Differences In Dosimetric Parameters Research Articles

Evaluation of Tumor Control and Normal Tissue Complication Probabilities in Patients Receiving Comprehensive Nodal Irradiation for Left-Sided Breast Cancer.

Women with left-sided breast cancer receiving adjuvant radiotherapy have increased incidence of cardiac mortality due to ischemic heart disease; to date, no threshold dose for late cardiac/pulmonary morbidity or mortality has been established. We investigated the likelihood of cardiac death and radiation pneumonitis in women with left-sided breast cancer who received comprehensive lymph node irradiation. The differences in dosimetric parameters between free-breathing (FB) and deep inspiration breath hold (DIBH) techniques were also addressed. Based on NTCP calculations, the probability of cardiac death was significantly reduced with the DIBH compared to the FB technique (p < 0.001). The risk of radiation pneumonitis was not clinically significant. There was no difference in coverage between FB and DIBH plans. Doses to healthy structures were significantly lower in DIBH plan than in FB plan for V20, V30, and ipsilateral total lung volume. Inspiratory gating reduces the dose absorbed by the heart without compromising the target range, thus reducing the likelihood of cardiac death.

Dosimetric validation for prospective clinical trial on GRID collimator-based spatially fractionated radiation therapy: Dose metrics consistency and heterogeneous pattern reproducibility.

The purpose of this study is to characterize the dosimetric properties of a commercial brass GRID collimator for high energy photon beams including 15 and 10 MV. Then, the difference in dosimetric parameters of GRID beams among different energies and linacs was evaluated. A water tank scanning system was used to acquire the dosimetric parameters, including the percentage depth dose (PDD), beam profiles, peak to valley dose ratios (PVDRs), and output factors (OFs). The profiles at various depths were measured at 100cm source to surface distance (SSD), and field sizes of 10×10 cm2 and 20×20 cm2 on three linacs. The PVDRs and OFs were measured and compared with the treatment planning system (TPS) calculations. Compared with the open beam data, there were noticeable changes in PDDs of GRID fields across all the energies. The GRID fields demonstrated a maximal of 3mm shift in dmax (Truebeam STX, 15MV, 10×10 cm2). The PVDR decreased as beam energy increases. The difference in PVDRs between Trilogy and Truebeam STx using 6MV and 15MV was 1.5%±4.0% and 2.1%±4.3%, respectively. However, two Truebeam linacs demonstrated less than 2% difference in PVDRs. The OF of the GRID field was dependent on the energy and field size. The measured PDDs, PVDRs, and OFs agreed with the TPS calculations within 3% difference. The TPS calculations agreed with the measurements when using 1mm calculation resolution. The dosimetric characteristics of high-energy GRID fields, especially PVDR, significantly differ from those of low-energy GRID fields. Two Truebeam machines are interchangeable for GRID therapy, while a pronounced difference was observed between Truebeam and Trilogy. A series of empirical equations and reference look-up tables for GRID therapy can be generated to facilitate clinical applications.

Dose-Volume Parameters of Spared Magnetic Resonance Imaging-Defined Active Bone Marrow Predict Hematologic Toxicity in Pelvic Malignancies Patients Undergoing Radiotherapy: A Cohort Study.

Background: The objective of this investigation is to evaluate the superiority of dose-volume parameters relying on magnetic resonance imaging (MRI)-defined active bone marrow (ABM) over those based on total bone marrow (TBM) contoured via CT in the prediction of hematologic toxicity (HT) occurrence among patients with pelvic malignancies undergoing radiotherapy. Methods: The clinical data of 116 patients with pelvic malignancies treated with pelvic radiotherapy were analyzed retrospectively. The ABM areas on T1-weighted MRI were contoured. The statistical significance between TBM and ABM dose-volume measures was assessed through the utilization of either Student's t-test or Wilcoxon signed rank test. Logistic and linear regression models were employed to analyze the correlation between dose-volume parameters (V5-V50) and HT occurrence in pelvic ABM and TBM. Receiver operating characteristic (ROC) curves were used to compare predictors of HT2+. Results: There were significant differences in dosimetric parameters between ABM and TBM. Logistic regression analysis showed that ABM V5, ABM V10, ABM V15, ABM V20, and TBM V5 were significantly associated with the occurrence of HT2+ in pelvic malignancies. Linear regression analysis showed that ABM V5, ABM V10, and ABM V15 were significantly associated with white blood cell (WBC), absolute neutrophil count (ANC), hemoglobin (Hb), and lymphocyte (Lym) nadir. ABM V5, ABM V10, ABM V15, and ABM V30 were predictive of HT2+. Conclusions: More accurate prediction of HT in patients receiving pelvic radiotherapy may be achieved by relying on dose-volume parameters of MRI-based ABM. Further prospective studies are needed to confirm this.

Influence and optimization strategy of the magnetic field in 1.5 T MR-linac liver stereotactic radiotherapy

ObjectiveTo compare intensity reduction plans for liver cancer with or without a magnetic field and optimize field and subfield numbers in the intensity-modulated radiotherapy (IMRT) plans designed for liver masses in different regions.MethodsThis retrospective study included 62 patients who received radiotherapy for liver cancer at Shandong Cancer Hospital. Based on each patient's original individualized intensity-modulated plan (plan1.5 T), a magnetic field-free plan (plan0 T) and static intensity-modulated plan with four different optimization schemes were redesigned for each patient. The differences in dosimetric parameters among plans were compared.ResultsIn the absence of a magnetic field in the first quadrant, PTV Dmin increased (97.75 ± 17.55 vs. 100.96 ± 22.78)%, Dmax decreased (121.48 ± 29.68 vs. 119.06 ± 28.52)%, D98 increased (101.35 ± 7.42 vs. 109.35 ± 26.52)% and HI decreased (1.14 ± 0.14 vs. 1.05 ± 0.01). In the absence of a magnetic field in the second quadrant, PTV Dmin increased (84.33 ± 19.74 vs. 89.96 ± 21.23)%, Dmax decreased (105 ± 25.08 vs. 104.05 ± 24.86)%, and HI decreased (1.04 ± 0.25 vs. 0.99 ± 0.24). In the absence of a magnetic field in the third quadrant, PTV Dmax decreased (110.21 ± 2.22 vs. 102.31 ± 26)%, L-P V30 decreased (10.66 ± 9.19 vs. 5.81 ± 3.22)%, HI decreased (1.09 ± 0.02 vs. 0.98 ± 0.25), and PTV Dmin decreased (92.12 ± 4.92 vs. 89.1 ± 22.35)%. In the absence of a magnetic field in the fourth quadrant, PTV Dmin increased (89.78 ± 6.72 vs. 93.04 ± 4.86)%, HI decreased (1.09 ± 0.01 vs. 1.05 ± 0.01) and D98 increased (99.82 ± 0.82 vs. 100.54 ± 0.84)%. These were all significant differences. In designing plans for tumors in each liver region, a total number of subfields in the first area of 60, total subfields in the second zone of 80, and total subfields in the third and fourth zones of 60 or 80 can achieve the dose effect without a magnetic field.ConclusionIn patients with liver cancer, the effect of a magnetic field on the target dose is more significant than that on doses to organs at risk. By controlling the max total number of subfields in different quadrants, the effect of the magnetic field can be greatly reduced or even eliminated.

Acute Gastrointestinal and Genitourinary Toxicity Results from a Prospective Randomized Phase II Trial Evaluating Adjuvant Pelvic Radiotherapy Using Either IMRT or 3-Dimensional Planning for Endometrial Cancer

To compare the incidence of grade ≥2 gastrointestinal (GI) or genitourinary (GU) toxicity for patients undergoing 3DRT versus IMRT in the post-operative setting for endometrial cancer. Patients were post-operatively enrolled in a prospective randomized phase II trial from 2010 to 2020. Those eligible were adults aged ≥18 scheduled to receive adjuvant pelvic radiotherapy (RT) for histologically confirmed endometrial carcinoma with the following AJCC 2009 grade/stage: Grade 2: stage IB (LVSI +/or >60 yrs); Grade 3: stage IA and IB; or Grade 1-3: Stage II and IIIA, IIIB and IIIC1; who had an ECOG-PS 0-2, and who had surgery consisting of total hysterectomy, +/- bilateral salpingo-oophorectomy, +/- lymph node sampling. Exclusion criteria included previous irradiation to the pelvic region, patients in whom concurrent chemotherapy was planned, a history of inflammatory bowel disease, and previous bowel surgery. Patients were randomly assigned to one of two parallel groups in 1:1 ratio, to have their RT delivered using either a 3DRT technique or using IMRT. Prescription dose was 45 Gy in 25 fractions over 5 weeks followed by 11 Gy in 2 fractions vaginal vault brachytherapy. Toxicity was graded according to CTCAE ver. 3.0. Acute toxicity was assessed weekly during RT. Fisher's exact tests were used to test for associations between toxicity and arm. Differences in dosimetric parameters for patients with or without toxicity were tested using Mann-Whitney U-tests. Ninety-two patients with a median age of 63 were enrolled, with 8 patients not evaluable for primary outcome. The median follow-up was 52 months. 14 (35%) participants from the 3DRT arm and 15 (34%) from the IMRT arm experienced acute grade ≥2 GI toxicity. 20 (50%) participants from the 3DRT arm and 25 (57%) from the IMRT arm experienced acute grade ≥2 GI or GU toxicity (p = .662). Grade 3 GI toxicity was 5 (12%) and 4 (9%) for 3DRT and IMRT, respectively. 12 (30%) patients from the 3DRT arm and 17 (39%) from the IMRT arm experienced acute grade ≥2 GU toxicity (p = .493). Rates for grade 3 GU toxicity were 4 (10%) and 4 (9%) for 3DRT and IMRT, respectively. Those with acute grade ≥2 GU toxicity had a median PTV D99% of 43.2 Gy (35.5-44.6) compared with a median of 43.4 Gy (41.5-44.6; p = 0.042) for those who did not have a grade ≥2 GU toxicity. No statistically significant differences in the incidence of acute GI or GU toxicity were found between patients treated with adjuvant IMRT versus 3DRT radiotherapy for endometrial cancer. Although IMRT can reduce dose to normal tissue, in this study no benefit in acute toxicity outcome was seen.

Late Urinary Toxicity and QoL with Curative Radiotherapy for High-Risk Prostate Cancer: Dose-Effect Relations in the POP-RT Randomized Phase III Trial

Whole pelvic radiotherapy (WPRT) showed better biochemical failure-free survival and metastasis-free survival than prostate-only radiotherapy (PORT) in the phase III randomized POP-RT trial for high and very high-risk prostate cancer, albeit with higher RTOG grade 2 late urinary toxicity. We report updated long term, symptom-wise comparison and dose-effect relations from this trial. Late urinary toxicity, and cumulative severity of each symptom over the follow-up period was graded using CTCAE v5.0. Grade 2+ toxicities were compared between the trial arms by chi square test. Bladder dosimetry in 5-Gy increments (V5, V10, V15...V65 Gy, V68 Gy) from the trial database of approved radiotherapy plans, was compared for each urinary symptom and overall late gr2+ toxicity by student t-test. Observed differences in dosimetric parameters were tested using multivariable logistic regression analysis, including age at diagnosis, known diabetes, tumor stage, trial arm, and prior transurethral resection of prostate (TURP). Urinary QOL scores were compared between arms using generalised linear mixed model. Combined late symptom-wise toxicity and dose-volume data were available for analysis for 193/224 patients. At a median follow-up of 75 months, cumulative CTCAE gr2+ late urinary toxicity remained higher with WPRT than PORT, though not statistically significant (36.5% vs 26.8%, p = 0.15). Grade 3 toxicity was low and similar in both arms. Symptom-wise cumulative rates showed no significant difference between arms (Table 1). Dosimetric comparison showed significantly higher bladder V5-V15 in patients with gr2+ toxicity over those with <gr2 urinary toxicity. On symptom-wise analysis, V5-V40 range was significantly higher for presence of dysuria, hematuria, and urgency. No significant differences were observed over higher dose range for any urinary symptom. On multivariable analysis, no significant association was identifiable between bladder dosimetry and urinary symptoms. Urinary QOL scores was similar between both the arms for all the symptoms. Compared to prostate-only radiotherapy, whole pelvic radiotherapy resulted similar Grade 3 urinary toxicity of about 5% with about 10% higher cumulative grade 2+ urinary toxicity over long term follow up. This difference was not reflected in patient-reported QOL. WPRT particularly increased urgency and hematuria. Larger bladder volume being irradiated with 5Gy to 15Gy dose range could contribute to increase in urinary symptoms.

Prospective randomised phase II trial evaluating adjuvant pelvic radiotherapy using either IMRT or 3-Dimensional planning for endometrial cancer

Objective To compare the incidence of grade ≥2 gastrointestinal (GI) or genitourinary (GU) toxicity for patients undergoing 3DRT versus IMRT in the postoperative setting for endometrial cancer. Methods Eligible patients were post-operatively randomly assigned to one of two parallel groups in a 1:1 ratio, to have their RT delivered using either a 3DRT technique or using IMRT. The prescription dose was 45 Gy in 25 fractions over 5 weeks followed by vaginal vault brachytherapy. Toxicity was graded according to National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) version (v) 3.0. Fisher’s exact tests were used to test for associations between toxicity and arm. Differences in dosimetric parameters for patients with or without toxicity were tested using Mann–Whitney U-tests. Results 84 patients with a median age of 62 were evaluable for primary outcome. The median follow-up was 52 months. 14 (35%) participants from the 3DRT arm and 15 (34%) from the IMRT arm experienced acute grade ≥2 GI toxicity with older patients having a statistically higher risk of grade ≥2 acute GI toxicity. 20 (50%) participants from the 3DRT arm and 25 (57%) from the IMRT arm experienced acute grade ≥2 GI or GU toxicity (p = .662). 12 (30%) patients from the 3DRT arm and 17 (39%) from the IMRT arm experienced acute grade ≥2 GU toxicity (p = .493). Conclusion Although IMRT can reduce dose to normal tissue, in this study no benefit in acute GI or GU toxicity outcome was seen.

Active bone marrow-sparing to reduce the incidence of grade 3+ acute hematologic toxicity in patients with locally advanced cervical cancer who receive chemoradiotherapy: A single-center prospective randomized controlled trial.

5524 Background: Acute haematologic toxicity is the most common side effect of chemoradiotherapy in patients with locally advanced cervical cancer .We aim to test the efficacy of single-photon emission computed tomography-defined active bone marrow-sparing volumetric-modulated arc therapy in reducing grade 3+ acute hematologic toxicity (HT) in locally advanced cervical cancer patients treated with chemoradiotherapy. Methods: This was a prospective, single-center, open label, randomized clinical trial that enrolled locally advanced cervical cancer patients. Participants were randomized to the 99mTc sulfur colloid SPECT-defined ABMS VMAT (ABMS group) or control group, who received weekly cisplatin concurrently with volumetric-modulated arc therapy followed by high-dose-rate intracavitary brachytherapy. The ABMS group additionally received SPECT-defined ABM dose constraints. The primary endpoint was the incidence of grade 3+ acute hematologic toxicity.Secondary objectives included acute gastrointestinal toxicity, planning Target Volume (PTV) coverage, dosimetric parameters of organs at risk (OARs), progression-free survival (PFS), overall survival (OS). Results: A total of 192 FIGO stage IB-IIIB patients were randomized treated (96 each in the ABMS control groups). The median follow-up was 24.0 months. The incidence of grade 3+ acute hematologic toxicity in the ABMS group was significantly lower than that in the control group (32.3% vs 53.1%, p&lt;0.01). The number of patients completing five cycles of cisplatin was 88.5% in the ABMS group and 75% in the control group, and the difference was significant (p=0.02). There were no significant differences in the mean dose to 95%, 97% and 99%of the PTV between the ABMS group (45.1 Gy, 44.6 Gy, and 43.3 Gy, respectively) and the control group (45.4 Gy, 44.8 Gy, and 43.6 Gy). There were no differences in dosimetric parameters of OARs ,acute gastrointestinal toxicity, 2-year PFS or 2-year OS between the two groups. Patients in the control group had nonsignificantly worse 2-year distant metastasis than patients in the ABMS group (17.8% vs. 11.1%, p=0.19). Conclusions: ABMS VMAT significantly reduced grade 3+ acute HT and improved chemotherapy delivery compared with the control treatment. We found weak evidence of the effect of ABMS VMAT on distant metastasis. Clinical trial information: ChiCTR-IOR-16010214 .

Dosimetric impact of applying a model-based dose calculation algorithm for skin cancer brachytherapy (interventional radiotherapy).

Brachytherapy (BT, interventional radiotherapy) is a well-established radiotherapy technique capable of delivering high doses to tumors while sparing organs at risk (OARs). Currently, the clinically accepted dose calculation algorithm used is TG-43. In the TG-186 report, new model-based dose calculation algorithms (MBDCA), such as Elekta's advanced collapsed cone engine (ACE), have been introduced, although their clinical application is yet to be fully realized. This study aimed to investigate two aspects of TG-186: firstly, a comparison of dose distributions calculated with TG-43 and TG-186 for skin tumors; and secondly, an exploration of the impact of using a water bolus on the coverage of clinical target volume (CTV) and OARs. Ten treatment plans for high-dose-rate IRT were developed. All plans were initially calculated using the TG-43 algorithm, and were subsequently re-calculated with TG-186. In addition, one of the treatment plans was assessed with both TG-43 and TG-186, using 10 different water bolus thicknesses ranging from 0 to 5 cm. To assess dose variations, the following dose-volume histogram (DVH) parameters were compared: D2cc and D0.01cc for OARs, and V150, V100, V95 and V90 for CTV coverage. The average dosimetric results for CTV and OARs, as calculated by both algorithms, revealed statistically significant lower values for TG-186 when compared with TG-43. The presence of a bolus was observed to enhance CTV coverage for the TG-186 algorithm, with a bolus thickness of 2 cm being the point at which ACE calculations matched those of TG-43. This study identified significant differences in dosimetric parameters for skin tumors when comparing the TG-43 and TG-186 algorithms. Moreover, it was demonstrated that the inclusion of a water bolus increased CTV coverage in TG-186 calculations.

Development and validation of a scatter-corrected CBCT image-guided method for cervical cancer brachytherapy.

Multiple patient transfers have a nonnegligible impact on the accuracy of dose delivery for cervical cancer brachytherapy. We consider using on-site cone-beam CT (CBCT) to resolve this problem. However, CBCT clinical applications are limited due to inadequate image quality. This paper implements a scatter correction method using planning CT (pCT) prior to obtaining high-quality CBCT images and evaluates the dose calculation accuracy of CBCT-guided brachytherapy for cervical cancer. The CBCT of a self-developed female pelvis phantom and five patients was first corrected using empirical uniform scatter correction in the projection domain and further corrected in the image domain. In both phantom and patient studies, the CBCT image quality before and after scatter correction was evaluated with registered pCT (rCT). Model-based dose calculation was performed using the commercial package Acuros®BV. The dose distributions of rCT-based plans and corrected CBCT-based plans in the phantom and patients were compared using 3D local gamma analysis. A statistical analysis of the differences in dosimetric parameters of five patients was also performed. In both phantom and patient studies, the HU error of selected ROIs was reduced to less than 15 HU. Using the dose distribution of the rCT-based plan as the baseline, the γ pass rate (2%, 2mm) of the corrected CBCT-based plan in phantom and patients all exceeded 98% and 93%, respectively, with the threshold dose set to 3, 6, 9, and 12 Gy. The average percentage deviation (APD) of D90 of HRCTV and D2cc of OARs was less than 1% between rCT-based and corrected CBCT-based plans. Scatter correction using a pCT prior can effectively improve the CBCT image quality and CBCT-based cervical brachytherapy dose calculation accuracy, indicating promising prospects in both simplified brachytherapy processes and accurate brachytherapy dose delivery.

Optimum Parameters for Imaging and Dose Calculation in Lung SBRT

<h3>Purpose/Objective(s)</h3> Efficiency, set up accuracy, patient comfort and accurate dose calculations are critical requirements in radiation therapy especially in stereotactic body radiotherapy (SBRT). There are several CT imaging parameters such as kV, mAs, image reconstruction algorithm filters, field of view and pitch that affect image quality used for volume delineation and dose calculation. Modifying the imaging parameters may lead to variation in Hounsfield Units (HU) that may affect the dose calculations. We investigated the relationship between the image reconstruction algorithms (Body (B) and Lung filter (L)), HU and dose distribution. We hypothesize that variation in the imaging parameters may lead to better image quality with clinically insignificant dose to target and organs at risk (OARs). <h3>Materials/Methods</h3> Ten lung SBRT patients were imaged on a 16 slice CT scanner. The standard clinical scan (C) is a B- reconstruction filter-based scan with low pitch. For selected patients, in additional to standard scan, sharp scans were acquired using greater pitch and L-filter algorithm to see the effect of density and dose calculation. Clinical workflow includes fusing the images acquired with B and L filter. Clinically B filter images are used for planning and treatment. For this study purposes, an additional plan was generated on L filtered images using appropriate HU to density curve. CT density phantom was scanned on a 16 slice CT scanner with standard Body (B) filter as well as standard images of CT density phantom were reconstructed with lung (L) filter algorithm to generate HU to physical density table for a treatment planning system and used for dose calculation. Image qualities for the two filter were evaluated visually by an attending radiation oncologist. The dosimetric differences in the target coverages were evaluated using the HU curve generated for B and L filter. <h3>Results</h3> For clinical cases, using lung SBRT protocols, planning target volume (PTV) coverage V100% were recorded. In addition to the target coverage mean physical density was recorded for the B and L filter and C-clinical scans. Average difference in the PTV physical density was 2.4%, 0.3% and 2.1% for B-C, L-C and B-L, where B stands for – B Filter density curve on the sharp scan, L – L Filter density curve on the sharp scan, C – Clinical scan. No significant differences were noted in PTV coverages for B-C 1.7% (p < 0.0004), L-C 2.03% (p < 0.0007) and B-L -0.29% (p < 0.0005) based plans for V100%. <h3>Conclusion</h3> The L filter high pitch combination improved image contrast and thus helped in contouring. No significant difference in the PTV coverage was observed when B filter HU curve was applied to sharp quality scan used for dose calculation. Thus, images acquired with L filter can be used clinically with existing B filter HU curve. Overall Differences in dosimetric parameters are insignificant compared to the small uncertainties in HU numbers.

Assessment of dose perturbations for metal stent in photon and proton radiotherapy plans for hepatocellular carcinoma

BackgroundThe present study aimed to investigate the dosimetric impact of metal stent for photon and proton treatment plans in hepatocellular carcinoma.MethodsWith computed tomography data of a water-equivalent solid phantom, dose perturbation caused by a metal stent included in the photon and proton treatment of hepatocellular carcinoma was evaluated by comparing Eclipse and RayStation treatment planning system (TPS) to a Monte Carlo (MC) based dose calculator. Photon and proton plans were created with anterior–posterior/posterior-anterior (AP/PA) fields using a 6 MV beam and AP/PA fields of a wobbling beam using 150 MeV and a 10 cm ridge filter. The difference in dose distributions and dosimetric parameters were compared depending on the stent's positions (the bile duct (GB) and intestinal tract (GI)) and angles (0°, 45°, and 90°). Additionally, the dose variation in the target volume including the stent was comparatively evaluated through dose volume histogram (DVH) analysis. And the comparison of clinical cases was carried out in the same way.ResultsPercentage differences in the dosimetric parameters calculated by MC ranged from − 7.0 to 3.9% for the photon plan and − 33.7 to 4.3% for the proton plan, depending on the angle at which the GB and GI stents were placed, compared to those without the stent. The maximum difference was observed at the minimum dose (Dmin), which was observed in both photon and proton plans in the GB and GI stents deployed at a 90° incidence angle. The parameter differences were greater in the proton plan than in photon plan. The target volume showed various dose variations depending on positions and angles of stent for both beams. Compared with no-stent, the doses within the target volume containing the GI and GB stents for the photon beam were overestimated in the high-dose area at 0°, nearly equal within 1% at 45°, and underestimated at 90°. These doses to the proton beam were underestimated at all angles, and the amount of underdose to the target volume increased with an increase in the stent angle. However, the difference was significantly greater with the proton plan than the photon plan.ConclusionsDose perturbations within the target volume due to the presence of the metal stent were not observed in the TPS calculations for photon and proton beams, but MC was used to confirm that there are dose variations within the target volume. The MC results found that delivery of the treatment beam avoiding the stent was the best method to prevent target volume underdose.

Determination of variation in dosimetric parameters of treatment planning with Co-60 and Ir-192 sources in high dose rate brachytherapy of cervical carcinoma

AimTo determine the differences in dosimetric parameters in patients of intracavitary brachytherapy and interstitial HDR brachytherapy using Co-60 and Ir-192 sources. Materials and methodsComputed tomography (CT) based treatment plans of 20 cervical carcinoma patients treated with intracavitary and interstitial high dose rate brachytherapy were retrospectively studied. Patients were planned using Co-60 and Ir-192 sources, keeping the same dwell positions and dose objectives. The dosimetric parameters such as V100, D90, homogeneity index (HI) and conformal index (CI) for target and D2cc, D1cc and D0.1cc for organs at risk (OAR) were compared for both sources. ResultsFor interstitial brachytherapy plans, HR-CTV mean V100 values for Co-60 and Ir-192-based plans were 97.03 ± 1.93% and 96.42 ± 2.18%, respectively. There was no significant difference found in target coverage (p = 0.370). Ir-192 based plans were more homogeneous (HI = 0.68 ± 0.09) than the Co-60 plans (HI = 0.59 ± 0.10). However, the conformity was similar with both the sources. No significant difference was found between D2cc, D1cc, and D0.1cc values of bladder and rectum. In intracavitary brachytherapy plans, we did not find any significant difference in the dosimetric parameters such as point A values, D90, V100, and OAR doses on comparing plans from both sources. ConclusionThere are no significant differences in dosimetric parameters and no clinical advantage of using Co-60 over Ir-192-based brachytherapy. However, when it comes to cost management, Co-60 has a longer half-life, which reduces the cost of frequent source replacement and disposal.

Mapping of Level I Axillary Lymph Nodes in Patients with Newly Diagnosed Breast Cancer: Optimal Target Delineation and Treatment Techniques for Breast and Level I Axilla Irradiation

PurposeTo map the locations of level I axilla (Ax-L1) lymph nodes (LNs), evaluate the clinical target volume (CTV) coverage defined by the Radiation Therapy Oncology Group (RTOG) Breast Cancer Atlas, and assess the optimal techniques for whole-breast and Ax-L1 irradiation (WBI + Ax-L1). Methods and MaterialsWe identified 76 patients newly diagnosed with breast cancer with 1 to 4 positive LNs confirmed by axillary dissection. The locations of 116 involved Ax-L1 LNs on diagnostic computed tomography (CT) were mapped onto simulated CT images of a standard patient. Ax-L1 LN coverage by the RTOG atlas was evaluated, and a modified Ax-L1 CTV with better coverage was proposed. Treatment plans were designed for WBI + Ax-L1 with high tangential simplified intensity modulated radiation therapy (HT-sIMRT) and volumetric modulated arc therapy (VMAT) and for WBI + RTOG Ax-L1 with VMAT with a prescription dose of 50 Gy in 25 fractions, respectively. The differences in dosimetric parameters were compared. ResultsThe RTOG Atlas missed 29.3% of LNs. Modification by extending 1 cm caudal and 0.5 cm anterior to the RTOG-defined CTV borders allowed the modified Ax-L1 CTV to encompass 90.5% of LNs. All plans met the required prescription dose to WBI and Ax-L1. The mean dose and the V20 and V5 (percentage volume receiving 20 Gy and 5 Gy) of the ipsilateral lung were 11.7 Gy, 23.0%, and 38.1% for HT-sIMRT WBI + Ax-L1 and 8.9 Gy, 16.4%, and 32.5% for VMAT WBI + Ax-L1 plans, respectively. The mean heart doses in the left-sided plans were 3.2 Gy and 3.0 Gy, respectively. The V30 of the humeral head and the minimum dose to the axillary-lateral thoracic vessel junction were 2.0% versus 1.8% and 45.5 Gy versus 45.7 Gy for VMAT WBI + Ax-L1 and VMAT WBI + RTOG Ax-L1 plans, respectively. ConclusionsA modified Ax-L1 CTV with expansion of the caudal and anterior borders might provide better coverage. Compared with HT-sIMRT WBI + Ax-L1, VMAT WBI + Ax-L1 provided an adequate dose to the Ax-L1 while decreasing the doses to most normal tissues. Coverage of the modified Ax-L1 did not increase the dose to organs at risk compared with coverage of RTOG Ax-L1.

A Comparative Study of Patients With Early-Stage Non-Small Cell Lung Cancer Treated With Stereotactic Body Radiation Therapy Using CyberKnife and Linear Accelerator–Based Volumetric Modulated Arc Therapy

PurposeStereotactic body radiation therapy (SBRT) has become the standard of care for medically inoperable early-stage non-small cell lung cancer. We investigated 2 modalities of lung SBRT, CyberKnife (CK) and volumetric modulated arc therapy (VMAT), for differences in dosimetric parameters, tumor control, and clinical outcomes. Methods and MaterialsPatients who underwent SBRT for T1-2N0M0 non-small cell lung cancer from 2012 to 2018 were included. Dosimetric parameters for target volume coverage and organ-at-risk dose distribution were collected. Survival outcomes were evaluated using the Kaplan-Meier method with log-rank test. A multivariate Cox proportional hazards model was analyzed for local, regional, and distant tumor control; overall survival (OS) and progression-free survival; and radiation pneumonitis. ResultsTwo hundred twenty-seven patients (142 CK, 85 VMAT SBRT) met inclusion criteria. Overall, the local, regional, and distant control rates were 89.3%, 86.3%, and 87.4% at 2 years, and the OS was 67.5% and 32.8% at 2 and 5 years, respectively. VMAT delivered higher maximum doses to the gross tumor volume and planning target volume and had a lower lung and heart V5. Although there was no difference in local or distant failure, progression-free survival, or OS, VMAT was associated with superior freedom from regional failure (adjusted hazard ratio, 0.26; P = .045). With no difference between treatment modalities, 11.9% of patients developed grade 1 to 2 radiation pneumonitis. There were no grade 3+ events of radiation pneumonitis. ConclusionsThis study revealed that VMAT and CK provided comparable local and distant control and survival outcomes; however, VMAT exhibited better regional control. Further study in this regard is imperative.

Evaluation of Doses to Target Volume and Organs at Risk by Conventional versus RTOG Contouring Based 3D Conformal Plans in Breast Cancer: A Prospective Study

Introduction: In radiotherapy, conventional field borders have often little anatomical correlation with the draining lymphatics. So, with the availability of more conformal techniques and delineation guidelines, an evident need exists to optimise our treatment plans with more focus on planning and dosimetric aspects. Aim: To evaluate the differences in dosimetric parameters to the Organs at Risk and target volumes in patients treated with conventional plans vis-à-vis Radiation Therapy Oncology Group contour guided treatment plans. Materials and Methods: A prospective interventional study was conducted in which 30 patients of histopathologically proven Infiltrating Ductal Carcinoma (IDC) breast, with age range of 18 to 80 years were enrolled. Patients were treated with 50 Gray in 25 fractions of radiation with additional 10 Gray in 5 fractions boost in Breast Conserving Surgery (BCS) patients by conventional treatment plans. Radiation Therapy Oncology Group (RTOG) guidelines were used for breast/Chest Wall (CW), axillary nodes, Supraclavicular Fossa (SCF), and Internal Mammary Node (IMN) delineation. Organs At Risk (OARs) included heart, Ipsilateral (I/L) lung, Contralateral (C/L) breast, oesophagus and spinal cord. Dose-Volume Histograms (DVHs) for these contours were generated from conventional treatment plans. Further, new treatment plans were generated to cover &gt;90% of Planning Target Volume (PTV) by 90% isodose line. DVH parameters of these two plans were compared using paired t-test. A p-value of &lt;0.05 was considered statistically significant. Results: Of the total 30 cases, the mean volume of breast/CW PTV covered by 90% isodose line (V90) was better in RTOG plan as compared to Conventional plan (93.39 vs 90.39, p-value=0.001). Similarly, mean V90 for total axilla (97.44 vs 90.39, p-value=0.0001) and combined PTV (92.60 vs 88.81, p-value=0.0001) was better with RTOG plan. For OARs, conventional vs RTOG plans; Dmean for heart was 2.56 vs 2.60Gy, p-value=0.63), I/L lung V20Gy was 28.77 vs 28.94%, p-value=0.71) and V5Gy for C/L breast was 0.48 vs 0.54%, p-value=0.47), respectively. In cases where IMN was irradiated, mean doses to the heart, I/L lung V20Gy, and contralateral breast V5Gy increased significantly. Conclusion: The present study showed that RTOG target volumes had inadequate coverage in conventional plans. On the contrary, plans directed at RTOG contours provided statistically better coverage for target volumes without increase in the doses to the OARs. In patients with IMN irradiation, the doses to some OARs were increased in RTOG as compared to conventional plans.

Feasibility of Synthetic Computed Tomography Images Generated from Magnetic Resonance Imaging Scans Using Various Deep Learning Methods in the Planning of Radiation Therapy for Prostate Cancer.

Simple SummaryMRI-only simulation in radiation therapy (RT) planning has received attention because the CT scan can be omitted. For MRI-only simulation, synthetic CT (sCT) is necessary for the dose calculation. Various methodologies have been suggested for the generation of sCT and, recently, methods using the deep learning approaches are actively investigated. GAN and cycle-consistent GAN (CycGAN) have been mainly tested, however, very limited studies compared the qualities of sCTs generated from these methods or suggested other models for sCT generation. We have compared GAN, CycGAN, and, reference-guided GAN (RgGAN), a new model of deep learning method. We found that the performance in the HU conservation for soft tissue was poorest for GAN. All methods could generate sCTs feasible for VMAT planning with the trend that sCT generated from the RgGAN showed best performance in dosimetric conservation D98% and D95% than sCTs from other methodologies.We aimed to evaluate and compare the qualities of synthetic computed tomography (sCT) generated by various deep-learning methods in volumetric modulated arc therapy (VMAT) planning for prostate cancer. Simulation computed tomography (CT) and T2-weighted simulation magnetic resonance image from 113 patients were used in the sCT generation by three deep-learning approaches: generative adversarial network (GAN), cycle-consistent GAN (CycGAN), and reference-guided CycGAN (RgGAN), a new model which performed further adjustment of sCTs generated by CycGAN with available paired images. VMAT plans on the original simulation CT images were recalculated on the sCTs and the dosimetric differences were evaluated. For soft tissue, a significant difference in the mean Hounsfield unites (HUs) was observed between the original CT images and only sCTs from GAN (p = 0.03). The mean relative dose differences for planning target volumes or organs at risk were within 2% among the sCTs from the three deep-learning approaches. The differences in dosimetric parameters for D98% and D95% from original CT were lowest in sCT from RgGAN. In conclusion, HU conservation for soft tissue was poorest for GAN. There was the trend that sCT generated from the RgGAN showed best performance in dosimetric conservation D98% and D95% than sCTs from other methodologies.

Parotid gland dose reduction in the hippocampus avoidance whole-brain radiotherapy using helical tomotherapy.

The present study aimed to reduce the parotid gland dose in the hippocampus avoidance with whole-brain radiotherapy (HA-WBRT) using the helical tomotherapy (HT). Ten patients who had previously undergone WBRT were randomly selected and enrolled in this study. During the treatment planning, two different techniques to the jaw were applied for each patient, namely, 1.0 cm fixed jaw and 2.5 cm dynamic jaw. To efficiently reduce the dose in the bilateral parotid glands, directional block (DB) mode was set. The DB is a function of a treatment planning system for the dose reduction in organs at risk. The standard HA-WBRT plan which did not reduce the parotid gland dose was also designed to compare the plan quality. Compared with the standard HA-WBRT plan, the parotid gland dose could be reduced by approximately 70% without extending the delivery time by adding the parotid gland on the DB mode to the dose constraint. In addition, the differences in dosimetric parameters observed between the plans employing the 1.0 cm fixed jaw and 2.5 cm dynamic jaw were almost negligible. Moreover, delivery time in the 2.5 cm dynamic jaw could be greatly reduced by 60% compared with that in the 1.0 cm fixed jaw.

Mapping of Level I Axillary Lymph Nodes in Patients With Newly Diagnosed Breast Cancer: Optimal Target Delineation and Treatment Techniques in Breast and Level I Axilla Irradiation

<h3>Purpose/Objective(s)</h3> In an era of increasingly use of axilla irradiation in high-risk breast cancer patients after breast-conserving surgery and sentinel lymph node (LN) biopsy, the optimal clinical target volume (CTV) for level I axilla (Ax-L1) LN is uncertain. We mapped the location of pretreatment LN metastases in the Ax-L1 of newly diagnosed breast cancer patients and propose modification of the CTV borders as defined by the Radiation Therapy Oncology Group (RTOG) breast cancer atlas. Further, we assessed the differences in dosimetric parameters of modified Ax-L1 planning target volume (PTV) and surrounding organs at risk (OAR) between whole breast irradiation with standard "high tangential" simplified IMRT (HT-sIMRT WBI) and whole breast plus Ax-L1 irradiation with VMAT (VMAT WBI+ Ax-L1). <h3>Materials/Methods</h3> We identified 76 newly diagnosed breast cancer patients with 1-4 positive LNs after curative-intent surgery and axillary lymph node dissection treated between 2016 and 2018. All patients had a pretreatment diagnostic computed tomography (CT) chest scan demonstrating involved Ax-L1 LNs. The locations of 116 involved Ax-L1 LNs were mapped onto simulation CT images of a standard patient and the appropriateness of RTOG atlas was assessed. A modified Ax-L1 CTV with better coverage for involved Ax-L1 LNs was proposed, and PTV was generated for plans. Standard "high tangential" sIMRT plans for WBI and VMAT plans for WBI+ Ax-L1 on each side (left side and right side) were designed with a prescription dose of 50 Gy in 25 fractions, and dosimetric parameters were compared. <h3>Results</h3> For the RTOG atlas, the mapped LNs were 70.7% (82/116) inside, 13.8% (16/116) marginal and 15.5% (18/116) outside the CTV borders. The RTOG atlas missed 29.3% of LNs: 50.0% (17/34) in the anterior, 23.5% (8/34) in the caudal, 14.7% (5/34) in the cranial, 11.8% (4/34) in the medial direction. Modification by extending 1 cm caudal and 0.5 cm anterior to the CTV borders of the RTOG atlas allowed the modified Ax-L1 CTV to encompass 90.5% (105/116) of LNs. For HT-sIMRT WBI and VMAT WBI+ Ax-L1 plans, the mean V50 of modified Ax-L1 PTV was 69.5% and 97.8%; the mean dose, V20 and V5 of ipsilateral lung were 8.9 Gy, 16.4%, 32.5% and 10.5 Gy, 20.8%, 33.8%; the mean heart dose in left-sided plans was 4.1 Gy and 3.0 Gy; the mean dose and V5 of liver in the right-sided plans were 1.5 Gy, 3.6% and 2.8 Gy, 10.3%, respectively. <h3>Conclusion</h3> According to the distribution of Ax-L1 LNs, the RTOG atlas might be insufficient for their coverage. We propose a modified Ax-L1 CTV with expansion of RTOG Ax-L1 CTV borders, most notably in the caudal and anterior directions. Standard "high tangential" sIMRT WBI plans failed to deliver a therapeutic dose adequately to the modified Ax-L1 PTV. VMAT plans intended for whole breast plus Ax-L1 irradiation provided adequate dose to Ax-L1 PTV without increasing the doses to OARs.

Hybrid Tomo-Helical and Tomo-Direct radiotherapy for localized prostate cancer.

PurposeThe aim of the study is to present a new planning approach to provide better planning target volume (PTV) coverage and reduce bladder and rectum dose with hybrid Tomo‐Helical (TH)/Tomo‐Direct (TD) radiotherapy (RT) for localized prostate cancer (LPC).MethodsTwenty‐five LPC patients were included in this retrospective study. TH plans, TD plans, and hybrid TH/TD plans were created. Lateral beams were used for the hybrid TD plan and the prescribed dose was 70 Gy in 28 fractions (hybrid plans were combined 45 Gy/ 18 fxs for TH and 25 Gy/10 fxs for TD). Doses of PTV (D2%, D98%, D50%, homogeneity index (HI), conformity index (CI), coverage) and organs at risk (OARs) (V50%, V35%, V25%, V5%, and V95%) were analyzed. The Wilcoxon signed‐rank test was used to analyze the difference in dosimetric parameters. p‐Value < 0.05 was considered statistically significant.ResultsTH plans showed better CI, and target coverage (p < 0.01) than TD and hybrid plans in all patient plan evaluations. However, TD plans D2%, D98%, and D50% doses were better than TH and hybrid plans. The HI values were similar between the three plans. Significant reductions in bladder and rectum V50%, V35%, and V25% doses (p < 0.001) were observed with hybrid plans compared to TH and TD. Penile bulb V95% and bowel V5% doses were better in the hybrid plans. Left and right femoral head V5% doses were higher in the hybrid plan compared to others (p < 0.001).ConclusionConcurrently hybrid TH/TD RT plan can be a good option to reduce the doses of the rectum and bladder in the RT of LPC.