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Potential for reduced radiation-induced toxicity using intensity-modulated arc therapy for whole-brain radiotherapy with hippocampal sparing.

ABSTRACT: The purpose of this study was to retrospectively investigate the accuracy, plan quality, and efficiency of using intensity-modulated arc therapy (IMAT) for whole brain radiotherapy (WBRT) patients with sparing not only the hippocampus (following RTOG 0933 compliance criteria) but also other organs at risk (OARs). A total of 10 patients previously treated with nonconformal opposed laterals whole-brain radiotherapy (NC-WBRT) were retrospectively replanned for hippocampal sparing using IMAT treatment planning. The hippocampus was volumetrically contoured on fused diagnostic T1-weighted MRI with planning CT images and hippocampus avoidance zone (HAZ) was generated using a 5 mm uniform margin around the hippocampus. Both hippocampi were defined as one paired organ. Whole brain tissue minus HAZ was defined as the whole-brain planning target volume (WB-PTV). Highly conformal IMAT plans were generated in the Eclipse treatment planning system for Novalis TX linear accelerator consisting of high-definition multileaf collimators (HD-MLCs: 2.5 mm leaf width at isocenter) and 6 MV beam for a prescription dose of 30 Gy in 10 fractions following RTOG 0933 dosimetric criteria. Two full coplanar arcs with orbits avoidance sectors were used. In addition to RTOG criteria, doses to other organs at risk (OARs), such as parotid glands, cochlea, external/middle ear canals, skin, scalp, optic pathways, brainstem, and eyes/lens, were also evaluated. Subsequently, dose delivery efficiency and accuracy of each IMAT plan was assessed by delivering quality assurance (QA) plans with a MapCHECK device, recording actual beam-on time and measuring planed vs. measured dose agreement using a gamma index. On IMAT plans, following RTOG 0933 dosimetric criteria, the maximum dose to WB-PTV, mean WB-PTV D2%, and mean WB-PTV D98% were 34.9 ± 0.3 Gy, 33.2 ± 0.4 Gy, and 26.0± 0.4Gy, respectively. Accordingly, WB-PTV received the prescription dose of 30Gy and mean V30 was 90.5% ± 0.5%. The D100%, and mean and maximum doses to hippocampus were 8.4 ± 0.3 Gy, 11.2 ± 0.3 Gy, and 15.6 ± 0.4 Gy, on average, respectively. The mean values of homogeneity index (HI) and conformity index (CI) were 0.23 ± 0.02 and 0.96 ± 0.02, respectively. The maximum point dose to WB-PTV was 35.3 Gy, well below the optic pathway tolerance of 37.5 Gy. In addition, compared to NC-WBRT, dose reduction of mean and maximum of parotid glands from IMAT were 65% and 50%, respectively. Ear canals mean and maximum doses were reduced by 26% and 12%, and mean and maximum scalp doses were reduced by 9 Gy (32%) and 2 Gy (6%), on average, respectively. The mean dose to skin was 9.7 Gy with IMAT plans compared to 16 Gy with conventional NC-WBRT, demonstrating that absolute reduction of skin dose by a factor of 2. The mean values of the total number of monitor units (MUs) and actual beam on time were 719 ± 44 and 2.34 ± 0.14 min, respectively. The accuracy of IMAT QA plan delivery was (98.1 ± 0.8) %, on average, with a 3%/3 mm gamma index passing rate criteria. All of these plans were considered clinically acceptable per RTOG 0933 criteria. IMAT planning provided highly conformal and homogenous plan with a fast and effective treatment option for WBRT patients, sparing not only hippocampi but also other OARs, which could potentially result in an additional improvement of the quality life (QoL). In the future, we plan to evaluate the clinical potential of IMAT planning and treatment option with hippocampal and other OARs avoidance in our patient's cohort and asses the QoL of the WBRT patients, as well as simultaneous integrated boost (SIB) for the brain metastases diseases.

SUBMITTER: Pokhrel D

PROVIDER: S-EPMC5690185 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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Potential for reduced radiation-induced toxicity using intensity-modulated arc therapy for whole-brain radiotherapy with hippocampal sparing.

Pokhrel Damodar D Sood Sumit S Lominska Christopher C Kumar Pravesh P Badkul Rajeev R Jiang Hongyu H Wang Fen F

Journal of applied clinical medical physics 20150908 5

The purpose of this study was to retrospectively investigate the accuracy, plan quality, and efficiency of using intensity-modulated arc therapy (IMAT) for whole brain radiotherapy (WBRT) patients with sparing not only the hippocampus (following RTOG 0933 compliance criteria) but also other organs at risk (OARs). A total of 10 patients previously treated with nonconformal opposed laterals whole-brain radiotherapy (NC-WBRT) were retrospectively replanned for hippocampal sparing using IMAT treatme ...[more]

PMID: 26699321

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Project description:Purpose:Dose-volume histogram (DVH) toxicity relationships are poorly defined in men who receive radiation after radical prostatectomy (RP). We evaluated Radiation Therapy Oncology Group (RTOG) study 0534 and institutional intact normal-tissue sparing guidelines, as well as dose to bladder trigone, for ability to minimize late toxicity. Methods and materials:164 men received intensity modulated radiation therapy (RT) to a median prostate bed dose of 66.6?Gy at a median of 22 months after RP. 46% of men were prescribed androgen deprivation therapy and pelvic lymph node irradiation to a median dose of 50.4?Gy. DVH relationships for the rectum, bladder, trigone, and bladder excluding the clinical target volume (bladder-CTV) were analyzed against the Common Terminology Criteria for Adverse Events late grade 2?+?(G2+) gastrointestinal (GI) and genitourinary (GU) toxicity by log-rank test. RTOG 0534 (rectum V65, 40 Gy ?35, 55%, and bladder-CTV V65, 40 ?50, 70%) and intact prostate RT institutional guidelines (rectum V70, 65, 40 ?20, 40, 80% and bladder V70, 65, 40 ?30, 60, 80%, respectively) guidelines were evaluated. Results:With a median follow-up time of of 33 months, the 4-year freedom from G2?+?GI and GU toxicity were both 91%. G2?+?GI (n?=?12) and GU (n?=?15) toxicity included 4% diarrhea (n?=?6), 4% hemorrhage (n?=?6), 1% proctitis (n?=?1), and 4% urinary frequency (n?=?7), 1% obstructive (n?=?2), 2% cystitis (n?=?3), and 3% incontinence (n?=?5), respectively. RTOG 0534 rectum and bladder goals were not achieved in 65% and 41% of cases, while the institutional intact prostate goals were not achieved in 21% and 25% of cases, respectively. Neither dose to the bladder trigone nor any of the proposed normal tissue goals were associated with late toxicity (P?>?.1). In the univariate analysis, age, pelvic RT, RT dose, anticoagulation use, androgen deprivation therapy, time from RP to RT, and tobacco history were not associated with toxicity. Conclusions:More than 90% of men were free from late G2?+?toxicity 4 years after post-RP intensity modulated RT. No tested parameters were associated with late toxicity. In the absence of established normal-tissue DVH guidelines in the postoperative setting, the use of intact guidelines is reasonable.

Project description:BackgroundWhile chemo-radiotherapy improves local control in patients with locally advanced rectal cancer, it can also increase acute hematological toxicity (HT), which leads to poor outcomes. Patients receiving bone marrow radiation have been shown to develop acute HT. However, the safety and efficacy of bone marrow sparing is undetermined. The aim of our study was to explore the feasible dosimetric constraints for pelvic bone marrow (PBM) that can be widely used in rectal cancer patients undergoing chemo-radiotherapy.Methods112 rectal cancer patients were selected and divided into the PBM sparing IMRT group (60 cases) and the non-PBM sparing IMRT group (52 cases). All patients underwent pelvic radiotherapy with concurrent capecitabine-based chemotherapy. The PBM dosimetric constraints in the PBM sparing IMRT group were set to:V10 ≤ 85%, V20 ≤ 65% and V30 ≤ 45%. An independent sample t test was applied for the dose-volume parameters, and Chi-squared analysis was applied for clinical parameters and adverse events.ResultsThe radiation dose to PBM (V5~V45, Dmean, P<0.05), PBM sub-regions (V10~V35, Dmean, P<0.05) and both femoral heads (V5~V40, Dmean, P<0.05) decreased significantly in the PBM sparing IMRT group compared with that of the non-PBM sparing IMRT group (P<0.05). There was no significant difference in any dose-volume parameters of the bladder and small bowel in either groups, and none in the planning target volume (PTV) dose homogeneity and conformity (P>0.05). For acute HT observation, the incidence of grade 3 acute HT (χ2 = 7.094, P=0.008) was significantly reduced in patients treated with PBM sparing IMRT compared with patients treated with non-PBM sparing IMRT. There was no statistical difference in the incidence of vomiting, diarrhea, fatigue, anorexia, nausea, hand-foot syndrome, cystitis, perianal pain and perianal dermatitis in patients of both groups (P >0.05).ConclusionsApplying PBM dosimetric constraints (V10 ≤ 85%, V20 ≤ 65% and V30 ≤ 45%) can significantly reduce the radiation dose to PBM. The patients treated with PBM sparing IMRT had a lower incidence of acute HT compared with those treated with non-PBM sparing IMRT. Applying the PBM dosimetric constraints proposed by our study can benefits the patients with rectal cancer undergoing capecitabine-based chemo-radiotherapy.

Project description:ObjectiveTo report acute hematological toxicity (HT) in patients receiving post-operative bowel sparing intensity-modulated radiotherapy (IMRT) and cisplatin and its dosimetric predictors.MethodsClinical database of Phase III trial (NCT01279135), that randomized patients to post-operative conformal or intensity modulated radiation therapy, was searched to select patient strata that received bowel sparing IMRT (50 Gy/25#/5 wks) and concurrent cisplatin (40 mg m-2). Pelvic bone marrow (BM) was retrospectively delineated in two sets: whole bone (WB), and freehand (FH) inner cavity of bone. Dose volume histograms (DVH) of BM were obtained. Receiver operating characteristic (ROC) curve identified DVH thresholds that predicted for Grade≥ II HT with highest specificity. Univariate and multivariate analysis was performed.ResultsOverall 75 patients received concurrent cisplatin. Grades I-V HT was observed in 38.7%, 42.7%, 14.7%, 0%, and 0% patients, respectively. Grade ≥ II leukopenia, neutropenia, anemia, and thrombocytopenia were observed in 26%, 40%, 26.5%, and 1.4% respectively. None of the HT resulted in treatment break. On univariate analysis, whole pelvis+ lumbar FH V30 >55% & V40>35%, whole pelvis WB and FH V40 > 35%, and lower pelvis WB and FH V40 >20% correlated for Grade ≥ II leucopenia and neutropenia. None of the BM dose volume constraints predicted for overall HT or neutropenia on multivariate analysis.ConclusionThe IMRT arm of NCT01279135 (PARCER study) that employed strict bowel constraints had unintentional but desirable BM sparing. None of the BM subvolume DVH parameters could be validated on multivariate analysis.Advances in knowledgeThe prospective study reports feasibility of bone marrow sparing with bowel sparing post-operative pelvic IMRT and concurrent chemotherapy for cervical cancer. The present study reports low incidence of hematological and gastrointestinal toxicity during post-operative chemoradiation with IMRT. As both whole bone and freehand pelvis BM contours predicted for HT, hence an easier method of whole bone contouring should continue to be used till further validation of more specific BM subvolumes becomes available. The study results highlight the need for further research into dose volume constraints during post-operative IMRT.

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Potential for reduced radiation-induced toxicity using intensity-modulated arc therapy for whole-brain radiotherapy with hippocampal sparing.

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Potential for reduced radiation-induced toxicity using intensity-modulated arc therapy for whole-brain radiotherapy with hippocampal sparing.

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