Tumour Shrinkage during Proton-based Chemoradiation for Non–small-cell Lung Cancer May Necessitate Adaptive Replanning during Treatment

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W Shi, RC Nichols, S Flampouri, W Hsi, Z Li, RH Henderson, NP Mendenhall, B Hoppe

Hong Kong J Radiol 2011;14:190-4

This study aimed to evaluate the dosimetric impact of tumour shrinkage during proton-based chemoradiotherapy. This dosimetric study describes a patient who presented with synchronous bilateral T2 non–small-cell lung cancers with no clinical or radiographical evidence of nodal or haematogenous dissemination. The patient was treated with three-dimensional conformal proton radiotherapy to an internal target volume dose of 75.6 Cobalt Gray Equivalent with concomitant weekly chemotherapy (paclitaxel 50 mg/m2 and carboplatin AUC 2). Computed tomographic scans were performed weekly to evaluate tumour shrinkage and density changes. Composite plans were generated with and without weekly adaptive replanning. During the course of proton radiation, tumour shrinkage of up to 80% was noted. With replanning, the initial target-volume coverage was maintained, while the spinal cord, oesophagus, and lung doses remained equal to or below initially planned levels. Although the target dose coverage was not compromised, without replanning, the actual doses to certain normal tissues would have exceeded the initial planned estimates by 250%. Tumour regression and density change during a course of proton-based chemoradiotherapy can substantially impact dosimetry. Close monitoring of tumour regression during the treatment course is crucial. Physicians and physicists treating lung cancer patients with protons should be open to adaptive replanning during treatment so as to maintain target volume coverage and minimise the risk of normal-tissue overexposure.




W Shi、 RC Nichols、 S Flampouri、W Hsi、Z Li、RH Henderson、NP Mendenhall、 B Hoppe

本研究評估質子放化療治療過程中,腫瘤萎縮對於放化療劑量的影響。本文報告一宗雙側同時患有 T2期非小細胞肺癌的病例。病人病發時並無臨床或放射性淋巴結或血原性散播,遂接受三維質子 適形放射治療。起初內靶體積劑量為75.6 CGE,同時配合每週化療(paclitaxel 50 mg/m2及carboplatin AUC 2)。每星期為病人進行CT掃瞄評估腫瘤的萎縮情況及密度改變,並可能按可規劃劑量重新 為病人計劃。質子放化療過程中顯示腫瘤已萎縮八成。經重新規劃後,起初的標靶體積維持不變, 脊髓、食道及肺的劑量則調較至原先或較低的水平。雖然目標劑量未受影響,可是如果沒有重新規 劃,一些正常組織所接受的劑量會遠超於原本計劃的2.5倍。進行質子放化療的過程中,腫瘤的萎 縮情況及密度改變可以大大影響放射劑量測定。所以在治療過程中密切監察腫瘤的萎縮情況相當重 要。醫生與物理師為肺癌病人進行質子放化療的過程中對於規劃劑量應採取開放的態度,以使達至 目標劑量的同時,亦可令正常組織接受的劑量減至最低。