Session Item

A detailed dosimetric comparison of the intensity-modulated-arc-therapy (IMAT), CyberKnife therapy (CK), single fraction interstitial high-dose-rate (HDR) and low-dose-rate (LDR) brachytherapy (BT) in low-risk prostate cancer.

Treatment plans of twenty patients treated with CK were selected and additional plans using IMAT, HDR and LDR BT were created on the same CT images (Figure). The prescribed dose was 2.5/70Gy in IMAT, 8/40Gy in CK (according to an ongoing phase II prospective trial at our institute), 21Gy in HDR and 145Gy in LDR BT to the prostate gland (according to our PROMOBRA prospective randomized study). EQD2 dose-volume parameters were calculated for each technique and compared using Friedman ANOVA and Fisher-LSD post-hoc tests. 1 year was estimated in LDR BT as overall treatment time, as during this time 89% of the prescribed dose is delivered.

EQD2 total dose of the prostate was significantly lower with IMAT and CK than with HDR and LDR BT, D90 was 79.5Gy, 116.4Gy, 169.2Gy and 157.9Gy (p<0.001), respectively. However, teletherapy plans were more conformal than BT, COIN was 0.84, 0.82, 0.76 and 0.76 (p<0.001), respectively. The D₂ to rectum and bladder were lower with HDR BT than with IMAT, CK or LDR BT, it was 66.7Gy, 68.1Gy, 36.0Gy and 68.0Gy (p=0.0427), and 68.4Gy, 78.9Gy, 51.4Gy and 70.3Gy (p=0.0091) in IMAT, CK, HDR and LDR BT plans, while D_0.1 to urethra was lower with both IMAT and CK than with BTs: 79.9Gy, 88.0Gy, 132.7Gy and 170.6Gy (p<0.001). D₂ to hips was higher with IMAT and CK, than with BTs: 13.4Gy, 20.7Gy, 0.4Gy and 1.5Gy (p<0.001), while D₂ to sigmoid, bowel bag, testicles and penile bulb was higher with CK than with the other techniques (Table).

Using single fraction HDR and LDR BT, total dose of the prostate is higher than with IMAT or CK techniques, and accordingly dose to urethra is also higher with both BT modalities using the recommended fractionation scheme. Dose to rectum and bladder is lower with HDR BT than with IMAT, CK or LDR BT, while dose to sigmoid, bowel bag, testicles and penile bulb are higher with CK than using the other examined techniques. Overall, HDR monotherapy yields the most advantageous plans, except for the dose to urethra, where IMAT proves to be the optimal modality in the radiotherapy of low- and selected intermediate risk prostate cancer.

This paper was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences and the ÚNKP-18-4 New National Excellence Program of the Ministry of Human Capacities.