ESTRO 2020 Abstract book

S835 ESTRO 2020

Minimum isodose coverage (Gy)

Low Risk (LR)

Moderate (MR)/Intermedia te risk (IR)

Dos e (Gy)

Protocol

Prostat e and SV base + 10mm Prostat e and SV base + 6mm Prostat e + 10mm/ 5 post Prostat e + 6mm / 3 post Prostat e + 5mm /0 post Prostat e + 3mm /0 post Prostat e + 10mm/ 7 post Prostat e + 5mm

Prostate + SV +10mm

CHHiP PTV1

48 45.6

CHHiP IGRT PTV1

Prostate + SV +6mm

48 45.6

Prostate

+

CHHiP PTV2

57.6 54.6

10mm/5 post

CHHiP IGRT PTV2

Prostate + 6mm /3 post

57.6 54.6

Prostate + 5 mm /0 post

CHHiP PTV3

60 57

CHHiP IGRT PTV3

Prostate + 3 mm /0 post

60 57

Prostate + proximal 1cm SV + 10 mm/7 post + proximal 1cm SV + 5mm + proximal 1cm SV + 3mm Prostate + SV + 6mm Prostate Prostate

CTV V60≥99%PT V V57≥99%

PROFIT PTV60

60

PACE PTV62

B

62 D98≥58.9G y

PIVOTALboo st PTV60 PIVOTALboo st PTV47

N/A

60 D98≥57Gy

N/A

47 D98≥44.65 Gy

Results Comparing the techniques showed more variations for the rectum then bladder. Lower doses (V24.6 – V40.8 Gy) to the rectum were more favourable for PACE and CHHiP IGRT plans. PROFIT and PACE plans tended to have highest rectal V57 – V60 doses compared with others (p ≤ 0.05). Bladder doses did not differ significantly across techniques (max dose volume change of 6.1%). Statistical significant bladder differences were seen only for PROFIT plans having higher bladder V60 than others and PACE IR plans higher than CHHiP IGRT (p ≤ 0.05). Penile bulb doses (Dmean, D2 %) were significantly higher (about twice as high) in CHHiP and PROFIT plans compared to the other techniques with their smaller margins.

Conclusion CHHiP and PROFIT plans gave less favourable dose to OARs than CHHiP IGRT, PACE and PIVOTALboost which the latter use smaller margins and reduced SV volume/doses. Comparing trials showed some significant differences which may play an important contributing factor in the level of toxicity experienced. This comparison may allow for a more informed decision regarding OAR doses given by the different trial protocols. PO-1468 Redefine the role of proton pencil beam scanning technique in the brain stereotactic radiosurgery G. Liu 1,2,3 , X. Li 1 , P. Chinnaiyan 1 , L. Zhao 1 , D. Yan 1 , C. Stevens 1 , P. Kabolizadeh 1 , X. Ding 1 1 Beaumont Health Proton Therapy Center, Radiation Oncology, Royal Oak, USA ; 2 Huazhong University of Science and Technology, Tongji Medical College, Wuhan, China ; 3 Cancer Center- Union Hospital-, Radiation Oncology, Wuhan, China