Purpose: To determine the necessity of a first-week CT rescan of patients receiving pencil beam scanning proton therapy treatment to the prostate and pelvic lymph nodes.
Methods: 44 patients with high-risk prostate cancer requiring treatment to the prostate and pelvic lymph nodes were retrospectively evaluated. The cohort consisted of intact prostate and post-prostatectomy patients. Treatment regimens included initial fields followed by a sequential boost, as well as a simultaneous integrated boost approach (both with and without a sequential boost). Prescriptions varied depending on whether the patient had an intact prostate or prostate bed. Plan geometry consisted of two lateral beams. All patients received pencil beam scanning proton plans, which were created using a single field optimization dosimetric matching technique. Per an in-house protocol, all high-risk prostate patients had at least one rescan evaluation during the first seven fractions. This rescan was used to determine whether the nominal plan was robust to daily setup uncertainties and anatomical variations. If more than 5 percent of the rescans failed clinical evaluation and required adaptive plans, the early-treatment rescan protocol would continue and the planning technique would be investigated.
Results: Of the 44 patients, five (11.4 percent) required an adaptive plan. These cases were investigated for root cause, which revealed that all replanned patients would have been rescanned within the first five fractions independent of the protocol. In each case, a physician, dosimetrist, or therapist requested the rescans to investigate specific areas of concern, which ultimately lead to the replans. As a result, these cases do not demonstrate the utility of the rescan protocol.
Conclusion: Our findings indicate that the planning technique is sufficiently robust an early-treatment rescan protocol is unnecessary. The protocol did not identify any clinically significant issues that would not have been caught through other means.
Protons, Prostate Therapy, Radiation Therapy
TH- External Beam- Particle/high LET therapy: Proton therapy – sensitivity to daily treatment anatomical changes