Volumetric modulated arc therapy for prostate cancer patients with hip prosthesis

Abstract

Aim

To study the use of RapidArc techniques in the treatment of prostate cancer patients with hip prosthesis.

Background

An important aspect of treatment planning is to achieve dose homogeneity inside the planning target volume (PTV). Especially for those patients presenting with hip prosthesis, it becomes a challenging task to achieve dose uniformity inside the PTV.

Materials and methods

Five prostate patients presenting with hip prosthesis who had undergone radical radiotherapy were selected for this study. Depending on the composition of prosthesis, a predefined set of Hounsfield values were assigned to each study set. RapidArc plans were generated on an Eclipse treatment planning system. Two arcs that include clockwise and counter-clockwise arcs were used in all these cases. To avoid beams passing through the prosthesis, a simple structure was defined around it with 1[[ce:hsp sp="0.25"/]]cm margin and a strict dose constraint applied to the block during VMAT optimization.

Results

The mean D2/D98 ratio of PTV for all the patients was 1.06[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.01. The mean percentage rectum volume receiving 50[[ce:hsp sp="0.25"/]]Gy, 60[[ce:hsp sp="0.25"/]]Gy, 70[[ce:hsp sp="0.25"/]]Gy and 75[[ce:hsp sp="0.25"/]]Gy for all the patients were 33.1[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]5.9, 21.7[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]5.5, 13.8[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]4.4 and 9.5[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]3.0, respectively.

Conclusions

This study shows that using a double arc RapidArc technique is a simple and effective treatment method of treating prostate cancer in patients presenting with a hip prosthesis. The definition of a beam avoidance structure encompassing the prosthesis and applying strict dose constraints to it reduces the beam contribution to the prosthesis