New Guidelines for Salvage Radiation Dimensions

It has always been troubling that only about half of all salvage radiation treatments after prostatectomy failure are successful. Usually, only the prostate bed is treated. But sometimes recurrent patients (or those with persistently elevated PSA) receive salvage radiation to the pelvic lymph nodes as well, or subsequently. Radiation oncologists usually follow RTOG (now called NRG Oncology) guidelines on what constitutes the dimensions of the prostate bed and the pelvic lymph nodes.

Prostate Bed Coverage

Often, the cancer has only penetrated into the bed or fossa. This is especially suspected if there are significant positive surgical margins. The 2010 RTOG consensus guidelines were updated in 2020 by the Francophone Group of Urological Radiotherapy (GFRU) based on standard imaging (MRI and CT). (Update 5/12/23) Dal Pra et al. Harmon et al. reported on 45 patients within the LOCATE trial who received a positive Axumin PET/CT upon recurrence or persistent PSA after prostatectomy.

• 30 patients had cancer in the prostate fossa
• The 2010 RTOG guidelines completely or partially missed cancer in 33% of the patients
• The 2020 GFRU guidelines completely or partially missed cancer in 10% of the patients

The new GFRU guidelines are clearly superior in terms of oncological outcomes, but toxicity must be considered as well.

Pelvic Lymph Node Coverage

In 2020, NRG Oncology revised its previous 2009 RTOG pelvic lymph node coverage consensus guidelines based on MRI and PET scans. They recommended coverage as high as the aortic bifurcation or common iliac lymph nodes (whichever is higher, depending on patient anatomy), which is about the level of the L4-L5 vertebrae. The expanded coverage area extends down to the pre-sacral nodes at the bottom of vertebra S3. Harmon et al. also validated the expanded NRG Oncology guidelines based on Axumin PET/CT scans. They found:

• There were 43 sites of cancer in the pelvic lymph nodes
• The 2009 RTOG guidelines completely or partially missed 32% of the nodal cancers
• The 2020 NRG Oncology guidelines completely or partially missed none of the nodal cancers

The SPPORT trial found that treating pelvic lymph nodes prophylactically improved outcomes with no increase in late-term genitourinary or gastrointestinal toxicity, and only minor increases in the short-term. This study did not examine the toxicity of the expanded coverage.  Careful contouring of the pelvic lymph node area to exclude bowel, bone, bladder, and muscle seems to prevent excess toxicity at the doses usually used (45-50.4 Gy). In one recent study of high-risk patients, a pelvic lymph node dose as high as 56 Gy was used without extra toxicity. Also there have been no second pelvic malignancies due to the expanded coverage in this study.

 Boosted site doses can also be utilized where PET/CT  or MRI has identified specific tumors. However, treatment should not be delayed until such tumors become apparent on imaging.