**10. Acknowledgements**

This work was supported by the National Natural Science Foundation of China (No. 81071237).

## **11. References**

82 Cancer of the Uterine Endometrium – Advances and Controversies

compared to both IMRT and tomotherapy. With respect to plan quality, it appears that tomotherapy can meet most of the dose-volume objectives, and can provide the most uniform dose to the PTV. For VMAT itself, the choice of 1 or 2 arcs represents a trade-off between plan quality and treatment time whereby single arc plans are expected to be deliverable in a shorter period of time. Adding an additional arc may improve the plan quality with an increase in the treatment time. However, a single arc that is delivered in less

VMAT reduces significantly the treatment time (beam on time) compared with both IMRT and tomotherapy. This in turn increases patient comfort, reduces patient motion and internal organ's displacement (e.g. bladder or rectum filling changes over time) during treatment. In addition to the shorter delivery time, VMAT is advantageous in its availability and versatility compared with helical tomotherapy. It can be implemented on the standard C-arm linacs, with wider utilization as, e.g., low and high energy photon beams, non-coplanar arcs in addition to dose rate, gantry speed and possibly collimator variations during delivery to better

The clinical interest of external beam radiotherapy for the gynecological cancer include the treatment of the primary site, and also the pelvic lymph nodes at various levels depending on stage, with proximity with highly sensitive OARs. As a result, gastrointestinal and genitourinary tracts are often highly involved and could lead to acute and late toxicities. The dose-volume objectives represent a significant challenge to the radiotherapy techniques, especially for the demanding cases. The dosimetric and clinical benefits of IMRT for postoperative WPRT have been demonstrated in endometrial cancer patients [8-9]. HT can deliver a more conformal dose to the target volume with greater degree of freedom of intensity modulation due to the helical pattern of dose delivery and unique binary MLC. The improved sparing of rectum and bladder of HT is expected to further reduce the acute and late toxicities, especially for the patients requiring local boost and concurrent/ sequential chemotherapy. However, these benefits of IMRT and HT are achieved generally at the cost of a greater volume of normal tissue in the irradiated volume receiving a low dose. Greater volume of pelvic bones exposed to a dose of 2-20 Gy could increase the risk of hematologic suppression [23] and bone fracture [24]. There has also been concern about the increase of normal tissue integral dose (ID) with multiple beams radiation therapy as a potential risk factor for the development of secondary malignancies in IMRT [25]. Given the life expectancy of the older patients with endometrial cancer, the risk of secondary cancers

The study published by D'Souza and Rosen [26] suggested that the total energy deposited in a patient is relatively independent of treatment planning parameters (such as beam orientation or relative weighting when many beams are used) for deep-seated targets, the ID to NT increases with increasing size of the anatomic region for similar tumor sizes, decreases with increasing size of targets for similar anatomic region size. HT slightly increased the ID to NT and pelvic bones in reference [18] compared with IMRT. This might be attributable to the larger and longer target volumes exposed to more radiation beams in the helical pattern of radiation delivery. This finding also suggests that one technique cannot be considered the "end-all" for everything, the advantage that HT has over IMRT is that while HT reduces the dose received by critical structures at the expense of a greater volume of normal tissue exposed to a low dose. Each approach should be evaluated in terms of the specific objectives when selecting the best option for a given patient. If the objective is to always minimize ID to normal tissue, protons are emerging as an important option [27-28].

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**Part 3** 

**Surgery and Staging** 

84 Cancer of the Uterine Endometrium – Advances and Controversies

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