1 Cervix Cancer

18FDG PET/CT is routinely used in the staging of primary cervix cancer for assessment of nodal involvement and distant metastasis (Fig. 12.1). A sensitivity and specificity of 83% and 95%, respectively, has been shown for detecting pelvic lymph node metastasis [1]. Whilst the sensitivity and specificity for para-aortic microscopic nodal disease is inferior, PET/CT has been incorporated into the radiotherapy planning process, primarily as an aid to defining nodal disease for dose escalation but also for GTV definition.

Fig. 12.1
figure 1

Fused FDG-PET/CT for staging of cervical cancer demonstrating primary tumour and extensive lymphadenopathy extending from the pelvis to supraclavicular fossa

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PET/CT-based GTV delineation has been compared to MRI both to define the superior border of pelvic/ para-aortic fields and in defining the primary target. The optimum SUVmax threshold for delineation is a subject of ongoing studies. Upasani et al. [2] have described a 30% SUVmax to have the best correlation with MRI-based primary tumour volume; others have utilised an SUVmax of 40% [3].

The main use of PET/CT in cervix radiotherapy planning has been the identification of lymph node targets for boosting dose (Fig. 12.2). Grigsby et al. [4] have reported 208 patients safely escalating dose to PET-positive pelvic lymph nodes 2–3 cm in size to 69.4 Gy, >3 cm to 74.1 Gy, using a concomitant IMRT boost technique to simultaneously irradiate uninvolved lymph node chains. The nodal failure rate was <2%. Others have performed planning studies to model dose escalation up to 60 Gy whilst maintaining dose constraints to organs at risk [5, 6]. Clinical evidence for a dose response and optimal boost dose are however lacking.

Fig. 12.2
figure 2

Fusion of planning CT and PET to aid target delineation in a case of para-aortic nodal relapse. Non-contrast CT does not demonstrate the target well; fusion of PET imaging allows accurate depiction of target volume

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Although MRI is established as the gold standard for brachytherapy planning, a few studies have assessed the use of PET. Malyapa et al. [7] reported the feasibility of performing PET with brachytherapy applicators in place. Lin et al. [8] compared PET-based dosimetry to the target volume with standard imaging and concluded that PET-based planning led to enhanced dose optimisation without increasing dose to organs at risk.

PET has also been studied to assess response during radiotherapy leading to adaptive planning based on functional volumes. Early lymph node complete response at 3 weeks can be correlated with an excellent prognosis [9] and local control [10]. These findings support the use of dose de-escalation in cases of initial good functional response, whilst poorly responding nodes and primary tumours can have plans adapted to escalate dose further.

2 Endometrial Cancer

The use of PET is less well established for endometrial cancer compared to cervical cancer. Its use lies mainly in the diagnosis of pelvic and distant metastatic disease, aiding decisions about pelvic lymph node dissection and in assessing local disease. As most radiotherapy delivered for endometrial cancer is delivered to the post-operative pelvis, no role for the use of PET in RT planning has yet been explored.

3 Novel PET Tracers

C-choline has the advantage of reduced urinary uptake, facilitating primary tumour identification in cervical cancer but with increased bowel uptake hampering nodal disease assessment. Comparison of 64Cu-ATSM and 60Cu-ATSM in cervix cancer found a better image quality with 64Cu-ATSM, because of lower noise, and concluded that 64Cu-ATSM appeared to be a safe radiopharmaceutical with high-quality images of tumour hypoxia. These hypoxic tracers may facilitate further clinical studies of functional dose painting in cervix cancer.

PET/CT is well established in the radiotherapy pathway for cervix cancer as a staging tool and for assessment of response. Increasingly it is incorporated into radiotherapy planning as a functional target for dose escalation.

Key Points

Cervix Cancer

  • 18FDG PET/CT is routinely used in the staging of primary cervix cancer for assessment of nodal involvement and distant metastasis.

  • PET/CT has been incorporated into the radiotherapy planning process, primarily as an aid to defining nodal disease for dose escalation, but also for GTV definition.

  • PET/CT-based GTV delineation has been compared to MRI both to define the superior border of pelvic/para-aortic fields and in defining the primary target.

  • The main use of PET/CT in cervix radiotherapy planning has been the identification of lymph node targets for boosting dose. PET-based planning led to enhanced dose optimisation without increasing dose to organs at risk.

  • PET has also been studied to assess response during radiotherapy leading to adaptive planning based on functional volumes.

Endometrial Cancer

  • Most radiotherapy delivered for endometrial cancer is delivered to the post-operative pelvis; no role for the use of PET in RT planning has yet been explored.