SBRT planning for spinal metastasis: indications from a large multicentric study.

BACKGROUND: The dosimetric variability in spine stereotactic body radiation therapy (SBRT) planning was investigated in a large number of centres to identify crowd knowledge-based solutions. METHODS: Two spinal cases were planned by 48 planners (38 centres). The required prescription dose (PD) was 3â€¯× 10 Gy and the planning target volume (PTV) coverage request was: VPD > 90% (minimum request: VPD > 80%). The dose constraints were: planning risk volume (PRV) spinal cord: V18Gy < 0.35 cm3, V21.9 Gy < 0.03 cm3; oesophagus: V17.7 Gy < 5 cm3, V25.2 Gy < 0.03 cm3. Planners who did not fulfil the protocol requirements were asked to re-optimize the plans, using the results of planners with the same technology. Statistical analysis was performed to assess correlations between dosimetric results and planning parameters. A quality index (QI) was defined for scoring plans. RESULTS: In all, 12.5% of plans did not meet the protocol requirements. After re-optimization, 98% of plans fulfilled the constraints, showing the positive impact of knowledge sharing. Statistical analysis showed a significant correlation (p < 0.05) between the homogeneity index (HI) and PTV coverage for both cases, while the correlation between HI and spinal cord sparing was significant only for the single dorsal PTV case. Moreover, the multileaf collimator leaf thickness correlated with the spinal cord sparing. Planners using comparable delivery/planning system techniques produced different QI, highlighting the impact of the planner's skills in the optimization process. CONCLUSION: Both the technology and the planner's skills are fundamentally important in spine SBRT planning optimization. Knowledge sharing helped to follow the plan objectives.

A feasibility dosimetric study on prostate cancer : are we ready for a multicenter clinical trial on SBRT?

PURPOSE: The Italian Association of Medical Physics (AIFM) started a working group dedicated to stereotactic body radiotherapy (SBRT) treatment. In this work, we performed a multicenter planning study on patients who were candidates for SBRT in the treatment of prostate cancer with the aim of evaluating the dosimetric consistency among the different hospitals. METHODS AND MATERIALS: Fourteen centers were provided the contours of 5 patients. Plans were performed following the dose prescription and constraints for organs at risk (OARs) of a reference paper. The dose prescription was 35 Gy in five fractions for the planning target volume (PTV). Different techniques were used (3D-CRT, fixed-Field IMRT, VMAT, CyberKnife). Plans were compared in terms of dose-volume histogram (DVH) parameters. Furthermore, the median DVH was calculated and one patient was re-planned. RESULTS: A total of 70 plans were compared. The maximum dose to the body was 107.9 ± 4.5 % (range 101.5-116.3 %). Dose at 98 % (D98 %) and mean dose to the clinical target volume (CTV) were 102.0 ± 0.9 % (global range 101.1-102.9 %) and 105.1 ± 0.6 % (range 98.6-124.6 %). Similar trends were found for D95 % and mean dose to the PTV. Important differences were found in terms of the homogeneity index. Doses to OARs were heterogeneous. The subgroups with the same treatment planning system showed differences comparable to the differences of the whole group. In the re-optimized plans, DVH differences among institutes were reduced and OAR sparing improved. CONCLUSION: Important dosimetric differences with possible clinical implications, in particular related to OARs, were found. Replanning allowed a reduction in the OAR dose and decreased standard deviations. Multicenter clinical trials on SBRT should require a preplanning study to standardize the optimization procedure.

HPV-related oropharyngeal carcinoma with Overt Level II and/or III metastases at presentation: The risk of subclinical disease in ipsilateral levels IB, IV and V.

BACKGROUND: To assess the risk of subclinical neck nodal involvement of levels IB, IV and V for early T-stage, node positive, human papilloma virus (HPV)-related oropharyngeal carcinoma. MATERIAL AND METHODS: We retrospectively identified the patients with clinically positive and un-violated neck that underwent upfront ipsilateral neck dissection for HPV-related oropharyngeal cancer between 1998 and 2010. From the pathology report we extracted the prevalence rate of involvement of each selected level and then estimated the risk that a level that does not contain any node larger than 10 mm at computed tomography (CT) harbors subclinical disease. Predictors of involvement were investigated as well. RESULTS: Ninety-one patients were analyzed. The risk of subclinical disease in both levels IB and V is < 5%, while it is 6.5% (95% CI 3.1-9.9%) for level IV. Level IB subclinical involvement slightly exceeds 5% when 2 + ipsilateral levels besides IB are involved. The risk of occult disease in level IV tends to be < 5% when level III is not involved. CONCLUSION: These data support the exclusion from the elective nodal volume of level V and level IB but when 2 + other levels are involved. Level IV might also be spared when level III is negative. Clinical implementation within a prospective study is justified.

Head and neck intensity modulated radiotherapy parotid glands: time of re-planning.

PURPOSE: To investigate the correct time point for re-planning by evaluating dosimetric changes in the parotid glands (PGs) during intensity-modulated radiotherapy (IMRT) in head and neck cancer patients. MATERIALS AND METHODS: Patients with head and neck cancer treated with IMRT were enrolled. During treatment all patients underwent cone-beam computed tomography (CBCT) scans to verify the set-up. CBCT scans at treatment days 10, 15, 20 and 25 were used to transfer the original plan (CBCTplan I, II, III, IV, respectively) using rigid registration between the two. The PGs were retrospectively contoured and evaluated with the dose-volume histogram. The mean dose, the dose to 50 % of volume, and the percentage of volume receiving 30 and 50 Gy were evaluated for each PG. The Wilcoxon sign ranked test was used to evaluate the effects of dosimetric variations and values <0.05 were taken to be significant. RESULTS: From February to June 2011, ten patients were enrolled and five IMRT plans were evaluated for each patient. All the dosimetric parameters increased throughout the treatment course. However, this increase was statistically significant at treatment days 10 and 15 (CBCTplan I, II; p = 0.02, p = 0.03, respectively). CONCLUSION: CBCT is a feasible method to assess the dosimetric changes in the PGs. Our data showed that checking the PG volume and dose could be indicated during the third week of treatment.

Monitor unit optimization in RapidArc plans for prostate cancer.

Intensity-modulated radiation therapy (IMRT) has become a standard treatment for prostate cancer based on the superior sparing of the bladder, rectum, and other surrounding normal tissues compared to three-dimensional conformal radiotherapy, despite the longer delivery time and the increased number of monitor units (MU). The novel RapidArc technique represents a further step forward because of the lower number of MUs per fraction and the shorter delivery time, compared to IMRT. This paper refers to MU optimization in RA plans for prostate cancer, using a tool incorporated in Varian TPS Eclipse. The goal was to get the lowest MU RA plan for each patient, keeping a well-defined level of PTV coverage and OAR sparing. Seven prostate RA plans (RA MU-Optimized) were retrospectively generated using the MU optimization tool in Varian Eclipse TPS. Dosimetric outcome and nontarget tissue sparing were, compared to those of RA clinical plans (RA Clinical) used to treat patients. Compared to RA Clinical, RA MU-Optimized plans resulted in an about 28% (p = 0.018) reduction in MU. The total integral dose (ID) to each nontarget tissue (but not the penile bulb) showed a consistent average relative reduction, statistically significant only for the femoral heads. Within the intermediate dose region (40-60 Gy), ID reductions (4%-17% p < 0.05) were found for the rectum, while a slight but significant (0.4%-0.9%, p < 0.05) higher ID was found for the whole body. Among the remaining data, the mean dose to the bladder was also reduced (-12%, p = 0.028). Plans using MU optimization are clinically applicable and more MU efficient, ameliorating the exposure of the rectum and the bladder to intermediate doses.

Impact of comorbidity in elderly prostate cancer patients treated with brachytherapy.

OBJECTIVE: To analyze the correlations among comorbidity and overall survival (OS), biochemical progression-free survival (b-PFS) and toxicity in elderly patients with localized prostate cancer treated with (125)I brachytherapy. METHODS: Elderly men, aged ≥65 years, with low-intermediate risk prostate cancer, were treated with permanent (125)I brachytherapy as monotherapy. Comorbidity data were obtained from medical reports using age-adjusted Charlson comorbidity index (a-CCI). The patients were categorized into two age groups (<75 and ≥75 years old), and two comorbidity score groups (a-CCI ≤3 and >3). Toxicity was scored with Radiation Therapy Oncology Group (RTOG) scale. RESULTS: From June 2003 to October 2009, a total of 92 elderly patients underwent prostate brachytherapy, including 57 men (62%) with low-risk prostate cancer, and 35 men (38%) with intermediate-risk prostate cancer. The median age of patients was 75 years (range, 65-87 years). Forty-seven patients (51%) had a-CCI ≤3 and 45 patients (49%) a-CCI >3. With a median follow-up period of 56 months (range, 24-103 months), the 5-year actuarial OS and b-PFS were 91.3% and 92.4% respectively, without statistical significance between two Charlson score groups. Toxicity was mild. None of the patients experienced gastrointestinal (GI) toxicity, and only 4 patiens (4%) experienced late genitourinary (GU) grade-3 (G3) toxicity. No correlation between acute GU and GI toxicity and comorbidity was showed (P=0.50 and P=0.70, respectively). CONCLUSIONS: Our data suggest that elderly men with low-intermediate risk prostate cancer and comorbidity can be considered for a radical treatment as (125)I low-dose rate brachytherapy.

Stereotactic Radiation Therapy for Brain Metastases: Factors Affecting Outcomes and Radiation Necrosis.

Stereotactic radiation therapy (SRT) is a proven effective treatment for brain metastases (BM); however, symptomatic radiation necrosis (RN) is a late effect that may impact on patient's quality of life. The aim of our study was to retrospectively evaluate survival outcomes and characterize the occurrence of RN in a cohort of BM patients treated with ablative SRT at Federico II University Hospital. Clinical and dosimetric factors of 87 patients bearing a total of 220 BMs treated with SRT from 2016 to 2022 were analyzed. Among them, 46 patients with 127 BMs having clinical and MRI follow-up (FUP) ≥ 6 months were selected for RN evaluation. Dosimetric parameters of the uninvolved brain (brain without GTV) were extracted. The crude local control was 91% with neither clinical factors nor prescription dose correlating with local failure (LF). At a median FUP of 9 (1-68) months, the estimated median overall survival (OS), progression-free survival (PFS), and brain progression-free survival (bPFS) were 16, 6, and 9 months, respectively. The estimated OS rates at 1 and 3 years were 59.8% and 18.3%, respectively; bPFS at 1 and 3 years was 29.9% and 13.5%, respectively; PFS at 1 and 3 years was 15.7% and 0%, respectively; and local failure-free survival (LFFS) at 1 and 3 years was 87.2% and 83.8%, respectively. Extracranial disease status was an independent factor related to OS. Fourteen (30%) patients manifested RN. At multivariate analysis, adenocarcinoma histology, left location, and absence of chemotherapy were confirmed as independent risk factors for any-grade RN. Nine (20%) patients developed symptomatic (G2) RN, which improved or stabilized after 1-16 months of steroid therapy. With prompt recognition and, when necessary, medical therapy, RN radiological and clinical amelioration can be obtained.

Patient-specific Monte Carlo-based organ dose estimates in spiral CT via optical 3D body scanning and adaptation of a voxelized phantom dataset: proof-of-principle.

Objective. We present a method for personalized organ dose estimates obtained before the computed tomography (CT) exam, via 3D optical body scanning and Monte Carlo (MC) simulations.Approach. A voxelized phantom is derived by adapting a reference phantom to the body size and shape measured with a portable 3D optical scanner, which returns the 3D silhouette of the patient. This was used as an external rigid envelope for incorporating a tailored version of the internal body anatomy derived from a phantom dataset (National Cancer Institute, NIH, USA) matched for gender, age, weight, and height. The proof-of-principle was conducted on adult head phantoms. The Geant4 MC code provided estimates of the organ doses from 3D absorbed dose maps in the voxelized body phantom.Main results. We applied this approach for head CT scanning using an anthropomorphic voxelized head phantom derived from 3D optical scans of manikins. We compared the estimates of head organ doses with those provided by the NCICT 3.0 software (NCI, NIH, USA). Head organ doses differed up to 38% using the proposed personalized estimate and MC code, with respect to corresponding estimates calculated for the standard (non-personalized) reference head phantom. Preliminary application of the MC code to chest CT scans is shown. Real-time pre-exam personalized CT dosimetry is envisaged with adoption of a Graphics Processing Unit-based fast MC code.Significance. The developed procedure for personalized organ dose estimates before the CT exam, introduces a new approach for realistic description of size and shape of patients via voxelized phantoms specific for each patient.

Local tumor control and treatment related toxicity after plaque brachytherapy for uveal melanoma: A systematic review and a data pooled analysis.

Uveal melanoma (UM) represents the most common primary intraocular tumor, and nowadays eye plaque brachytherapy (EPB) is the most frequently used visual acuity preservation treatment option for small to medium sized UMs. The excellent local tumor control (LTC) rate achieved by EPB may be associated with severe complications and adverse events. Several dosimetric and clinical risk factors for the development of EPB-related ocular morbidity can be identified. However, morbidity predictive models specifically developed for EPB are still scarce. PRISMA methodology was used for the present systematic review of articles indexed in PubMed in the last sixteen years on EPB treatment of UM which aims at determining the major factors affecting local tumor control and ocular morbidities. To our knowledge, for the first time in EPB field, local tumor control probability (TCP) and normal tissue complication probability (NTCP) modelling on pooled clinical outcomes were performed. The analyzed literature (103 studies including 21,263 UM patients) pointed out that Ru-106 EPB provided high local control outcomes while minimizing radiation induced complications. The use of treatment planning systems (TPS) was the most influencing factor for EPB outcomes such as metastasis occurrence, enucleation, and disease specific survival, irrespective of radioactive implant type. TCP and NTCP parameters were successfully extracted for 5-year LTC, cataract and optic neuropathy. In future studies, more consistent recordings of ocular morbidities along with accurate estimation of doses through routine use of TPS are needed to expand and improve the robustness of toxicity risk prediction in EPB.

A retrospective analysis after low-dose-rate prostate brachytherapy with permanent (125)I seed implant: clinical and dosimetric results in 70 patients.

AIMS AND BACKGROUND: To evaluate the biochemical disease-free survival (bDFS) rate after (125)I permanent-implant prostate brachytherapy. METHODS: Patients with a diagnosis of prostate adenocarcinoma and adequate PSA follow-up were selected for this retrospective study. Brachytherapy with permanent (125)I seeds was performed as monotherapy, with a prescribed dose of 145 Gy to the prostate. Patients were stratified into recurrence risk groups according to the National Comprehensive Cancer Network (NCCN) guidelines. Biochemical failure was defined using the American Society of Therapeutic Radiology and Oncology (ASTRO) guidelines. The post-implant D90 (defined as the minimum dose covering 90% of the prostate) was obtained for each patient. Two cutoff points were used to test the correlation between D90 and bDFS results: 130 Gy and 140 Gy. bDFS was calculated from the implant date to the date of biochemical recurrence. Univariate and multivariate analysis were performed using the SPSS software and included clinical stage, pretreatment PSA, Gleason score (GS), androgen deprivation therapy, D90, and risk groups. In the univariate analysis we used a cutoff point of 5.89 ng/mL for PSA and 5 for GS. RESULTS: From June 2003 to April 2007, 70 patients were analyzed. The patients' distribution into recurrence risk groups was as follows: 39 patients (56%) in the low-risk group, 23 patients (33%) in the intermediate-risk group, and 8 patients (11%) in the high-risk group. At a median follow-up of 47 months (range, 19-70 months) bDFS was 88.4%, with a global actuarial 5-year bDFS of 86%. Disease-related factors including initial PSA level, GS and risk group were significant predictors of biochemical failure ( P = 0.01, P = 0.01, P = 0.006, respectively). In multivariate analysis, risk group (P = 0.005) and GS (P = 0.03) were statistically significant. CONCLUSION: Our data are in agreement with those in the literature and, despite the short follow-up, confirm the advantage of brachytherapy for patients at low and intermediate risk of recurrence.

The influence of small field output factors simulated uncertainties on the calculated dose in VMAT plans for brain metastases: a multicentre study.

OBJECTIVES: This multicentric study was carried out to investigate the impact of small field output factors (OFs) inaccuracies on the calculated dose in volumetric arctherapy (VMAT) radiosurgery brain plans. METHODS: Nine centres, realised the same five VMAT plans with common planning rules and their specific clinical equipment Linac/treatment planning system commissioned with their OFs measured values (OFbaseline). In order to simulate OFs errors, two new OFs sets were generated for each centre by changing only the OFs values of the smallest field sizes (from 3.2 × 3.2 cm2 to 1 × 1 cm2) with well-defined amounts (positive and negative). Consequently, two virtual machines for each centre were recommissioned using the new OFs and the percentage dose differences ΔD (%) between the baseline plans and the same plans recalculated using the incremented (OFup) and decremented (OFdown) values were evaluated. The ΔD (%) were analysed in terms of planning target volume (PTV) coverage and organs at risk (OARs) sparing at selected dose/volume points. RESULTS: The plans recalculated with OFdown sets resulted in higher variation of doses than baseline within 1.6 and 3.4% to PTVs and OARs respectively; while the plans with OFup sets resulted in lower variation within 1.3% to both PTVs and OARs. Our analysis highlights that OFs variations affect calculated dose depending on the algorithm and on the delivery mode (field jaw/MLC-defined). The Monte Carlo (MC) algorithm resulted significantly more sensitive to OFs variations than all of the other algorithms. CONCLUSION: The aim of our study was to evaluate how small fields OFs inaccuracies can affect the dose calculation in VMAT brain radiosurgery treatments plans. It was observed that simulated OFs errors, return dosimetric calculation accuracies within the 3% between concurrent plans analysed in terms of percentage dose differences at selected dose/volume points of the PTV coverage and OARs sparing. ADVANCES IN KNOWLEDGE: First multicentre study involving different Planning/Linacs about undetectable errors in commissioning output factor for small fields.

The influence of basic plan parameters on calculated small field output factors - A multicenter study.

PURPOSE: The influence of basic plan parameters such as slice thickness, grid resolution, algorithm type and field size on calculated small field output factors (OFs) was evaluated in a multicentric study. METHODS AND MATERIALS: Three computational homogeneous water phantoms with slice thicknesses (ST) 1, 2 and 3 mm were shared among twenty-one centers to calculate OFs for 1x1, 2x2 and 3x3 cm2 field sizes (FSs) (normalized to 10x10 cm2 FS), with their own treatment planning system (TPS) and the energy clinically used for stereotactic body radiation therapy delivery. OFs were calculated for each combination of grid resolution (GR) (1, 2 and 3 mm) and ST and finally compared with the OFs measured for the TPS commissioning. A multivariate analysis was performed to test the effect of basic plan parameters on calculated OFs. RESULTS: A total of 509 data points were collected. Calculated OFs are slightly higher than measured ones. The multivariate analysis showed that Center, GR, algorithm type, and FS are predictive variables of the difference between calculated and measured OFs (p < 0.001). As FS decreases, the spread in the difference between calculated and measured OFs became larger when increasing the GR. Monte Carlo and Analytical Anisotropic Algorithms, presented a dependence on GR (p < 0.01), while Collapsed Cone Convolution and Acuros did not. The effect of the ST was found to be negligible. CONCLUSIONS: Modern TPSs slightly overestimate the calculated small field OFs compared with measured ones. Grid resolution, algorithm, center number and field size influence the calculation of small field OFs.

Dose-Response of TLD-100 in the Dose Range Useful for Hypofractionated Radiotherapy.

PURPOSE: The aim of the study was to exploit the feasibility of thermoluminescent dosimeters (TLDs) in radiation therapy techniques in which high dose per fraction is involved. METHODS: Dose-response of TLD-100 (LiF: Mg, Ti) was investigated in both 6-MV photon and 6-MeV electron beams. The element correction factor (ECF) generation method was applied to check the variability of the TLDs response. Two batches of 50 TLDs were divided into groups and exposed in the dose range 0 to 30 Gy. Regression analysis was performed with both linear and quadratic models. For each irradiation beam, the calibration curves were obtained in 3 dose range 0 to 8 Gy, 0 to 10 Gy, and 0 to 30 Gy. The best-fitting model was assessed by the Akaike Information Criterion test. RESULTS: The ECF process resulted a useful tool to reduce the coefficients of variation from original values higher than 5% to about 3.5%, for all the batches exposed. The results confirm the linearity of dose-response curve below the dose level of 10 Gy for photon and electron beam and the supralinear trend above. CONCLUSION: The TLDs are suitable dosimeters for dose monitoring and verification in radiation treatment involving dose up to 30 Gy in a single fraction.

Integration between in vivo dosimetry and image guided radiotherapy for lung tumors.

The article reports a feasibility study about the potentiality of an in vivo dosimetry method for the adaptive radiotherapy of the lung tumors treated by 3D conformal radiotherapy techniques (3D CRTs). At the moment image guided radiotherapy (IGRT) has been used for this aim, but it requires taking many periodic radiological images during the treatment that increase workload and patient dose. In vivo dosimetry reported here can reduce the above efforts, alerting the medical staff for the commissioning of new radiological images for an eventual adaptive plan. The in vivo dosimetry method applied on 20 patients makes use of the transit signal St on the beam central axis measured by a small ion chamber positioned on an electronic portal imaging device (EPID) or by the EPID itself. The reconstructed in vivo dosimetry at the isocenter point Diso requires a convolution between the transit signal St and a dose reconstruction factor C that essentially depends on (i) tissue inhomogeneities along the beam central axis and (ii) the in-patient isocenter depth. The C factors, one for every gantry angle, are obtained by processing the patient's computed tomography scan. The method has been recently applied in some Italian centers to check the radiotherapy of pelvis, breast, head, and thorax treatments. In this work the dose reconstruction was carried out in five centers to check the Diso in the lung tumor during the 3D CRT, and the results have been used to detect the interfraction tumor anatomy variations that can require new CT imaging and an adaptive plan. In particular, in three centers a small ion chamber was positioned below the patient and used for the St measurement. In two centers, the St signal was obtained directly by 25 central pixels of an a-Si EPID, equipped with commercial software that enabled its use as a stable detector. A tolerance action level of +/- 6% for every checked beam was assumed. This means that when a difference greater than 6% between the predicted dose by the treatment planning system, Diso,TPS, and the Diso was observed, the clinical action started to detect possible errors. 60% of the patients examined presented morphological changes during the treatment that were checked by the in vivo dosimetry and successively confirmed by the new CT scans. In this work, a patient that showed for all beams Diso values outside the tolerance level, new CT scans were commissioned for an adaptive plan. The lung dose volume histograms (DVHs) for a Diso,TPs=2 Gy for fraction suggested the adaptive plan to reduce the dose in lung tissue. The results of this research show that the dose guided radiotherapy (DGRT) by the Diso reconstruction was feasible for daily or periodic investigation on morphological lung tumor changes. In other words, since during 3D CRT treatments the anatomical lung tumor changes occur frequently, the DGRT can be well integrated with the IGRT.

Technological evolution of radiation treatment: Implications for clinical applications.

The contemporary approach to the management of a cancer patient requires an "ab initio" involvement of different medical domains in order to correctly design an individual patient's pathway toward cure. With new therapeutic tools in every medical field developing faster than ever before the patient care outcomes can be achieved if all surgical, drug, and radiation options are considered in the design of the appropriate therapeutic strategy for a given patient. Radiation therapy (RT) is a clinical discipline in which experts from different fields continuously interact in order to manage the multistep process of the radiation treatment. RT is found to be an appropriate intervention for diverse indications in about 50% of cancer patients during the course of their disease. Technologies are essential in dealing with the complexity of RT treatments and for driving the increasingly sophisticated RT approaches becoming available for the treatment of Cancer. High conformal techniques, namely intensity modulated or volumetric modulated arc techniques, ablative techniques (Stereotactic Radiotherapy and Stereotactic Radiosurgery), particle therapy (proton or carbon ion therapy) allow for success in treating irregularly shaped or critically located targets and for the sharpness of the dose fall-off outside the target. The advanced on-board imaging, including real-time position management systems, makes possible image-guided radiation treatment that results in substantial margin reduction and, in select cases, implementation of an adaptive approach. The therapeutic gains of modern RT are also due in part to the enhanced anticancer activity obtained by coadministering RT with chemotherapy, targeted molecules, and currently immune checkpoints inhibitors. These main clinically relevant steps forward in Radiation Oncology represent a change of gear in the field that may have a profound impact on the management of cancer patients.

Auto- versus human-driven plan in mediastinal Hodgkin lymphoma radiation treatment.

BACKGROUND: Technological advances in Hodgkin lymphoma (HL) radiation therapy (RT) by high conformal treatments potentially increase control over organs-at-risk (OARs) dose distribution. However, plan optimization remains a time-consuming task with great operator dependent variability. Purpose of the present study was to devise a fully automated pipeline based on the Pinnacle3 Auto-Planning (AP) algorithm for treating female supradiaphragmatic HL (SHL) patients. METHODS: CT-scans of 10 female patients with SHL were considered. A "butterfly" (BF) volumetric modulated arc therapy was optimized using SmartArc module integrated in Pinnacle3 v. 9.10 using Collapsed Cone Convolution Superposition algorithm (30 Gy in 20 fractions). Human-driven (Manual-BF) and AP-BF optimization plans were generated. For AP, an optimization objective list of Planning Target Volume (PTV)/OAR clinical goals was first implemented, starting from a subset of 5 patients used for algorithm training. This list was then tested on the remaining 5 patients (validation set). In addition to the BF technique, the AP engine was applied to a 2 coplanar disjointed arc (AP-ARC) technique using the same objective list. For plan evaluation, dose-volume-histograms of PTVs and OARs were extracted; homogeneity and conformity indices (HI and CI), OARs dose-volume metrics and odds for different toxicity endpoints were computed. Non-parametric Friedman and Dunn tests were used to identify significant differences between groups. RESULTS: A single AP objective list for SHL was obtained. Compared to the manual plan, both AP-plans offer comparable CIs while AP-ARC also achieved comparable HIs. All plans fulfilled the clinical dose criteria set for OARs: both AP solutions performed at least as good as Manual-BF plan. In particular, AP-ARC outperformed AP-BF in terms of heart sparing involving a lower risk of coronary events and radiation-induced lung fibrosis. Hands-on planning time decreased by a factor of 10 using AP on average. CONCLUSIONS: Despite the high interpatient PTV (size and position) variability, it was possible to set a standard SHL AP optimization list with a high level of generalizability. Using the implemented list, the AP module was able to limit OAR doses, producing clinically acceptable plans with stable quality without additional user input. Overall, the AP engine associated to the arc technique represents the best option for SHL.

A multi-center output factor intercomparison to uncover systematic inaccuracies in small field dosimetry.

Large uncertainties in output factor (OF) small fields dosimetry motivated multicentric studies. The focus of the study was the determination of the OFs, for different linacs and radiosurgery units, using new-generation detectors. Intercomparison studies between radiotherapy centers improved quality dosimetry practices. Results confirmed the effectiveness of the studies to uncover large systematic inaccuracies in small field dosimetry.

Frontiers in planning optimization for lung SBRT.

Emerging data are showing the safety and the efficacy of Stereotactic Body Radiation therapy (SBRT) in lung cancer management. In this context, the very high doses delivered to the Planning Target Volume, make the planning phase essential for achieving high dose levels conformed to the shape of the target in order to have a good prognosis for tumor control and to avoid an overdose in relevant healthy adjacent tissue. In this non-systematic review we analyzed the technological and the physics aspects of SBRT planning for lung cancer. In particular, the aims of the study were: (i) to evaluate prescription strategies (homogeneous or inhomogeneous), (ii) to outline possible geometrical solutions by comparing the dosimetric results (iii) to describe the technological possibilities for a safe and effective treatment, (iv) to present the issues concerning radiobiological planning and the automation of the planning process.

SBRT for prostate cancer: Challenges and features from a physicist prospective.

Emerging data are showing the safety and the efficacy of Stereotactic Body Radiation Therapy (SBRT) in prostate cancer management. In this context, the medical physicists are regularly involved to review the appropriateness of the adopted technology and to proactively study new solutions. From the physics point of view there are two major challenges in prostate SBRT: (1) mitigation of geometrical uncertainty and (2) generation of highly conformal dose distributions that maximally spare the OARs. Geometrical uncertainties have to be limited as much as possible in order to avoid the use of large PTV margins. Furthermore, advanced planning and delivery techniques are needed to generate maximally conformal dose distributions. In this non-systematic review the technology and the physics aspects of SBRT for prostate cancer were analyzed. In details, the aims were: (i) to describe the rationale of reducing the number of fractions (i.e. increasing the dose per fraction), (ii) to analyze the features to be accounted for performing an extreme hypo-fractionation scheme (>6-7Gy), and (iii) to describe technological solutions for treating in a safe way. The analysis of outcomes, toxicities, and other clinical aspects are not object of the present evaluation.

Small field output factors evaluation with a microDiamond detector over 30 Italian centers.

PURPOSE: The aim of the study was a multicenter evaluation of MLC&jaws-defined small field output factors (OF) for different linear accelerator manufacturers and for different beam energies using the latest synthetic single crystal diamond detector commercially available. The feasibility of providing an experimental OF data set, useful for on-site measurements validation, was also evaluated. METHODS: This work was performed in the framework of the Italian Association of Medical Physics (AIFM) SBRT working group. The project was subdivided in two phases: in the first phase each center measured OFs using their own routine detector for nominal field sizes ranging from 10×10cm2 to 0.6×0.6cm2. In the second phase, the measurements were repeated in all centers using the PTW 60019 microDiamond detector. RESULTS: The project enrolled 30 Italian centers. Micro-ion chambers and silicon diodes were used for OF measurements in 24 and 6 centers respectively. Gafchromic films and TLDs were used for very small field OFs in 3 and 1 centers. Regarding the measurements performed with the user's detectors, OF standard deviations (SD) for field sizes down to 2×2cm2 were in all cases <2.7%. In the second phase, a reduction of around 50% of the SD was obtained using the microDiamond detector. CONCLUSIONS: The measured values presented in this multicenter study provide a consistent dataset for OFs that could be a useful tool for improving dosimetric procedures in centers. The microDiamond data present a small variation among the centers confirming that this detector can contribute to improve overall accuracy in radiotherapy.