Acute haematological toxicity is a known side effect of chemo-radiotherapy with a 30-45% incidence rate when fields encompass bone marrow (BM). Extended-field radiation therapy (EF-RT) for gynaecological cancers irradiates BM in the lumbar spine and pelvis. However, BM is not routinely defined as an organ at risk (OAR) with constraints to minimise dose during the radiation therapy (RT) treatment planning process.
In 2019, one cervical cancer patient receiving EF-RT experienced grade 3 anaemia and thrombocytopenia, grade 4 leukopenia, neutropenia and lymphopenia. This required >20 blood product transfusions, a month-long hospital admission and multiple treatment breaks. This highlighted a quality improvement (QI) need to reduce haematological toxicity for future EF-RT patients.
A planning study was conducted utilising three previous EF-RT patient CT datasets. Pelvic BM contouring definitions and dose constraints were determined from a literature review. These were also applied to the Lumbar BM due to a lack of specific lumbar constraints. Treatment plans were re-optimised incorporating the BM constraints with comparison to the original treated plans. The Lumbar BM showed the largest dose reductions, in V10, V20, V30 and V40 reduced by 15.8%, 24.6%, 16.2% and 8.9% respectively. The V10 and V20 doses to the Pelvic BM demonstrated small reductions while the V30 and V40 remained consistent. Target volume coverage and doses to other OARs were maintained within clinically acceptable tolerances.
CT-based BM sparing was deemed feasible and selected for expedited implementation. Gynecological RT planning guidelines were updated to include BM objectives, and a progressive implementation followed over a 24-month period as follows: (i) EF-RT patients, (ii) all concurrent chemotherapy gynaecological patients, (iii) all gynaecological patients. Quality assurance procedures and multidisciplinary review are conducted on all plans to ensure quality standards are maintained before approval for treatment delivery.
A retrospective audit is currently ongoing, aiming to demonstrate the clinical impact of the implementation of this new planning technique on BM dose and haematological toxicity.
Future QI includes investigating MRI-based active BM delineation and identifying biological predictors for haematological toxicity.