RapidArc can be used in several different ways as a radiation delivery tool. RapidArc is a device that delivers radiation by a method called VMAT - Volumetric Modulated Arc Therapy. This is a little different from conventional IMRT - Intensity Modulated Radiation Therapy. It has been used for prostate cancer in 4 different ways that I can think of:
1) If there is assurance that the cancer is still well contained, as in low risk cases, and with proper image-guidance, it can be used to deliver radiation with sub-millimeter accuracy to a tightly defined target. I was treated with it in this way, called SBRT. There were 5 treatments of 8 Gy each.
2) If there is assurance that the cancer is still well contained, as in low risk cases, it can be used to deliver radiation to the prostate in a conventional manner - 80 Gy delivered in about
40 treatments of 2 Gy each.
3) When metastases have been identified, it can be used to treat bone or lymph node mets, using it in the SBRT manner (5 treatments)
4) If there is suspicion that the cancer has already spread regionally,
but has not yet metastasized, as in some high risk cases, it can be used to deliver radiation to both the prostate and a wide area around it. When it is used this way, called combo therapy, the entire area may be given about
50 Gy, delivered in 25 treatments of 2 Gy each
and an extra dose, called a boost, is delivered to the prostate itself. The boost can be delivered with HDR brachy, LDR brachy or with the RapidArc alone.
Combo therapy seems to have the best outcomes in high risk cases, but carries a risk of higher amounts of SEs. At Memorial Sloan Kettering, 93% of high risk men treated with IMRT+HDR brachy boost had no detectable disease progression 5 years later.
Comparison of PSA relapse-free survival in patients treated with ultra-high-dose IMRT versus combination HDR brachytherapy and IMRT.Redwing57 and I are not clear about
which of the 4 different ways your RO is proposing to use RapidArc with you. If there are known bone mets, RapidArc will typically
not be used to treat the prostate along with HDR brachy, because the cancer is no longer regionally contained. The one exception might be if a C11 Pet scan has been used to identify 5 or fewer mets, and they can be treated along with combo therapy of the prostate region.