Efficacy of tangential irradiation with volumetric modulated arc therapy on scalp angiosarcoma using medical linac

PurposeTo increase the superficial dose and reduce the brain dose for radiotherapy of scalp angiosarcoma, we propose a novel irradiation technique of tangential irradiation volumetric modulated arc therapy (TI-VMAT).MethodsTI-VMAT and the conventional VMAT treatment plans for thirteen scalp angiosarcoma patients were created with a prescribed dose of 70 Gy. Each treatment was normalized to cover 95% of the planning target volume (PTV) with its prescribed dose. To realize TI-VMAT, an avoidance structure (AS) function was applied. AS was defined as a contour subtracted PTV by a certain space from the brain contour. TI-VMAT treatment plans for six different spaces between PTV and AS were developed and compared with the conventional VMAT treatment plan with respect to the following dosimetric parameters: homogeneity index (HI) and conformity index (CI) of the PTV, mean brain dose, and brain volume irradiated with 20% (V_20% [cc]), 40% (V_40% [cc]), 60% (V_60% [cc]), 80% (V_80% [cc]), and 100% (V_100% [cc]) of the prescribed dose.ResultsHI and CI were comparable between TI-VMAT and the conventional VMAT, the mean brain dose for TI-VMAT with AS defined by a space of 2.0 cm and jaw tracking was 14.27 Gy, which was significantly lower than that for the conventional VMAT (21.20 Gy). In addition, dosimetric parameters such as V_20% [cc] were significantly suppressed compared to those for high doses.ConclusionOur proposed irradiation technique TI-VMAT shows the potential to reduce radiation doses in the brain with maintaining higher dose coverage on the PTV.     

Prospective study on dosimetric comparison of helical tomotherapy and 3DCRT for craniospinal irradiation – A single institution experience

Aim

This prospective study aims to assess feasibility of helical tomotherapy (HT) for craniospinal irradiation (CSI) and perform dosimetric comparison of treatment plans for both HT and 3D conformal radiotherapy (3DCRT).

Background

CSI is a challenging procedure. Large PTV size requires field matching due to technical limitations of standard linear accelerators, which cannot irradiate such volumes as a single field. HT could help to avoid these limitations as irradiation of long fields is possible without field matching.

Materials and methods

Three adults were enrolled from 2009 to 2010. All patients received radiochemotherapy. Treatment plans in prone position for 3DCRT and in supine position for HT were generated. The superior plan was used for patients’ irradiation. Plans were compared with the application of DVH, Dx parameters – where x represents a percentage of the structure volume receiving a normalized dose and homogeneity index (HI).

Results

All patients received HT irradiation. The treatment was well tolerated. The HT plans resulted in a better dose coverage and uniformity in the PTV: HI were 5.4, 7.8, 6.8 for HT vs. 10.3, 6.6, 10.4 for 3DCRT. For most organs at risk (OARs), the D(V80) was higher for HT than for 3DCRT, whereas D(V5) was lower for HT.

Conclusions

HT is feasible for CSI, and in comparison with 3DCRT it improves PTV coverage. HT reduces high dose volumes of OARs, but larger volumes of normal tissue receive low radiation dose. HT requires further study to establish correlations between dosimetrical findings and clinical outcomes, especially with regard to late sequelae of treatment.     

The use of PET/CT in radiotherapy of patients with non-small cell lung cancer

The goal of this paper was to investigate the influence of FDG-PET/CT scan on the modification of staging and irradiation planning in patients suffering from non-small cell lung cancer (NSCLC). Fifteen patients suffering from NSCLC were analyzed by the authors from January, 2008 to July, 2009. The aim of the analysis was to examine the influence of FDG-PET/CT on irradiation planning and on decision-making of the complex oncologic therapy. The FDG-PET/CT scan was carried out in the position of irradiation performed later. For irradiation planning, planning target volumes (PTV) and the organs of risk were contoured on the patients' topometric CT slides as well as on the fused FDG-PET/CT slides. We evaluated how the application of PET/CT modified the stage of the illness, the complex oncologic therapeutic plan, the volume and the localization of the PTV, and the irradiation doses of the organs at risk. The mean and maximum dose of the spinal cord, the mean and V20 dose load of the lungs and the mean dose loads of the heart as well as of the left ventricle were measured. In 8 of 15 cases the stage of the disease and the treatment strategy was modified, since distant metastases were detected by the PET/CT. We evaluated the modification of the PTV and dose load of the organs at risk in 7 cases. According to the PET/CT the PTV was reduced in 5 cases (mean: 393.6 cm3) and was increased in 2 cases (mean: 250.8 cm3). Concerning the risk organs we found that the average (8.8 Gy/9.5 Gy) and maximum (33.4 Gy/36.4 Gy) dose load of the spinal cord increased, while the average (24.5 Gy/13.8 Gy) and V20 (33.7%/22.1%) dose load of the lungs decreased. We likewise found a decrease in the mean dose load of the heart (17.3 Gy/16.8 Gy) and left ventricle (12.9 Gy/9.6 Gy). In the majority of the cases the FDG-PET/CT scan modified the therapeutic decision, the size of the irradiated volume, and the dose load of the lung, the organ at risk causing the most difficulties at irradiation planning, was also reduced. The PET/CT scan plays an essential role in the complex oncologic treatment and irradiation therapy of NSCLC.     

Calculation and measurement of doses in the surface layers of a phantom when using Tomotherapy

BackgroundThe calculation and measurement on the surface of the skin presents a significant dosimetric problem because of numerous factors which have an influence on the dose distribution in this region.AimThe overall aim of this study was to check the agreement between doses measured with thermoluminescent detectors (TLD) during tomotherapy photon beam irradiation of the skin area of a solid water cylindrical phantom with doses calculated with Hi-Art treatment planning system (TPS).Material and MethodThe measurements of the dose were made with the use of a solid water cylindrical phantom - Cheese Phantom. Two bolus phantoms were used: 5 mm and 10 mm Six different planning treatments were generated. The doses were measured using TL detectors.ResultsIn the case of a tumor located near the surface of the skin, the mean dose for 0.5 cm bolus was - 1.94 Gy, and for 1 cm bolus - 2.03 Gy. For the tumor located inside the phantom and organ at risk on the same side that TL detectors, for a 0.5 cm bolus, mean dose was 0.658 Gy, and for a 1 cm bolus, 0.62 Gy.ConclusionThe analysis of results showed that the relative percentage difference between measured and planned dose in the field of irradiation was less than 10%, while the largest differences were on the board of the field of radiation and outside of the field of irradiation, where the dose was 0.08 Gy to 1 Gy.     

Field matching in breast irradiation

INTRODUCTION: In this paper the authors have combined different irradiation techniques for breast and adjacent supraclavicular lymph nodes. The aim was to reduce inhomogeneity in the match-line. METHODS: The CadPlan 6.1.5 three-dimensional treatment planning system was applied in this study for CT based plan using a standard medial and lateral wedged tangential breast portals with the adjacent supraclavicular field. Isocenter is placed at depth on the match-line, where asymmetric jaws are used to produce non-divergent field edges. The tangential fields are shaped using multi-leaf collimator (MLC), by following the curvature of the thorax. In this way the cranial vertical match plane is maintaned without using the breast board. The prescribed dose was 50 Gy at the isocentre. RESULTS: The calculated dose distributions were evaluated in three dimension in the match region of supraclavicular field and the two opposing tangential fields. This method produces a more uniform dose distribution in the target volume and in the match-line. Set-up is fast, this is done without the need for table rotation, or vertical cephalad blocks. The average dose to the ipsilateral lung is reduced using the IMRT (intensity modulated radiotherapy) technique by approximately 10% compared with the conventional technique. Furthermore, this new technique has the possibility to improve the field match between the tangential fields and the parasternal field, while maintaning the field match between the tangential fields and the axillary and supraclavicular fields.     

Dose-escalated volumetric modulated arc therapy for total marrow irradiation: A feasibility dosimetric study with 4DCT planning and simultaneous integrated boost

PurposeTo evaluate the planning feasibility of dose-escalated total marrow irradiation (TMI) with simultaneous integrated boost (SIB) to the active bone marrow (ABM) using volumetric modulated arc therapy (VMAT), and to assess the impact of using planning organs at risk (OAR) volumes (PRV) accounting for breathing motion in the optimization.MethodsFive patients underwent whole-body CT and thoraco-abdominal 4DCT. A planning target volume (PTV) including all bones and ABM was contoured on each whole-body CT. PRV of selected OAR (liver, heart, kidneys, lungs, spleen, stomach) were determined with 4DCT. Planning consisted of 9–10 full 6 MV photon VMAT arcs. Four plans were created for each patient with 12 Gy prescribed to the PTV, with or without an additional 4 Gy SIB to the ABM. Planning dose constraints were set on the OAR or on the PRV. Planning objective was a PTV D_mean < 110% of the prescribed dose, a PTV V_110% < 50%, and OAR D_mean ≤ 50–60%.ResultsPTV D_mean < 110% was accomplished for most plans (n = 18/20), while all achieved V_110%<50%. SIB plans succeeded to optimally cover the boost volume (median ABM D_mean = 16.3 Gy) and resulted in similar OAR sparing compared to plans without SIB (median OAR D_mean = 40–54% of the ABM prescribed dose). No statistically significant differences between plans optimized with constraints on OAR or PRV were found.ConclusionsAdding a 4 Gy SIB to the ABM for TMI is feasible with VMAT technique, and results in OAR sparing similar to plans without SIB. Setting dose constraints on PRV does not impair PTV dosimetric parameters.     

Evaluation of volumetric modulated arc therapy (VMAT) — based total body irradiation (TBI) in pediatric patients

BackgroundThe dosimetric characterization of volumetric modulated arc therapy (VMAT)-based total-body irradiation (TBI) in pediatric patients is evaluated.Materials and methodsTwenty-two patients between the ages of 2 and 12 years were enrolled for VMAT-based TBI from 2018 to 2020. Three isocenters were irradiated over three overlapping arcs. While prescribing 90% of the TBI dose to the planning treatment volume (PTV), two fractions (2 Gy each) were delivered each day; hence 12 Gy was delivered in six fractions. During treatment optimization, the mean lung and kidney doses were set not to exceed 7 Gy and 7.5 Gy, respectively. The maximum lens dose was also set to less than 4 Gy. Patient quality assurance was carried out by comparing treatment planning system doses to the 3-dimensional measured doses by the ArcCHECK^® detector. The electronic portal imaging device (EPID) gamma indices were also obtained.ResultsThe average mean lung dose was 7.75 ± 0.18 Gy, mean kidney dose 7.63 ± 0.26 Gy, maximum lens dose 4.41 ± 0.39 Gy, and the mean PTV dose 12.69 ± 0.16 Gy. The average PTV heterogeneity index was 1.15 ± 0.03. Average differences in mean kidney dose, mean lung dose, and mean target dose were 2.79% ± 0.88, 0.84% ± 0.45 and 0.93% ± 0.47, respectively; when comparing planned and ArcCHECK^® measured doses. Only grade 1–2 radiation toxicities were recorded, based on CTCAE v5.0 scoring criteria.ConclusionsVMAT-TBI was characterized with good PTV coverage, homogeneous dose distribution, planned and measured dose agreement, and low toxicity.     

Characteristics and dosimetric impact of intrafraction motion during peripheral lung cancer stereotactic radiotherapy: is a second midpoint cone beam computed tomography of added value?

BackgroundIn our department, during lung stereotactic body radiation therapy (SBRT), all patients receive an intra-fractional midpoint cone beam computed tomography (CBCT). This study aimed to quantify the benefit of adding a second midpoint CBCT over a course of peripheral lung SBRT.Materials and methodsSix-hundred-sixty-four CBCTs from 166 patients were retrospectively analyzed. Treatments were based on the internal target volume (ITV) approach. An isotropic 0.5 cm margin was used to create the planning target volume (PTV) around the ITV. The prescribed dose was 48 Gy in 4 fractions to the PTV. Patients were divided into two groups: patients for whom the 3D-intra-fractional-variation (IFV) was < 0.5 cm (105 patients, low risk group) and patients with at least one 3D-IFV ≥ 0.5 cm (61 patients, high-risk group). Plans simulating the dosimetric impact of the IFV were created as follows: the original 2 arcs (ARC ) were copied into a new plan consisting of 4 times ARC 1 and 4 times ARC 2. The delivery of ARC 1 was always assumed to have occurred with the isocenter initially coordinated, whereas the positions of ARC 2 were modified for each arc by the measured the 3D-IFV.ResultsFor the PTV, we obtained: D99% (Gy) = 45.2 vs. 48.2 Gy (p < 0.0001); Dmean = 53 vs. 54 Gy (p < .0001) for the reconstructed vs. planned dose values, respectively. For the ITV, the changes are less pronounced: D99% (Gy) = 52.2 vs. 53.6 Gy (p = 0.0007); Dmean = 56 vs. 56.8 Gy (p = 0.0144). The V48 Gy(%)-ITV coverage did not statistically change between the delivered vs. planned dose (p = 0.1803). Regarding the organs at risk for both groups, dose-volume-histograms were near-identical.ConclusionWe demonstrated that a single CBCT is sufficient and reliable to manage the IFV during peripheral lung SBRT.     

Improved biological dosimetric margin model for different PTV margins with stereotactic body radiation therapy in homogeneous and nonhomogeneous tumor regions

BackgroundThe purpose of this study was to improve the biological dosimetric margin (BDM) corresponding to different planning target volume (PTV) margins in homogeneous and nonhomogeneous tumor regions using an improved biological conversion factor (BCF) model for stereotactic body radiation therapy (SBRT).Materials and methodsThe PTV margin was 5–20 mm from the clinical target volume. The biologically equivalent dose (BED) was calculated using the linear–quadratic model. The biological parameters were α/β = 10 Gy, and the dose per fraction (DPF) was d = 3–20 Gy/fr. The isocenter was offset at intervals of 1 mm; 95% of the clinical target volume covered more than 90% of the prescribed physical dose, and BED was defined as biological and physical DMs. The BCF formula was defined as a function of the DPF.ResultsThe difference in the BCF caused by the DPF was within 0.05 for the homogeneous and nonhomogeneous phantoms. In the virtual nonhomogeneous phantom, the data with a PTV margin of 10–20 mm were not significantly different; thus, these were combined to fit the BCF. In the virtual homogeneous phantom, the BCF was fitted to each PTV margin.ConclusionsThe current study improved a scheme to estimate the BDM considering the size of the PTV margin and homogeneous and nonhomogeneous regions. This technique is expected to enable BED-based treatment planning using treatment systems based on physical doses for SBRT.     

A novel dynamic field-matching technique for treatment of patients with para-aortic node-positive cervical cancer: Clinical experience

Aim

To report outcomes for patients with para-aortic lymph node positive cervical cancer treated with a dynamic field-matching technique.

Background

PET staging of cervical cancer has increased identification of patients with para-aortic lymph node metastasis. IMRT enables dose escalation in this area, but matching IMRT fields with traditional whole pelvis fields presents a challenge.

Materials and methods

From 2003 to 2012, 20 patients with cervical cancer and para-aortic lymph node metastasis were treated utilizing the dynamic field-matching technique. As opposed to single-isocenter half-beam junction techniques, this technique employs wedge-shaped dose junctions for the abutment of fields. We reviewed the records of all patients who completed treatment with the technique and abstracted treatment, toxicity, and disease-related outcome data for analysis.

Results

Median prescribed dose to the whole pelvis field was 45 Gy and para-aortic IMRT field 50.4 Gy. All but 3 patients underwent HDR (13 pts) or LDR (4 pts) brachytherapy. All patients developed lower GI toxicity; 10 grade 1, 9 grade 2, and 1 grade 4 (enterovaginal fistula). Median DFS was 12.4 months with 1 and 2-year DFS 60.0% and 38.1%. One-year OS was 83.7% and 2-year OS, 64.4%. A total of 10 patients developed recurrence; none occurred at the matched junction.

Conclusions

The dynamic field-matching technique provides a means for joining conventional whole pelvis fields and para-aortic IMRT fields that substantially reduces dose deviations at the junction due to field mismatch. Treatment with the dynamic matching technique is simple, effective, and tolerated with no apparent increase in toxicity.     

Potential interest of developing an integrated boost dose escalation for stereotactic irradiation of primary prostate cancer

IntroductionThe stereotactic irradiation is a new approach for low-risk prostate cancer. The aim of the present study was to evaluate a schema of stereotactic irradiation of the prostate with an integrated-boost into the tumor.Material and methodsThe prostate and the tumor were delineated by a radiologist on CT/MRI fusion. A 9-coplanar fields IMRT plan was optimized with three different dose levels: 1) 5 × 6.5 Gy to the PTV1 (plan 1), 2) 5 × 8 Gy to the PTV1 (plan 2) and 3) 5 × 6.5 Gy on the PTV1 with 5 × 8 Gy on the PTV2 (plan 3). The maximum dose (MaxD), mean dose (MD) and doses received by 2% (D2), 5% (D5), 10% (D10) and 25% (D25) of the rectum and bladder walls were used to compare the 3 IMRT plans.ResultsA dose escalation to entire prostate from 6.5 Gy to 8 Gy increased the rectum MD, MaxD, D2, D5, D10 and D25 by 3.75 Gy, 8.42 Gy, 7.88 Gy, 7.36 Gy, 6.67 Gy and 5.54 Gy. Similar results were observed for the bladder with 1.72 Gy, 8.28 Gy, 7.01 Gy, 5.69 Gy, 4.36 Gy and 2.42 Gy for the same dosimetric parameters. An integrated SBRT boost only to PTV2 reduced by about 50% the dose difference for rectum and bladder compared to a homogenous prostate dose escalation. Thereby, the MD, D2, D5, D10 and D25 for rectum were increased by 1.51 Gy, 4.24 Gy, 3.08 Gy, 2.84 Gy and 2.37 Gy in plan 3 compared to plan 1.ConclusionsThe present planning study of an integrated SBRT boost limits the doses received by the rectum and bladder if compared to a whole prostate dose escalation for SBRT approach.     

Thermoluminescence dosimetry of the dose received by scrotum and testes in radiotherapy of rectal cancer,compared to the point doses calculated by 3D-planning software

PurposeRadiation received by the testes in the course of radiotherapy for rectal cancer may cause oligospermia and azospermia. We sought to determine the dose to the scrotum and testes with thermoluminescence dosimetry (TLD), and compare it to the dose calculated by 3D planning software.MethodsThe TLDs were fixed to the scrotum in six points anteriorly and posteriorly in two fractions of radiotherapy. All patients received a 50–50.4 Gy total dose in prone position with 3D-planning. The average dose of TLD measurements was compared to the average of 6 relevant point doses calculated by the planning software.ResultsThe mean scrotal dose of radiation in 33 patients as measured by TLD was 3.77 Gy (7.5% of the total prescribed dose), and the mean of point doses calculated by the planning software was 4.11 Gy (8.1% of the total dose), with no significant difference. A significant relationship was seen between the position of the inferior edge of the fields and the mean scrotal dose (P = .04). Also body mass index (BMI) was inversely related with the scrotal dose (P = .049).ConclusionWe found a dose of about 4 Gy received by the scrotum and testes from a total prescribed dose of 50 Gy in the radiotherapy of rectal carcinoma patients, with TLD measurements confirming testicular dose estimations by the planning software. This dose could be significantly harmful for spermatogenesis. Thus careful attention to the testicular dose in radiotherapy of rectal cancer for men desiring continued fertility is a necessity.     

Dose measurements in a thorax phantom at 3DCRT breast radiation therapy

BackgroundThe anthropomorphic and anthropometric phantom developed by the research group NRI (Núcleo de Radiações Ionizantes) can reproduce the effects of the interactions of radiation occurring in the human body. The whole internal radiation transport phenomena can be depicted by film dosimeters in breast RT. Our goal was to provide a dosimetric comparison of a radiation therapy (RT) plan in a 4MV 3D-conformal RT (4MV-3DCR T) and experimental data measured in a breast phantom.Materials and methodsThe RT modality was two parallel opposing fields for the left breast with a prescribed dose of 2.0 Gy in 25 fractions. The therapy planning system (TPS) was performed on CA T3D software. The dose readings at points of interest (POI) pre-established in TPS were recorded. An anthropometric thorax-phantom with removal breast was used. EBT2 radiochromic films were inserted into the ipisilateral breast, contralateral breast, lungs, heart and skin. The irradiation was carried out on 4/80 Varian linear accelerator at 4MV.ResultsThe mean dose at the OAR’s presented statistically significant differences (p < 0.001) of 34.24%, 37.96% and 63.47% for ipsilateral lung, contralateral lung, and heart, respectively. The films placed at the skin-surface interface in the ipsilateral breast also showed statistically significant differences (p < 0.001) of 16.43%, −10.16%, −14.79% and 15.67% in the four quadrants, respectively. In contrast, the PTV dosimeters, representative of the left breast volume, encompassed by the electronic equilibrium, presented a non-significant difference with TPS, p = 0.20 and p = 0.90.ConclusionThere was a non-significant difference of doses in PTV with electronic equilibrium; although no match is achieved outside electronic equilibrium.     

Matrix metalloproteinase-8 mediates the unfavorable systemic impact of local irradiation on pharmacokinetics of anti-cancer drug 5-Fluorouracil

Concurrent chemoradiation with 5-fluorouracil (5-FU) is widely accepted for cancer treatment. However, the interactions between radiation and 5-FU remain unclear. Here, we evaluated the influence of local irradiation on the pharmacokinetics of 5-FU in rats. The single-fraction radiation was delivered to the whole pelvic fields of Sprague-Dawley rats after computerized tomography-based planning. 5-FU at 100 mg/kg was prescribed 24 hours after radiation. A high-performance liquid chromatography system was used to measure 5-FU in the blood. Matrix metalloproteinase-8 (MMP-8) inhibitor I was administered to examine whether or not RT modulation of 5-FU pharmacokinetic parameters could be blocked. Compared with sham-irradiated controls, whole pelvic irradiation reduced the area under the concentration versus time curve (AUC) of 5-FU in plasma and, in contrast, increased in bile with a radiation dose-dependent manner. Based on protein array analysis, the amount of plasma MMP-8 was increased by whole pelvic irradiation (2.8-fold by 0.5 Gy and 5.3-fold by 2 Gy) in comparison with controls. Pretreatment with MMP-8 inhibitor reversed the effect of irradiation on AUC of 5-FU in plasma. Our findings first indicate that local irradiation modulate the systemic pharmacokinetics of 5-FU through stimulating the release of MMP-8. The pharmacokinetics of 5-FU during concurrent chemoradiaiton therapy should be rechecked and the optimal 5-FU dose should be reevaluated, and adjusted if necessary, during CCRT.     

Scanning irradiation device for mice in vivo with pulsed and continuous proton beams

A technical set-up for irradiation of subcutaneous tumours in mice with nanosecond-pulsed proton beams or continuous proton beams is described and was successfully used in a first experiment to explore future potential of laser-driven particle beams, which are pulsed due to the acceleration process, for radiation therapy. The chosen concept uses a microbeam approach. By focusing the beam to approximately 100 × 100 μm(2), the necessary fluence of 10(9) protons per cm(2) to deliver a dose of 20 Gy with one-nanosecond shot in the Bragg peak of 23 MeV protons is achieved. Electrical and mechanical beam scanning combines rapid dose delivery with large scan ranges. Aluminium sheets one millimetre in front of the target are used as beam energy degrader, necessary for adjusting the depth-dose profile. The required procedures for treatment planning and dose verification are presented. In a first experiment, 24 tumours in mice were successfully irradiated with 23 MeV protons and a single dose of 20 Gy in pulsed or continuous mode with dose differences between both modes of 10%. So far, no significant difference in tumour growth delay was observed.     

Effect of patient positioning on carbon-ion therapy planned dose distribution to pancreatic tumors and organs at risk

PurposePancreatic tumor treatment dose distribution variations associated with supine and prone patient positioning were evaluated.MethodsA total of 33 patients with pancreatic tumors who underwent CT in the supine and prone positions were analyzed retrospectively. Gross tumor volume (GTV), planning target volume (PTV), and organs at risk (OARs) (duodenum and stomach) were contoured. The prescribed dose of 55.2 Gy (RBE) was planned from four beam angles (0°, 90°, 180°, and 270°). Patient collimator and compensating boli were designed for each field. Dose distributions were calculated for each field in the supine and prone positions. To improve dose distribution, patient positioning was selected from supine or prone for each beam field.ResultsCompared with conventional beam angle and patient positioning, D2cc of 1st-2nd portion of duodenum (D1-D2), 3rd-4th portion of duodenum (D3-D4), and stomach could be reduced to a maximum of 6.4 Gy (RBE), 3.5 Gy (RBE), and 4.5 Gy (RBE) by selection of patient positioning. V10 of D1-D2, D3-D4, and stomach could be reduced to a maximum of 7.2 cc, 11.3 cc, and 11.5 cc, respectively. D95 of GTV and PTV were improved to a maximum of 6.9% and 3.7% of the prescribed dose, respectively.ConclusionsOptimization of patient positioning for each beam angle in treatment planning has the potential to reduce OARs dose maintaining tumor dose in pancreatic treatment.     

Gonadal-sparing total body irradiation with the use of helical tomotherapy for nonmalignant indications

BackgroundThe aim was to demonstrate the feasibility and technique of gonadal sparing total body irradiation (TBI) with helical tomotherapy. Total body irradiation is a common part of the conditioning regimen prior to allogeneic stem cell transplantation. Shielding or dose-reduction to the gonads is often desired to preserve fertility, particularly in young patients undergoing transplant for non-malignant indications. Helical tomotherapy (HT) has been shown to be superior to traditional TBI delivery for organ at risk (OA R) doses and dose homogeneity.Materials and methodsWe present two representative cases (one male and one female) to illustrate the feasibility of this technique, each of whom received 3Gy in a single fraction prior to allogeneic stem cell transplant for benign indications. The planning target volume (PTV) included the whole body with a subtraction of OA Rs including the lungs, heart, and brain (each contracted by 1cm) as well as the gonads (testicles expanded by 5 cm and ovaries expanded by 0.5 cm).ResultsFor the male patient we achieved a homogeneity index of 1.35 with a maximum and median planned dose to the testes of 0.53 Gy and 0.35 Gy, respectively. In-vivo dosimetry demonstrated an actual received dose of 0.48 Gy. For the female patient we achieved a homogeneity index of 1.13 with a maximum and median planned dose to the ovaries of 1.66 Gy and 0.86 Gy, respectively.ConclusionGonadal sparing TBI is feasible and deliverable using HT in patients with non-malignant diseases requiring TBI as part of a pre-stem cell transplant conditioning regimen.     

Estimation of radiation-induced second cancer risk associated with the institutional field matching craniospinal irradiation technique: A comparative treatment planning study

AimTo estimate and compare the lifetime attributable risk (LAR) of radiation-induced second cancer (SC) in pediatric medulloblastoma patients planned with institutional 3D conformal field matching method, gap junction method and Intensity Modulated Radiotherapy (IMRT).BackgroundThe epidemiological studies on childhood cancer survivors reported that long-term cancer survivors who received radiotherapy are at a significantly increased risk for the development of SC. Hence, the increased concern to predict the SC risk for long-term survivors.Materials and methodsIn addition to institutional field matching planning method, IMRT and gap junction methods were created for ten pediatric medulloblastoma patients. The risk estimates were made based on the site-specific cancer risk coefficient provided by the BEIR VII committee according to the organ equivalent dose for various critical organs. Also, plans were compared for target volume dose distribution and dose received by critical organs.ResultsWhen compared to the gap junction method, the IMRT and institutional field matching method were superior in normal tissue sparing and dose conformity. However, highly significant volume of low dose associated with IMRT was the main concern for the SC risk. The accumulated LAR for all the critical organs with 3D conformal gap junction and IMRT method was 23–25% while for the 3D conformal field matching method it was 21%.ConclusionThe LAR associated with the institutional field matching technique was substantially lower. As this method is highly robust and easy to set up, it can be a better choice of a craniospinal irradiation technique where 3DCRT is the only choice of treatment.     

Dosimetric selection for helical tomotherapy based stereotactic ablative radiotherapy for early-stage non-small cell lung cancer or lung metastases

Background

No selection criteria for helical tomotherapy (HT) based stereotactic ablative radiotherapy (SABR) to treat early stage non-small cell lung cancer (NSCLC) or solitary lung metastases has been established. In this study, we investigate the dosimetric selection criteria for HT based SABR delivering 70 Gy in 10 fractions to avoid severe toxicity in the treatment of centrally located lesions when adequate target dose coverage is desired.

Materials and Methods

78 HT-SABR plans for solitary lung lesions were created to prescribe 70 Gy in 10 fractions to the planning target volume (PTV). The PTV was set to have ≥95% PTV receiving 70 Gy in each case. The cases for which dose constraints for ≥1 OAR could not be met without compromising the target dose coverage were compared with cases for which all target and OAR dose constraints were met.

Results

There were 23 central lesions for which OAR dose constraints could not be met without compromising PTV dose coverage. Comparing to cases for which optimal HT-based SABR plans were generated, they were associated with larger tumor size (5.72±1.96 cm vs. 3.74±1.49 cm, p<0.0001), higher lung dose, increased number of immediately adjacent OARs ( 3.45±1.34 vs. 1.66±0.81, p<0.0001), and shorter distance to the closest OARs (GTV: 0.26±0.22 cm vs. 0.88±0.54 cm, p<0.0001; PTV 0.19±0.18 cm vs. 0.48±0.36 cm, p = 0.0001).

Conclusion

Delivery of 70 Gy in 10 fractions with HT to meet all the given OAR and PTV dose constraints are most likely when the following parameters are met: lung lesions ≤3.78 cm (11.98 cc), ≤2 immediately adjacent OARs which are ≥0.45 cm from the gross lesion and ≥0.21 cm from the PTV.