Value of FDG-PET/CT Examinations in Different Cancers of Children, Focusing on Lymphomas

Diagnosis and management of lymphoblastic lymphoma in children, adolescents and young adults

Lymphoblastic lymphoma (LBL) is the second most common type of non-Hodgkin Lymphoma (NHL) in children, adolescents, and young adults (CAYA), accounting for 25-35% of all cases. T-lymphoblastic lymphoma (T-LBL) comprises 70-80% of cases, while precursor B-lymphoblastic lymphoma (pB-LBL) makes up the remaining 20-25% of cases. Event-free and overall survival (EFS and OS) for paediatric LBL patients both exceed 80% with current therapies. Treatment regimens, especially in T-LBL with large mediastinal tumours, are complex with significant toxicity and long-term complications. Though prognosis overall is good for T-LBL and pB-LBL with upfront therapy, outcomes for patients with relapsed or refractory (r/r) disease remain dismal. Here, we review new understanding about the pathogenesis and biology of LBL, recent clinical results and future directions for therapy, and remaining obstacles to improve outcomes while reducing toxicity.

Lymphoblastic lymphoma in children and adolescents: review of current challenges and future opportunities

Lymphoblastic lymphoma (LBL) is the second most common type of Non-Hodgkin Lymphoma (NHL) in childhood and adolescence, accounting for 25-35% of all cases. The majority, 70-80%, is of T-lymphoblastic origin while 20-25% arise from B lymphoblasts. With current therapy, the event-free and overall survivals for paediatric LBL patients now exceeds 80%. Therapy, especially in T-LBL with large mediastinal tumours, is challenging, with both significant morbidity and late sequela. An additional challenge is the dismal prognosis of patients with refractory or relapsed disease. This review article will focus on the growing knowledge of the pathogenesis and biology of LBL, recent advances and challenges in the therapy of LBL, and ongoing and future efforts and opportunities in optimizing therapy and developing novel targeted treatment approaches.

Use of PET/CT instead of CT-only when planning for radiation therapy does not notably increase life years lost in children being treated for cancer

BACKGROUND

PET/CT may be more helpful than CT alone for radiation therapy planning, but the added risk due to higher doses of ionizing radiation is unknown.

OBJECTIVE

To estimate the risk of cancer induction and mortality attributable to the [F-18]2-fluoro-2-deoxyglucose (FDG) PET and CT scans used for radiation therapy planning in children with cancer, and compare to the risks attributable to the cancer treatment.

MATERIALS AND METHODS

Organ doses and effective doses were estimated for 40 children (2-18 years old) who had been scanned using PET/CT as part of radiation therapy planning. The risk of inducing secondary cancer was estimated using the models in BEIR VII. The prognosis of an induced cancer was taken into account and the reduction in life expectancy, in terms of life years lost, was estimated for the diagnostics and compared to the life years lost attributable to the therapy. Multivariate linear regression was performed to find predictors for a high contribution to life years lost from the radiation therapy planning diagnostics.

RESULTS

The mean contribution from PET to the effective dose from one PET/CT scan was 24% (range: 7-64%). The average proportion of life years lost attributable to the nuclear medicine dose component from one PET/CT scan was 15% (range: 3-41%). The ratio of life years lost from the radiation therapy planning PET/CT scans and that of the cancer treatment was on average 0.02 (range: 0.01-0.09). Female gender was associated with increased life years lost from the scans (P < 0.001).

CONCLUSION

Using FDG-PET/CT instead of CT only when defining the target volumes for radiation therapy of children with cancer does not notably increase the number of life years lost attributable to diagnostic examinations.

PET/CT-guided treatment planning for paediatric cancer patients: a simulation study of proton and conventional photon therapy

OBJECTIVE

To investigate the impact of including fluorine-18 fludeoxyglucose ((18)F-FDG) positron emission tomography (PET) scanning in the planning of paediatric radiotherapy (RT).

METHODS

Target volumes were first delineated without and subsequently re-delineated with access to (18)F-FDG PET scan information, on duplicate CT sets. RT plans were generated for three-dimensional conformal photon RT (3DCRT) and intensity-modulated proton therapy (IMPT). The results were evaluated by comparison of target volumes, target dose coverage parameters, normal tissue complication probability (NTCP) and estimated risk of secondary cancer (SC).

RESULTS

Considerable deviations between CT- and PET/CT-guided target volumes were seen in 3 out of the 11 patients studied. However, averaging over the whole cohort, CT or PET/CT guidance introduced no significant difference in the shape or size of the target volumes, target dose coverage, irradiated volumes, estimated NTCP or SC risk, neither for IMPT nor 3DCRT.

CONCLUSION

Our results imply that the inclusion of PET/CT scans in the RT planning process could have considerable impact for individual patients. There were no general trends of increasing or decreasing irradiated volumes, suggesting that the long-term morbidity of RT in childhood would on average remain largely unaffected.

ADVANCES IN KNOWLEDGE

(18)F-FDG PET-based RT planning does not systematically change NTCP or SC risk for paediatric cancer patients compared with CT only. 3 out of 11 patients had a distinct change of target volumes when PET-guided planning was introduced. Dice and mismatch metrics are not sufficient to assess the consequences of target volume differences in the context of RT.