Influence of target dose heterogeneity on dose sparing of normal tissue in peripheral lung tumor stereotactic body radiation therapy

Evaluation of the influence of radiation-induced cohort effect in cell populations receiving different doses

PURPOSE

A non-targeted effect called radiation-induced cohort effect, which results in interactions among irradiated neighboring cells through cellular communication, has been reported. In high-precision radiotherapy, the dose is localized to the tumor, and rapid spatial changes occur in dose distribution. However, the effect of irradiating a population of cells with non-uniform doses remains unknown. In this study, we evaluated the influence of cohort effect by creating cell populations irradiated with different doses using human oral squamous cell carcinoma (SAS) and human lung (A549) cells.

MATERIALS AND METHODS

Cell populations irradiated with different doses were created in two ways: direct contact co-culture (DCC) using a cell tracer dye and indirect contact co-culture (ICC) using cell culture inserts to assess the effects of soluble factors. Target cells were irradiated with 4 Gy and co-cultured cells with 0, 0.8, 3.2, and 4 Gy. In DCC, cell proliferation assays were performed using a flow cytometer, and in ICC, modified high-density survival, clonogenic, and apoptosis assays were performed.

RESULTS

In DCC, irradiation of co-cultured cells with X-rays increased the relative proliferation rate of the target cells. Similarly, irradiating co-cultured cells using ICC with X-rays increased the relative survival rate of target cells.

CONCLUSIONS

The results of this study showed that, even if there is a sharp decrease in dose near the tumor, the cytocidal effect on the tumor is not adversely affected. In addition, soluble factors were found to be involved in cohort effect.

Stereotactic Radiation Therapy Planning, Dose Prescription and Delivery in Veterinary Medicine: A Systematic Review on Completeness of Reporting and Proposed Reporting Items

Increasing numbers of dogs and cats with cancer are treated with stereotactic radiosurgery, stereotactic radiation therapy or stereotactic body radiotherapy (SRS, SRT or SBRT). We provide a systematic review of the current data landscape with a focus on technical and dosimetric data of stereotactic radiotherapy in veterinary oncology. Original peer-reviewed articles on dogs and cats with cancer treated with SRT were included. The systematic search included Medline via PubMed and EMBASE. The study was performed according to the Preferred Reporting Items for Systematic Reviews (PRISMA) statement. We assessed the manuscripts regarding outcome reporting, treatment planning, dose prescription, -delivery and -reporting as well as quality assurance. As of February 2024, there are 80 peer-reviewed publications on various disease entities on SRS, SRT and SBRT in veterinary medicine. Overall, we found often insufficient or highly variable technical data, with incomplete information to reproduce these treatments. While in some instances, technical factors may not impact clinical outcome, the variability found in protocols, outcome and toxicity assessments precludes accurate and reliable conclusions for a benefit of stereotactic radiotherapy for many of the treated diseases. In line with the extensive recommendations from human stereotactic radiotherapy practise, we propose a draft of reporting items for future stereotactic radiation treatments in veterinary medicine. SRS, SRT and SBRT have specific clinical and technological requirements that differ from those of standard radiation therapy. Therefore, a deep understanding of the methodologies, as well as the quality and precision of dose delivery, is essential for effective clinical knowledge transfer.

Dosimetric comparison in sparing normal tissue dosage by using auto-SBRT planning in oligo liver tumors

Purpose

The study aimed to compare the dosimetric distribution of VMAT plans by increasing the number of half arcs in liver SBRT and investigate the effect by using automatic plan software in plan optimization.

Method

Thirty-one patients with oligo liver tumors were randomly selected. VMAT treatment plans with different numbers of coplanar half arcs were generated.

Result

Adding arcs significantly increased the PTV, D2%, D50%, and CI, but sacrificed the plan homogeneity. It also decreased the maximum dose of normal tissues such as the stomach, duodenum, and spinal cord and reduced Dmean, D500cc, and D700cc for the liver. Nevertheless, the diminishing effect gradually decayed into three arcs. Meanwhile, the addition of arcs substantially extended the beam-on time.

Conclusion

In the context of SBRT for oligo liver tumors, increasing the number of coplanar half arcs will improve PTV conformity and offer better protection for OARs, albeit at the expense of increased treatment duration. Considering the trade-off between plan quality and treatment efficiency, a three-arc plan may be more suitable for clinical implementation.

Alternating Expiration and Inspiration Breath-Hold Spares the Chest Wall During Stereotactic Body Radiation Therapy for Peripheral Lung Malignancies

PURPOSE

The proximity of tumors to the chest wall brings additional risks of chest wall pain during stereotactic body radiation therapy. Herein, we dosimetrically compared alternated breath-hold (ABH) plans with single BH plans and determined the common characteristics of eligible patients who may obtain better chest wall sparing using this technique.

METHODS AND MATERIALS

Twenty patients with lung lesions adjacent to the chest wall were enrolled and received respiratory training. Their half-fraction end expiration BH and deep inspiration BH plans were summed to generate the ABH plans. Dosimetric parameters of the chest wall were compared between single and alternated BH plans, and the correlation between tumor location and the outcome of chest wall sparing was quantitatively evaluated. Pretreatment cone beam computed tomography variations in eligible patients were recorded as well.

RESULTS

Compared with the end expiration BH and deep inspiration BH plans, the ABH plans reduced chest wall dosimetric results with median reductions of 2.0% and 3.9% (Dmax: maximum point dose), 15.4% and 14.8% (D1cc: dose to a volume of 1 cm³), and 48.8% and 63% (V30: volume receiving 30 Gy or more), respectively. Relative tumor displacements (ratio of tumor displacement in the superior-inferior direction to planning target volume diameter) were greater in the lower lobe than in the upper and middle lobes (1.17 vs 0.18). Meanwhile, better median reductions of 44% (Dmax), 46% (D1cc), and 98% (V30) were obtained in the lower lobe cohort using the ABH technique. Pretreatment variations for all BHs met the 5-mm threshold.

CONCLUSIONS

The ABH technique can significantly spare the adjacent chest wall without compromising planning target volume coverage in comparison with the single BH, and patients with tumors in the lower lobes can obtain better chest wall sparing than in the upper and middle lobes. Further investigation is warranted to validate these findings.