Making radiation therapy more effective in the era of precision medicine

Plastic scintillator-based dosimeters for ultra-high dose rate (UHDR) electron radiotherapy

This paper reports the development of dosimeters based on plastic scintillating fibers imaged by a charge-coupled device camera, and their performance evaluation through irradiations with the electron Flash research accelerator located at the Centro Pisano Flash Radiotherapy. The dosimeter prototypes were composed of a piece of plastic scintillating fiber optically coupled to a clear optical fiber which transported the scintillation signal to the readout systems (an imaging system and a photodiode). The following properties were tested: linearity, capability to reconstruct the percentage depth dose curve in solid water and to sample in time the single beam pulse. The stem effect contribution was evaluated with three methods, and a proof-of-concept one-dimensional array was developed and tested for online beam profiling. Results show linearity up to 10 Gy per pulse, and good capability to reconstruct both the timing and spatial profiles of the beam, thus suggesting that plastic scintillating fibers may be good candidates for low-energy electron Flash dosimetry.

Efficiency of moderately hypofractionated radiotherapy in NSCLC cell model

Background

The current standard of radiotherapy for inoperable locally advanced NSCLCs with single fraction doses of 2.0 Gy, results in poor outcomes. Several fractionation schedules have been explored that developed over the past decades to increasingly more hypofractionated treatments. Moderate hypofractionated radiotherapy, as an alternative treatment, has gained clinical importance due to shorter duration and higher patient convenience. However, clinical trials show controversial results, adding to the need for pre-clinical radiobiological studies of this schedule.

Methods

We examined in comparative analysis the efficiency of moderate hypofractionation and normofractionation in four different NSCLC cell lines and fibroblasts using several molecular-biological approaches. Cells were daily irradiated with 24x2.75 Gy (moderate hypofractionation) or with 30x2 Gy (normofractionation), imitating the clinical situation. Proliferation and growth rate via direct counting of cell numbers, MTT assay and measurements of DNA-synthesizing cells (EdU assay), DNA repair efficiency via immunocytochemical staining of residual γH2AX/53BP1 foci and cell surviving via clonogenic assay (CSA) were experimentally evaluated.

Results

Overall, the four tumor cell lines and fibroblasts showed different sensitivity to both radiation regimes, indicating cell specificity of the effect. The absolute cell numbers and the CSA revealed significant differences between schedules (P < 0.0001 for all employed cell lines and both assays) with a stronger effect of moderate hypofractionation.

Conclusion

Our results provide evidence for the similar effectiveness and toxicity of both regimes, with some favorable evidence towards a moderate hypofractionation. This indicates that increasing the dose per fraction may improve patient survival and therapy outcomes.

3D-printed bolus ensures the precise postmastectomy chest wall radiation therapy for breast cancer

Purpose

To investigate the values of a 3D-printed bolus ensuring the precise postmastectomy chest wall radiation therapy for breast cancer.

Methods and materials

In the preclinical study on the anthropomorphic phantom, the 3D-printed bolus was used for dosimetry and fitness evaluation. The dosimetric parameters of planning target volume (PTV) were assessed, including D_min, D_max, D_mean, D_95%, homogeneity index (HI), conformity index (CI), and organs at risk (OARs). The absolute percentage differences (|%diff|) between the theory and fact skin dose were also estimated, and the follow-up was conducted for potential skin side effects.

Results

In preclinical studies, a 3D-printed bolus can better ensure the radiation coverage of PTV (HI 0.05, CI 99.91%), the dose accuracy (|%diff| 0.99%), and skin fitness (mean air gap 1.01 mm). Of the 27 eligible patients, we evaluated the radiation dose parameter (median(min–max): D_min 4967(4789–5099) cGy, D_max 5447(5369–5589) cGy, D_mean 5236(5171–5323) cGy, D_95% 5053(4936–5156) cGy, HI 0.07 (0.06–0.17), and CI 99.94% (97.41%–100%)) and assessed the dose of OARs (ipsilateral lung: D_mean 1341(1208–1385) cGy, V₅ 48.06%(39.75%–48.97%), V₂₀ 24.55%(21.58%–26.93%), V₃₀ 18.40%(15.96%–19.16%); heart: D_mean 339(138–640) cGy, V₃₀ 1.10%(0%–6.14%), V₄₀ 0.38%(0%–4.39%); spinal cord PRV: D_max 639(389–898) cGy). The skin doses in vivo were D_theory 208.85(203.16–212.53) cGy, D_fact 209.53(204.14–214.42) cGy, and |%diff| 1.77% (0.89–2.94%). Of the 360 patients enrolled in the skin side effect follow-up study (including the above 27 patients), grade 1 was the most common toxicity (321, 89.2%), some of which progressing to grade 2 or grade 3 (32, 8.9% or 7, 1.9%); the radiotherapy interruption rate was 1.1%.

Conclusion

A 3D-printed bolus can guarantee the precise radiation dose on skin surface, good fitness to skin, and controllable acute skin toxicity, which possesses a great clinical application value in postmastectomy chest call radiation therapy for breast cancer.

The value of the tumour-stroma ratio for predicting neoadjuvant chemoradiotherapy response in locally advanced rectal cancer: a case control study

BACKGROUND

The tumour-stroma ratio (TSR) is recognized as a practical prognostic factor in colorectal cancer. However, TSR assessment generally utilizes surgical specimens. This study aims to investigate whether the TSR evaluated from preoperative biopsy specimens by a semi-automatic quantification method can predict the response after neoadjuvant chemoradiotherapy (nCRT) of patients with locally advanced rectal cancer (LARC).

METHODS

A total of 248 consecutive patients diagnosed with LARC and treated with nCRT followed by resection were included. Haematoxylin and eosin (HE)-stained sections of biopsy specimens were collected, and the TSR was evaluated by a semi-automatic quantification method and was divided into three categories, using the cut-offs determined in the whole cohort to balance the proportion of patients in each category. The response to nCRT was evaluated on the primary tumour resection specimen by an expert pathologist using the four-tier tumour regression grade (TRG) system.

RESULTS

The TSR can discriminate patients that are major-responders (TRG 0-1) from patients that are non-responders (TRG 2-3). Patients were divided into stroma-low (33.5%), stroma-intermediate (33.9%), and stroma-high (32.7%) groups using 56.3 and 72.8% as the cutoffs. In the stroma-low group, 58 (69.9%) patients were major-responders, and only 39 (48.1%) patients were considered major-responders in the stroma-high group (P = 0.018). Multivariate analysis showed that the TSR was the only pre-treatment predictor of response to nCRT (adjusted odds ratio 0.40, 95% confidence interval 0.21-0.76, P = 0.002).

CONCLUSION

An elevated TSR in preoperative biopsy specimens is an independent predictor of nCRT response in LARC. This semi-automatic quantified TSR could be easily translated into routine pathologic assessment due to its reproducibility and reliability.