By using the feature of tumor stiffness, the accuracy of preoperative staging for rectal tumors with shear-wave elastography was improved compared with endorectal US in the pilot study, but was not significantly different in the validation cohort, potentially due to small sample size. PurposeTo compare the value of endorectal ultrasonography (US) with shear-wave elastography (SWE) in staging rectal tumors before surgery.Materials and MethodsThis prospective study was approved by the institutional review board and written informed consent was obtained. In a pilot cohort from April 2015 to January 2016, 70 patients with rectal adenocarcinomas and/or adenomas confirmed with histopathologic examination underwent both endorectal US and SWE. Tumor stiffness and three regions of reference backgrounds, as well as tumor stiffness ratios (SRs) versus these backgrounds, were analyzed. The optimal staging feature was selected by using receiver operating characteristic analysis, and the concordance rate with pathologic stage was analyzed and compared with endorectal US. The results were validated in an independent cohort of 30 patients from February 2016 to July 2016.ResultsIn the pilot study, from rectal adenoma to stage T3 cancers, the tumor stiffness, stiffness of peritumoral fat, tumor SR versu...

Ultrahigh-dose-rate therapy, also known as FLASH radiotherapy (RT), is an emerging technique that is garnering significant interest in cancer treatment due to its potential to revolutionize therapy. This method can achieve comparable tumor control to conventional-dose-rate RT while offering the enhanced protection of normal tissue through the FLASH-sparing effect. This innovative technique has demonstrated promising results in preclinical studies involving animals and cell lines. Particularly noteworthy is its potential application in treating head and neck (HN) cancers, especially in patients with challenging recurrent tumors and reirradiation cases, where the toxicity rates with conventional radiotherapy are high. Such applications aim to enhance tumor control while minimizing side effects and preserving patients’ quality of life. In comparison to electron or photon FLASH modalities, proton therapy has demonstrated superior dosimetric and delivery characteristics and is a safe and effective FLASH treatment for human malignancies. Compared to the transmission proton FLASH, single-energy Bragg peak FLASH is a novel delivery method that allows highly conformal doses to targets and minimal radiation doses to crucial OARs. Proton Bragg peak FLASH for HN cancer has still not been well studied. This review highlights the significance of proton FLASH in enhancing cancer therapy by examining the advantages and challenges of using it for HN cancer reirradiation.

Bragg peak FLASH radiotherapy (RT) uses a distal tracking method to eliminate exit doses and can achieve superior OAR sparing. This study explores the application of this novel method in stereotactic body radiotherapy prostate FLASH-RT. An in-house platform was developed to enable intensity-modulated proton therapy (IMPT) planning using a single-energy Bragg peak distal tracking method. The patients involved in the study were previously treated with proton stereotactic body radiotherapy (SBRT) using the pencil beam scanning (PBS) technique to 40 Gy in five fractions. FLASH plans were optimized using a four-beam arrangement to generate a dose distribution similar to the conventional opposing beams. All of the beams had a small angle of two degrees from the lateral direction to increase the dosimetry quality. Dose metrics were compared between the conventional PBS and the Bragg peak FLASH plans. The dose rate histogram (DRVH) and FLASH metrics of 40 Gy/s coverage (V_40Gy/s) were investigated for the Bragg peak plans. There was no significant difference between the clinical and Bragg peak plans in rectum, bladder, femur heads, large bowel, and penile bulb dose metrics, except for D_max. For the CTV, the FLASH plans resulted in a higher D_max than the clinical plans (116.9% vs. 103.3%). For the rectum, the V_40Gy/s reached 94% and 93% for 1 Gy dose thresholds in composite and single-field evaluations, respectively. Additionally, the FLASH ratio reached close to 100% after the application of the 5 Gy threshold in composite dose rate assessment. In conclusion, the Bragg peak distal tracking method can yield comparable plan quality in most OARs while preserving sufficient FLASH dose rate coverage, demonstrating that the ultra-high dose technique can be applied in prostate FLASH SBRT.