Homogeneous Dose Distribution Research Articles

Comparative dosimetric and radiobiological assessment of left-sided whole breast and regional nodes with advanced radiotherapy techniques.

The aim of this study was to analyze the dosimetric and radiobiologic differences of the left-sided whole breast and regional nodes in intensity-modulated radiotherapy (IMRT), volume-modulated arc therapy (VMAT), and helical tomotherapy (HT). The IMRT, VMAT, and HT plans in this study were generated for thirty-five left-sided breast cancer patients after breast-conserving surgery (BCS). The planning target volume (PTV) included the whole breast and supraclavicular nodes. PTV coverage, homogeneity index (HI), conformity index (CI), dose to organs at risk (OARs), secondary cancer complication probability (SCCP), and excess absolute risk (EAR) were used to evaluate the plans. Compared to IMRT, the VMAT and HT plans resulted in higher PTV coverage and homogeneity. The VMAT and HT plans also delivered a lower mean dose to the ipsilateral lung (9.19±1.36 Gy, 9.48±1.17 Gy vs. 11.31±1.42 Gy) and heart (3.99±0.86 Gy, 4.48±0.62 Gy vs. 5.53±1.02 Gy) and reduced the V5Gy, V10Gy, V20Gy, V30Gy, and V40Gy of the ipsilateral lung and heart. The SCCP and EAR for the ipsilateral lung were reduced by 3.67%, 3.09% in VMAT, and 22.18%, 19.21% in HT, respectively. While were increased for the contralateral lung and breast. This study showed that VMAT plans provide a more homogeneous dose distribution to the PTV, minimizing exposure to ipsilateral structures and significantly reducing SCCP and EAR, and slightly increasing dose to contralateral structures. Overall, the VMAT plan can be considered a beneficial technique for BCS patients whose PTV includes the whole breast and regional nodes.

Dosimetric comparison of 3DCRT and IMRT in radical chemoradiotherapy of squamous cell carcinoma esophagus.

Radical chemoradiation is the standard of treatment for locally advanced squamous cell carcinoma of esophagus and for patients with operable disease, but who are medically unfit or unwilling for surgery. As the esophagus is a central organ, the planning target volume (PTV) is central, lies close to the spinal cord and heart, and is surrounded by the lung, which is a radiosensitive organ. Irradiation of these critical structures is reduced by the use of three-dimensional conformal radiation therapy (3DCRT). Intensity-modulated radiation therapy (IMRT) has the potential to improve the uniformity of dose distribution to the tumor and reduce the dose received by surrounding normal tissues. 1. To compare the dose distribution, conformity, and homogeneity indices in radical radiotherapy of squamous cell carcinoma of esophagus using 3DCRT and IMRT techniques 2. To compare the doses received by critical structures such as heart, lung, spinal cord, and liver. All cases of squamous cell carcinoma esophagus treated with radical chemoradiation to a dose of 50 Gy in 25 fractions using 3DCRT technique from January 2018 to July 2019 were included. IMRT plans were generated for these cases.The parameters that represent dose distribution to the target volume and the dose received by the organs at risk were obtained from the dose-volume histogram. The difference in the mean values of the parameters between the two techniques was calculated. The statistical significance of the difference was determined using Student's t-test and Wilcoxon signed-rank test. The volume of PTV receiving 105% and 107% of prescribed dose was significantly lower with IMRT (3.540% and 0.008%, respectively) compared to 3DCRT (7.654% and 0.623%). The homogeneity index was better with IMRT (0.088 vs. 0.107) than 3DCRT. Conformity index was found to be better with IMRT (1.149 vs. 1.573). Mean heart dose (18.216 vs. 24.591 Gy) and the volume of heart receiving 30 Gy were reduced with IMRT. The volume of lung receiving 20 Gy and the volume receiving 5 Gy were not significantly different between 3DCRT and IMRT. Maximum dose to spinal cord was similar with 3DCRT and IMRT. IMRT avoids areas of excessive irradiation within the PTV. IMRT improves dose conformity to the target volume and homogeneity of dose distribution within the PTV. The cardiac dose is significantly reduced with IMRT. The mean lung dose remains similar to 3DCRT. There is no significant increase in the volume of lung receiving low-dose radiation with IMRT.

Influence of Homogeneous Dose Distribution Inside the Cancer Target on Local Control in Glioblastomas

Purpose: Assessment of the effect of homogeneous distribution inside the radiation target on local control in glioblastoma.
 Material and methods: In patients under the age of 50, fractionation with the prescribed dose of 2 and 3 Gy was alternately used: the first patient was prescribed a regimen with a dose of 3 Gy, the next – with a dose of 2 Gy (a study involving a pairwise selection strategy). The same approach is used for the older age group (50 years and more). A total of 141 patients had morphologically confirmed glioblastoma (grade 4). 10 patients who had not completed a full course of radiation therapy were excluded. Additionally, 27 patients with GBM were added, treated in the experimental study of National Medical Research Radiological Centre without methodological features. In total, 158 patients were included in the study. 74 patients were treated with the prescribed dose of 2 Gy, 84 had a dose of 3 Gy.
 Results: The median homogeneity index in our study was 7.5 (95% Cl: 6,7-8,3). The minimum HI indicator was at the level of 2.5, the maximum – 36.9. We managed to identify the most informative level of the homogeneity index according to the criterion of local control. The median disease-free survival in the group with HI>=8.5 was 7.9 months (n=62; 95 % Cl: 1.6-14.2), in the group with a lower level of homogeneity - 5.4 months (n=96; p=0.024). The significance of the highlighted HI range depended on the fractionation mode used. The median relapse–free survival with fractionation of 3 Gy in the group with HI>=8.5 was 12.7 months (n=38), in the group with a lower level of homogeneity - 8.3 months (n=46; p=0.020). In the group with fractionation regime of 2 Gy: 6.4 and 3.8 months, respectively (n=24/50; p=0.336). The median overall survival in the group with HI>=8.5 was 27.2 months, in the group with a lower level of homogeneity – 21.2 months (p=0.904).
 Conclusion: The level of homogeneity has no significance according to the criterion of overall survival. Despite the fact that this predictor is of value only in scientific terms, the fact of its influence on local control allows to continue research in this direction. This primarily concerns the fractionation regimen with a prescribed dose of 3 Gy.

Challenges in commissioning the "TSET" technique: A new approach towards monitor unit calculation and beam profile measurements.

Total skin electron beam therapy, commonly known as TSET, is a good choice of treatment for patients suffering from mycosis fungoides. The aim of this study was to introduce a new approach to the beam profile measurement using diodes and to calculate the monitor units required for the TSET treatment by the use of a simple setup of output measurement. Dosimetric measurements required for the treatment were taken to establish the Stanford technique in the department, and the measured data was compared with the published data. High-energy Linear Accelerator Clinac-DHX, Varian medical system, Palo Alto, CA, was commissioned for TSET. The output of the machine was measured by the use of a Parallel-Plate Chamber (PPC40) as per the TRS 398 recommendation. Diode dosimeters (EDD2 and EDD5) were used for beam profile measurements due to easy setup and to reduce the measurement time. Homogeneous dose distribution within a field size of 80 cm x160 cm was observed with the variation of -5.0% on the horizontal axis and -5.4% on the vertical axis. The calculated monitor unit to deliver 200 cGy per fraction per field at the source to surface (SSD) of 416 cm was 489 MU. The technique described for the output measurements is simple and accurate. Results of the absorbed dose and MU measured were within good agreement compared to the published literature.

Dose Distribution of High Dose-Rate and Low Dose-Rate Prostate Brachytherapy at Different Intervals—Impact of a Hydrogel Spacer and Prostate Volume

The study aimed to compare the dose distribution in permanent low-dose-rate brachytherapy (LDR-BT) and high-dose-rate brachytherapy (HDR-BT), specifically focusing on the impact of a spacer and prostate volume. The relative dose distribution of 102 LDR-BT patients (prescription dose 145 Gy) at different intervals was compared with the dose distribution of 105 HDR-BT patients (232 HDR-BT fractions with prescription doses of 9 Gy, n = 151, or 11.5 Gy, n = 81). A hydrogel spacer (10 mL) was only injected before HDR-BT. For the analysis of dose coverage outside the prostate, a 5 mm margin was added to the prostate volume (PV+). Prostate V100 and D90 of HDR-BT and LDR-BT at different intervals were comparable. HDR-BT was characterized by a considerably more homogenous dose distribution and lower doses to the urethra. The minimum dose in 90% of PV+ was higher for larger prostates. As a consequence of the hydrogel spacer in HDR-BT patients, the intraoperative dose at the rectum was considerably lower, especially in smaller prostates. However, prostate volume dose coverage was not improved. The dosimetric results well explain clinical differences between these techniques reported in the literature review, specifically comparable tumor control, higher acute urinary toxicity rates in LDR-BT in comparison to HDR-BT, decreased rectal toxicity after spacer placement, and improved tumor control after HDR-BT in larger prostate volumes.

Dosimetric comparison of target volume coverage and sparing of organs at risk (OARs) between helical intensity modulated radiotherapy (H-IMRT) versus volumetric arc therapy (VMAT) for mid and lower thoracic oesophageal carcinoma.

469 Background: To evaluate the effectiveness of H-IMRT and VMAT in covering target volume while adequately sparing the OARs for patients with mid and distal oesophageal carcinoma, on the basis of dosimetric analysis. Methods: The target areas and organs at risk in 30 patients with locally advanced carcinoma oesophagus undergoing neo-adjuvant chemo-radiotherapy were specified and transmitted to Eclipse, Version 13.6, Varian Medical Systems) & Accuray Treatment Planning System (Accuray Precision, Version 2.1.4, Accuray Medical System). Two plans (H-IMRT and VMAT) were generated for each patient for a total dose of 41.4 Gy delivered to the PTV in 23 fractions, and the Homogeneity Index (HI), Conformity Index (CI) and the dose distribution to the OARs (spinal cord, heart, lungs, kidneys and liver) were compared using dose volume histograms. Results: H-IMRT resulted in a more homogeneous dose distribution to the target (HI- 0.059) as compared to VMAT (HI- 0.07) [p-0.004]. The Conformity Indices showed no significant difference between the two techniques (H-IMRT – 0.989, VMAT – 0.987) [p-0.66]. VMAT resulted in a significantly less dose to the spinal cord (23.598 Gy vs .25.657 Gy) [p-0.021]. With VMAT plans, the heart mean dose (18.101 Gy vs. 20.031) [p- 0.00007], heart V40 (4.902% vs. 6.143) [p-0.002,] the averaged lung V20 [p-0.00005] and the mean dose to the left kidney (3.84 Gy vs. 4.721 Gy) [p- 0.010] were significantly less as compared to H-IMRT No statistically significant difference in both techniques with respect to heart V30, Mean Lung Dose (MLD), and mean dose to the righ and left kidney was observed Conclusions: VMAT proved to be better at sparing of OARs whilst providing almost the same Conformity as compared to a H-IMRT. H-IMRT has statistically better dose homogeneity but, it tends to deposit a slightly higher dose to the OARs. Whether the aforementioned differences in the dosimetric parameters translate into clinical benefits has to be evaluated by clinical outcome studies.

3D range-modulators for proton therapy: near field simulations with FLUKA and comparison with film measurements

The 3D range-modulator is a device used in particle delivery systems that can create a highly conformal and homogeneous dose distribution in the target volume with mono-energetic beams, providing an option for high dose-rate FLASH therapy. In the normal case, the modulators are positioned at a typical distance of 30-50 cm in front of the target in order to avoid the fluence ripples resulting from the periodic structure of the modulators. FLUKA Monte Carlo simulation package was used to investigate the fluence distributions of protons penetrating through the 2D range-modulator, the simplified version of the 3D range-modulator, and to determine the minimum distance at which the fluence is homogeneous enough for the treatment. To implement the complex geometry of the modulator in FLUKA, a dedicated FLUKA user routine was developed for the simulation of the periodic pin structures. The highest fluence ripple occurred at a few centimetres behind the modulators and then faded away as the distance increased, which can be described by the edge-scattering effect and later by the blur-out of the overlapping contributions from the pins. Moreover, the dose distribution in water was investigated, particularly for small distances between the modulators and the water phantom. Furthermore, the Monte Carlo results were compared with radiochromic film measurements irradiated with a 3D-printed range modulator and showed a good qualitative agreement. Prospectively, for low modulator-to-target distances, the strong dose inhomogeneities which appear in the proximal part of the target, could introduce additionally a kind of ‘mini beam’ normal-tissue sparing by the 3D range-modulators.

Introducing new plan evaluation indices for prostate dose painting IMRT plans based on apparent diffusion coefficient images

BackgroundDose painting planning would be more complicated due to different levels of prescribed doses and more complex evaluation with conventional plan quality indices considering uniform dose prescription. Therefore, we tried to introduce new indices for evaluating the dose distribution conformity and homogeneity of treatment volumes based on the tumoral cell density and relative volumes of each lesion in prostate IMRT.MethodsCT and MRI scans of 20 male patients having local prostate cancer were used for IMRT DP planning. Apparent diffusion coefficient (ADC) images were imported to a MATLAB program to identify lesion regions based on ADC values automatically. Regions with ADC values lower than 750 mm2/s and regions with ADC values higher than 750 and less than 1500 mm2/s were considered CTV70Gy (clinical tumor volume with 70 Gy prescribed dose), and CTV60Gy, respectively. Other regions of the prostate were considered as CTV53Gy. New plan evaluation indices based on evaluating the homogeneity (IOE(H)), and conformity (IOE(C)) were introduced, considering the relative volume of each lesion and cellular density obtained from ADC images. These indices were compared with conventional homogeneity and conformity indices and IOEs without considering cellular density. Furthermore, tumor control probability (TCP) was calculated for each patient, and the relationship of the assessed indices were evaluated with TCP values.ResultsIOE (H) and IOE (C) with considering cellular density had significantly lower values compared to conventional indices and IOEs without considering cellular density. (P < 0.05). TCP values had a stronger relationship with IOE(H) considering cell density (R2 = -0.415), and IOE(C) without considering cell density (R2 = 0.624).ConclusionIOE plan evaluation indices proposed in this study can be used for evaluating prostate IMRT dose painting plans. We suggested to consider cell densities in the IOE(H) calculation formula and it’s appropriate to calculate IOE(C) without considering cell density values.

Automated field-in-field whole brain radiotherapy planning.

We developed and tested an automatic field-in-field (FIF) solution for whole-brain radiotherapy (WBRT) planning that creates a homogeneous dose distribution by minimizing hotspots, resulting in clinically acceptable plans. A configurable auto-planning algorithm was developed to automatically generate FIF WBRT plans independent of the treatment planning system. Configurable parameters include the definition of hotspots, target volume, maximum number of subfields, and minimum number of monitor units per field. This algorithm iteratively identifies a hotspot, creates two opposing subfields, calculates the dose, and optimizes the beam weight based on user-configured constraints of dose-volume histogram coverage and least-squared cost functions. The algorithm was retrospectively tested on 17 whole-brain patients. First, an in-house landmark-based automated beam aperture technique was used to generate the treatment fields and initial plans. Second, the FIF algorithm was employed to optimize the plans using physician-defined goals of 99.9% of the brain volume receiving 100% of the prescription dose (30 Gy in 10 fractions) and a target hotspot definition of 107% of the prescription dose. The final auto-optimized plans were assessed for clinical acceptability by an experienced radiation oncologist using a five-point scale. The FIF algorithm reduced the mean (± SD) plan hotspot percentage dose from 35.0 Gy (116.6%) ± 0.6 Gy (2.0%) to 32.6 Gy (108.8%) ± 0.4 Gy (1.2%). Also, it decreased the mean (± SD) hotspot V107% [cm3 ] from 959 ± 498 cm3 to 145 ± 224 cm3 . On average, plans were produced in 16 min without any user intervention. Furthermore, 76.5% of the auto-plans were clinically acceptable (needing no or minor stylistic edits), and all of them were clinically acceptable after minor clinically necessary edits. This algorithm successfully produced high-quality WBRT plans and can improve treatment planning efficiency when incorporated into an automatic planning workflow.

Combining Step-and-Shoot Intensity Modulated Radiation Therapy Concomitant Boost to Tumor Bed and 3D Breast Field-in-Field Plans for Hypofractionated Breast Radiotherapy

<h3>Purpose/Objective(s)</h3> To investigate the efficacy and safety of step-and-shoot intensity modulated radiation therapy (IMRT) concomitant boost (CB) to tumor bed (TB) combined with 3D breast field-in-field (FIF) plans for hypofractionated breast radiotherapy. <h3>Materials/Methods</h3> We initiated prospective cohort study since January, 2020. The patients with early-stage breast cancer or breast ductal carcinoma in situ who received breast-conserving surgery underwent sixteen-fraction treatment. All received prescribed dose of 40 Gy 3D FIF plans to breast, CB with 8 Gy to TB by IMRT. We applied the identical contours and PTV coverage to compare the original plans with the re-plans using conventional fractions of breast FIF followed by en face electron beams to TB on the same patients. Plan quality including maximum dose, RTOG conformal index (CI) and homogeneity index (HI) of PTV_TB, mean dose and volumes irradiated to doses of 5 Gy (V₅) of heart and V₂₀ of ipsilateral lung, in addition to acute toxicity and any recurrence were evaluated. Lyman normal tissue complication probability (NTCP) model for moderate to severe breast fibrosis established by Cambridge and EORTC trials was also calculated. Paired sample t-test and Wilcoxon signed-rank test were used. <h3>Results</h3> Thirty patients with sixty treatment plans were reviewed. The majority (19/30) were pathological prognostic stage I breast cancer and half of the patients were left-sided diseases. No patient experienced more than grade 2 acute toxicity. No recurrence was observed during the follow-up. Mean HI (D₂-D₉₈/D_p × 100; where D₂ = minimum dose to the 2% of the target volume, D₉₈ = minimum dose to the 98% of the target volume, and D_p = prescribed dose) of PTV_TB is 9.4 vs. 18.5 (<i>P</i> < .05). Maximum dose divided by reference dose was also lower in the CB group by 2.9% (<i>P</i> < .05). Mean CI is 1.45 in the CB group compared to 1.63 in the conventional fraction plans (<i>P</i> = .07). In terms of EQD2, mean dose and V₅ of heart for left-sided breast cancer are similar (<i>P</i> = .12 and 0.10). Besides, mean dose and V₂₀ of ipsilateral lung are comparable (<i>P</i> = .26 and 0.43). NTCP for breast fibrosis were all lower in the CB group (Mean: 20.02% vs. 22.13%; <i>P</i> < .05). <h3>Conclusion</h3> Hypofractionated breast radiotherapy combing 3D FIF plans and IMRT CB to TB decreased breast moderate to severe fibrosis by Lyman NTCP model and improved homogenous dose distributions without excessive dose to normal tissue, when compared to conventional fractions using FIF and electron beams. It may reduce the toxicity, and is also labor-saving for patients, radiation oncologists and staff.

Comparison of Dose Calculation Algorithms for Accelerated Partial Breast Intensity Modulated Radiation Therapy

<h3>Purpose/Objective(s)</h3> Accelerated partial breast irradiation (APBI) using intensity modulated radiation therapy (IMRT) has been introduced recently as an alternative treatment to whole breast irradiation for early-stage breast cancer after lumpectomy. Plan dose volume constraints for IMRT APBI are complex, requiring a more conformal and homogenous dose distribution compared to traditional tangential beam based whole breast planning. Anisotropic Analytical Algorithm (AAA) has been widely used for photon dose calculation. An Advanced Dose Calculation algorithm (AXB) is known to achieve comparable accuracy to Monte Carlo (MC) algorithm, the golden standard dose calculation, in heterogeneous media. However, the clinical assessment of AXB has been lacking. As a preliminary study, we investigated the dosimetric differences between the AAA, AXB and MC calculations on APBI IMRT. <h3>Materials/Methods</h3> Six patients with left breast cancer who previously received APBI IMRT were analyzed for this study. All patients received 30 Gy in 5 fractions with a multi beam IMRT technique using AAA 15.6 in the planning system. The following dose volume constraints were used for acceptable plan criteria based on the APBI IMRT Florence trial and all 6 cases previously treated met these criteria: For target (lumpectomy PTV), V28.5 Gy=100%, maximum dose to target < = 105% and V105% <= 2%. For critical organs, uninvolved breast with V15 Gy < 25%, ipsilateral lung volume with V10 Gy < 20%, contralateral breast maximal dose < 1 Gy, heart with V3 Gy < 10%. For a dosimetric comparison, plans were generated with AXB 15.6, reporting dose to medium, for each corresponding AAA plan by re-optimizing with the same dose constraints. After that, AXB plans were re-calculated with MC algorithm using XVMC and compared to AXB. <h3>Results</h3> The re-calculated plans using AXB for the same monitor units with an identical beam setup from AAA plans did not meet the acceptable dose volume criteria. For re-optimized plans with AXB, target conformity index, V28.5Gy and critical organs met the criteria but maximum dose and V105% were still higher than AAA plans (107-110% vs. 104-105.5% for max dose; <i>p</i>=0.02, 2.5- 5.0% vs. 0-2% for V105; <i>p</i> <0.001). The plan comparison between AXB and MC calculations showed similarity in dose distributions and hotspot area, and minimum difference in dose volume histogram. <h3>Conclusion</h3> The present data is the first report to assess the AXB for APBI IMRT. All 6 plans needed the re-optimization for AXB from plans with AAA to comply with the dose volume constraints. However hot spot size was better with AAA plans. MC calculation confirmed the dose distribution and hot spot area produced by AXB. Therefore, the clinical use of AXB for APBI IMRT will need careful evaluation due to a discrepancy in dose distributions and hot spot sizes between AAA and AXB calculations.

Dosimetric evaluation of VMAT and helical tomotherapy techniques comparing conventional volumes with clinical target volumes based on new ESTRO ACROP post-mastectomy with immediate implant reconstruction contouring guidelines

BackgroundThe ESTRO-ACROP Consensus Guideline (EACG) recommends implant excluded clinical target volume (CTVp) definitions for post-mastectomy radiation therapy after implant-based immediate breast reconstruction (IBR). The purpose of this study is to investigate the effectiveness of Helical Tomotherapy (HTp) and Volumetric Modulated Arc Therapy (VMATp) treatment techniques in terms of CTVp coverage and reduced organ at risk (OAR), normal tissue and implant doses when CTVp was used for treatment planning as the target structure instead of conventional CTV.MethodsEight left-sided and eight right-sided breast cancer patients who underwent IBR after mastectomy were included in this study. Planning CT data sets were acquired during free breathing and patients were treated with HT technique targeted to conventional CTV. Retrospectively, CTVp was delineated based on EACG by the same radiation oncologist, and treatment plans with HTp and VMATp techniques were generated based on CTVp. For each patient, relevant dosimetric parameters were obtained from three different treatment plans.ResultsThere was no statistically significant difference on target coverage in terms of, PTVp-D95, PTVp-Vpres, homogeneity index (p > 0.05) between HTp and VMATp plans. But, the conformity numbers were significantly higher (HTp vs VMATp, 0.69 ± 0.15 vs 0.79 ± 0.12) for VMATp (Z = − 2.17, p = 0.030). While HTp significantly lowered Dmax and Dmean for LAD (LAD-Dmax: χ2 = 12.25, p = 0.002 and LAD-Dmean: χ2 = 12.30, p = 0.002), neither HTp nor VMATp could reduce maximum and mean dose to heart (p > 0.05). Furthermore, heart volume receiving 5 Gy was significantly higher for VMATp when compared to HTp (21.2 ± 9.8 vs 42.7 ± 24.8, p: 0.004). Both techniques succeeded in reducing the mean dose to implant (HTp vs HT, p < 0.001; VMATp vs HT, p < 0.001; VMATp vs HTp, p = 0.005).ConclusionBoth HTp and VMATp techniques succeeded to obtain conformal and homogeneous dose distributions within CTVp while reducing the mean implant dose. HTp was found to be superior to VMATp with regards to lowering all OAR doses except for CB.

Robustly optimized hybrid intensity-modulated proton therapy for craniospinal irradiation.

The aim of the study was to investigate the hybrid robust optimization planning approach in intensity-modulated proton therapy (IMPT) of craniospinal irradiation (CSI). Five IMPT-based adult CSI plans in supine position were created using Raystation treatment planning system (TPS) modelled for Proteus plus proton therapy system. A hybrid planning strategy was implemented, where clinical target volume was robustly optimized (RB) for set up uncertainties and planning target volume was optimized for target coverage using minimax algorithm in the TPS. Beam angle selection, optimization, and dose calculation approach were carefully performed to ensure optimum organ at risk (OAR) sparing, even with potential setup and range errors. The complementary dose gradients in junctions were generated using spot assignment and RB technique. Dosimetric outcomes in both nominal plan and the 16 error scenarios (±3 mm setup and 3.5% range) were analyzed using standard dose volume histogram. This planning approach resulted in a homogeneous dose distribution in the target volume of CSI, including the junction regions, by explicitly reducing number of robust optimization scenarios. The proposed technique was also able to achieve excellent coverage to cribriform plate with lower lens doses and minimal dose to other OARs. Target and OAR doses in the nominal plans as well as in the worst case scenarios with setup and range errors were able to meet the predefined clinical goal. This proposed planning technique is efficient, robust against the uncertainties. It could be adopted in other proton therapy centers.

Dosimetric evaluation of different radiotherapy techniques in mastectomized left-sided breast cancer.

Inclusion of internal mammary lymph nodes in mastectomized left breast cancer radiotherapy may lead to high dose receiving risk of the heart, lung, and contralateral breast. The aim of this study is to compare the dosimetric differences of field-in-field (FIF), volumetric-modulated arc therapy (VMAT), seven-field intensity-modulated radiotherapy (7F-IMRT), and helical tomotherapy (HT) planning techniques for mastectomized left breast cancer. Computed tomography images of ten patients treated with the FIF technique were used to compare four different treatment planning techniques. Planning target volume (PTV) included chest wall and regional lymph nodes. The heart, left anterior descending coronary artery (LAD), left and whole lung, thyroid, esophagus, and contralateral breast were identified as organs-at-risks (OARs). Except for HT, a single isocenter in PTV and bolus of thickness 0.3 cm on the chest wall was used. Complete and directional blocks were applied in HT, and the dosimetric parameters of PTV and OARs for four different techniques were analyzed using the Kruskal-Wallis test. 7F-IMRT, VMAT, and HT were superior to the FIF technique in providing homogeneous dose distribution covering the PTV (P < 0.0001). Mean doses (Dmean) of the contralateral breast and esophagus, lung, and body-PTV V5 (volume receiving 5 Gy) were reduced in FIF, whereas in the HT, Heart Dmean, LAD Dmean , Dmax, healthy tissue (body-PTV) Dmean , heart and left lung V20, and thyroid V30 were significantly reduced (P < 0.0001). FIF and HT techniques were found to be significantly advantageous over 7F-IMRT and VMAT for OARs. Using those three multiple-beam techniques reduced high-dose volumes of healthy tissues and organs in mastectomized left breast cancer radiotherapy but also increased low-dose volumes and contralateral lung and breast doses. Complete and directional blocks applied in HT reduce heart, lung, and contralateral breast doses.

Spot-scanning hadron arc (SHArc) therapy: A proof of concept using single- and multi-ion strategies with helium, carbon, oxygen, and neon ions.

To present particle arc therapy treatments using single and multi-ion therapy optimization strategies with helium (4 He), carbon (12 C), oxygen (16 O), and neon (20 Ne) ion beams. An optimization procedure and workflow were devised for spot-scanning hadron arc therapy (SHArc) treatment planning in the PRECISE (PaRticle thErapy using single and Combined Ion optimization StratEgies) treatment planning system (TPS). Physical and biological beam models were developed for helium, carbon, oxygen, and neon ions via FLUKA MC simulation. SHArc treatments were optimized using both single-ion (12 C, 16 O, or 20 Ne) and multi-ion therapy (16 O+4 He or 20 Ne+4 He) applying variable relative biological effectiveness (RBE) modeling using a modified microdosimetric kinetic model (mMKM) with (α/β)x values of 2, 5, and 3.1Gy, respectively, for glioblastoma, pancreatic adenocarcinoma, and prostate adenocarcinoma patient cases. Dose, effective dose, linear energy transfer (LET), and RBE were computed with the GPU-accelerated dose engine FRoG and dosimetric/biophysical attributes were evaluated in the context of conventional particle and photon-based therapies (e.g., volumetric modulated arc therapy [VMAT]). All SHArc plans met the target optimization goals (3GyRBE) and demonstrated increased target conformity and substantially lower low-dose bath to surrounding normal tissues than VMAT. SHArc plans using a singleion species (12 C, 16 O, or 20 Ne) exhibited favorable LET distributions with the highest-LET components centralized in the target volume, with values ranging from ∼80-170keV/μm, ∼130-220keV/μm, and ∼180-350keV/μm for 12 C, 16 O, or 20 Ne, respectively, exceeding mean target LET of conventional particle therapy (12 C:∼55, 16 O:∼75 20 Ne:∼95keV/μm). Multi-ion therapy with SHArc delivery (SHArcMIT ) provided a similar level of target LET enhancement as SHArc compared to conventional planning, however, with additional benefits of homogenous physical dose and RBE distributions. Here, we demonstrate that arc delivery of light and heavy ion beams, using either a single-ion species (12 C, 16 O, or 20 Ne) or combining two ions in a single fraction (16 O+4 He or 20 Ne+4 He) affords enhanced physical and biological distributions (e.g., LET) compared with conventional delivery with photons or particle beams. SHArc marks the first single- and multi-ion arc therapy treatment optimization approach using light and heavy ions.

3D-CRT versus RapidArc in Deep Tempero-Parietal High Grade Gliomas: Do We Really Need Higher Technology?

Purpose:The aim of this study was to dosimetrically compare single arc RapidArc with conventional 3D-CRT plans for tempero-parietal high grade gliomas with respect to PTV coverage and doses perceived by surrounding critical organs at risk. Methods:Thirty patients with the pathological diagnosis of high grade gliomas (WHO grade III-IV) were selected to be enrolled in our study. Patients were referred to our center (center of Clinical Oncology and Radiotherapy, Cairo University) during the period March 2020 till June 2021 for post-operative irradiation using 3D-CRT technique. For all patients, the dose prescribed to the planning target volume (PTV) was 60 Gy in 30 fractions. A RA plan was performed for each patient and dosimetrically was compared to the 3D-CRT plan. Results:The PTV coverage in terms of V95% was significantly superior in the RA plans with values of 98.4 ± 1.7 compared to 94.4 ± 2.6 for the 3D-CRT plans (p-value of 0.004). The doses risk structures ( eyes, optic nerves and cochleae) was lower with the RA plans as contrasted to the 3D-CRT plan with an exception for the intraocular lens which received higher doses in the RA plan with a statistically significant p-value of 0.001 and 0.002 for the Ipsilateral and contralateral lens, respectively. The average number of MUs ± SD was 358.6± 44.4 for the RA plans versus 247.6 ± 16.1 for 3D-CRT plans (p-value 0.001). The Dmean of healthy brain tissue was nearly equal for both plans (p-value of 0.071). Conclusion:The plans achieved by RA showed superior dose conformity, PTV coverage, more homogeneous dose distribution when contrasted to 3D-CRT plans. With the exception of both intraocular lenses, the RA plans showed better OAR sparing and utilized a higher number of MUs compared to the 3D-CRT.

IMRT Head and Neck Cancer Treatment Plans with a Novel Fast Ring-Gantry Radiotherapy System

<h3>Purpose/Objective(s)</h3> A novel fast ring-gantry radiotherapy system delivers radiation beamlets using a high-speed binary multi-leaf collimator (100 transitions /sec). This study investigated plan quality and delivery efficiency of IMRT Head and Neck (H&N) cancer cases using the novel radiotherapy system. <h3>Materials/Methods</h3> Three IMRT H&N cases were planned on the novel radiotherapy treatment planning system using the ICRU 83 guidelines to deliver 54 Gy to the planning target volume (PTV) in 30 fractions. Each H&N case was planned with 1 and 2 cm field width (FW). The treatment time-PTV correlation coefficient (C2_TT-PTV), homogeneity index (HI), conformity index (CI), mean dose (D_mean), D_near-max (D_2%), D_near-min (D_98%) of the PTVs and the mean dose to the 19 organs-at-risk (OARs) were investigated. <h3>Results</h3> All the H&N plans met the ICRU 83 guidelines. The C2_TT-PTV for 1 cm FW and 2 cm FW were 0.95 and 0.99, respectively. In addition, the average HI and CI for 1 cm FW were 1.20±0.00 and 1.23±0.15, while the average HI and CI for 2 cm FW were 1.23±0.06 and 1.30±0.17. The average D_mean, D_98% and D_2% were 57.65±0.36, 50.56±4.07 and 62.63±1.17 Gy for 1 cm FW. Also, the average D_mean, D_98% and D_2% for 2 cm FW were 57.68±0.69, 50.77±3.53 and 63.2±1.95 Gy, respectively. <h3>Conclusion</h3> The novel radiotherapy system can be used to deliver H&N cancer radiotherapy treatment efficiently while meeting dosimetric constraints and achieving homogenous dose distribution to the PTV structures.

Development, Monte Carlo simulations and experimental evaluation of a 3D range-modulator for a complex target in scanned proton therapy

The purpose of this work was to develop and manufacture a 3D range-modulator (3D RM) for a complex target contour for scanned proton therapy. The 3D RM is considered to be a viable technique for the very fast dose application in patient-specific tumors with only one fixed energy. The RM was developed based on a tumor from a patient CT and manufactured with high-quality 3D printing techniques with both polymer resin and aluminum. Monte Carlo simulations were utilized to investigate its modulating properties and the resulting dose distribution. Additionally, the simulation results were validated with measurements at the Marburg Ion-Beam Therapy Centre. For this purpose, a previously developed water phantom was used to conduct fast, automated high-resolution dose measurements. The results show a very good agreement between simulations and measurements and indicate that highly homogeneous dose distributions are possible. The delivered dose is conformed to the distal as well as to the proximal edge of the target. The 3D range-modulator concept combines a high degree of dose homogeneity and conformity, comparable to standard IMPT with very short irradiation times, promising clinically applicable dose distributions for lung and/or FLASH treatment, comparable and competitive to those from conventional irradiation techniques.

Pulmonary toxicity of craniospinal irradiation using helical tomotherapy

Craniospinal irradiation using helical tomotherapy (HT-CSI) has advantages in aspects of homogeneous dose distribution. Physicians, however, still have concerns of pulmonary toxicity due to HT-CSI’s relatively large, low-dose irradiated volume from continuous and 360° rotation delivery. In this study, we investigated the pulmonary toxicity of HT-CSI. We retrospectively reviewed 105 patients who received HT-CSI between January 2014 and December 2019. Grade 2 + pulmonary toxicities were evaluated. Intensive systemic treatment was defined as systemic treatment administration before, during, and after HT-CSI. VX Gy was defined as % volume receiving ≥ X Gy. Thirteen patients (12.4%) presented with grade 2 + pulmonary toxicities after HT-CSI. Of these patients, only one experienced grade 2 radiation pneumonitis combined with pembrolizumab-induced pneumonitis. Conversely, pneumonia was observed in 12 patients. Intensive systemic treatment (p = 0.004), immunosuppressive drugs (p = 0.031), and bilateral lung V5 Gy ≥ 65% (p = 0.031) were identified as independent risk factors for pneumonia. The risk factor for pneumonia in pediatric patients were immunosuppressive drugs (p = 0.035) and bilateral lung V5 Gy ≥ 65% (p = 0.047). HT-CSI can be a safe treatment modality with tolerable pulmonary toxicities. Intensive systemic treatment, immunosuppressive drugs, and bilateral lung V5 Gy ≥ 65% were significantly associated with pneumonia. In these patients, close follow-up should be considered for proper management of pneumonia.

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)