Multiple trials have shown that dose-escalation of radiation for prostate cancer provides a biochemical progression-free survival benefit (bPFS); however, rectal constraints are often limiting. In this dosimetric study, we hypothesized that a well-placed rectal hydrogel (RH) would permit improved dose-escalation and target coverage.
We selected patients with good-quality RH and created plans with and without RH, prescribing 70 Gy in 28 fractions to the prostate and proximal seminal vesicles (PSV), and a peripheral zone (PZ) boost to 84 Gy, 98 Gy, or 112 Gy. We then compared plans with and without RH, prescribing a 112 Gy boost to 1 to 2 cm simulated dominant intraprostatic lesions (DIL). In the 18 plans created with a PZ boost, the PTV_boost D95% was higher in RH plans compared to non-RH plans (median 98.5 Gy vs 75.53 Gy, p < 0.01). The PSV planning target volume (PTV_PSV) D95% was also marginally higher with RH (71.87 Gy vs 71.04 Gy, p < 0.01). All rectal metrics were improved with RH. For the 32 plans created for simulated DILs treated to 112 Gy, the PTV_boost coverage (median D95% 112.48 Gy vs 102.63 Gy, p < 0.01) and rectal metrics were improved with RH. Four non-RH plans with at least a 4 mm rectal-PTV_boost gap achieved D95% > 98% of the prescription dose for the PTV_boost. Our study showed that placement of a high-quality RH allowed for GEDE-EBRT up to 112 Gy in 28 fractions (EQD2 160 Gy with α/β = 2.5). This concept should be tested prospectively, particularly to assess for increases in nonrectal toxicities.
Medical dosimetry : official journal of the American Association of Medical Dosimetrists. 2023 Sep 02 [Epub ahead of print]
Jamie S K Takayesu, Paul Heckman, Eric Short, Patrick Hurley, Vrinda Narayana, Patrick W McLaughlin
Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, USA. Electronic address: ., Department of Radiation Oncology, Assarian Cancer Center, Ascension Providence Hospital, Novi, MI, USA., Department of Urology, Ascension Providence Hospital, Novi, MI, USA., Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, USA.
PubMed http://www.ncbi.nlm.nih.gov/pubmed/37666707