Magnetic resonance imaging organ at risk delineation for nasopharyngeal radiotherapy: Measuring the effectiveness of an educational intervention.

INTRODUCTION: Magnetic resonance imaging (MRI) demonstrates superior soft tissue contrast and is increasingly being used in radiotherapy planning. This study evaluated the impact of an education workshop in minimising inter-observer variation (IOV) for nasopharyngeal organs at risk (OAR) delineation on MRI. METHODS: Ten observers delineated 14 OARs on 4 retrospective nasopharyngeal MRI data sets. Standard contouring guidelines were provided pre-workshop. Following an education workshop on MRI OAR delineation, observers blinded to their original contours repeated the 14 OAR delineations. For comparison, reference volumes were delineated by two head and neck radiation oncologists. IOV was evaluated using dice similarity coefficient (DSC), Hausdorff distance (HD) and relative volume. Location of largest deviations was evaluated with centroid values. Observer confidence pre- and post-workshop was also recorded using a 6-point Likert scale. The workshop was deemed beneficial for an OAR if ≥50% of observers mean scores improved in any metric and ≥50% of observers' confidence improved. RESULTS: All OARs had ≥50% of observers improve in at least one metric. Base of tongue, larynx, spinal cord and right temporal lobe were the only OARs achieving a mean DSC score of ≥0.7. Base of tongue, left and right lacrimal glands, larynx, left optic nerve and right parotid gland all exhibited statistically significant HD improvements post-workshop (P < 0.05). Brainstem and left and right temporal lobes all had statistically significant relative volume improvements post-workshop (P < 0.05). Post-workshop observer confidence improvement was observed for all OARs (P < 0.001). CONCLUSIONS: The educational workshop reduced IOV and improved observers' confidence when delineating nasopharyngeal OARs on MRI.

The dosimetric advantages of perirectal hydrogel spacer in men with localized prostate cancer undergoing stereotactic ablative radiotherapy (SABR).

To evaluate the dosimetric differences for patients receiving a perirectal hydrogel spacer (PR-HS) using SpaceOAR undergoing stereotactic ablative radiotherapy (SABR) for localized prostate cancer with the CyberKnife VSI system. Gold fiducial markers and a PR-HS was inserted in 22 consecutive patients with histologically confirmed localized prostate cancer. For planning comparison, dosimetry from the clinical plans was compared against replans based on a simulated rectum volume designed to recreate a clinically appropriate spacer-less anatomy for each patient. Both sets were planned to 36.25 Gy in 5 fractions using the treatment planning system associated with the CyberKnife VSI system. The aim was to ensure equivalent target coverage for both plans and to evaluate doses to the organs-at-risk (OARs): rectum, bladder and penile bulb. The median PR-HS implant volume was 11.2 cc (range 8.8 to 14.9 cc). The maximal median perirectal separation was 15.5 mm (10.5 to 20.7 mm). Statistically significant reductions were noted for the 3 OARs, with no statistically significant difference in planning target volumes or clinical target volume coverage. All rectal dose constraints were significantly improved in the PR-HS plans with a percentage dose difference of at least 24% (rectum V18.1Gy (%)) to 60.5% (rectum V36Gy (cc)). The bladder and penile bulb dose constraints parameters were also significantly improved: the bladder V37Gy was reduced by 17.1%, V18.1Gy was reduced by 4.2%; the penile bulb D50% was reduced by 7.7%. The use of PR-HS was able to significantly reduce planned dose to the rectum, bladder and penile bulb with SABR techniques associated with the CyberKnife VSI system.

Estimating cancer risks due to whole lungs low dose radiotherapy with different techniques for treating COVID-19 pneumonia.

BACKGROUND: Low dose radiotherapy (LDRT) of whole lungs with photon beams is a novel method for treating COVID-19 pneumonia. This study aimed to estimate cancer risks induced by lung LDRT for different radiotherapy delivery techniques. METHOD: Four different radiotherapy techniques, including 3D-conformal with anterior and posterior fields (3D-CRT AP-PA), 3D-conformal with 8 coplanar fields (3D-CRT 8 fields), eight fields intensity-modulated radiotherapy (IMRT), and volumetric modulated arc therapy using 2 full arcs (VMAT) were planned on the CT images of 32 COVID-19 patients with the prescribed dose of 1 Gy to the lungs. Organ average and maximum doses, and PTV dose distribution indexes were compared between different techniques. The radiation-induced cancer incidence and cancer-specific mortality, and cardiac heart disease risks were estimated for the assessed techniques. RESULTS: In IMRT and VMAT techniques, heart (mean and max), breast (mean, and max), and stomach (mean) doses and also maximum dose in the body were significantly lower than the 3D-CRT techniques. The calculated conformity indexes were similar in all the techniques. However, the homogeneity indexes were lower (i.e., better) in intensity-modulated techniques (P < 0.03) with no significant differences between IMRT and VMAT plans. Lung cancer incident risks for all the delivery techniques were similar (P > 0.4). Cancer incidence and mortality risks for organs located closer to lungs like breast and stomach were higher in 3D-CRT techniques than IMRT or VMAT techniques (excess solid tumor cancer incidence risks for a 30 years man: 1.94 ± 0.22% Vs. 1.68 ± 0.17%; and women: 6.66 ± 0.81% Vs. 4.60 ± 0.43%: cancer mortality risks for 30 years men: 1.63 ± 0.19% Vs. 1.45 ± 0.15%; and women: 3.63 ± 0.44% Vs. 2.94 ± 0.23%). CONCLUSION: All the radiotherapy techniques had low cancer risks. However, the overall estimated risks induced by IMRT and VMAT radiotherapy techniques were lower than the 3D-CRT techniques and can be used clinically in younger patients or patients having greater concerns about radiation induced cancers.

The risk of induced cancer and ischemic heart disease following low dose lung irradiation for COVID-19: estimation based on a virtual case.

BACKGROUND: Recently, low dose radiotherapy delivered to the whole lung has been proposed as treatment for the pneumonia due to COVID-19. Although there is biological plausibility for its use, the evidence supporting its effectiveness is scarce, and the risks associated with it may be significant. Thus, based on a virtual case simulation, we estimated the risks of radiation-induced cancer (RIC) and cardiac disease. METHODS: Lifetime attributable risks (LAR) of RIC were calculated for the lung, liver, esophagus, and breast of female patients. The cardiovascular risk of exposure-induced death (REID) due to ischemic heart disease was also calculated. The doses received by the organs involved in the treatment were obtained from a simulation of conformal radiotherapy (RT) treatment, delivering a dose of 0.5 Gy-1.5 Gy to the lungs. We considered a LAR and REID <1% as acceptable, 1-2% cautionary, and >2% unacceptable. RESULTS: The lung was at the highest risk for RIC (absolute LAR below 5200 cases/100,000 and 2250 cases/100,000 for women and men, respectively). For women, the breast had the second-highest LAR, especially for young women. The liver and esophagus had LARs below 700/100,000 for both sexes, with a higher incidence of esophageal cancer in women and liver cancer in men. Regarding the LAR cutoff, we observed an unacceptable or cautionary LAR for lung cancer in all women and men <60 years with an RT dose >1 Gy. LAR for lung cancer with an RT dose of 1 Gy was cautionary for women >60 years of age and men <40 years of age. No LAR estimation was unacceptable for the RT dose ≤0.7 Gy in all groups irrespective of sex or age at exposure. Only 0.5 Gy had an acceptable REID. CONCLUSIONS: A RT dose ≤0.5 Gy provides an acceptable LAR estimate (≤1%) for RIC and REID, irrespective of sex and age. The current ongoing trials should initially use doses ≤0.5 Gy to maintain the risks at an acceptable level and include only patients who fail or do not have any other treatment option.

Low dose radiation therapy for COVID-19: Effective dose and estimation of cancer risk.

BACKGROUND AND PURPOSE: The objective of this work is to evaluate the risk of carcinogenesis of low dose ionizing radiation therapy (LDRT), for treatment of immune-related pneumonia following COVID-19 infection, through the estimation of effective dose and the lifetime attributable risk of cancer (LAR). MATERIAL AND METHODS: LDRT treatment was planned in male and female computational phantoms. Equivalent doses in organs were estimated using both treatment planning system calculations and a peripheral dose model (based on ionization chamber measurements). Skin dose was estimated using radiochromic films. Later, effective dose and LAR were calculated following radiation protection procedures. RESULTS: Equivalent doses to organs per unit of prescription dose range from 10 mSv/cGy to 0.0051 mSv/cGy. Effective doses range from 204 mSv to 426 mSv, for prescription doses ranging from 50 cGy to 100 cGy. Total LAR for a prescription dose of 50 cGy ranges from 1.7 to 0.29% for male and from 4.9 to 0.54% for female, for ages ranging from 20 to 80 years old. CONCLUSIONS: The organs that mainly contribute to risk are lung and breast. Risk for out-of-field organs is low, less than 0.06 cases per 10000. Female LAR is on average 2.2 times that of a male of the same age. Effective doses are of the same order of magnitude as the higher-dose interventional radiology techniques. For a 60 year-old male, LAR is 8 times that from a cardiac CT, when prescription dose is 50 cGy.

Paracervical blocks facilitate timely brachytherapy amidst COVID-19.

PURPOSE: The COVID-19 pandemic presents serious challenges for brachytherapists, and in the time-sensitive case of locally advanced cervical cancer, the need for curative brachytherapy (BT) is critical for survival. Given the high-volume of locally advanced cervical cancer in our safety-net hospital, we developed a strategy in close collaboration with our gynecology oncology and anesthesia colleagues to allow for completely clinic-based intracavitary brachytherapy (ICBT). METHODS AND MATERIALS: This technical report will highlight our experience with the use of paracervical blocks (PCBs) and oral multimodal analgesia (MMA) for appropriately selected cervical ICBT cases, allowing for completely clinic-based treatment. RESULTS: 18 of 19 (95%) screened patients were eligible for in-clinic ICBT. The excluded patient had significant vaginal fibrosis. 38 of 39 intracavitary implants were successfully transitioned for entirely in-clinic treatment utilizing PCBs and oral MMA (97% success rate). One case was aborted due to inadequate analgesia secondary to a significantly delayed case start time (PO medication effect diminished). 95% of patients reported no pain at the conclusion of the procedure. The median (IQR) D2cc for rectum and bladder were 64.8 (58.6-70.2) Gy and 84.1 (70.9-89.4) Gy, respectively. Median (IQR) CTV high-risk D90 was 88.0 (85.6-89.8) Gy. CONCLUSIONS: In a multidisciplinary effort, we have successfully transitioned many ICBT cases to the clinic with the use of PCB local anesthesia and oral multimodality therapy in direct response to the current pandemic, thereby mitigating exposure risk to patients and staff as well as reducing overall health care burden.