Radiation Dose and Technique

**Radiation Dose and Technique**
	In the past, when using external beam radiation, the whole pelvis was treated to a dose of approximately 5000cGy (for the purpose of hitting the lymph nodes and adjacent areas where there may be early spread) and then an additional 1600 to 2000cGy was given to a small field (boost field) designed to hit only the prostate with a small area around it (often to include the seminal vesicles). As noted below the recommended dose is now up to 7500 - 8000cGy (go here). See the IMRT section here

Most studies that have looked at the field size have not shown a significant benefit from treating the larger field (including the RTOG trial 77-06 Int J Radiat Oncol Biol Phys 1998 Mar 1;40(4):769-782 ) Nevertheless many radiotherapists still treat the pelvis and pelvic nodes except in patients with very early stage disease (low PSA and low Gleason score.)

Similarly, the proper dose of radiation is still unsettled. In the past doses in the range of 6000 to 6600 where considered as high as safe. With 3D conformal therapy or IMRT it is possible to use higher doses safely (well over 7200cGy) and with apparent benefit (at least in high risk patients with PSA > 10) as noted below. (see data here.) (see NCCN guidelines.)

The randomized dose trial from MD Anderson (Pollack on the left) showed that high risk patients need a high dose but lower risk patients probably do well with doses of about 70Gy. (Go here for update).

A number of other papers make the case for higher doses of radiation using 3D (see section on dose.) As noted we treat all patients with conformal therapy or IMRT but have preferred to use more modest doses of external beam irradiation 7560cGy) and in high risk patients (who may benefit from more aggressive therapy) add hormonal therapy or use combined external beam plus seeds for those patients .

(The preliminary data from RTOG 94-06 showed that 79.2Gy was safe using 3D conformal. Ryu IJROBP;51:136)

Our standard techniques are as noted.

IMRT techniques will allow for even higher dose of radiation to be safely given (an MD Anderson trial compared IMRT to conformal therapy and found "The volume of rectum irradiated above 70 Gy was 23-50% less for the IMRT plans compared to the conformal plans. The bladder volume irradiated above 70 Gy was up to 30% less for the IMRT plans. The mean doses to prostate were 4-5% higher for IMRT compared to 3DCRT" Dong IJROBP 2001;51:320)