique features of the Halcyon system. The study collected and analyzed dose volume histogram (DVH) data for two groups of treatment plans implemented using the Halcyon system. The first group consisted of 19 patients who received conventional fractionated (CF) treatment with a total dose of 50 Gy in 25 fractions, while the second group comprised 9 patients who received hypofractionated (HF) treatment with a total dose of 42.56 Gy in 16 fractions. The DVH data was used to calculate various parameters, including tumor control probability (TCP), normal tissue complication probability (NTCP), and equivalent uniform dose (EUD), using radiobiological models. The results indicated that the CF plan resulted in higher TCP but lower NTCP for the lungs compared to the HF plan. The EUD for the HF plan was approximately 49 Gy (114% of its total dose) while that for the CF plan was around 53 Gy (107% of its total dose). The analysis suggests that while the CF plan is better at controlling tumors, it is not as effective as the HF plan in minimizing side effects. Additionally, it is suggested that there may be an optimal configuration for the HF plan that can provide the same or higher EUD than the CF plan.

Tumor Control Probability and Small-Scale Monte Carlo Dosimetry: Effects of Heterogenous Intratumoral Activity Distribution in Radiopharmaceutical Therapy.

In radiopharmaceutical therapy, intratumoral uptake of radioactivity usually leads to heterogeneous absorbed dose distribution. The likelihood of treatment success can be estimated with the tumor control probability (TCP), which requires accurate dosimetry, estimating the absorbed dose rate per unit activity to individual tumor cells. Methods: Xenograft cryosections of the prostate cancer cell line LNCaP treated with [177Lu]Lu-PSMA-617 were evaluated with digital autoradiography and stained with hematoxylin and eosin. The digital autoradiography images were used to define the source in a Monte Carlo simulation of the absorbed dose, and the stained sections were used to detect the position of cell nuclei to relate the intratumoral absorbed dose heterogeneity to the cell density. Simulations were performed for 225Ac, 177Lu, and 90Y. TCP was calculated to estimate the mean necessary injected activity for a high TCP. A hypothetical case of activity mainly taken up on the tumor borders was generated and used to simulate the absorbed dose. Results: The absorbed dose per decay to tumor cells was calculated from the staining and simulation results to avoid underestimating the tumor response from low absorbed doses in tumor regions with low cell density. The mean of necessary injected activity to reach a 90% TCP for 225Ac, 177Lu, and 90Y was found to be 18.3 kBq (range, 18-22 kBq), 24.3 MBq (range, 20-29 MBq), and 5.6 MBq (range, 5-6 MBq), respectively. Conclusion: To account for the heterogeneous absorbed dose generated from nonuniform intratumoral activity uptake, dosimetry models can estimate the mean necessary activity to reach a sufficient TCP for treatment response. This approach is necessary to accurately evaluate the efficacy of suggested radiopharmaceuticals for therapy.

Simulating the Potential of Model-Based Individualized Prescriptions for Ultracentral Lung Tumors

The use of stereotactic body radiation therapy for ultracentral lung tumors is limited by increased toxicity. We hypothesized that using published normal tissue complication probability (NTCP) and tumor control probability (TCP) models could improve the therapeutic ratio between tumor control and toxicity. A proposed model-based approach was applied to virtually replan early-stage non-small cell lung cancer (NSCLC) tumors. The analysis included 63 patients with ultracentral NSCLC tumors treated at our center between 2008 and 2017. Along with current clinical constraints, additional NTCP model-based criteria, including for grade 3+ radiation pneumonitis (RP3+) and grade 2+ esophagitis, were implemented using 4 different fractionation schemes. Scaled dose distributions resulting in the highest TCP without violating constraints were selected (optimal plan [Planopt]). Planopt predictions were compared with the observed local control and toxicities. The observed 2-year local control rate was 72% (95% CI, 57%-88%) compared with 87% (range, 6%-93%) for Planopt TCP. Thirty-nine patients had Planopt with TCP > 80%, and 14 patients had Planopt TCP < 50%. The Planopt NTCPs for RP3+ were reduced by nearly half compared with patients' observed RP3+. The RP3+ NTCP was the most frequent reason for TCP of Planopt < 80% (14/24 patients), followed by grade 2+ esophagitis NTCP (5/24 patients) due to larger tumors (>40 cc vs ≤40 cc; P=.002) or a shorter tumor to esophagus distance (≥5 cm vs <5 cm; P < .001). We demonstrated the potential for model-based prescriptions to yield higher TCP while respecting NTCP for patients with ultracentral NSCLC. Individualizing treatments based on NTCP- and TCP-driven simulations halved the predicted relative to the observed rates of RP3+. Our simulations also identified patients whose TCP could not be improved without violating NTCP due to larger tumors or a near tumor to esophagus proximity.

Metabolic factors associated with the prognosis of oligometastatic patients treated with stereotactic body radiotherapy.

Over the past two decades, it has been established that cancer patients with oligometastases, i.e., only a few detectable metastases confined to one or a few organs, may benefit from an aggressive local treatment approach such as the application of high-precision stereotacticbody radiotherapy (SBRT). Specifically, some studies have indicated that achieving long-term local tumor control of oligometastases is associated with prolonged overall survival. This motivates investigations into which factors may modify the dose-response relationship of SBRT by making metastases more or less radioresistant. One such factor relates to the uptake of the positron emission tomography tracer 2-deoxy-2-[18F]fluoro-D-glucose (FDG) which reflects the extent of tumor cell glycolysis or the Warburg effect, respectively. Here we review the biological mechanisms how the Warburg effect drives tumor cell radioresistance and metastasis and draw connections to clinical studies reporting associations between high FDG uptake and worse clinical outcomes after SBRT for oligometastases. We further review the evidence for distinct metabolic phenotypes of metastases preferentially seeding to specific organs and their possible translation into distinct radioresistance. Finally, evidence that obesity and hyperglycemia also affect outcomes after SBRT will be presented. While delivered dose is the main determinant of a high local tumor control probability, there might be clinical scenarios when metabolic targeting could make the difference between achieving local control or not, for example when doses have to be compromised in order to spare neighboring high-risk organs, or when tumors are expected to be highly therapy-resistant due to heavy pretreatment such as chemotherapy and/or radiotherapy.

CBCT-guided adaptive radiotherapy using self-supervised sequential domain adaptation with uncertainty estimation.

Adaptive radiotherapy (ART) is an advanced technology in modern cancer treatment that incorporates progressive changes in patient anatomy into active plan/dose adaption during the fractionated treatment. However, the clinical application relies on the accurate segmentation of cancer tumors on low-quality on-board images, which has posed challenges for both manual delineation and deep learning-based models. In this paper, we propose a novel sequence transduction deep neural network with an attention mechanism to learn the shrinkage of the cancer tumor based on patients' weekly cone-beam computed tomography (CBCT). We design a self-supervised domain adaption (SDA) method to learn and adapt the rich textural and spatial features from pre-treatment high-quality computed tomography (CT) to CBCT modality in order to address the poor image quality and lack of labels. We also provide uncertainty estimation for sequential segmentation, which aids not only in the risk management of treatment planning but also in the calibration and reliability of the model. Our experimental results based on a clinical non-small cell lung cancer (NSCLC) dataset with sixteen patients and ninety-six longitudinal CBCTs show that our model correctly learns weekly deformation of the tumor over time with an average dice score of 0.92 on the immediate next step, and is able to predict multiple steps (up to 5 weeks) for future patient treatments with an average dice score reduction of 0.05. By incorporating the tumor shrinkage predictions into a weekly re-planning strategy, our proposed method demonstrates a significant decrease in the risk of radiation-induced pneumonitis up to 35% while maintaining the high tumor control probability.

Modeling clinical outcomes in radiotherapy: NTCP, TCP and the "TECs".

Radiation therapy is a double-edged sword which damages both tumor and normal cells. Achieving treatments with high tumor control probability (TCP) yet low normal tissue complication probability (NTCP) is often a struggle because we rarely have a unified understanding of the dosimetric and clinical correlates of the desired outcomes. I am fortunate to have participated in some of these struggles, including analyzing and using in-house data and being involved in the AAPM and ASTRO "TEC" projects-QUANTEC (Quantitatie Analysis of Normal Tissue Effects in the Clinic), HyTEC (Hypofractionated Treatment Effects in the Clinic) and PENTEC (Pediatric Normal Tissue Effects in the Clinic).

Evaluation of risk-tailored individualized selection of radiation therapy target volume for head and neck carcinoma of unknown primary.

Intensity-modulated radiation therapy (IMRT) has enabled risk-tailored approach to elective mucosal and nodal clinical target volumes (CTVs) in treatment of head and neck carcinoma of unknown primary (HNCUP). This study report outcomes following such approach. HNCUP patients treated with definitive IMRT between 2005 and 2018 were reviewed. Local failure (LF), regional failure (RF), distant metastasis (DM), overall survival (OS) and grade ≥3 late toxicity (LT) were analyzed. Multivariable analysis (MVA) was used to identify OS predictors for entire cohort and cN2-3 subgroup. A total of 203 patients were eligible: cN1 (7%), cN2a (14%), cN2b (46%), cN2c (14%) and cN3 (19%). Among 118 patients with known HPV status (by p16 staining), 81 (68%) were positive. IMRT target volume spared contralateral tonsil (55%), bilateral or contralateral sides of hypopharynx (72%), nasopharynx (72%), larynx (87%) and contralateral uninvolved neck (21%). Median follow-up was 5years. Five-year LF, RF, DM, OS, and LT were 3%, 14%, 10%, 79%, and 7% respectively. Four patients developed mucosal recurrence: 3 within and 1 at the margin of the elective mucosal CTV. None of ipsilateral neck irradiation patients failed in the contralateral uninvolved neck. MVA identified cN2c-N3, HPV-negative status and older age as predictors for inferior OS. Within cN2-3 subgroup (n=189): cN2c-N3, HPV-negative status and older age predicted lower OS, while concurrent chemotherapy was associated with better OS. Definitive IMRT with risk-adaptive radiation volume de-escalation for HNCUP resulted in high probability of tumor control with acceptable rate of late toxicity.

Adaptive dose painting for prostate cancer.

PurposeDose painting (DP) is a radiation therapy (RT) strategy for patients with heterogeneous tumors delivering higher dose to radiation resistant regions and less to sensitive ones, thus aiming to maximize tumor control with limited side effects. The success of DP treatments is influenced by the spatial accuracy in dose delivery. Adaptive RT (ART) workflows can reduce the overall geometric dose delivery uncertainty. The purpose of this study is to dosimetrically compare ART and non-adaptive conventional RT workflows for delivery of DP prescriptions in the treatment of prostate cancer (PCa).Materials and methodsWe performed a planning and treatment simulation study of four study arms. Adaptive and conventional workflows were tested in combination with DP and Homogeneous dose. We used image data from 5 PCa patients that had been treated on the Elekta Unity MR linac; the patients had been imaged in treatment position before each treatment fraction (7 in total). The local radiation sensitivity from apparent diffusion coefficient maps of 15 high-risk PCa patients was modelled in a previous study. these maps were used as input for optimization of DP plans aiming for maximization of tumor control probability (TCP) under rectum dose constraints. A range of prostate doses were planned for the homogeneous arms. Adaptive plans were replanned based on the anatomy-of-the-day, whereas conventional plans were planned using a pre-treatment image and subsequently recalculated on the anatomy-of-the-day. The dose from 7 fractions was accumulated using dose mapping. The endpoints studied were the TCP and dose-volume histogram metrics for organs at risk.ResultsAccumulated DP doses (adaptive and conventional) resulted in high TCP, between 96-99%. The largest difference between adaptive and conventional DP was 2.6 percentage points (in favor of adaptive DP). An analysis of the dose per fraction revealed substantial target misses for one patient in the conventional workflow that—if systematic—could jeopardize the TCP. Compared to homogeneous prescriptions with equal mean prostate dose, DP resulted in slightly higher TCP.ConclusionCompared to homogeneous dose, DP maintains or marginally increases the TCP. Adaptive DP workflows could avoid target misses compared to conventional workflows.

Improved cellular automata model shows that indirect apoptotic cell death due to vascular damage enhances the local control of tumors by single fraction high-dose irradiation

We investigated the effects of indirect apoptotic cell death due to vascular damage on tumor response to a single large dose with an improved two-dimensional cellular automata model. The tumor growth was simulated by considering the oxygen and nutrients supplied to the tumor through the blood vessels. The cell damage processes were modeled by taking account of the direct cell death and the indirect death due to the radiation-induced vascular damages. The radiation increased the permeation of oxygen and nutrients through the blood vessel or caused the breakdown of the vasculature. The amount of oxygen in cancer cells affected the response of cancer cells to radiation and the tumor growth rate after irradiation. The lack of oxygen led to the apoptotic death of cancer cells. We calculated the tumor control probability (TCP) at different radiation doses, the probability of apoptotic death, the threshold of the oxygen level for indirect apoptotic death, the average oxygen level in cancer cells and the vessel survival probability after radiation damage. Due to the vessel damage, indirect cell death led to a 4% increase in TCP for the dose ranging from 15 Gy to 20 Gy. TCP increased with increasing the probability of apoptotic death and the threshold of the oxygen level for indirect apoptotic death due to increased apoptotic death. The variation of TCP as a function of the average oxygen level exhibited the minimum at the average oxygen level of 2.7%. The apoptosis increased as the average oxygen level decreased, leading to an increasing TCP. On the other hand, the direct radiation damage increased, and the apoptosis decreased for higher average oxygen level, resulting in a higher TCP. We showed by modeling the radiation damage of blood vessels in a 2D CA simulation that the indirect apoptotic death of cancer cells, caused by the reduction of the oxygen level due to vascular damage after high dose irradiation, increased TCP.

P05.01 Personalized Optimization of TCP Using NTCP Based Constraints for Ultracentral Lung Tumors

Hypofractionated radiation of ‘ultracentral’ lung tumors (abutting the proximal bronchial tree/esophagus), results in high toxicity rates. Normal tissue complication probability (NTCP) and tumor control probability (TCP) models valid in early stage NSCLC have been derived; here, we apply them to evaluate whether higher TCP can be achieved while respecting NTCP constraints and study patient characteristics where TCP couldn’t be improved.

Long-term outcome in meningiomas involving the major dural sinuses with combined therapy of subtotal resection and early postoperative gamma knife radiosurgery.

Total resection of meningiomas involving the major dural sinuses (MIMDS) is still challenging for neurosurgeons. Gamma knife radiosurgery (GKRS) was shown to have a high probability of tumor control. The current study evaluated the clinical outcomes of patients who underwent subtotal resection alone or in combination with postoperative GKRS for the treatment of WHO grade I MIMDS. From January 2006 to December 2016, 204 patients with MIMDS underwent Simpson IV subtotal resection in Wuhan Union Hospital. In 151 patients, no additional treatment was performed, while the tumor remnant was treated with GKRS in 53 patients. All patients were monitored with regular MR follow-ups. We retrospectively reviewed the clinical data, radiological characteristics, and outcomes of these 204 patients. Progression-free survival (PFS) was determined by Kaplan-Meier analysis. Related factors were determined by univariate Cox regression analyses. The mean follow-up period was 75.5 months. The tumor recurrence/progression rates were 13.9% in the microsurgery group and 3.8% in the combined therapy group (p = 0.045). The 5- and 10- year progression-free survival (PFS) rates were 92.3 and 80.7%, respectively, in the microsurgery group and 100.0 and 88.5% in the combined therapy group. Treatment approach was found to be an independent prognostic factor for tumor recurrence/progression in the univariable analyses (p=0.04). Compared with microsurgery alone, targeted Simpson grade IV resection combined with early gamma knife treatment resulted in longer progression-free survival without increased complications for WHO grade I MIMDS.

Adaptive time management for patients who have non-small cell lung cancer and underwent definitive radiotherapy: a dosimetric study of different gap duration scenarios

Purpose The purpose of this study was to evaluate the tumor control probability (TCP), normal tissue complication probability (NTCP) and adaptive time management (ATM) in patients who had non-small cell lung cancer (NSCLC) and underwent radiotherapy with same gap length at different treatment weeks. Material and Methods Twenty patients’ definitive radiotherapy treatments, completed in 6.5 weeks, were evaluated retrospectively. Three different scenarios with gaps in 5 fractions at different weeks of treatment (2nd, 4th, and 6th week) were planned. Three ATM models (biologically effective dose (CBED), time-dose-fractionation (CTDF) and in-house developed (CInH)) were calculated for each scenario. TCP and NTCP were calculated and compared with the dose-volume histogram (DVH) of each model. Results TCP was accepted as 100% in uninterrupted treatments. When treatment was interrupted and not compensated with ATM, the highest TCP difference was determined as 23.46% in the 4th week (p<.001). Based on comparisons of ATM models, the lowest TCP decrease was found in CInH. Increasing the fraction size by CInH and CBED provided more TCP improvement than increasing the number of fractions by CTDF. Conclusion The treatment gap to be given in the middle of the treatment is more challenging in terms of tumor control. Adaptive approaches that maintain overall treatment time while increasing fractional dose offer increased TCP.

Possible role of radiotherapy in the management of orbital solitary fibrous tumors

AbstractAs solitary fibrous tumors (SFT) are rare orbital neoplasms, the role of radiotherapy in their management remains unclear. We report three SFT cases who underwent radiotherapy for different clinical scenarios. Case 1 was a 20‐year‐old woman who presented with a 2‐year history of worsening left eye proptosis, eventually leading to its enucleation. A histopathological diagnosis of SFT was established. Recurrence was noted after 3 months and was partially resected, as limited by its location and extent. The residual tumor was given 60 Gy through three‐dimensional conformal radiotherapy. Case 2 was a 23‐year‐old man who had been experiencing painless right eye proptosis for 8 months before undergoing excision, which revealed a diagnosis of SFT. With no residual mass detected on imaging, 54 Gy was delivered to the postoperative bed through intensity‐modulated radiotherapy. Case 3 was a 49‐year‐old man with a 3‐year history of blurred vision and left eye proptosis who underwent subtotal resection, which revealed a diagnosis of malignant SFT. A dose of 64 Gy was delivered to the residual tumor through intensity‐modulated radiotherapy.Grade 2 dermatitis was noted. No worsening in vision was observed. The patients remained recurrence‐free after 18, 12, and 5 months, respectively.Radiotherapy might provide a high tumor control probability in orbital SFT.

RADT-30. COPLANAR AND NON-COPLANAR VMAT ARC SETTING FOR GLIOBLASTOMA MULTIFORME – DOSIMETRIC AND RADIOBIOLOGICAL COMPARISONS

Abstract OBJECTIVES To evaluate three different arc arrangements in glioblastoma multiforme (GBM) treatment planning. METHODS Eighteen GBM patients were replanned by using one full arc (1FA), two full coplanar arcs (2FA), and three full non- coplanar arcs (3FA). Dose-volume histograms (DVHs) were used to calculate conformity (CI), homogeneity (HI) and gradient indices (GI), the dose received by 5% (D5%) and 95% (D95%) of the planning target volume (PTV) and maximum (Dmax) and minimum (Dmin) absorbed dose for organs at risk (OARs), including normal brain (brain excluding PTV). General equivalent uniform dose (gEUD) for both PTV and OARs and EUD based tumor control probability (TCP) and normal tissue control probability (NTCP) were calculated as radiobiological parameters. Monitor units (MUs) were also computed and compared. RESULTS All three plans resulted in similar conformity, while 2FA resulted in a better homogeneity than 1FA (0.06vs. 0.07, p=0.007). 2FA vs. 1FA dose analysis for PTV revealed a lower D5% (61.28 vs. 61.37 Gy, p=0.014), a higher D95% (58.7 vs. 58.47 Gy, p=0.008) and a higher TCP (37.73 vs.37.38%, p=0.008). The utilization of 3FA did not significantly change the outcome of PTV but managed to decrease GI in comparison to both 1FA and 2FA (4.11 vs. 5.19 and 5.49, p&amp;lt; 0.05). Regarding NB, 1FA scored a higher Dmax than 2FA (62.32 vs. 61.98 Gy, p=0.005), while 3FA scored a higher Dmin than 1FA and 2FA (2.52 vs. 1.08 and 1.10 Gy, p&amp;lt; 0.05). No difference in NB NTCP was noted between techniques. Furthermore, 3FA yielded more MUs when compared to coplanar patters (566.74 vs. 486.78, p= 0.015 for 1FA and 495.98, p=0.019 for 2FA). CONCLUSION Although all three approaches resulted in clinical admissible outcome, the utilization of complex non-coplanar arrangement resulted in a stepper dose fall off but did not improve PTV results and increased machine MUs.

Associating dose-volume characteristics with theoretical radiobiological metrics for rapid Gamma Knife stereotactic radiosurgery plan evaluation.

PurposeTo examine general dose–volume characteristics in Gamma Knife (GK) plans which may be associated with higher tumor control probability (TCP) and equivalent uniform dose (EUD) using characteristic curve sets.MethodsTwo sets of dose–volume histograms (DVHs) were exported alongside an analytical purpose‐generated DVH: (a) single‐shot large collimator (8 or 16 mm) emulated with multiple shots of 4 mm collimator. (b) shot‐within‐shot (SWS) technique with isodose lines (IDLs) of 40–75%. TCP, average dose, EUD in single‐fraction (EUDT) and 2 Gy fractionated regimens (EUDR) were examined for trends with cumulative DVH (cDVH) shape as calculated using a linear‐quadratic cell survival model (α/β = 10.0 Gy, N0 = 1 × 106) with both α = 0.20 Gy−1 and α = 0.23 Gy−1.ResultsUsing α = 0.20 Gy−1 (α = 0.23 Gy−1), plans in the analytical set with higher shoulder regions had TCP, EUDT, EUDR increased by 180%, 5.9%, 10.7% (11.2%, 6.3%, 10.0%), respectively. With α = 0.20 Gy−1 (α = 0.23 Gy−1), plans with higher heels had TCP, EUDT, EUDR increased by 4.0%, <1%, <1% (0.6%, <1%, <1%), respectively. In emulating a 16 (8) mm collimator, 64 (12) shots of the small collimators were used. Plans based on small collimators had higher shoulder regions and, with α = 0.20 Gy−1 (α = 0.23 Gy−1), TCP, EUDT, EUDR was increased up to 351.4%, 5.0%, 8.8% (270.4%, 5.0%, 6.8%) compared with the single‐shot large collimator. Delivery times ranged from 10.2 to 130.3 min. The SWS technique used 16:8 mm collimator weightings ranging from 1:2 to 9.2:1 for 40–75% IDL. With α = 0.20 Gy−1 (α = 0.23 Gy−1), the 40% IDL plan had the highest shoulder with increased TCP, EUDT, EUDR by 130.7%, 9.6%, 17.1% (12.9%, 9.1%, 16.4%) over the 75% IDL plan. Delivery times ranged 6.9–13.8 min.ConclusionsThe magnitude of the shoulder region characteristic to GK cDVHs may be used to rapidly identify superior plan among candidates. Practical issues such as delivery time may require further consideration.

Study of the Radiotherapy Treatment Margins in Prostate Cancer with Fuzzy Logic Model

Start your abstract here…External beam radiation therapy (EBRT) is a process in which therapeutic radiation dose is delivered to targettissues whilst seeking the risk of healthynormal and critical organs is minimal. In case of Complex radiation therapy technique such as volumetric modulated arc radiotherapy (VMAT), there is requirement of precise and optimal treatment margin selection so that not only the resulting dose distributions gives high tumor control probability(TCP) but also dose close to critical organs will get minimal. A fuzzy logic application was used here to derive the optimal radiotherapy treatment margins to be used in radiation therapy treatment planning. Here major all possible radiotherapy uncertainties accounted such as translational set-up, organdelineation and organ motion-induced errors for calculating the quantitative variations in target volume radiobiological parameters for treatment plans using fixed step sized increments of treatment margins up to maximum possible variations of tumor volumes. Therules and membership functions were adopted from dosimetricresults of treatment planning for the fuzzy inference system. The imprecision and smoothness of the original fuzzy output was corrected with application of a convolution technique. The results demonstrate that performance of the applied fuzzy model margins against current used radiotherapy margins was consistent inlower range of error magnitude but beyond that a significant non-linearly margin performance was found when considering the normal tissue complication probability (NTCP) and constraint factors into account in the margin recipe formulation. With the new margins obtained then applied for the study of prostate cancer treatment planning and results were compared well with current volumetric modulated arc radiotherapy (VMAT)technique.

Personalized re-treatment strategy for uveal melanoma local recurrences after interventional radiotherapy (brachytherapy): single institution experience and systematic literature review

PurposeTo report the results of a patient’s tailored therapeutic approach using a second course of interventional radiotherapy (brachytherapy) in patients with locally recurrent uveal melanoma.Material and methodsPatients who had already undergone ocular brachytherapy treated at our IOC (Interventional Oncology Center) were considered. Five patients who has received a second course of treatment with a plaque after local recurrences were included in our study. Re-irradiation was performed with Ruthenium-106 (prescribed dose to the apex 100 Gy) or with Iodine-125 plaques (prescribed dose to the apex 85 Gy). Moreover, a systematic literature search was conducted through three electronic databases, including Medline/PubMed, Scopus, and Embase.ResultsAll patients were initially treated with Ruthenium-106 plaque; the re-irradiation was performed with Ruthenium-106 plaque in three cases and with Iodine in two cases. Mean time between the first and the second plaque was 56.8 months (range, 25-93 months). Local tumor control rate was 100%, no patient underwent secondary enucleation owing to re-treatment failure. Distant metastasis occurred in 1 patient after 6 months from re-treatment. After a median follow-up of 44.2 months (range, 26-65 months) from re-treatment, all patients experienced worsening of the visual acuity (median visual acuity was 0.42 at time of recurrence and decline to 0.24 at the most recent follow-up); cataract occurred in two cases, no patient developed scleral necrosis. We considered 2 papers for a systematic review.ConclusionsIn selected cases, especially in presence of marginal local recurrence, a personalized re-treatment strategy with a plaque may offer high probability of tumor control and organ preservation but worsening of visual acuity.

The Role of radiobiological parameters on Tumor control probability (TCP) in prostate cancer

Introduction: The aim of this study was to evaluation radiobiological modeling parameters on tumor control probability (TCP) for prostate cancer in three different models. These parameters included α⁄β ratios and cell surviving fraction at 2 Gy (SF2). Materials and Methods: The Poisson, equivalent uniform dose (EUD) and linear quadratic (LQ) models was used as the radiobiological models. TCP was calculated in 10 prostate cancer patients as a function of α⁄β ratios (1.5-20) for all radiobiological models and SF2 (0.3-0.7) for LQ model. For each patient, 3D-CRT and IMRT plans were designed to deliver, on average 76 Gy and 82 Gy to planning target volume, respectively. Results: The TCPs calculated by Poisson model were dependent on α/β, results demonstrated that dose escalation from 76 Gy in 3D-CRT to 82 Gy for IMRT caused 5% improvement in TCP for prostate cancer considering the α/β of 10 and higher TCP for IMRT relative to 3D-CRT was seen for α/β higher than 5. According to our results for EUD model the TCPs were independent on α/β. In the LQ model with increase in α/β in specific SF2, TCP will not change remarkable. but with the change of SF2 from 0.7 to 0.3, TCP values change from 0 to 100 % at the prescribed doses in both treatment planning’s. Conclusion: Different mathematical models provided different quantitative outcome for TCP of prostate cancer plans. The IMRT plans were significantly advantageous over the 3DCRT plans with some small variations in each patient. more studies are needed for the optimization of radiobiological models for the prediction of the treatment outcomes in radiation therapy.

Stereotactic Radiosurgery for Trigeminal Schwannomas: A 28-Year Single-Center Experience and Review of the Literature

To assess outcomes and complications of stereotactic radiosurgery treatment for trigeminal schwannoma (TS). A retrospective analysis was performed to describe the presentation and outcomes of patients undergoing Gamma Knife radiosurgery (GKRS) for TS. Clinical, radiographic, and stereotactic radiosurgery dose plans were reviewed. Descriptive statistics and univariate analysis were performed to identify factors associated with poor tumor control. A total of 22 patients with TS were treated with GKRS between 1990 and 2018. One patient had a history of neurofibromatosis type II. Of the study population, 81% underwent GKRS as a first-line treatment. The average tumor volume was 3.3 cm3 and the average margin treatment dose was 14.1 Gy. The median clinical and radiographic follow-up period were 18.5 and 27 months, respectively. Tumor control was achieved in 17 patients (77.3%). Symptomatic improvement was noted in 8 patients (42.1%). Tumor expansion was observed in 7 patients (31.8%) and was associated with poor tumor control at last follow-up (P < 0.05). Patients who developed transient tumor expansion had higher margin doses (14.9 ± 1.1 Gy) compared with patients who did not have expansion (13.6 ± 1.3 Gyk P < 0.05). GKRS provides effective control for most TS. Increased margin doses are associated with tumor expansion, which was a poor prognostic event associated with progression and clinical decline. Based on these results, combined with analysis of available data from other series of TS treated with GKRS, we believe that margin dose between 13 and 14 Gy offers a high probability of tumor control, yet minimizing risk of adverse radiation effects.