Stereotactic ablative radiotherapy for ultra-central lung tumors: prioritize target coverage or organs at risk?

AbstractPurpose:Dose distribution index (DDI) is a treatment planning evaluation parameter, reflecting dosimetric information of target coverage that can help to spare organs at risk (OARs) and remaining volume at risk (RVR). The index has been used to evaluate and compare prostate volumetric modulated arc therapy (VMAT) plans using two different plan optimisers, namely photon optimisation (PO) and its predecessor, progressive resolution optimisation (PRO).Materials and methods:Twenty prostate VMAT treatment plans were created using the PO and PRO in this retrospective study. The 6 MV photon beams and a dose prescription of 78 Gy/39 fractions were used in plans with the same dose–volume criteria for plan optimisation. Dose–volume histograms (DVHs) of the planning target volume (PTV), as well as of OARs such as the rectum, bladder, left and right femur were determined in each plan. DDIs were calculated and compared for plans created by the PO and PRO based on DVHs of the PTV and all OARs.Results:The mean DDI values were 0·784 and 0·810 for prostate VMAT plans created by the PO and PRO, respectively. It was found that the DDI of the PRO plan was about 3·3% larger than the PO plan, which means that the dose distribution of the target coverage and sparing of OARs in the PRO plan was slightly better. Changing the weighting factors in different OARs would vary the DDI value by ∼7%. However, for plan comparison based on the same set of dose–volume criteria, the effect of weighting factor can be neglected because they were the same in the PO and PRO.Conclusions:Based on the very similar DDI values calculated from the PO and PRO plans, with the DDI value in the PRO plan slightly larger than that of the PO, it may be concluded that the PRO can create a prostate VMAT plan with slightly better dose distribution regarding the target coverage and sparing of OARs. Moreover, we found that the DDI is a simple and comprehensive dose–volume parameter for plan evaluation considering the target, OARs and RVR.

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Radiation during deep inspiration allows loco-regional treatment of left breast and axillary-, supraclavicular- and internal mammary lymph nodes without compromising target coverage or dose restrictions to organs at risk

Acta Oncologica ◽

10.3109/0284186x.2011.618510 ◽

2011 ◽

Vol 51 (3) ◽

pp. 333-344 ◽

Cited By ~ 76

Author(s):

Mari H. B. Hjelstuen ◽

Ingvil Mjaaland ◽

Johan Vikström ◽

Kjell Ivar Dybvik

Keyword(s):

At Risk ◽

Lymph Nodes ◽

Organs At Risk ◽

Left Breast ◽

Target Coverage ◽

Deep Inspiration ◽

Internal Mammary Lymph Nodes ◽

Internal Mammary ◽

Regional Treatment

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Comparative Study of Conventional Planning and MRI Based Volume Optimized Planning of Intracavitary Brachytherapy of Cervical Cancer

Journal of Evidence Based Medicine and Healthcare ◽

10.18410/jebmh/2020/624 ◽

2020 ◽

Vol 7 (50) ◽

pp. 3061-3066

Author(s):

Niharika Darasani

Keyword(s):

Cervical Cancer ◽

At Risk ◽

Large Volume ◽

Organs At Risk ◽

External Beam Radiation ◽

Intracavitary Brachytherapy ◽

Target Coverage ◽

Cancer Cervix ◽

Beam Radiation ◽

The Mean

BACKGROUND Cervical cancer is one of the commonest malignancies among women in India. The main stay of treatment is the combination of External Beam Radiation Therapy (EBRT) and Intracavitary Brachytherapy (ICBT) in these patients. We compared conventional point A based treatment planning and MRI based volume optimized planning in ICBT of cervical carcinoma along with doses to organs at risk in both plans. We also compared the radiation doses to organs at risk in both the plans by International Committee on Radiation Units (ICRU) recommended points and dose volume histograms. METHODS Eighteen Patients with cancer cervix (72.22% with stage IIB) received EBRT on linear accelerator by four field technique using 15 MV energy for a dose of 46 Gray (Gy) – 50 Gy in 23-25 fractions 2.0 Gy per fraction, five days per week, for 5 weeks to whole pelvis. Most of the patients received at least three doses of chemotherapy. A total of 50 high-dose rate intracavitary brachytherapy (HDR-ICBT) applications done in 18 patients were used for analysis in the study. Clinical history, gynaecology examination and punch biopsy were undertaken. The patients were assessed during EBRT after 2 weeks, for ICBT application and suitable patients were selected for the procedure. CT based point A planning and MRI based volume optimised planning were done for each ICBT application before intracavity brachytherapy. Contouring of rectum, bladder, right and left femoral heads, and small bowel were done. RESULTS The median age of patients in this study was 50.4 ± 03.25 years. 72.22% (13/18) of the patients were of stage IIB. The mean dose delivered to 90% high-risk clinical target volume (D90- HR-CTV) for all 50 applications by volume optimized planning was 06.87 ± 0.942 Gy. The mean D90-HR-CTV by point A based conventional planning was 13.69 ± 1.06 GY. The mean D100-HR-CTV by volume optimized planning was 05.30 Gy (± 0.20). The mean D100-HR-CTV by point A based conventional planning was 08.91 ± 0.74 Gy. Maximum doses in the bladder and rectum were significantly lower (p<0.05) for MRI planning than for the conventional approach (06.49 GY Vs. 07.45 GY) for bladder; (04.57 GY vs. 05.06 GY) for rectum respectively. Both bladder (D2cc) and rectum (D2cc) doses could be reduced significantly by volume optimization. CONCLUSIONS D90-HR-CTV adequately covered by MRI based volume optimized planning was superior to conventional point A based planning in terms of both conformity of target coverage and evaluation of Organ at Risk (OARs), including the rectum and bladder. Both bladder and rectum doses in the most irradiated 2cc volume are significantly reduced in volume optimized planning. Hence, volume optimized planning would be more beneficial in large volume diseases to get better target coverage at the same time sparing the organs in small volume diseases. Hence, the use of MRI-based volume optimization brachytherapy for patients with large volume tumours with parametrial invasion is beneficial. KEYWORDS Cancer, Cervix, Woman, Radiotherapy, Brachytherapy, EBRT, ICBT, Prognosis

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Comparison of Ray Tracing and Monte Carlo Calculation Algorithms for Spine Lesions Treated with CyberKnife

10.21203/rs.3.rs-280719/v1 ◽

2021 ◽

Author(s):

Jun Li ◽

Xile Zhang ◽

Yuxi Pan ◽

Hongqing Zhuang ◽

Ruijie Yang

Keyword(s):

At Risk ◽

Monte Carlo ◽

Ray Tracing ◽

Thoracic Spine ◽

Organs At Risk ◽

Target Coverage ◽

Dose Volume Histograms ◽

Percentage Volume ◽

Calculation Algorithms ◽

Sacral Spine

Abstract Purpose: This study attempts to evaluate Ray Tracing (RT) and Monte Carlo (MC) algorithm for CyberKnife treatments of spine lesions and determine whether MC algorithm is necessary for all spine treatment and analyze which sites of spine lesion for which RT algorithm is comparable to MC algorithm. Methods: The CyberKnife is used for stereotactic body radiotherapy for lesions in the cervical spine (30), thoracic spine (50), lumbar spine (30) and sacral spine (15). Dose was calculated using RT and MC algorithms for patients planned with the same beam angles and monitor units. Dose-volume histograms of the target and selected critical structures are evaluated. Results: The average target coverage of prescribed dose with MC algorithms was 94.80%, 88.47%, 92.52% and 93.41% respectively in cervical, thoracic, lumbar and sacral spine. For thoracic spine, RT algorithm significantly overestimates the percentage volume of target covered by the prescribed dose, as well as overestimates doses to organs at risk in most cases, including lung, spinal cord and esophagus. For cervical, lumbar and sacral spine, the differences of the target coverage of prescription dose were generally less than 3% between the RT and MC algorithms. The differences of doses to organs at risk varied with lesion sites and surrounding organs. Conclusions: In the thoracic spine lesions with beams through air cavities, RT algorithm should be limited and verified with MC algorithm, but the RT algorithm is adequate for treatment of cervical, lumbar and sacral spine lesions without or small amount of beams passing through the lungs.

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