A treatment planning strategy for heavy-charged-particle radiotherapy of lung cancer by the use of computed tomography with projection data-based temporal maximum-intensity projection.

To design a range-compensating bolus for heavy-charged-particle radiotherapy of lung cancer, we propose an image-processing method that uses CT projection data for treatment planning. We studied six lung cancer patients in 4DCT mode. Three types of range-compensating bolus were designed with use of (1) each bolus for 4DCT images, (2) image-based maximum-intensity projection data (4DIM), and (3) CT images reconstructed by the use of maximum-attenuation projection data (4DPM) along the time axis around exhale (=respiratory-gated treatment). Carbon-ion dose distributions were calculated by the use of these designed range-compensating boluses and were compared. The dose distribution with 4DIM caused overdosing beyond the target. However, the dose distribution with 4DPM was similar to that with a composite of the range-compensating bolus (CCB) designed for the respiratory phases. Furthermore, the volume of the receiving dose for >95% (D95) for CTV and the volume of the lung receiving dose for >20 GyE (V20) with 4DPM were similar to that with the CCB. The range-compensating bolus with 4DPM provides dose distributions similar to that with the CCB in peripheral lung cancer and improves the calculating efficiency over CCB.