From the Guidelines
The primary radiation constraint for the spleen is typically a mean dose of ≤5 Gy, as exceeding this dose can lead to reduced immune function, increased susceptibility to infections, and potential need for antibiotic prophylaxis. When planning radiation therapy near the spleen, oncologists aim to keep the average radiation dose to the entire organ below this threshold. To achieve this, radiation oncologists use techniques like:
- Intensity-modulated radiation therapy (IMRT)
- Image-guided radiation therapy (IGRT)
- Respiratory gating These methods help shape the radiation beam and minimize exposure to the spleen while targeting nearby tumors. However, the provided evidence does not directly address the radiation constraints for the spleen, but rather focuses on dose-volume constraints for other organs such as the lungs, esophagus, and spinal cord 1. In the context of real-life clinical medicine, it is essential to prioritize caution and adhere to established guidelines for radiation exposure near the spleen, even if the provided evidence does not explicitly state these constraints. The spleen's high sensitivity to radiation necessitates careful planning and monitoring to minimize potential risks, including reduced immune function and increased infection susceptibility. In cases where higher doses to the spleen are unavoidable, close monitoring of blood counts and immune function may be necessary during and after treatment, as supported by general medical knowledge and principles of radiation oncology. Patients may need to be counseled about increased infection risks and the importance of prompt medical attention for fevers or other signs of infection. Given the lack of direct evidence on spleen radiation constraints in the provided study, the recommendation is based on general medical knowledge and principles of radiation oncology, prioritizing caution and patient safety.
From the Research
Radiation Exposure Constraints Near the Spleen
The constraints for radiation exposure near the spleen are crucial to prevent long-term splenic dysfunction and potentially fatal late sepsis 2.
- The risk of radiation-induced splenic injury is significant, and there is currently no corresponding protective strategy 3.
- A threshold dose of 40 Gy is often cited, but the risk of mortality from overwhelming infection is poorly recognised 2.
- It is recommended to keep the mean spleen dose as low as reasonably achievable, ideally <10 Gy, without compromising target volumes 2.
- Spleen doses received in practice are often in excess of 10 Gy, and more than half of patients assessed received spleen doses above this level 2.
- A relative mortality risk of 5.5 has been reported with spleen doses in the 10-20 Gy range 2.
Low-Dose Radiation Therapy
Low-dose radiation therapy has been used to treat symptomatic splenomegaly, with effective results and a low rate of side effects 4, 5, 6.
- Doses per fraction of 0.5 Gy every two days, with a total dose of 10 Gy, have been used to treat symptomatic splenomegaly 4.
- Splenic pain and abdominal discomfort have been shown to improve with low-dose radiation therapy, and cytopenias have risen to secure levels 4, 6.
- Short-time irradiation schedules with conventional dosage (2 Gy/fraction) have been compared to low-dose prolonged treatment schedules (<1 Gy/fraction), with both showing efficacy in relieving splenomegaly-associated symptoms 5.
Radiation-Induced Splenic Injury
Radiation-induced splenic injury can be alleviated by the use of a novel compound preparation named CB001, which has been shown to ameliorate white pulp atrophy and excessive apoptosis in spleen tissue induced by radiation exposure 3.
- The radio-protective activity of CB001 involves the BAX-caspase-3 signaling and NLRP3 inflammasome signaling pathways 3.
- The crosstalk between apoptosis signaling and NLRP3 inflammasome signaling in mediating the radio-protective activity of CB001 has been clarified, with the pro-apoptotic protein BAX found to be downstream of NLRP3 3.