CYPArm2 is a CYP450 Monooxygenase with Protoilludene 13-Hydroxylase Activity Involved in the Biosynthesis of Armillyl Orsellinate-Type Sesquiterpenoids.

The melleolides are a family of structurally and functionally diverse sesquiterpenoids with potential applications as fungicides, antimicrobials, and cancer therapeutics. The initial and terminal steps of the biosynthesis pathway in Armillaria spp. have been characterized, but the intermediate steps are unclear. Biosynthetic gene clusters in A. mellea and A. gallica were shown to encode a terpene cyclase, a polyketide synthase, and four CYP450 monooxygenases. We have characterized CYPArm3, which is responsible for the hydroxylation of Δ-6-protoilludene, but the functions of the other CYP450s remain to be determined. Here we describe CYPArm2, which accepts Δ-6-protoilludene and 8α-hydroxy-6-protoilludene as substrates. To investigate the products in more detail, we generated recombinant Saccharomyces cerevisiae strains overexpressing CYPArm2 in combination with the previously characterized protoilludene synthase and 8α-hydroxylase. Using this total biosynthesis approach, sufficient quantities of product were obtained for NMR spectroscopy. This allowed the identification of 8α,13-dihydroxy-protoilludene, confirming that CYPArm2 is a protoilludene 13-hydroxylase.

Isolation of a gene cluster from Armillaria gallica for the synthesis of armillyl orsellinate-type sesquiterpenoids.

Melleolides and armillyl orsellinates are protoilludene-type aryl esters that are synthesized exclusively by parasitic fungi of the globally distributed genus Armillaria (Agaricomycetes, Physalacriaceae). Several of these compounds show potent antimicrobial and cytotoxic activities, making them promising leads for the development of new antibiotics or drugs for the treatment of cancer. We recently cloned and characterized the Armillaria gallica gene Pro1 encoding protoilludene synthase, a sesquiterpene cyclase catalyzing the pathway-committing step to all protoilludene-type aryl esters. Fungal enzymes representing secondary metabolic pathways are sometimes encoded by gene clusters, so we hypothesized that the missing steps in the pathway to melleolides and armillyl orsellinates might be identified by cloning the genes surrounding Pro1. Here we report the isolation of an A. gallica gene cluster encoding protoilludene synthase and four cytochrome P450 monooxygenases. Heterologous expression and functional analysis resulted in the identification of protoilludene-8α-hydroxylase, which catalyzes the first committed step in the armillyl orsellinate pathway. This confirms that ∆-6-protoilludene is a precursor for the synthesis of both melleolides and armillyl orsellinates, but the two pathways already branch at the level of the first oxygenation step. Our results provide insight into the synthesis of these valuable natural products and pave the way for their production by metabolic engineering. KEY POINTS: • Protoilludene-type aryl esters are bioactive metabolites produced by Armillaria spp. • The pathway-committing step to these compounds is catalyzed by protoilludene synthase. • We characterized CYP-type enzymes in the cluster and identified novel intermediates.

Phase II open-label study investigating apalutamide in patients with biochemical progression after radical prostatectomy.

Apalutamide, a competent inhibitor of the androgen receptor, has shown promising clinical efficacy results for patients with advanced prostate cancer. Here, we describe the rationale and design for the SAVE trial, a multi-center, Phase II study, wherein 202 men with biochemical progression after radical prostatectomy are randomly assigned 1:1 to apalutamide plus salvage radiotherapy (SRT) or androgen-deprivation therapy with an luteinizing hormone-releasing hormone agonist or antagonist plus SRT. The primary objective is to compare sexual function between the two treatment arms based on the expanded prostate cancer index-26 sexual domain score at nine months after start of hormonal treatment. The key secondary objectives are to assess quality of life, to evaluate the safety profile and the short-term efficacy of apalutamide in combination with SRT. ClinicalTrials.gov identifier: NCT03899077.

Tumor volume regression during preoperative chemoradiotherapy for rectal cancer: a prospective observational study with weekly MRI.

PURPOSE: Few data is available on rectal tumor shrinkage during preoperative chemoradiotherapy (CRT). This regression pattern is interesting to optimize timing of dose escalation on the tumor. METHODS: Gross tumor volumes (GTV) were contoured by two observers on magnetic resonance imaging (MRI) obtained before, weekly during, 2-4 weeks after, and 7-8 weeks after a 5-week course of concomitant CRT for rectal cancer. RESULTS: Overall, 120 MRIs were acquired in 15 patients. A statistically significant tumor volume reduction is seen from the first week, and between any two time points (p < .007). At the end of CRT, 46.3% of the initial tumor volume remained, and 32.4% at time of surgery. PTV measured 61.2% at the end of treatment. Tumor shrinkage is the fastest in the beginning of treatment (26%/week), slows down to 7%/week in the last 2 weeks of CRT, and finally to 1.3%/week in the last 5 weeks before surgery. CONCLUSIONS: The main rectal tumor regression occurs during CRT course itself, and mostly in the first half, with shrinking speed decreasing over the course. This suggests that a sequential boost is preferably done after the elective fields, yielding an average PTV-reduction of 39%. A simultaneous integrated boost strategy could benefit from adaptive planning during the course.

Metabolic engineering of Clostridium cellulolyticum for the production of n-butanol from crystalline cellulose.

BACKGROUND: Sustainable alternatives for the production of fuels and chemicals are needed to reduce our dependency on fossil resources and to avoid the negative impact of their excessive use on the global climate. Lignocellulosic feedstock from agricultural residues, energy crops and municipal solid waste provides an abundant and carbon-neutral alternative, but it is recalcitrant towards microbial degradation and must therefore undergo extensive pretreatment to release the monomeric sugar units used by biofuel-producing microbes. These pretreatment steps can be reduced by using microbes such as Clostridium cellulolyticum that naturally digest lignocellulose, but this limits the range of biofuels that can be produced. We therefore developed a metabolic engineering approach in C. cellulolyticum to expand its natural product spectrum and to fine tune the engineered metabolic pathways. RESULTS: Here we report the metabolic engineering of C. cellulolyticum to produce n-butanol, a next-generation biofuel and important chemical feedstock, directly from crystalline cellulose. We introduced the CoA-dependent pathway for n-butanol synthesis from C. acetobutylicum and measured the expression of functional enzymes (using targeted proteomics) and the abundance of metabolic intermediates (by LC-MS/MS) to identify potential bottlenecks in the n-butanol biosynthesis pathway. We achieved yields of 40 and 120 mg/L n-butanol from cellobiose and crystalline cellulose, respectively, after cultivating the bacteria for 6 and 20 days. CONCLUSION: The analysis of enzyme activities and key intracellular metabolites provides a robust framework to determine the metabolic flux through heterologous pathways in C. cellulolyticum, allowing further improvements by fine tuning individual steps to improve the yields of n-butanol.

Preoperative Radiotherapy with a Simultaneous Integrated Boost Compared to Chemoradiotherapy for cT3-4 Rectal Cancer: Long-Term Results of a Multicenter Randomized Study.

BACKGROUND: Preoperative chemoradiotherapy (CRT) is the standard treatment for T3-4 rectal cancer. Here, we compared image-guided and intensity-modulated RT (IG-IMRT) with a simultaneous integrated boost (SIB) (instead of concomitant chemotherapy) versus CRT in a multi-centric randomized trial. METHODS: cT3-4 rectal cancer patients were randomly assigned to receive preoperative IG-IMRT 46 Gy/23 fractions plus capecitabine 825 mg/m² twice daily (CRT arm) or IG-IMRT 46 Gy/23 fractions with an SIB to the rectal tumor up to a total dose of 55.2 Gy (RTSIB arm). RESULTS: A total of 174 patients were randomly assigned between April 2010 and May 2014. Grade 3 acute toxicities were 6% and 4% in the CRT and RTSIB arms, respectively. The mean fractional change in SUVmax at 5 weeks after completion of preoperative RT were -55.8% (±24.0%) and -52.9% (±21.6%) for patients in the CRT arm and RTSIB arm, respectively (p = 0.43). The pathologic complete response rate was 24% with CRT compared to 14% with RTSIB. There were no differences in 5-year overall survival (OS), progression-free survival (PFS) or local control (LC). CONCLUSIONS: The preoperative RTSIB approach was not inferior to CRT in terms of metabolic response, toxicity, OS, PFS and LC, and could be considered an available option for patients unfit for fluorouracil-based CRT.

Cloning and characterization of an Armillaria gallica cDNA encoding protoilludene synthase, which catalyzes the first committed step in the synthesis of antimicrobial melleolides.

Melleolides and related fungal sesquiterpenoid aryl esters are antimicrobial and cytotoxic natural products derived from cultures of the Homobasidiomycetes genus Armillaria. The initial step in the biosynthesis of all melleolides involves cyclization of the universal sesquiterpene precursor farnesyl diphosphate to produce protoilludene, a reaction catalyzed by protoilludene synthase. We achieved the partial purification of protoilludene synthase from a mycelial culture of Armillaria gallica and found that 6-protoilludene was its exclusive reaction product. Therefore, a further isomerization reaction is necessary to convert the 6-7 double bond into the 7-8 double bond found in melleolides. We expressed an A. gallica protoilludene synthase cDNA in Escherichia coli, and this also led to the exclusive production of 6-protoilludene. Sequence comparison of the isolated sesquiterpene synthase revealed a distant relationship to other fungal terpene synthases. The isolation of the genomic sequence identified the 6-protoilludene synthase to be present as a single copy gene in the genome of A. gallica, possessing an open reading frame interrupted with eight introns.

The Road to Dissemination: The Concept of Oligometastases and the Barriers for Widespread Disease.

Over the last years, the oligometastatic disease state has gained more and more interest, and randomized trials are now suggesting an added value of stereotactic radiotherapy on all macroscopic disease in oligometastatic patients; but what barriers could impede widespread disease in some patients? In this review, we first discuss the concept of oligometastatic disease and some examples of clinical evidence. We then explore the route to dissemination: the hurdles a tumoral clone has to overtake before it can produce efficient and widespread dissemination. The spectrum theory argues that the range of metastatic patterns encountered in the clinic is the consequence of gradually obtained metastatic abilities of the tumor cells. Tumor clones can obtain these capabilities by Darwinian evolution, hence early in their genetic progression tumors might produce only a limited number of metastases. We illustrate selective dissemination by discussing organ tropism, the preference of different cancer (sub)types to metastasize to certain organs. Finally we discuss biomarkers that may help to distinguish the oligometastatic state.

High-Titer De Novo Biosynthesis of the Predominant Human Milk Oligosaccharide 2'-Fucosyllactose from Sucrose in Escherichia coli.

Human milk oligosaccharides (HMOs) are unique components of human breast milk. Their large-scale production by fermentation allows infant formulas to be fortified with HMOs, but current fermentation processes require lactose as a starting material, increasing the costs, bioburden, and environmental impact of manufacturing. Here we report the development of an Escherichia coli strain that produces 2'-fucosyllactose (2'-FL), the most abundant HMO, de novo using sucrose as the sole carbon source. Strain engineering required the expression of a novel glucose-accepting galactosyltransferase, overexpression of the de novo UDP-d-galactose and GDP-l-fucose pathways, the engineering of an intracellular pool of free glucose, and overexpression of a suitable α(1,2)-fucosyltransferase. The export of 2'-FL was facilitated using a sugar efflux transporter. The final production strain achieved 2'-FL yields exceeding 60 g/L after fermentation for 84 h. This efficient strategy facilitates the lactose-independent production of HMOs by fermentation, which will improve product quality and reduce the costs of manufacturing.

Assessment of rectal distention in radiotherapy of prostate cancer using daily megavoltage CT image guidance.

PURPOSE: Assessment of rectal distention in a group of patients who are not receiving daily rectum emptying procedures during a course of prostate cancer radiotherapy to investigate which patients could benefit from daily rectum emptying. METHODS AND MATERIALS: Eighteen patients underwent daily megavoltage CT (MVCT) scanning with positioning based on bony anatomy. Emptying the rectum was only performed before planning CT and not during the actual treatment. The rectal average cross-sectional area (CSA) was determined on the MVCTs. The relative CSA (CSA(rel)) was defined as CSA on MVCT / CSA on planning CT. Additional prostate soft tissue matching was performed to verify the influence of rectal distention on prostate motion. RESULTS: Two distinct subgroups could be defined a posteriori. One group had a limited and stable rectal distention with a CSA (mean+/-SD) of 6.6+/-2.1cm(2), in contrast with a second group with large and variable rectal filling with a CSA of 9.5+/-3.7cm(2) (p<0.01). Mean anterior-posterior prostate displacement was 0.4+/-2.4 mm in the stable group versus -2.4+/-6.1 mm in the unstable group (p<0.01). A mean CSA(rel) of 1.35 of the first 3 days as cut-off value allowed for a correct a priori classification of 90% and 85% of the patients from groups 1 and 2, respectively. CONCLUSION: Based on a few measurements of the CSA by daily MVCT imaging at the first days of treatment, rectum emptying may be omitted in part of the patients.

Helical tomotherapy with simultaneous integrated boost for high-risk and lymph node-positive prostate cancer: early report on acute and late toxicity.

The use of whole pelvic radiotherapy (WPRT) for high-risk and lymph node-positive prostate cancer (PC) remains controversial. The purpose of this study was to evaluate the acute toxicity associated with helical tomotherapy in the treatment of high-risk and lymph node-positive prostate cancer. To do so, twenty-eight patients were treated to a dose of 54 Gy in daily fractions of 1.8 Gy to the pelvic lymph node area, while the prostate and the seminal vesicles received a simultaneous integrated boost (SIB) to a dose of 70.5 Gy. A SIB to a dose of 60 Gy was delivered to the involved lymph node region(s) in 8 patients with pelvic lymph node metastases. All patients received concurrent hormonal treatment. The incidence of grade 2 and 3 acute gastrointestinal (GI) toxicity was 7% and 0% respectively. Grade 2 and 3 acute genito-urinary (GU) side effects were observed in 14% and 4% of the patients respectively. No grade 4 side effects occurred. No increased toxicity was observed in the 8 lymph node-positive patients receiving a simultaneous pelvic nodal dose escalation. In conclusion, WPRT with a SIB to the prostate and seminal vesicles by helical tomotherapy resulted in a favourable toxicity profile. Pelvic nodal dose escalation in node-positive patients is feasible without increasing toxicity.

The METABANK score: A clinical tool to predict survival after stereotactic radiotherapy for oligometastatic disease.

BACKGROUND AND PURPOSE: Stereotactic radiotherapy (SRT, SBRT) is widely used in oligometastatic cancer, but the heterogeneity of the population complicates estimation of the prognosis. We investigated the role of different clinical and inflammatory parameters. MATERIALS AND METHODS: We included all patients treated with SRT for 1-5 oligometastases between 2003 and 2017 in our center. Patients were randomized between a model training set (2/3) and a separate validation set (1/3). A Cox regression model was built, validated and risk points were attributed to the resulting parameters. RESULTS: 403 patients received SRT for 760 metastases. Treated sites were mainly lung, liver, nodal areas, and brain. Most common primaries were colorectal and lung cancer. Median follow-up for living patients reached 42 months and median overall survival (MS) was 26.6 months (95% CI 23.8-29.3). Five independent adverse factors were discriminated: male sex, synchronous timing of oligometastases, brain metastasis, non-adenocarcinoma histology, KPS <80. A risk score is formed by summation of the points of each factor (M:4, T:2, B:7, N:7, K:8). Four risk groups were defined: (1) 0-2 points: MS 41.2 months (95% CI 30.2-52.3); (2) 3-8 points: 29.3 months (24.6-34.0); (3) 9-13 points: 17.4 months (10.1-24.7), and (4) 14-28 points: 7.9 months (5.5-10.3). CONCLUSION: We propose a prognostic score applicable in a variety of primary tumors and disease locations, including presence of brain metastases. The nomogram and risk groups can be used to stratify patients in new trials and to support individualized care for oligometastatic patients. An online calculator will become available at predictcancer.org.

Phase II study of preoperative helical tomotherapy for rectal cancer.

PURPOSE: To explore the efficacy and toxicity profile of helical tomotherapy in the preoperative treatment of patients with rectal cancer. PATIENTS AND METHODS: Twenty-four patients with T3/T4 rectal cancer were included in this nonrandomized noncontrolled study. A dose of 46 Gy in daily fractions of 2 Gy was delivered to the presacral space and perineum if an abdominoperineal resection was deemed necessary. This dose was increased by a simultaneous integrated boost to 55.2 Gy when the circumferential resection margin was less than 2 mm on magnetic resonance imaging. Acute toxicity was evaluated weekly. Metabolic response was determined in the fifth week after the end of radiotherapy by means of fluorodeoxyglucose-positron emission tomography scan. A metabolic response was defined as a decrease in maximal standardized uptake value of more than 36%. RESULTS: The mean volume of small bowel receiving more than 15 Gy and mean bladder dose were 227 ml and 20.8 Gy in the no-boost group and 141 ml and 21.5 Gy in the boost group. Only 1 patient developed Grade 3 enteritis. No other Grade 3 or 4 toxicities were observed. Two patients developed an anastomotic leak within 30 days after surgery. The metabolic response rate was 45% in the no-boost group compared with 77% in the boost group. All except 1 patient underwent an R0 resection. CONCLUSIONS: Helical tomotherapy may decrease gastrointestinal toxicity in the preoperative radiotherapy of patients with rectal cancer. A simultaneous integrated radiation boost seems to result in a high metabolic response rate without excessive toxicity.

Assessment of intrafractional movement and internal motion in radiotherapy of rectal cancer using megavoltage computed tomography.

PURPOSE: The aim of this study was to provide estimates of setup and internal margins of patients treated for rectal carcinoma using helical tomotherapy and to assess possible margin adaptations. Using helical tomotherapy, highly conformal dose distributions can be created, and the integrated megavoltage computed tomography (MVCT) modality allows very precise daily patient positioning. In clinical protocols, however, margins originating from traditional setup procedures are still being applied. This work investigates whether this modality can aid in redefining treatment margins. METHODS AND MATERIALS: Ten patients who were treated with tomotherapy underwent MVCT scanning before and after 10 treatments. Using automatic registration the necessary setup margin was investigated by means of bony landmarks. Internal margins were assessed by delineating and describing the mesorectal movement. RESULTS: Based on bony landmarks, movement of patients during treatments was limited to 2.45 mm, 1.99 mm, and 1.09 mm in the lateral, longitudinal, and vertical direction, respectively. Systematic errors were limited to <1 mm. Measured movement of the mesorectal space was -1.6 mm (+/- 4.2 mm) and 0.1 mm (+/- 4.0 mm) for left and right lateral direction. In the antero-posterior direction, mean shifts were -2 mm (+/- 6.8 mm) and -0.4 mm (+/- 3.8 mm). Mean shifts in the cranio-caudal direction were respectively -3.2 mm (+/- 5.6 mm) and -3.2 mm (+/- 6.8 mm). CONCLUSIONS: The use of the integrated MVCT on the tomotherapy system can minimize the setup margin for rectal cancer, and can also be used to adequately describe the internal margin allowing for direct treatment margin adaptation.

Metabolic engineering of taxadiene biosynthesis in yeast as a first step towards Taxol (Paclitaxel) production.

Metabolic engineering in microbes could be used to produce large amounts of valuable metabolites that are difficult to extract from their natural sources and too expensive or complex to produce by chemical synthesis. As a step towards the production of Taxol in the yeast Saccharomyces cerevisiae, we introduced heterologous genes encoding biosynthetic enzymes from the early part of the taxoid biosynthetic pathway, isoprenoid pathway, as well as a regulatory factor to inhibit competitive pathways, and studied their impact on taxadiene synthesis. Expression of Taxus chinensis taxadiene synthase alone did not increase taxadiene levels because of insufficient levels of the universal diterpenoid precursor geranylgeranyl diphosphate. Coexpression of T. chinensis taxadiene synthase and geranylgeranyl diphosphate synthase failed to increase levels, probably due to steroid-based negative feedback, so we also expressed a truncated version of 3-hydroxyl-3-methylglutaryl-CoA reductase (HMG-CoA reductase) isoenzyme 1 that is not subject to feedback inhibition and a mutant regulatory protein, UPC2-1, to allow steroid uptake under aerobic conditions, resulting in a 50% increase in taxadiene. Finally, we replaced the T. chinensis geranylgeranyl diphosphate synthase with its counterpart from Sulfolobus acidocaldarius, which does not compete with steroid synthesis, and codon optimized the T. chinensis taxadiene synthase gene to ensure high-level expression, resulting in a 40-fold increase in taxadiene to 8.7+/-0.85mg/l as well as significant amounts of geranylgeraniol (33.1+/-5.6mg/l), suggesting taxadiene levels could be increased even further. This is the first demonstration of such enhanced taxadiene levels in yeast and offers the prospect for Taxol production in recombinant microbes.

Potential of memory T cells in bridging preoperative chemoradiation and immunotherapy in rectal cancer.

The management of locally advanced rectal cancer has passed a long way of developments, where total mesorectal excision and preoperative radiotherapy are crucial to secure clinical outcome. These and other aspects of multidisciplinary strategies are in-depth summarized in the literature, while our mini-review pursues a different goal. From an ethical and medical standpoint, we witness a delayed implementation of novel therapies given the cost/time consuming process of organizing randomized trials that would bridge an already excellent local control in cT3-4 node-positive disease with long-term survival. This unfortunate separation of clinical research and medical care provides a strong motivation to repurpose known pharmaceuticals that suit for treatment intensification with a focus on distant control. In the framework of on-going phase II-III IG/IMRT-SIB trials, we came across an intriguing translational observation that the ratio of circulating (protumor) myeloid-derived suppressor cells to (antitumor) central memory CD8+ T cells is drastically increased, a possible mechanism of tumor immuno-escape and spread. This finding prompts that restoring the CD45RO memory T-cell pool could be a part of integrated adjuvant interventions. Therefore, the immunocorrective potentials of modified IL-2 and the anti-diabetic drug metformin are thoroughly discussed in the context of tumor immunobiology, mTOR pathways and revised Warburg effect.

The long- and short-term variability of breathing induced tumor motion in lung and liver over the course of a radiotherapy treatment.

PURPOSE: To evaluate the short and long-term variability of breathing induced tumor motion. MATERIALS AND METHODS: 3D tumor motion of 19 lung and 18 liver lesions captured over the course of an SBRT treatment were evaluated and compared to the motion on 4D-CT. An implanted fiducial could be used for unambiguous motion information. Fast orthogonal fluoroscopy (FF) sequences, included in the treatment workflow, were used to evaluate motion during treatment. Several motion parameters were compared between different FF sequences from the same fraction to evaluate the intrafraction variability. To assess interfraction variability, amplitude and hysteresis were compared between fractions and with the 3D tumor motion registered by 4D-CT. Population based margins, necessary on top of the ITV to capture all motion variability, were calculated based on the motion captured during treatment. RESULTS: Baseline drift in the cranio-caudal (CC) or anterior-poster (AP) direction is significant (ie. >5 mm) for a large group of patients, in contrary to intrafraction amplitude and hysteresis variability. However, a correlation between intrafraction amplitude variability and mean motion amplitude was found (Pearson's correlation coefficient, r = 0.72, p < 10-4). Interfraction variability in amplitude is significant for 46% of all lesions. As such, 4D-CT accurately captures the motion during treatment for some fractions but not for all. Accounting for motion variability during treatment increases the PTV margins in all directions, most significantly in CC from 5 mm to 13.7 mm for lung and 8.0 mm for liver. CONCLUSION: Both short-term and day-to-day tumor motion variability can be significant, especially for lesions moving with amplitudes above 7 mm. Abandoning passive motion management strategies in favor of more active ones is advised.

Quality Assurance of a 50-kV Radiotherapy Unit Using EBT3 GafChromic Film: A Feasibility Study.

PURPOSE: Radiochromic EBT3 film is gaining acceptance as a valuable dosimetry system for high-energy photon beams. The advantages of these films over other dosimetry systems are low spectral sensitivity and high spatial resolution. The aim of this study was to validate EBT3 film as a dosimeter for machine and treatment quality assurance (QA) of a 50-kV radiotherapy unit. METHODS AND MATERIALS: Absolute and relative doses were acquired using EBT3 GafChromic films and compared to a parallel-plate ionization chamber (IC), the standard IC for low-energy X-rays. EBT3 was also used to evaluate beam profiles and output factors. Two films above each other, mimicking the clinical situation of a dosimeter on top of the skin, were simultaneously irradiated to evaluate EBT3 as in vivo dosimeter. All films were irradiated for 3 minutes, which corresponds with a surface dose of 3.25 ± 0.07 Gy. RESULTS: A fifth-order polynomial function was found to be the best fit for the calibration curves. Good agreement between IC and EBT3 was found for absolute (0.92% for green and red color channels) and relative (1.2% and 1.0% for green and red color channels, respectively) dosimetry. Output factors for IC and EBT3 were comparable within 2.04% and 1.02% for the green and red color channels, respectively. Flatness and symmetry at the surface were within 2%. By applying film as in vivo dosimeter, an absorption of 4.70% needs to be taken into account with respect to the surface dose. CONCLUSION: EBT3 GafChromic film is a feasible and valuable QA and dosimetry tool for a 50-kV radiotherapy unit. EBT3 can be used for absolute and relative dosimetry, measurement of output factors and beam profiles. In vivo patient-specific QA can also be performed if one corrects for the dose absorption of the film.

Evaluation of a dedicated brain metastases treatment planning optimization for radiosurgery: a new treatment paradigm?

PURPOSE: To investigate the feasibility of a novel dedicated treatment planning solution, to automatically target multiple brain metastases with a single isocenter and multiple inversely-optimized dynamic conformal arcs (DCA), and to benchmark it against the well-established multiple isocenter DCA (MIDCA) and volumetric modulated arc therapy (VMAT) approaches. MATERIAL AND METHODS: Ten previously treated patients were randomly selected, each representing a variable number of lesions ranging between 1 to 8. The original MIDCA treatments were replanned with both VMAT and the novel brain metastases tool. The plans were compared by means of Paddick conformity (CI) and gradient index (GI), and the volumes receiving 10 Gy (V10) and 12 Gy (V12). RESULTS: The brain metastases software tool generated plans with similar CI (0.65 ± 0.08) as both established treatment techniques while improving the gradient (mean GI = 3.9 ± 1.4). The normal tissue exposure in terms of V10 (48.5 ± 35.9 cc) and V12 (36.3 ± 27.1 cc) compared similarly to the MIDCA technique and surpassed VMAT plans. CONCLUSIONS: The automated brain metastases planning algorithm software is an optimization of DCA radiosurgery by increasing delivery efficiency to the level of VMAT approaches. Improving dose gradients and normal tissue sparing over VMAT, revives DCA as the paradigm for linac-based stereotactic radiosurgery of multiple brain metastases.